Anode Catalyst Research Articles

Sulfur-Phosphorus Doped Metal Composites As Superior Catalyst for Electrolytic Hydrogen Production in Real Seawater

In the face of the increasingly severe global energy crisis and challenges posed by climate change, promoting energy transition has become an international consensus. Among various renewable energy sources, hydrogen is considered an ideal energy carrier due to its clean and efficient characteristics. The electrolysis of seawater for hydrogen production has garnered widespread attention for its ability to fully utilize abundant seawater resources and the advantage of zero carbon dioxide emissions. However, achieving efficient, stable, and economically viable hydrogen production in seawater still faces many challenges, with catalyst design and optimization being recognized as key issues.Firstly, NiFe-LDH was synthesized using a simple one-pot solvothermal method. Subsequently, phosphorization, sulfurization, and sulfur-phosphorus co-doping were conducted to obtain samples namely NiFe-P, NiFe-S and NiFe-SP, respectively. Various electrochemical tests, including hydrogen evolution reaction (HER), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were firstly performed in simulated seawater to evaluate the electrochemical performance of the synthesized catalysts. The overall seawater splitting reaction was conducted with the same catalysts for both anode and cathode sides.After comparing the electrochemical activity of four different catalysts, it was found that NiFe-SP performs superior HER activity in alkaline simulated seawater. NiFe-SP required merely -0.143 V to deliver 100 mA cm-2 current density, which was 95 mV lower than NiFe-LDH to achieve the same current density. In EIS tests, NiFe-SP exhibited a smaller charge transfer resistance than NiFe-LDH, and NiFe-SP had the largest double-layer capacitance (Cdl) value in ECSA measurements, indicating that NiFe-SP possessed and lowest reaction resistance and the maximum electrochemically active surface area.X-ray Diffraction (XRD) and Raman spectroscopy analyses indicate that the catalyst, after sulfur-phosphorus doping, does not exhibit a pure-phase LDH structure but transforms into a heterogeneous structure of Ni3S2 and FeS2. Scanning Electron Microscopy (SEM) observations suggest that sulfur-phosphorus co-doping causes the original spherical structure of NiFe-LDH to aggregate, with the appearance of some lamellar structures on the surface. Energy Dispersive Spectroscopy (EDS) also confirms the successful doping of sulfur and phosphorus elements into NiFe-LDH, with uniform distribution on the material's surface.Finally, the catalyst underwent a 2000-hours continuous stability test at a constant current of 100 mA cm-² in real seawater. The results indicate that the potential of NiFe-SP increased by only 5%, demonstrating that the doping of sulfur and phosphorus not only reduces the catalytic overpotential but also significantly sustains potential retention. This suggests that the metal composite structure obtained after sulfur-phosphorus co-doping is well-formed and stable. The systematic electrochemical tests and stability evaluation in this study highlights the potential of sulfur-phosphorus co-doped metal composite NiFe-SP as an efficient and stable catalyst for real seawater electrolysis. This not only contributes to a deeper understanding of the fundamental principles governing catalyst behavior but also opens new possibilities for the practical application of hydrogen production technology. Figure 1

(Invited) PEM Water Electrolysis Stack Development and Related Characterization Tools

For decades, proton-exchange membrane (PEM) water electrolysis (WE) has been mainly used for oxygen generation in anaerobic environments. Over the past two decades, however, it has been increasingly used for hydrogen generation in the industrial sectors at various scales. The PEMWE technology is also considered a key in the ongoing energy transition, if the process of hydrogen generation by means of WE is linked to renewable energy sources, such as wind, solar, etc.The following key elements enable the operation of a PEM WE plant for hydrogen production: a PEM-based WE stack and the balance of plant. The related system includes, but not limited to such key modules as the water and oxygen management systems, hydrogen gas management system, water input system, safety system, power electronics and electrolysis cell stack power supply, control system, and some other.A WE stack comprises several cells connected in series with electrically conductive bipolar plats and end plates. General design principles for the stack involve reducing efficiency losses, while aiming at lower costs and increase in durability. WE stacks should be designed in such a way, that an even current distribution is maintained, the water feed is optimized, suitable compression ratios are achieved, and preferably high discharge pressure of hydrogen can be enabled. For the stack level, in simple terms, efficiency is benchmarked by the total applied voltage, which includes the Nernst potential, anode and cathode overpotentials, and ohmic overpotentials due to the membrane ionic resistance and interfacial resistance at given current density. Overpotential represents inefficiencies in a cell stack, and some of stack design efforts focus on reducing these overpotential contributions. However, a compromise has to be found between (a) costs reduction challenges (that are often associated with the reduction of PGM-based catalyst loading, attempts to replace Ti as a key material for the bipolar plates, and the less expensive SPE membrane), (b) sufficient durability, (c) performance of the stack, (d) increase in power density of a stack.This talk will focus on the WE stack, and its subcomponents review, as well as characterization methods for both, a single cell and a stack and also challenges of the large-scale stack manufacturing. The key components of the WE stack include ion-conductive solid polyelectrolyte membranes (SPE), anode and cathode catalyst layers (CL), bipolar plates and current collectors/ gas diffusion layers (porous transport layers).In order to gain fundamental understanding of the relationships between electrical loses, degradation of the stack components and strategies to increase power density of the stacks, advanced characterization and modelling tools need to be used. These include, but not limited to electrochemical impedance spectroscopy (EIS), current interrupt (CI), dynamic compression measurements with piezoelectric senor plates, current mapping, gas cross-over analysis, computational fluid dynamics (CFD) simulations modelling, various visualization tools, etc. For example, CFD could assist in understanding and improving fluid flow dynamics in a WE stack as it is a complex challenge that requires a detailed examination of the geometry, channel design, and operating conditions within the stack. As for EIS, the usage of the distribution of relaxation times (DRT) approach would potentially allow to focus on the direct analysis of the data rather focusing on the equivalent circuit development.Approximately 15 years ago the South African Government approved a national program HySA: Hydrogen South Africa, which resulted in the development of the expertise and capacity to conduct research, development, and earlier commercial activities around green hydrogen production by means of water electrolysis. These activities include the development of local IP at the components, stack, and system levels.

Operando X-Ray Scattering for Electrocatalysis and Beyond

The energy transition stands as one of the greatest challenges of today’s society. In this context, electrocatalyst materials at the heart of electrochemical energy conversion devices such as fuel cells and water electrolyzers are expected to play an increasing crucial role in the near future. The urgent bottleneck to be overcome in electrocatalyst materials development to allow the widespread deployment of electrochemical systems is thus reaching combined high activity and long-term stability at low cost. Despite the diversity in electrocatalyst materials, the latter being largely imposed by the various types of electrochemical systems (noble vs. non-noble metals in acidic vs. alkaline media for example) and the prerequisites of the different electrochemical processes (oxidation or reduction reactions of various species at different electrode potential ranges), most activity and stability properties of electrocatalysts directly derive from their (surface) chemistry and structure [1]. Such properties (and their temporal evolution) can thus be directly investigated by means of in situ or operando high energy X-ray scattering (XRD) technique [2].In this presentation, the versatility of in situ and operando XRD technique in addressing key bottlenecks in electrocatalyst materials development, notably by probing adsorption and oxidation trends [3], will be showcased. After an overview of previous contributions from the literature, the talk will focus on our ongoing works which encompass the study of Pt-based nanocatalysts for the oxygen reduction reaction (ORR) at proton-exchange membrane fuel cells (PEMFCs) anode, carbon-capped Ni@C catalyst for the hydrogen oxidation reaction (HOR) at anion-exchange membrane fuel cells (AEMFCs) anode and IrCu unsupported aerogel catalyst for the oxygen evolution reaction (OER) at proton-exchange membrane water electrolyzers (PEMWEs) anode.Finally, the ability of operando XRD to provide device-relevant insights at the macroscale (such as ionomer hydration in PEMFCs or water distribution in AEMFCs) beyond electrocatalysts microstructural properties will be presented.

