Single-Ni Sites Embedded in Multilayer Nitrogen-Doped Graphene Derived from Amino-Functionalized MOF for Highly Selective CO2 Electroreduction

Abstract

CO₂ electroreduction using renewable electricity is a promising pathway for CO₂ utilization. However, the development of highly active and selective catalysts for CO₂ reduction still poses significant challenges. Here, we report the use of an amino-functionalized metal–organic framework as a precursor to derive Ni-N-C active sites embedded in multilayer graphene shells as the dominant active sites for CO₂ electroreduction. During the process of high-temperature annealing and acid washing, the −NH₂ groups in the MOF precursors exhibit a greater tendency to generate structural defects on graphene layers and derive abundant Ni-N-C sites by Ni migration. Aggregated Ni particles, which incline to catalyze the competitive hydrogen evolution reaction, are successfully removed during the posttreatment, exposing numerous Ni-N-C active sites to facilitate the CO₂ electroreduction. The resulting catalyst displays excellent electrochemical CO₂ reduction activity to CO with Faradaic efficiencies above 90% in a wide range of potentials from −0.6 to −1.2 V versus reversible hydrogen electrode. The maximum Faradaic efficiency of 97% can be achieved at a low overpotential of 0.79 V with a CO partial current density of 27.2 mA cm–², which is among the best performance of Ni-based electrocatalysts reported so far. This work provides useful insights into the tuning of the metal sites by the coordination environment of MOFs toward the fabrication of highly active and selective electrocatalysts for CO₂ reduction.