Future Sustainable Energy Systems Research Articles

Large–Scale, High-Performance, Durable and Low-Cost Membrane Electrode Assemblies for Proton Exchange Membrane Water Electrolyzers

Proton exchange membrane (PEM) water electrolyzers, designed to produce hydrogen from intermittent renewable energy, will play a key role in future sustainable energy systems.1 However, the widespread commercialization of PEM water electrolyzers is obstructed by their high cost, low durability, and safety concerns related to the hydrogen crossover. Currently, the production cost of green H2 is in the range of $3-8 kg-1. In order to boost the commercialization of this clean energy devices and lower the production cost of green H2, DOE implemented targets of $2 kg-1 by 2025 and $1 kg-1 hydrogen by 2030.2 In addition, the durability of all electrolyzer components has to be improved in order to increase the lifetime of a PEM water electrolyzer stack to the targeted 80,000 hours. These challenging targets inspired the researchers all over the world to work on development of novel catalyst and catalyst layers with decreased platinum group metal (PGM) loadings, invent new cost-effective methods for fabrication of membrane electrode assemblies (MEAs), develop innovative designs for the MEAs capable of decreasing the hydrogen crossover, and improve the corrosion resistance of the cell hardware and the other stack components to enhance their durability.In this work, the unique Reactive Spray Deposition Technology (RSDT) is used to fabricate a high-performance, durable, and low-cost MEAs with geometric area of 680 cm2. These large scale MEAs have one order of magnitude lower PGM loadings in their catalyst layers in comparison to the state-of-the-art (SOA) commercial MEAs. The RSDT is a flame-based method that combines the catalysts synthesis and electrodes deposition in one step and thus substantially reduces the time and cost for MEAs fabrication.3–5 As fabricated large-scale MEAs with 680 cm2 geometric area of their electrodes, have loadings of 0.2 mgPt/cm2 in the cathode and 0.3 mgIr/cm2 in the anode, which are 10 times lower than the loadings in the SOA MEAs. The MEAs of interest have been tested at steady-state conditions that are typical for an industrial hydrogen production system for over 1000 hours. The cell voltage transients, as well as the periodically measured polarization curves during the test, clearly show that as fabricated MEAs have excellent activity and durability performance. Furthermore, the RSDT fabricated MEAs have integrated dual recombination layers that effectively reduce the hydrogen crossover to below 10 % LFL at all measured current densities (from 0.58 to 1.8 A/cm2). In addition, the MEA was subjected to comprehensive post-test analysis to study the degradation mechanisms governing the performance loss during the long-term durability test, and the results obtained will be presented and discussed in this presentation.Reference1. C. Van Pham, D. Escalera-López, K. Mayrhofer, S. Cherevko, and S. Thiele, Adv. Energy Mater., 11 (2021).2. https://www.energy.gov/eere/fuelcells/hydrogen-shot-summit-proceedings-panel-session-1-electrolysis3. H. Yu, N. Danilovic, Y. Wang, W. Willis, A. Poozhikunnath, L. Bonville, C. Capuano, K. Ayers, and R. Maric, Appl. Catal. B Environ., 239, 133–146 (2018).4. G. Mirshekari, R. Ouimet, Z. Zeng, H. Yu, S. Bliznakov, L. Bonville, A. Niedzwiecki, C. Capuano, K. Ayers, and R. Mari, Int. J. Hydrogen Energy, 46, 1526–1539 (2021).5. H. Yu, L. Bonville, J. Jankovic, and R. Maric, Appl. Catal. B Environ., 260, 118194 (2020).

(Invited) Towards the Development of High-Performance Crystalline Rutile Iridium Dioxide Electrocatalysts for the Oxygen Evolution Reaction

