Effects of Electrochemical Conditioning on Nickel-Based Oxygen Evolution Electrocatalysts

Electrochemical conditioning via chronopotentiom-etry (CP) and cyclic voltammetry (CV) is essential for the activation of oxygen evolution reaction (OER) electrocatalysts. While many reports have activated OER electrocatalysts using either CP or CV, the inherent differences between these two electrochemical conditioning methods for the activation of OER electrocatalytic materials have yet to be explored. Here, we investigate the effects of CP and CV electrochemical conditioning on a Ni-based OER precatalyst and substrate in Fe-purified and Fe-unpurified KOH electrolytes by employing (i) Ni foil, (ii) NiSe precatalyst films with different thicknesses on the fluorine-doped tin oxide glass substrate, and (iii) NiSe precatalyst films on Ni foil substrates. It was found that CV electrochemical conditioning can result in a higher degree of in situ oxidation and Fe incorporation for Ni-based precatalysts and substrates compared to CP electrochemical conditioning. In turn, this brought about different material properties (e.g., in situ oxidized layer thickness, composition, crystallinity, and morphology) and electrochemical characteristics (e.g., active surface area, electron transport limitation, and intrinsic activity) of Ni-based electrocatalysts, thereby not only affecting their OER activity but also complicating the interpretation of the origin of OER activity. This study identifies the distinct effects of CP and CV electrochemical conditioning on Ni-based OER electrocatalysts and provides insight into the choice of the electrochemical conditioning method to better investigate OER electrocatalysts.