Catalyst Utilization Research Articles

Durable Ion-Pair High-Temperature Proton Exchange Membrane Fuel Cells with a Low Platinum Loading Intermetallic Catalyst

Conventional high-temperature proton exchange membrane fuel cells (HT-PEMFCs) often necessitate a relatively high platinum cathode loading, primarily due to the undesirable issue of phosphate poisoning. Previous research has suggested that employing ordered Pt-alloy catalysts could mitigate this problem [1, 2]. Our study demonstrates that an ion-pair proton exchange membrane (PEM) based on quaternary ammonium functionalized membrane can further alleviate phosphate poisoning by reducing the concentration of phosphoric acid in the electrode [3, 4].In this study, we integrate two strategies: the utilization of intermetallic catalysts and the ion-pair PEM platform, aiming to decrease the Pt loading of the catalyst without compromising performance and durability. Carbon-supported intermetallic PtCoNiCrN catalysts were synthesized via a single thermal annealing process [5, 6]. Their crystallographic structure was confirmed through X-ray diffraction, atomic-resolution transmission electron microscopy, and in-/ex-situ X-ray absorption spectroscopy.Rotating disk electrode (RDE) experiments revealed that the half-wave potential of ORR of the intermetallic PtCoNiCrN/C in 0.1 M H3PO4 with 0.1 M HClO4 was 876 mV, surpassing that of disordered PtCoNiCrN/C (829 mV) and commercial Pt/C (TEC10E20E) catalysts (769 mV). In membrane electrode assembly (MEA), the MEA utilizing the intermetallic catalyst with a platinum loading of 0.3 mg cm-2 exhibited a current density of 0.212 A cm-2 at 0.7 V and the peak power density (PPD) of 713 mW cm-2 under H2/air conditions, significantly outperforming the MEA employing the commercial Pt/C catalyst with optimized electrode composition (0.103 A cm-2 at 0.7 V and PPD of 625 mW cm-2).Remarkably, the intermetallic catalyst demonstrated stable operation for 1,000 hours at 160 °C under anhydrous conditions without notable performance degradation. This study presents a pathway to reduce the catalyst loading of HT-PEMFCs, emphasizing the crucial role of the crystallographic structure of nanoparticles in enhancing the performance of HT-PEMFCs. Acknowledgments This work was supported by the US Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office (L’Innovator program).

Impact of Metal Oxide Nanoparticles in Anode Catalyst Layer on Membrane Degradation and Output Performance of PEFC

The chemical degradation of polymer electrolyte membranes (PEMs) is one of the most serious issues that need to be addressed to achieve a long lifetime for the polymer electrolyte fuel cells (PEFCs). The PEMs such as Nafion (perfulorinated sulfonic acid polymers) are attacked by ·OH radicals generated from the decomposition of H2O2molecules, which are predominantly produced at the Pt/C anode catalyst layer (ACL).1 The addition of metal oxide nanoparticles (NPs) such as CeO2 and MnO2 to PEM or anode side has been introduced as one of the effective solutions to demolish the chemical degradation of PEM by scavenging the ·OH radical through the redox properties of these metal ions.1‒3 Although the lifetime of the PEMs have effectively prolonged, the proton conductivity of both the PEM and the ionomer binder in the cathode catalyst layer (CCL) has dramatically decreased, resulting in an appreciable loss of the output performance,4, 5 i.e., trade-off relationship between the durability and the output performance. To suppress the membrane degradation accompanied with increased output performance, we have proposed a unique concept of addition of metal oxide NPs without releasing the metal ions into ACL. The silica NPs were the first that exhibited such excellent properties.6 In the present research, we offer a new candidate of metal(IV) oxide (MO2) NPs which played a great role in increasing the lifetime of Nafion-PEM much longer than in the case of using silica NPs. The catalyst-coated membranes (CCMs) of the current study have been prepared as reported in our previous work.6 The fabricated CCMs comprised Nafion 211 (NRE-211; 25 µm in thickness) as the PEM, heat-treated Pt/graphitized carbon black (Pt/GCB-HT, TEC10EA50E-HT, 50.2 wt%-Pt) as the cathode catalyst, and Pt supported on carbon black (Pt/C, TEC10E50E, 46.4 wt%-Pt) as the anode catalyst, in which MO2-NPs were incorporated with a changeable volume ratio to the carbon content (VMO 2/VC, ranging from 0 to 0.4). Each CCM was mounted in a single cell (geometric electrode area 29.2 cm2). The chemical stability of the PEM was examined via an accelerated stress test (AST) in which the single cell was maintained at open circuit voltage (OCV) in a 40% humidified H2/air at Tcell = 90 °C and a backpressure of 160 kPa-G.6 As a measure of the durability of the PEM, the lifetime is defined as the time at which the OCV reached 0.85 V (ca. 10% loss).Figure 1 shows the changes of the OCV and the total amount of fluoride (F−) ions emitted during the AST. The OCV of the cell without any metal oxide in the ACL (denoted as Pt/C only in Fig. 1) has rapidly dropped, reaching values below 0.85 V with a very high F− emission rate (FER, slope of the line in Fig. 1b) after ca. 150 h of durability testing. With the addition of silica at VSiO2/VC = 0.2 in the ACL, the lifetime has appreciably increased (ca. 570 h) with a low FER. It is striking for the MO2-based ACL with VMO2/VC =0.2 that the lifetime has been remarkably prolonged, reaching ca. 1650 h (ca. 11 times increase of the Nafion lifetime) together with the lowest FER.Also, it has been found that the use of silica NPs has provided a reduced ohmic resistance (increase in water content of PEM and ionomers) and an effective utilization of Pt cathode catalyst in a single cell, which contributed to increase the output I-V performance.6 A similar effect was observed for the incorporation of MO2 NPs into the ACL. Such an improvement of the output performance accompanied with the remarkable increase in the durability of PEM is quite distinct from the trade-off effect of conventional radical scavengers. The mechanism for suppression of membrane degradation, as well as the changes in the microstructure of CCM, are under progress in our laboratory.This work was supported by funds for the “R&D of novel anode catalyst project” from the New Energy and Industrial Technology Development Organization (NEDO) of Japan. References Endoh, ECS Trans., 16(2), 1229 (2008).Zhao, B.L. Yi, H.M. Zhang, and H.M. Yu, J. Membr. Sci., 346, 143 (2010).Wang, C. Cai, J. Tan, and M. Pan, Int. J. Hydrogen Energy, 46, 34867 (2021).Lin, C. Cao, H. Zhang, H. Huang, and J. Ma, Int. J. Hydrogen Energy, 37, 4648 (2012).H. Wong and E. Kjeang, J. Electrochem. Soc., 166, F128 (2019).Mohamed R. Berber, M. Imran, H. Nishino, and H. Uchida, ACS Appl. Mater. Interfaces, 15, 13219 (2023). Figure 1

