Life cycle assessment methodology evaluation and greenhouse gas impact of hydrogen production routes in Australia

Abstract

The environmental impacts of hydrogen production can vary widely depending on the production energy source and process. This implies that the collection and management of sustainability data for hydrogen production globally is desired to ensure accountable development of the sector. Life cycle assessment (LCA) is an internationally recognized tool for environmental impact assessment. Integrating LCA in the holistic evaluation of the hydrogen value chain is desirable to ensure the cleanness and sustainability of the various available hydrogen production pathways. The objective of this review is to evaluate the methodology used in assessing the life cycle impact of hydrogen production including proposed documentation such as the guarantee of origin (GO) and certification schemes, and review case studies from Australia. An analysis of the sustainability strategies and schemes designed by the Australian government, aimed at mitigating climate change and promoting the hydrogen economy, was conducted. The case studies that were discussed identified the preferred available scaled routes of clean hydrogen production to be water electrolysis, which is based on technologies using renewable energy. Other dominant technologies which incorporate carbon capture and storage (CCS) were envisaged to continue playing a role in the transition to a low carbon economy. Additionally, it is critical to assess the greenhouse gas (GHG) emissions using appropriate system boundaries, in order to classify clean hydrogen production pathways. Harmonizing regulatory stringency with appropriate tracking of renewable electricity can promote clean hydrogen production through certification and GO schemes. This approach is deemed critical for the sustainable development of the hydrogen economy at the international level.

Graphical abstract

Keywords

hydrogen certification / guarantee of origin (GO) / hydrogen energy / sustainability / life cycle assessment (LCA) / Australia

1 Introduction

1.1 Background

Hydrogen production using renewable electricity has been labeled as green and is being considered a clean fuel. There are various other designated hydrogen colors such as gray, blue, gold, yellow and turquoise based on how and from which sources of energy or raw materials hydrogen is produced. However, net carbon intensity of produced hydrogen is the main concern if it is to be used as an energy carrier to decarbonize the power production, transport, and industry sectors where it is hard to decarbonize.

The proposition for a hydrogen economy on a global scale is not an intended alternative to traditional energy sources but rather to complement global decarbonization efforts and will be suitable for application in specific industries. Therefore, the transition to a hydrogen economy is expected to be implemented in phases (short, medium, and long-term). Recent advances in technological research and development (R&D) efforts, commitments in supportive policy making and deployment of hydrogen infrastructure have indicated, through the learning curve, a decline in future investment costs for hydrogen production [1,2]. However, similar efforts using a life cycle assessment (LCA) approach will need to be put in place to precisely determine the cleanness (low-carbon-emission status) of a hydrogen production pathway including an assessment of the production process, its subsystems, and the lifecycle of the equipment used. Credible sustainability data has been identified as a critical aspect which remains lacking, as industries and energy markets globally are facing pressure to decarbonize, and meet the net zero emission targets set in various countries around the world [3].

The Group of Twenty (G20) member countries are responsible for the majority of global CO₂ emissions. Therefore, it is imperative that the G20 member countries should also take the lead role by developing clean energy technologies for promoting the energy transition toward a low carbon economy. R&D institutes from the G20 nations have the infrastructure and capabilities to provide clean energy options through progressive technological developments. Through scientific cooperation, G20 countries can play a major role in decarbonizing economies. Therefore, the “Research and Development 20 for Clean Energy Technologies (RD20)” was formed in 2019 to bring together the heads of leading R&D institutions from the G20 members. The RD20 provides a platform and leadership for sharing R&D ideas, best practices and experiences around clean energy technologies. A task force was formed to collect and collate standard practices and methodologies required to estimate the carbon intensity of hydrogen production in each country. The purpose of this review is to report the development of the LCA methodology for Australian hydrogen projects, with some example cases presented.

1.2 Major routes of hydrogen production

The Australian National Hydrogen Roadmap [4] outlines three primary categories under which the technological pathways of hydrogen production fall and are described as follows:

1) Thermochemical: Hydrogen is produced from fossil fuel feedstock. The process is required to be paired with carbon capture and storage (CCS) to produce clean hydrogen. Mature technologies in this category include steam methane reforming (SMR) and coal gasification (CG).

2) Electrochemical: Hydrogen is produced by splitting water using electricity. The process requires the use of low emissions renewable electricity to produce clean hydrogen. Mature technologies in this category include proton exchange membrane (PEM) and alkaline water electrolysis (AWE).

3) Emerging: A range of other less mature technologies fall under this category with some examples including hydrogen production by photolysis and subsurface formation of natural hydrogen.

SMR still remains the cheapest form of hydrogen production in Australia, but this is not expected to be sustained, as future investment developments in natural gas will remain challenging for a range of reasons including decarbonization policies and resources depletion [4,5]. Furthermore, CG also presents its own challenges as coal reserves in the Australian states of Queensland and New South Wales have no clear CCS potential [6], leaving the potential option for largescale hydrogen production from brown coal to be met through the Hydrogen Energy Supply Chain (HESC) in Victoria (Latrobe Valley) [7].

Electrolysis on the other hand, has been assessed by the National Hydrogen Roadmap [4], to be a more suitable modular approach that could be deployed across Australia to likely meet major hydrogen demand prior to 2030. AWE which is a more established technology will continue to play an important role in the development of the industry, while the PEM electrolysis develops into a more competitive technology for hydrogen production.

Some of the outlined categories of hydrogen production will be further discussed in more details in this section. As aforementioned, the major routes of hydrogen production are those already commercially established, with a significant portion of the traditional production processes being the fossil fuel-based ones viz. SMR and CG. It is estimated that approximately 96% of current hydrogen production is of fossil origin, while the remaining 4% is from electrolysis and a few other technologies [8].

Currently, natural gas reforming without CCS is considered as a dominant hydrogen production technology. The reason for this is that the technology has been scaled and it is able to meet stipulated cost targets of below $2/kg. However, the ultimate goal is to reach this target via low emission pathways, which may include SMR with CCS at costs around $1‒2/kg [9]. The steps involved in SMR for hydrogen production are shown in Fig.1.

