Large-scale Hydrogen Production Research Articles

Plate structure design guideline for commercial alkaline water electrolyzers (AWEs) with improved liquid flow uniformity: Multi-scale quantitative criteria and experimental validation

Alkaline water electrolyzers (AWEs) holds great promise for large-scale green hydrogen production, but its commercialization is impeded by high electrical energy costs. Improving flow uniformity in AWEs is crucial to reduce energy consumption, necessitating optimized plate structure designs. Regrettably, the quantitative investigation of flow uniformity in electrolyzers is rare, due to the complex flow behavior. As a consequence, the existing designs primarily rely on empirical knowledge, lacking an efficient and systematic design guidance. This study establishes a general plate structure design strategy for commercial AWEs by introducing quantitative criteria for flow uniformity in multi-scale. The strategy comprises four steps: 1) single unit design to improve lateral liquid distribution, 2) evaluation of velocity magnitude discrepancy at horizontal sections, 3) flow behavior prediction by RTD analysis, and 4) validation through performance test. The strategy incorporates three quantitative parameters φ, δ, θ to evaluate the performance in three different levels. Two novel designs, namely, the rhombus and wedge electrolyzers are proposed to demonstrate the design strategy. Additionally, an in-situ electrolysis visualization/performance test platform is developed to vividly depict the gas-liquid flow during electrolysis and validate the effectiveness of our design guidelines. The proposed design guideline provides step-by-step guidance for the plate structure design of future high-performance commercial AWEs.

Multiple criteria evaluation of hydrogen production processes for use in automotive sector

This work evaluates large-scale hydrogen production processes - those capable of providing hydrogen for an eventual automotive hydrogen program in a community and along highways - with the aim to Sidentify which of the production processes of hydrogen is more attractive for an eventual automotive hydrogen program. To perform the research, the MACBETH (Measuring Attractiveness by the Category-Based Assessment Technique) method and the computational code M-MACBETH 3.2.0 are used taking into account multiple criteria. Thus, this work used the computational code M-MACBETH 3.2.0 to evaluate twelve hydrogen production processes and build rankings of attractiveness of hydrogen production processes, considering the following criteria: economic (invested capital and production cost), technical (the purity of the hydrogen produced) and environmental (the amount of energy used to produce 1 kg of hydrogen and the CO2 emissions to produce 1 kg of hydrogen). In the end, three rankings are produced considering three scenarios, which allow to conclude that: if decisions regarding hydrogen are made taking into account that economic and financial aspects have the same weight as sustainability aspects, the more attractive hydrogen plants are those that use the Solar Thermochemical Plants; if decisions are made taking into account that economic and financial aspects are more important than aspects of sustainability, the production process more attractive will be the one that uses the SR technology - Ethanol and Natural Gas Steam Reforming; and that Solar Thermochemical Plants becomes more attractive than all others alternatives when, in decision-making, sustainability environmental aspects prevail over economic and financial aspects.

Electrodeposition synthesis of cobalt-molybdenum bimetallic phosphide on nickel foam for efficient water splitting

A reasonable design of excellent bifunctional catalyst is an effective strategy for large-scale hydrogen production. In this study, a two-stage electrodeposition method was used to prepare a crystalline-amorphous structure cobalt molybdenum phosphide layered particles with different sizes on a nickel foam (NF) substrate. Electron rearrangement at the Co/CoMoP2@CoMoO4 heterogeneous interface can reduce the reaction energy barrier for HER and OER, and accelerate the catalytic reaction kinetics. The doping of Mo can promote the synergistic effect between Co and Mo, thereby optimizing the Gibbs free energy of hydrogen adsorption/desorption. This layered arrangement of different size particles greatly improves the active area of the catalyst. In alkaline solution, achieving a current density of 10 mA cm−2 only required overpotentials of 40 mV for HER and 278 mV for OER, respectively. The cell voltage required for the CoMo-P/NF||CoMo-P/NF electrolytic cell is only 1.53 V at 10 mA cm−2. This study provides a reference for the rapid, efficient, and environmentally friendly preparation of high-activity water splitting catalysts with large surface areas.

