Low‐Dimensional Electrocatalysts for Acidic Oxygen Evolution: Intrinsic Activity, High Current Density Operation, and Long‐Term Stability

Abstract

Water electrolysis can occur in alkaline, neutral, and acidic media. Neutral water electrolysis is environmentally friendly and suitable for microbial electrolysis, but is faced with problems of sluggish kinetics induced by the low concentration of adsorbed reactants on the catalyst surface and a large energy loss during the reaction. [4] In comparison, alkaline water electrolysis has a wider application due to the low cost and good stability of the catalysts but currently suffers from problems of a high ohmic resistance, sluggish kinetics, and a low current density. [5] Compared with neutral and alkaline water electrolysis, acidic water electrolysis such as a proton exchange membrane water electrolyzer (PEMWE) can reach a higher current density (>2 A cm -2 ) due to higher proton conductivity and lower ohmic resistance. In addition, PEMWE has the advantages of high purity H 2 production, a fast response speed and few side reactions. [6] In recent years, much effort has been devoted to acidic water electrolysis, but there are still several challenges for its large-scale applications. A major challenge is the poor performance at the anode, which requires high-performance catalysts to reduce the overpotential and improve the overall efficiency. [7] First, the intrinsic activity of acidic OER catalysts needs to be improved due to the sluggish four-electron-transfer kinetics of the OER compared with the two-electron-transfer hydrogen evolution reaction (HER), which needs to be improved. Second, most reported catalysts cannot reach high current density (>200 mA cm -2 ) and meet the requirements of industrial use. Third, the dissolution and peeling of the catalyst from the electrode in oxidative and corrosive OER conditions worsen their activity and stability, and thus limits the long-term use of these catalysts.OER occurs at the interface between a catalyst and an acidic electrolyte, where the absorption and desorption of the intermediates is crucial for the whole catalytic reaction. Therefore, it is important to control the absorption and desorption energy of intermediates to improve the overall reaction efficiency. [8] Low-dimensional materials including 0D (nanoparticles/ nanodots), 1D (nanorods/nanowires), and 2D (nanosheets/ nanoplates) have received much attention in the energy conversion field because of their high specific surface area, abundant active sites, tunable electronic structure, and possible different

Iridium-based catalysts for oxygen evolution reaction in acidic media: Mechanism, catalytic promotion effects and recent progress

“…The current density in PEMWE is expected to be higher than 1 A•cm -2 , with the operating temperature around 60 to 80 °C, and the energy efficiency is expected to be between 75% and 80% [228,229]. Actually, though many catalysts have been demonstrated to have good catalytic performance in acidic OER, they might not be available in the practical PEMWE application [36]. For a real application, the cost of raw materials and manufacturing processes, as well as potential mass production, should be considered.…”

“…Considering the current exciting and inspiring achievements of Ir-based catalysts in the field of acidic OER, an overview of this important field will help the community understand the progress and will be instructive for the development of novel and efficient Ir-based catalysts. There are also several review reports concerning the OER catalyst development in acidic conditions [34][35][36]. For example, the catalysts classified into metal nanostructures (Ir and Ru-based), noble metal oxides, non-noble metal oxides, and carbon-based nanomaterials have been summarized in the progress of electrocatalyst design for acidic OER [35]; the lowdimensional electrocatalysts in acidic media was also reviewed from the aspects of intrinsic activity, high current density operation, and long-term stability [37]; starting from the synergistic effect of multi-metallic systems and their catalytic performance, the multi-metallic electrocatalysts were introduced carefully in the acidic media [3].…”

Recent Advances in Carbon‐Supported Noble‐Metal Electrocatalysts for Hydrogen Evolution Reaction: Syntheses, Structures, and Properties

“…At present, most high-current electrolyzers usually use IrO 2 /RuO 2 as the anode to generate oxygen, [174] which leads to the high cost of catalysts and hinders the wide application of water electrolysis technology. In addition to design and develop various efficient OER catalysts [175] and HER/OER bifunctional catalysts, [171,176] replacing OER by a more easily oxidative reaction, such as hydrazine, [178,179] urea, [180] and some small organic molecules, [181] can reduce the reaction voltage and improve the energy conversion efficiency for green hydrogen production. [177]…”

Acidic oxygen evolution reaction: Mechanism, catalyst classification, and enhancement strategies

“…[17,18] In particular, the process of OER is even slower in acidic environments. [19,20] Consequently, the inherent high potential of the OER process in PEMWE and the severe corrosion under a strong acidic environment make the long-term operation of the catalyst face huge challenges. [21] The appropriate degree of antiorbital filling and the level of orbital hybridization allows Ir-and Ru-based materials with relatively high acidic OER activity.…”