(Invited) Cost Reduction Strategies in Low Temperature Water Electrolysis with Improved Catalytic Activity

Proton exchange membrane water electrolysis (PEMWE) technology is especially advantageous for green H2 production as a clean energy vector. During the water electrolysis process, the oxygen evolution reaction (OER) requires a large amount of iridium (2-3 mgIr cm−2) as catalyst. This material is scarce and expensive, representing a major bottleneck for large-scale deployment of electrolyzers. Recently, Retuerto et al. have synthesized different Ir double perovskites (Sr2CaIrO6) with the Ir atoms in a high oxidation state (Ir6+/5+) 1 and their catalytic activity was extensively investigated. Specifically, a Ca-based double perovskite (Sr2CaIrO6) has showed the highest OER activity similar to those of Ir or Ir oxides-based catalysts while being stable for the OER in half cell measurements. We report the development of a membrane electrode assembly taking advantage of the high activity of the Sr2CaIrO6 catalyst that has only 0.2 mgIr cm−2, around 10 times lower compared to what it is used in the anodes of commercial PEMWE, showing superior performance and stability. The morphology/structure of the developed anode and Sr2CaIrO6 catalyst, before and after operation in PEMWE, were extensively characterized by X-ray diffraction (XRD, high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption near edge structure (XANES). We discuss in this contribution how the finding of this work can provide a strategy to lower the Ir content in commercial PEMWE.Anion exchange membrane water electrolysis (AEMWE) combines the advantages of proton exchange membrane water electrolysis (PEMWE), i.e., high current density while maintaining high efficiency and fast dynamic response with the advantages of alkaline water electrolysis (AWE), i.e., low-cost materials. However, AEMWE technology is still depends on a supporting electrolyte and its durability is low. In this regard, the German Aerospace Center (DLR) is developing novel approaches and cell components. Raney-nickel electrodes were developed via vacuum plasma spraying, reaching performance and stability comparable to SoA MW size PEMWE. The electrodes were further refined, switching to lower cost atmospheric plasma spraying while maintaining high performance. Studying the effect of supporting electrolyte concentration it was found, that lowering the ohmic resistance is by far the largest challenge for high performance AEMWE, especially at low KOH concentrations and electrode kinetics are less impactful. Moreover, a 17% efficiency uplift was achieved by applying a carefully tuned, thermally sprayed, nickel-based macro porous layer (MPL) onto a traditional mesh porous transport layer. Both ohmic and mass transport resistances were found to be lowered by the MPL. FIB-SEM and µCT analysis revealed an ideal structure, i.e., 30-40% porosity, almost exclusively open pores, and a broad pore size distribution2. In a fundamental study3, the mechanism of the OER activity was investigated as well as the effect of trace amounts of iron in Ni(OH)2. X-ray diffraction (XRD) and Thermogravimetric analysis (TGA) TGA analysis lead to the conclusion, that iron stabilized the α-Ni(OH)2which is the most active. CV analysis showed that an important redox switching step is also accelerated by Fe-doping. M. Retuerto, L. Pascual, J. Torrero, M. A. Salam, Á. Tolosana-Moranchel, D. Gianolio, P. Ferrer, P. Kayser, V. Wilke, S. Stiber, V. Celorrio, M. Mokthar, A. S. Gago, K. A. Friedrich, M. A. Peña, J. A. Alonso, D. G. Sanchez, S. Rojas, Highly Active and Stable OER Electrocatalysts Derived from Sr2MIrO6 for Proton Exchange Membrane Water Electrolyzers. Nat. Commun. 2022, 13, 7935. Razmjooei, F.; Morawietz, T.; Taghizadeh, E.; Hadjixenophontos, E.; Mues, L.; Gerle, M.; Wood, B. D.; Harms, C.; Gago, A. S.; Ansar, S. A.; Friedrich, K. A., Increasing the performance of an anion-exchange membrane electrolyzer operating in pure water with a nickel-based microporous layer. Joule 2021, 5 (7), 1776-1799. Wang, L.; Saveleva, V. A.; Eslamibidgoli, M. J.; Antipin, D.; Bouillet, C.; Biswas, I.; Gago, A. S.; Hosseiny, S. S.; Gazdzicki, P.; Eikerling, M. H.; Savinova, E. R.; Friedrich, K. A., Deciphering the Exceptional Performance of NiFe Hydroxide for the Oxygen Evolution Reaction in an Anion Exchange Membrane Electrolyzer. ACS Applied Energy Materials 2022, 5 (2), 2221-2230.

The Effect of Water Quality on PEM Electrolyzer Performance

There has been growing interest in the use of removable, clean, and sustainable energy sources as a solution to eliminate environmental problems caused by fossil fuels. In particular, the electrolysis of water to produce green hydrogen is one of the most promising technologies. Among various electrolysis techniques, proton exchange membrane water electrolyzer (PEMWE) stands out as the most promising for mobility and large-scale energy-storage applications (1). Hydrogen production by PEMWEs requires approximately 45 kg of high-quality water to produce 5 kg of hydrogen. It has been estimated that about 22% of the total cost of a state-of-the-art PEMWE system is for water deionization treatment (2). This water purity requirement is not only an economic barrier, but also a constraint for the use of this system in areas where high-quality water is not accessible or in areas where water for human consumption is a scarce resource. Therefore, studying the effect of water quality on PEMWE performance is an important first step in identifying key degradation mechanisms on the path to discovering new PEMWE architectures that are more tolerant of poor-quality feed waters.In this work, the effect of common impurities, such as Na+ and Mg2+, in feed water on the performance of common PEMWE architectures is studied. The main goals of the work are: 1) to understand the tolerance range for long term operation, 2) to identify major degradation mechanisms when the failure occurs. Experiments were carried out in an electrolyzer equipped with platinized Ti electrodes, IrO2 and Pt/C as anodic and cathodic catalysts, respectively, and a 115 Nafion® membrane. Durability studies of 100-hour duration and electrochemical characterization of the electrolyzer at different time intervals (polarization curves and impedance spectroscopy) were performed. The membrane/electrode assembly was probed by SEM /EDX before and after the experiments and cation concentrations in the water were monitored by ICP. An electrochemical model is proposed to explain the observed behavior of the electrolyzer with DI water and in the presence of impurities.The results show that the presence of cations affects the performance of the electrolyzer at different levels depending on the concentration of the cation and its valence (Mg2+ > Na+ >DI water). Mg+2 had the same effect as Na+ even at 5 times lower concentration. Cations have higher affinity than protons for sulfonic acid groups (-SO3 -), leading to a displacement of protons and a consequent reduction in the membrane proton conductivity. However. according to the polarization curves, there are effects beyond the ohmic potential due to the increase in membrane resistance. The major effect of cations is on the reaction kinetics, which is the primary reason for the observed increase in cell voltage. The presence of cations within the membrane blocks the transport of protons, which creates a lack of protons at the cathode, resulting in the kinetic change from proton reduction to reduction of water. Moreover, the EDX results showed that Na+ and Mg2+ ions transfer from anode to cathode and deposit on the membrane and catalyst layers, which may cover the active catalyst sites, block the proton transport inside the membrane and degrade the catalyst ionomer layers.References Sazali N. Emerging technologies by hydrogen: A review. International Journal of Hydrogen Energy. 2020 (45): 18753-18771Becker H, Murawski J, Shinde DV, Stephens IEL, Hinds G, Smith G. Impact of impurities on water electrolysis: A review. Sustainable Energy & Fuels. 2023;7(7):1565-603.