Unveiling the origin of activity in RuCoOx-anchored nitrogen-doped carbon electrocatalyst for high-efficiency hydrogen production and hydrazine oxidation using Raman spectroscopy

Hydrazine-assisted water electrolysis has gained much attention nowadays as an energy-saving strategy for the large-scale production of hydrogen fuel. Regardless, the synthesis of highly proficient bifunctional electrocatalysts remains a major challenge. Metal–organic frameworks (MOF) derived electrocatalysts have recently demonstrated excellent bifunctional activity in water electrolysis. Herein, we developed a new type of Ru-MOF on rod-like Co-MOF (Ru/Co-MOF) microstructures via a two-step solvothermal route. Subsequently, the Ru/Co-MOF was used as a precursor and self-template to synthesize an electrocatalytically active RuO2/Co3O4 anchored nitrogen-doped carbon (RuCoOx@NC) composite via a one-pot pyrolysis–oxidation strategy under atmospheric air. The RuCoOx@NC composite showed an ultralow overpotential of 44 mV for the hydrogen evolution reaction and 255 mV for the oxygen evolution reaction at 10 mA cm−2 in a 1 M KOH solution. Besides, the RuCoOx@NC composite exhibited an ultra-small working potential of − 0.040 V (vs. reversible hydrogen electrode (RHE)) for the hydrazine oxidation reaction at 10 mA cm−2 in a 1 M KOH/0.5 M hydrazine solution. The assembled RuCoOx@NC∥RuCoOx@NC membrane-free overall hydrazine splitting electrolyzer only required ultralow cell voltages of 0.063 and 0.505 V to produce 10 and 100 mA cm−2, with remarkable long-term stability, demonstrating its exceptional bifunctional activity. Ex situ Raman spectroscopy results indicate that both Co3O4 and RuO2 species contribute to the electrocatalytic activity of the RuCoOx@NC composite. This work suggests a potential strategy for developing bifunctional electrocatalytic materials for energy-saving hydrogen production to solve future energy demands.

Upscaling rocks mechanical properties to study Underground Hydrogen Storage feasibility

Underground Hydrogen Storage (UHS) is a feasible option for large-scale energy storage considering the advancements of the large-scale production of green hydrogen. One of the main engineering objective is to ensure the continuous safety of the storage, such that subsurface operations can be carried under safe stress regimes. Despite obvious similarities to Carbon Capture and Storage, a few differences make the task a new research challenge.
 The first one relates to the cyclic nature of UHS, which is expected to be carried at variable frequency and injection/production loads. Current models are not adequate for the lower frequency range considered in this application. In that case, the visco-plastic nature of rocks becomes non-negligible and needs to be taken into account.
 As a second observation, UHS revolves around a new gas, much lighter than CH4 and super critical CO2. Hydrogen’s atoms are so small they can diffuse even inside rock and this absorption causes rock matrix mechanical properties to weaken. This process is know as Hydrogen Embrittlement. When unaccounted for, such physical phenomenon could lead to catastrophic failure of the caprock, which is supposed to maintain stability to ensure safe storage. The caprock being responsible for the confinement of the hydrogen in the reservoir, development of cracks would enhance greatly permeability of an otherwise impermeable medium, resulting in an environmental disaster as the hydrogen suddenly leaks towards the subsurface and through groundwater aquifers.
 No empirical model is able to capture those two behaviours at the macro-scale since they are both phenomena principally related to grain-scale physics. As such, this contribution presents a Digital Rock Physics framework to upscale rock mechanical properties from the grain-scale. Rocks of interest are microCT-scanned to extract the digitized microstructure. Direct numerical simulations of elasto-plasticity are performed for different stress paths in order to compute the full yield surface (see Figure 1) instead of just the Uniaxial Compressive Strength. While most studies use Discrete Element Modelling to consider grain contacts explicitly, our simulator uses Finite Element Modelling which allows more flexibility in the approach to model multiphysics processes present during UHS. The contacts are modelled instead as an upscaled plastic law. Details of the numerical algorithms are presented in [1].
 As a first case study for this framework, we present a comprehensive parametric study on the impact of cementation on rock strength for real microstructures of granular materials. The framework is then coupled with a numerical erosion algorithm that simulates homogeneous precipitation of mineral matter to represent cementation. New results on the influence of cement property namely Young’s modulus, friction and cohesion on the rock’s yield surface are explored. This study contributes to preliminary results on Hydrogen Embrittlement which directly influences those same mechanical properties. However more work is needed to model realistically the Hydrogen Embrittlement, which is the aim of our new PhD project OCEAN. The process will be observed experimentally at the micro-scale in order to calibrate the simulator. MicroCT-scan images will determine the spatial distribution of the phenomenon. Visco-plasticity will be implemented from [2] to go one step further and determine the effect of Hydrogen Embrittlement during cyclic injection/production of hydrogen.

