Sulfur-doped graphene anchoring of ultrafine Au25 nanoclusters for electrocatalysis

The biggest challenge of exploring the catalytic properties of under-coordinated nanoclusters is the issue of stability.We demonstrate herein that chemical dopants on sulfur-doped graphene(S-G)can be utilized to stabilize ultrafine(sub-2 nm)Au_(25)(PET)18 clusters to enable stable nitrogen reduction reaction(NRR)without significant structural degradation.The Au_(25)@S-G exhibits an ammonia yield rate of 27.5μgNH_(3)·mgAu^(-1)·h^(-1)at-0.5 V with faradic efficiency of 2.3%.More importantly,the anchored clusters preserve~80%NRR activity after four days of continuous operation,a significant improvement over the 15%remaining ammonia production rate for clusters loaded on undoped graphene tested under the same conditions.Isotope labeling experiments confirmed the ammonia was a direct reaction product of N2 feeding gas instead of other chemical contaminations.Ex-situ X-ray photoelectron spectroscopy and X-ray absorption near-edge spectroscopy of post-reaction catalysts reveal that the sulfur dopant plays a critical role in stabilizing the chemical state and coordination environment of Au atoms in clusters.Further ReaxFF molecular dynamics(RMD)simulation confirmed the strong interaction between Au nanoclusters(NCs)and S-G.This substrate-anchoring process could serve as an effective strategy to study ultrafine nanoclusters’electrocatalytic behavior while minimizing the destruction of the under-coordinated surface motif under harsh electrochemical reaction conditions.