Effect of Catalyst and Electrode Structures on the Operating Current Densities of Liquid Alkaline Water Electrolyzers

Liquid Alkaline Water Electrolyzers (LAWEs) stand out as the technology best-suited for cost-effective hydrogen production. They do not require expensive platinum group metal catalysts and have proven durability afforded by nickel-based electrodes and porous separators. While nickel electrodes and porous separators provide chemical stability in highly alkaline conditions, they do suffer from lower catalytic activity for hydrogen and oxygen evolution reactions (HER and OER), and separators possess higher ohmic resistance due to the absence of ion-conducting groups. Consequently, most LAWEs operate at low current densities ranging from 0.2 to 0.6 A/cm2, resulting in a bulky footprint and comparatively lower energy efficiency due to a reduced hydrogen production rate. To address these challenges, considerable efforts have been directed towards developing thin separators and efficient transition metal-based electrocatalysts for HER and OER in alkaline media. However, the majority of studies related to catalysts are limited to half cells, with only a limited number of catalysts evaluated in relevant LAWE configurations.In this work, we introduce a next-generation Zero-gap LAWE testing capability, benchmarked for performance through H2NEW consortia. Employing this setup, we have evaluated hydrogen and oxygen evolution catalysts under LAWE-relevant conditions on different electrode substrates, each offering a unique electrode structure. Our preliminary findings indicate that Zero-gap LAWEs, when coupled with NiMo cathode and NiFe-type anode catalysts, can operate at current densities exceeding 0.75 A/cm2 at approximately 1.8 V without compromising their short-term durability. In contrast, the benchmark cell exhibited a meager current density of around 0.22 A/cm2. In this presentation, effects of electrode structure, catalyst type, and other relevant parameters related to Zero-gap LAWEs will be discussed in detail. Acknowledgement:This research is supported by the U.S. Department of Energy (DOE) Hydrogen and Fuel Cell Technologies Office through the Hydrogen from Next-generation Electrolyzers of Water (H2NEW) consortium.

Enhanced Local Ion Transport in High-Performance Anion Exchange Membrane Water Electrolyzers Via Quaternary Ammonium-Functionalized Metal-Organic Framework Electrocatalysts

Anion-exchange membrane water electrolyzers (AEMWEs) present a multitude of advantages, particularly in the utilization of non-platinum group (non-PGM) catalysts. While diverse catalysts have demonstrated notable electrocatalytic activity in alkaline conditions, the integration of the ionomer with the electrocatalyst at the active catalyst layer is crucial for enhancing overall AEMWE performance in practical device demonstrations by improving mass transport. However, the intrinsic instability of polymeric ionomers, leading to physical detachments or alkaline (chemical) degradation, poses a challenge that can potentially diminish performance. In this study, drawing inspiration from the aforementioned ionomer chemistry, we introduce non-PGM NiFe-based metal-organic frameworks (MOFs) incorporating quaternary ammonium (QA) cation moieties covalently functionalized to benzenedicarboxylic acid (BDC) ligands as promising electrocatalysts for the oxygen evolution reaction (OER) in alkaline environments. Three specifically designed functional groups with varying ion exchange capacities (IEC) and alkaline stability—trimethylamine (TMA), N-methylpyrrolidine (C4N), and N-methylpiperidine (C5N)—were directly tethered to BDC ligands. The alkaline OER activity of Ni2Fe1-QA-MOF was meticulously assessed using rotating disk electrodes and AEMWE devices. These directly tethered QA groups markedly facilitated improved ionic transport of OH- ions at the catalyst/electrolyte interfaces compared to BDC ligands, ultimately leading to a significant enhancement in half-cell activity and AEMWE performance. In-situ IR/RAMAN spectroscopy revealed that QA moieties highly promoted local ionic transport at the interfaces, as evidenced by characteristic peaks indicating a robust interaction between QA and OH- ions. Unexpectedly, QA moieties not only contributed to ionic transport in local environments but also induced oxidation states of Ni metal sites, while Fe sites exhibited no changes during the applied potential in the OER region, as comprehensively revealed by synchrotron X-ray absorption spectroscopy (XAS). In comparison with conventional NiFe layered double hydroxide (LDH) structures, we posit that the substantial structural transformation of Ni moieties can be attributed to an increased degree of M-O bond interaction, enhanced by the local interaction between QA and OH- ions. Density functional theory (DFT) calculations also validate the balanced adsorption of OER intermediates on QA-MOFs. Finally, QA-NiFe-MOF was directly synthesized on a porous transport layer (PTL), and its AEMWE performance was evaluated without the use of any ionomer. At 1.0 M KOH, C4N, C5N, and TMA-based NiFe MOFs exhibited current densities of 9.35 A/cm2, 9.11 A/cm2, and 7.6 A/cm2, respectively. These current densities surpassed those of bare BDC-NiFe MOF and commercial IrO2 anode catalysts, which exhibited only 7.39 A/cm2 and 6.4 A/cm2, respectively. Consequently, we emphasize that the facilitation of local ionic transport could yield remarkable AEMWE performance, even in the absence of conventional polymeric ionomers.

(Invited) Catalyst and Anode Design for Durable Alkaline-Membrane Electrolysis

Commercialized membrane electrolyzers use acidic proton exchange membranes (PEMs). These systems offer high performance but require the use of expensive precious-metal catalysts such as IrO2 and Pt that are nominally stable under locally acidic conditions. Alkaline-exchange-membrane (AEM) electrolyzers in principle offer the performance of PEM electrolyzers with the ability to use earth-abundant catalysts and inexpensive bipolar plate materials. I will highlight our fundamental work in understanding the chemical and electrochemical processes in earth-abundant water-oxidation catalysts over the past decade and we are using that understanding to drive progress in high-performance AEM electrolyzers.Baseline systems operate at 1 A·cm-2 in pure water feed at < 1.9 V at a moderate temperature of ~70 °C using either IrO2 or Co3O4 anode catalyst layers, PiperION alkaline ionomers, and stainless-steel porous transport layers. These devices, however, degrade rapidly compared to PEM electrolyzers which we link to chemical and structural changes in the ionomer-catalyst reactive zone using a combination of integrated reference-electrode device architectures, impedance, and cross-sectional and post-mortem materials analysis. We further discover that dynamic Fe-based OER catalysts – that have world-record performance in traditional liquid alkaline electrolyzer systems – perform poorly with enhanced degradation rates in alkaline membrane electrolysis, illustrating fundamentally different chemical design principles for OER catalysts.Given this baseline understanding, I will end with new chemical strategies we have developed to mitigate degradation and enhance performance using novel ionomers, passivated electrolyte-catalyst interfacial architectures, and specifically designed multicomponent anode oxygen catalysts to target stable performance without supporting soluble electrolyte: <10 μV/h degradation at currents > 2 A cm-2 and cell voltages < 2V.