A Low-Cost Bipolar Plate Comprising a Channeled Porous Transport Layer for Proton and Anion Exchange Membrane Electrolyzers

Hydrogen is gaining acceptance as a viable energy vector for renewable energy and as a green molecule for chemical synthesis, but its production in a sustainable, efficient, and affordable manner requires further optimization. Proton exchange membrane electrolyzers (PEMELs) can be efficient for hydrogen production. Within the PEMEL stack, the repeating unit cell consists of a bipolar plate, two porous transport layers (PTLs), two catalyst layers, and one proton exchange membrane (PEM). The oxygen evolution reaction at the anode creates a corrosive environment, therefore, titanium is used as the anode bipolar plate material. The anode bipolar plate is typically machined from a block of titanium for small volume production or stamped for large volume production, which is time-consuming and challenging due to frequent tool breakage resulting in high cost. Furthermore, ineffective in-plane water transport within the anode PTL can cause inadequate water supply to the catalyst layer resulting in unutilized catalyst. To alleviate these problems, we have designed a novel PEMEL cell containing channeled titanium foam enclosed within a PTFE frame that functions both as the bipolar plate and the PTL, termed channeled porous transport layer (CPTL). In our design, the channels face the current collector such that the water flows through the channels and the pores of the foam in both the through-plane and in-plane directions, thereby maximizing catalyst coverage and utilization. Similarly, the pores and channels of the CPTL provide an effective pathway for the evacuation of oxygen gas evolved at the anode catalyst layer. Most importantly, the channels in the titanium foam can be formed as part of the PTL production process which could greatly reduce PEMWE manufacturing costs and lower the cost of hydrogen. The same CPTL design can also be employed in anion exchange membrane electrolyzers (AEMELs) whose anode environment permits the use of nickel foam which further reduces material costs. We will present experimental results for PEMELs and AEMELs performance with this new design and compare them with those obtained with conventional bipolar plates.

Investigation on the Interaction of Catalyst and Ionomer in AEM Electrolysis

In low temperature electrolysis, anion exchange membrane (AEM) systems combine the advantages of alkaline and proton exchange membrane (PEM) electrolysis in generating high purity hydrogen and reducing material costs from catalysts and component coatings [1]. Recent studies in AEM electrolysis have focused on improving cell performance, minimizing catalyst dissolution and mitigating ionomer/membrane degradation with different operating conditions. Ionomers play a critical role in the electrode because they provide ion conductivity, enhance mechanical support, and create preferred morphologies for electrolyte and produced gas to move [2, 3]. Optimizing catalyst-ionomer interactions by varying ionomer content, chemistries, and forms can accelerate the development of AEM electrolysis in terms of performance enhancement, cost and lifetime.In this work, different forms of ionomer (powdered and dispersed) with two polymer backbones were evaluated in AEM electrolysis cell testing. Ni- and Co-based oxides and IrO2 were applied as anode catalysts. In Figure 1, the anodes with powdered ionomer outperform the dispersed samples. With Co3O4 catalyst, the overpotential can be improved by 0.9 V at 1 A/cm2 (iR-free voltage of Co3O4 with powdered ionomer: 1.68 V at 1 A/cm2). By electrochemical diagnostic and modeling methods, the improved performance with powdered ionomer is attributed to better reaction kinetic from more active area between catalysts and ionomers, less ohmic overpotentials due to better contact between the electrode and the transport layer and preferred transport properties with higher porosity created by powdered ionomer. Scanning electron microscopy data verifies that the anodes with powdered ionomer provide more homogeneous distribution of catalysts and ionomer in the electrode, while dispersed samples have the issues of agglomerates and uneven coverage of catalysts, which could worsen the catalyst utilization and trigger mass transport issues.[1] Ayers, Katherine, et al. "Perspectives on low-temperature electrolysis and potential for renewable hydrogen at scale." Annual review of chemical and biomolecular engineering 10 (2019): 219-239.[2] Lee, Sol A., et al. "Anion exchange membrane water electrolysis for sustainable large‐scale hydrogen production." Carbon Neutralization 1.1 (2022): 26-48.[3] Favero, Silvia, Ifan EL Stephens, and Maria‐Magdalena Titirci. "Anion Exchange Ionomers: Design Considerations and Recent Advances‐An Electrochemical Perspective." Advanced Materials 36.8 (2024): 2308238. Figure 1

Optimizing Electrochemical Interfaces and Device Architectures for Electrochemical Cox Reduction