Although dominantly composed of methane, natural gas also contains higher hydrocarbons. These higher hydrocarbons are converted to methane and carbon oxides with the aid of nickel catalysts in the initial pre-forming process. Subsequently, the SMR process takes place in the main reformer. During this process, the high temperature reaction between steam and natural gas forms carbon monoxide (CO) and hydrogen, as represented by the reaction in

(1)\mathrm{C}{\mathrm{H}}_4+{\mathrm{H}}_2\mathrm{O} \to \mathrm{C} \mathrm{O}+3{\mathrm{H}}_2

Another methane reformation method is autothermal reforming (ATR), which could react oxygen and steam or CO₂ with methane to produce syngas. ATR is generally operated at temperatures of 950–1050 °C and a pressure range of 3–5 MPa. The main difference between SMR and ATR is that ATR requires oxygen. The ATR is followed by a water gas shift reaction (WGR) in two steps of high and low temperature reactions. Steam is used to convert CO to CO₂ and produce hydrogen gas, with the reaction represented by

(2)\mathrm{C}\mathrm{O}+{\mathrm{H}}_2\mathrm{O}\to \mathrm{C}{\mathrm{O}}_2+ {\mathrm{H}}_2

The acid gas removal (AGR) unit is used for sulfur content and gaseous hydrogen sulfide (H₂S) removal. The desulfurized, decarbonized syngas from the AGR unit undergoes further purification using processes such as pressure swing adsorption (PSA) to recover a 99.99% pure hydrogen. When considering the pyrolysis of methane at high temperature thermally or catalytically to degrade the hydrocarbon into hydrogen (turquoise hydrogen) and solid carbon, the process does not require oxygen and therefore no carbon dioxide is generated. This process avoids further downstream processing when compared to SMR, and the reaction can be represented by

(3)\mathrm{C}{\mathrm{H}}_4\to \mathrm{C}+2{\mathrm{H}}_2

CG is another popular commercial hydrogen production process. The coal is partially oxidized into syngas in oxygen and steam at temperatures of 800–1300 °C and under pressures from 3 to 7 MPa, with the steps involved shown in Fig.2. The air separation unit (ASU) is used to separate and supply oxygen to the gasifier, where the CG takes place wrecking the coal into volatiles and char. The WGR further enriches the syngas to recover additional hydrogen as well as other similar subsequent steps as described in the SMR process. CG has an efficiency of approximately 55%, less than that of SMR, which has a process efficiency of ~76% [10].

The CG process can be represented by Eq. (4), and subsequently combining Eq. (2) i.e., the additional hydrogen recovery through WGR with Eq. (4) yields the overall reaction in Eq. (5).

(4)\mathrm{C}+{\mathrm{H}}_2\mathrm{O}\to \mathrm{C}\mathrm{O}+{\mathrm{H}}_2

(5)\mathrm{C}+2{\mathrm{H}}_2\mathrm{O}\to \mathrm{C}{\mathrm{O}}_2+2{\mathrm{H}}_2

Biomass is another abundant resource domestically available from a wide range of sources including forest and agricultural residue, municipal solid waste, macro- and microalgae, non-crop trees, etc. Like CG, biomass can be gasified to produce hydrogen. However, biomass does not gasify as easily as coal does, and it also produces a mixture of other hydrocarbon compounds during the process [11]. This creates an additional processing requirement to reform the exiting hydrocarbons using various catalysts.

In the electrochemical technologies category of hydrogen production, electrolysis is used to cleave water into hydrogen and oxygen using electricity in a device known as the electrolyzer, also referred to as the stack. In this process, hydrogen ions of positive charge are attracted to the cathode to form hydrogen gas and oxygen ions of negative charge are attracted to the anode to form oxygen gas, both of which are separately collected. To complete this process, the electrolyzer requires a balance of plant (BoP), which comprises of other supplementary equipment (e.g. pumps, compressors and valves).

AWE operates via the transport of hydroxide ions (OH⁻) to the anode from the cathode via the electrolyte, to produce hydrogen at the cathode end. Fig.3 illustrates the AWE hydrogen production process.

Alkaline electrolyte is used in AWE at pH above 7 (typically KOH or NaOH), in which the major ionic species of the hydroxyl group are anions. AWEs are built in either unipolar or bipolar configurations, with smaller tank type units more likely to be unipolar and larger filter press units being bipolar. In a unipolar configuration, electrolyzer cells are packed closely to sum up the voltage from each cell, while in the bipolar configuration, the cells connect in series having lower current demands [8,12]. The AWE system is known to have 60%–70% efficiency on commercial scales. The cathodic and anodic electrochemical reactions are represented by Eqs. (6) and (7), respectively.

(6)2{\mathrm{H}}_2\mathrm{O}+{\mathrm{e}}^{-}\to {\mathrm{H}}_2+2\mathrm{O}{\mathrm{H}}^{-}

(7)2\mathrm{O}{\mathrm{H}}^{-}\to {\mathrm{H}}_2\mathrm{O}+\frac{1}{2}{\mathrm{O}}_2+2{\mathrm{e}}^{-}

In PEM electrolyzers, the electrolyte is a solid specialty polymer membrane, which serves as an ionic conductor. The membrane transfers positively charged hydrogen ion (H⁺) from the anode to the cathode and separates the hydrogen from the oxygen gas. A unique feature of PEM cells is that the solid electrolyte is bound on both sides of the porous electrodes, providing a higher energy efficiency with a lower carbon footprint [13]. Fig.4 illustrates the PEM hydrogen production process.

The most common membrane material is Nafion® from DuPont [14]. The anodic and cathodic electrochemical reactions are represented in Eqs. (8) and (9), respectively.

(8){\mathrm{H}}_2\mathrm{O}\to 2{\mathrm{H}}^{+}+ \frac{1}{2}{\mathrm{O}}_2+2{\mathrm{e}}^{-}

(9)2{\mathrm{H}}^{+}+ 2{\mathrm{e}}^{-}\to {\mathrm{H}}_2

Solid oxide electrolysis (SOE) as a hydrogen production technique achieves water splitting at a high temperature through oxygen ion conduction. SOE uses a non-porous solid metal oxide electrolyte that is oxygen ion (O²⁻) conductive. The materials and technology used in SOE are based on that of solid oxide fuel cells. The most common electrolyte material is yttria-stabilized zirconia (YSZ), with a cathode containing a YSZ porous matrix joint with cerium or nickel [12,14].

1.3 Emerging hydrogen production technologies

There are other relatively novel emerging technologies used to produce hydrogen, which are at varying technology readiness levels (TRL) and are progressively recognized as promising approaches to diversify low emissions hydrogen production. The development of these novel technologies is focused on improving specific areas of existing technologies where challenges have been identified, with a view to improve process efficiency and reduce hydrogen production costs, which includes reductions in the use of rare earth metals, and energy efficiency or structural design improvements. Tab.1 summarizes some novel promising technologies with potential to advance the development of a hydrogen economy [2].

1.4 Hydrogen production pathways and definition of color labels

There are several pathways of hydrogen production with varying carbon intensity ranging from low to high. Therefore, it becomes necessary to define “green” hydrogen standards and apply that in the certification of low-carbon hydrogen [15]. Additionally, hydrogen production technologies are now categorized using color labels to distinguish different production routes [2,16]. Various pathways of producing hydrogen have been described with color coding (e.g. green, low-carbon, and brown or black). Brown or black hydrogen is produced from fossil fuels with high carbon emissions. Examples of brown or black hydrogen include CG without CCS, and grey hydrogen is from natural gas SMR without CCS, with most of the hydrogen production globally made via SMR. Low-carbon hydrogen could be of fossil origin but combined with CCS and/or from renewable energy sources. Renewable hydrogen generation is typically from electrolysis.

