Ammonia, with its high hydrogen storage density of 17.7 wt.% (mass fraction), cleanliness, efficiency, and renewability, presents itself as a promising zero-carbon fuel. However, the traditional Haber−Bosch (H−B) process for ammonia synthesis necessitates high temperature and pressure, resulting in over 420 million tons of carbon dioxide emissions annually, and relies on fossil fuel consumption. In contrast, dielectric barrier discharge (DBD) plasma-assisted ammonia synthesis operates at low temperatures and atmospheric pressures, utilizing nitrogen and hydrogen radicals excited by energetic electrons, offering a potential alternative to the H−B process. This method can be effectively coupled with renewable energy sources (such as solar and wind) for environmentally friendly, distributed, and efficient ammonia production. This review delves into a comprehensive analysis of the low-temperature DBD plasma-assisted ammonia synthesis technology at atmospheric pressure, covering the reaction pathway, mechanism, and catalyst system involved in plasma nitrogen fixation. Drawing from current research, it evaluates the economic feasibility of the DBD plasma-assisted ammonia synthesis technology, analyzes existing dilemmas and challenges, and provides insights and recommendations for the future of nonthermal plasma ammonia processes.
Developing efficient anode catalysts for direct ammonia solid oxide fuel cells (NH3-SOFCs) under intermediate-temperatures is of great importance, in support of hydrogen economy via ammonia utilization. In the present work, the pyrochlore-type La2Zr2–xNixO7+δ (LZNx, x = 0, 0.02, 0.05, 0.08, 0.10) oxides were synthesized as potential anode catalysts of NH3-SOFCs due to the abundant Frankel defect that contributes to the good conductivity and oxygen ion mobility capacity. The effects of different content of Ni2+ doping on the crystal structure, surface morphology, thermal matching with YSZ (Yttria-stabilized zirconia), conductivity, and electrochemical performance of pyrochlore oxides were examined using different characterization techniques. The findings indicate that the LZNx oxide behaves as an n-type semiconductor and exhibits an excellent high-temperature chemical compatibility and thermal matching with the YSZ electrolyte. Furthermore, LZN0.05 exhibits the smallest conductive band potential and bandgap, making it have a higher power density as anode material for NH3-SOFCs compared to other anodes. As a result, the maximum power density of the LZN0.05-40YSZ composite anode reaches 100.86 mW/cm2 at 800 °C, which is 1.8 times greater than that of NiO-based NH3-SOFCs (56.75 mW/cm2) under identical flow rate and temperature conditions. The extended durability indicates that the NH3-SOFCs utilizing the LZN0.05-40YSZ composite anode exhibits a negligible voltage degradation following uninterrupted operation at 800 °C for 100 h.
Bio-oil from biomass pyrolysis cannot directly substitute traditional fuel due to compositional deficiencies. Catalytic hydrodeoxygenation (HDO) is the critical and efficient step to upgrade crude bio-oil to high-quality bio-jet fuel by lowering the oxygen content and increasing the heating value. However, the hydrocracking reaction tends to reduce the liquid yield and increase the gas yield, causing carbon loss and producing hydrocarbons with a short carbon-chain. To obtain high-yield bio-jet fuel, the elucidation of the conversion process of biomass catalytic HDO is important in providing guidance for metal catalyst design and optimization of reaction conditions. Considering the complexity of crude bio-oil, this review aimed to investigate the catalytic HDO pathways with model compounds that present typical bio-oil components. First, it provided a comprehensive summary of the impact of physical and electronic structures of both noble and non-noble metals that include monometallic and bimetallic supported catalysts on regulating the conversion pathways and resulting product selectivity. The subsequent first principle calculations further corroborated reaction pathways of model compounds in atom-level on different catalyst surfaces with the experiments above and illustrated the favored C–O/C=O scission orders thermodynamically and kinetically. Then, it discussed hydrogenation effects of different H-donors (such as hydrogen and methane) and catalysts deactivation for economical and industrial consideration. Based on the descriptions above and recent researches, it also elaborated on catalytic HDO of biomass and bio-oil with multi-functional catalysts. Finally, it presented the challenges and future prospective of biomass catalytic HDO.
