bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Decoupled Water Splitting for Green Hydrogen Production: Reshaping Water Electrolysis
Authors: Rothschild Avner , Dotan Hen , Landman Avigail , Grader Gideon
Published: September 2023

Green hydrogen produced by splitting water molecules into hydrogen and oxygen using electricity from renewable energy sources is essential to reduce CO2 emissions, especially in hard-to-abate industrial sectors such as steelmaking and ammonia production. It is a critical component in the energy transition to fight climate change. The present technologies for green hydrogen production are alkaline and polymer electrolyte membrane water electrolysis. One thing in common to these technologies is the coupling between the hydrogen and oxygen evolution reactions (HER and OER, respectively), where both reactions occur concurrently in the same electrolytic cell. Therefore, a membrane or diaphragm divides the cell into two compartments to avoid hazardous H2/O2 mixing. This membrane architecture complicates the electrolyzers construction by adding gaskets and compression sealing to prevent H2/O2 crossover. This adds substantial costs and limits operation at high pressures and low-purity water. In addition, substantial energy losses, mostly due to the difficult OER, increase the cost of energy in this energy intensive technology. These drawbacks give rise to high cost of green hydrogen.

To overcome these challenges, we developed alternative processes that decouple the generation of hydrogen and oxygen into two consecutive stages (time separation),1 or two cells (space separation),2 avoiding the need for membrane and sealing. In addition, we divided the OER, a difficult electrochemical reaction that requires four electrons and protons to generate an oxygen molecule on a single atomic reaction site, into two sub-reactions that occur on four sites, thereby enabling facile reactions and reducing the energy losses in water electrolysis. An ultrahigh efficiency of nearly 99% was demonstrated at lab scale,2 and we expect reaching above 90% at system scale. To bring this breakthrough process to reality we established H2Pro, an Israeli startup company that aims to produce green hydrogen at $1/kg by the end of this decade, based on our invention.3

Landman et al., Photoelectrochemical water splitting in separate oxygen and hydrogen cells, Nature Materials 16, 646–651 (2017).

Dotan et al., Decoupled hydrogen and oxygen evolution by a two-step electrochemical – chemical cycle for efficient overall water splitting, Nature Energy 4, 786–795 (2019).

Rothschild et al., Methods and system for hydrogen production by water electrolysis, United States Patent No. 2020/0040467 A1 (2020).
Comparative Studies of Ir-Based PEM Electrolyzers Via Operando ‘Tender’ X-Ray AP-XPS
Authors: Hamlyn Rebecca , Crumlin Ethan J.
Published: September 2023

Ir-based catalysts are considered the state-of-the-art cathode material for the oxygen evolution reaction (OER) in water splitting devices. However, large scale hydrogen production from such devices will require reduced Ir loadings and/or new materials due to factors such as Ir scarcity, cost and loss during electrolysis operation. In the hopes of enabling progress of rational design for OER catalysts, effective characterization of the electrode-liquid interface is crucial. Synchrotron-based X-ray Photoelectron Spectroscopy (XPS) offers a versatile way to obtain surface chemical and elemental characterization of these materials. The use of X-rays in the ‘tender’ regime (~2-6 keV) allows for deeper probing than the conventional ‘soft’ x-ray (< 2000 eV) set up that is common at synchrotrons and lab-based sources. The photoelectrons generated from tender x-rays have enough energy to penetrate tens of nanometers through low density components such as a layer of liquid or polymeric electrolyte. This opens the door to access the chemistry at the interface of liquid and ionomer electrolyte-electrocatalyst materials. With the use of a fully operational two-electrode system, we are able to study these membrane electrode assemblies under active water splitting conditions.

My talk will highlight recent AP-XPS results on iridium-based polymer electrolyte membranes for water splitting. With application of elevated potential, we can correlate the iridium valency and surface species with the appearance of product traces in a mass spectrum. I will show trends within and between Ir catalyst types that lend to a better understanding of these OER cathodes.

Figure 1
(Invited) Green Hydrogen R&D in South Africa
Authors: Bessarabov Dmitri
Published: September 2023

For decades, proton-exchange membrane (PEM) water electrolysis (WE) has been used mainly for oxygen generation in anaerobic environments. Over the past two decades, however, it has been increasingly used for hydrogen generation in the industrial sector at various and increasing scale. The PEMWE technology is also considered as a key one in the frame of 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.

Among other existing water electrolysis technologies, such as alkaline, solid oxide, the technology based on proton-exchange membranes has received a great deal of interest in South Africa. One of the reasons is endowment of South Africa with its PGM resources, such as platinum (Pt) and iridium (Ir) that are used in PEM water electrolysis (WE) catalytic components. As it is known, PEMWE technology is very well suited to accommodate intermittency of energy supply associated with renewables. PEMWE technology can also deliver relatively high-pressure hydrogen gas of high purity. South Africa has also superior endowment of both onshore wind and solar. It is known thar renewable energy (RE) is one of the largest operational cost components in the production of green hydrogen. Other factors contributing to the interest in green hydrogen water electrolysis technology in South Africa that are not obvious, but important, include large tracts of sparsely populated land with little alternative use, which can be dedicated for RE production. South Africa also has a suitable geographical position with deep water ports for the potential export of large quantity of hydrogen and its derivatives such as ammonia.