The 2-Propanol Fuel Cell: Direct CO2-Free Electrification with a Liquid Hydrogen Carrier

Molecular hydrogen is a gas at ambient conditions and requires compression or cryogenic liquefaction for storage and transport, leading to significant losses in efficiency. Therefore, liquid hydrogen carriers are desirable as they are storable without losses. One such fuel that has shown promise recently is 2-propanol (isopropanol), which is converted with high selectivity to acetone in a fuel cell.[1],[2],[3] Power densities over 200 mW/cm2 have been reported for direct isopropanol fuel cells (DIFCs), which rivals the best direct methanol fuel cells (DMFCs), and unlike methanol, isopropanol is non-toxic and it is not fully oxidized to CO2. [4] The literature has demonstrated many advantages of DIFCs, yet significant challenges remain.[5] Continuous operation at high current densities can be limited due to anodic catalyst layer network effects: slow removal of acetone from active sites and out of the catalyst layer. Additionally, perfluorinated sulfonic acid (PFSA) ionomers are not fully chemically compatible with 2-propanol and acetone. Operation at higher temperatures with a vaporized 2-propanol feed partially mitigates both of these disadvantages, yet the high energy cost of vaporization reduces the overall efficiency of the system. Future research should focus on stable, high-power operation with a liquid 2-propanol feed.This contribution chronicles the progress that has been made and discusses the current state-of-the-art and outlook of direct electrification with DIFCs. Recent advances in liquid-fed DIFCs are presented, including design of membrane-electrode-assemblies and operation strategies in full cells. Finally, the concept of using the 2-propanol/acetone couple as an electrochemical liquid organic hydrogen carrier is briefly introduced: a reversible hydrogenation and dehydrogenation cycle for storing and releasing molecular hydrogen on demand.

Understanding Mass Transport at High Current Densities in an Industrial Scale PEM Electrolysis Test Cell - a Segmented Along-the-Channel Approach

Industrial PEM water electrolysis stack designs can suffer from an unevenly distributed water amount over the cell area. This can lead to performance differences and thermal hot spots due to the lack of reactant supply and poor thermal management. Undersupplied spots could also degrade more quickly [1,2]. Especially in the water flow direction, gradients are expected due to the water consumption and gas evolution and accumulation along the supply channels.To face these issues, we built up a segmented along the channel (AtC) PEM electrolysis test cell in industrial scale for locally-resolved investigations. The cell has a length of 30 cm at 2 cm cell width with a straight parallel flow field. To minimize transverse currents the cell is divided into 10 equal segments along the channels. The main focus of our investigation is locally-resolved electrochemical impedance spectroscopy (EIS). With a shunt resistor approach, it is feasible to measure the impedance of each segment and the mean cell in parallel. Additionally, it is possible to measure the current density and temperature distribution of the anodic bipolar plate highly resolved using 120 sensors over the cell length.With this test cell we want to understand mass transport processes along the channel in industrial scale. Diffusion and mass transport overpotentials are usually dominant at high current densities. To be able to face extreme conditions and investigate possible future operation points the cell was designed up to 10 A∙cm-2 (600 A absolute) and successfully tested. Furthermore, an operation of 10 bar differential and equal pressure is possible.Figure 1 shows the cell design (a), the mean cell polarization curve of the AtC cell (60 cm²) in comparison with measurements of the same setup in our 4 cm² test cell (b) and locally-resolved high frequency resistance (HFR) free EIS at 7 A∙cm-2 (c). It is noticeable, that the here used commercially available materials do not show high mass transport limitations, neither in the 4 cm² ISE-reference cell nor in the 60 cm² AtC cell. An increase of the slope of the polarization curve towards higher current densities remains out, see Figure 1 (b). Instead of this the slope of the polarization curve is constantly decreasing. This can not only be explained by the temperature increase of the catalyst-coated membrane (CCM) due to higher heat dissipation. Using EIS, we here can detect an additional electrochemical process at low frequencies of inductive type which is increasing with increasing current density. In the locally-resolved EIS in Figure 1 (c) the inductive process (positive imaginary values) is detectable as the so called “inductive loop”. This phenomenon has a negative resistance magnitude and therefore a beneficial impact on the cell performance. Inductive Loops are discussed in several electrochemical applications, like batteries and fuel cells [3,4]. Despite this, in PEM electrolysis this process has not been discussed yet. We could show that this phenomenon is reproducible and has an important impact on the cell performance and impedance-based performance analyses when operating at current densities > 1 A∙cm-2 [5].For diffusion analyses, the inductive loop is essential to be considered since both processes happen at similar frequencies. In Figure 1 (c) an increasing of the number of time constants at frequencies < 100 Hz is detectable towards the cell outlet (e.g. segment 9 and 10). These slow processes are most likely diffusion related.Our upcoming investigations will face locally-resolved measurements with varying structural parameters of porous transport layers (PTL) and CCMs with different anodic catalyst loadings to gain a better understanding of mass transport processes for future PEM electrolysis cells along the channel.Reference List:[1] IMMERZ, C., et al. Experimental characterization of inhomogeneity in current density and temperature distribution along a single-channel PEM water electrolysis cell. Electrochimica acta, 2018, 260. Jg., S. 582-588.[2] VERDIN, B., et al. Operando current mapping on PEM water electrolysis cells. Influence of mechanical stress. International Journal of Hydrogen Energy, 2017, 42. Jg., Nr. 41, S. 25848-25859.[3] KLOTZ, Dino. Negative capacitance or inductive loop?–A general assessment of a common low frequency impedance feature. Electrochemistry Communications, 2019, 98. Jg., S. 58-62.[4] GERLING, Christophe, et al. Experimental and Numerical Investigation of the Low-Frequency Inductive Features in Differential PEMFCs: Ionomer Humidification and Platinum Oxide Effects. Journal of The Electrochemical Society, 2023, 170. Jg., Nr. 1, S. 014504.[5] HENSLE, Niklas, et al. On the role of inductive loops at low frequencies in PEM electrolysis. Electrochemistry Communications, 2023, 155. Jg., S. 107585. Figure 1

(Invited) Degradation and Poisoning of Proton-Exchange Membrane Water Electrolyzer Anode Catalysts

