Water Electrolysis Technology Research Articles

Nitrogen-doped carbon layer encapsulating NiFeP nanosheet arrays as high-performance electrocatalyst for oxygen evolution reaction

With water electrolysis restricted to the slow kinetics of oxygen evolution reaction (OER), developing catalysts with both high activity and durability has become an urgent requirement for the development of current water electrolysis technology. Herein, we successfully prepared nitrogen-doped carbon layer encapsulating NiFe phosphide nanosheet arrays (denoted as N-C@NiFeP) catalysts by using a simple hydrothermal method combined with low temperature plasma technique. Phosphating conversion, carbonization, and nitrogen doping were realized by the same high-efficiency plasma treatment process. The nitrogen-doped carbon-coated structure modifies the NiFeP electronic structure, resulting in remarkable OER performances of N-C@NiFeP nanosheet arrays. The N-C@NiFeP nanosheet arrays possessed a tiny Tafel slope value of 27 mV dec−1 and a low overpotential of 229 mV at 10 mA cm−2. Meanwhile, the N-C@NiFeP nanosheet arrays also exhibited impressive long-term durability of 100 h under sequential OER testing at 100 mA cm−2. Our work was instrumental in paving new pathways for the construction of efficient and stable OER electrocatalysts.

Cactus-like NC/CoxP electrode enables efficient and stable hydrogen evolution for saline water splitting

Designing efficient and robust catalysts for hydrogen evolution reaction (HER) is imperative for saline water electrolysis technology. A catalyst composed of CoxP nanowires array with N-doped carbon nanosheets (NC) was fabricated on Ni foam (NF) by an in-situ growth strategy. The material is designated as NC/CoxP@NF. In the preparation process, Co(OH)2 nanowires were transformed into a metal organic framework of cobalt (ZIF-67) on NF by the dissolution-coordination of endogenous Co2+ and 2-methylimidazole. The resulting cactus-like microstructure gives NC/CoxP@NF abundant exposed active sites and ion transport channels, which improve the HER catalytic reaction kinetics. Furthermore, the interconnected alternating nanowires and free-standing nanosheets in NC/CoxP@NF improve its structural stability, and the formation of surface polyanions (phosphate) and a NC nanosheet protective layer improve the anti-corrosive properties of catalysts. Thus, the NC/CoxP@NF has an excellent performance, requiring overpotentials of 107 and 133 mV for HER to achieve 10 mA cm−2 in 1.0 mol L−1 KOH and 1.0 mol L−1 KOH + 0.5 mol L−1 NaCl, respectively. This in-situ transformation strategy is a new way of constructing highly-efficient HER catalysts for saline water electrolysis.

An organic–inorganic hybrid method to fabricate bimetallic phosphide nanospheres as efficient electrocatalyst for hydrogen evolution reaction

Hydrogen evolution reaction (HER) serves as a crucial half reaction in electrolytic water splitting. Pt is deemed to the most active HER electrocatalyst, but the scarcity and high cost of Pt limit its massive application. Developing efficient, low-cost and well-structured HER catalysts is quite vital for advancing the development of water electrolysis technology. Herein, we present a facile organic–inorganic hybrid method to achieve a novel bimetallic phosphide of MoP-RuPx/NPC catalyst, showing superior electrocatalytic activity with an overpotential of 24 and 94 mV at 10 mA cm−2 in alkaline and acid media, respectively. Moreover, MoP-RuPx/NPC also exhibits an outstanding electrochemical stability with a negligible degradation in HER activity after long-term stability measurements. The eminent electrocatalytic performance of MoP-RuPx/NPC catalyst should be ascribed to the high surface specific area, multiple heterogeneous interfaces, strong electronic synergistic effect between MoP and RuPx, and abundant defects. The organic–inorganic hybrid strategy implemented in this work can be used for synthesizing other bimetallic phosphide catalysts.