Approximately 15 years ago South African Government approved national program HySA: Hydrogen South Africa that resulted in developing expertise and capacity to conduct research, development, and earlier commercial activities around green hydrogen production by means of water electrolysis. These activities include development of local IP at the components, stack and system levels. Recently, a number of “catalytic” projects have been identified in order to increase a demand in green hydrogen and stimulate investments.

Recently, an international R&D project between South Africa and Japan was launched to develop further expertise in both green hydrogen and ammonia technologies [1]. Most recently, large companies, such as SASOL, made commitments to lead green hydrogen production at a large scale for the variety of applications, aiming at decarbonisation of mining and petrochemical sectors [2]. On the Governmental level, South Africa recently has approved its national hydrogen road map [3].

This talk will provide a comprehensive update on the research, technology, and commercialisation activities in South Africa in the area of green hydrogen production.
(Invited) Advances in Composite Membranes Design and Scale up for Proton Exchange Membrane Water Electrolysis
Authors: Agapov Alexander , Kobaisy Amr , Wilbert Christin , McCloskey Ellie , Abraham Prashanth , Johnson Raya , Chen Yingying , Kiernan Paul , Gardner John , Hamamoto Taichi
Published: September 2023

Hydrogen is proposed as a future solution for a global, sustainable energy network, allowing optimization of energy efficiency while dramatically reducing emissions and decarbonizing the economies.

Lack of scaled, cost-effective environmentally friendly methods of hydrogen generation and infrastructure is a major challenge for widespread adoption of hydrogen for transportation, energy grid, integration with chemical processes, and plants.

Water electrolysis (WE) method of hydrogen generation and its integration into infrastructure is therefore rapidly gaining industrial interest all around the world.

This talk will focus on the challenges in low temperature proton exchange membrane (PEM) WE systems, particularly on design of composite PEM that can enable high efficiency, low total-cost-of-ownership WE systems that in turn enable lower levelized cost of hydrogen.

Applying the fundamental knowledge generated in fuel cell research with further tailoring of material properties to the needs of WE generated membranes with the thickness in the range of 50 micron that can withstand more than 400psi differential pressure, while possessing only half of the proton resistance of an industry benchmark non-reinforced membranes. These advancements enable high pressure, high current density operation of a WE system. We will also discuss how Gore leverages its fuel cell platform with robust supply chain developed over last 20 years for the scale-up of these novel WE PEM composites.
Development of High Durable Pore-Filling Anion Exchange Membranes for Water Electrolysis Application
Authors: Jeong Dahye , Lee Minyoung , Park Jong-Hyeok , Chae Soryong , Park Jin Soo
Published: September 2023

Water electrolyzer is a device that converts renewable electrical energy into environmentally friendly chemical energy, hydrogen. Water electrolysis is mainly categorized into proton exchange membrane water electrolysis (PEMWE) and anion exchange membrane water electrolysis (AEMWE). Non-precious electrocatalysts and hydrocarbon-based polymeric membranes are used for two different systems. It is advantageous for AEMWE in terms of cost. However, low current density and chemical stability for current anion exchange membrane technology (AEM) restricts early market penetration. Thus, thedevelopment of low resistance and high durable AEMs is of importance. In this study, superior ion conductivity and high durable pore-filling AEMs were developed for AEMWE. Pore-filling AMEs with different contents of crosslinking monomers were prepared by the monomers using chemically stable anion exchangeable functional groups in a porous polyethylene(PE) substrate. Properties of the AEMs were characterized through areal resistance, ionic conductivity, ion exchange capacity, water uptake, swelling ratio, mechanical strength and hydrogen crossover. In addition, AEMWE performance and durability tests were also conducted.

Acknowledgments

This research was supported in part by Cooperative Research Program for Agriculture Science and Technology Development (Project No. PJ016253), Rural Development Administration, Republic of Korea and by 2021 Green Convergence Professional Manpower Training Program of the Korea Environmental Industry and Technology Institute funded by the Ministry of Environment.
Earth-Abundant Electrocatalysts for the Oxygen Evolution Reaction Supported on Layered Zirconium Phosphate Nanomaterials
Authors: Colon Jorge L
Published: September 2023

