Online Electrochemistry–Mass Spectrometry Evaluation of the Acidic Oxygen Evolution Reaction at Supported Catalysts

Electrocatalytic current density and especially onset potential or overpotential, as the key parameters for evaluating electrocatalytic performance, are problematic metrics when electron-consuming side processes can take place. This includes the widely studied electrocatalytic oxygen evolution reaction (OER), which is often accompanied by anodic currents associated with the activation or degradation of the catalyst and/or support. Herein, we use an online chip-based electrochemistry–mass spectrometry (chip EC-MS) system to decouple the OER from the complex electrochemical reactions for a graphene-supported ruthenium (Ru) catalyst with high OER activity in an acidic medium. In this manner, we can quantitatively evaluate the current contribution from the OER during cyclic voltammetry (CV) tests and chronopotentiometry (CP) tests and are thus enabled to realize the accurate measurement of the onset potential and Faradaic efficiency (FE) toward the OER. The OER process, including the activation, steady-state, and degradation processes, as well as the side reaction, is also studied using such a chip EC-MS technique. This work is of practical importance to clarify some critical issues remaining in the study of OER electrocatalysis.