Surface-Bound Formate Oxyanions Destabilize Hydration Layers to Pave OH^– Transport Pathways for Oxygen Evolution

Abstract

Sluggish mass transfer of OH– in alkaline oxygen evolution reaction (OER), resulting from densely packed hydrated layers at the outer Helmholtz plane (OHP), becomes one of the main bottlenecks to improve overall efficiency of electrochemical devices. Herein, we report a hydration-layer-destabilizing route by binding formate oxyanions onto the catalyst surface to form OH– transport pathways, favorable for fast OH– transport and significantly improving OER activity. The electrochemical experiments indicate that surface formate-modified NiCo hydroxide (NiCo–HCOO–) shows increased OH– transfer kinetics, smaller overpotential, and higher turnover frequency (TOF) than that without surface formate modification. The theoretical calculations reveal that surface formate-induced hydrogen-bonding interaction with water molecules could destabilize densely packed hydrated potassium ion layers at the OHP, lowering OH– transport resistance and paving a pathway for OH– transfer. The assembled flow electrolyzer with the NiCo–HCOO– anode could operate at 400 mA cm–2 with only 2.1 V for over 300 h. This study provides an efficient strategy for designing high-activity OER electrocatalysts toward advanced energy conversion devices.