Balancing molecular level influences of intermolecular frustrated Lewis pairs (FLP) for successful design of FLP catalysts for hydrogen storage applications

The rise in energy demands and the deleterious environmental issues related to fossil fuels has led to a surge of interest in hydrogen as a “green” alternative. Hydrogen's extraordinary energy density makes it a potential energy and economic “power”-house. Significant research has been dedicated to materials-based hydrogen storage. One area, liquid organic hydrogen carriers (LOHC) is of substantial interest for the reversible transportation of hydrogen from production to end-use facilities. There are challenges associated with this technology including the dependency on precious metal-based catalysts. Recent work in frustrated Lewis pair (FLP) catalysis demonstrates promise for addressing these challenges. This review is focused on assessing recent literature on the utilization of intermolecular FLP main group catalysts for improved hydrogenation/dehydrogenation of various substrates including potential LOHC complexes. This review will present an overview of FLPs, highlight potential hydrogen storage applications, and propose areas where knowledge gaps exist that require further investigations.     

改进中国能源平衡表的建议

中国能源平衡表尚不完善,国际能源组织已有成熟方法与约定,建议与国际接轨,并主要从“四破三扩二改一增加”进行改进。“四破”:破“工厂法”,企业填报能源终端消费数据时,要按能源平衡表部门细分进行填表。破“原煤法”,煤炭平衡数据改用经洗选除掉杂质后的商品煤。破“标准煤法”,改tce为toc表示。破“火电煤耗法”,电力的二次能源和一次能源投入,按物理含能量计算其当量;“三扩”:扩细“其他石油制品”、“其他焦化产品”、“其他煤气”、“其他能源”四个产品。扩分“交通运输”、“用作原材料”两个项目。扩大和完善“分析指标”;“两改”:电的一次能源形式改用投入产出法。能源生产和转换部门的生产过程消费不计入终端能源消费;“一增加”即增加“非常规能源”指标。     

Thermal Hydrogen: An emissions free hydrocarbon economy

Envisioned below is an energy system named Thermal Hydrogen developed to enable economy-wide decarbonization. Thermal Hydrogen is an energy system where electric and/or heat energy is used to split water (or CO₂) for the utilization of both byproducts: hydrogen as energy storage and pure oxygen as carbon abatement. Important advantages of chemical energy carriers are long term energy storage and extended range for electric vehicles. These minimize the need for the most capital intensive assets of a fully decarbonized energy economy: low carbon power plants and batteries. The pure oxygen pre-empts the gas separation process of “Carbon Capture and Sequestration” (CCS) and enables hydrocarbons to use simpler, more efficient thermodynamic cycles. Thus, the “externality” of water splitting, pure oxygen, is increasingly competitive hydrocarbons which happen to be emissions free. Methods for engineering economy-wide decarbonization are described below as well as the energy supply, carrier, and distribution options offered by the system.     

On capital utilization in the hydrogen economy: The quest to minimize idle capacity in renewables-rich energy systems

The hydrogen economy is currently experiencing a surge in attention, partly due to the possibility of absorbing variable renewable energy (VRE) production peaks through electrolysis. A fundamental challenge with this approach is low utilization rates of various parts of the integrated electricity-hydrogen system. To assess the importance of capacity utilization, this paper introduces a novel stylized numerical energy system model incorporating the major elements of electricity and hydrogen generation, transmission and storage, including both “green” hydrogen from electrolysis and “blue” hydrogen from natural gas reforming with CO₂ capture and storage (CCS). Concurrent optimization of all major system elements revealed that balancing VRE with electrolysis involves substantial additional costs beyond reduced electrolyzer capacity factors. Depending on the location of electrolyzers, greater capital expenditures are also required for hydrogen pipelines and storage infrastructure (to handle intermittent hydrogen production) or electricity transmission networks (to transmit VRE peaks to electrolyzers). Blue hydrogen scenarios face similar constraints. High VRE shares impose low utilization rates of CO₂ capture, transport and storage infrastructure for conventional CCS, and of hydrogen transmission and storage infrastructure for a novel process (gas switching reforming) that enables flexible power and hydrogen production. In conclusion, all major system elements must be considered to accurately reflect the costs of using hydrogen to integrate higher VRE shares.     