Broadly, hydrogen is produced from a range of processes including thermochemical, electrolytic and biological processes, and it may also occur naturally by either abiotic or biotic processes in the earth’s crust. Thermochemical processes use heat and chemical reactions to produce hydrogen form either water, fossil fuels (e.g. coal and natural gas), biomass or other organic materials to release hydrogen from their molecular structure. Some examples of thermochemical processes include natural gas reforming, coal and biomass gasification with or without CCS. Electrolysis is applied to cleave water into hydrogen and oxygen using electricity, and the technology is well developed to efficiently use intermittent renewable energy supplies, with the four most common types being AWE, AEM, PEM, and SOE. Other relatively newer approaches in their early stages of development and deployment include direct solar water splitting process involving the use of light energy to split water, and biological processes using bacteria and/or microalgae to produce hydrogen through photobiological reactions and biomass conversion [11]. Another fossil fuel-based hydrogen production technology which is gaining attention is chemical looping reforming (CLR). CLR uses oxidation-reduction reaction of solid oxygen ions to reform hydrogen from hydrocarbons and offers a low carbon technology option [1,17]. Alongside the newer hydrogen production pathways is natural hydrogen which occurs by geogenic processes within a range of geological environments, including geothermal and mineral systems, as well as in conventional and unconventional oil and gas fields [18]. There are various processes responsible to produce natural hydrogen underground, chiefly the cleaving of oxygen from water through diagenic or radiolytic processes [19].

The selected technological route of hydrogen production will determine the carbon footprint and cost associated with the product. There are various routes of hydrogen production, and to illustrate the range of options, a summary of the production along with their color codes are presented in Fig.5. The hydrogen colors help with the categorization of different production pathways [16].

The color of the hydrogen produced is determined only by the energy or technology type used in its production, not taking into consideration the deep cleanness assessment. For instance, gray hydrogen is produced from using fossil fuels with a ratio of H₂ and CO₂ of 1:10, while blue hydrogen produced similarly includes CCS and for this reason it is considered cleaner. It is interesting to note that biogas hydrogen produced via biogas pyrolysis could be produced with a negative carbon footprint [10]. Apparently, brighter colors are used to indicate cleaner hydrogen production pathways. However, the proliferation of different color shades may be overly complicating the discussions in this field [20].

Therefore, it becomes obvious that the current color-coding model of hydrogen does not precisely say how clean a particular color from the spectrum is, in terms of low-carbon emission, because it does not indicate the GHG emissions from the production process [2]. For these reasons, it is pertinent that an international certification scheme needs to be developed and deployed to track hydrogen production processes, which could be later expanded to include the process water consumption and other externalities. This approach could allow specific and appropriate definition of hydrogen as being “low emission” with reference to agreed international standards [21].

There has also been gradually more focus on carbon intensity or carbon equivalence in addition to the discussions on color shades. The carbon intensity is usually expressed in kg CO_2eq per kg of hydrogen produced, and it is considered a technology-neutral criterion to assess the emission footprint of the hydrogen. Applying the use of carbon intensity in technology assessment allows competitive evaluation of hydrogen production routes to select options with the least cost at a specified threshold of carbon intensity. It is expected that such valuation will vary from one case to another. For example, producing hydrogen from renewable electricity can be more appropriate in one case and including CCS in a fossil fuel-based process more suitable in another case [20]. Such practice will allow for the sustainable development of economic activities globally.

2 Development of standards and certification schemes of hydrogen production pathways

The development of standards and certification schemes for “green” and “low emission” hydrogen production continues to evolve, with the qualification of green hydrogen also becoming complicated. The European schemes define green hydrogen as hydrogen produced from renewable energy using several pathways and producing a carbon intensity below a specified threshold. The green hydrogen standard in the UK focuses on the carbon intensity rather than the technology or source of feedstock. This implies that any production method that meets a low-carbon threshold would be eligible for certification under this standard.

For accounting purposes, it is important to set the appropriate system boundaries when assessing GHG emissions for the classification of green hydrogen. LCA is an internationally recognized methodology applicable for such accounting. While some LCA studies set the system boundary within the point of production, others extend the emissions to include the point of use. The exclusion of either or both feedstock and transport elements from within the system boundary creates the potential of omitting certain supply chain emissions [22].

How green hydrogen is defined will have implications on the large-scale development of commercial hydrogen. Hydrogen production and fuel cell technologies have had limited inclusions in public policy making due to the paucity of recognized international standards. Fig.6 shows an example of greenhouse gas footprint in kg CO₂ equivalent unit per kg of H₂ produced from various technologies, in relation to the threshold and benchmark levels set by Europe’s CertifHy hydrogen certification scheme [23].

In May 2020, the Department of Industry, Science, Energy and Resources (DISER) of the Australian Government began consulting state/territory stakeholders, industry representatives, and other participants who would be producers and consumers of hydrogen, through a survey. This survey outlined three key areas of interest including the domestic and international boundary of a scheme, when a scheme should begin operating and how a scheme would align with existing regulations and frameworks.

The initial proposal from the DISER was an international certification scheme to track production technology, i.e., the so-called Scope 1 and Scope 2 carbon emissions, and the production location. As earlier mentioned, the DISER noted that this approach would allow different countries (or regions) to define their own “green” or “low-emissions” hydrogen with reference to international standards – much like the CertifHy scheme, which has definitions of both green and low-emissions hydrogen based on the production process [21].

This initial survey was followed by a workshop in September 2020, in which both federal and state governments, as well as industry representatives discussed the three key areas of interest. In addition, the system boundary, accounting methodologies for emissions, offset and/or renewable energy certificates possibilities and governance model for the scheme were also discussed as main items in the workshop.

The subsequent stage in the development was a discussion paper released by the DISER in June of 2021. The DISER noted that it had been working to develop a hydrogen Guarantee of Origin (GO) scheme from both domestic and international fronts. On the international front, DISER is involved on behalf of the Australian Government as a member of the International Partnership for Hydrogen and Fuel Cells in the Economy’s (IPHE) Hydrogen Production Analysis Taskforce, which aims to develop a methodology to determine the carbon emissions associated with hydrogen production.

Australia is at the fore of IPHE’s methodologies development efforts to certify hydrogen produced from electrolysis and CG, as shown in Tab.2. The end goal is for this effort to form part of an international hydrogen standard. Thus, it currently appears that the proposed certification scheme would include hydrogen produced through electrolysis, gasification with CCS, and SMR with CCS. DISER proposes that data would be collected for a 12-month hydrogen production period, which aligns with the view of the IPHE and would broadly include information on the facility, the type of production, production volume, total emissions, waste products, CCS (if applicable), and coproducts.

This information would be reported under specific methodologies that is discussed and outlined in detail within a discussion paper. This discussion paper also contains more details of the proposed design of the GO scheme, which will then be used to trial a pilot scheme to evaluate Australia’s position in the international development of a scheme with the IPHE.

Thus, the DISER noted that the next steps will include testing the proposed methodologies of the three production options viz. electrolysis, gasification with CCS, and SMR with CCS. This will allow for the refining of the methodologies before their eventual adoption [25].