Recently, we have demonstrated improved electrocatalytic activity of layered zirconium phosphate (ZrP) nanomaterials loaded with earth-abundant metal ions suitable as catalysts for the oxygen evolution reaction (OER). We compared the catalytic efficiency of ZrP nanoparticles ion-exchanged with transition metals (Fe, Ni, Co) in the interior of the layers as well as in the external surface to a system in which the metal catalysts are confined exclusively on the external ZrP surface. Linear sweep voltammetry revealed that the electrocatalytic systems with metal catalysts on the external ZrP nanomaterials’ surface had improved OER activity compared to systems with metals intercalated in the ZrP interlayers. This result prompted us to study a system of exfoliated ZrP particles which provide only external surfaces to the electrocatalytic metal ions. A comparison between adsorbed Co or Ni catalysts on ZrP nanoparticles and those same catalysts on exfoliated ZrP nanoplatelets proved that the later systems were more active, with diminished overpotentials and reduced Tafel plot slopes. Comparison between Co and Ni catalyst on ZrP particles with different morphologies (hexagonal platelets, rods, cubes, and spheres) revealed that the more active Co catalysts are those on hexagonal ZrP platelets, whereas the best Ni catalysts are those on ZrP spheres. More recently, efficient OER catalysts were obtained with cobalt porphyrin molecular electrocatalysts both intercalated in ZrP and adsorbed on exfoliated ZrP nanoplatelets. Mixed metal NiFe-intercalated ZrP electrocatalysts at 90% Fe metal content proved to have superior OER electrocatalytic performance (decreased overpotentials, increased mass activities, reduced Tafel slopes) compared to adsorbed counterparts. We are exploring OER activities of other mixed-metal catalysts on ZrP, bifunctional catalysts, and operando synchrotron X-ray absorption spectroscopy studies to elucidate the nature of the active species.
Value-Added Electrolysis Hydrogen Production Via Anodic Oxidation of Ethylene Glycol over an Efficient Pd-Based Single-Atom Catalyst
Authors: Tsai Meng-Che , Moges Endalkachew , Su Wei-Nien , Hwang Bing-Joe
Published: September 2023

A promising way of generating hydrogen is electrochemical water splitting for future sustainable green energy source technology options to replace nonrenewable and environmentally pollutant hydrocarbon energy sources. However, the anodic oxygen evolution reaction (OER) is the leading resource of high energy consumption due to its high overpotential. Notably, the generated O2 at the anode side is less needed in practical use. Based on this, why not consider looking for anodic reactions with lower energy consumption and forming value-added products during electrolysis? Ethylene glycol oxidation (EGO) as a small organic molecule is one of the candidates to match the consideration. Therefore, we developed a Pd-based single-atom catalyst prepared via the electrochemical method. The Pd-based single-atom catalyst exhibits excellent EGO activity compared to the commercial Pd/C. In addition, it possesses excellent glycolate selectivity (above 88%) in an alkaline solution with an onset oxidation potential as low as 0.6 V (vs. RHE), much lower than 1.23 V (vs. RHE) of H2O/O2 equilibrium potential. As a result, this work shows a new strategy for electrochemical hydrogen production at far lower anodic potential by designing a stable and efficient Pd-based single-atom catalyst.
(Invited) The Evolution of Membrane Electrochemical Cell Stacks and Balance of Plant Integration with Increasing Product Scale and Manufacturing Volume Ramp up
Authors: Dalton Luke T. , Roemer Andy B. , Brown Jason
Published: September 2023

As PEM and similar electrochemical devices get further scaled to meet the growing demand for renewable hydrogen solutions, the real-world design elements of electrochemical cell to balance of plant integration are key factors in the timeline for product development and manufacturing volume increases, for the system performance, and for the overall cost of hydrogen. The optimization of both cell components such as porous transport layers and bipolar plates, as well as system components such as AC-DC rectifiers for real devices need to consider and incorporate the existing volume and size constraints within the supply chain. Form factors of cells, number of cells per stack, number of stacks per plant and the corresponding layout of rectifiers, fluid pipes, and phase separators are considerations for optimization in product stack and system design. As the scale of product manufacturing and the scale of individual building blocks increases, the balance of these trades will evolve over time, requiring flexibility in design approaches to meet near term plants in the 10-MW class and medium-term plants in the 100-MW class. The discussion of these inter-relationships will explain how this evolution has proceeded to date and evaluate the impact of decisions made today on future product roll-out.
(Invited) Extended Thin Film Platinum Group Metal Electrocatalysts with Different Mesoscale Morphologies
Authors: Arges Christopher G. , Bhattacharya Deepra
Published: September 2023

The lack of sufficiently active oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalysts is a bottleneck to the proliferation of PEM fuel cells and water electrolyzers. Commercially available PGM electrocatalysts fail to attain DOE technical targets due to instabilities and activity losses incurred at low loadings. Morphology control of PGM nanostructures is an enticing route towards activity and stability enhancements of electrocatalysts, but not much is known about the structure-property relationships between PGM mesoscale geometry (5 to 100 nm) and their activity and stability.

This talk presents our work on model Pt extended surface electrocatalysts of tunable feature sizes and morphologies prepared from self-assembled block copolymer templates. The morphology, either perpendicular lamellae, cylinders, or perforated cylinders, of the extended surface electrocatalyst was controlled by the block copolymer volume fraction. The periodic lateral feature sizes (10 to 40 nm in this work) were controlled by the block copolymer degree of polymerization. The self-assembled block copolymers were transformed into extended surfaces using sequential infiltration synthesis to prepare aluminum oxide followed by reactive ion etching to remove the block copolymer template. Pt was sputtered onto the aluminum oxide supports. ORR data in a RDE with the new extended nanostructured thin films of Pt showed mass activity values of 0.35 A mgPt-1 to 0.46 A mgPt
-1 at 0.9 V vs. RHE. The measured electro-chemically active surface area (ECSA) values obtained from hydrogen underpotential deposition were 64 to 70 m2 gPt
-1. The lower values hailed from lamellae morphology while the larger values corresponded to a cylindrical morphology. The measured mass activity values, which have no cobalt or nickel additives and are unoptimized and display competitive mass activity values for ORR. We envision that the block copolymer templated extended surfaces could be an alternative to 3M’s state-of-the-art nanostructured thin film technology.
(Invited) Component Design and Electrode Optimization for AEM Electrolyzers
Authors: Ul Hassan Noor , Kohl Paul , Mustain William Earl
Published: September 2023