Hydrogen: A clean energy source

In this review, hydrogen has been considered as a “clean” energy source and carrier and discussed in comparison with present day energy sources mainly based on fossil fuels and nuclear energy. In particular, the environmental and safety issues connected with both nuclear power and coal gasification plants, such as those due to nuclear wastes, acid rain and carbon dioxide, have been considered. Conventional as well as advanced methods of hydrogen production have been examined, attention drawn to direct hydrogen production from alternative energy sources, and an overview provided on the state of the art. A brief insight into hydrogen storage and distribution as well as into conversion and utilization concludes the review.     

Steps toward the hydrogen economy

The hydrogen economy is defined as the industrial system in which one of the universal energy carriers is hydrogen (the other is electricity) and hydrogen is oxidized to water that may be reused by applying an external energy source for dissociation of water into its component elements hydrogen and oxygen. There are three different primary energy-supply system classes which may be used to implement the hydrogen economy, namely, fossil fuels (coal, petroleum, natural gas, and as yet largely unused supplies such as shale oil, oil from tar sands, natural gas from geo-pressured locations, etc.), nuclear reactors including fission reactors and breeders or fusion nuclear reactors over the very long term, and renewable energy sources (including hydroelectric power systems, wind-energy systems, ocean thermal energy conversion systems, geothermal resources, and a host of direct solar energy-conversion systems including biomass production, photovoltaic energy conversion, solar thermal systems, etc.). Examination of present costs of hydrogen production by any of these means shows that the hydrogen economy favored by people searching for a non-polluting gaseous or liquid energy carrier will not be developed without new discoveries or innovations. Hydrogen may become an important market entry in a world with most of the electricity generated in nuclear fission or breeder reactors when high-temperature waste heat is used to dissociate water in chemical cycles or new inventions and innovations lead to low-cost hydrogen production by applying as yet uneconomical renewable solar techniques that are suitable for large-scale production such as direct water photolysis with suitably tailored band gaps on semiconductors or low-cost electricity supplies generated on ocean-based platforms using temperature differences in the tropical seas.     

Numerical study on laminar flame velocity of hydrogen-air combustion under water spray effects

In the context of hydrogen safety and explosions in hydrogen-oxygen systems, numerical simulations of laminar, premixed, hydrogen/air flames propagating freely into a spray of liquid water are carried out. The effects on the flame velocity of hydrogen/air flames of droplet size, liquid-water volume fraction, and mixture composition are numerically investigated. In particular, an effective reduction of the flame velocity is shown to occur through the influence of water spray.To complement and extend the numerical results and the only scarcely available experimental results, a “Laminar Flame Velocity under Droplet Evaporation Model” (LVDEM) based on an energy balance of the overall spray-flame system is developed and proposed. It is shown that the estimation of laminar flame velocities obtained using the LVDEM model generally agrees well with the experimental and numerical data.     

Analysis of the effect and potential of energy conservation in China

In this paper, a quantitative algorithm for direct and indirect energy savings is developed based on the database analysis of China's energy consumption per GDP in the last two decades. The result shows that direct energy savings due to improved energy conversion and end-use utilization efficiencies only account for 26.5% of the total energy savings, and that indirect energy savings due to increased added value of products, product shifts, and structure shifts in industries account for 73.5% of the total energy savings. Factors affecting indirect energy savings are then analyzed, and total energy system efficiencies and direct energy savings in 2020 are quantitatively estimated, which shows that enlarging indirect energy savings is a more crucial task for China's macro-energy conservation in the future. The paper suggests that China should pay more attention to indirect energy savings to improve the energy utilization output benefits by increasing the added value of products, optimizing product and industry structures, and improving production technologies. The potential of indirect energy savings in China is more significant compared with developed countries.     