Electrochemical and chemical cycle for high-efficiency decoupled water splitting in a near-neutral electrolyte

Green hydrogen produced by water splitting using renewable electricity is essential to achieve net-zero carbon emissions. Present water electrolysis technologies are uncompetitive with low-cost grey hydrogen produced from fossil fuels, limiting their scale-up potential. Disruptive processes that decouple the hydrogen and oxygen evolution reactions and produce them in separate cells or different stages emerge as a prospective route to reduce system cost by enabling operation without expensive membranes and sealing components. Some of these processes divide the hydrogen or oxygen evolution reactions into electrochemical and chemical sub-reactions, enabling them to achieve high efficiency. However, high efficiency has been demonstrated only in a batch process with thermal swings that present operational challenges. This work introduces a breakthrough process that produces hydrogen and oxygen in separate cells and supports continuous operation in a membraneless system. We demonstrate high faradaic and electrolytic efficiency and high rate operation in a near-neutral electrolyte of NaBr in water, whereby bromide is electro-oxidized to bromate concurrent with hydrogen evolution in one cell, and bromate is chemically reduced to bromide in a catalytic reaction that evolves oxygen in another cell. This process may lead the way to high-efficiency membraneless water electrolysis that overcomes the limitations of century-old membrane electrolysis.

Progress in carbon-free oxygen evolution electrocatalysts for high-current-density water electrolysis in acidic media

A review of carbon-free electrocatalysts (CFECs) for high-current-density (HCD) acidic oxygen evolution reaction is presented, including the introduction of proton exchange membrane water electrolysis, along with recent advances and prospects in CFECs.

An overview of green hydrogen production system through low temperature water electrolysis using solar energy

Climate change and the increasing demand for energy become major issues in public discussions today. The Paris Agreement is one of the results of such public discussions that focuses on achieving the 2050 Net Zero Emission target. Many energy agencies have created scenarios to achieve this target. In this regard, green hydrogen is expected to have a significant role in energy transition plan. For this reason, in recent years, research related to green hydrogen production using the water electrolysis method continues to develop. The paper aimed primarily to conduct an overview of alternative technologies that can be used in producing green hydrogen with the solar energy based low temperature water electrolysis method. Secondarily, it would present information about several solar energy-based electrolysis project plans and a summary of challenges and opportunities in the development of solar energy based low temperature water electrolyzers in the future. Furthermore, to achieve commercially viable green hydrogen production, it is important to find new ideas, potential solutions, and constructive recommendations as soon as possible for further development research. This paper expectedly would be able to help initiate the development of green hydrogen production research through water electrolysis technology that is efficient, cost effective economically, and environmentally friendly.

Bi-doped ruthenium oxide nanocrystal for water oxidation in acidic media.

There is an urgent need to develop a cost-effective and highly efficient acidic OER catalyst to support the progress of proton exchange membrane water electrolysis technology. Ruthenium-based catalysts, which possess high activity and significantly lower cost compared to iridium-based catalysts, emerge as competitive candidates. However, their suboptimal stability constrains the wide application of RuO2. Herein, we develop ultra-small Bi0.05Ru0.95O2 nanocrystal with diameter of approximately 6.5 ± 0.1 nm for acidic OER. The Bi0.05Ru0.95O2 nanocrystal electrocatalyst exhibits a low overpotential of 203.5 mV at 10 mA cm-2 and 300+ hour stability at a high water-splitting current density of 100 mA cm-2 in 0.5 M H2SO4 with a low decay rate of 0.44 mV h-1. Density functional theory (DFT) calculation results confirmed the adsorbate evolving mechanism (AEM) occurring on Bi0.05Ru0.95O2, which prevents lattice oxygen from participating in the reaction, thus avoiding the collapse of the structure. We proved that the Bi dopants could play a crucial role in not only reducing the energy barrier of the potential-determining step, but also delivering electrons to Ru sites, thereby alleviating the over-oxidation of Ru active sites and enhancing operation durability.

Recent advances in the synthesis of transition metal hydroxyl oxide catalysts and their application in electrocatalytic oxygen evolution reactions.

