Nickel Structures as a Template Strategy to Create Shaped Iridium Electrocatalysts for Electrochemical Water Splitting

Recent Development of Ir- and Ru-Based Electrocatalysts for Acidic Oxygen Evolution Reaction

Proton exchange membrane (PEM) water electrolyzers are one type of the most promising technologies for efficient, nonpolluting and sustainable production of high-purity hydrogen. The anode catalysts account for a very large fraction of cost in PEM water electrolyzer and also determine the lifetime of the electrolyzer. To date, Ir- and Ru-based materials are types of promising catalysts for the acidic oxygen evolution reaction (OER), but they still face challenges of high cost or low stability. Hence, exploring low Ir and stable Ru-based electrocatalysts for acidic OER attracts extensive research interest in recent years. Owing to these great research efforts, significant developments have been achieved in this field. In this review, the developments in the field of Ir- and Ru-based electrocatalysts for acidic OER are comprehensively described. The possible OER mechanisms are first presented, followed by the introduction of the criteria for evaluation of the OER electrocatalysts. The development of Ir- and Ru-based OER electrocatalysts are then elucidated according to the strategies utilized to tune the catalytic performances. Lastly, possible future research in this burgeoning field is discussed.

Oxygen Vacancy-Enhanced Ni3N-CeO2/NF Nanoparticle Catalysts for Efficient and Stable Electrolytic Water Splitting

Highly efficient and cost-effective electrocatalysts are of critical significance in the domain of water electrolysis. In this study, a Ni3N-CeO2/NF heterostructure is synthesized through a facile hydrothermal technique followed by a subsequent nitridation process. This catalyst is endowed with an abundance of oxygen vacancies, thereby conferring a richer array of active sites. Therefore, the catalyst demonstrates a markedly low overpotential of 350 mV for the Oxygen Evolution Reaction (OER) at 50 mA cm-2 and a low overpotential of 42 mV for the Hydrogen Evolution Reaction (HER) at 10 mA cm-2. Serving as a dual-function electrode, this electrocatalyst is employed in overall water splitting in alkaline environments, demonstrating impressive efficiency at a cell voltage of 1.52 V of 10 mA cm-2. The in situ Raman spectroscopic analysis demonstrates that cerium dioxide (CeO2) facilitates the rapid reconfiguration of oxygen vacancy-enriched nickel oxyhydroxide (NiOOH), thereby enhancing the OER performance. This investigation elucidates the catalytic role of CeO2 in augmenting the OER efficiency of nickel nitride (Ni3N) for water electrolysis, offering valuable insights for the design of high-performance bifunctional catalysts tailored for water splitting applications.

Recent advances in proton exchange membrane water electrolysis

Proton exchange membrane water electrolyzers (PEMWEs) are an attractive technology for renewable energy conversion and storage. By using green electricity generated from renewable sources like wind or solar, high-purity hydrogen gas can be produced in PEMWE systems, which can be used in fuel cells and other industrial sectors. To date, significant advances have been achieved in improving the efficiency of PEMWEs through the design of stack components; however, challenges remain for their large-scale and long-term application due to high cost and durability issues in acidic conditions. In this review, we examine the latest developments in engineering PEMWE systems and assess the gap that still needs to be filled for their practical applications. We provide a comprehensive summary of the reaction mechanisms, the correlation among structure-composition-performance, manufacturing methods, system design strategies, and operation protocols of advanced PEMWEs. We also highlight the discrepancies between the critical parameters required for practical PEMWEs and those reported in the literature. Finally, we propose the potential solution to bridge the gap and enable the appreciable applications of PEMWEs. This review may provide valuable insights for research communities and industry practitioners working in these fields and facilitate the development of more cost-effective and durable PEMWE systems for a sustainable energy future.

Supported Iridium-based Oxygen Evolution Reaction Electrocatalysts - Recent Developments

The commercialization of acidic proton exchange membrane water electrolyzers (PEMWE) is heavily hindered by the price and scarcity of oxygen evolution reaction (OER) catalyst, i. e. iridium and its oxides. One of the solutions to enhance the utilization of this precious metal is to use a support to distribute well dispersed Ir nanoparticles. In addition, adequately chosen support can also impact the activity and stability of the catalyst. However, not many materials can sustain the oxidative and acidic conditions of OER in PEMWE. Hereby, we critically and extensively review the different materials proposed as possible supports for OER in acidic media and the effect they have on iridium performances.

Multistep Sulfur Leaching for the Development of a Highly Efficient and Stable NiSx/Ni(OH)2/NiOOH Electrocatalyst for Anion Exchange Membrane Water Electrolysis

Nickel (poly)sulfides have been widely studied as anodic catalysts for alkaline water electrolysis owing to their diverse morphologies, high catalytic activities in the oxygen evolution reaction (OER), and low cost. To utilize low-cost and high-efficiency polysulfides with industry-relevant cycling stability, we develop a Ni-rich NiS_x/Ni(OH)₂/NiOOH catalyst derived from NiS₂/Ni₃S₄ nanocubes. Ni-rich NiS_x/Ni(OH)₂/NiOOH shows improved OER catalytic activity (η = 374 mV@50 mA cm^-2) and stability (0.1% voltage increase) after 65 h of a galvanostatic test at 10 mA cm^-2 compared with commercial Ni/NiO and hydrothermally synthesized Ni(OH)₂ (both show η > 460 mV@50 mA cm^-2 along with 4.40 and 1.92% voltage increase, respectively). A water-splitting electrolyzer based on Pt/C||AF1-HNN8-50||NiS_x/Ni(OH)₂/NiOOH exhibits a current density of 1800 mA cm^-2 at 2.0 V and 500 h high-rate stability at 1000 mA cm^-2 with negligible attenuation of only 0.12 mV h^-1. This work provides an understanding of truly stable species, intrinsic active phases of Ni polysulfides, their high-rate stability in a real cell, and sheds light on the development of stable chalcogenide-based anodic electrocatalysts for anion exchange membrane water electrolysis (AEMWE).