Identifying the forefront of electrocatalytic oxygen evolution reaction: Electronic double layer

[Display omitted] •Opposite effect of scan rate on oxygen evolution for IrOx and NiCo2O3.•Catalyst performance dependence on interfacial capacitance and reconstruction.•Establishing relationship between oxygen evolution and electronic double layer. Developing a fundamental understanding of oxygen evolution reactions (OER) is essential to advancing state-of-the-art energy conversion and storage technologies such as electrolysis. However, it is extremely difficult to directly observe the forefront of the reaction interface, i.e. the electronic double layer (EDL). Herein, electrochemical diagnostic tools are developed to study interfacial behaviors during alkaline OER. Using the traditional linear sweep voltammetry method, we observe that increasing the potential scan rate improves the performance of amorphous Ir oxides, while, for cubic NiCo2O3 with higher mass-transport resistance, the effect of scan rate is reversed. The results further confirm that the EDL capacitive and pseudocapacitive processes have a significant impact on electrocatalytic OER. Moreover, continuous EDL reconstruction is observed from double-potential-step chronoamperometry. This reconstruction, mainly caused by chemical phase modification, has a positive influence on OER performance for the Ni-Co oxide, but a negative influence for the Ir oxide. By studying EDL effects, our findings open up new strategies to design promising catalysts and elucidate OER mechanisms.