Publications

Significant research efforts are directed towards finding new ways to reduce the cost increase efficiency and decrease the environmental impact of power-generation systems. The poly-generation concept is a promising strategy that enables the development of a sustainable power system. Over the past few years the Proton Exchange Membrane Fuel Cell-based Poly-Generation Systems (PEMFC-PGSs) have received accelerated developments due to the low-temperature operation high efficiency and low environmental impact. This paper provides a comprehensive review of the main PEMFC-PGSs including Combined Heat and Power (CHP) co-generation systems Combined Cooling and Power (CCP) co-generation systems Combined Cooling Heat and Power (CCHP) tri-generation systems and Combined Water and Power (CWP) co-generation systems. First the main technologies used in PEMFC-PGSs such as those related to hydrogen production energy storage and Waste Heat Recovery (WHR) etc. are detailed. Then the research progresses on the economic energy and environmental performance of the different PEMFC-PGSs are presented. Also the recent commercialization activities on these systems are highlighted focusing on the leading countries in this field. Furthermore the remaining economic and technical obstacles of these systems along with the future research directions to mitigate them are discussed. The review reveals the potential of the PEMFC-PGS in securing a sustainable future of the power systems. However many economic and technical issues particularly those related to high cost and degradation rate still need to be addressed before unlocking the full benefits of such systems.

H2 is clean energy and an important component of natural gas. Moreover it plays an irreplaceable role in improving the hydrocarbon generation rate of organic matter and activating ancient source rocks to generate hydrocarbon in Fischer-Tropsch (FT) synthesis and catalytic hydrogenation. Compared with hydrocarbon reservoir system a complete hydrogen (H2) accumulation system consists of H2 source，reservoirs and seal. In nature the four main sources of H2 are hydrolysis organic matter degradation the decomposition of substances such as methane and ammonia and deep mantle degassing. Because the complex tectonic activities the H2 produced in a geological environment is generally a mixture of various sources. Compared with the genetic mechanisms of H2 the migration and preservation of H2 especially the H2 trapping are rarely studied. A necessary condition for large-scale H2 accumulation is that the speed of H2 charge is much faster than diffusion loss. Dense cap rock and continuous H2 supply are favorable for H2 accumulation. Moreover H2O in the cap rock pores may provide favorable conditions for short-term H2 accumulation.

Water electrolysis using solid oxide electrolysis cells is a promising method for hydrogen production because it is highly efficient clean and scalable. Recently a lot of researches focusing on development of high-power stack system have been introduced. However there are very few studies of economic analysis for this promising system. Consequently this study proposed 20-kW-scale high-power solid oxide electrolysis cells system config urations then conducted economic analysis. Especially the economic context was in South Korea. For com parison a low-power system with similar design was used as a reference; the levelized cost of hydrogen of each system was calculated based on the revenue requirement method. Furthermore a sensitivity analysis was also performed to identify how the economic variables affect the hydrogen production cost in a specific context. The results show that a high-power system is superior to a low-power system from an economic perspective. The stack cost is the dominant component of the capital cost but the electricity cost is the factor that contributes the most to the hydrogen cost. In the first case study it was found that if a high-power system can be installed inside a nuclear power plant the cost of hydrogen produced can reach $3.65/kg when the electricity cost is 3.28¢/kWh and the stack cost is assumed to be $574/kW. The second case study indicated that the hydrogen cost can decrease by 24% if the system is scaled up to a 2-MW scale.