Along with mitigation, the effective utilization of waste CO and CO2 from point sources in combination with renewable electrons has the potential to address climate challenges and change the manufacturing paradigm. Numerous funding offices and governments have set device level goals and reduction targets for CO2 emissions putting momentum behind and a focus on electrochemical CO/CO2 reduction. To enable this vision, the identification of limiting phenomena,[1] scalable integration and fabrication methods, and corresponding critical breakthroughs to improve stability (constant operation) and/or durability (dynamic operation), combined with selective and energy efficient operation are necessary.The implementation of gas diffusion electrodes over the last several years has enabled higher current densities and lower cell voltages for electrochemical CO/CO2 reduction.[2,3] Here, we pull from our experience in the fuel cell space,[4] aiming to serve as a node for the development of cell and electrode architectures that would help the community integrate novel materials (electrocatalysts, membranes, and ionomers) and test devices at scales commensurate with the standards in the fuel cell and electrolysis community (>25 cm2). To this end, we will present limiting phenomena for CO2 to formate, CO2 to CO, and CO to various products, focusing on the effects of cathode composition, ionomer binder chemistry[5] and content, electrode fabrication processes[6], device configuration[7], and reactant concentrations.[1] P. Saha, D. Henckel, F. Intia, L. Hu, T.V. Cleve, K.C. Neyerlin, Anolyte Enhances Catalyst Utilization and Ion Transport Inside a CO2 Electrolyzer Cathode, J. Electrochem. Soc. 170 (2023) 014505. https://doi.org/10.1149/1945-7111/acb01d.[2] Y. Chen, A. Vise, W.E. Klein, F.C. Cetinbas, D.J. Myers, W.A. Smith, T.G. Deutsch, K.C. Neyerlin, A Robust, Scalable Platform for the Electrochemical Conversion of CO 2 to Formate: Identifying Pathways to Higher Energy Efficiencies, ACS Energy Letters 5 (2020) 1825–1833. https://doi.org/10.1021/acsenergylett.0c00860.[3] D. Higgins, C. Hahn, C. Xiang, T.F. Jaramillo, A.Z. Weber, Gas-Diffusion Electrodes for Carbon Dioxide Reduction: A New Paradigm, ACS Energy Letters 4 (2019) 317–324. https://doi.org/10.1021/acsenergylett.8b02035.[4] T. Van Cleve, G. Wang, M. Mooney, C.F. Cetinbas, N. Kariuki, J. Park, A. Farghaly, D. Myers, K.C. Neyerlin, Tailoring electrode microstructure via ink content to enable improved rated power performance for platinum cobalt/high surface area carbon based polymer electrolyte fuel cells, Journal of Power Sources 482 (2021) 228889. https://doi.org/10.1016/j.jpowsour.2020.228889.[5] Y. Chen, J.A. Wrubel, A.E. Vise, F. Intia, S. Harshberger, E. Klein, W.A. Smith, Z. Ma, T.G. Deutsch, K.C. Neyerlin, The effect of catholyte and catalyst layer binders on CO2 electroreduction selectivity, Chem Catalysis 2 (2022) 400–421.[6] D. Henckel, P. Saha, F. Intia, A.K. Taylor, C. Baez-Cotto, L. Hu, M. Schellekens, H. Simonson, E.M. Miller, S. Verma, S. Mauger, W.A. Smith, K.C. Neyerlin, Elucidation of Critical Catalyst Layer Phenomena toward High Production Rates for the Electrochemical Conversion of CO to Ethylene, ACS Appl. Mater. Interfaces 16 (2024) 3243–3252. https://doi.org/10.1021/acsami.3c11743.[7] L. Hu, J.A. Wrubel, C.M. Baez-Cotto, F. Intia, J.H. Park, A.J. Kropf, N. Kariuki, Z. Huang, A. Farghaly, L. Amichi, P. Saha, L. Tao, D.A. Cullen, D.J. Myers, M.S. Ferrandon, K.C. Neyerlin, A scalable membrane electrode assembly architecture for efficient electrochemical conversion of CO2 to formic acid, Nat Commun 14 (2023) 7605. https://doi.org/10.1038/s41467-023-43409-6.

Design and Manufacturing of Cost-Effective Water Electrolyzers at Industrial Current Densities Via an Ink-Free Integrated Dual Electrode Assembly

The clean and sustainable “green hydrogen” is highly attractive as an alternative energy.[1] However, the excessive cost of “green hydrogen” hinders its large-scale application, which is limited by the costly membrane electrode assembly (MEA) in proton exchange membrane electrolyzer cells (PEMECs).[2, 3] Conventional MEA fabrication involves numerous complex ink processes, resulting in a relatively high manufacturing costs. In addition, the ink-formed catalyst layers usually have poor electron conductivity and relatively large thickness, which causes significant catalyst underutilization.[3, 4] To simplify the manufacturing and increase the catalyst utilization, we revolutionize the conventional MEA via a facile ink-free and cost-effective integrated dual electrode assembly (IDEA) for reducing the costs and enhancing the performance of PEMECs. IDEA not only greatly simplifies fabrication processes of MEAs from over ten steps to three steps but also significantly increases hydrogen production rate simultaneously (45.26% more hydrogen at 1.8 V). Benefiting from the nano-thick catalyst layers, the IDEA can achieve an industrial “overload” current density of 6 A/cm2 at a low cell voltage of 1.82 V with an 83.9% noble catalyst saving, which outperforms most reported PEMECs. Particularly, the degradation rate of IDEA is only 24 μV/h at 1.8 A/cm2. References Pivovar, B., N. Rustagi, and S. Satyapal, Hydrogen at scale (H2@ Scale): key to a clean, economic, and sustainable energy system. The Electrochemical Society Interface, 2018. 27(1): p. 47.Ding, L., et al., Electrochemically grown ultrathin platinum nanosheet electrodes with ultralow loadings for energy-saving and industrial-level hydrogen evolution. Nano-Micro Letters, 2023. 15(1): p. 144.Mo, J., et al., Discovery of true electrochemical reactions for ultrahigh catalyst mass activity in water splitting. Science advances, 2016. 2(11): p. e1600690.Yang, G., et al., Role of electron pathway in dimensionally increasing water splitting reaction sites in liquid electrolytes. Electrochimica Acta, 2020. 362: p. 137113. Figure 1

Atmospherically Plasma-Sprayed Macro Porous Layers for Anion Exchange Membrane Water Electrolysis Operating with Alkaline Supporting Electrolyte