The massive international investment in water electrolysis has accelerated the need to reduce cost and increase durability. In recent years, Anion exchange membrane electrolyzers (AEMELs) have been touted as a possible low-cost option to supplant traditional alkaline electrolyzers and proton exchange membrane electrolyzers because they promise to combine the benefits of both – namely high current density operation, high discharge pressure, the use of noble-metal free catalysts, and the ability to use a wider range of materials for other cell components. As AEMELs are still early in their developmental stage, much of the reported work in the literature has dealt with the development of new catalysts or membranes for these devices and have worried less about engineering aspects of AEMEL design such as loading optimization, the structure and composition of the porous transport layers (PTL), the balance of IEC between the cathode, membrane and anode, etc. This presentation intends to take the audience through a systematic optimization of the anode and cathode electrodes for AEMELs. Some of the variables to be discussed are: i) IEC and cross-linker content of the ionomers; ii) ionomer physical structure; iii) catalyst loading; iv) PTL density and thickness; and v) number of layers that comprise the catalyst layer. The balance and sometimes compromise between performance and durability will also be discussed. By the end of the presentations of electrodes will be demonstrated that were integrated into AEMELs and are able to show very low voltage operation on both deionized water (1.9 V @ l.0 A/cm2) and 0.3 M KOH (1.65 V @ 1.0 A/cm2 and < 2 V @ 3.0 A/cm2) as well as stable operation for as much as 720 hours (30 days).
High Surface Area Metal Carbide Aerogels as Durable Catalyst for the Hydrogen Evolution Reaction
Authors: Elbaz Lior , Lori Oran
Published: September 2023

Electrolyzers’ technologies are essential for the Hydrogen Economy scheme, and in order to drive the hydrogen production price down, their lifetime need to be extended. One important parameter that has not been given enough attention in this context is catalyst durability. In this work, a durable platinum-group metal-free catalyst was developed for hydrogen evolution reaction based on porous, high-surface area molybdenum carbide aerogel. Molybdenum oxide aerogel was synthesized by sol–gel method and carburized by methane-treatment. A three-dimensional molybdenum carbide network was obtained by reacting molybdenum oxide aerogel with CH4/H2 mixture at 700°C. Surface area measurement confirmed a substantial increase in the volume of micropores in the transition from oxide to carbide. The carbide aerogel has low density (<0.4 g/ml) with relatively high surface area of 109 m2/g (reduced from 188 m2/g after methane treatment). The molybdenum carbide aerogel shows remarkable durability compared to Pt/C catalyst, with only 10 mV overpotential shift vs. 100 mV for Pt/C after stability test.
Multi-Element Doping Boosts a Layered Metal Oxide Electrode for Superior Water Oxidation
Authors: Wang Jian
Published: September 2023

More than precisely controlling the active species to optimize the binding with reaction intermediates, applying lab-designed electrocatalysts for practical water electrolysis requires overcoming limitations of mass and electron transports, which are however difficult to achieve by a single strategy. Here, based on a category of layered cobalt oxides (ACoO2, A = alkali metal), we report a multi-element doping method to favor the in-situ reconstruction of more-active species during water oxidation, boost the electronic conductivities, and extend the potential range of kinetic currents. Specifically, various doping elements including both cationic and anionic ones were screened experimentally for ACoO2 and the composition of LiCo1-x-y-zNixFeyPdzO2 was identified with the optimal catalytic properties. Compared with common cobalt oxides and (oxy)hydroxides, LiCo1-x-y-zNixFeyPdzO2 regulated the in-situ catalyst reconstruction during both room- and high-temperature water oxidation, and boosted electronic conductivity by 2-4 orders of magnitudes. Consequently, LiCo1-x-y-zNixFeyPdzO2 outperformed RuO2, Co3O4, α- and β-Co(OH)2 by delivering an anion exchange membrane water electrolysis current density of 1 A cm-2 at about 1.75 V, and showed little degradation during the 500-hour stability test. This work represents a step forward in rationally boosting the catalytic properties of anode materials for practical membrane water electrolysis.
Effects of Porous Transport Layer Coating Inhomogeneities on PEM Water Electrolyzer
Authors: Liu Chang , Wrubel Jacob A , Padgett Elliot , Bender Guido
Published: September 2023

The porous transport layer (PTL) is a critical component of polymer electrolyte membrane (PEM) water electrolyzers, transporting water to the anode catalyst layer, conducting electrons, and removing the produced oxygen. Ti materials such as felts, mesh, and sintered powders are commonly used as PTLs at the anode due to the good corrosion resistance and conductivity of Ti. However, Ti forms an electrically resistive oxide surface layer that has detrimental effects on the performance and durability of PEM electrolyzer cells. In order to permit the use of Ti PTLs in PEM electrolyzers, platinum group metals (PGMs) such as Pt and Ir can be used as a conductive, protective layer [1-3]. However, use of PGM coatings adds to the cost of PEM electrolyzers, and it is likely that future systems will use thinner coatings to minimize cost. To implement the PEM water electrolysis on a larger scale, it is essential to minimize the cost of mass-manufactured cell components while ensuring that inhomogeneities do not adversely affect the performance and durability of the cell and ultimately the stack. Improved understanding of impact of inhomogeneities on cell performance and durability is key to enabling this goal.