Recent Trends in Transition Metal Phosphide (TMP)-Based Seawater Electrolysis for Hydrogen Evolution

Large-scale hydrogen (H2) production is an essential gear in the future bioeconomy. Hydrogen production through electrocatalytic seawater splitting is a crucial technique and has gained considerable attention. The direct seawater electrolysis technique has been designed to use seawater in place of highly purified water, which is essential for electrolysis, since seawater is widely available. This paper offers a structured approach by briefly describing the chemical processes, such as competitive chloride evolution, anodic oxygen evolution, and cathodic hydrogen evolution, that govern seawater electrocatalytic reactions. In this review, advanced technologies in transition metal phosphide-based seawater electrolysis catalysts are briefly discussed, including transition metal doping with phosphorus, the nanosheet structure of phosphides, and structural engineering approaches. Application progress, catalytic process efficiency, opportunities, and problems related to transition metal phosphides are also highlighted in detail. Collectively, this review is a comprehensive summary of the topic, focusing on the challenges and opportunities.

Modelling large-scale hydrogen uptake in the Mexican refinery and power sectors

Due to the emissions reduction commitments that Mexico compromised in the Paris Agreement, several clean fuel and renewable energy technologies need to penetrate the market to accomplish the environmental goals. Therefore, there is a need to develop achievable and realistic policies for such technologies to ease the decision-making on national energy strategies. Several countries are starting to develop large-scale green hydrogen production projects to reduce the carbon footprint of the multiple sectors within the country. The conversion sectors, namely power and refinery, are fundamental sectors to decarbonise due to their energy supply role. Nowadays, the highest energy consumables of the country are hydrocarbons (more than 90%) causing a particular challenge for deep decarbonisation. The purpose of this study is to use a multi-regional energy system model of Mexico to analyse a decarbonisation scenario in line with the latest National Energy System Development Program. Results show that if the country wants to succeed in reducing 22% of its GHG emissions and 51% of its short-lived climate pollutants emissions, green hydrogen could play a role in power generation in regions with higher energy demand growth rates. These results show, regarding the power sector, that H2 could represent 13.8 GW or 5.1% of the total installed capacity by 2050, while for the refinery sector H2 could reach a capacity of 157 PJ/y, which is around 31.8% of the total share, and it is mainly driven by the increasing demands of the transport, industry, and power sectors. Nevertheless, as oil would still represent the largest energy commodity, CCS technologies would have to be deployed for new and retrofitted refinery facilities.

Recent progress of enhanced bubble separation in alkaline water electrolyzer

Alkaline water electrolysis has a large industrial application and development potential in hydrogen energy owing to its high maturity and low cost. However, its moderate energy efficiency, especially caused by bubble effects, inhibits its use for large-scale hydrogen production. To overcome this shortcoming, this review first analyzes the bubble effect and summarizes the external operation methods, such as external field intensification, flow operation, fluctuation operation, and surfactant addition to the electrolyte, to enhance bubble separation in the electrolyzer. Then, electrode and flow channel structure optimization, particularly superhydrophilic and superaerophobic electrodes, and flow channels with varying heights, square column arrangements, and inlet/outlet numbers are highlighted. Finally, future research directions in alkaline water electrolysis technology are suggested to advance the industrial application of large-scale alkaline water electrolysis.

Modeling and analysis for enhanced hydrogen production in process simulation of methanol reforming