Proton exchange membrane water electrolysis (PEMWE) offers a promising route for the production of green hydrogen from renewable energy sources and could be the master key to unlocking a future sustainable energy system (1). One of the main barriers delaying the wide-spread adoption of PEMWE technologies is the slow kinetics of the oxygen evolution reaction (OER) occurring at the anode and the need for high-cost, low-abundance precious metal electrocatalysts. Iridium-based oxides are still considered the only feasible option for practical applications due to their high activity and considerable corrosion stability under the harsh electrochemical reaction conditions. To improve the overall efficiency of PEMWEs, future electrocatalyst development strategies must concomitantly address performance metrics in terms of activity, stability and material cost.Towards enhancing iridium utilisation, efforts are aimed at increasing the electrochemical surface area of the catalyst per mass of iridium, thereby increasing the number of available electrocatalytic surface sites. In this regard, amorphous iridium oxide (IrOx) nanoparticles have been shown to achieve a high intrinsic activity (2). However, this comes at the expense of catalyst stability (3) and a loss of intrinsic electronic conductivity (4) associated with the lower degree of crystallinity. By maximising the dispersion of Ir-based nanoparticles, the use of high surface area support materials have also been shown to improve OER performance (5, 6).However, to address long-term stability concerns for Ir-based OER catalysts, highly crystalline rutile iridium dioxide (IrO2) materials may still offer the best prospects. The drawback of using this approach is that the formation of crystalline IrO2 nanoparticles often involves high temperature thermal oxidative treatment causing particle growth and loss of surface area, ultimately leading to decreased OER activities (7). Therefore, novel synthesis methods that retain a high degree of crystallinity without a loss of surface area for IrO2 nanoparticles are required.In this talk, we discuss two synthesis strategies geared towards the preparation of highly crystalline IrO2 nanoparticles with high OER performance. Firstly, we present a novel wet-chemistry synthesis method that avoids the use of reducing agents and eliminates the need for high temperature thermal oxidative treatment. The resultant nano-sized IrO2 nanoparticles were found to have excellent Ir mass-specific OER activity and durability attributed to the small nanoparticle size and high degree of crystallinity.Secondly, we present a novel metalorganic chemical deposition process as a simple, one-step preparation method for highly crystalline IrO2 nanoparticles supported on Sb-doped tin oxide (ATO) (8). The superior OER performance was attributed to the epitaxial anchoring of well dispersed, crystalline IrO2 nanoparticles onto the ATO support. We further discuss the versatility of the method to the application of other conductive oxide support materials such as indium tin oxide and F-doped tin oxide, with the ability of tuning the chemical state of the Ir-based nanoparticles by changing the reaction conditions, i.e., temperature and gas environment as well as the nature of the support.Finally, using a series detailed physico-chemical characterisation techniques to elucidate the nature the iridium phase, composition, morphology and structure, we relate these properties to the electrochemical activity and stability of the prepared materials for the OER. Herein, we highlight some of the challenges often encountered with the analysis of physical and electrochemical characterisation data for IrO2 nanoparticles, particularly when supported on other oxide materials. Acknowledgements This work is funded by the Department of Science and Innovation (DSI, South Africa) Impala Platinum Holdings Limited (Implats) and the Federal Minister of Education and Research (BMBF, Germany). References K. Ayers, Current Opinion in Electrochemistry, 18, 9 (2019). T. Reier, I. Weidinger, P. Hildebrandt, R. Kraehnert and P. Strasser, ECS Transactions, 58, 39 (2013). T. Binninger, R. Mohamed, K. Waltar, E. Fabbri, P. Levecque, R. Kötz and T. J. Schmidt, Scientific Reports, 5, 12167 (2015). M. Bernt, C. Schramm, J. Schröter, C. Gebauer, J. Byrknes, C. Eickes and H. A. Gasteiger, Journal of The Electrochemical Society, 168, 084513 (2021). H.-S. Oh, H. N. Nong, T. Reier, A. Bergmann, M. Gliech, J. Ferreira de Araújo, E. Willinger, R. Schlögl, D. Teschner and P. Strasser, Journal of the American Chemical Society, 138, 12552 (2016). A. Hartig-Weiss, M. Miller, H. Beyer, A. Schmitt, A. Siebel, A. T. S. Freiberg, H. A. Gasteiger and H. A. El-Sayed, ACS Applied Nano Materials, 3, 2185 (2020). J. Quinson, Advances in Colloid and Interface Science, 303, 102643 (2022). Z. S. H. S. Rajan, T. Binninger, P. J. Kooyman, D. Susac and R. Mohamed, Catalysis Science & Technology, 10, 3938 (2020).