This study investigates the impacts of PTL coating inhomogeneities on the performance of PEM water electrolyzers. Coating inhomogeneities of various geometries were artificially made on Ti felt PTLs to investigate the effects on the cell performance and understand fabrication tolerances. In addition, a model is developed to analyze the impacts of coating geometry on the surface current density distribution and local electric potential of the cell.

Reference

Kang, Z., et al., Effects of interfacial contact under different operating conditions in proton exchange membrane water electrolysis. 2022. 429: p. 140942.

Liu, C., et al., Constructing a Multifunctional Interface between Membrane and Porous Transport Layer for Water Electrolyzers. 2021. 13(14): p. 16182-16196.

Liu, C., et al., Exploring the Interface of Skin
‐Layered Titanium Fibers for Electrochemical Water Splitting. Advanced Energy Materials, 2021. 11(8): p. 2002926.
Design of Noble-Metal-Free Membrane Electrode Assemblies Based on Metal Chalcogenides for Electrochemical Hydrogen Production Via Alkaline Seawater Electrolysis
Authors: Ngo Thanh Trung , Arinchtein Aleks , Frisch Marvin , Hager Linus , Buchheister Paul Wolfgang , Kerres Jochen Alfred , Strasser Peter
Published: September 2023

The production of large amounts of green hydrogen (H2) by electrochemical water splitting represents one of the key pillars to reach net-zero by 2050. As one of the major drawbacks, both low-temperature proton-exchange membrane (PEM) as well as anion-exchange membrane (AEM) electrolysis still rely on the utilization of noble metals in the catalyst layers driving the evolution of H2 and oxygen (O2) on the cathode (HER) and on the anode (OER), respectively. Beyond that, the requirement for highly pure water feeds to prevent degradation of the cell performance over time was previously addressed as one of the main concerns. In particular, this holds true for arid regions located close to the ocean. Advantageously, these coastal arid zones provide essentially unlimited access to seawater, coupled with ample solar irradiation and wind throughout the entire year.[1]

One of the major challenges for direct seawater electrolysis lies in the development of selective catalysts, especially for the anode due to the inherently faster reaction kinetics of the competing two-electron chlorine evolution reaction (ClER). Nickel-iron layered double hydroxides (NiFe-LDH) were identified as active and selective OER electrocatalysts in a previous study[2] by our group. Dionigi et al.[3] recently reported a general design principle for selective seawater electrolysis, in which alkaline pH values > 7.5 are claimed to favor OER over ClER for overpotentials < 480 mV.

At the cathode, state-of-the-art electrolyzers utilize Pt-based catalysts for an efficient HER.[2] For direct seawater electrolysis, however, not only the high cost but also the weak stability due to chloride-induced corrosion restrict the applicability of Pt-based electrodes. In our contribution, we thus present noble-metal free catalyst materials based on metal chalcogenides with high HER activity and improved stability in alkaline seawater electrolyte in a single-cell electrolyzer setup. Membrane-electrode assemblies (MEAs) with superior corrosion-resistance by a modification of the porous transport layers (PTLs) for both cathode and anode will be presented, which outperform reference MEAs containing Pt-based cathodes in alkaline seawater electrolysis. The optimized noble-metal-free electrode design (fig. 1) combined with well-controlled electrolyte feeding enables alkaline seawater electrolysis operating at industrially relevant current densities.

References

[1] S. Dresp, F. Dionigi, M. Klingenhof, P. Strasser, ACS Energy Lett. 2019, 4, 933.

[2] S. Dresp, T. N. Thanh, M. Klingenhof, S. Brückner, P. Hauke, P. Strasser, Energy Environ. Sci. 2020, 13, 1725.

[3] F. Dionigi, T. Reier, Z. Pawolek, M. Gliech, P. Strasser, ChemSusChem 2016, 9, 962.