Green hydrogen produced via water electrolysis plays an important role in the decarbonisation of the global energy economy. Besides reducing electricity prices and increasing electrolyser efficiency, lowering electrolyser investment cost is an important avenue to make electrolysis technology more economically attractive. 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, an optimised porous transport layer (PTL) component for AEMWE is yet to be developed.Typically, PTLs in commercial electrolysers are metallic foams, felts, meshes, sintered sheets or graphitic fibre laminates, although these structures either perform poorly or they are extremely expensive. Furthermore, a high number of low-resistance contact points at the interface between the catalyst layer and the PTL is required to enable high catalyst utilisation. At the same time, operation at high current densities requires an especially efficient liquid/gas exchange at this interface. Both important functions, good electrical contact and mass transport facilitation, are fulfilled by a macro porous layer (MPL). Stiber et al designed and characterized a titanium/niobium MPL deposited via vacuum plasma spraying (VPS) on a stainless-steel mesh substrate, vastly improving the performance of a PEMWE [1]. Similarly, Razmjooei et al deposited a nickel layer via atmospheric plasma spraying (APS) and demonstrated the performance-increasing effect in AEMWE operating with pure water [2].In this work, within the frame of the German project AEM-Direkt, a Ni-based MPL was developed to improve high current density operation in AEMWE working with a supporting alkaline electrolyte. For this, a Ni-C composite powder was deposited on a stainless-steel multi-mesh PTL via APS (Fig. a). The carbon acts as a pore forming agent and is subsequently removed by an ex-situ oxidation step in air at 700°C followed by a reduction step in ammonia at 500°C. A highly porous, smooth and flat Ni-MPL is formed. Using the MPL on the anode, the AEMWE single cell achieves 2 V at 3 A cm-2 (Fig. b), which is comparable to the performance of PEMWE. As anode catalyst layer a novel 20 nm thickness sputtered nickel layer designed and manufactured by Siemens-Energy was used, deposited on a DURAION® AEM, manufactured by Evonik Operations GmbH. As cathode, a Pt/C based catalyst coated substrate (CCS) was employed.In continuation of this study, the designed MPL will be further optimised and characterised as cathode MPL as well. Acknowledgement This work is carried out within the project AEM-Direkt (Förderkennzeichen 03HY130) funded by the German Ministry of Science and Education (BMBF). References Stiber S, Sata N, Morawietz T, Ansar SA, Jahnke T, Lee JK, et al. A high-performance, durable and low-cost proton exchange membrane electrolyser with stainless steel components. Energy & Environmental Science. 2022;15(1):109-22.Razmjooei F, Morawietz T, Taghizadeh E, Hadjixenophontos E, Mues L, Gerle M, et al. Increasing the performance of an anion-exchange membrane electrolyzer operating in pure water with a nickel-based microporous layer. Joule. 2021;5(7):1776-99. Figure 1

Structured Carbon Nanofibrous Electrode for Mass Transport Enhanced MEA for PEMFCs

Polymer electrolyte membrane fuel cell (PEMFC) technology is advancing towards commercialization, with efforts focusing on the mass production of various materials to reduce development costs. Despite these efforts, the use of platinum-based catalysts—a key component in fuel cells—presents a challenge for cost reduction. As a result, the proportion of catalyst costs in the final price of fuel cells has been increasing, currently accounting for approximately 40%. Enhancing the activity and durability of the electrode layer, along with efficient catalyst utilization, could significantly lower these costs and facilitate broader market adoption of fuel cell technology.Traditional fuel cell electrodes are fabricated by applying a mixture of platinum, carbon, and ionomers onto a polymer electrolyte membrane. The performance of these electrodes, however, is heavily influenced by the interactions among the components, making the technology less universally applicable due to its sensitivity to even minor changes in componentry.This research introduces a novel approach by employing carbon nanofibers, created through electrospinning and subsequent graphitization, as a structural basis for the electrode layer. This carbon nanofiber layer offers structural and chemical stability, enabling a secure physical and chemical anchorage for the catalyst and ionomer. It also features well-connected macro-pores, which enhance internal reactant supply and improve gas transport within the fuel cell. Utilizing this method, an electrode layer demonstrating superior performance—approximately 800 mW/cm2 at 0.1 mgPt/cm2 and 0.65 V, with a peak performance of 1080 mW/cm2—was developed. Moreover, this electrode exhibited minimal performance degradation over 20,000 cycles under a carbon corrosion protocol, indicating significant advancements in fuel cell durability and efficiency.

Multilayer Porous Transport Layers for Polymer Electrolyte Water Electrolysis to Replace Thin Protective Pt Coating at Low IrO2 Loading

The use of expensive PGM catalysts for the OER and HER leads to high production costs of Polymer electrolyte water electrolysis (PEWE). Moving towards lower iridium oxide (IrOx) catalyst loadings for the anode side can severely affect performance and stability [1]. Recent studies revealed that the structure of the interface between the anodic porous transport layer (PTL) and the catalyst layer (CL) is a crucial factor limiting cell efficiency and contributes significantly to the performance and use of the CL. The coarse structure PTL can develop inactive zones of the catalyst layer, which happens when the catalyst layer is not “close” to the connecting titanium structure [2]. The situation becomes worse when the IrO2 catalyst loading is reduced, and the catalyst layers become thinner. Recent evidence has shown that having additional Microporous layers (MPL) can overcome some of these issues by maximizing catalyst utilization and increasing cell efficiency. However, at low Ir loadings, a thin protective Pt coating on MPL is needed to avoid formation of TiOx passivation layer on the MPL surface and increase surface conductivity [3].In this work, we attempt to replace the thin protective Pt coating by adding an additional layer of Ti or TiN on the existing MPL aiming when using low loadings of IrO2 (0.5 – 0.1 mgIr cm-2). Vacuum plasma spraying (VPS) technology was used to apply TiN on the surface of MPL, while Ti was spray-coated, and vacuum sintered to create a hierarchically structured 3-layer PTL. Electrochemical performances of both Ti and TiN coated MPLs were evaluated by polarization curves and Electrochemical Impedance Spectroscopy measurements. The results are compared with a Pt coated MPL reference.