Solar energy utilisation: Current status and roll-out potential

• Three types of temperature distributions: uniform, Gaussian and anti-Gaussian were indicated. • PV performance under three types of temperature fields was studied. • It could produce the highest electrical efficiency under the Gaussian temperature field. To meet the well-known energy transition challenge, a rapid shift from fossil fuels to the broader exploitation of renewable energy sources is needed; solar energy represents the most abundant and readily available resource amongst the renewable energy sources. This vision paper aims at shedding light on the current knowledge and emerging pathways for solar energy utilisation. Specifically, after a general introduction and a brief overview of the current knowledge, open issues are discussed regarding photovoltaic/thermal (PV/T) collectors, building integrated photovoltaic/thermal (BIPV/T) systems, concentrating solar power plants, solar thermochemistry, solar-driven water distillation, and solar thermal energy storage technologies. Subsequentially, this vision article defines key fundamental challenges that need to be addressed for these technologies to play a significant role in future sustainable energy systems. The identified challenges include developing new materials, enhanced performance, accelerated system installation and improved manufacturing processes, combining solar energy with other clean energy production and storage systems, and integrating solar energy utilisation with local energy utilisation patterns.

Investigation of Combined Heating and Cooling Systems with Short- and Long-Term Storages

Modern buildings in cold climates, like Norway, may have simultaneous heating and cooling demands. For these buildings, integrated heating and cooling systems with heat pumps, as well as short-term and long-term thermal storage, are promising solutions. Furthermore, combining this integrated system with renewables aids in the transition to future sustainable building energy systems. However, cost-effectively designing and operating such a complicated system is challenging and rarely addressed. Therefore, this research proposed an integrated heating and cooling system that incorporated a short-term water tank and a long-term borehole thermal storage. Meanwhile, three operating modes: heating, cooling, and free cooling were defined based on different heating and cooling load conditions. A detailed system model was developed in MATLAB using heat pump manufacture data as well as simulated and measured building loads. Following that, sensitivity studies were performed to investigate the impacts of ground properties, thermal storage size, setpoint temperature, heat pump characteristics, and load conditions. The findings identified the crucial factors that influence the system’s overall energy efficiency and the functioning of the key system components. Particularly, it revealed that low cooling to heating ratios caused an imbalance in charging and discharging, further reducing the ground temperature and degrading the heat pump’s performance.

Design analysis and tri-objective optimization of a novel integrated energy system based on two methods for hydrogen production: By using power or waste heat

Hydrogen is rapidly turning into one of the essential energy carriers for future sustainable energy systems. The main reason for this is the possibility of off-peak excess power production and storage of renewable stations such as wind farms, photovoltaic plants, etc. For hydrogen (itself) or its sub-productions methanol, ammonia, etc. Such energy systems are so-called power2X technologies. For hydrogen and other biogases, using a fuel cell is a promising method for returning the fuel to the power grid or electric cars in the form of electricity. In this paper, a novel hybrid energy system consisting of a molten carbonate fuel cell (MCFC) and different options to generate hydrogen from the waste heat of the MCFC is investigated. The system consists of two scenarios of weather using proton exchange membrane electrolyzer (PEME) of vanadium chloride (VCL) cycle. The article presents a comprehensive thermodynamic, economic, and environmental analysis of the system optimized by tri-objective optimization (as an innovative optimization) methods. The aim of the optimization task here is to minimize the costs and emissions while maximizing efficiency. A parametric study is conducted to see the effect of different design parameters on the system's performance. Results demonstrate that fuel utilization factor, stack temperature, and current density have the most critical effect on the system performance. In addition, the system coupled with the VCL cycle exhibits better performance than the system with PEME. In addition, at the optimized point, the efficiency, cost rate, and emission become 69.28%, 3.73 ($/GJ), and 1.16 kg/kWh, respectively. In addition, the produced hydrogen in VCL and PEME are 585 kg/day and 293 kg/day respectively.

