Materials,technological status,and fundamentals of PEM fuel cells – A review

PEM (Polymer Electrolyte Membrane) fuel cells have the potential to reduce our energy use, pollutant emissions, and dependence on fossil fuels. In the past decade, significant advances have been achieved for commercializing the technology. For example, several PEM fuel cell buses are currently rated at the technical readiness stage of full-scale validation in realistic driving environments and have met or closely met the ultimate 25,000-h target set by the U.S. Department of Energy. So far, Toyota has sold more than 4000 Mirai PEM fuel cell vehicles (FCVs). Over 30 hydrogen gas stations are being operated throughout the U.S. and over 60 in Germany. In this review, we cover the material, design, fundamental, and manufacturing aspects of PEM fuel cells with a focus on the portable, automobile, airplane, and space applications that require careful consideration in system design and materials. The technological status and challenges faced by PEM fuel cells toward their commercialization in these applications are described and explained. Fundamental issues that are key to fuel cell design, operational control, and material development, such as water and thermal management, dynamic operation, cold start, channel two-phase flow, and low-humidity operation, are discussed. Fuels and fuel tanks pertinent to PEM fuel cells are briefly evaluated.The objective of this review is three fold: (1) to present the latest status of PEM fuel cell technology development and applications in the portable and transportation power through an overview of the state of the art and most recent technological advances; (2) to describe materials and water/thermal transport management for fuel cell design and operational control; and (3) to outline major challenges in the technology development and the needs for fundamental research for the near future and prior to fuel cell world-wide deployment.     

固体氧化物燃料电池电化学与热分析耦合的二维模型

计算机模拟是燃料电池设计的一个重要辅助工具。本文在分析了燃料电池的电学和热学性质之后,设计了一套二维平板型团体氧化物燃料电池(SOFC)的模拟软件,软件能回答诸如温度场分布、电流场分布、输出功率等问题,作为应用例子,该软件被用于分析比较不同气流流向(交叉流、并流、对流)设计的燃料电池工作情况,指出了它们的优缺点,为燃料电池设计提供了有益的信息。     

Nanopore Confinement of Electrocatalysts Optimizing Triple Transport for an Ultrahigh-Power-Density Zinc–Air Fuel Cell with Robust Stability

Metal–air fuel cells with high energy density, eco-friendliness, and low cost bring significantly high security to future power systems. However, the impending challenges of low power density and high-current-density stability limit their widespread applications. In this study, an ultrahigh-power-density Zn–air fuel cell with robust stability is highlighted. Benefiting from the water-resistance effect of the confined nanopores, the highly active cobalt cluster electrocatalysts reside in specific nanopores and possess stable triple-phase reaction areas, leading to the synergistic optimization of electron conduction, oxygen gas diffusion, and ion transport for electrocatalysis. As a result, the as-established Zn–air fuel cell shows the best stability under high-current-density discharging (>90 h at 100 mA cm⁻²) and superior power density (peak power density: >300 mW cm⁻², specific power: 500 Wg_cat⁻¹) compared to most reported non-noble-metal electrocatalysts. The findings will provide new insights in the rational design of electrocatalysts for advanced metal–air fuel cell systems.     

适合分布式冷热电联供系统的中小型发电装置

分布式冷热电联供（combined cooling,heating and power,CCHP）系统是一种小型、临近用户的新型供能方式,可避免能量长距离传输过程损失,同时具有灵活、高效、环保特点,成为大规模、集中式供能方式的重要补充。中小型发电装置是分布式冷热电联供系统的核心,制冷和制热也都围绕发电装置余热展开。对适合分布式冷热电联供系统的2类中小型发电装置的基本工作原理、热力性能和相关研究进展进行综述。一类是以化石燃料为能源输入的中小型发电装置,包括微型燃气轮机、燃气内燃机、小型燃气轮机和燃料电池;另一类是以发电装置余热或太阳能集热等其他热源为能源输入的中小型发电装置,包括有机朗肯循环、正逆耦合循环、热声发电机等。最后,对2类中小型发电装置的优缺点进行对比分析,为分布式供能系统的发电装置选型、系统方案设计等提供参考。     

天然气冷热电联产运行模式的探讨

介绍了一种具有很高一次能源利用率的天然气冷热电三联产系统及其在国内外的应用情况;阐述了几种天然气冷热电联产系统的运行方式与特点,包括基于燃气机、燃气轮机、联合循环、斯特林发动机和燃料电池的冷热电三联产系统;分析了冰蓄冷技术在冷热电联产系统中的意义与作用;对近年来各运行方式的主要研究成果进行了总结与评述;根据国内外天然气冷热电联产系统的研究与应用现状,对未来的主要研究方向作了一些有益的探讨。     

