1 Introduction
An engineering front refers to important directions that have a significant impact on and lead the future innovation of engineering science and technology. It is characterized by its forward looking, leading, and exploratory nature. Since 2017, the Chinese Academy of Engineering (CAE) has annually organized a project known as “Global Engineering Fronts,” identifying and releasing engineering research fronts and engineering development fronts, tracking the trends in engineering science and technology, and actively guiding the academic development and promoting innovation in engineering science and technology. An engineering research front focuses on theoretical exploration, while an engineering development front emphasizes practical applications [
1–
3].
Engineering Fronts 2023, released on December 20, 2023, reported a total of 93 engineering research fronts and 94 engineering development fronts. Three engineering research fronts and three engineering development fronts have been selected in the field of
Energy and Electrical Science and Technology [
2,
3], mainly concentrating in the hydrogen production technology, energy storage technology, power batteries, and smart grids. These fronts are closely related to the development of clean energy technologies and the goals of achieving the carbon peaking and carbon neutrality, which guide promoting innovation in the field of
Energy and Electrical Science and Technology and provide a reference for the topic selection of energy sub-journal
Frontiers in Energy of the flagship journal,
Engineering, of CAE.
2 Research methodology
The basic process of the selection of engineering research fronts in the field of Energy and Electrical Science and Technology involves three stages: data preparation, data analysis, and expert review. In the data preparation stage, the domain, library, and information experts identify the Science Citation Index (SCI) journals and conferences as the sources for data mining. In the data analysis stage, high-impact papers that are ranked the top 10% of citations published between 2017 and 2022 were selected through data mining from the retrieval sources. The co-citation clustering analysis was performed on the co-citation of these papers, obtaining cutting-edge topics. To address the lacking of novelty due to the limitations in data mining algorithms or lagging data, the domain experts were invited to nominate cutting-edge topics. In the expert review stage, domain experts merged, revised, refined, and expanded the cutting-edge topics obtained from data mining and expert nomination. Afterward, through questionnaire surveys and multiple rounds of conference discussions, three engineering research fronts were selected and interpreted.
The research process for engineering development fronts is similar to that of engineering research fronts. The difference lies in the data mining sources in the data preparation and mining stages, which is based on the Derwent Innovation patent database. Based on the initial patent data retrieval scope and search strategies formulated by domain experts and library and information experts, the top 10000 highly cited patents in the enhanced patent data—Derwent World Patents Index (DWPI) and Derwent Patent Citation Index (DPCI) collection published between 2017 and 2022 were obtained for literature topic clustering using DWPI titles and abstracts to create an ThemeScape patent map. The domain experts interpreted the ThemeScape patent map and nominated candidate front topics. After questionnaire surveys and multiple rounds of domain expert seminars, three engineering development fronts are ultimately determined and interpreted.
3 Reports in the field of Energy and Electrical Science and Technology
3.1 Top 3 engineering research fronts
3.1.1 Research of direct hydrogen production from seawater
Direct hydrogen production from seawater is a technology that directly decomposes seawater into hydrogen and oxygen without pretreatment processes like desalination. However, due to the extremely complex composition of seawater (up to 92 chemical elements), it faces many challenges such as chlorination, membrane clogging, and corrosion. Since the proposal of the concept of direct seawater electrolysis in 1975, the four major paths of direct seawater electrolysis for hydrogen production have still been the main focus internationally for half a century. One is direct seawater electrolysis by developing catalysts, through improving electrochemical activity, introducing selective site or constructing protective coatings to avoid the competition between chlorination and oxygen precipitation reactions. The second is direct seawater electrolysis based on asymmetric electrolyte, which is achieved by adding a pure electrolyte at the anode side and seawater at the cathode side. The third is to isolate purity ions via the hydrophilic reverse osmosis membrane. The last is seawater electrolysis based on physical mechanics, through the construction of a gas–liquid phase interface between seawater and electrolyte, and the use of the difference in saturated vapor pressure between the two as the mass transfer driving force, inducing the seawater in the form of gaseous water migration across the membrane to the electrolyte, completely isolating seawater ions and at the same time realizing the seawater without desalination process, side reactions, additional energy consumption of the seawater for the purpose of direct hydrogen production. The development of the direct seawater electrolysis technology for hydrogen production will help promote the global emerging strategic industry of “offshore wind power and other renewable energy utilization—seawater hydrogen production.”
