UC Berkeley

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) Au25(PET)18 clusters to enable stable nitrogen reduction reaction (NRR) without significant structural degradation. The Au25@S-G exhibits an ammonia yield rate of 27.5μgNH3⋅mgAu−1⋅h−1$$27.5\,{\rm{\mu }}{{\rm{g}}_{{\rm{N}}{{\rm{H}}_3}}} \cdot {\rm{m}}{{\rm{g}}_{{\rm{Au}}}}^{ - 1} \cdot {{\rm{h}}^{ - 1}}$$ 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.