A 3D Macroporous Carbon NiCu Single-Atom Catalyst for High Current Density CO2 Electroreduction

Transition metal and nitrogen co-decorated carbon materials are promising platforms for CO₂ electroreduction. A hard-template 2-step pyrolysis method is proposed for the fabrication of highly dispersed Ni and Cu atomic active sites on a 3D macroporous carbon matrix. The pyrrolic N-type Ni−N_x sites serve as dominant active sites toward selective CO₂ electroreduction to CO. The incorporation of Cu alters the distribution of N species and simultaneously optimizes the electronic state and geometric structure of the Ni−N_x moiety, thereby improving its adsorption and activation capacity for CO₂. Moreover, the isolated Cu atomic sites enhance the resistance of corresponding gas-diffusion electrodes against electrolyte flooding. The optimal catalyst 3D NiCu-69 achieves nearly exclusive production of CO with a Faraday efficiency (FE_CO) of 98% at a current density of −700 mA cm⁻² in a CO₂-gas-fed flow-through electrolyzer and delivers a CO production rate of 1363 mol(m²s)⁻¹, which is exceeding most reported electrocatalysts. The FE_CO remained as high as 94% after electrolyzing at a current density of −100 mA cm⁻² for 22 h. 3D NiCu-69 exhibits a favorable performance in both acidic and neutral conditions, with a high FE_CO of ≈90.2% within the current density range of −100 to −500 mA cm⁻².