Figure 1
Membrane Electrolyzers for Hydrogen Production: From Catalyst Fundamentals to Devices
Authors: Lindquist Grace , Boettcher Shannon W.
Published: September 2023

Water electrolysis powered by renewable sources such as wind or solar produces clean hydrogen gas, which is used for many industrial processes and will be essential in a future clean energy economy. Commercialized membrane electrolyzers use acidic proton exchange membranes (PEMs), which offer high performance but require the use of expensive precious-metal catalysts such as IrO2 and Pt that are nominally stable under the locally acidic conditions. Anion 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 present our fundamental work in understanding the chemical and electrochemical processes in earth-abundant water-oxidation catalysts, including the use of integrated reference-electrode device architectures and cross-sectional materials analysis, as well as progress in building high-performance AEM electrolyzers. Baseline systems operate at 1 A·cm-2 in pure water feed at < 2 V at a moderate temperature of ~70 °C using either IrO2 or Co3O4 anode catalyst layers, Versogen TP-85 alkaline ionomers, and stainless-steel porous transport layers. These devices, however, degrade rapidly compared to PEM electrolyzers. The voltage profile corresponding to degradation has initial fast (~10 mV/h) and steady-state slow components (~1 mV/h), which we link to chemical and structural changes in the ionomer catalyst reactive zone. 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. Lastly, I will discuss these processes in electrolyzer devices and in model systems, as well as present promising new chemical strategies we have developed to mitigate degradation and enhance performance using novel ionomers and electrode catalyst compositions and architectures.
Metallic Glass Nanofoam Anode Catalysts for Anion-Exchange Membrane Water Electrolyzers
Authors: Shi Qiurong , Zachman Michael J. , Myers Deborah J. , Xu Hui , Wu Gang
Published: September 2023

Alkaline anion-exchange membrane water electrolyzers (AEMWEs) for hydrogen production are now receiving intensive attention due to their feasibility to use sustainable, low-cost platinum group metal (PGM-free) catalysts. Although a variety of highly efficient PGM-free catalysts for the oxygen evolution reaction (OER) have been explored, few of them demonstrated satisfied performance in real AEMWEs due to the insufficient electrical conductivity and unfavorable interfaces with ionomers in 3D porous electrodes. Herein, we report a series of highly porous ternary NiFeM (M: Cu, Co, and Mn) metallic glassy catalysts featured with nanofoam network morphologies, which are composed of amorphous OER active metal oxide shells and highly electrically conductive metallic glass alloy cores. Due to these unique properties, these NiFeM nanofoam catalysts demonstrated promising OER activities and stabilities in the half-cell with aqueous alkaline electrolytes, especially at high potentials. We also examined their magnetic properties and found no direct correlation with measured OER activity. These ternary NiFeM catalysts are further integrated with unique ionomers and AEMs to fabricate AEMWEs, showing superior performance to binary NiFe and commercial IrO2 catalysts when utilizing diluted KOH electrolytes. A different trend was identified when directly using desirable but challenging pure water, and the NiFeCu catalyst performed the best comparable to IrO2 especially at high current densities. Although deep understanding on limiting factor of pure water AEMWEs is still required, these NiFeM catalysts with favorable catalytic and morphological properties representing a new class of highly efficient PGM-free anode catalysts for viable AEMWEs toward clean hydrogen generation.
Autonomous Catalyst Development for Alkaline Electrolysis
Authors: Moretti Enzo , Kiebach Ragnar , Kraglund Mikkel Rykær , Fisker-Bødker Nis , Vegge Tejs
Published: September 2023

NiFe LDH based materials are promising candidates for cheap, high performance catalysts for alkaline OER. While suffering from degradation effects, the presence of Fe, even in trace amounts, increases their OER activity manifold compared to plain Ni hydroxide. Although discovered in the mid-80s, the exact catalytic mechanism of this “Fe effect” is still not fully understood. Additionally, other doping elements like Co, Cr, Al and others have shown to both further improve OER activity and increase stability. The properties of those materials are often highly dependent on the doping ratio, resulting in an enormous number of possible material combinations. Modern techniques like DFT simulations and machine learning can help to speed up the search for the optimal compositions, but ultimately manual experimentation often limits how fast better materials can be discovered, as the process remains both resource and time-consuming.

In this work, we combine an autonomous high-throughput experiment with machine learning assisted optimization of material compositions to a closed-loop system in an attempt to substantially accelerate the search for high performance alkaline OER catalysts. The system screens an eight variable phase space of doped NiFe LDH for compositions that yield optimal OER performance. Its centerpiece is a 4-axis robotic arm from North Robotics with sample, vial and liquid handling capabilities. The samples are prepared by means of a dip-coating process on Ni foam substrates that allows for doping with different metals. Electrochemical investigations are carried out in 1M KOH in an automated test cell, including EIS, CV and CP measurements at current densities of up to 200mA/cm2. From these results, a figure of merit for the OER activity is calculated and fed into a bayesian optimizer (Dragonfly). This algorithm determines the most promising next test candidate based on the principles of exploration and exploitation and initiates the next experiment accordingly. The experimental procedure can be divided into independent sub-steps, allowing for smart scheduling. This can reduce downtime of the robotic arm and therefore increase the throughput significantly, such that up to 1000 experiments per week can be achieved.