Hydrogen production for energy: An overview

Power to hydrogen is a promising solution for storing variable Renewable Energy (RE) to achieve a 100% renewable and sustainable hydrogen economy. The hydrogen-based energy system (energy to hydrogen to energy) comprises four main stages; production, storage, safety and utilisation. The hydrogen-based energy system is presented as four corners (stages) of a square shaped integrated whole to demonstrate the interconnection and interdependency of these main stages. The hydrogen production pathway and specific technology selection are dependent on the type of energy and feedstock available as well as the end-use purity required. Hence, purification technologies are included in the production pathways for system integration, energy storage, utilisation or RE export. Hydrogen production pathways and associated technologies are reviewed in this paper for their interconnection and interdependence on the other corners of the hydrogen square.Despite hydrogen being zero-carbon-emission energy at the end-use point, it depends on the cleanness of the production pathway and the energy used to produce it. Thus, the guarantee of hydrogen origin is essential to consider hydrogen as clean energy. An innovative model is introduced as a hydrogen cleanness index coding for further investigation and development.     

Integrated hydrogen production options based on renewable and nuclear energy sources

Due to varied global challenges, potential energy solutions are needed to reduce environmental impact and improve sustainability. Many of the renewable energy resources are of limited applicability due to their reliability, quality, quantity, and density. Thus, the need remains for additional sustainable and reliable energy sources that are sufficient for large-scale energy supply to complement and/or back up renewable energy sources. Nuclear energy has the potential to contribute a significant share of energy supply with very limited impacts to global climate change. Hydrogen production via thermochemical water decomposition is a potential process for direct utilization of nuclear thermal energy. Nuclear hydrogen and power systems can complement renewable energy sources by enabling them to meet a larger extent of global energy demand by providing energy when the wind does not blow, the sun does not shine, and geothermal and hydropower energies are not available. Thermochemical water splitting with a copper–chlorine (Cu–Cl) cycle could be linked with nuclear and selected renewable energy sources to decompose water into its constituents, oxygen and hydrogen, through intermediate copper and chlorine compounds. In this study, we present an integrated system approach to couple nuclear and renewable energy systems for hydrogen production. In this regard, nuclear and renewable energy systems are reviewed to establish some appropriate integrated system options for hydrogen production by a thermochemical cycle such as Cu–Cl cycle. Several possible applications involving nuclear independent and nuclear assisted renewable hydrogen production are proposed and discussed. Some of the considered options include storage of hydrogen and its conversion to electricity by fuel cells when needed.     

Fuel cells: the present state of the technology and future applications,with special consideration of the alkaline hydrogen/oxygen (air) systems

Fuel cells are electrochemical energy converters which have a principal advantage over heat engines: they can utilize the chemical energy of fuels with a high efficiency. Space power systems operating on hydrogen and oxygen have been built successfully. A need exists today to develop a small power plant for the propulsion of automobiles and larger stationary power plants within a city, eliminating pollution problems. During the last decade catalyst costs have been reduced drastically, mass production possibilities have opened up. The combination of water electrolysis and hydrogen-oxygen fuel cells still looks very attractive for space-energy storage applications.     

Petroleum plantations and synthetic chloroplasts

In considering the subject of this conference it seemed proper to examine the idea of how best to use the knowledge acquired through basic research to help solve the worldwide problem of diminishing energy supply and increasing energy needs. The green plants are presently one of the most effective means available to restore a positive balance to the energy and materials account. Sunshine and its conversion into chemical energy and material through the pathways of carbon reduction and quantum conversion in the green plant is the ultimate energy source, universally available on an annually renewable basis and environmentally clean. Learning how to use the green plant in the most efficient way possible is necessary, both for itself and for the model it provides for synthetic devices.Through the mechanism of the photosynthetic carbon cycle, the green plant captures the carbon dioxide from the atmosphere and, with the aid of sunshine, separates hydrogen from the water to reduce the carbon dioxide first to carbohydrate. Some plant species can take the carbohydrate and reduce it all the way to hydrocarbon. The plant that comes most immediately to mind is the Hevea rubber tree which produces latex by reducing the carbon all the way to hydrocarbon. The idea that plants containing hydrocarbon-like materials, such as the latex from Hevea, could be used as a source of hydrocarbons gave rise to the work currently underway in the Laboratory of Chemical Biodynamics, University of California.With the natural green plant as a model, it seemed feasible to try to construct a purely synthetic system capable of capturing solar quanta and storing them in some stable form. This synthetic system, called “synthetic chloroplasts”, would not resemble the natural entity in detailed construction but would be capable of a similar function, that is, it would mimic the way the green plant captures solar quanta to generate oxygen on one side and to reduce power on the other side of a membrane. The potential reactants could be separated and stored and brought together later in a suitably constructed physical system for energy recovery. These synthetic systems could thus capture the quanta and convert them to some other energy form and store that energy for indefinitely long periods with the possibility of future recovery at will in some convenient form. These artificial systems could be used to generate hydrogen, for example, which could be used in chemical processing. or as an energy source, and thus release some of the petroleum products now used in this way for other purposes.     