Durable Anode Electrodes with Facile and Scalable Electrodeposition for Green Hydrogen Production at Industrial Scale

Highly efficient electrodes with facile fabrication, excellent performance, low cost, and high durability are of paramount significance for the development of gigawatt-scale proton exchange membrane electrolyzer cells (PEMECs).1-5 In this study, amorphous Ir0.8Ru0.2Ox (80% Ir, 20% Ru) catalysts with high intrinsic activity are first deposited on Ti sintered powder via a room temperature electrodeposition process, serving as high-performance anode electrodes in PEMECs. Different Ir loadings of 0.16, 0.24, 0.4, and 0.72 mg/cm2 were deposited and evaluated in PEMECs. As a result, low average cell voltages of 1.623 and 1.875 V are achieved at 2 and 6 A/cm2, respectively, achieving high cell efficiency of 91%-94% at 2 A/cm2, superior to the commercial CCM.1, 3, 6 Moreover, with an Ir loading of 0.4 mg/cm2, the Ir0.8Ru0.2Ox electrode shows a low-performance loss after a 900-h operation at an ultrahigh current density of 5 A/cm2, resulting in a low degradation rate of only about 39 uV/h in the last 200 h. The remarkable performance and durability of the Ir0.8Ru0.2Ox electrode are mainly due to the high intrinsic activity of Ir0.8Ru0.2Ox catalysts exposing abundant active sites, sufficient Ir3+ content, a well-controlled Ir and Ru ratio, efficient phase transformation, and excellent catalyst support. References Mo, Jingke, Zhenye Kang, Scott T. Retterer, David A. Cullen, Todd J. Toops, Johney B. Green Jr, Matthew M. Mench, and Feng-Yuan Zhang. "Discovery of True Electrochemical Reactions for Ultrahigh Catalyst Mass Activity in Water Splitting." Science Advances 2, no. 11 (2016): e1600690.Ding, Lei, Weitian Wang, Zhiqiang Xie, Douglas S. Aaron, Adam Paxson, Monjid Hamdan, Matthew M. Mench, and Feng-Yuan Zhang. "Efficient Integrated Electrode Enables High-Current Operation and Excellent Stability for Green Hydrogen Production." ACS Sustainable Chemistry & Engineering 11, no. 30 (2023): 11219-11228.Ding, Lei, Zhiqiang Xie, Shule Yu, Weitian Wang, Alexander Y. Terekhov, Brian K. Canfield, Christopher B. Capuano, Alex Keane, Kathy Ayers, David A. Cullen, Feng-Yuan Zhang. "Electrochemically Grown Ultrathin Platinum Nanosheet Electrodes with Ultralow Loadings for Energy-Saving and Industrial-Level Hydrogen Evolution" Nano-Micro Letters 15, 144 (2023).Ding, Lei, Weitian Wang, Zhiqiang Xie, Kui Li, Shule Yu, Christopher B. Capuano, Alex Keane, Kathy Ayers, and Feng-Yuan Zhang. "Highly Porous Iridium Thin Electrodes with Low Loading and Improved Reaction Kinetics for Hydrogen Generation in PEM Electrolyzer Cells." ACS Applied Materials & Interfaces (2023): 24284.Xie, Zhiqiang, Shule Yu, Xiaohan Ma, Kui Li, Lei Ding, Weitian Wang, David A. Cullen et al. "MoS2 Nanosheet Integrated Electrodes with Engineered 1T-2H Phases and Defects for Efficient Hydrogen Production in Practical PEM Electrolysis." Applied Catalysis B: Environmental 313 (2022): 121458.Xie, Zhiqiang, Lei Ding, Shule Yu, Weitian Wang, Christopher B. Capuano, Alex Keane, Kathy Ayers, David A. Cullen, Harry M. Meyer III, and Feng-Yuan Zhang. "Ionomer-free nanoporous iridium nanosheet electrodes with boosted performance and catalyst utilization for high-efficiency water electrolyzers." Applied Catalysis B: Environmental 341 (2024): 123298. Figure 1

Improving Performance of PEM Water Electrolysis Utilizing Nanofiber-Enhanced Porous Transport Electrodes with Low Iridium Content

As the world strives to reduce its reliance on fossil fuels and transition towards cleaner energy sources, Membrane Water Electrolysis (PEMWE) emerges as a promising solution for generating clean hydrogen with its ability to utilize renewable energy sources such as solar and wind power. It is essential to select the appropriate materials for PEMWE for enhancing its efficiency, lifetime, and cost-effectiveness. A common PEMWE cell consists of a Membrane Electrode Assembly (MEA), which includes a proton exchange membrane coated with platinum (Pt) as the catalyst for Hydrogen Evolution Reaction (HER) and iridium (Ir) as the catalyst for Oxygen Evolution Reaction (OER), along with a carbon-based material and a Porous Transport Layer (PTL) as gas diffusion layers on the cathode and anode sides, respectively. A primary challenge within this cell structure lies in minimizing the usage of the rare and precious metal, Ir. As outlined by the U.S. Department of Energy (DOE), the target Ir content in electrodes should be reduced to less than 0.5 mg/cm2 by 2026 [1].Smoltek Hydrogen is committed to reducing Ir catalyst loading on the anode side by developing a unique Porous Transport Electrode (PTE) with its patented nanofiber structure [2]. By growing these nanofibers vertically on the PTLs, surface area is significantly enhanced. Through the electrodeposition method, Ir catalyst can form a thin layer along the nanostructure. This not only maximizes Ir catalyst utilization, achieving loading levels as low as 0.1 mg/cm2 but also reduces contact resistance between the catalyst layer and PTL substrates.The performance of PEMWE depends significantly on the materials utilized in each layer and the quality of their interfaces. A key strategy to enhance cell conductivity and minimize energy loss is to reduce cell thickness while improving interfacial contact [3].In our investigation, we explored various parameters to boost the performance of PEMWE utilizing our specialized PTE. The results demonstrate that incorporating Nafion ionomer between the OER catalyst layer and the membrane, along with assembling the PTE with the membrane using the hot-pressing method, greatly improves interfacial contact and enhances the initial performance of PEMWE. Additionally, reducing the thickness of the PTL and membrane can further optimize cell conductivity. Moreover, factors such as cell pressure, parameters of the cell pre-conditioning step, as well as testing conditions such as temperature and water flow rates in the electrolyzer test systems, significantly influence performance. This study is focused on identifying the optimal cell conditions for Smoltek Hydrogen's PTEs. References https://www.energy.gov/eere/fuelcells/technical-targets-proton-exchange-membrane-electrolysishttps://www.smoltek.com/hydrogen/Katherine Ayers. Current Opinion in Chemical Engineering, 2021, 33, 100719.https://publications.jrc.ec.europa.eu/repository/handle/JRC10404 Figure 1. (a) SEM cross-section image of Smoltek PEMWE single cell. (b) SEM cross-section observation zooming in the Ir-coated nanofibers. (c) SEM image of nanofibers with Ir catalyst. (d) Polarization Curves observed at 80˚C, following the JRC Protocol [4], comparing the performance between PTEs with and without ionomers Figure 1