Independent of this government-led development, in December 2020, an industry-led development of a certification scheme was announced by the Smart Energy Council. This scheme is noted to be an alternative to the scheme proposed by the DISER and will be limited to green hydrogen, while blue hydrogen will not to be considered under this scheme.

For context, the GO concept was originally developed to certify electricity, heating and cooling particularly from renewable energy sources and has gained application in hydrogen certification. Following the development of global trends, hydrogen has been included in several GO standards and certification schemes. For instance, in Europe, the EN16325 standard which specifies requirements for GO of electricity from all energy sources is being revised to extend its scope to include hydrogen and biomethane [27], and an additionality delegated act of the Renewable Energy Directives II (RED II) outlines conditions under which hydrogen-based fuels can be considered as renewable fuels of non-biological origin (RFNBO) [28]. The GO is used as an instrument to evidence the origin of energy generated from renewable resources. The GO scheme is an internationally aligned assurance scheme for the tracking and verification of emissions [29]. A GO scheme can be administered through the issuance of GO certificates, with each certificate representing a specified amount of product that can be traded among producers, consumers and traders. The GO can be issued by an accredited registry, which could be international or restricted to a specific location. Once the specified amount of product has been physically consumed, i.e., it has been utilized or reached its expiry date, the GO certificate is cancelled from the registry [30]. In Australia, GO is expected to help decarbonize the economy, as it will show where a product comes from, the process through which it was made and the attributed emissions at each life stage. This will help identify areas with high carbon emission and encourage producers to focus on reducing the carbon intensity. Globally multiple guarantees of origin schemes are currently being used, as illustrated in Tab.3. Both the government-led and industry-led developments of a certification scheme have mentioned utilizing some forms of the CertifHy scheme currently in pilot stage in the European Union (EU).

In 2019, the COAG Energy Council Working Group of the Australian Government released a strategy issues paper regarding guarantees of origin [31]. Included in the issues paper was the comparison of possible emissions associated with hydrogen production technologies in relation to thresholds of the CertifHy GO, as presented in Tab.4.

3 Review of the status of the Australian GO Scheme

Clean production technology was identified as a critical item in the establishment of Australia as a leading producer and consumer of hydrogen in the National Hydrogen Strategy published by the Australian Government in November 2019 [32,33]. There was also the issue of the development of hydrogen certification and GO schemes raised by the Australian Government in June 2021 [34]. Australia’s National Hydrogen Strategy designed the framework to develop a sustainable and commercial hydrogen industry to 2030 and beyond. This design resulted from collaborative efforts between the Department of Climate Change, Energy, the Environment and Water (DCCEEW)), and the Clean Energy Regulator (CER). The CER will administer the scheme with responsibilities for management of the GO certificate creation, tracking of certificates through the GO registry, and compliance monitoring. Hydrogen can be made in several ways, and hydrogen production can involve varying amounts of carbon emissions. Green hydrogen is produced by cleaving water using renewable energy, while other hydrogen production options from coal and gas are also available, with or without CCS. It will be important for hydrogen customers to know what they are buying, and what certification can provide this assurance [35].

A hydrogen certification scheme is a standardized process that provides consumers of hydrogen with transparency of the location, the production method, and the attributable environmental impacts (such as GHG emissions) of hydrogen purchased and used. A hydrogen certification scheme can trace and certify where and how hydrogen is made; and using a component that is new to certification schemes in Australia. Furthermore, the GO and the hydrogen certification scheme can also track the hydrogen through its supply chain [36]. The GO label provides potential customers with relevant information on the source of purchased products. Originally, GO serves as a tracing method to ensure the quality of electricity, which has now been extended to hydrogen. A hydrogen GO scheme will serve similar purpose as the green electricity GO scheme, to make hydrogen available globally from reliable sources.

The GO scheme for hydrogen includes several components such as the GO governance, eligibility assessment and enlisting of production plants, general information content, authorization, transfer and cancellation of operations, producers inventory and register system, as well as a trading platform. Hydrogen certification scheme aims to create a path for a legitimate and authorized scheme providing traceable products.

A study by Cheng and Lee [37] interrogated the commitment of national hydrogen strategies to achieve decarbonization from a list of 28 jurisdictions around the world including Australia. Four parameter types were considered in the study viz. fossil fuel penalties, hydrogen certifications, innovation facilitation and dimensions to phase-out coal. Majority of the countries were categorized in the transitioning group, where a “scale first and clean later” approach was being deployed. Countries in this category prioritize the scaling up of the hydrogen economy to specifically meet their domestic or export demands. Although part of the agenda, climate objectives are not guaranteed due to a lack of clear regulatory measures in such countries. The study identified challenges and areas where national hydrogen strategies need to improve, to appropriately regulate the hydrogen economy and contribute to rapid decarbonization. Key areas of focus should include environmental rigor in the characterization of “green,” “clean”, and “low carbon” or “low emission” hydrogen; articulate objectives for applying technology neutrality; and harmonized regulatory strategies for certification to promote trading of hydrogen in the global market.

Globally, the development of a hydrogen certification scheme has been identified as a key enabler for market growth. This will present an opportunity for hydrogen producers and exporters to apply a standardized framework in quantifying and disclosing the environmental attributes (particularly GHG emissions) of their products [38]. However, another important aspect in the development of hydrogen certification schemes is the need to provide transparency in the scheme, which should be accessible to both exporters and importers, to fulfil common objectives of certification [22]. For example, the production of hydrogen from grid connected electrolyzers should consider the renewable energy component of the selected grid in assessing how green or low carbon the product could be as part of the certification process [39]. The inclusion of all relevant aspects will in turn create opportunities for securing government support, addressing customer needs and concerns, and thrive competitively in an international market.

Potential key challenge areas and gaps need to be addressed in developing a vibrant GO scheme for Australia. Therefore, the flexible approach in allowing the use of renewable energy certificates will need to be reevaluated. To elucidate this further, the scheme proposes to allow the use of renewable energy certificates to offset grid electricity consumption for electrolysis-based hydrogen production. However, no ‘time matching’ requirements are placed between the selected certification and hydrogen production, potentially creating a loophole in the approach. Furthermore, it will be essential that the variations in grid electricity mix are accurately reflected and accounted to avoid inconsistencies when applying residual mix factors (RMFs) [40]. The RMF applies a factor to reflect the balance of generated electricity and emissions that would remain in the grid to account for the proportion that is claimed through a GO scheme [41]. This concept is useful in grid electricity mix assessment, especially where market-based Scope 2 emissions are evaluated, and helps to avoid double counting. The risk of double counting is increased when renewable electricity is tracked across multiple certification schemes [40].