Compact and fast-response 150 kW hydrogen-oxygen steam generator

Burning of hydrogen produces high-grade heat, which can be used for zero-carbon power generation and/or heating and in heat-intensive industries. In combination with water electrolysis, hydrogen combustion provides efficient energy storage method for variable renewables. Hydrogen combustion systems are compact, powerful and highly maneuverable in comparison with fuel cells. We present experimental results of fire tests of a water-cooled hydrogen-oxygen steam generator (HOSG). This fast-response device has start-up time less than 15 s to thermal capacity of 147 kW. Temperature of generated steam is within 1173–1273 K, parameters of steam and energy conversion efficiency can be adjusted the water-to-hydrogen ratio. The maximum efficiency of conversion of chemical energy of hydrogen into enthalpy of steam is 98.7%.     

The energy transition towards hydrogen utilization for green life and sustainable human development in Patagonia

Energy transitions towards cleaner and transparent systems in Patagonia are examined, considering energy data for hydrogen utilization to store variable renewable energy. The interrelated sectors – power, heating, cooling and transport – demand large amounts of energy and power. Wind transformation and distributed energy management can achieve synergies towards a new energy paradigm. Fossil fuels should be replaced by a system capable of storing massive amounts of electricity and fuels. Full energy services are not affordable employing only rechargeable batteries or air and water pumping. We analyze wind resources, electricity grids, and hydrogen developments carried out in Argentina, and the perspective of large wind-hydrogen facilities for export. We verify the current demand of natural gas and electricity, and propose the start of distributed production, management and utilization of hydrogen in Patagonia and to supply the most populated areas reaching Buenos Aires. Hydrogen sea transportation from South Patagonia to Rio de la Plata could be feasible. “The whole process would help the training of qualified human resources and also encourage the establishment of companies dedicated to renewable and hydrogen technology activities.”     

太阳能等效转化利用模型及其效益研究

以能源局域网为依托,研究太阳能在转化利用过程中不同“能质”能量之间的等效转化关系及其效益模型。综合考虑负荷需求特性及当前能源消费价格因素对太阳能利用方式的影响,以太阳能利用率最大和系统运行综合效益最大化为目标,构建太阳能转化利用多目标优化模型;然后,采用量子行为的粒子群优化算法对模型进行优化求解,并与传统单一供能模式进行对比分析。结果表明,所提模型能有效提高能耗系统对太阳能的综合利用率及消纳能力,并取得更高的能售效益。验证了所提模型及其运行方式的有效性和可行性,为大规模太阳能的开发和利用提供了一个新的思路。     

A statistical approach to model simplification and multiobjective analysis

Evolving national energy supply/demand distribution systems rely, at least in part, on quantifiable factors such as local and national environmental restrictions, resource availability (type, price, and quantity) and the associated transportation infrastructure, the amount and price of capital available to consumers and suppliers of energy, total annualized system cost, including the annualized cost of end-use devices, and the demands for energy and their price/supply responsiveness. The evolution also depends on nonquantifiable factors such as personal, regionally aggregated, or even national “utility functions” and institutional or social barriers. Many models have been formulated which attempt to simulate these complex interactions.This paper describes a systematic statistical methodology for capturing, both visually and quantitatively, the trade-offs between competing quantifiable, differentiable objective functions in a model of the national energy system (Brookhaven Energy System Optimization Model). The aim is to provide decision makers with a more easily understood tool and a more easily defensible methodology on which trade-offs between certain sensitive and competing energy issues can be based. The methodology has the additional advantage of providing insights into the inherent structural relationships of the model (model simplification).     

