Enhanced Electrochemical CO₂ Reduction of Cu@Cu_xO 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@Cu_xO nanoparticles are deposited onto VG-Ar (Cu/VG-Ar) through a galvanostatic pulsed electrodeposition method. These Cu@Cu_xO 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@Cu_xO 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@Cu_xO, thus impeding the excessive oxidation of Cu₂O species deposited on VG-Ar. The defective VG-Ar and stabilized Cu@Cu_xO enhances CO₂ adsorption and promotes electron transfer to the adsorbed CO₂ and intermediates on the catalyst surface, thus improving the overall CO₂ reduction performance.