Electrochemical Preparation of Crystalline Hydrous Iridium Oxide and Its Use in Oxygen Evolution Catalysis

Recent achievements in noble metal-based oxide electrocatalysts for water splitting

The search for sustainable energy sources has accelerated the exploration of water decomposition as a clean H2 production method. Among the methods proposed, H2 production via water electrolysis has garnered considerable attention. However, the process of H2 production from water electrolysis is severely limited by the slow kinetics of the anodic oxygen evolution reaction and large intrinsic overpotentials at the anode; therefore, suitable catalysts need to be found to accelerate the reaction rate. Noble metal-based oxide electrocatalysts retain the advantages of abundant active sites, high electrical conductivity of noble metals, and low cost, which make them promising electrocatalysts; however, they suffer from the challenge of an imbalance between catalytic activity and stability. This review presents recent research progress in noble metals and their oxides as electrocatalysts. In this review, two half-reactions (the hydrogen evolution reaction and the oxygen evolution reaction) of water electrolysis are described. Recently reported methods for the synthesis of noble metal-based oxide electrocatalysts, improvement strategies, and sources of enhanced activity and stability for these types of catalysts are presented. Finally, the challenges and future perspectives in the field are summarised. This review is expected to help improve the understanding of noble metal-based oxide electrocatalysts.

Ru/Ir-Based Electrocatalysts for Oxygen Evolution Reaction in Acidic Conditions: From Mechanisms, Optimizations to Challenges

The generation of green hydrogen by water splitting is identified as a key strategic energy technology, and proton exchange membrane water electrolysis (PEMWE) is one of the desirable technologies for converting renewable energy sources into hydrogen. However, the harsh anode environment of PEMWE and the oxygen evolution reaction (OER) involving four-electron transfer result in a large overpotential, which limits the overall efficiency of hydrogen production, and thus efficient electrocatalysts are needed to overcome the high overpotential and slow kinetic process. In recent years, noble metal-based electrocatalysts (e.g., Ru/Ir-based metal/oxide electrocatalysts) have received much attention due to their unique catalytic properties, and have already become the dominant electrocatalysts for the acidic OER process and are applied in commercial PEMWE devices. However, these noble metal-based electrocatalysts still face the thorny problem of conflicting performance and cost. In this review, first, noble metal Ru/Ir-based OER electrocatalysts are briefly classified according to their forms of existence, and the OER catalytic mechanisms are outlined. Then, the focus is on summarizing the improvement strategies of Ru/Ir-based OER electrocatalysts with respect to their activity and stability over recent years. Finally, the challenges and development prospects of noble metal-based OER electrocatalysts are discussed.