The complexity of the emission accounting approach would be challenging for some producers, particularly when developing a framework that effectively covers the entire hydrogen value chain [33]. While the approach to estimating emissions could be designed to be like the National Greenhouse and Energy Reporting Scheme (NGERS), the application of broad system boundary will require producers to account for both upstream and downstream emissions. Therefore, decisions regarding the system boundary (e.g., well-to-wheel) and the choice of appropriate emission factors must be included. Furthermore, emissions allocation to coproducts (e.g., oxygen from electrolysis) will need to be understood and dealt with appropriately. Understanding and addressing these gaps will requirement a commitment on the part of hydrogen producers to understand the mechanics of the scheme.

4 Methodology for LCA calculation

The process of conducting LCA involves a systematic analysis of the environmental impacts and resources depletion associated with a product or process throughout its life cycle. The process is guided by the International Organization for Standardization (ISO) standards viz. LCA principles and framework (ISO14040) [42] and LCA requirements and guidelines (ISO14044) [43]. On the global outlook, the ISO14040 and ISO14044 standards were developed through the efforts of working groups from the Society of Environmental Toxicology and Chemistry (SETAC) and the United Nations Environment Program (UNEP), including a range of other contributors [44]. While at the local and national levels, the development of schemes, strategies, and methods for conducting LCA keep progressing. Process data and database for several industrial sectors include energy, transport, building and agriculture to form the fundamental part of LCA studies [45]. The process of LCA typically involves four stages: goal and scope definition, methodology and inventory analysis, impact assessment and, and interpretation, as shown in Fig.7 and the process is iterative, where outputs from subsequent stages can be reused as inputs for a previous stage to refine the whole process.

4.1 Accounting methodology in Australia

In Australia, the peak professional organization for people involved in the use and development of LCA is the Australian Life Cycle Assessment Society (ALCAS). ALCAS has developed and delivered the Australian National Life Cycle Inventory Database (AusLCI), an invaluable tool for those involved with environmental assessment [46].

NGERS is the framework for reporting emissions data across Australia. NGERS emanated through the Intergovernmental Panel on Climate Change (IPCC) guidelines, and also in accordance with the broader LCA framework and guidelines of ISO 14040 [42] and ISO 14044 [43]. The focus of NGERS is tailored for Australia’s national greenhouse gas (GHG) inventory and forms the basis for the country’s GHG reporting.

According to NGERS guidelines, Scopes 1‒3 emissions can be reported. Emissions that are released into the atmosphere as a direct result of an activity or series of activities within the production process are Scope 1. Indirect emissions from consumption of purchased electricity, heat, steam or cooling energy comprise Scope 2. Indirect GHG emissions other than Scope 2 emissions associated with equipment manufacture and other wider processes are Scope 3. Scope 3 emissions can occur both upstream of the entity or downstream after the manufactured product.

If these emissions are calculated, life cycle-based emissions for cradle to gate boundaries are Scope 1 + Scope 2 + Scope 3 upstream emissions. Depending on the goal of the LCA, if a full life cycle-based emission is considered, it is recommended that Scope 3 downstream emissions be included in the evaluation.

Additionally, depending on the goal and scope of the LCA, a cut-off criterion could be used to include or exclude inputs and outputs to be evaluated in the study. The cut-off specifies the amount of material, energy flow or level of environmental significance considered, and it is used to reduce complexity and increase significant focus on impacts [42]. To estimate the emission intensity per unit of hydrogen produced, the stages to be included within the scope and system boundary of the assessment are first identified, then data associated with those stages collected. The emissions for each processing stage can be calculated as the product of the activity data for the stage and the associated emission factor as presented in Eq. (10). The emissions factor is a coefficient that describes the rate at which a given activity releases GHGs into the atmosphere. The NGERS provides emission factors for various fuels and grid electricity in different states across Australia. The total emissions can be obtained from a summation of the emissions from each stage and comprises both direct and indirect emission and it is presented in Eq. (11). The net emissions represent the emissions released into the atmosphere after generation, recovery, and sinks have been combined. The net emissions take into consideration any carbon that is captured and/or offset during the process. The net emissions are presented in Eq. (12). The emission intensity is then obtained by dividing the net emissions by the total hydrogen produced as presented in Eq. (13).

(10)\begin{array}{rl}{\mathrm{S}\mathrm{t}\mathrm{a}\mathrm{g}\mathrm{e}\mathrm{E}\mathrm{m}\mathrm{i}\mathrm{s}\mathrm{s}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{s}(\mathrm{k}\mathrm{g}\mathrm{C}\mathrm{O}}_{2\mathrm{e}\mathrm{q}})=& \mathrm{S}\mathrm{t}\mathrm{a}\mathrm{g}\mathrm{e}\mathrm{a}\mathrm{c}\mathrm{t}\mathrm{i}\mathrm{v}\mathrm{i}\mathrm{t}\mathrm{y}\mathrm{d}\mathrm{a}\mathrm{t}\mathrm{a}\\ & \times \mathrm{E}\mathrm{m}\mathrm{i}\mathrm{s}\mathrm{s}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{F}\mathrm{a}\mathrm{c}\mathrm{t}\mathrm{o}\mathrm{r},\end{array}

(11){\mathrm{T}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{l}\mathrm{E}\mathrm{m}\mathrm{i}\mathrm{s}\mathrm{s}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{s}(\mathrm{k}\mathrm{g}\mathrm{C}\mathrm{O}}_{2\mathrm{e}\mathrm{q}})= \sum (\mathrm{S}\mathrm{t}\mathrm{a}\mathrm{g}\mathrm{e}\mathrm{E}\mathrm{m}\mathrm{i}\mathrm{s}\mathrm{s}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{s}),

(12){\mathrm{N}\mathrm{e}\mathrm{t}\mathrm{E}\mathrm{m}\mathrm{i}\mathrm{s}\mathrm{s}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{s}(\mathrm{k}\mathrm{g}\mathrm{C}\mathrm{O}}_{2\mathrm{e}\mathrm{q}})= \mathrm{D}\mathrm{i}\mathrm{r}\mathrm{e}\mathrm{c}\mathrm{t}\mathrm{E}\mathrm{m}\mathrm{i}\mathrm{s}\mathrm{s}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{s}+\mathrm{I}\mathrm{n}\mathrm{d}\mathrm{i}\mathrm{r}\mathrm{e}\mathrm{c}\mathrm{t}\mathrm{E}\mathrm{m}\mathrm{i}\mathrm{s}\mathrm{s}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{s}+\mathrm{U}\mathrm{p}\mathrm{s}\mathrm{t}\mathrm{r}\mathrm{e}\mathrm{a}\mathrm{m}\mathrm{E}\mathrm{m}\mathrm{i}\mathrm{s}\mathrm{s}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{s}-\mathrm{E}\mathrm{m}\mathrm{i}\mathrm{s}\mathrm{s}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{O}\mathrm{f}\mathrm{f}\mathrm{s}\mathrm{e}\mathrm{t}\mathrm{s},

(13)\mathrm{H}\mathrm{y}\mathrm{d}\mathrm{r}\mathrm{o}\mathrm{g}\mathrm{e}\mathrm{n}\mathrm{P}\mathrm{r}\mathrm{o}\mathrm{d}\mathrm{u}\mathrm{c}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{E}\mathrm{m}\mathrm{i}\mathrm{s}\mathrm{s}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{I}\mathrm{n}\mathrm{t}\mathrm{e}\mathrm{n}\mathrm{s}\mathrm{i}\mathrm{t}\mathrm{y}(\mathrm{k}\mathrm{g}\mathrm{C}{\mathrm{O}}_{2\mathrm{e}\mathrm{q}}/\mathrm{k}\mathrm{g}{\mathrm{H}}_2\mathrm{p}\mathrm{r}\mathrm{o}\mathrm{d}\mathrm{u}\mathrm{c}\mathrm{e}\mathrm{d})=\frac{\text{Net Emission (kg C}{\text{O}}_{\text{2eq}})}{\text{Total Hydrogen Produced (kg}{\text{H}}_2)}.