With the extensive use of fossil energy, people will face the depletion of fossil energy and increasingly severe problems. As a non-polluting, high specific energy density energy source, hydrogen energy is expected to solve this problem by producing hydrogen through electrolysis of water through renewable energy power generation. Water electrolysis technology involves two important half-reactions: the cathode hydrogen evolution reaction (HER) and anode oxygen evolution reaction (OER). The OER is a 4-electron transfer process with a high energy barrier. In order to achieve higher energy conversion, OER catalyst technology is a key part of the process. Researchers have conducted a lot of research into high-performance, high-stability, and highly economical OER catalysts, among which oxyhydroxide (MOOH), as an active substance for OER, has received particular attention. This article provides a timely follow-up to the research on oxyhydroxides, first introducing the two catalytic mechanisms of OER, namely the adsorbate evolution mechanism (AEM) and lattice-oxygen-mediated mechanism (LOM). Then, strategies are proposed to improve OER catalytic performance by increasing catalytic active surface area/active sites, optimizing intermediate adsorption energy based on the AEM, triggering the LOM, and enhancing catalyst stability. Finally, the challenges and future development directions of MOOH catalysts are analyzed, which provides guidance for the design and preparation of high-performance OER catalysts in the future.

A perspective on interface engineering of transition metal dichalcogenides for high-current-density hydrogen evolution

Water electrolysis for green hydrogen production is important for the global carbon neutrality. The industrialization of this technology requires efficient and durable electrocatalysts under high-current-density (HCD) operations. However, the insufficient mass and charge transfer at the various interfaces lead to unsatisfactory HCD activity and durability. Interface engineering is important for designing efficient HCD electrocatalysts. In this perspective, we analyze the processes taking place at three interfaces including the catalyst-substrate, catalyst-electrolyte, and catalyst-gas interfaces, and reveal the correlations between interface interactions and the challenges for HCD electrolysis. We then highlight the development of HCD electrocatalysts that focus on interface engineering using the example of transition metal dichalcogenide based catalysts, which have attracted widespread interests in recent years. Finally, we give an outlook on the development of interface engineering for the industrialization of water electrolysis technology.

Development and application of ordered membrane electrode assemblies for water electrolysis.

With the development of hydrogen energy, there has been increasing attention toward fuel cells and water electrolysis. Among them, the zero-gap membrane electrode assembly (MEA) serves as an important triple-phase reaction site that determines the performance and efficiency of the reaction system. The development of efficient and durable MEAs plays a crucial role in the development of hydrogen energy. Consequently, a great deal of effort has been devoted to developing ordered MEAs that can effectively increase catalyst utilization, maximize triple-phase boundaries, enhance mass transfer and improve stability. The research progress of ordered MEAs in recent advances is highlighted, involving hydrogen fuel cells and low temperature water electrolysis technology. Firstly, the fundamental scientific understanding and structural characteristics of MEAs based on one-dimensional nanostructures such as nanowires, nanotubes and nanofibers are summarized. Then, the classification, preparation and development of ordered MEAs based on three-dimensional structures are summarized. Finally, this review presents current challenges and proposes future research on ordered MEAs and offers potential solutions to overcome these obstacles.

Unveiling the potential of amorphous nanocatalysts in membrane-based hydrogen production.

Hydrogen, as a clean and renewable energy source, is a promising candidate to replace fossil fuels and alleviate the environmental crisis. Compared with the traditional H-type cells with a finite-gap, the design of membrane electrodes can reduce the gas transmission resistance, enhance the current density, and improve the efficiency of hydrogen production. However, the harsh environment in the electrolyser makes the membrane electrode based water electrolysis technology still limited by the lack of catalyst activity and stability under the working conditions. Due to the abundant active sites and structural flexibility, amorphous nanocatalysts are alternatives. In this paper, we review the recent research progress of amorphous nanomaterials as electrocatalysts for hydrogen production by electrolysis at membrane electrodes, illustrate and discuss their structural advantages in membrane electrode catalytic systems, as well as explore the significance of the amorphous structure for the development of membrane electrode systems. Finally, the article also looks at future opportunities and adaptations of amorphous catalysts for hydrogen production at membrane electrodes. The authors hope that this review will deepen the understanding of the potential of amorphous nanomaterials for application in electrochemical hydrogen production, facilitating future nanomaterials research and new sustainable pathways for hydrogen production.