Electrochemical Ammonia Synthesis and Ammonia Fuel Cells

Ammonia is a promising platform molecule for the future renewable energy infrastructure owing to its high energy density (when liquefied) and carbon‐free nature. In particular, the interconversion between the chemical and electrical energies leveraging the nitrogen cycle could be an effective approach in mitigating the intermittency of renewable electricity production. However, efficient methods to store and release energy into and from ammonia, respectively, are still under development. Here, the latest developments in electrochemical ammonia synthesis and ammonia fuel cells are presented, and perspectives in the technical challenges and possible remedies are outlined. N₂ electrolysis, plasma‐enabled N₂ activation, and electro‐thermochemical looping are three potential approaches for electrochemical ammonia synthesis; however, achieving high selectivity and energy efficiency remains challenging. Direct ammonia fuel cells are suitable for a broad range of mobile and transportation applications but are limited by the lack of active catalysts for ammonia oxidation.     

新疆某电厂#1机组排烟余热回收系统的设计与运行

论述了新疆某厂一期锅炉增设烟气余热回收系统（LLHS）降低排烟温度的技术路线及节能效果,提出热系统参数的优化原则及纯凝-供热联合系统切换运行模式。增设LLHS后排烟温度降低不小于25℃。机组年均供电煤耗降低2.56g/kWh（含供热期）,每台锅炉年节省标煤2270t,年节水量4.37万t,减少烟囱内净烟气含水率24%,为脱硫系统正常运行提供了保证。     

能量回馈式车辆主动悬架的可行性研究

通过对车辆被动悬架减振器的阻尼功耗的估算,及其与一个最优主动悬架能量需求的比较,分析了主动悬架设计中回收振动能量的潜力。在振动能量回收可行性分析基础上,提出了一个馈能式电动主动悬架设计方案,并介绍了其结构和工作原理。初步的研究分析表明,所提出的新结构及控制方法可为车辆振动的主动控制和能量回收提供新途径,也为未来电动车悬架系统的电动化提供了必要的设计依据。     

Catalyst Engineering for Electrochemical Energy Conversion from Water to Water: Water Electrolysis and the Hydrogen Fuel Cell

In the context of the current serious problems related to energy demand and climate change, substantial progress has been made in developing a sustainable energy system. Electrochemical hydrogen–water conversion is an ideal energy system that can produce fuels via sustainable, fossil-free pathways. However, the energy conversion efficiency of two functioning technologies in this energy system—namely, water electrolysis and the fuel cell—still has great scope for improvement. This review analyzes the energy dissipation of water electrolysis and the fuel cell in the hydrogen–water energy system and discusses the key barriers in the hydrogen- and oxygen-involving reactions that occur on the catalyst surface. By means of the scaling relations between reactive intermediates and their apparent catalytic performance, this article summarizes the frameworks of the catalytic activity trends, providing insights into the design of highly active electrocatalysts for the involved reactions. A series of structural engineering methodologies (including nanoarchitecture, facet engineering, polymorph engineering, amorphization, defect engineering, element doping, interface engineering, and alloying) and their applications based on catalytic performance are then introduced, with an emphasis on the rational guidance from previous theoretical and experimental studies. The key scientific problems in the electrochemical hydrogen–water conversion system are outlined, and future directions are proposed for developing advanced catalysts for technologies with high energy-conversion efficiency.     

Discovering Reactant Supply Pathways at Electrode/PEM Reaction Interfaces Via a Tailored Interface-Visible Characterization Cell

In situ and micro-scale visualization of electrochemical reactions and multiphase transports on the interface of porous transport electrode (PTE) materials and solid polymer electrolyte (SPE) has been one of the greatest challenges for electrochemical energy conversion devices, such as proton exchange membrane electrolyzer cells (PEMECs), CO₂ reduction electrolyzers, PEM fuel cells, etc. Here, an interface-visible characterization cell (IV-CC) is developed to in situ visualize micro-scaled and rapid electrochemical reactions and transports in PTE/SPE interfaces. Taking the PEMEC of a green hydrogen generator as a study case, the unanticipated local gas blockage, micro water droplets, and their evolution processes are successfully visualized on PTE/PEM interfaces in a practical PEMEC device, indicating the existence of unconventional reactant supply pathways in PEMs. Further comprehensive results reveal that PEM water supplies to reaction interfaces are significantly impacted with current densities. These results provide critical insights about the reaction interface optimization and mass transport enhancement in various electrochemical energy conversion devices.     

