Recent Advances in the Development of Water Oxidation Electrocatalysts at Mild pH

Abstract

Developing anodic oxygen evolution reaction (OER) electrocatalysts with high catalytic activities is of great importance for effective water splitting. Compared with the water‐oxidation electrocatalysts that are commonly utilized in alkaline conditions, the ones operating efficiently under neutral or near neutral conditions are more environmentally friendly with less corrosion issues. This review starts with a brief introduction of OER, the importance of OER in mild‐pH media, as well as the fundamentals and performance parameters of OER electrocatalysts. Then, recent progress of the rational design of electrocatalysts for OER in mild‐pH conditions is discussed. The chemical structures or components, synthetic approaches, and catalytic performances of the OER catalysts will be reviewed. Some interesting insights into the catalytic mechanism are also included and discussed. It concludes with a brief outlook on the possible remaining challenges and future trends of neutral or near‐neutral OER electrocatalysts. It hopefully provides the readers with a distinct perspective of the history, present, and future of OER electrocatalysts at mild conditions.

Fe‐Doped Ni3S2 Nanowires with Surface‐Restricted Oxidation Toward High‐Current‐Density Overall Water Splitting

“…[58] The active NiOOH phase exhibits better performance and greater stability, which can obviously prevent the inactivation due to the newly established structure. [33] The in situ formed abundant solid-solid interfaces promote the concurrent chemisorption for both oxygen and hydrogen-containing intermediates, thus leading to outstanding bifunctional OER and HER activity. [66] Commonly, the intrinsic catalytic activity of electrocatalyst can be illustrated with the current standardized to ECSA.…”

Effect of the Solvent Ratio (Ethylene Glycol/Water) on the Preparation of an Iron Sulfide Electrocatalyst and Its Activity towards Overall Water Splitting

“…The Tafel slopes of all the materials were found to be lower in magnitude compared to Pt/C, indicating their superiority as HER electrocatalyst. The Tafel slope is a parameter for catalytic activity evaluation which can be expressed as “how fast the current increased with the increase of overpotential” . Although Pt/C achieved benchmarking current density at lower overpotential, it required greater potential to increase its current density by ten times.…”

Value‐Added Formate Production from Selective Methanol Oxidation as Anodic Reaction to Enhance Electrochemical Hydrogen Cogeneration

“…The OER is a four‐electron oxidation process (4 OH − →O 2 +2 H 2 O+4 e − ) that requires a high overpotential, which leads to a greater energy input than that for the HER to afford the same current density . Besides, the product O 2 is of limited value, and the formation of explosive H 2 /O 2 mixtures as a result of gas crossover in the water electrolyzer might lead to safety issues . Therefore, the OER is considered as the bottleneck that restricts the efficiency of H 2 production in overall water splitting.…”

“…Much research effort has been devoted to overcome these problems . Apart from the development of efficient OER electrocatalysts, an alternative strategy is to replace the OER with other oxidation reactions that are more thermodynamically favorable and economically attractive. Compared with OER, the oxidation of more readily oxidizable species presents a significant reduction of the overall potential required to produce H 2 .…”