Hydrogen production through water electrolysis is a crucial technology to enable the transition to a carbon neutral, hydrogen-based economy. One of the primary types of electrolyzers is the low-temperature proton-exchange membrane water electrolyzer (PEMWE). As with the analogous proton-exchange membrane fuel cells, platinum group metal electrocatalysts are utilized due to their activity and stability in acidic environment. Electrocatalysis R&D efforts for PEMWEs primarily focus on the oxygen evolution reaction (OER) since it is several orders of magnitude kinetically slower than the hydrogen evolution reaction (HER).1 Iridium-based metal oxides (IrOx) are regarded as the best PEM electrolyzer electrocatalysts as they balance activity and stability.2 However, improvements are needed in both areas to enable minimization of Ir loading to meet system cost targets while also meeting challenging performance and lifetime targets.3 An understanding of the factors affecting both the activity and stability of Ir-based OER catalysts is needed to develop strategies to enable both high OER activity and long-term stability of the PEMWE anode catalyst.This presentation will describe our studies of the effects of perfluorosulfonic acid (PFSA) binder on the OER kinetics and the factors influencing the stability of two commercial Ir-based OER catalysts, one comprised of IrOx only and the other also containing TiOx. Measurements of OER kinetics as a function of ionomer to catalyst ratio utilizing rotating disc electrode and cavity microelectrode methods in an acidic aqueous electrochemical environment will be described. Dissolution and loss of Ir under the operating conditions of the PEMWE anode is considered to be one of the main PEMWE anode degradation mechanisms.4 To understand the factors affecting this phenomenon, the potential and time-dependence of Ir (and Ti) were determined using an electrochemical flow cell system connected to an inductively-coupled plasma-mass spectrometer (ICP-MS) capable of detecting trace concentrations (<ppb) of dissolved elements in solution. The electrochemical data combined with the ICP-MS data have been used to evaluate the influence of various factors such as potential, potentiodynamic profile parameters (e.g., scan rate, upper and lower potential limits) on the dissolution processes in acidic aqueous electrolyte at room temperature.AcknowledgementsThis research is supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office under the auspices of the H2NEW Consortium. Argonne National Laboratory is managed for the U.S Department of Energy by the University of Chicago Argonne, LLC, also under contract DE-AC-02-06CH11357.References A. Raveendran, M. Chandran, and R. Dhanusuraman, RSC Adv., 13 (2023) 3843.J. Ouimet, J.R. Glenn, D.D. Porcellinis, A.R. Motz, M. Carmo, K.E. Ayers, ACS Catalysis, 12 (2022) 6159."Technical Targets for Proton Exchange Membrane Electrolysis", U.S. Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office, March, 2023.Zeng, R. Ouimet, L. Bonville, A. Niedzwiecki, C. Capuano, K. Ayers, A.P. Soleymani, J. Jankovic, H. Yu, R. Maric, et al., J. Electrochem. Soc., 169(5) (2022) 054536.

(Invited) Novel Polymer and Membrane Development Strategies for Water Electrolysis

Water electrolysis processes play a crucial role in transitioning to a climate-friendly society. They facilitate the integration of renewable energy, offer a clean and versatile energy carrier, decarbonize industries, improve energy storage and grid stability, and support the development of sustainable transportation solutions. As technology advances and economies of scale are realized, electrolysis is expected to play an increasingly significant role in the clean energy landscape, contributing to a more sustainable and resilient future.Various water-splitting electrolysis processes currently exist, including alkaline, solid oxide, proton exchange membrane (PEM), anion exchange (AEM), acidic-alkaline amphoteric, microbial, and photoelectrochemical methods [1]. In our research group, we are actively involved in membrane development for both PEM and AEM water electrolysis.In PEM electrolysis membrane development, our group explores several approaches, such as (a) aromatic main-chain block copolymers[2],(b) acid-base blend membranes using sulfonated and partially fluorinated aromatic polyether, polybenzimidazole, and a PSU-derived basic polymer[2], (c) poly(fluorene)-based sulfonated ionomers, (d) sulfonated and phosphonated poly(pentafluorostyrene) polymers with flexible side groups, and (d) nanophase-separated block copolymers based on phosphonated[3] or sulfonated pentafluorostyrene and octylstyrene. Additionally, we investigate (e) H+-conductive fiber-mat reinforced perfluorosulfonic acid (PFSA) polymers[4].The development of anion exchange membranes in our research group includes (a) polystyrene-based side chain anion exchange polymers and their blends with polybenzimidazole[5], (b) polynorbornene-based optionally ionically and covalently crosslinked anion exchange polymers and membranes, (c) side chain anion exchange polymers and membranes prepared by polyhydroxyalkylation[6], and (d) anion exchange blend membranes made from polydiallyldimethylammonium salts and polybenzimidazole.This contribution highlights the application of two polymer types in PEM and AEM membrane water electrolysis, respectively:(A) PEM Water Electrolysis (PEMWE): Membranes from PEM types (a) and (b) demonstrated good performance. PEM (a) achieved 2.2 V@6 A/cm2, and PEM (b) reached 2.26 V@6 A/cm2 (compared to Nafion212: 2.26 V@6 A/cm2)[2]. These performances were accomplished with non-optimized membrane-electrode assemblies using Nafion as the electrode ionomer. Further performance improvements are expected with optimized electrodes containing the same ionomers as used in the membrane.(B) AEM Water Electrolysis (AEMWE): Blend membranes from AEM type (a) exhibited excellent alkali stability (no conductivity decrease after 1000 hrs of storage in 1M KOH@85°C) and good AEMWE performance (CuCo anode catalyst, 1M KOH, 70°C, 2 V@3 A/cm2)[5]. Type (c) AEMs were applied to a seawater electrolysis cell at 60°C, achieving a performance of 2 V@1 A/cm2 using completely noble metal-free catalysts in both the anode and cathode[6].[1] M. F. Ahmad Kamaroddin, N. Sabli, T. A. Tuan Abdullah, S. I. Siajam, L. C. Abdullah, A. Abdul Jalil, A. Ahmad, Membranes 2021, 11.[2] J. Bender, B. Mayerhöfer, P. Trinke, B. Bensmann, R. Hanke-Rauschenbach, K. Krajinovic, S. Thiele, J. Kerres, Polymers 2021, 13.[3] S. Auffarth, M. Wagner, A. Krieger, B. Fritsch, L. Hager, A. Hutzler, T. Böhm, S. Thiele, J. Kerres, ACS Materials Lett. 2023, 5, 2039.[4] M. S. Mu'min, M. Komma, D. Abbas, M. Wagner, A. Krieger, S. Thiele, T. Böhm, J. Kerres, Journal of Membrane Science 2023, 685, 121915.[5] L. Hager, M. Hegelheimer, J. Stonawski, A. T. S. Freiberg, C. Jaramillo-Hernández, G. Abellán, A. Hutzler, T. Böhm, S. Thiele, J. Kerres, J. Mater. Chem. A 2023.[6] M. L. Frisch, T. N. Thanh, A. Arinchtein, L. Hager, J. Schmidt, S. Brückner, J. Kerres, P. Strasser, ACS Energy Lett. 2023, 8, 2387.