Hydrogen-Based Energy Systems: Current Technology Development Status, Opportunities and Challenges

The use of hydrogen as an energy carrier within the scope of the decarbonisation of the world’s energy production and utilisation is seen by many as an integral part of this endeavour. However, the discussion around hydrogen technologies often lacks some perspective on the currently available technologies, their Technology Readiness Level (TRL), scope of application, and important performance parameters, such as energy density or conversion efficiency. This makes it difficult for the policy makers and investors to evaluate the technologies that are most promising. The present study aims to provide help in this respect by assessing the available technologies in which hydrogen is used as an energy carrier, including its main challenges, needs and opportunities in a scenario in which fossil fuels still dominate global energy sources but in which renewables are expected to assume a progressively vital role in the future. The production of green hydrogen using water electrolysis technologies is described in detail. Various methods of hydrogen storage are referred, including underground storage, physical storage, and material-based storage. Hydrogen transportation technologies are examined, taking into account different storage methods, volume requirements, and transportation distances. Lastly, an assessment of well-known technologies for harnessing energy from hydrogen is undertaken, including gas turbines, reciprocating internal combustion engines, and fuel cells. It seems that the many of the technologies assessed have already achieved a satisfactory degree of development, such as several solutions for high-pressure hydrogen storage, while others still require some maturation, such as the still limited life and/or excessive cost of the various fuel cell technologies, or the suitable operation of gas turbines and reciprocating internal combustion engines operating with hydrogen. Costs below 200 USD/kWproduced, lives above 50 kh, and conversion efficiencies approaching 80% are being aimed at green hydrogen production or electricity production from hydrogen fuel cells. Nonetheless, notable advances have been achieved in these technologies in recent years. For instance, electrolysis with solid oxide cells may now sometimes reach up to 85% efficiency although with a life still in the range of 20 kh. Conversely, proton exchange membrane fuel cells (PEMFCs) working as electrolysers are able to sometimes achieve a life in the range of 80 kh with efficiencies up to 68%. Regarding electricity production from hydrogen, the maximum efficiencies are slightly lower (72% and 55%, respectively). The combination of the energy losses due to hydrogen production, compression, storage and electricity production yields overall efficiencies that could be as low as 25%, although smart applications, such as those that can use available process or waste heat, could substantially improve the overall energy efficiency figures. Despite the challenges, the foreseeable future seems to hold significant potential for hydrogen as a clean energy carrier, as the demand for hydrogen continues to grow, particularly in transportation, building heating, and power generation, new business prospects emerge. However, this should be done with careful regard to the fact that many of these technologies still need to increase their technological readiness level before they become viable options. For this, an emphasis needs to be put on research, innovation, and collaboration among industry, academia, and policymakers to unlock the full potential of hydrogen as an energy vector in the sustainable economy.

Highly Durable Membrane–Electrode-Assemblies Using High M w and Ether-Free Polyfluorene-Based Electrolytes for Anion Exchange Membrane Water Electrolyzer