ABSTRACT Hydrogen has emerged as the most suitable fuel for a nation’s greener and sustainable development. In contrast, the feedstock and hydrogen production methods remain a concern for environmental pollution. This study uses methanol as the feedstock for hydrogen production via a low-temperature methanol-reforming process. A simulation model was developed in Aspen Hysys, where an equilibrium reactor is used in the reforming process, and examined the effects of parameters like temperature, pressure, and Methanol-to-Water (M-to-W) molar ratio. Hydrogen mole fraction and selectivity increase by roughly 18.5% and 10.5% when the reaction temperature increases from 100°C to 400°C. At the same time, the methanol conversion rate reaches 95% at 400°C. Reactor pressure shows inverse effects where pressure rises from 1 atm. to 7 atm. that reduces hydrogen mole fraction and selectivity by about 10% and 6%, and a similar reduction of 5% is noticed in the methanol conversion rate. M-to-W molar ratio plays a crucial role in the reaction pathway and the M-to-W ratio between 0.5 and 1.5 at 400°C and 1 atm. reactor pressure showed the highest hydrogen mole fraction (>0.57) and a maximum methanol conversion rate (>90%). Therefore, the present simulation model successfully determines the impacts of various parameters to help design a commercial plant for large-scale hydrogen production via the reforming process.

A Ni-Fe-V trimetallic phosphorus-selenium composite supported on carbon cloth as freestanding electrocatalyst for oxygen evolution reaction

Developing highly active non-noble metal oxygen evolution reaction (OER) electrocatalysts is still urgent and significant to enable the large-scale hydrogen production. Herein, we propose a freestanding electrocatalyst of Ni-Fe-V trimetallic phosphorus-selenium composite on carbon cloth (NiV2P/FeSe@CC) for this issue, which is realized by the in-situ growth of V-MOF, the introduction of Ni and Fe components by electrodeposition, and the synchronous phosphatization and selenization treatment. The well-designed composite exhibits an excellent electrical conductivity and multi-level pore structure, which makes for rapid charge/mass transport and sufficient exposure of catalytic sites. The electrochemical deposition process allows Ni and Fe components to be uniformly deposited on the V-MOF, while the phosphorus and selenium co-doping can modulate the catalyst electronic structure and promote the adsorption of reaction intermediates, thus improving the OER catalytic activity. Consequently, the freestanding electrocatalyst exhibits an ultra-low overpotential of 168 mV under a current density of 10 mA cm−2 and a small Tafel slope of 44.32 mV dec-1 in alkaline environment. The outstanding performance is maintained in the integrated electrolyzer, presenting a small voltage of 1.53 V getting a current density of 10 mA cm−2 and an ultrastability for 160 h under 100 mA cm−2.

Ru-doped MoO2/Mo2C coupled with N-doped carbon as an efficient pH-universal electrocatalyst for hydrogen generation

The preparation of stable, efficient and pH-universal hydrogen evolution reaction (HER) electrocatalysts is urgent and significant for large-scale hydrogen production. Herein, a simple and efficient method was developed to fabricate Ru-doped MoO2/Mo2C onto N-doped carbon nanoparticles (Ru-MoO2/Mo2C/NC). The formed smaller nanoparticles by Ru doping can provide abundant accessible active sites and interfaces. Moreover, the synergistic effects of Ru and Mo-based compounds also played a key role in promoting the catalytic kinetics. The as-prepared Ru-MoO2/Mo2C/NC exhibited low overpotentials of 38, 61, 67 and 75 mV in alkaline, neutral, acidic electrolyte solutions and alkaline seawater at 10 mA cm−2, respectively. This work proposes a valid method for the design of efficient electrocatalysts through precise component regulation.

Safety and efficiency problems of hydrogen production from alkaline water electrolyzers driven by renewable energy sources

Alkaline water electrolysis has become the most promising solution for hydrogen production considering certain factors such as cost, lifetime and maturity of technology. By developing the large-scale hydrogen production by alkaline water electrolysis as the energy buffering, the consuming pressure of the power system caused by the growing penetration of renewable energy sources such as wind and solar energy can be relieved effectively. However, when the alkaline water electrolysis is integrated with renewable energy sources, the unclear underlying mechanism and interaction characteristics limit large-scale application for hydrogen production. Aiming at this problem, from the aspects of efficiency and consistency, power regulation flexibility and gas purity, this paper studies safety and efficiency problems about the wide-range operation of alkaline water electrolyzers driven by renewable energy sources. The corresponding mechanism analyses are carried out and possible solutions for the future research are given, which are expected to provide a comprehensive review and useful guide for this research topic.

