Unsaturated edge-anchored Ni single atoms on porous microwave exfoliated graphene oxide for electrochemical CO<inf>2</inf>

Abstract

© 2018 Elsevier B.V. Supported single atom catalysts (SACs), emerging as a new class of catalytic materials, have been attracting increasing interests. Here we developed a Ni SAC on microwave exfoliated graphene oxide (Ni-N-MEGO) to achieve single atom loading of ~6.9 wt%, significantly higher than previously reported SACs. The atomically dispersed Ni atoms, stabilized by coordination with nitrogen, were found to be predominantly anchored along the edges of nanopores (< 6 nm) using a combination of X-ray absorption spectroscopy (XAS) and aberration-corrected scanning transmission electron microscopy (AC-STEM). The Ni-N-MEGO exhibits an onset overpotential of 0.18 V, and a current density of 53.6 mA mg-1 at overpotential of 0.59 V for CO2 reduction reaction (CO2RR), representing one of the best non-precious metal SACs reported so far in the literature. Density functional theory (DFT) calculations suggest that the electrochemical CO2-to-CO conversion occurs more readily on the edge-anchored unsaturated nitrogen coordinated Ni single atoms that lead to enhanced activity toward CO2RR.