Dynamic stabilization of nickel-based oxygen evolution electrocatalysts in the presence of chloride ions using a phosphate additive

Abstract

Achieving a highly stable and selective oxygen evolution reaction (OER) in the presence of chloride ions (Cl⁻) is imperative for the future practical application of seawater splitting technology. This approach can streamline complex purification processes and avoid competition with the demand for drinking water. In this report, we present novel electrolyte engineering through mixed buffers – specifically, the utilization of borate/phosphate at a non-extreme pH of 9.2 – to achieve stable OER. Our findings demonstrate that borate serves as the primary buffer, maintaining localized pH stability, while the addition of phosphate acts as the main stabilizer for the Ni component. Electrochemical analysis and ex situ/operando spectroscopic characterization reveal that phosphate selectively forms a stabilized Ni complex. This complex effectively suppresses the corrosion and dissolution of Ni, resulting in an extended operational lifetime without compromising OER performance, even in the presence of Cl⁻. Furthermore, electrochemical measurements conducted with various redox probes indicate the formation of a passive Ni layer which leads to improved stability rather than the charge repulsion effect proposed in an alkaline pH environment. This study underscores the significant potential arising from the simultaneous advancement of both electrocatalysts and electrolytes.