Simultaneous pseudocapacitive oxidation and oxygen evolution reaction: reciprocity or incompatibility?

Abstract

With the increasing demand for energy conversion and storage and importance of research on multifunctional materials in recent years, more and more studies focus on pseudocapacitive energy storage (PES) and electrocatalytic oxygen evolution reaction (OER). As is well known, optimizing materials could reduce the overpotential required for catalyzing OER, which brings the starting point of OER reaction closer to another type of oxidation reaction in the system—pseudocapacitive oxidation reaction (POR)—or even results in the potential range overlap of these two types of oxidation reactions, especially in alkaline aqueous electrolyte systems. The OER potential is low enough that when the above situation occurs, the role of active sites on the material and how they affect the final performance has long been overlooked. We designed and synthesized a novel FeOOH/high-entropy-LDH to deeply explore these questions. We attempt to explain the reasons for the potential overlap and its implications. Furthermore, the function transformation of active sites is discovered. Briefly, it is a challenge for materials with high OER catalytic activity to exhibit excellent PES performance. Recommendations for the activation stages and the correct selection of potentials (windows) are proposed for pseudocapacitance and OER tests of such material. This work aims to alert scientists to the complexity of such material research, and hopefully, through joint efforts to obtain recognized and feasible standards for material design and testing, pave the way for subsequent research in this field.