5G Wireless Networks in the Future Renewable Energy Systems

This paper focuses on the strategies that employ the fifth generation (5G) wireless networks in the optimal management of demand-side response in the future energy systems with the high penetration of renewable energy sources (RES). It also provides a comparison between advantages and challenges of 5G networks in demand-response renewable energy grids. Large-scale renewable energy integration always leads to a mismatch between generation and load demand in the short run due to the intermittency. It is often envisioned that 5G wireless networks that were recently launched and would most likely be fully deployed worldwide by 2035 would bring many technological and economic benefits for a plethora of the future high-renewables grids featuring electric transport and heating as well as prosumers generating renewable energy and trading it back to the grid (for example, in the vehicle-to-grid (V2G) framework) and among themselves using peer-to-peer (P2P) networks. Our paper offers a comprehensive analysis of 5G architecture with the perspectives of optimal management of demand-side response in the smart grids of the future. We show that the effective deployment of faster and more reliable wireless networks would allow faster data transfers and processing, including peer-to-peer (P2P) energy trade market, Internet of Vehicles (IoV) market, or faster smart metering, and thence open the path for the full-fledged Internet of Energy (IoE). Moreover, we show that 5G wireless networks might become in the future sustainable energy systems paving the road to even more advanced technologies and the new generations of networks. In addition, we demonstrate that for the effective management of energy demand-side response with a high share of renewables, certain forms of governments funding and incentives might be needed. These are required to strengthen the support of RES and helping to shift to the green economy.

S-doped CoP nanoneedles assembled urchin-like structure for efficient water oxidation

The electrocatalysts with low-price and high-efficiency for oxygen evolution reaction (OER) are of significant importance for water splitting, which is believed as the promising technique for future sustainable energy system. Herein, sulfur is doped into carbon cloth supported CoP nanoneedles assembled urchin-like structure to acquire improved intrinsic catalysis efficiency, fast charge diffusion, and additional catalysis sites for enhanced OER performance. The specific urchin-like assembly structure is beneficial for highly exposed active sites and short charge transfer path for catalysis. Benefited from the advantages, the obtained sample exhibits advanced OER activity even better than RuO2 in alkaline solution, achieving low overpotentials of 248 and 380 mV at current densities of 10 and 100 mA cm−2, respectively. This study may set a blueprint for exploring efficient transition metal pounds based catalyst for water splitting with nonmetal doping engineering.

Optimal Integration of Renewable Sources and Latent Heat Storages for Residential Application

Given the large amount of energy required in the building sector, an interesting opportunity to reach future sustainable energy systems is the path towards low energy buildings. This work proposes an approach for optimally integrating building-scale energy technologies (both traditional and renewable) to enhance the transformation of the existing buildings (often energetically inefficient) in low-carbon systems. The approach promotes a transition sustainable from both the economic and environmental perspectives. Both operation and design optimization are considered with the aim of suggesting the best set of capacity of the technologies to be installed taking into account the expected operations. The building-scale technologies are integrated with proper storage units: Li-ion batteries and thermal storage (latent heat, that requires low installation space). As a dispatchable renewable technology, a biogas small-scale combined heat and power unit is included in the system. Once the key role played by this component in meeting the loads is proved, an analysis of the impact of the cost of the primary energy carrier of this technology on the system design is carried out. Two optimization approaches have been adopted (both based on non-linear programming). Results show that operation costs can be reduced by up to 29%. The adoption of a combined approach that takes into account both operation and design optimization lead to a reduction in installation and operating costs by up to 27%. In the analyzed cases, the use of the combined optimization confirms that latent heat storage is more suitable to be installed than electric storage (about −4.5% cost).

High Centrifugal Field Coupling with Electrolyte Circulation Internals: Process Intensification toward Efficient Water Electrolysis for Hydrogen Storage via Power-to-Gas

Water electrolysis has the potential to become a key element for the conversion of surplus wind/solar electricity into H2 via power-to-gas (P2G) in a future sustainable energy system. However, water electrolysis suffers from low energy efficiency owing to the high overpotential and large ohmic voltage drop. In this study, the effect of the centrifugal field on the hydrogen evolution reaction (HER) was studied, and the overpotential of the HER was measured by Tafel polarization. The results showed that the HER overpotential was reduced significantly as the centrifugal coefficient increased because the bubble separation from the electrode surface was improved. To reduce the ohmic voltage drop, a novel water electrolysis system with electrolyte circulation internals was designed. The cell voltage in water electrolysis was reduced, and thus, the electrolytic efficiency increased. This was attributed to the reduction of the solution resistance by the discharge of bubbles in the electrolyte. Therefore, high centrifugal field coupling with electrolyte circulation internals is an effective way to enhance the efficiency of water electrolysis. This study provides a theoretical basis for the development of new industrial water electrolysis devices for hydrogen production.