Enhancing Electrocatalytic Water Splitting by Strain Engineering

Electrochemical water splitting driven by sustainable energy such as solar, wind, and tide is attracting ever‐increasing attention for sustainable production of clean hydrogen fuel from water. Leveraging these advances requires efficient and earth‐abundant electrocatalysts to accelerate the kinetically sluggish hydrogen and oxygen evolution reactions (HER and OER). A large number of advanced water‐splitting electrocatalysts have been developed through recent understanding of the electrochemical nature and engineering approaches. Specifically, strain engineering offers a novel route to promote the electrocatalytic HER/OER performances for efficient water splitting. Herein, the recent theoretical and experimental progress on applying strain to enhance heterogeneous electrocatalysts for both HER and OER are reviewed and future opportunities are discussed. A brief introduction of the fundamentals of water‐splitting reactions, and the rationalization for utilizing mechanical strain to tune an electrocatalyst is given, followed by a discussion of the recent advances on strain‐promoted HER and OER, with special emphasis given to combined theoretical and experimental approaches for determining the optimal straining effect for water electrolysis, along with experimental approaches for creating and characterizing strain in nanocatalysts, particularly emerging 2D nanomaterials. Finally, a vision for a future sustainable hydrogen fuel community based on strain‐promoted water electrolysis is proposed.     

Catalytic Nanoframes and Beyond

The ever-increasing need for the production and expenditure of sustainable energy is a result of the astonishing rate of consumption of fossil fuels and the accompanying environmental problems. Emphasis is being directed to the generation of sustainable energy by the fuel cell and water splitting technologies. Accordingly, the development of highly efficient electrocatalysts has attracted significant interest, as the fuel cell and water splitting technologies are critically dependent on their performance. Among numerous catalyst designs under investigation, nanoframe catalysts have an intrinsically large surface area per volume and a tunable composition, which impacts the number of catalytically active sites and their intrinsic catalytic activity, respectively. Nevertheless, the structural integrity of the nanoframe during electrochemical operation is an ongoing concern. Some significant advances in the field of nanoframe catalysts have been recently accomplished, specifically geared to resolving the catalytic stability concerns and significantly boosting the intrinsic catalytic activity of the active sites. Herein, general synthetic concepts of nanoframe structures and their structure-dependent catalytic performance are summarized, along with recent notable advances in this field. A discussion on the remaining challenges and future directions, addressing the limitations of nanoframe catalysts, are also provided.     

“Heat pumps — status and trends” in Asia and the Pacific

In Asian and Pacific regions, economic growth in the last decade has propelled the use of air-conditioners for space cooling along with the use of reversible heat pumps for year round space conditioning. This has led to the rapid increase of electricity demand for air conditioning in summer. To cope with the increasing power demand and the requirement for efficient energy use for space conditioning, governments and energy supply utilities have encouraged effective use and leveling of power load using a heat pump with thermal storage systems and gas cooling systems, by enacting financial and promotional supports. Status and trends of heat pumps in Asian and Pacific regions, related to the use of heat pumps for space heating and cooling were surveyed from the view points of climate, energy consumption, technologies, markets and promotion measures.     

Materials engineering for a better global environment

The role of materials engineering including ceramics technology for a better global environment is discussed. Present global environmental issues will be solved by resourceful energy technology and waste management under a minimum pollution of environment. The materials technology will play an important role to mitigate the global environmental issues. Research program on future energy technology and waste management should be considered according to a condition of domestic and/or international regulation. Energy saving and domestic waste management including pollution prevention of atmosphere, water and soil are near term research areas. Medium and long term research areas are non-fossil energy technology and global waste management including removal and/or reuse of greenhouse gas CO₂ and nuclear waste management. To mitigate future global environmental issues, traditional materials technology should be reconstructed to build environment benign materials technology which could provide minimum environmental load.     

A novel pilot-scale production of fuel gas by allothermal biomass gasification using biomass micron fuel (BMF) as external heat source

A novel pilot-scale allothermal biomass gasification system integrating steam gasification, thermal cracking, and catalytic reforming aiming at fuel gas production was developed. Biomass micron fuel (BMF) was used as external heat source by combusting with air in the combustor. Biomass feedstock was gasified with steam, and then, tar in the produced gas was decomposed by thermal cracking and catalytic reforming. The waste heat of high-temperature flue gas and fuel gas was recovered and used for biomass feedstock pre-heating and steam generation, respectively. The fuel gas yield is 1.36 Nm³/kg with lower heating value of 11.61 MJ/Nm³. An overall energy analysis of the system was also investigated. The results showed that the cold gas efficiency and energy conversion efficiency in this system are 88.11 and 63.59 %, respectively. Meanwhile, combustion of BMF accounts for 25.66 % of the total energy input.     