Solid oxide electrolysis cell (SOEC) is a promising water electrolysis technology that produces hydrogen or syngas through water electrolysis or water and carbon dioxide co-electrolysis. Green hydrogen or syngas can be produced by SOEC with renewable energy. Thus, SOEC has attracted continuous attention in recent years for the urgency of developing environmentally friendly energy sources and achieving carbon neutrality. Focusing on 1276 related articles retrieved from the Web of Science (WoS) database, the historical development of SOECs are depicted from 1983 to 2023 in this paper. The co-occurrence networks of the countries, source journals, and author keywords are generated. Moreover, three main clusters showing different content of the SOEC research are identified and analyzed. Furthermore, the scientometric analysis and the content of the high-cited articles of the research of different topics of SOECs: fuel electrode, air electrode, electrolyte, co-electrolysis, proton-conducting SOECs, and the modeling of SOECs are also presented. The results show that co-electrolysis and proton-conducting SOECs are two popular directions in the study of SOECs. This paper provides a straightforward reference for researchers interested in the field of SOEC research, helping them navigate the landscape of this area of study, locate potential partners, secure funding, discover influential scholars, identify leading countries, and access key research publications.
The depletion of energy resources poses a significant threat to the development of human society. Specifically, a considerable amount of low-grade heat (LGH), typically below 100 °C, is currently being wasted. However, efficient utilization of this LGH can relieve energy shortages and reduce carbon dioxide emissions. To address this challenge, reverse electrodialysis heat engine (REDHE) which can efficiently convert LGH into electricity has emerged as a promising technology in recent years. Extensive efforts have been dedicated to exploring more suitable thermal distillation technologies for enhancing the performance of REDHE. This paper introduces a novel REDHE that incorporates helium-gap diffusion distillation (HGDD) as the thermal separation (TS) unit. The HGDD device is highly compact and efficient, operating at a normal atmospheric pressure, which aligns with the operational conditions of the reverse electrodialysis (RED) unit. A validated mathematical model is employed to analyze the impacts of various operating and structural parameters on the REDHE performance. The results indicate that maintaining a moderate molality of the cold stream, elevating the inlet temperatures of hot and cold streams, lengthening hot- and cold-stream channels, and minimizing the thickness of helium gaps contribute to improving the REDHE performance. Especially, a maximum energy conversion efficiency of 2.96% is achieved by the REDHE when decreasing the thickness of helium gaps to 3 mm and increasing the length of stream channels to 5 m.
Knowing the correct phase connectivity information plays a significant role in maintaining high-quality power and reliable electricity supply to end-consumers. However, managing the consumer-phase connectivity of a low-voltage distribution network is often costly, prone to human errors, and time-intensive, as it involves either installing expensive high-precision devices or employing field-based methods. Besides, the ever-increasing electricity demand and the proliferation of behind-the-meter resources have also increased the complexity of leveraging the phase connectivity problem. To overcome the above challenges, this paper develops a data-driven model to identify the phase connectivity of end-consumers using advanced metering infrastructure voltage and current measurements. Initially, a preprocessing method that employs linear interpolation and singular value decomposition is adopted to improve the quality of the smart meter data. Then, using Kirchoff’s current law and correlation analysis, a discrete convolution optimization model is built to uniquely identify the phase to which each end-consumer is connected. The data sets utilized are obtained by performing power flow simulations on a modified IEEE-906 test system using OpenDSS software. The robustness of the model is tested against data set size, missing smart meter data, measurement errors, and the influence of prosumers. The results show that the method proposed correctly identifies the phase connections of end-consumers with an accuracy of about 98%.