Power to gas: an option for 2060 high penetration rate of renewable energy scenario of China.

Replacing conventional fossil fuel power plants with large-scale renewable energy sources (RES) is a crucial aspect of the decarbonization of the power sector and represents a key part of the carbon-neutral strategy of China. The high penetration rate of renewable energy in the electricity system, however, implies the challenges of dealing with the intermittency and fluctuation of RES. Power to gas (P2G), which can convert surplus renewable power into a chemical form of energy (i.e., synthetic gas), can help handle this challenge and supply new energy carriers for various energy sectors. By modeling three potential 2060 energy mix scenarios in China, this paper aims to describe the possible contribution of the high penetration rate of renewable energy combined with P2G in the future sustainable energy system. Different schemes are listed and compared, and the results are used in a basic economic evaluation of the synthetic gas production cost for the P2G plants. Ideally, nearly 18 million tons of carbon dioxide would be recycled and transformed into methane (around 9.37 km3) annually in China. Considering a zero price for the excess renewable power and future costs of the components, the levelized cost of energy (LCOE) of the final production of methane is estimated at 0.86 $/m3SNG.

Regional suitability for energy carriers in Japan considering socioeconomic conditions and environmental performance

The implementation of energy carriers, such as hydrogen, is an option for future sustainable energy systems with decentralized renewable resources. Such an implementation requires holistic system changes from energy production to end-use technologies over multiple sectors; thus, for an effective implementation of the energy carriers, region prioritizing is required. The implementation effects (e.g., reduction in greenhouse gas emission and economic performance) of energy carriers can be affected by regional characteristics, but the regional suitability for energy carrier implementation cannot be judged only by the implementation effects. Regions need to have enough driving force to overcome barriers in the implementation. We propose an approach to analyze the regional suitability of the energy carrier based on three criteria, namely the regional scale, the socioeconomic driving force, and the unit implementation effect. Each of these criteria was subdivided into multiple categories for clarifying the analytical basis of regional suitability. The results of the case study in Japan demonstrated that regions can be differentiated by regional positions based on the three criteria. This analysis would contribute to prioritizing regions from the viewpoint of socioeconomic driving forces as well as implementation effects. The analysis can also be used for region-specific strategic planning according to the differences in socioeconomic driving force indicators. The cluster analysis was useful for understanding the relative positions of regions among all regions, identifying regions that have similar conditions, and tracking changes in the positions with different indicator combinations. This cluster would also be used to share knowledge of energy carrier implementation depending on the socioeconomic and energy-related conditions.

Power-to-hydrogen & district heating: Technology-based and infrastructure-oriented analysis of (future) sector coupling potentials

Numerous studies suggest that power-to-hydrogen (PtH2) will take a decisive part in future sustainable energy systems. District heating (DH) networks are also assigned a crucial role for the overall efficiency of such. In this regard, heat flows resulting from PtH2 may lead to synergies with the heat supply of DH systems.This paper discusses the potentials of PtH2 as a relevant heat source for DH (with focus on Austrian system conditions). Technology-specific efficiencies, heat flows and temperatures are put in context with today's and future DH system specifications and synergies are analyzed. A qualitative analysis summarizes the opportunities and challenges that arise from a system perspective, e.g. electrolyzer location, user type, and user-specific operation (i.e. generation load).It is found that high-temperature electrolysis is likely to be fully integrated in industrial utility operations and heat utilization corresponds to the well-known challenges of integrating industrial waste heat into DH networks. The location of low-temperature electrolysis is subject to infrastructure limitations and the economics of utilizing by-products. Operation is likely to be more electricity-market-oriented and may seasonally differ from heat demand. However, its waste heat is sufficient to feed modern low-temperature DH networks and by 2030 could cover up to 12% of Austria's current DH demands and up to 4% of the EU demand for heat below 100 °C.

Is iridium demand a potential bottleneck in the realization of large-scale PEM water electrolysis?

