A New Strategy for Accelerating Dynamic Proton Transfer of Electrochemical CO2 Reduction at High Current Densities

Developing single-atom electrocatalysts with high activity and superior selectivity at a wide potential window for CO2 reduction reaction (CO2RR) still remains a great challenge. Herein, a porous Ni-N-C catalyst containing atomically dispersed Ni-N-4 sites and nanostructured zirconium oxide (ZrO2@Ni-NC) synthesized via a post-synthetic coordination coupling carbonization strategy is reported. The as-prepared ZrO2@Ni-NC exhibits an initial potential of -0.3 V, maximum CO Faradaic efficiency (F.E.) of 98.6% +/- 1.3, and a low Tafel slope of 71.7 mV dec(-1) in electrochemical CO2RR. In particular, a wide potential window from -0.7 to -1.4 V with CO F.E. of above 90% on ZrO2@Ni-NC far exceeds those of recently developed state-of-the-art CO2RR electrocatalysts based on Ni-N moieties anchored carbon. In a flow cell, ZrO2@Ni-NC delivers a current density of 200 mA cm(-2) with a superior CO selectivity of 96.8% at -1.58 V in a practical scale. A series of designed experiments and structural analyses identify that the isolated Ni-N-4 species act as real active sites to drive the CO2RR reaction and that the nanostructured ZrO2 largely accelerates the protonation process of *CO2- to *COOH intermediate, thus significantly reducing the energy barrier of this rate-determining step and boosting whole catalytic performance.

Automated summary

This study reports a porous Ni-N-C catalyst, ZrO2@Ni-NC, synthesized using a post-synthetic coordination coupling carbonization strategy, which shows high activity and selectivity in CO2RR. The isolated Ni-N-4 species are identified as the real active sites, while the nanostructured ZrO2 accelerates the protonation process, reducing the energy barrier and enhancing catalytic performance.