Ultralow Overpotential of Hydrogen Evolution Reaction using Fe‐Doped Defective Graphene: A Density Functional Study

Abstract We report great promises of single (transition metal) atom catalysts (SACs) anchored to single‐ and double‐ vacancy sites of the defective graphene structures for hydrogen evolution reaction (HER). Among 120 candidates with all 3d, 4d, and 5d‐block transition metals considered, the inexpensive Fe‐based SAC catalyst shows a theoretical overpotential of 5 mV, the lowest value reported to date theoretically or experimentally. With the help of various electronic structural analysis, we reveal that the key to the observed superior HER activity of Fe‐based SAC is the enhanced ionicity of bonding between hydrogen and the corresponding SAC and the lack of ensemble effect that causes the *H binding weaker to be nearly at the top of the HER activity volcano.