Proton exchange membrane water electrolysis (PEMWE) is a key technology for future sustainable energy systems. Proton exchange membrane (PEM) electrolysis cells use iridium, one of the scarcest elements on earth, as catalyst for the oxygen evolution reaction. In the present study, the expected iridium demand and potential bottlenecks in the realization of PEMWE for hydrogen production in the targeted GW a−1 scale are assessed in a model built on three pillars: (i) an in-depth analysis of iridium reserves and mine production, (ii) technical prospects for the optimization of PEM water electrolyzers, and (iii) PEMWE installation rates for a market ramp-up and maturation model covering 50 years. As a main result, two necessary preconditions have been identified to meet the immense future iridium demand: first, the dramatic reduction of iridium catalyst loading in PEM electrolysis cells and second, the development of a recycling infrastructure for iridium catalysts with technical end-of-life recycling rates of at least 90%.

Robust Hydrogen Production from Additive-Free Formic Acid via Mesoporous Silica-Confined Pd-ZrO2 Nanoparticles at Room Temperature

Hydrogen (H2) is becoming the most promising candidate for the future sustainable energy systems because it is clean and regenerable. Formic acid (FA, HCOOH), one of the high-value products of the ...

Stabilizing Pt-Based Electrocatalysts for Oxygen Reduction Reaction: Fundamental Understanding and Design Strategies.

Proton exchange membrane fuel cells (PEMFCs) with high efficiency and nonpollution characteristics have attracted massive attention from both academic and industrial communities due to their irreplaceable roles in building the future sustainable energy system. However, the stability issue of Pt-based catalysts for oxygen reduction reaction (ORR) has become a central constraint to the widespread deployment of the devices relative to the catalytic activity. This review aims to provide comprehensive insights into how to improve the stability of Pt-based catalysts for ORR. First, the basic physical chemistry behind the catalyst degradation, including the fundamental understandings of carbon corrosion, catalyst dissolution, and particle sintering, is highlighted. After a discussion of advanced characterization techniques for the catalyst degradation, the design strategies for improving the stability of Pt-based catalysts are summarized. Finally, further insights into the remaining challenges and future research directions are also provided.

Expanding the applicability of daytime radiative cooling: Technological developments and limitations

Daytime radiative cooling is regarded as the gold promise of future sustainable building energy systems and a breakthrough in the fight against local climate change. Despite the fervid research interest, most literature reports exceptional theoretical performances under ideal, desert-like conditions, but overlooks the cooling impairment that occurs under low atmospheric transparency (cloudy, humid, polluted conditions) and reduced sky access (packed urban contexts). Power recovery and stabilization call for decoupling of incoming and outgoing radiation at equal wavelengths. Enhanced directionality and high-contrast, broadband asymmetric transmission have been recently proposed to expand the applicability of radiative coolers over a wider spectrum of climates, weathers and terrains. This review offers itself as a first, timely synthesis of the current technological arena. Physical principles, materials and designs, collected from a variety of applicative fields, are detailed and discussed in terms of performance and feasibility, to inspire the transition into sustainable building cooling, worldwide. Major grey areas and serious concerns on potential violations of the 2nd law of thermodynamics reinforce the need for experimental demonstrations in future research.

Comprehensive Modelling of Renewable Energy Based Microgrid for System Level Control Studies

Renewable energy will constitute the backbone of the future sustainable energy systems by forming onsite microgrids. This reduces the utility grid burden and outages. Besides, microgrids can address the issues of greenhouse gasses, global warming, fossil fuel evaporations, slow start-up/shutdown times, etc. However, their dependency on geography/climatic conditions lead to the exhibition of intermittent output characteristics. Moreover, a majority of microgrids must be interfaced with the utility grid through power electronic converters, which are static and do not possess any kinetic energy. Due to this nature, these systems are highly sensitive to events, and thereby, creating issues with fast detection of islanding during abnormalities. Furthermore, for superior power quality, stability, energy yield, reliability, and protection, they must be properly coordinated with the utility grid or neighbour microgrids via robust control mechanisms. To study all these factors, lead to a better system, it is desired to have a perfect model of the system. Many literary works have developed microgrid models by focusing on a very particular aspect or component of it with respect to their area of research. But, comprehensive models are much required for many different studies as mentioned above. Further, the comprehensive model helps in detailed system-level studies. So, with this intension, this paper proposes the development of comprehensive model of the microgrid which involves all its key characteristics/elements. Further, system-level control study is presented to persuade the importance of this proposed model. From results, the WJC method is recommended as the best method to design microgrid’s controller.

