Insight into the Mechanism for Catalytic Activity of the Oxygen/Hydrogen Evolution Reaction on a Dual-Site Catalyst

The dual-site catalysts consisting of two adjacent single-atom sites on graphene have exhibited promising catalytic activity of the electrochemical oxygen/ hydrogen evolution reaction (OER/HER). However, the electrochemical mechanisms of the OER/HER on dual-site catalysts have still been ambiguous. In this work, we employed density functional theory calculations to study the catalytic activity of the OER/HER with a O-O (H-H) direct coupling mechanism on dual-site catalysts. Specifically, these element steps should be classified into two categories: a step evolving proton-coupled electron transfer (PCET step) that needs to be driven by electrode potential and a step without PCET (non-PCET step) that occurs naturally under mild conditions. Our calculated results show that both the maximal free energy change (Delta GMax) contributed by the PCET step and the activity barrier (Ea) of the non-PCET step must be examined to evaluate the catalytic activity of the OER/HER on the dual site. Importantly, it is a basically inevitable negative relationship between Delta GMax and Ea, which would play a critical role in guiding the rational design of effective dual-site catalysts for electrochemical reactions.