Large-Scale Artificial-Photosynthetic Production of Formate and Isolation of Pure Formic Acid

We proposed a concept of an artificial-photosynthetic system to produce pure formic acid using CO2, water, and solar energy, generating no waste, as illustrated in Fig. 1.1 The system consists of an artificial-photosynthetic reaction process and a product isolation process. We proved the concept by small-scale experiments, and constructed a practically large-sized solar-driven CO2 electrolyzer as the first step toward widespread use of artificial photosynthesis.2,3 We adopted a single-compartment configuration of the solar-driven CO2 electrolyzer without ion-exchange membranes and a near-neutral pH electrolyte of a potassium phosphate buffer aqueous solution to simplify the reactor structure. The large-sized electrolyzer was composed of eight-stacked cathode-anode-electrode pairs of 1 m×1 m in size and powered by crystalline silicon solar cells installed on the electrolyzer housing via a DC-DC converter. The raw material of 100% CO2 gas was dissolved in the electrolyte and supplied to the cathode-electrode surfaces uniformly with the help of well-designed flow channels. The electrochemically synthesized formic acid was dissolved in the electrolyte and ejected from the electrolyzer. Insertion of nanoporous separator between the facing anode/cathode electrodes prevented O2 bubbles produced on the anodes from reaching the cathodes, suppressing the crossover reaction of O2 reduction. We developed a novel Ru complex polymer (RuCP)-based cathode catalyst loaded on carbon supports and an IrO x -based anode catalyst, and achieved a Faradaic efficiency as high as 96% for the formic acid synthesis at an extremely low operating voltage of 1.65 V (overpotential of only 0.22 V) and a large current of 65 A, resulting in a high solar-to-chemical energy conversion efficiency of 10.5%. This significant performance was realized by the low-resistive Ti substrates of the cathode and anode electrodes, sufficient CO2 supply to whole of the cathode surfaces, etc., which have greater impacts on a larger electrolyzer, in addition to the high catalytic activity of the RuCP and IrO x . Further, we tackled to improve both activity and durability of the anode and cathode electrodes,4,5 and to realize direct reduction of CO2 in a flue gas to eliminate energy-consuming CO2 capture processes.6 Moreover, we designed tandem solar modules suitable for direct coupling with the electrolyzers using organic-inorganic hybrid perovskite solar cells.7 The next challenge was isolation of the synthesized formic acid dissolved in the aqueous electrolyte. The formic acid cannot be isolated by distillation because its boiling point (101 °C) is virtually the same as that of water. Thus, we developed an isolation process on the basis of reactive extraction, including three sequential steps.1 The first step was reactive extraction of the formic acid from the electrolyte using an extraction solution composed of an organic base (tri-n-octylamine, TOA, boiling point 366 °C) as an extractant and an organic solvent (dichloromethane, DCM, boiling point 40 °C) as a diluent. Although formic acid is highly miscible in water, it was extracted into DCM because the formic acid formed a complex salt with TOA that is insoluble in water. The second step was removal of DCM from the mixture of the extracted formic acid, TOA, and DCM produced in the first step, by evaporation at 40 °C at 0.03 MPa. Finally, the residue was heated at 160 °C at 0.02 MPa for isolation of the formic acid by distillation in the third step. The large differences in the boiling points among these three chemicals secured few contaminations in the second and third steps. In addition, the composition of the electrolyte was tuned for promotion of the formation of the formic acid-TOA complex salt. Thus, we achieved an over 90% isolation yield of pure formic acid. The new electrolyte was confirmed to lower the energy conversion efficiency by only 10%(relative) and to secure similarly high durability compared with the original electrolyte. The great feature of the isolation process is that all the electrolyte, TOA, and DCM are reused for the next synthesis and isolation after the formic acid is isolated. Thus, we established a highly sustainable artificial-photosynthetic system that consumes no chemicals other than the raw materials of CO2 and water, or generates no waste.References M. Shiozawa,et al., Energy & Fuels, submitted.N. Kato, et al., Joule, (2021) 5, 687.N. Kato, et al., ACS Sustain. Chem. Eng.,(2021) 9, 16031.M. Shiozawa, et al., Electrocatalysis, (2022)13, 830.N. Kato, et al., submitted to 245th ECS Meeting , Symposium I04: Electrosynthesis of Fuels 8 (2024).Y. Takeda, et al., J. CO2 Util., (2023)71, 102472.Y. Takeda, et al., J. Appl. Phys., (2022)132, 075002. Figure 1

Comprehensive Characterization of Porous Transport Electrodes with SEM, XPS, and Tof-SIMS

Advancements towards more efficient design and manufacturability of polymer electrolyte membrane electrolyzers include recent efforts to better integrate the porous transport layer (PTL) and adjacent anodic catalyst layer (CL), forming the porous transport electrode (PTE). It is well known that characterizations of the PTL alone, especially when combined with a protective coating, present numerous challenges. The PTE structure is even more complex, and it is difficult to comprehensively characterize all components and interfaces. In prior work, we established Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) as a characterization technique for the PTLs coated with protective coatings. This work demonstrates ToF-SIMS as a powerful technique for the characterization of PTLs integrated with CLs. A series of sintered Ti PTLs were first coated with protective Pt coatings and then coated with various IrOx and IrRuOx catalysts via electrodeposition. Prepared PTE samples ranged in catalyst loadings and catalyst composition. Selected samples were also subjected to annealing post-treatments to further modify catalyst composition. X-ray photoelectron spectroscopy (XPS) was conducted to identify surface chemical speciation and states of the catalysts. ToF-SIMS analysis was conducted using Cs in both positive and negative modes to identify chemical species, including Ir, Ru, and their oxides as a function of catalyst layer depth. These two methods were complemented by Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy (SEM- EDS) analysis to evaluate morphology and distribution of catalysts. This comprehensive physical and chemical characterization of the PTEs provides insights that are useful for the characterization of as produced, modified, and degraded PTE samples.