The mechanical properties of materials deteriorate when hydrogen embrittlement (HE) occurs seriously threatening the reliability and durability of the hydrogen system. Therefore it is important to summarize the status and development trends of research on HE. This study reviewed 6676 publications concerned with HE from 1997 to 2022 based on the Web of Science Core Collection. VOSviewer was used to conduct the bibliometric analysis and produce visualizations of the publications. The results showed that the number of publications on HE increased after 2007 especially between 2017 and 2019. Japan was the country with the highest numbers of productive authors and citations of publications and the total number of citations of Japanese publications was 24589. Kyushu University was the most influential university and the total number of citations of Kyushu University publications was 7999. Akiyama was the most prolific and influential author publishing 88 publications with a total of 2565 citations. The USA South Korea and some European countries are also leading in HE research; these countries have published more than 200 publications. It was also found that the HE publications generally covered five topics: “Hydrogen embrittlement in different materials” “Effect of hydrogen on mechanical properties of materials” “Effect of alloying elements or microstructure on hydrogen embrittlement” “Hydrogen transport” and “Characteristics and mechanisms of hydrogen related failures”. Research hotspots included “Fracture failure behavior and analysis” “Microstructure” “Hydrogen diffusion and transport” “Mechanical properties” “Hydrogen resistance” and so on. These covered the basic methods and purposes of HE research. Finally the distribution of the main subject categories of the publications was determined and these categories covered various topics and disciplines. This study establishes valuable reference information for the application and development of HE research and provides a convenient resource to help researchers and scholars understand the development trends and research directions in this field.

Although alkaline water electrolysis (AWE) is the most widespread technology for hydrogen production by electrolysis its electrochemical and fluid dynamic optimization has rarely been addressed simultaneously using Computational Fluid Dynamics (CFD) simulation. In this regard a two-dimensional (2D) CFD model of an AWE cell has been developed using COMSOL® software and then experimentally validated. The model involves transport equations for both liquid and gas phases as well as equations for the electric current conservation. This multiphysics approach allows the model to simultaneously analyze the fluid dynamic and electrochemical phenomena involved in an electrolysis cell. The electrical response was evaluated in terms of polarization curve (voltage vs. current density) at different operating conditions: temperature electrolyte conductivity and electrode-diaphragm distance. For all cases the model fits very well with the experimental data with an error of less than 1% for the polarization curves. Moreover the model successfully simulates the changes on gas profiles along the cell according to current density electrolyte flow rate and electrode-diaphragm distance. The combination of electrochemical and fluid dynamics studies provides comprehensive information and makes the model a promising tool for electrolysis cell design.

This review provides a comprehensive overview of the dynamics of low-temperature water electrolyzers and their influence on coupling the three major technologies alkaline Proton Exchange Membrane (PEM) and Anion Exchange Membrane (AEM) with photovoltaic (PV) systems. Hydrogen technology is experiencing considerable interest as a way to accelerate the energy transition. With no associated CO2 emissions and fast response water electrolyzers are an attractive option for producing green hydrogen on an industrial scale. This can be seen by the ambitious goals and large-scale projects being announced for hydrogen especially with solar energy dedicated entirely to drive the process. The electrical response of water electrolyzers is extremely fast making the slower variables such as temperature and pressure the limiting factors for variable operation typically associated with PV-powered electrolysis systems. The practical solar-to-hydrogen efficiency of these systems is in the range of 10% even with a very high coupling factor exceeding 99% for directly coupled systems. The solar-to-hydrogen efficiency can be boosted with a battery potentially sacrificing the cost. The intermittency of solar irradiance rather than its variability is the biggest challenge for PV-hydrogen systems regarding operation and degradation.

Despite the potential of hydrogen as a sustainable energy carrier existing studies analysing the recent evolution of this technology are scattered typically focusing on a specific type of hydrogen technology within a single country or region. In this paper we adopt a broader perspective providing an overview of the evolution of knowledge generation across different types of hydrogen fuel and the leading countries in developing new technologies in this field. Using data from the European Patent Office we map knowledge generation on hydrogen fuel technologies exploring its geographic distribution and its link with environmental sustainability. While the United States leads the generation of new knowledge other Asian and European countries show greater dynamism in growth and specialisation. Our study shows that although hydrogen fuel is considered environmentally friendly most recent technological developments are still related to fossil energy sources. However a faster growth rate is observed in the knowledge of hydrogen fuel from renewable sources pointing to a promising path towards sustainability. Moreover our analysis of the knowledge interconnection between different hydrogen types suggests that those technologies developed for hydrogen based on fossil energy sources have enabled novel applications based on renewable energies.