We present the first results of a screening study conducted with this system and compare it to a manual study in terms of accuracy, reproducibility and throughput. Selected, particularly high performing compositions found in this study are also tested in a flow cell setup under industrially relevant conditions (30 wt. % KOH, 60 °C) for several hundred hours.
(Energy Technology Division Supramaniam Srinivasan Young Investigator Award) Fundamental Insights into the Oxygen Evolution Reaction from Epitaxial Oxide Thin Films
Authors: Stoerzinger Kelsey A
Published: September 2023

The intermittent nature of renewable energy sources requires a clean, scalable means of converting and storing energy. One Earth-abundant storage option is water electrolysis: storing energy in the bonds of O2 and H2, and later extracting electricity by the electrochemical reaction of gasses in a fuel cell. The efficiency of this process is primarily limited by the sluggish kinetics of the oxygen evolution reaction (OER) at the anode, resulting in extensive use of precious metal electrocatalysts in current devices. We have worked to build mechanistic understanding of the OER on benchmark catalysts rutile IrO2 and RuO2, and have investigated competition with the chlorine evolution reaction (CER) in saline feeds, where breaking scaling relations between oxidative processes can broaden the range of acceptable water sources for electrolysis. We have also investigated earth-abundant oxide materials as alternatives, especially nickel-based perovskites, focusing on fundamental understanding of the electrode/electrolyte interface and its relation to catalyst electronic structure.

I will present studies of model oxide electrodes grown by pulsed laser deposition (PLD) and molecular beam epitaxy (MBE) that display a known crystallographic orientation, strain, surface area, and path for charge transport. Such measurements can establish the intrinsic activity of oxide catalysts in a way that cannot be realized with polydisperse nanoparticle systems, and we use these findings to rationally design composition and structure to maximize activity.
Investigation of Surface Chemistry of Pemwes Iridium Oxide Catalyst Layers as a Function of Ink Aging Time
Authors: Foster Jayson , LIU Xiang , Creel Erin , Li Jianlin , Yu Haoran , Cullen David A. , Kariuki Nancy N. , Park Jaehyung , Myers Deborah J. , Serov Alexey , Pylypenko Svitlana
Published: September 2023

Proton exchange membrane water electrolyzers (PEMWEs) are an advanced and effective solution to producing hydrogen from water for green hydrogen production. To improve PEMWEs operation, it is necessary to analyze the catalyst layer (CL) to better understand relationships between surface properties and processing, performance, and durability. However, understanding the CL composition, structure, and morphology at all relevant scales is difficult. X-ray photoelectron spectroscopy (XPS) is a surface-sensitive technique that is capable of measuring subtle differences in chemistry of a sample’s surface within top 3-10 nms. However, there are several challenges associated with limited information that has been reported in the literature thus far.

This study focuses on investigating the CLs made with IrO2 catalysts using Mayer Bar coating method, one of the scalable fabrication routes. XPS analysis was conducted using a recently developed approach that mitigates issues with degradation of ionomer induced during X-ray exposure. First, XPS was used to probe variations between different areas of the CLs to assess spatial homogeneity to confirm good quality of the coatings. XPS was also employed to investigate CLs made with inks aged for different amount of time (0, 3, and 14 days), noting some differences in the surface chemistry. Results from this study will discuss the effect of ink age on surface composition at the catalyst-ionomer interface, as well as address specific challenges in fitting the O 1s and Ir 4f core level spectra which are inherently challenging to curve fit. This work motivates further studies investigating other aspects related to processing and fabrication as well as investigations of CLs stability.
(Invited) Effects of PTL Coating Thickness on PEM Water Electrolyzer Performance
Authors: Bender Guido , Ware Sam , Schuler Tobias , Kang Zhenye , Young James L.
Published: September 2023

Low temperature electrolysis (LTE) is a very promising technology that can support the decarbonization of the energy sector through the production of hydrogen from water using renewable energy sources. For the introduction of LTE at scale several advances are required such as the reduction of voltage losses and platinum group metal (PGM) loadings without sacrificing the current lifetimes of 60000+ hours. Thrifting these PGM materials will be one essential step to reduce the component cost. In LTE systems PGM materials are used as catalysts, i.e. IrOx on the anode and platinum (Pt) supported on high surface carbon on the cathode, and also as protective coatings of the titanium base anode PTLs. At the acidic conditions and high potentials of the anode titanium develops an oxide layer that passivates the material surface with regards to its thermal and electrical conductivity and hampers the functionality of the LTE device. The literature shows that this process can be prevented by applying a protective PGM layer to the PTL. In this presentation we discuss the effect of PTL coating thickness on cell performance and contact resistance. PTL coatings were systematically varied by physical vapor deposition and the resulting PTL materials were subsequently measured using in-situ and ex-situ diagnostics and a range of operating conditions. Results will be discussed in detail during the presentation and indicate that the PTL / catalyst layer interface is key to high performance electrolysis performance. Note that PTL materials were additional characterized at the nano scale with techniques such as ToF-SIMS, STEM-EDS, FIB, SEM, EDS. These results will be reported in separate talks.
Mechanistic Interrogation of the Role of Electrode Microstructural Attributes in PEM Water Electrolysis
Authors: Goswami Navneet , Ayyaswamy Abhinand , Vishnugopi Bairav Sabarish , Mukherjee Partha P.
Published: September 2023