New Electrocatalyst with the Content of Ir

Introduction Proton exchange membrane (PEM) water electrolysis (WE) is a promising technology for hydrogen production. However, the local environment of the anode in PEMWE is highly acidic and high potential due to the oxygen evolution reaction (OER; 2H2O → O2 + 4H+ + 4e-), and the available anode materials are limited to precious metal elements such as Pt, Ru and Ir. In the current technology, Ir-based materials are the mainstream anode catalysts, and Ir loading of 1-2 mg/cm2 is necessary to achieve both activity and durability. On the other hand, the annual production of Ir is said to be only 5-7 tons. The demand for hydrogen is expected to increase to the GW scale in the future. For example, if water electrolysis is operated at 2 A/cm2 and 2 V with Ir loading of 2 mg/cm2 (0.5 mgIr/W), it is difficult to meet the demand with the existing Ir resources. Tosoh have been engaged in the electrolytic manganese dioxide (EMD) business. EMD is synthesized thorough anodic oxidation of Mn2+ ion (Mn2+ + 2H2O → MnO2 + 4H+ + 2e-) under acidic conditions, therefore it is potentially suitable for the anode environment of PEMWE. In this study, a very small amount of Ir (<0.1 mg/cm2) was successfully composited with EMD. The resulting composite consisting of Ir and EMD showed more active than commercial Ir oxide with the same Ir content, and operated stably for at least 1000 h. Experiment EMD thin film was electrodeposited anodically on Pt-coated Ti fibers (Pt/Ti) thorough electrolyzing a mixed solution of MnSO4 and H2SO4. The obtained EMD-coated Pt/Ti were immersed in an Ir-containing solution, and then annealed to obtain Ir-containing EMD (hereinafter referred to as "Ir-EMD"). The Pt-coated Ti fibers are used as a porous transport layer (PTL) in PEMWE cells, and our developed material serves as both an OER catalyst and a PTL. OER property was evaluated using a PEMWE cell at 80°C in a two-electrode system. Pt-supported carbon was used as the cathode catalyst and Nafion®-115 as the PEM. See Fig. 1 for PEMWE cell construction flow. Result and discussion The Ir content in Ir-EMD was determined to be 0.1 mg/cm2 by ICP-AES. This Ir content is 10-20 times lower than that used in current PEMWE electrolyzers. The OER activity of Ir-EMD was evaluated by linear sweep voltammetry (LSV) (Fig. 2). For comparison, EMD (with no Ir) and Ir oxide (commercial product) with an Ir content of 0.1 mg/cm2 were evaluated in the same way. The slow OER property of EMD was improved dramatically by introducing Ir into EMD. Also, at the same amount of Ir, Ir-EMD exhibited higher OER activity than that of Ir oxide. The inset in Fig. 2 shows Tafel plots corresponding to LSVs, and the slope of the linear region (Tafel slope) can be used to predict which elementary reaction is the rate-limiting step in the OER. The Tafel slope of Ir-EMD is 58 mV/dec., which is close to the Tafel slope of Ir oxide, 50 mV/dec. This suggests that OER on Ir-EMD proceeds by the same mechanism as Ir oxide. The durability of Ir-EMD and Ir oxide was tested at a current density of 2 A/cm2 (Fig. 3). Ir oxide was deactivated within only 8 days, and it is confirmed that Ir have disappeared after electrolysis. On the other hand, Ir-EMD has operated stably for more than 42 days (≈1000 h), with a degradation rate of only 13 μV/h. In other words, Ir-EMD has practical durability while reducing the amount of Ir by more than 10 times compared to current technology.Acknowledgements : This presentation is based on results obtained from a project, JPNP20003, subsidized by the New Energy and Industrial Technology Development Organization (NEDO). Figure 1

(Invited) IrOx Nanoparticle Catalysts on a Unique Microstructure of Doped Tin Oxide to Dramatically Boost the Oxygen Evolution Reaction Activity for PEM Water Electrolysis

Proton exchange membrane water electrolyzers (PEM WEs) has a potential to produce high-purity green hydrogen. PEMWEs have been commercialized with the use of high loadings of the noble metal Ir-based anode catalyst for the oxygen evolution reaction (OER). To lower the Ir loading amount, it is critically important to develop efficient catalysts with increased Ir utilization and higher OER activity. One-dimensional Ir oxide nanorod/nanoparticles catalysts supported on doped SnO2 with a unique microstructure were invented to show their exceptionally high activity in the OER catalysis, with the Ir-mass specific activity being 10 times higher than that of commercial IrOx catalyst at 1.5 V vs. RHE.[1] The experiment also found that the OER activation energy was greatly lower than that of commercial Ir oxide. The interaction between Ir oxide nanorod/nanoparticles and doped SnO2 support occurs a lower degree of Ir oxidation which allows the surface terminal oxygens to be closer together while allowing facile desorption of nonreactive oxygenated species. The electronic state of Ir oxide nanorod/nanoparticles catalysts could play an important role in facilitating the crucial step of the OER, thereby enhancing the OER activity. These priorities of the catalysts would promise the reduction of the Ir usage in PEMWEs.Reference[1] G. Shi, T. Tano, D.A. Tryk, T. Uchiyama, A. Iiyama, M. Uchida, K. Terao, M. Yamaguchi, K. Tamoto, Y. Uchimoto and K. Kakinuma, ACS Catalysis, 13 (2023) 12299. Figure 1

Two-Dimensional Modeling of Proton Exchange Membrane Water Electrolyzer

Proton exchange membrane water electrolyzers (PEMWEs) are a central focus in the quest for clean fuel production from water. A comprehensive computational modeling of PEMWE is essential for predicting and optimizing the performance of PEMWE, enabling efficient design and advancement in clean energy technologies. In this study, a 2-D, transient, multiphysics, and multiphase model is developed to study the performance of PEMWE with a focus on morphological and geometrical features of porous transport layer (PTL), liquid saturation, gas pressure, and operating temperature. User Defined Function (UDF), an add-on of Ansys Fluent® is used to solve the transport equations in different layers of the PEMWE model. The model is first validated against experimental data (figure 1) from the literature. Mass transfer of each species (hydrogen, oxygen, vapor, and dissolved water) and heat transfer are analyzed in each layer of PEMWE, including PTL, anode catalyst layer, membrane, cathode catalyst layer, and gas diffusion layer. Besides, the electronic and ionic potential in all domains, along with the liquid water saturation distribution in porous layers, are investigated. Different governing parameters such as cell voltage, and operating temperature are varied to get the performance of the electrolyzer cell. The findings will provide new insights into electrolyzer cell performance under various operating conditions, offering valuable information for adjusting parameters and optimizing the design of electrolyzer cells. Figure 1

The Impact of Catalyst Layer Fabrication Procedure on Layer Morphology, Transport Properties and Performance in Low-Temperature PEM Fuel Cell

Hydrogen mobility represents a progressive, low carbon imprint option for the replacement of internal combustion engines. A core of this technology is low-temperature fuel cell with proton-exchange membrane (LTPEMFC), using hydrogen and atmospheric oxygen as fuel and oxidant, respectively. The membrane-electrode assembly (MEA) which makes up a cell consists of polymer electrolyte membrane, cathodic and anodic catalyst layers and carbon-based porous gas-diffusion layers. LTPEMFC require Pt catalyst on both the anode and the cathode in non-negligible total amount, increasing investing costs for stack unit. In order to maximise fuel cell performance, the formation of three-phase boundary has to be achieved during deposition of catalyst layers, interconnecting Pt nanoparticles on carbon support and ionomer with membrane in complex, porous structure. The quality of catalyst layer determines to high degree final MEA performance.Catalyst layers can be deposited either on gas-diffusion layers or onto the membrane, with latter being considered a more advantageous and feasible approach. Deposition itself can be realised by various methods, including airbrush spraying, decal printing, doctor blade deposition from paste and, most often used nowadays, ultrasonically-assisted spray coating. Each of these methods brings its own advantages and disadvantages, though the common problem of these methods is low suitability for serial production. On the other hand, the quality of so-prepared catalyst layers is sufficient. Methods for large-capacity coating of catalyst layers, especially roll-to-roll technology have exactly opposite pros and cons, high output but unsatisfactory layer quality. An interesting alternative to state-of-the-art catalyst layer fabrication procedures is inkjet printing.Inkjet printing is a well-established technology, though the application in LTPEMFC field brings various issues, mainly connected to quality of layers and prevention of nozzle-clogging during the deposition. Solving of these issues, however, will result in technology suitable for catalyst layer printing, combining high production throughput, very good reproducibility, minimal losses of the ink, suitability to additive manufacturing and possibility of printing specific geometries with gradient layer thickness. Accordingly, the goal of this study is the comparison of catalyst layers, deposited onto the membrane by ultrasonically-assisted spray coating and inkjet printing, in terms of morphology, electric conductivity, permeability and performance in LTPEMFC, using commercially-available materials for layer fabrication.Catalyst layers of the same composition and Pt loading were deposited by either ultrasonically-assisted spray coating or inkjet printing onto FTO conductive glass for the determination of electric conductivity, onto gas-diffusion layer for permeability determination in Loschmidt cell and FIB-SEM morphology studies and onto the membrane for the fabrication of MEA and evaluation of its performance in LTPEMFC. Characterisation of layers deposited on materials above underlined feasibility of inkjet printing for catalyst layer fabrication. In comparison with sprayed layers, layers prepared by inkjet printing tend to be thinner, more homogenous and compact. This results in superior electric conductivity but lower permeability at the same time. Single cell tests proved that performance of inkjet-printed layers is at least on par with sprayed ones, surpassing them with optimised ink composition and Pt loading. Overall, inkjet printing technology is a highly attractive technology for industrial catalyst layer production with great possibilities for contributing to decrease LTPEMFC unit’s investment costs.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 958174. This project is co-financed from the state budget by the Technology agency of the Czech Republic under the M-ERA.Net Programme, project No. TH80020006. This work was supported by the project "The Energy Conversion and Storage", funded as project No. CZ.02.01.01/00/22_008/0004617 by Programme Johannes Amos Commenius, call Excellent Research. This project is co-financed with tax funds on the basis of the budget passed by the Saxon state parliament.