The Role of Porous Transport Layer in Enabling Low Anode Catalyst Loadings

Hydrogen (H2) is a focal point of the U.S. Department of Energy’s (DOE) plan for a future energy economy that is secure, resilient, and environmentally friendly [1]. And proton exchange membrane water electrolysis (PEMWE) is a promising technology for renewable H2 production. Yet, state-of-the-art PEMWEs use significant amounts of expensive platinum group metals (PGMs), namely, Pt and Ir, which leads to large capital expenses (CapEx). Techno-economic analysis has shown that CapEx is just as, if not more, important as operating expenses (OpEx) for enabling $1/kgH2.In recent years, the price of Ir has significantly increased, even compared to Pt. Reducing the Ir loading in a PEMWE cell or stack is a straightforward way to reduce CapEx. However, anode catalyst layers (ACLs) with reduced Ir loadings tend to suffer from poor electrical in-plane conductivity and low utilization, leading to significantly higher overpotentials. Supported catalyst materials, i.e., Ir decorated onto a conductive substrate material, could help address these drawbacks, but the catalyst support material must also be stable at the elevated potentials seen by the anode. To date there is no suitable support material that offers both stability and good performance. Therefore, strategies to improve performance using unsupported Ir are of great value.In this work, we studied 6 different commercial porous transport layer (PTL) materials to observe their effect on cell performance as the anode Ir content was reduced. The PTL is responsible for conducting electrons from the ACL. The morphology of the PTL and the structure of the ~2D interface it creates with the ACL can strongly affect overpotentials associated with in-plane electronic resistance and impact catalyst utilization. All PTLs studied were made from pure Ti. They included both fibrous and sintered particle archetypes. Beginning of life and 1000 h durability results from studies with both 0.1 mgIr/cm2 and 0.4 mgIr/cm2 loadings will be discussed in the presentation. For example, as seen in Figure 1, we found that the PTL greatly influences cell performance at ACL loadings of 0.1 mgIr/cm2, though the effect was less pronounced at 0.4 mgIr/cm2. Changes in both ohmic and kinetic overpotentials were observed.

Advanced Nano-Porous Thin Films: Automating Water Electrolysis with Spark Ablation Printing

The current commercial loading of Platinum grade materials (PGMs) per membrane electrode assembly (MEA) stands at 2 mg/cm2, necessitating significant efforts to redesign electrocatalyst materials through a nano-architecture approach, requiring a thousandfold increase in surface area (from µm to nm scale) and a tenfold reduction in mass loading (from mg to µg). This objective can be realized through innovative surface engineering and manufacturing techniques as traditional wet synthesis methods pose several steps leading to spot errors (during ink formulation and coating) and high manufacturing costs (during drying steps) hampering scale-up efforts especially for low PGM loading < 0.5 mg/cm2 in PEM-WE.VSPARTICLE developed a nano-printing technology utilizing spark ablation. This dry-synthesis method generates nanoparticle films only by using metal rods and electricity, and immobilize nano-porous electrocatalyst thin films on any substrate. In this presentation, we will unveil the latest findings concerning oxygen evolution reaction (OER) electrodes employing Ir-based and Ni-based catalysts produced through the innovative VSP-P1 nano-printing technology. The MEAs prepared using spark ablation had significantly lower loading (e.g., 0.1 and 0.4 mg/cm2) than the commercial state-of-the-art without compromising performance. The study integrates comprehensive flow-cell experiments, meticulous control tests, and characterization techniques on proxy samples, leveraging the versatility of VSP-P1 to create identical nano-porous films on various substrates. The scalability of this dry manufacturing process, coupled with rapid iteration capability for tuning material parameters and test-beds, promises a tenfold acceleration in electrocatalyst utilization.In conclusion, this presentation unveils an efficient strategy for catalyst utilization through nano-printed layers, significantly reducing the time required to bring novel materials to market. The methodology outlined herein holds great promise for advancing hydrogen deployment and sustainable transitions in hard-to-decarbonize sectors. Figure 1. a) The automated print technology in process based on NanoPrinter (P1), b) printing of Ir process, c) cross sectional and HR-SEM image of the thin film, d) PEMWE results Ir(VSP)-NPs tested at ambient temperature and pressure Figure 1

Metal-Organic Framework-Derived PGM-Free Electrocatalysts for Hydrogen Evolution Reaction in Alkaline Media

Nickel (Ni)-based materials are among the most promising platinum group metal-free (PGM-free) electrocatalysts for hydrogen evolution reaction (HER) in alkaline media. With the growing demand for green hydrogen production, the HER activity of Ni-based catalysts must be enhanced to meet the goal of low-cost and sustainable hydrogen production.1 Carbon-supported Ni-based catalysts are typically prepared through the heat-treatment of Ni-based precursors with carbon supports.2 However, the catalysts obtained by this approach suffer from high content of inactive carbon and a non-uniform distribution of Ni-based nanoparticles, leading to low HER activity. These issues amplify the need for novel Ni-based catalysts with a well-controlled catalyst structure designed for maximizing catalyst utilization and minimizing electrode thickness.In this talk, we will present our recent progress in developing Ni-based HER catalysts derived from metal-organic framework (MOF) precursors. Taking advantage of the characteristics of well-defined structure, high porosity, and flexible chemistry of MOF precursors3, the MOF-derived catalysts exhibit very promising activity towards HER allowing to reach 10 mA/cm2 at an overpotential of less than 100 mV in alkaline media. We will discuss how the ligand in MOF precursors and heat treatment conditions influence the structure and HER performance of Ni-based catalysts. This understanding promises to provide much needed guidance for the advancement of Ni-based catalysts for HER in alkaline media. Acknowledgement This work has been partially supported by the Center for Alkaline Based Energy Solutions (CABES) funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award DE-SC0019445.

