Oxygen Evolution Reaction and Its Competition with Chlorine Oxidation Reaction on Electrode/Electrolyte Interfaces

Nickel (Ni)-based electrocatalysts show excellent performance for the oxygen evolution reaction (OER) in alkaline electrolytes. However, their active site structure evolution and degradation mechanisms have remained debated over the past decade, especially across a wide range of current densities and applied potentials. In direct seawater splitting, competition from the chlorine oxidation reaction (COR) further complicates mechanistic and kinetic studies of the OER. Additionally, the degradation mechanism of active sites in Ni-based electrocatalysts under COR competition conditions remains unrevealed. This work uses rotating ring and disk electrode (RRDE) and in situ Raman spectroscopy techniques to examine electrode/electrolyte interfaces during OER of various electrodes across a wide interfacial pH range, uncovering mass transfer, kinetics, and interface behavior during the competition between OER and COR. Main findings include the following: (1) In an alkaline electrolyte, mass transfer of OH– significantly affects OER performance. (2) The coverage of NiOOH, the active intermediates for OH– oxidation on Ni, is affected by both applied potential and bulk electrolyte pH. (3) Cl– in the electrolyte attacks NiOOH, reducing its coverage to zero and diminishing OER performance and stability, especially when the electrode/electrolyte interface becomes neutral/acidic. We believe this work will enhance understanding of electrode/electrolyte interfaces during OER and improve interface design for both water splitting and direct seawater splitting.