Knowledge Mapping of Energy Systems Research in 1970-2020

This study presents a brief bibliometric overview of large scientific literature data related to issues of energy systems research from 1970 to 2020 in the Scopus database. The six periods depending on different publication activity rates were analyzed to observe the evolution of research topics of energy systems. VOSviewer software was used to construct scientific knowledge maps and to discover valuable main topics for each period. Proposed visualization of the energy knowledge domain can be considered as a necessary step for a holistic understanding of complex development pathways towards the future sustainable energy systems.

Microscopic Insights into the Degradation Mechanisms of Electrocatalysts in PEM Electrolyzers

Water electrolysis has the potential to become a key element in coupling the electricity, mobility, heating and chemical sectors via power-to-liquid or power-to-gas in a future sustainable energy system [1]. While proton exchange membrane electrolyzer cells (PEMEC) offer several advantages over traditional electrolysis technologies, the high cost of catalysts and associated components remain a barrier for their wide industrial commercialization [2]. Fundamental understanding of the PEMEC degradation mechanisms is crucial to elucidate the key parameters for developing new high-performance, low-cost and durable materials. This work aims to reveal degradation mechanisms of two novel material systems as investigation models. Electron microscopy methods, including transmission electron microscopy/scanning transmission electron microscopy (TEM/STEM) and energy dispersive X-ray spectroscopy (EDS) are applied to quantify the degradation of iridium- and platinum-based electrocatalysts in membrane electrode assemblies (MEAs).The first material system involves an ultra-low catalyst loaded MEA with Pt loading of 0.3 mg cm−2 and Ir loading of 0.08 mg cm−2. A long-term test of ~4500 h at 1.8 A cm−2 and 2.76 MPa differential pressure was performed on the MEA. A mechanism of cathode degradation is proposed using established physical models from two aspects: (1) direct Pt dissolution from nanoparticles due to the Gibbs-Thomson relation and (2) transient Pt dissolution due to rapid Pt oxide reduction during start/stop of operation [3]. Furthermore, as Ir dissolves and migrates through the membrane, Pt-Ir precipitates are formed in the membrane. The degradation mechanisms and the distribution of platinum and iridium across the MEA are provided from this study.The second material system involves a catalyst-coated liquid/gas diffusion layers (CCLGDLs) to reduce the cost of traditional Ti MEAs [4]. The CCLGDLs are significantly thinner than commercial catalyst-coated membranes (CCMs) and PTLs where the LGDL is less than 100 µm thick and the catalyst layer (CL) is less than 0.3 µm thick. The catalyst coated LGDLs demonstrated excellent PEMEC performance with cell potential less than 1.85 V at 2 A/cm2. This work examines and compares as-prepared and post-test CCLGDLs to investigate their morphology, composition, and stability relative to traditional electrode layers.In summary, quantitative analysis from microscopic imaging (TEM/STEM) and chemical analysis (EDS) is an effective tool for analyzing catalyst morphology, dissolution, and re-distribution in degraded MEAs. Quantitative microscopic insights into catalyst degradation mechanisms, such as those presented here, help to accelerate research into improved PEMEC performance and durability.

Self-Current Sharing in Dual-Transformer-Based Triple-Port Active Bridge DC–DC Converter With Reduced Device Count

A self-current balancing structure of the dual-transformer-based triple-port active bridge (DT-TAB) converter with the reduced component count is proposed in this article for future sustainable energy system applications. The proposed topology inherits good characteristics of the conventional triple-port active bridge (TAB) with even power sharing in an open loop as a newly added function. It can achieve high power density over the existing TAB converters that possess current-balancing function because the need for an auxiliary magnetic circuit or sophisticated control scheme in equalizing the shared power is eliminated. Besides, the demagnetization and magnetic short-circuit problems associated with the conventional TAB converters that are been eradicated, decoupled power flow management is achieved at all conditions. Moreover, the phase shift between the input H bridges gives an additional control degree of freedom that permits the control of the output power or offers independent control of voltage magnitude during the reverse power flow, thereby extending the system-operating range. The proposed DT-TAB converter has been adapted for the two-port operation. All the power switches achieved zero-voltage-switching turn- on . Finally, the robust operation performances of the proposed DT-TAB converter have been verified by the laboratory prototype assembled and tested up to 1 kW. The experimental results presented at the end are the proof-of-concept.