4.2 Allocation to co-products

According to conventional and international standards, allocation of emission is recommended based on physical attributes such as mass, energy, or molar basis. System expansion is suggested where applicable, so emission for alternative products in the market, assuming that co-products can replace each other and can replace the emission of the alternative product, is recommended for the co-product. Economic or value-based allocation is suggested as the last resort. In this case, price or revenue for each product is used to proportionate emission to each product.

Mass allocation does not produce acceptable results of emission impact if the price of the products varies significantly. In that case, price based, or economic allocation is recommended. However, the price of some precious commodities is volatile, thus although long-term average price is used, it is unlikely that the emission profile of a product will spike significantly due to the spike in the market or spot price which will have effect on the long-term average. In this case, a new method is suggested by a precious metal company in Europe that the operating cost of production within a boundary can be used to allocate emission. For example, the cost of intermediate alloy production would be similar but the refining cost of each metal, particularly for a precious metal is likely to be significantly higher. In the scenario for multiple products, and to produce intermediate and final products, both are used to allocate impact to a high value but low volume product with a lower mass. In the case of hydrogen, if oxygen is considered as co-product, these allocation issues may need to be considered carefully. If sea water is used for electrolysis, the contributions from energy and chemicals used for waste brine management need to be accounted for. It is likely that if the price of multiple products is vastly different, mass-based allocation will yield least accurate results. However, price-based allocation may be problematic if the fluctuation and volatility of product is very high. If operating cost method is considered, it may produce results that may fall between these two in terms of accuracy. Whatever method is used, if it is justified, stated clearly, and provides reasonable results, that should be acceptable. However, a common approach for allocation is recommended for comparative studies.

5 Selected case studies

Case 1: An assessment of the carbon emissions from hydrogen production technologies using various feedstock and Australian based energy options

Background, context and methodological modeling approach

In Australia, there are over a hundred pilot, demonstration, and small-scale hydrogen production projects in various stages of operation with frequently updated information provided by Geoscience Australia’s resources map tool [47] (see also Table S1 in Supplementary Material). LCA was conducted by Hosseini et al. [48] to investigate the environmental impacts of several hydrogen production pathways from various feedstocks including natural gas, coal, biomass and water. A range of fossil fuels, biomass based, and electrolysis routes for hydrogen production were investigated as summarized in Tab.5. The processes included natural gas SMR, CG, biomass pyrolysis and gasification, natural gas pyrolysis, AWE and PEM electrolysis. The natural gas SMR production process required pretreatment for sulfur removal, followed by a preforming to prevent coke formation in the reformer. Syngas is generated in the main reformer through the reforming reaction with steam, is then sent to the WGR reactor to increase the hydrogen yield. Subsequent removal of acid gases and purification and compression of the hydrogen product completed the process. To produce hydrogen from coal the stages include included pretreatment, gasification, WGR, AGR, and hydrogen purification and compression. For the biomass-based hydrogen production, the stages included the pretreatment, pyrolysis (for pyrolysis production option) and gasification (for the gasification production option), WGR, AGR, and hydrogen purification. For electrolysis options, water and electricity from both the grid and renewable sources (wind and solar PV) were considered. The electrolyzer stack for hydrogen production comprises the electrolyzer cells (i.e., the anode, cathode, membrane, and electrolyte unit set up) [13]. Fig.1‒Fig.4 provide schematic illustrations of the process block flow to further elucidate the processes investigated. The potential impacts of each production technology were evaluated for carbon footprint, considering Scopes 1 and 2 emissions. After the conceptualization of each hydrogen production pathway option to be evaluated, the base case assumptions are populated either through direct measurements or from literature and other database and industry reports. These inputs are used to develop the process flowsheet and generate the initial process results. A step-by-step evaluation of each process can then be performed to optimize the design. Scope 1 emissions related to direct activities within the production process are estimated. Similarly, indirect emissions from consumption of purchased electricity, heat, steam, or cooling energy in the production process are estimated as Scope 2 emissions, including possible fugitive emissions that could occur in processes related to the feedstock supply. The summation of the Scopes 1 and 2 emissions provides for total process emission used in the estimation of the net hydrogen production emission associated with each pathway. The modeling approach used in this case study is outlined in Fig.8.

The results from each technology option were assessed as presented in Fig.9. Grid connected electrolyzers were found to have the highest carbon footprint, and this was closely followed by the black coal to hydrogen production process. Natural gas SMR and ATR were found to have similar carbon footprints. Natural gas pyrolysis was also found to be a better option than natural gas SMR and CG, even when SMR and CG included CCS. For the biomass processed hydrogen, the included biogenic CO₂ is presented in green color on Fig.9, indicating the process does not contribute to the overall atmospheric CO₂ emission and if CCS is coupled to the process, it would be a carbon negative process.

The grid mixes across Australia varies significantly from one state/territory to another and this is reflected in the associated emissions when the same electrolyzer module was set up to run on grid power in different locations across Australia. Fig.10 presents a comparison for the operation of an electrolyzer on grid power for various locations in Australia. Carbon emissions associated with grid-connected electrolyzers were location dependent and varied with the grid mix [49]. A grid connected electrolyzer in Victoria (VIC) has 50–55 kg CO_2eq/kg H₂ emissions, while Tasmania (TAS) has the lowest emissions (~10 kg CO_2eq/kg H₂) due to the renewable energy components within its grid mix.

The study findings indicate that it is required to develop, scale and deploy large scale renewable energy to rapidly progress Australia’s low-carbon economy drive, while contributions from other low emission alternatives should be maintained and improved.

Case 2: Fossil based hydrogen versus renewable hydrogen emissions comparison

Several countries that advocate “clean hydrogen” consider fossil fuel-based feedstock with CCS for hydrogen production as a similar alternative to hydrogen produced using renewable electricity with zero emissions. The study by Longden et al. [50] compared these technologies including an assessment of fugitive emissions and lower capture rates. Although carbon capture is a matured technology applied in arrange of industries, its CO₂ reduction potentials vary widely and can be hard to estimate in some cases. Furthermore, the post capture scenario, i.e., what happens to CO₂ after it is collected also needs to be evaluated.

