Regulating CO2/H2O ratio of Ni-N-C single-atom catalysts through hydrophobicity engineering for acidic CO2 electroreduction

Abstract

Acidic electrolysis of CO₂ has been considered as a promising route to inhibit carbonate formation, and enhances CO₂ utilization efficiency. Suppressing hydrogen evolution reaction (HER) in the excessive H⁺ environment remains a considerable challenge, however, necessitating concerted efforts toward advanced catalysts and electrode designs to facilitate the CO₂ diffusion. Herein, a Ni-N-C catalyst with a hydrophobic property (hydrophobic Ni-N-C) was synthesized as electrocatalyst for CO₂ reduction, which showed a high faradaic efficiency of 98.9 % towards CO at 200 mA cm⁻² compared to the hydrophilic Ni-N-C catalyst (77.8 %). Remarkably, when integrated into a gas diffusion electrode (GDE) in a flow cell, the hydrophobic Ni-N-C was capable of delivering carbon utilization up to 82.8 %, surpassing all of the other CO₂ reduction electrocatalysts in alkaline electrolysis in the literature. Such outstanding performance could be contributed to the hydrophobic Ni-N-C with multiple three-phase interface, which provided superior gas-phase transfer channels for CO₂ supply and impeded the H⁺-enriched on the catalyst surface, thus successfully suppressing the HER during the acidic CO₂ electrolysis. This work may inspire further optimization of the wettability of catalyst electrode for electrochemical CO₂ reduction and other gas consumption electrosynthesis in acidic electrolysis.