3.1.2 Power-to-X technologies based on renewable energy sources
The Power-to-X technology is the use of green electricity generated from renewable energies (solar, wind, hydro, etc.) to produce green hydrogen, green methanol, green ammonia, and other products. This emerging technology can realize the transformation of intermittent renewable energies into storable chemical energy, thus contributing to the large-scale storage of renewable electricity. Meanwhile, Power-to-X enables linking renewable energies to industry, transportation, energy and power sectors. Therefore, it provides a suitable solution for the global economy decarbonization and for the provision of non-fossil fuel products.
At present, water electrolysis toward hydrogen is the key field of the Power-to-X technology. Meanwhile, coupling green hydrogen with CO2 and/or N2 can provide a wealth of products. The direct conversion of H2O with CO2 and/or N2 toward green methanol, green ammonia, and other products is also an active field of the Power-to-X technology. Of note, co-electrolysis of H2O/CO2 toward syngas, in combination with distributed micro-Fischer-Tropsch process holds a grand promise for generating carbon-neutral fuels and chemicals. Biomass and bio-derived platform molecules are one family of abundant renewable resources on earth with diverse molecular framework, active functional groups, and flexible molecular tailorability compared with CO2 and N2. Thus, it is a suitable object for green electricity processing. Moreover, biomass-based products are perfectly compatible with the economic system. Therefore, the Power-to-X technology coupled with biomass conversion has a great potential in carbon-neutral economy.
Breaking the key scientific and technological bottlenecks of the whole chain of material-electrode-electrolyzer-system, improving the energy conversion efficiency and the economic value of the products, and optimizing the linking method between the Power-to-X technology and the industrial, transportation and energy and power sectors is at the core of this grand topic.
3.1.3 High-energy density lithium metal batteries
As an anode in second batteries, lithium (Li) metal has a very high theoretical specific capacity of 3860 mAh/g and the lowest redox potential. Thus, it is the ultimate choice of anode material for high energy second batteries. In the 1970s, attempts were made to use metallic Li as the anode in rechargeable batteries. However, it was found that Li dendrites were easily formed during charging (i.e., electrochemical deposition of Li), which could pierce the separator film and cause internal short-circuit, leading to thermal runaway and combustion explosion. In addition, Li dendrites could fracture to result in Li pulverization that will enhance the reactivity and safety risk. These fatal flaws block the commercialization of Li metal second batteries. Then, more attention was paid to Li+ intercalation anode materials. Finally, Li-ion batteries based on graphite anodes entered the market in 1991. With the rapid development of electric vehicles and energy storage in the recent 10 years, second batteries with a higher energy density are demanded, and Li metal second batteries have come into sight again. Li–S battery and other new systems with an energy density above 400 Wh/kg have been intensively investigated. Nevertheless, two major problems of Li dendrite growth and low cycling efficiency related to Li metal anode still need to be solved. Optimization of the current collector structure, modification of the anode surface, and use of Li metal composites can effectively suppress Li dendrite growth. Moreover, the electrochemical performance of Li metal anode is strongly dependent on the paired electrolytes. The optimization of liquid electrolyte compositions can improve the property of solid-electrolyte interphase layer, and in turn, suppress Li dendrite growth and enhance the Coulombic efficiency. In particular, the use of organic/inorganic composite electrolytes or inorganic electrolytes is expected to fundamentally solve the problems of Li metal anode. With the continuous emergence of new materials and the optimization of cell structures and charging mode, the practical application of Li metal second batteries might be realized.