Recent advances in ammonia synthesis technologies: Toward future zero carbon emissions

As a carbon-free molecule, ammonia has gained great global interest in being considered a significant future candidate for the transition toward renewable energy. Numerous applications of ammonia as a fuel have been developed for energy generation, heavy transportation, and clean, distributed energy storage. There is a clear global target to achieve a sustainable economy and carbon neutrality. Therefore, most of the research's efforts are concentrated on generating cost-effective renewable energy on a large scale rather than fossil fuels. However, storage and transportation are still roadblocks for these technologies, for example, hydrogen technologies. Ammonia could be replaced as a viable fuel for a clean and sustainable future of global energy. More efforts from governments and scientists can lead to making ammonia a clean energy vector in most energy applications. In this review, ammonia synthesis was assessed, including conventional Haber–Bosch technology. Current hydrogen technologies as the key parameters for ammonia generation are also evaluated. The role of ammonia as a hydrogen-based fuel and generation roadmap are discussed for future utilization of energy mix. Further, ammonia generation processes are addressed in depth, including blue and green ammonia generation. A survey of ammonia synthesis catalytic materials was conducted and the role of catalyst materials in ammonia generation was compared, which showed that the Ru-based catalyst generated the maximum ammonia after 20 h of starting experiment. An end-use plan for using ammonia as a clean energy fuel in vehicles, marines, gas turbines as well as fuel cells, is briefly discussed to recognize the potential applications of ammonia use. The practical and future end-use vision of energy sources is proposed to achieve great benefits at low carbon emissions and costs. This review can provide prospective knowledge of large-scale aspects and environmental considerations of ammonia. Herein, we conclude that ammonia will become the “clean energy carrier link” that will achieve the global energy and economy sustainability targets.     

Hydrogen as an energy carrier in stand-alone applications based on PV and PV–micro-hydro systems

The paper compares two different models of a hypothetical stand-alone energy system based only on renewable sources (solar irradiance and micro-hydro power) integrated with a system for the production of hydrogen (electrolyzer, compressed gas storage and proton exchange membrane fuel cell or PEMFC). The models of both systems have been designed to supply the electricity needs of a residential user in a remote area (a valley of the Alps in Italy) during a complete year of operation, without integration of traditional fossil fuel energy devices. A simulation model has been developed to analyze the energy performance of these systems. The technical feasibility and the behavior of the systems will be evaluated through the analysis of some data (e.g. the production and consumption of electricity along the year by the different components; the heat management; the production, storage and utilization of hydrogen).     

The value chain of green hydrogen for fuel cell buses – A case study for the Rhine-Main area in Germany

As an immanent necessity to reduce global greenhouse gas emissions, the energy transition poses a major challenge for the next 30 years, as it includes a cross-sectoral increase of fluctuating renewable energy production, grid extension to meet regional electricity supply and demand as well as an increase of energy storage capacity. Within the power-to-gas concept, hydrogen is considered as one of the most promising solutions.The paper presents a scenario-based bottom-up approach to analyse the hydrogen supply chain to substitute diesel with fuel cell buses in the Rhine-Main area in central Germany for the year 2025. The analysis is based on field data derived from the 6 MW power-to-gas plant “Energiepark Mainz” and the bus demonstration project “H₂-Bus Rhein-Main”. The system is modelled to run simulations on varying demand scenarios. The outcome is minimised hydrogen production costs derived from the optimal scheduling of a power-to-gas plant in terms of the demand. The assessment includes the energy procurement for hydrogen production, different hydrogen delivery options and spatial analysis of potential power-to-gas locations.     

Combustion characteristics and energy distribution of hydrogen engine under high oxygen concentration

Integrated Vehicle Fluid (IVF) system is a promised energy management system for cryogenic upper stage. The power unit of IVF is hydrogen-oxygen internal combustion engine (ICE) whose energy utilization is close to 100% in IVF system. The oxygen concentration of intake gas was gradually raised during ICE tests as a preliminary study. The power of hydrogen-oxygen ICE reaches 4 kW at 3000 r/min, which satisfies the power requirement of IVF system. At this time, the exhaust loss reaches 41.6%, the heat transfer loss is 35.9%, and the output power only accounts for 21.9%. The heat transfer loss shows a parabolic trend which first rises and then falls with increasing oxygen concentration. But the exhaust loss keeps growing with the increases in oxygen concentration and engine speed. It is significant for the design of regenerative cooling system and other subsystems in IVF system at specific engine speed.