Progress in the Development of Fe‐Based PGM‐Free Electrocatalysts for the Oxygen Reduction Reaction

Development of alternative energy sources is crucial to tackle challenges encountered by the growing global energy demand. Hydrogen fuel, a promising way to store energy produced from renewable power sources, can be converted into electrical energy at high efficiency via direct electrochemical conversion in fuel cells, releasing water as the sole byproduct. One important drawback to current fuel‐cell technology is the high content of platinum‐group‐metal (PGM) electrocatalysts required to perform the sluggish oxygen reduction reaction (ORR). Addressing this challenge, remarkable progress has been made in the development of low‐cost PGM‐free electrocatalysts synthesized from inexpensive, earth‐abundant, and easily sourced materials such as iron, nitrogen, and carbon (Fe–N–C). PGM‐free Fe–N–C electrocatalysts now exhibit ORR activities approaching that of PGM electrocatalysts but at a fraction of the cost, promising to significantly reduce overall fuel‐cell technology costs. Herein, recent developments in PGM‐free electrocatalysis, demonstrating increased fuel‐cell performance, as well as efforts aimed at understanding the key limiting factor, i.e., the nature of the PGM‐free active site, are summarized. Further improvements will be accomplished through the controlled and/or rationally designed synthesis of materials with higher active‐site densities, while at the same time establishing methods to mitigate catalyst degradation.     

Thermodynamic performance analysis of three solid oxide fuel cell and gas microturbine hybrid systems for application in auxiliary power units

In this study, three different configurations of a solid oxide fuel cell and gas microturbine hybrid system are evaluated for application in auxiliary power units. The first configuration is a common hybrid system in auxiliary power units, utilizing a fuel cell stack in the structure of the gas turbine cycle. The other configurations use two series and parallel fuel cell stacks in the structure of the gas turbine cycle. The main purpose of this research is thermodynamic analysis, evaluation of the performance of the proposed hybrid systems in similar conditions, and selection of an appropriate system in terms of efficiency, power generation, and entropy generation rate. In this study, the utilized fuel cells were subjected to electrochemical, thermodynamic, and thermal analyses and their working temperatures were calculated under various working conditions. Results indicate that the hybrid system with two series stacks had maximum power generation and efficiency compared with the other two cases. Moreover, the simple hybrid system and the system with two parallel stacks had relatively equal pure power generation and efficiency. According to the investigations, hybrid system with two series fuel cell stacks, which had 3424 and 1712 cells, respectively, can achieve the electrical efficiency of over 48%. A hybrid system with two parallel fuel cell stacks, in which each stack had 2568 cells, had the electrical efficiency of 46.3%. Findings suggested that maximum electrical efficiency occurred between the pressure ratios of 5–6 in the proposed hybrid systems.     

Hybrid solar-driven interfacial evaporation systems: Beyond water production towards high solar energy utilization

Owing to its promising approach to tackling freshwater scarcity, solar-driven interfacial evaporation (SDIE) which confines the photothermal heat at evaporating surface has attracted tremendous research attention. Optimizing efforts on photothermal conversion and thermal management have greatly improved the SDIE performance. By taking advantage of the heat localization strategy, hybrid SDIE systems have been designed to enhance the solar energy utilization beyond water production. In this review, the development of SDIE and energy flow in hybrid system are discussed. The advanced conceptual designs of different hybrid applications such as electricity generation, fuel production, salt collection, photodegradation and sterilization are comprehensively summarized. Moreover, the current challenges and future perspectives of the hybrid systems are emphasized. This article aims to provide a systematic review on the recent progresses in hybrid SDIE systems to inspire both fundamental and applied research in capitalizing the undervalued auxiliary energy sources for future integrated water, energy and environmental systems.     

Axiomatic design of the sandwich composite endplate for PEMFC in fuel cell vehicles

To fasten a fuel cell stack in a polymer electrolyte membrane fuel cell (PEMFC), two thick steel endplates have been used to maintain a proper contact pressure at the interfaces among gaskets, gas diffusion layer (GDL), membrane electrode assemblies (MEA), and bipolar plates. The proper contact pressure is required both to improve its energy efficiency by decreasing ohmic loss and to prevent leakage of fluid such as hydrogen, air, or coolant. Since the thick steel endplates are not only heavy, but also have high thermal conductivity and thermal inertia, which deteriorate the cold-start characteristics of fuel cell stack, a new development of the endplate with light weight and better thermal properties is necessary.     

Green nanotechnology of trends in future energy

It is well known that current fossil fuel usage is unsustainable and associated with greenhouse gas production. The amount of the world's primary energy supply provided by renewable energy technologies is required urgently. Therefore, the relevant technologies such as hydrogen fuel, solar cell, biotechnology based on nanotechnology and the relevant patents for exploiting the future energy for the friendly environment are reviewed. At the same time, it is pointed out that the significantly feasible world's eco-energy for the foreseeable future should not only be realized, but also methods for using the current energy and their by-products more efficiently should be found correspondingly to ensure the minimal environmental impact.