A study of ammonia-hydrogen-electricity cogeneration coupled to a very high-temperature heat source

Nuclear hydrogen production is recognized as a promising way of achieving large-scale hydrogen production. However, the high product temperature increases the cost of conventional high-pressure or liquid hydrogen storage and transportation. Ammonia shows considerable promise as a hydrogen carrier. However, vast heat is required in the ammonia production process. Therefore, this paper proposes a model of ammonia production by nuclear heat. The relatively higher grade thermal energy from the reactor is applied for hydrogen production, and the lower is for electricity generation. High-temperature oxygen, a by-product, provides heat for the Haber-Bosch process, converting hydrogen into ammonia and achieving reasonable cascade utilization of energy. The results show that the thermal efficiency production reaches 67.8%. The total energy efficiency increases by 7.5% after introducing ammonia production.

A floatable hydrogel-based photocatalytic system for large-scale solar hydrogen production

The effectiveness of scaling up photocatalysis is constrained by the agglomeration of photocatalysts. A floatable hydrogel-based photocatalytic system at the air-water interface reported by Hyeon et al. in the current issue of Nature Nanotechnology offers benefits for scaling up solar H2 production with effective light delivery and fast gas separation.

Highly efficient hydrogen evolution of Ni3S2-MoS2@CoMoO4/NF from in situ reaction of metal-organic framework in alkaline media

BackgroundHydrogen energy, as the most promising renewable resource in the future, is severely limited in its development due to electrocatalysts, so the preparation of highly efficient and low-cost non-precious-metal catalysts is crucial for large-scale hydrogen production via electrolysis of water. MethodsHerein, Ni3S2−MoS2@CoMoO4/NF was successfully synthesized for the first time by in situ ion-exchange reaction and sulfidation reaction using Co-MOF/NF as a template. Significant FindingsThe electrochemical tests revealed that the overpotential was only 62.4 mV at a current density of 10 mA cm−2, which was similar to that of the noble metal Pt sheet electrode, the long-term durability of the catalysts was more than 24 h at a constant potential, which demonstrated that the catalysts possessed excellent HER performance in alkaline media. In addition, XPS, SEM, XRD, and Raman characterization also demonstrated the successful growth and loading of Ni3S2, MoS2, and CoMoO4. In this study, transition metal sulfides and transition metal sulfide complexes with good electrochemical properties were prepared using metal-organic frameworks (MOFs) as precursors, providing a new idea for the preparation of HER catalysts with high activity in alkaline media.

A multi-scenario site suitability analysis to assess the installation of large scale photovoltaic-hydrogen production units. Case study: Eastern Morocco

Due to the rapid integration of renewable energy sources, challenges related to intermittence and grid stability have emerged, prompting scientists to seek an efficient and sustainable storage system to address these issues. Among the existing storage solutions, green hydrogen has demonstrated its high capacity as an energy vector, making it a promising solution to significantly enhance the transition to a 100% renewable energy society. However, the production costs of green hydrogen remain high, necessitating a thorough investigation to identify optimal locations for its production, ensuring high capacity and cost-effectiveness. In this context, the present paper introduces a multi-scenario, water-based approach aimed specifically at identifying optimal locations for large-scale photovoltaic-powered hydrogen production units. To achieve this objective, we have developed an integrated framework that combines the Analytical Hierarchy Process method and the Geographic Information System tool. This framework takes into account four main criteria and ten sub-criteria, and it has been applied to the Eastern region of Morocco as a case study. Furthermore, a techno-economic comparison is conducted among the three scenarios, considering the amount of hydrogen produced and the Levelized Cost of Hydrogen. The analysis results reveal that the Eastern region of Morocco emerges as a target area for large-scale photovoltaic-powered hydrogen production units installations, where the sites ranked as “excellent” account for 18.1% of the total surface area under the first scenario. Moreover, the findings demonstrate that the first scenario represents the optimal choice for the Eastern region, offering the highest annual hydrogen production (1,875 tons) with the most advantageous cost of 3.690$/kg. The study's conclusions are of great significance for overseas investors and local policymakers, offering valuable insights into the region's opportunities for hydrogen industry development, given the rising global interest in green hydrogen market.

Hierarchical Heterogeneous NiFe Layered Double Hydroxides for Efficient Solar-Powered Water Oxidation.