(Invited) Electron Microscopy Investigation of PEM Electrolyzer Degradation at Low Iridium Loadings

The employment of hydrogen as an energy carrier provides a promising solution toward zero carbon emission and battling climate change. To meet the DOE’s Hydrogen Shot goal of $1 per kilogram of hydrogen by 2031, proton exchange membrane (PEM) water electrolysis is a key technology of hydrogen production from renewable energy sources. Successful deployment of PEM electrolyzers requires reducing cost while simultaneously improving performance and lifetime. While cost reduction is expected from a variety of strategies including scaling up, operation optimization, and advanced manufacturing, it remains vital to reduce the use of noble-metal catalyst due to its scarcity and vulnerable supply chain subject to market disturbance. [1]Reducing the loading of iridium catalyst on the anode while maintaining electrolyzer performance and durability is of great challenge. In this talk, we discuss issues in PEM electrolyzer component development and advanced manufacturing of electrode layers related to catalyst loading reduction with an emphasize on analytical electron microscopy which provides valuable insight on materials morphology, crystalline structure, and chemical compositions. The batch-to-batch variance of catalyst morphology and elemental composition/distribution from commercial suppliers will be examined for catalyst down-selection. We then analyze the effect of reducing Ir loading on the electrode layer structure and ionomer distribution. These results are correlated with electrochemical measurements in the electrolyzer cell, which help elucidate the effect of low catalyst loading on electrolyzer performance. Morphologies of degraded low-loading anode catalyst layer and gas recombination layers will be investigated, and the dissolution and migration of iridium will be studied. We will also examine impact of different roll-to-roll manufacturing strategies for low-loading catalyst layers and on electrolyzer durability. Last but not least, we analyze MEAs subject to cation contamination and recovery procedure with electron microscopy. [2]References[1] Alia, S.M., Current Opinion in Chemical Engineering 2021, 33:100703.[2] Funding for this work was provided by U.S. Department of Energy Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office through the H2NEW Consortium. Electron microscopy research conducted as part of a user project at the Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory.

Development of an Onboard Urea Electrolyser to Reduce NOx Emissions in Vehicles By Enhancing the Selective Catalytic Reduction with the Produced H2 and NH3

In the persistent pursuit of reducing nitrogen oxide emissions from diesel exhaust, challenges arise in achieving optimal performance at lower temperatures, especially in urban driving conditions. This research focuses on a pragmatic approach – development of an onboard urea electrolyser using diesel exhaust fluid (DEF) as the hydrogen-rich carrier. The primary goal is to enhance the NOx reduction efficiency at temperatures below 200oC by providing the electrolyser products – hydrogen and ammonia [1]. The reason behind this innovation lies in recognising DEF as a viable electrolyte, offering both safety and a promise of performance increase due to splitting of urea instead of water. Beyond the contribution to NOx reduction, this approach aligns with the broader societal and political imperatives of integrating cleaner energy solutions within the automotive sector. However, the development of a functional urea electrolyser involves certain complexities. The key considerations are the material stability under operating conditions, anode catalyst dissolution in DEF, mass transport limitations, and the reduction of relatively high cathode overpotentials. A notable aspect of our research involves addressing these challenges in scenarios both with and without potassium hydroxide alongside DEF, requiring a nuanced understanding of the electrochemical processes involved. Additionally, weight, packaging, and system integration play an important role in the development of an onboard urea electrolyser.This study systematically explores these challenges to devise a comprehensive understanding of the underlying electrochemical processes involved as well as the integration and operation strategy. The research methodology adopts single cell tests for which activation and measurement protocols have been established to achieve representative and comparable performance curve recordings and electrochemical impedance spectroscopy (EIS) data. Additionally, to various operating conditions of the electrolyte, the cell components screening adds to a considerable effort of this study. We explore the influence on the materials and design of the bipolar plates (BP) and porous transport layers (PTL); electrode performance and durability as well as the membrane selection. Within this study we consider anion exchange membranes (AEM) and bipolar membranes (BPM) for the performance comparison. Adopting both catalyst-coated membrane (CCM) and catalyst-coated substrate (CCS) approaches enables for examination of electrode preparation techniques and their influence on performance of the electrolysis cell. The initial results are promising, especially when employing 1 M KOH in the DEF electrolyte at 70oC, reaching 0.85 A cm-1 at 2 V. The respective performance curve is presented in Figure 1., together with a diagram of the electrolyser system integration into an existing Diesel exhaust line.This research represents a practical stride towards realising the denitrification of transportation sector especially in city cycle driving when the exhaust gases temperature is too low for the state-of-the-art SCR systems. By addressing identified challenges and optimising key parameters, our study lays a robust foundation for the scalable implementation of a functional urea electrolyser for transport applications and a basic understanding of the electrochemical processes behind the performance and stability of such a system.Figure 1.Depicts a recorded polarisation curve of a single cell using an anion exchange membrane (AEM) and nickel catalyst anode fed DEF and 1 M KOH as an electrolyte at 70oC. Below, the suggested integration of the electrolyser into latest generation Diesel exhaust aftertreatment system. It includes diesel oxidation catalyst (DOC), selective Diesel particulate filter (sDPF), hydrogen supported denitrification catalyst ‘H2-deNOx’ and finally a selective catalytic reduction (SCR) step.Reference: Esser, E., Kureti, S., Heckemüller, L., Todt, A. et al., "Low-Temperature NOx Reduction by H2 in Diesel Engine Exhaust," SAE Int. J. Adv. & Curr. Prac. in Mobility 4(5):1828-1845, 2022, https://doi.org/10.4271/2022-01-0538. Figure 1