Ni single-atom catalysts for highly efficient electrocatalytic CO2 reduction: hierarchical porous carbon as a support and plasma modification

Electrocatalytic CO2 conversion promises a sustainable alternative to producing CO2-based green chemicals and fuels concomitant with the storage of fluctuating renewable energy. Herein, isolated Ni single-atom catalysts supported by nitrogen-doped hierarchical porous carbon (Ni-SACs/NHPC) were designed with large specific surface area (1115.6 m2 g−1) and abundant micropore structures. The synthesized Ni-SACs/NHPC demonstrated excellent activity (CO faradaic efficiency, FECO > 90%) for CO2 electrocatalytic reduction with a broad reaction potential window from −0.74 to −1.24 V vs. reversible hydrogen electrode (RHE), while flow cell design increased the current density while maintaining high CO faradaic efficiency. Additionally, non-thermal Ar-plasma was used to enhance the adhesion at the electrocatalyst–substrate interface, resulting in a significantly high CO partial current density (16.8 mA cm−2) achieved at −1.04 V vs. RHE with CO faradaic efficiency of ∼96%. Density functional theory (DFT) calculations revealed the highly dispersed single-atom Ni could effectively weaken the Ni–C bond energy and avoid the excessive accumulation of *CO to promote electrocatalytic CO2-to-CO conversion.