Highly active, stable, and low-cost oxygen evolution reaction (OER) electrocatalysts are urgently needed for the realization of large-scale industrial hydrogen production via water electrolysis. Layered double hydroxides (LDHs) stand out as one of the most promising nonprecious electrocatalysts worth pursuing. Here, a hierarchical heterogeneous Ni2+Fe3+@Ni2+Fe2+ LDH was successfully synthesized via a sequential electrodeposition technique using separate electrolytes containing iron precursors with different valence states (Fe2+, Fe3+). The underlying highly crystalline Ni2+Fe2+ LDH nanosheet array provides a large surface for the catalytically more active Ni2+Fe3+ LDH overlayer with low crystallinity. The resulting Ni2+Fe3+@Ni2+Fe2+ LDH demonstrates excellent OER activity with overpotentials of 218 and 265 mV to reach current densities of 10 and 100 mA cm-2, respectively, as well as good long-term stability for 30 h even at a high current density of 500 mA cm-2. In an overall water splitting, an electrolyzer using an electrocatalyst of Sn4P3/CoP2 as a cathode requires only a cell voltage of 1.55 V at 10 mA cm-2. Furthermore, the solar-powered overall water splitting system consisting of our electrolyzer and a perovskite/Si tandem solar cell exhibits a high solar-to-hydrogen conversion efficiency of 15.3%.

Self-supported crystalline-amorphous composites of metal phosphate and NiS for high-performance water electrolysis under industrial conditions

Developing affordable and efficient electrocatalysts toward water electrolysis under industrial conditions is crucial for large-scale production of green hydrogen. In this regard, we propose a facile and mild method to construct crystalline-amorphous composites of metal phosphate (MPi) and NiS on nickel foam (NF) for practical water electrolysis. The as-prepared electrodes exhibit excellent performance, achieving a remarkable current density of 1000 mA cm–2 at the ultralow overpotential of 345 and 223 mV for FePi-NiS/NF (oxygen evolution reaction, OER) and NiCoPi-NiS/NF (hydrogen evolution reaction, HER), respectively. The composites can undergo an in-situ transformation into highly active and targeted species under high current density, which possess a unique pore structure interconnected by nanosheets that provides an abundance of catalytic sites and open channels for efficient bubble diffusion. When operated under industrial conditions (6 M KOH, 70 °C), the assembled electrode requires only 1.712 V to attain a current density of 1000 mA cm−2. The electrodes also demonstrate exceptional performance in alkaline electrolysis with an anion exchange membrane (AEMWE) when scaled up to a larger size (area: ≈ 25 cm2). Specifically, they achieve a substantial current of 12.5 A at 1.87 V with a high energy efficiency of 79.2 % and remarkable durability over 30 h under industrial electrolysis conditions (1 M KOH, 50 °C), outperforming benchmark Pt/C/NF || IrO2/NF electrodes with energy saving of 0.215 kWh Nm–3. This work provides a cost-effective and efficient strategy for designing and constructing stable and active catalysts for water electrolysis under harsh industrial conditions.

Thermal modulation of radiation fields enhancing the adaptability of CPV-Hydrogen systems to hot outdoor conditions

Photovoltaic (PV) coupled with water electrolysis (EC) provides a clean and reliable hydrogen supply. However, commercial PV often undergo severe performance degradation under high temperature outdoor conditions. In this work, we report a novel thermally integrated concentrated PV-EC system using a pipeline-based liquid spectral beam splitting (SBS) filter as the electrolyte preheater. Unlike previous designs where heat is collected on the backside of the PV, the liquid-filled tubular SBS filter effectively modulates solar irradiation both spatially and spectrally prior to reaching the PV surface. The infrared wavelengths are absorbed by the electrolyte prior to their conversion into thermochemical losses in the PV, thereby augmenting the temperature and efficiency of electrolysis. Efficient allocation of thermal energy can simultaneously satisfy the lower temperature requirement for PV and the higher temperature demand for EC. The PV surface temperature can be decreased by as high as 23.5 K owing to this thermally integrated mode. The optimized allocation of thermal energy resulted in a notable increase in the average efficiency of photovoltaics, electrolysis, and solar hydrogen production by 7.5%, 8.1%, and 5.2% respectively. As a result, out design can significantly suppress the decreasing trend of efficiency in outdoor experiments during summer midday. The proposed system design, characterized by its simplistic structure and utilization of cost-effective materials, presents a feasible alternative for large-scale solar hydrogen production in hot outdoor environments.

Comparative Studies of Ir-Based PEM Electrolyzers Via Operando ‘Tender’ X-Ray AP-XPS

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