The analysis conducted by Longden et al. [50] compared the emissions intensity of hydrogen production from coal and natural gas including emissions from the fossil fuel combustion. The data analyzed were based on techno-economic analysis provided by the International Energy Agency (IEA) Greenhouse Gas R&D program for SMR, a report of the National Academy of Engineering for CG, emission factors from the IPCC default data tables, and the emission intensity was calculated as kilograms of CO₂ equivalent emissions per unit of thermal energy (kg CO_2eq/GJ) or hydrogen energy with a lower heating value (LHV) [50]. Total emissions from the various fuels used in the production process were evaluated, including direct emissions from the combustion of fuels (e.g., coal and natural gas); process emissions from equipment associated with the chemical transformation of raw materials and inputs to produce hydrogen; and fugitive emissions from unintentional release, losses and leaks of gases and vapors. The results from the study are presented in Fig.11.

Further comparison of the emission levels of the analyzed results was made in relation to the carbon intensity threshold developed by the CertifHy certification scheme. The CertifHy low carbon threshold is defined as 60% reduction in emission intensity below the standard SMR production process, which corresponds to 4.4 kg CO_2eq/kg H₂. The GO scheme of CertifHy accounts for the origin of hydrogen, including the use of renewable energy or non-renewable low emission energy sources with CCS. From Fig.11, it is indicative that only hydrogen produced from natural gas with a high capture rate of 90% was found to be below the CertifHy threshold.

The analysis by Longden et al. [50] demonstrated the possibility of “low emission” hydrogen production from fossil fuels still contains a significant amount of emissions. The study also reiterated that considering fugitive emissions is critical to the appropriate assessment of any hydrogen production technology. The likelihood of unwanted hydrogen that could occur at different stages of the supply also need to be considered and evaluated in addition to fugitive emission from other gases, as it will have implications for certification purposes [51].

6 Summary and conclusions

Hydrogen production via electrolysis using renewable electricity will remain key to the development of a hydrogen economy for the global market. Recent advances in technological R&D efforts, commitments in supportive policy making, and the continuous deployment of hydrogen infrastructure will drive the development of the hydrogen economy. Using LCA approach will need to be incorporated alongside other efforts to precisely determine the cleanness (low-carbon-emission status) of a hydrogen production pathway, including an assessment of the production process, its subsystems and the lifecycle of the equipment used.

G20 member countries have been identified as key stakeholders in the hydrogen economy, and they are expected to contribute toward developing clean energy production alternatives toward global decarbonization of major industries. In a similar context, Australia as a member of the RD20 and a leading producer and consumer of hydrogen, is making efforts at a national level to regulate the environmental impacts of hydrogen production across a range of supply chain areas. The efforts made by the Australian government include the development of GO certification schemes. Furthermore, the DCCEEW and the CER through extensive consultations developed Australia’s National Hydrogen Strategy, which provides the framework for Australia to develop a sustainable and commercial hydrogen industry to 2030 and beyond.

Hydrogen certification has been identified as an effective tool to measure the cleanness of hydrogen production routes. GO schemes will provide a reliable method to track renewable electricity, ensure additionality that could be benefited through electrolysis with renewable electricity, and ease verification and auditing in the hydrogen market. This can be done reliably by integrating GO schemes with hydrogen certification systems to provide comprehensive tracking and carbon intensity calculation. Implementing the suggested measures could provide a reliable and transparent method of ensuring cleanness claims related to hydrogen production which can be substantiated and verified through such management schemes.

In the Australian context, the implementation of a robust, internationally accepted GO scheme, which sets out a standardized process for accounting for the emissions associated with hydrogen production and evaluating these associated environmental impacts such as GHG emissions, will be a key measure of success to Australia’s progress toward its hydrogen vision and as an action item to support this progress. Globally, there are a limited number of established international hydrogen certification schemes, while there are a few more are in their early developmental stages. Therefore, Australia does not stand alone in this quest to develop and implement certification and GO schemes.

Challenges have been identified in key areas that require attention including improving the environmental rigor in the characterization of “green,” “clean” and “low carbon” or “low emissions” hydrogen; articulate objectives for applying technology neutrality; and harmonized regulatory strategies for certification to promote trading of hydrogen in the global market. Furthermore, achieving harmonization in the categorization of hydrogen, setting appropriate threshold, supply chain tracking and overall governance are among key aspects which have been prescribed for the development of compatible LCA methodologies across certification schemes [52].

It is critical to assess the associated GHG emissions to appropriately classify clean hydrogen production pathways. The consideration of where to set the system boundaries is still a matter of debate, particularly in the interest of proper carbon accounting. It will be important to use the similar system boundaries when comparing hydrogen produced through different routes. Consistent inclusion of the supply chain components including infrastructure and feedstock could be supported through policy development to improve the standardization of GO certification schemes for more appropriate hydrogen production emissions accounting in Australia. LCA is an internationally recognized methodology for such accounting. Its implementation in hydrogen certification and GO schemes will be critical to the development of the hydrogen economy in Australia.

Case studies discussed in this review indicate that current best available routes of clean hydrogen production are through the electrolysis of water using renewable energy. However other dominant technologies which incorporate CCS will continue to play a key role as the world transits to a low carbon economy.

Enhancing regulatory stringency in hydrogen production at both national and international levels using tools like LCA through hydrogen certification and GO schemes will ensure sustainable development of the hydrogen industry.

References

[1] Huang J, Balcombe P, Feng Z. Technical and economic analysis of different colours of producing hydrogen in China. Fuel, 2023, 337: 127227

[2] Dawood F, Anda M, Shafiullah G M. Hydrogen production for energy: An overview. International Journal of Hydrogen Energy, 2020, 45(7): 3847–3869

[3] Heeß P, Rockstuhl J, Körner M F. . Enhancing trust in global supply chains: Conceptualizing digital product passports for a low-carbon hydrogen market. Electronic Markets, 2024, 34(1): 10–20

[4] BruceS, Temminghoff M, HaywardJ, et al. National hydrogen roadmap. CSIRO, Australia, 2018

[5] Climate Council. The future of gas is small and dwindling. 2023-6-9, available at website of Climate Council

[6] Beyond Zero Emissions. Carbon Capture and Storage: Information paper. 2015-2, available at website of Beyond Zero Emissions

[7] Hydrogen Energy Supply Chain Project. Hydrogen Production. 2023-7-27, available at website of Hydrogen Energy Supply Chain

[8] Da RosaA V, Ordóñez J C. Fundamentals of Renewable Energy Processes. Massachusetts: Academic Press, 2021

[9] International Energy Agency. Global hydrogen review. 2021

[10] Osman A I, Mehta N, Elgarahy A M. . Hydrogen production, storage, utilisation and environmental impacts: A review. Environmental Chemistry Letters, 2022, 20(1): 153–188

[11] Hydrogen and Fuel Cell Technologies Office . Hydrogen production processes. 2023-7-26, available at website of US Office of Energy Efficiency & Renewable Energy