The decarbonization of the energy sector has been a subject of research and of political discussions for several decades gaining significant attention in the last years. It is commonly acknowledged that the most obvious way to achieve decarbonization is the use of renewable energy sources. Within the context of the energy sector decarbonization many mainly industrialized countries recently started developing national plans to establish a hydrogen-based economy in the very near future. The plans for green hydrogen initially try to (a) target sectors that are difficult to decarbonize and (b) address issues related to the storage and transportation of CO2-free energy. To achieve almost complete decarbonization electric power must be generated exclusively from renewable sources. In so-called Power-to-X (PtX) technologies green hydrogen is generated from electricity and subsequently converted to another energy carrier which can be further stored transported and used. In PtX X stands for example for liquid hydrogen methanol or ammonia. The challenges associated with decarbonization include those associated with (a) the expansion of renewable energies (e.g. high capital demand political and social issues) (b) the production transportation and storage of hydrogen and the energy carriers denoted by X in PtX (e.g. high cost and low overall efficiency) and (c) the expected significant increase in the demand for electrical energy. The paper discusses whether and under which conditions the current national and international hydrogen plans of many industrialized countries could lead to a maximization of decarbonization in the world. It concludes that in general as long as the conditions for generating large excess amounts of green electricity are not met the quick establishment of a hydrogen economy could not only be very expensive but also counterproductive to the worldwide decarbonization efforts.

Contrary to microgrids (MGs) for which grid code or legislative support are lacking in the majority of cases energy communities (ECs) are one of the cornerstones of the energy transition backed up by the EU’s regulatory framework. The main difference is that unlike MGs ECs grow and develop organically through citizen involvement and investments in the existing low-voltage (LV) distribution networks. They are not planned and built from scratch as closed distribution systems that are independent of distribution system operator plans as assumed in the existing literature. An additional benefit of ECs could be the ability to transition into island mode contributing to the resilience of power networks. To this end this paper proposes a three-stage framework for analyzing the islanding capabilities of ECs. The framework is utilized to comprehensively assess and compare the islanding capabilities of ECs whose organic development is based upon three potential energy vectors: electricity gas and hydrogen. Detailed dynamic simulations clearly show that only fully electrified ECs inherently have adequate islanding capabilities without the need for curtailment or additional investments.

High-accuracy gas dispersion models are necessary for predicting hydrogen movement and for reducing the damage caused by hydrogen release accidents in chemical processes. In urban areas where obstacles are large and abundant computational fluid dynamics (CFD) would be the best choice for simulating and analyzing scenarios of the accidental release of hydrogen. However owing to the large computation time required for CFD simulation it is inappropriate in emergencies and real-time alarm systems. In this study a non-linear surrogate model based on deep learning is proposed. Deep convolutional layer data-driven autoencoder and batch normalized deep neural network is used to analyze the effects of wind speed wind direction and release degree on hydrogen concentration in real-time. The typical parameters of hydrogen diffusion accidents at hydrogen refuelling stations were acquired by CFD numerical simulation approach and a database of hydrogen diffusion accident parameters is established. By establishing an appropriate neural network structure and associated activation function a deep learning framework is created and then a deep learning model is constructed. The accuracy and timeliness of the model are assessed by comparing the results of the CFD simulation with those of the deep learning model. To develop a dynamic reconfiguration prediction model for the hydrogen refuelling station diffusion scenario the algorithm is continuously enhanced and the model is improved. After training is finished the model's prediction time is measured in seconds which is 105 times quicker than field CFD simulations. The deep learning model of hydrogen release in hydrogen refuelling stations is established to realize timely and accurate prediction and simulation of accident consequences and provide decision-making suggestions for emergency rescue and personnel evacuation which is of great significance for the protection of human life health and property safety.