To increase the power generated by solid oxide fuel cells (SOFCs), multiple cells have to be connected into a stack. Nonuniformity of cell performance is a worldwide concern in the practical application of stack, which is known to be unavoidable and caused by manufacturing and operating conditions. However, the effect of such nonuniformity on SOFCs that are connected in parallel has not been discussed in detail so far. This paper provides detailed experimental data on the current distribution within a stack with nonuniform cells in parallel connection, based on the basics of electricity and electrochemistry. Particular phenomena found in such a parallel system are the “self-discharge effect” in standby mode and the “capacity-proportional-load sharing effect” under normal operating conditions. It is believed that the experimental method and results proposed in this paper can be applied to other types of fuel cell or even other energy systems.
Formic acid (FA) is a potential biomass resource of syngas with contents of carbon monoxide (CO, 60 wt.%) and hydrogen (H2, 4.4 wt.%). Among the technologies for FA conversion, the photoreforming of FA has received widespread attention due to its use of green solar energy conversion technology and mild reaction conditions. Herein, a V–W bimetallic solid solution, VxW1−xN1.5 with efficient co-catalytic properties was first and facilely synthesized. When CdS was used as a photocatalyst, the activity performance of the V0.1W0.9N1.5 system was over 60% higher than that of the W2N3 system. The computational simulations and experiments showed the V0.1W0.9N1.5 had great metallic features and large work functions, contributing a faster photo-generated carrier transfer and less recombination, finally facilitating a great performance in cocatalyst for syngas production in photoreforming FA. This work provides an approach to synthesizing novel transition metal nitrides for photocatalysis.
Spectral beam split is attracting more attention thanks to the efficient use of whole spectrum solar energy and the cogenerative supply for electricity and heat. Nanofluids can selectively absorb and deliver specific solar spectra, making various nanofluids ideal for potential use in hybrid photovoltaic/thermal (PV/T) systems for solar spectrum separation. Clarifying the effects of design parameters is extremely beneficial for optimal frequency divider design and system performance enhancement. The water-based SiO2 nanofluid with excellent thermal and absorption properties was proposed as the spectral beam splitter in the present study, to improve the efficiency of a hybrid PV/T system. Moreover, a dual optical path method was applied to get its spectral transimissivity and analyze the impact of its concentration and optical path on its optical properties. Furthermore, a PV and photothermal model of the presented system was built to investigate the system performance. The result indicates that the transimissivity of the nanofluids to solar radiation gradually decreases with increasing SiO2 nanofluid concentration and optical path. The higher nanofluid concentration leads to a lower electrical conversion efficiency, a higher thermal conversion efficiency, and an overall system efficiency. Considering the overall efficiency and economic cost, the optimal SiO2 nanofluid concentration is 0.10 wt.% (wt.%, mass fraction). Increasing the optical path (from 0 to 30 mm) results in a 60.43% reduction in electrical conversion efficiency and a 50.84% increase in overall system efficiency. However, the overall system efficiency rises sharply as the optical path increases in the 0–10 mm range, and then slowly at the optical path of 10–30 mm. Additionally, the overall system efficiency increases first and then drops upon increasing the focusing ratio. The maximum efficiency is 51.93% at the focusing ratio of 3.
As the next-generation oxy-fuel combustion technology for controlling CO2 emissions, pressurized oxy-fuel combustion (POC) technology can further reduce system energy consumption and improve system efficiency compared with atmospheric oxy-fuel combustion. The oxy-fuel combustion causes high CO2 concentration, which has a series of effects on the combustion reaction process, making the radiation and reaction characteristics different from air-fuel conditions. Under the pressurized oxy-fuel condition, the combustion reaction characteristics are affected by the coupling effect of pressure and atmosphere. The radiation and heat transfer characteristics of the combustion medium are also affected by pressure. In recent years, there have been many studies on POC. This review pays attention to the thermal-science fundamental research. It summarizes several typical POC systems in the world from the perspective of system thermodynamic construction. Moreover, it reviews, in detail, the current research results of POC in terms of heat transfer characteristics (radiant heat transfer and convective heat transfer), combustion characteristics, and pollutant emissions, among which the radiation heat transfer and thermal radiation model are the focus of this paper. Furthermore, it discusses the development and research direction of POC technology. It aims to provide references for scientific research and industrial application of POC technology.