Proton-exchange membrane water electrolyzer (PEMWE) is a potential candidate that can help meet the demands of a green hydrogen energy ecosystem by performing electrochemical water-splitting reactions at low temperatures. However, challenges that plague its widespread adoption in its present form are concerning high Iridium loadings at the anode catalyst layer, corrosion propensity of the support structure, challenges in the form of bubble formation, and the lack of novel electrocatalysts that have high activity and stability to sustain the slow oxygen evolution reaction (OER). Controlling the mass transport limitations in the electrode architecture as a result of the various physicochemical mechanisms can be critical for obtaining better performance and propelling toward achieving high hydrogen throughput at a lower operational cost. In this work, we investigate the impact of key microstructural constituents such as catalyst loadings, cathode support ratios, and electrode thicknesses on the resulting electrochemical landscape through a pore-scale model. The crucial role of the ionomer content which provides percolation pathways for protons in the porous network of the catalyst layer electrodes is revealed. The synergistic interactions between the anode and the cathode in dictating the kinetic-transport resistances and bubble overpotentials are further elaborated.
Anodic/Cathodic Properties of Ni Based Catalysts for Anion Electrolyte Membrane Water Electrolysis
Authors: Kakinuma Katsuyoshi , Shi Guoyu , Tano Tetsuro , Tryk Donald A. , Yamaguchi Miho , Uchida Makoto , Iida Kazuo , Arata Chisato , Watanabe Sumitaka , Iiyama Akihiro
Published: September 2023

Anion electrolyte membrane water electrolysis (AEM WE) using non-precious metal catalyst is one of the most prospective systems for pure hydrogen generation. The Ni based oxide shows relatively lower overpotential of oxygen evolution reaction (OER) by adding the transition metals of Co, Fe and Mn, and approaches that of precious metal of Ir based oxide. Our previous study reported that the Ni-Co based catalyst was highest OER activity at operating temperature. The crystallized Ni-Co metal-based core particles with amorphous Ni oxyhydrates of top surface (shell) was confirmed to be preferable to obtain the higher OER activity by rotating disk electrode method, transmission electron microscopy and DFT calculation. Moreover, the fused aggregated network microstructure of Ni-Co based catalyst assisted to show a metallically electronic conductivity. In this study, we evaluated both OER and hydrogen evolution reaction (HER) activity of Ni based catalysts to confirm the prospective non-precious metal catalysts for AEM WE.

Each Ni based catalysts with additive of transition metals were synthesized by the flame oxide-synthesis method.1 The OER and HER activities of these catalysts were evaluated in 1 M KOH at 20 to 80 oC by use of the RDE. The Ni-Co based catalyst was highest OER activity in these Ni based catalysts obtained above. The amorphous top surface layer was correlated with a negative shift in the oxyhydroxide formation peak potential from the results of DFT calculations. 2 The HER activity of the Ni-Fe based catalyst also showed the higher OER activity. Especially, the Ni-Fe based catalyst had highest HER activity in these Ni cased catalysts above. The HER activity enhanced by the construction of well crystallized top surface in comparison with its amorphous or poorly crystalline ones. DFT calculation indicated that the defective or disordered surface was not as active for the HER. These results will provide a strategy of Ni based catalysts optimization for AEM.

Acknowledgement

This work was partially supported by funds for the JSPS KAKENHI (20H02839), and the project from the New Energy and Industrial Technology Development Organization (NEDO) of Japan.

References

Kakinuma, M. Uchida, T. Kamino, H. Uchida, and M. Watanabe, Electrochim. Acta, 56, 2881 (2011).

Shi, T. Tano, D. A. Tryk, A. Iiyama, M. Uchida, and K. Kakinuma, ACS Catal., 11, 5222 (2021).

Figure 1
Bifunctional Oxygen Electrocatalysis on Manganese Oxide
Authors: Carlson Evan , Bajdich Michal , Chueh William C. , Mefford J. Tyler
Published: September 2023

Limited supply of precious metals impedes the scale up of electrolyzer production. To enable 100s of GWs of PEM electrolyzer capacity by 2030, iridium supply must grow by more than 10x.[1] Alternatively, catalysts made of cheaper, more abundant manganese could relieve these constraints, if engineered to have comparable activity and stability. The unique bifunctional OER/ORR activity of Mn oxide could also enable electrolyzers that both produce and consume fuel with a single catalyst. Yet rational design of Mn oxide catalysts requires a better understanding of the structural and chemical motifs that lead to high bifunctional performance.

In this talk, we will discuss our investigation of the bifunctional OER & ORR activity of Mn oxide and its unusual pH dependence. Our model system, 𝛼-KxMnO2, is among the best reported Mn oxide catalysts for both the OER and the ORR, with ORR activity matching that of Pt.[2] While the OER activity of Mn oxide has been shown to increase at higher pH,[3] we will show that its ORR activity improves as well. We will discuss our attempts to understand this phenomenon with operando scanning transmission x-ray microscopy (STXM), which enables spectroscopic investigation of single catalyst particles during reaction with spatial resolution down to 25 nm. Complementary surface DFT calculations provide further evidence for identification of the active crystal facets and insights into the pH-dependency of the OER & ORR mechanisms. We will discuss the implications of this work on the design of bidirectional electrolyzers with low-cost, non-precious metal catalysts.

[1] IRENA. Green Hydrogen Cost Reduction. 2020

[2] Meng, Y. et al.
J. Am. Chem. Soc.
2014, 136 (32), 11452–11464.

[3] Takashima, T. et al.
J. Am. Chem. Soc.
2012, 134 (3), 1519–1527.