Water electrolysis technology, which produces hydrogen through electrolysis of water using electricity derived from renewable energy, is attracting attention as a way to realize a carbon-neutral society. Among water electrolysis systems, anion exchange membrane water electrolysis (AEMWE) can achieve high energy conversion efficiency and quick response to fluctuating power supplies by using thin polymer electrolyte membranes, and operates in an alkaline environment, allowing the use of inexpensive non-precious metals for bipolar plates and electrodes. However, conventional AEMs and ionomers exhibit low durability in high-temperature and alkaline environments, which is a critical issue in realizing high-performance and highly durable membrane–electrode assemblies (MEAs) for AEMWE.Our group developed high-molecular-weight (M w) and ether-free, polyfluorene-based anion conducting polyelectrolyte (PFT-Cx-TMA, Cx represent the number of carbon atoms in the alkyl side chain) as shown in Fig. 1a.1 These polyelectrolytes show high OH− conductivity over 100 mS cm− 1, high chemical durability (stable in 8 M NaOH at 80 °C for 168 h), and high tensile strength (25–42 MPa, comparable to a Nafion membrane). This study applied PFT-Cx-TMA to AEMs and ionomers in MEAs to evaluate the durability against various AEMWE operations (constant current operation and start-stop operation in different voltage ranges), demonstrating MEAs with both high performance and high durability.Fig. 1b shows the constant current durability of the MEA with PFT-C8-TMA as AEM and ionomer.2 This test was performed at the constant current density of 0.2 A cm− 2 and 80 °C using a 1 M KOH aqueous solution fed to the anode. Here, to investigate the effects of AEMs and ionomers on MEA durability, conventional precious metal catalysts (anode: IrO2, cathode: Pt/C or PtRu/C) were used in the MEA. The MEA with PFT-C8-TMA exhibited a current density of 1.0 A cm− 2 at 1.79 V and there was almost no voltage change even after the constant current operation for over 100 h. It is noteworthy that the MEAs using PFT-C8-TMA and PFT-C10-TMA demonstrated high performance and high durability not only in the alkaline-fed operation but also in the pure-water-fed operation.Next, this study investigated the start-stop durability of MEAs using voltage cycles simulating the start-stop operation of water electrolyzer. Here, square-wave voltage cycling of holding at 1.8 V and 0.1 V for 1 min each was used for the start-stop test at 80 °C with a 1 M KOH solution fed to the anode. As a comparison, the MEA was prepared using a commercial AEM (Sustainion X37-50, 50 μm in thickness) and ionomer (Sustaionion XB-7). As shown in Fig. 1c, the MEA using a PFT-C10-TMA AEM (56 μm in thickness) and ionomer was highly durable in the start-stop test compared to the MEA using commercial Sustaionion. During the test, the elution of black solid particles from the catalyst layer and the increase in charge transfer resistance (Rct) were observed in the MEA with Sustaionion, whereas no elution of catalyst materials and no change in Rct were confirmed in the MEA with PFT-C10-TMA. These results suggest that nonlinear mechanical stress via rapid bubble formation and shutdown during start-stop cycles caused the leaching of catalysts, resulting in the performance loss of the MEA with Sustainion. The commercial ionomer (Sustainion XB-7) exhibits a large dimensional change (156%) compared to the PFT-C10-TMA membrane (34%) at 80 °C in a 1 M KOH aqueous solution. Catalyst particles covered with a highly swollen ionomer are easily detached from a catalyst layer by the nonlinear mechanical stress. On the other hand, the PFT-C10-TMA ionomer has a high molecular weight (M w = 240000 g mol−1), low swelling degree, and well-entangled polymer chains, hence preventing leaching of the catalyst particles.In summary, this study demonstrates that MEAs using high M w and ether-free polyfluorene-based electrolytes with both high chemical and mechanical durability have excellent durability for AEMWE operations including constant and dynamic (start-stop voltage cycling) operations. Acknowledgement This presentation is based on results obtained from a project, JPNP14021, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). References (1) S. Miyanishi and T. Yamaguchi, Polym. Chem., 2020, 11, 3812–3820.(2) R. Soni, S. Miyanishi, H. Kuroki, and T. Yamaguchi, ACS Appl. Energy Mater., 2021, 4, 1053–1058. Figure 1

In-Situ X-Ray Observation of Bubbles in Porous Transport Layer of PEM Water Electrolysis

