Enhanced Electrochemical CO2 Reduction of Cu@CuxO Nanoparticles Decorated on 3D Vertical Graphene with Intrinsic sp3-type Defect

Defective 3D vertical graphene (VG) with a relatively large surface area, high defect density, and increased surface electrons is synthesized via a scalable plasma enhanced chemical vapor deposition method, together with a postsynthesis Ar-plasma treatment (VG-Ar). Subsequently, Cu@CuxO nanoparticles are deposited onto VG-Ar (Cu/VG-Ar) through a galvanostatic pulsed electrodeposition method. These Cu@CuxO nanocatalyst systems exhibit a superior electrochemical CO2 reduction performance when compared to Cu-based catalysts supported on commercial graphene paper or pristine VG without postsynthesis Ar-plasma treatment. The Cu/VG-Ar achieves the highest CO2 reduction Faradaic efficiency of 60.6% (83.5% of which are attributed to liquid products, i.e., formate, ethanol, and n-propanol) with a 5.6 mA cm(-2) partial current density at -1.2 V versus reversible hydrogen electrode (RHE). The improved CO2 reduction performance of Cu/VG-Ar originates from the well-dispersed Cu@CuxO nanoparticles deposited on the defective VG-Ar. The intrinsic carbon defects on VG-Ar can suppress the hydrogen evolution reaction as well as tune the interaction between VG and Cu@CuxO, thus impeding the excessive oxidation of Cu2O species deposited on VG-Ar. The defective VG-Ar and stabilized Cu@CuxO enhances CO2 adsorption and promotes electron transfer to the adsorbed CO2 and intermediates on the catalyst surface, thus improving the overall CO2 reduction performance.