燃料電池の膨張触媒層の3次元構造のクライオSTEMトモグラフィー

In order to improve the power generation properties of fuel cells, it is important to understand and control the fine pore structure of the fuel cell catalyst layer, which affects the flow of gas and water. It is inferred that the ionomer having a hydrophilic group is in a swollen state when a fuel cell is operating because of the high temperature and high humidity state of the catalyst layer. Therefore, in order to understand the flow of gas and water, information is required not only on the pore structure due to Pt/C aggregates but also on the distribution state of the swollen ionomer. A three-dimensional observation method is needed to obtain the three-dimensional structural information necessary for detailed analysis of the correlation between performance evaluation results, such as electrical characteristics, and electrode structures. Detailed investigation of the fine pore structure of a fuel cell catalyst layer requires electron microscopy techniques such as transmission electron microscopy (TEM) and scanning electron microscopy (SEM) due to the scale involved. However, since a typical electron microscope is a vacuum device, materials containing moisture are observed in a dry state. Furthermore, data are obtained as images, which are basically two-dimensional. Cryo-electron microscopy is a method that allows samples containing water and particles in liquid to be observed while being kept in a wet state without drying them, as the sample is quickly frozen and observed in that condition with an electron microscope. Cryo-electron microscopy has been established mainly in biological fields, and there are many issues to be solved in adapting it to investigations of materials. For example, in biological fields, objects to be observed are basically composed of light elements, while heavy elements are included in the materials field. In addition, the solvents are not only water but also mixed ones of organic solvents, and the freezing conditions and tendency of electron beam irradiation damage during observation are also different, requiring a different approach from that used in biological fields. Electron tomography is a three-dimensional observation method using TEM, in which information on the three-dimensional structure of a sample can be obtained by continuously tilting it and performing Radon-inverse Radon conversion from the obtained transmission image. Since many images are acquired during continuous tilt imaging, it is important to control the electron beam dose to the sample for samples that are susceptible to electron beam irradiation damage. To address these issues, a low-dose scanning transmission electron microscopy (STEM) mode creates a parallel electron beam without converging the beam, which suppresses electron beam irradiation damage and emphasizes scattering contrast, though it has the disadvantage of reducing resolution. It is thus expected that this method will also be effective in distinguishing between ionomers and carbon. Since the catalyst layer contains heavy elements such as precious metals, STEM observation is considered to be even more optimal as it has higher transparency than TEM. In this research, we used cryo-STEM tomography to analyse differences in the pore structure in the swollen ionomer of catalyst layers of samples with different electrical properties, and investigated the correlation between the pore structure and those properties. Three types of catalyst layers samples were fabricated using commercial catalyst powder (TEC10V30E, TKK) and Nafion as the ionomer with different ionomer-to-carbon ratios (I/C:0.1, 0.5, 1.0) for the analyses. Cell performance was investigated on MEAs with the catalyst layers for the cathodes, respectively. The performance at 80°C and 80% was lower for the samples with lower I/C. The performance of the I/C=0.1 sample was especially low, which was primarily attributed to the low catalyst utilization and high proton resistance. In order to understand these phenomena, we investigated in detail the three-dimensional distribution of the ionomer in the porous structure composed of Pt/C aggregates and compared the results found for the samples. This work is partly supported by NEDO FC-Platform project.

From Structure to Performance: Insights into the Role of Porous Transport Layers in PEM Water Electrolysis via Electrode Engineering

Proton Exchange Membrane Water Electrolyzers (PEMWEs) are a promising technology to combat the deleterious effects of climate change [1]. It uses intermittent electricity from sustainable energy sources to electrochemically generate green hydrogen – a carbon-free energy carrier. Most importantly, the integration of water electrolyzers with fuel cells into a single reversible system is an enabler to achieving hydrogen-based long-duration energy storage. To make PEMWE systems more cost-competitive and technologically viable, it is essential to control the ohmic and mass transport limitations, a significant contribution of which stems from the fibrous porous transport layers (PTLs). In this work, we present a multiscale framework to investigate the effect of PTL electrode parameters on the electrochemical response of the PEMWE. Our starting point is stochastically generated PTL configurations with a host of microstructural features such as fiber diameter, porosity, fiber orientation, etc. The salient morphology-dependent transport properties like tortuosities, effective electronic conductivities, and two-phase permeabilities are then evaluated by employing pore-network modeling [2]. These are subsequently deployed to a physics-based multiphase reactive transport model [3] of the electrolyzer to quantify the concomitant overpotential modes. The interplay of operating regimes and PTL structural parameters on the resistive signature is further delineated. An optimization of the PTL architecture along with its pore size distribution investigated in this study can guide the design of experiments towards high-performing PEMWEs with enhanced catalyst utilization and mass transport.