As renewable energies become increasingly popular as a countermeasure against global warming, hydrogen is attracting attention as a new energy medium. This is because surplus electricity from renewable energy sources, whose generation is unstable, can be used to electrolyze water (water electrolysis) and convert it into storable hydrogen, which can then be reconverted into electricity by fuel cells and used when needed. By using hydrogen for long-term energy storage and utilizing surplus energy, dependence on fossil fuels can be reduced, resulting in a decrease in greenhouse gas emissions. Water electrolysis technology, particularly Proton Exchange Membrane (PEM) water electrolysis, is currently receiving attention due to its high efficiency, high safety, and a large operational range of current density.In PEM water electrolysis cells, bubbles are produced in the liquid water due to an electrochemical reaction in which water is decomposed into oxygen at the catalyst layer inside the anode. There is a concern that the concentration overvoltage increases as these bubbles remain inside the porous transport layer (PTL), resulting in a decrease in the efficiency of electrolysis. However, the behavior of bubbles during the electrolysis has not been fully clarified, and it is necessary to understand the discharge behavior of bubbles in the PTL. This study aims to clarify the bubble retention behavior in the PTL of PEM water electrolysis cell by in-situ bubble visualization using an X-ray microscopy system. Measurements were taken on 2 types of PTL made from carbon or titanium dioxide with different fiber diameters, pore sizes, and wettability to investigate the effect of PTL structure on bubble accumulation and discharge behaviors. Two-dimensional X-ray images were taken before the start of water electrolysis (when the PTLs were filled with liquid water) and during water electrolysis (when bubbles were generated), and the bubble distribution within the PTL and the channel was quantified from the changes in brightness. By tuning the X-ray transmission thickness of the PTL and X-ray energy, the bubble behavior during the electrolysis were successfully visualized. In the case of the carbon PTL (Fig. 1(a), fiber diameter: 10 μm, pore diameter: 150 μm), bubbles were accumulated under the rib area (Fig. 1(b)), while in the case of the titanium PTL (Fig. 1(c), fiber diameter: 25 μm, pore diameter: 50 μm), bubbles were relatively uniformly distributed (Fig. 1(d)). This result is believed to be due to the titanium's superior wettability, which prevents the accumulation of bubbles by inhibiting their bridging between pores. Furthermore, the titanium PTL is attributed to have a lower gas saturation ratio owing to its smaller pore diameter, which effectively prevents bubble coalescence. These results suggested that the pore size and the wettability of the PTL strongly affect the bubble behavior, and the in-situ observation is quite important to understand it. Figure 1

Rapid Fabrication of Efficient and Stable Microporous Electrodes for Practical Alkaline Water Electrolysis

Efficient and stable electrode is paramount for advancing practical alkaline water electrolysis (AWE) technology. In this study, we employed a rapid and scalable laser texturing process to create microporous nickel electrodes, demonstrating promising catalytic performances for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The alkaline electrolyzer cell (AEL) incorporating laser-textured electrodes (NP-LT30) exhibited a remarkable improvement, with voltage drops exceeding 300 mV under a current density of 1 A cm−1, compared to conventional perforated Ni plate electrodes (NP) based cell. This enhancement resulted from a substantial boost in mass transport, as unveiled by in-situ electrochemical impedance analysis. Of particular note is the unique multi-channel porous structure within the NP-LT30 electrode, enabling rapid mass transport through an innovative convection mode driven by an intermittent bubble eruption (IBE) mechanism, outperforming the traditional convection mode. Furthermore, AEL using NP-LT30 electrodes demonstrated exceptional durability, maintaining performance at 1.0 A cm–2 for an impressive 300 hours. This study highlights the capability of the multi-channel structure within NP-LT30 electrodes to expedite mass transport in practical AWE applications significantly. Moreover, the cost-effective and scalable nature of laser-textured porous electrodes positions them for commercialization, enabling the production of highly efficient electrodes for practical AWE implementation.

Platinum Group Metal-Free Catalyst Loading Optimization for Dry Cathode Operation in Anion Exchange Membrane Water Electrolysis