3.2 Top 3 engineering development fronts
3.2.1 Fast charging and management technology for batteries
The capability of Li-ion/Na-ion batteries determines the competitiveness and performance of electric vehicles. The full charging time of the existing power battery is approximately 60 min, which is 20 times of the refueling time of the car. As a result, achieving fast-charging can enhance the market share and broaden applications of electric vehicles. The United States Advanced Battery Consortium has proposed specific indicators for power battery charging, requiring 80% of the total battery power to be charged within 15 min. However, due to the polarization from sluggish ion transport, fast-charging often causes metal plating at the anode side, leading to capacity decay and safety issues. Management technologies and battery material modification are two major strategies towards fast-charging. These strategies enhance the fast-charging capability of batteries by lowering the energy barrier of the rate-limiting step for the entire charging process. The aforementioned management technologies include battery intelligent temperature control system and algorithm optimized charging protocol, while material modification mainly focuses on electrode design, anode material, binder, electrolyte, and solid electrolyte interphase (SEI). Nevertheless, the rate-limiting step of the entire charging process is hard to identify, and may vary with external conditions or cycling parameters, which makes strategies aiming at a single step less effective. Under this circumstance, it is necessary to switch from suppressing Li or Na plating to regulating Li or Na plating. Through a series of metal plating regulation methods such as SEI engineering, a uniformly-distributed, less-dendritic, and highly-reversible Li or Na plating at the anode side in fast-charging operations can be realized. This not only intrinsically solves safety problems from Li or Na dendrite plating, restoring the cycling life, but also increases the state of charge under fast-charging. Therefore, this Li or Na plating regulation as well as morphology control is one of the most important tendencies in future development of fast-charging, which is an important trend in the development of fast charging technology in the future.
3.2.2 Long-term and large-scale thermal energy storage and thermo-mechanical energy storage technologies
Thermal energy storage (TES) and thermo-mechanical energy storage (TMES) technologies are energy storage techniques based on heat and mass transfer, and reversible heat-work conversion. They make large-scale energy storage possible from both technical and economic perspectives and realize long-term and seasonal energy storage. With advantages such as high energy density, flexible utilization, high overall efficiency, and controllable costs, they are crucial for promoting the green transformation of energy and building zero-carbon power systems based on renewable energy sources. TES technologies include sensible heat storage, latent heat storage, and thermochemical heat storage. TMES technologies encompass compressed-air/CO2 energy storage, liquid-air/CO2 energy storage, and Carnot batteries (also known as pumped-thermal electricity/energy storage).
The main technical directions for long-term and large-scale TES and TMES technologies include the construction of multiscale coupling mechanisms between heat storage and heat/mass transfer, active control strategies for the physical and chemical properties of heat storage materials, the development and preparation of safe and efficient encapsulation and insulation materials, structural optimization techniques for heat storage units based on the topology optimization theory and AI algorithms, high entropy efficiency compression and expansion techniques under extreme temperature and pressure conditions, thermodynamic and economic analyses of TES and TMES systems, and intelligent operation and control techniques for multi-scenario operation of TES and TMES systems.
The development trend in this field at the material level is that novel composite heat storage materials can be designed and prepared actively based on comprehensive considerations of their thermo-physical properties, corrosiveness, and stability. At the component level, in combination with additive manufacturing technologies such as 3D printing, heat storage units and compressors/turbines with a high degree of freedom for specific targets can be explored and developed. At the system level, TES and TMES systems can be integrated with the zero-carbon power and fuel systems, and extend to smart energy systems that provide flexible energy solutions.
3.2.3 Data-driven technology for security operation and monitoring system of intelligent power distribution networks
As informatization and automation of intelligent power distribution networks continues to improve, the amount of data collected from the operation of power distribution networks has increased dramatically. At the same time, the deep integration of power distribution networks and the Internet of Things has also promoted data interaction within and outside power companies. There gradually forms a big data environment for the secure operation and monitoring of intelligent power distribution networks. However, the types of data obtained from power distribution networks are diverse and the granularity of data is high. In addition, the correlation between online and offline data is extremely complex. Existing model-based analysis, calculation, and optimization control methods for power distribution networks cannot be adapted for practical application. It is urgent to explore data-driven analysis and decision-making, operation optimization, monitoring and control technologies for intelligent power distribution networks to achieve comprehensive intelligent improvement in monitoring, dispatching, protection, control of power distribution systems empowered by big data. The main research directions of data-driven secure operation and monitoring technology for intelligent power distribution networks include development of multi-parameter sensors and edge computing devices for intelligent power distribution networks; security and privacy protection mechanisms for distribution network data communication networks; operation situation awareness and digital twin AI modeling technology for intelligent power distribution networks; multiscale, refined data mining and data fusion technology for intelligent power distribution networks; data-driven aggregation control and interactive support technology for massive demand-side resources in power distribution systems; data-driven source-network-load-storage optimization scheduling method for intelligent power distribution networks; and protection and control technology for smart distribution networks based on fault data mining.
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