Investigation of Ultra-Low Loading of Metallic Oxide Supported Iridium-Based Catalysts in the Proton Exchange Membrane Water Electrolyzers

Iridium (Ir)-based catalysts have been considered as the most promising oxygen evolution reaction (OER) in the proton exchange membrane water electrolyzer (PEMWE). The scarce supply of Ir potentially restricts the development of the PEMWE technology. Reducing the use of Ir catalysts has become one of the most critical tasks. The activity and durability of PEMWE depend heavily on the catalyst loading.[1] Poor in-plane electric conductivity due to catalyst layer not being continuous at ultra-low loadings (~0.1-0.2 mgIr/cm2) catalyst, results in loss of electronic connection of some portions of catalyst layer. Several studies have proposed various strategies to lower the loading of Ir catalysts,such as altering catalyst morphology,[2] introducing a microporous layer (MPL) between the catalyst layer and PTL to improve electron transport in disconnected catalyst layers,[3] or doping Ir-based catalysts with support materials. [4-5] These approaches enhance both in-plane and through-plane electric conductivity, thereby increasing catalyst utilization.In this work, heteroatoms were used as supports or dopants to enhance Ir catalyst utilization and enhance the structural and interfacial stability of the catalyst layer. The microstructure of the metallic oxide support allows IrO2 particles to disperse uniformly, thus enhancing the in-plane conductivity of the catalysts layer. Both commercial metallic oxides supported IrO2 catalysts [6] and laboratory-synthesized catalysts were employed in PEMWE. Different catalyst loadings were investigated, including the ultra-low loading (0.11-0.13 mgIr/cm2) catalysts in this study. We conducted several electrochemical characterization experiments to confirm the improvement of the durability and activity for the IrO2/TiOx and IrO2/NbOx, comparing to the unsupported IrOx catalysts with the identical low Ir loading. A 2V-hold for 100-hour of the accelerated stress testing (AST) indicates the more moderate decay in the current density for supported IrO2 catalysts. Cyclic voltammetry (CV) allows us to monitor the changes of surface oxidation state and the morphology of the Ir-based catalysts during the different operating conditions. Finally, the cell performance of various catalysts on the anode in PEMWE were also evaluated and compared. This study is expected to provide a comprehensive understanding of ultra-low Ir loading in PEMWE.

Impact of cell design and conditioning on polymer electrolyte membrane water electrolyzer operation

Integration of polymer electrolyte membrane water electrolyzers (PEMWEs) for clean hydrogen generation requires a robust understanding of the impact cell designs and conditioning protocols have on operation and stability. Here, catalyst-coated electrode and catalyst-coated membrane cells employing Pt/C cathode catalyst layer, an IrO2 anode catalyst layer, with a platinized titanium mesh or a carbon paper with a microporous layer as the porous transport layer were developed. The impact of cell conditioning above and below 0.25 A cm−2 was investigated using advanced electrochemical impedance spectroscopy analyses and microscopic imaging, with the electrochemical response related to physicochemical processes. Operation below 0.25 A cm−2 prior to operation above 0.25 A cm−2 resulted in anode corrosion and titanium cation contamination, increasing the cell voltage at 1 A cm−2 by 200 mV compared to uncontaminated cells. Conditioning above 0.25 A cm−2 led to non-negligible hydrogen transport resistances due to cathode flooding that resulted in a ca. 50 mV contribution at 1 A cm−2 and convoluted with the anode impedance response. The presence of a microporous layer increased catalyst utilization but increased the cell voltage by 300 mV at 1 A cm−2 due to increased anodic mass transport resistances. These results yield critical insights into the impact of PEMWE cell design and operation on corresponding cell performance and stability while highlighting the need for application dependent standardized operating protocols and operational windows.

Bimetallic MOF sulfurized In2S3/Fe3S4 for efficient photo-Fenton degradation of atrazine under weak sunlight: Mechanism insight and degradation pathways

Atrazine (ATZ) permeates into aquatic environments due to agricultural activities, presenting potential health risks and necessitating effective degradation strategies. In this paper, bimetallic MOF MIL-68(In/Fe) sulfurized heterostructured In2S3/Fe3S4 (M-ISFS) was synthesized successfully by a two-step solvothermal reaction. M-ISFS demonstrated ample Fe sites, facilitating the Fenton reaction. The heterostructures facilitated electron transfer in M-ISFS, resulting in a significant acceleration of the reduction of Fe3+. M-ISFS demonstrated an efficient degradation capacity ATZ (99.6 % in 60 min), under a low catalyst dosage (0.15 g·L−1) and weak sunlight intensity (26.79 mW·cm−2). It also retained 88.7 % degradation efficiency after undergoing 4 cycles. 1O2, ·OH and ·O2− were identified to be the main reactive species in the photo-Fenton reaction. The detailed degradation mechanism and pathway were investigated via mass spectrometry (MS) and density functional theory (DFT). Toxicity assessment of intermediates showed that M-ISFS-mediated photo-Fenton degradation attenuates ATZ toxicity to aquatic organisms. This study will broaden the utilization of catalysts sulfurized from MOFs for improving photo-Fenton degradation.

Novel large-scale integrated non-precious metal electrodes for efficient and stable oxygen evolution reaction at high current density in 2.5 kW anion exchange membrane water electrolysis

The utilization of non-precious catalysts to substitute precious metal catalysts on anode side under high current density conditions and with long-term resistance is crucial for the implementation of alkaline anion-exchange membrane water electrolysis (AEMWE) applications. To accommodate industrial applications, a combination of chemical solution and electrodeposition was used to construct NiFeCo layered double hydroxide and NiS nanosheet heterostructures on Ni foam (NiFeCo LDH/NiS/NF). Both experiments and theoretical calculations show that the heterogeneous structure reduces the activation energy barrier of the catalytic reaction and provides an appropriate electronic structure. This not only guarantees the exposure of the active site but also adjusts the local coordination environment and chemisorption properties. Consequently, the reduction in energy barrier affects the rate-determining step (RDS) from *O to *OOH, as well as the energy barriers of all four steps in the oxygen evolution reaction (OER). Consequently, the optimized NiFeCo LDH/NiS/NF catalyst demonstrates a low voltage of 288 mV to operate 1.0 A cm−2. Additionally, the catalyst was conducted with commercial Pt/C coated onto carbon paper (Pt/C/CP) for 2 × 2 cm2 AEMWE exhibited 1.63 V cell voltage to attain 1 A cm−2 and operated for 2100 h from 1 A cm−2 to 2.5 A cm−2 (1.69 V to 1.92 V). Further, the catalyst was prepared scalable to 15 × 15 cm2 for application into a 2.5 kW AEMWE device, which required only 1.77 V at 60 °C to catch 1 A cm−2 for 1000 h, which shows extremally promising application for stable AEMWE device.