With an increasing interest for green hydrogen as an important fuel for the global energy transition and as a raw material for green chemistry, extensive research efforts are currently devoted to increase the performance of water electrolysis technologies. In this frame work, Anion Exchange Water Electrolysis (AEMWE) has a strategic role promising to boost electrolytic hydrogen production without relying on scarce resources as AEMWE does not need Iridium or other Platinum group metals (PGM) catalysts, unlike Proton Exchange Membrane Water Electrolysis (PEMWE), to reach high power density [1].In this work, the focus is on electrode optimization for dry cathode operation. Operating without a liquid feed on the cathode reduces the extent of the drying of hydrogen gas and simplifies the balance of the plant. However, water must be transported from the anode to the cathode where it is consumed by the hydrogen evolution reaction (HER) [2]. Also, ionic connection from the membrane to catalyst surface must be provided by the ionomer without a supporting electrolyte which is generally employed in AEMWE to improve performance [1]. Under these premises, it is clear that using high catalyst loading to compensate for the intrinsic low activity of Platinum group metals-free (PGM-free) catalysts will result in lower utilization of the catalyst layer as a function of the electrode thickness [3].To study how transport limitations hinder cathode performance, we manufactured catalyst coated membranes (CCMs) via decal transfer method and varied the cathode catalyst loading thereby adjusting catalyst layer (CL) thickness. RaneyTM Nickel served as the cathode catalyst and Super PTM Carbon as the conductive additive. It was found that increasing the catalyst loading between 0.65 mg/cm2 and 1.65 mg/cm2 greatly improved cell performance (Figure 1). However, cell voltage proved to be less sensitive to cathode loading for higher loadings. In fact, to reasonably improve the performance further, a loading of 4.55 mg/cm2 was necessary. Noticeably, the high frequency resistance (HFR) was found to be independent of catalyst loading (i.e. CL thickness) due to the high electronic conductivity of the cathode CL with carbon additive.This works sheds light on how AEMWE performance are related to cathode catalyst loading when the cathode is dry operated. It is found that performance improvement is limited at high loading (above 1.65 mg/cm2). This shows how the ionic conductivity of the electrode should be improved to mitigate the low mass activity of PGM-free catalyst.[1] Ayers, Katherine, Nemanja Danilovic, Ryan Ouimet, Marcelo Carmo, Bryan Pivovar, and Marius Bornstein. “Perspectives on Low-Temperature Electrolysis and Potential for Renewable Hydrogen at Scale.” Annual Review of Chemical and Biomolecular Engineering 10, no. 1 (June 7, 2019): 219–39.[2] Koch, Susanne, Joey Disch, Sophia K. Kilian, Yiyong Han, Lukas Metzler, Alessandro Tengattini, Lukas Helfen, Michael Schulz, Matthias Breitwieser, and Severin Vierrath. “Water Management in Anion-Exchange Membrane Water Electrolyzers under Dry Cathode Operation.” RSC Advances 12, no. 32 (2022): 20778–84.[3] Liu, Jiangjin, Zhenye Kang, Dongguo Li, Magnolia Pak, Shaun M. Alia, Cy Fujimoto, Guido Bender, Yu Seung Kim, and Adam Z. Weber. “Elucidating the Role of Hydroxide Electrolyte on Anion-Exchange-Membrane Water Electrolyzer Performance.” Journal of The Electrochemical Society 168, no. 5 (May 1, 2021): 054522.Figure 1 Polarization curve of CCMs with different cathode catalyst loading. The cathode contains 65 % catalyst (RaneyTM Nickel), 10% ionomer and 25% Super PTM Carbon. NiFe nanoparticles are used in the anode with 5% ionomer (AP-1-HNN5-00-X). The measurements are conducted at 60 °C feeding 1 M KOH to anode. Figure 1

ALD-Based IrOx/Ir Supported Electrocatalysts for Water Electrolysis Technology

Hydrogen (H2) is an alternative energy vector to replace fossil fuels, with potential applications like hydrogen fuel cell-powered vehicles and in the chemical industry. H2 production through polymer electrolyte membrane (PEM) water electrolysis (WE) appears to be a highly promising technology. While iridium oxide is the most commonly used anode oxygen evolution reaction (OER) catalyst for PEMWE, its scarcity makes it an extremely critical raw material. In order to obtain active and stable anodes with an ultra-low iridium loading, we are developing a strategy based on doped metal oxides as conductive supports, on which iridium-based thin films and/or nanostructures are deposited using atomic layer deposition (ALD). ALD can indeed allow the control of the amount of deposited species at sub-nanometric scale by changing the number of ALD cycles, thus ensuring a minimal iridium loading for efficient OER catalysis. In this study, the influence of the temperature of deposition was investigated to obtain either IrOx ultrathin films or Ir nanoparticles. The morphology and composition of these deposits were characterized by scanning and transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. The nature and crystallinity of these electrocatalysts will indeed have a huge impact on their catalytic activity and the subsequent electrode’s efficiency as well as in their long-term durability. In brief, we will present the production of nano-structured OER electrocatalysts, in which the bulk consists of a sufficiently conductive metal oxide support with the surface uniformly coated with an ultra-low loading of iridium deposited via conformal ALD.