[12] DincerI, Ishaq H. Renewable hydrogen production. In: Dincer I, Ishaq H, eds. Hydrogen Production Methods. Netherlands: Elsevier, 2022, 35–90

[13] SmartS, Ashman P, ScholesC, et al. Technoeconomic Modelling of Future Fuel Production Pathways: Summary Report. 2023

[14] BessarabovD, Wang H, LiH, et al. PEM Electrolysis for Hydrogen Production: Principles and Applications. Florida: CRC Press, Florida

[15] Velazquez Abad A, Dodds P E. Green hydrogen characterisation initiatives: Definitions, standards, guarantees of origin, and challenges. Energy Policy, 2020, 138: 111300

[16] van ZoelenR,ChaudhryS. Factors determining emission intensity of hydrogen production pathways in the Netherlands. 2024, available at website of newenergycoalition

[17] Edrisi A, Mansoori Z, Dabir B. Urea synthesis using chemical looping process—Techno-economic evaluation of a novel plant configuration for a green production. International Journal of Greenhouse Gas Control, 2016, 44: 42–51

[18] Boreham C J, Edwards D S, Czado K. . Hydrogen in Australian natural gas: Occurrences, sources and resources. APPEA Journal, 2021, 61(1): 163

[19] Frery E, Langhi L, Maison M. . Natural hydrogen seeps identified in the North Perth Basin, Western Australia. International Journal of Hydrogen Energy, 2021, 46(61): 31158–31173

[20] World Energy Council. Working Paper | National Hydrogen Strategies. 2021

[21] Department of Industry, Science, Energy and Resources, Hydrogen Certification Survey. 2020-05-20, available at website of Australian Government Department of Industry, Science, Energy and Resources

[22] White L V, Fazeli R, Cheng W. . Towards emissions certification systems for international trade in hydrogen: The policy challenge of defining boundaries for emissions accounting. Energy, 2021, 215: 119139

[23] HINICIO. CertifHy-Developing an European Framework for the generation of guarantees of origin for green hydrogen. Definition of green hydrogen, outcome & scope of LCA analysis 2016.2022-8, available at website of HINICIO

[24] BarthF, Vanhoudt W, LondoM, et al. CertifHy—Developing a European framework for the generation of guarantees of origin for green hydrogen, 2019-04-25, available at website of European Commission

[25] Department of Climate Change, Energy, the Environment and Water (DCCEEW). Trials start for hydrogen Guarantee of Origin scheme. 2023-7-272023-7-27 available at website of Australian Government DCCEEW

[26] Department of Industry, Science, Energy and Resources. Hydrogen guarantee of origin scheme: Discussion paper. 2021. 2024-4-5, available at website of Australian Government DISER

[27] ZhouY, Baldino C. Gas definitions for the European Union: Setting thresholds to reduce life-cycle greenhouse gas emissions. Working Paper 2022-32. 2024-10-9, available at website of the International Council on Clean Transportation

[28] Christopher JonesP T, Borchardt K D, Kettlewell W J. European Union published rules on “renewable” hydrogen. 2023-3-22, available at website of globalcompliancenews

[29] Clean Energy Regulator. What is the guarantee of origin? 2024-6-27, available at website of Clean Energy Regulator

[30] CerQlar. Your guide to guarantees of origin. 2023-2-20, available at website of CerQlar

[31] Department of Climate Change, Energy, the Environment and Water (DCCEEW). National Hydrogen Strategy: Issues papers. 2020-1-14, available at website of Australian Government DCCEEW

[32] COAG Energy Council Hydrogen Working Group . Australia’s national hydrogen strategy. 2019

[33] Department of Industry, Science, Energy and Resources (DISER) . Hydrogen guarantee of origins for Australia: Options paper. 2024-2-24, available at website of Australian Government DISER

[34] Departmentof Climate ChangeEnergyEnvironmentthe (DCCEEW)Water. Hydrogen guarantee of origin scheme: Discussion paper. 2023–06-21, available at website of Australian Government DCCEEW

[35] Australian Hydrogen Council. Position statement: Hydrogen certification. 2022-10, available at website of Australian Hydrogen Council

[36] Corke C, Muir M, Busch C. What should a hydrogen certification and guarantee of origin scheme look like in Australia? 2023-8-11, available at website of Corrs Chambers Westgarth

[37] ChengW, Lee S. How green are the national hydrogen strategies? Sustainability, 2022, 14(3): 1930

[38] TariB, Seeto P. Australia’s one step closer to finalising its hydrogen guarantee of origin scheme. 2023-11, available at website of Energetics

[39] WhiteL, Fazeli R, BaldwinK, et al. Implications of European Union Legislation for hydrogen production pathways in Australia. 2023, available at SSRN website

[40] TariH P B. Guarantee of origin for hydrogen and renewable electricity open for consultation. 2022-11, available at website of Energetics

[41] U.S. Environmental Protection Agency (USEPA) . Greenhouse gas inventory guidance indirect emissions from purchased electricity. 2023-12, available at website of USEPA

[42] International Organization for Standardization . Environmental management: Life cycle assessment—Principles and Framework. 2006, ISO14040:2006

[43] InternationalOrganization for Standardization. Environmental management: Life cycle assessment—Requirements and guidelines. 2006: ISO14044:2006

[44] Rosenbaum R K, Bachmann T M, Gold L S. . USEtox—The UNEP-SETAC toxicity model: Recommended characterisation factors for human toxicity and freshwater ecotoxicity in life cycle impact assessment. International Journal of Life Cycle Assessment, 2008, 13(7): 532–546

[45] HaqueN. The Life Cycle Assessment of Various Energy Technologies. Amsterdam: Elsevier, 2020

[46] GrantT. AusLCI database manual. 20162016

[47] Geoscience Australia. Hydrogen economic fairways tool. 2022, available at the website of CSIRO

[48] HosseiniT, Musa M, LaiT, et al. Life cycle assessment of various hydrogen production technologies. In: the 11th Australian Conference on Life Cycle Assessment, Coolangatta, Australia, 2023

[49] Departmentof Climate ChangeEnergyEnvironmentthe Water. Australian national greenhouse accounts factors. 2023, available at website of Australian Government Department of Climate Change, Energy, the Environment and Water

[50] Longden T, Beck F J, Jotzo F. . ‘Clean’hydrogen?—Comparing the emissions and costs of fossil fuel versus renewable electricity based hydrogen. Applied Energy, 2022, 306: 118145

[51] SharmaA, Fazeli R, BaldwinK. Impact of fugitive hydrogen emissions from Australian gas networks and export supply chains. In: Proceedings of the Australian Hydrogen Research Conference, Sydney, Australia, 2023

[52] Gonçalves Dias Ponzi G, Jacks Mendes dos Santos V H, de Medeiros Engelmann P. . The hydrogen life cycle assessment methodology: An overlooked puzzle piece in harmonizing hydrogen certification and trade. Clean Technologies and Environmental Policy, 2024, 26(8): 1–24

RIGHTS & PERMISSIONS

Higher Education Press