Exploring the linear relationship between potential dynamics and interfacial capacitance: implications for enhancing the turnover frequency in electrochemical water splitting

Abstract

Distinguishing various electrochemical parameters in terms of ‘total’ and ‘intrinsic’ activity has gained vast attention for developing a suitable electrocatalyst toward oxygen evolution reaction (OER) via water electrolysis. Total electrode activity parameters such as overpotential and Tafel slope are essential for practical applications but miss the mark to provide any information regarding the molecular origin of catalyst activity. The intrinsic activity parameters, such as turnover frequency (TOF), could reveal such information. For 3d transition metal-based electrocatalysts, it is calculated via redox peak information. However, this redox peak information deriving the number of electrochemical active sites (ECAS), followed by TOF, is largely influenced by the employed potential dynamics or scan rate. The ECAS is inversely proportional to the potential dynamics for NiO-modified working electrodes. However, different ECAS information with fixed catalyst loading and redox integration is strange and unclear about its origin. In this perspective, we systematically investigated the strange variations of ECAS and TOF values for the very first time. It was found that this variation of ECAS information originated due to the change in the IHP capacitance (C_i) as a function of potential dynamics. The predominant diffusion-controlled (as a result of rapid ion movement) process causes a high C_i value for a high scan rate.