Study on the synergistic regulation strategy of load range and electrolysis efficiency of 250 kW alkaline electrolysis system under high-dynamic operation conditions

Alkaline water electrolysis (AWE) has the highest technological maturity among all the water electrolysis technologies for hydrogen production, however, reducing the minimum load boundary and improving the electrolysis efficiency are the technical challenges of the AWE system that still exist and urgently require optimization. The minimum load is primarily limited by the hydrogen to oxygen (HTO) from cross-diaphragm transfer and lye mixing, with HTO above 2.0% being a significant safety risk. Reducing the lye flow rate and pressure are effective while two of the few ways by regulating the operating parameters to improve the HTO thus extend the minimum load boundary, but will worsen electrolysis efficiency. Therefore, this study proposes a synergistic regulation strategy of pressure and lye flow rate: maximizing pressure and lye flow rate during high load period to ensure high electrolysis efficiency; adjusting lye flow rate and pressure during medium load period to ensure HTO≤2.0% and maximize the electrolysis efficiency; and reducing lye flow rate and pressure to a low level during the low load period to broaden the minimum load so as to improve overall efficiency of AWE system when loading with fluctuant green electric. This work elaborates the HTO routes, influencing factors and parameter optimization mechanism by building a system-level steady-state and dynamic gas purity model. The optimal combination curve of pressure and lye flow rate is obtained and its control effect on performance parameters, in terms of minimum load, system energy consumption, energy utilization, electrolysis efficiency and so on, is compared and verified in high dynamic wind and photovoltaic (PV) power scenarios. Finally, the optimal wind & PV power ratios are explored based on the optimal operation curve, which will provide a reference for the future large-scale development of hydrogen production scenarios direct-coupled with wind and PV power. The minimum load is extended from 42.0% in the lye flow rate alone control to 21.2% in the pressure alone control and finally to 15.6% in the lye flow rate and pressure synergistic control method. In the absence of electrical replenishment, wind and PV energy utilization efficiency can reach up to 98.3% and 95.6%, respectively.

Experimental and numerical study of thermal coupling on catalyst-coated membrane for proton exchange membrane water electrolyzer

During the long-term operation of proton exchange membrane water electrolyzers (PEMWEs), Formation of localized hotspots in the catalyst-coated membrane (CCM) will seriously threaten the safe and efficient operation of the electrolyzer. This paper adopts a combination of dynamic experiments and numerical simulation analysis, aiming to develop the in-situ characterization technology of the thermal characteristics as well as the theoretical analysis of the multiphysics field for the·PEMWE. Based on both experimental and theoretical results, it is concluded that: (1) The high current density leads to an extremely uneven temperature distribution on the surface of the CCM. High temperature difference (as high as 34.04 °C) and high local temperature (up to 98.08 °C) are observed; (2) 30–50% of the electrical energy during the electrolyzer is converted into heat, of which the polarization heat accounts for the major part, followed by proton-conductive Joule heat; (3) The accumulation of gas phase during the transfer process of gas-liquid two phases is the primary cause of the deterioration of heat transfer, which further leads to local overheating. This study provides an experimental and theoretical basis for the safe and efficient operation of proton exchange membrane water electrolysis technology.

Absolute Sustainability Assessment of Flue Gas Valorization to Ammonia and Synthetic Natural Gas.

Carbon capture and utilization has gained attention to potentially curb CO2 emissions while generating valuable chemicals. These technologies will coexist with fossil analogs, creating synergies to leverage circular economy principles. In this context, flue gas valorization from power plants can assist in the transition. Here, we assessed the absolute sustainability of a simulated integrated facility producing ammonia and synthetic natural gas from flue gas from a combined-cycle natural gas power plant based in Germany, using hydrogen from three water electrolysis technologies (proton exchange membrane, alkaline, and solid oxide cells), nitrogen, and CO2. For the first time, we applied the planetary boundaries (PBs) framework to a circular integrated system, evaluating its performance relative to the safe operating space. The PB-LCA assessment showed that the alternative technologies could significantly reduce, among others, the impact on climate change and biosphere integrity when compared to their fossil counterparts, which could be deemed unsustainable in climate change. Nevertheless, these alternative technologies could also lead to burden shifting and are not yet economically viable. Overall, the investigated process could smoothen the transition toward low-carbon technologies, but its potential collateral damages should be carefully considered. Furthermore, the application of the PBs provides an appealing framework to quantify the absolute sustainability level of integrated circular systems.