S Doping Optimized Intermediate Energetics of FeCoOOh for Enhanced Oxygen Evolution Catalytic Activity

Abstract

Transition metal sulfides have been demonstrated to be more active electrocatalysts than the corresponding (hydr)oxides for oxygen evolution reaction (OER). The nature of active sites, however, remains unclear. Herein, we study whether S could promote the OER activity of FeCoOOH and try to identify the catalytically active centers. Density functional theory suggests that two coordinating S could work synergistically with one adjacent Fe to optimize the electronic states of Co, resulting in decreased binding energy of OH* (ΔEOH) while little changed ΔEOH, and thus significantly lowering the catalytic overpotential. Further experimental studies validate the synergistic effect between S and Fe on tuning the electronic structure and the greatly improved catalytic activity with a small overpotential of 205.4 mV to drive 20 mA cm-2. This study unveils the origin of the high catalytic activity of transition metal sulfides and provides insights into the design of efficient OER electrocatalysts.