The electrocatalytic reduction of CO₂ to value-added products with utilizing the renewable electricity is a promising alternative for using fossil fuels and an attractive solution for mitigating the constant rise in atmospheric CO₂ emissions.

Among all kinds of metal catalysts, copper is the only one that has capability to produce considerable amounts of hydrocarbons and alcohols at a moment. However, the selectivity control towards products is a main challenge for using a copper as a catalyst.

In recent studies, oxide-derived copper has emerged as an efficient electrocatalyst candidate for better C-C coupling ability and lower overpotentials. Although the reason for this enhanced ability is still under debate, the residual oxygen or Cu⁺ in nanostructured subsurface region has been proposed as a critical factor to improve selectivity towards C2 products and in-situ analyses examined this suggestion.

Here, we synthesized copper nanoparticles (NPs) directly grown on carbon support by wet-chemically facile one-pot method. We prepared two kinds of Cu NPs with different morphology and chemical state by controlling the synthesis temperature. The one is Cu₂O with cube shape and the other is Cu/CuO_x with sphere shape, which are confirmed by TEM, XPS and Cu K-edge XANES analysis. The electrocatalytic CO₂ reduction reaction (CO2 RR) was conducted in 0.1 M KHCO₃ aqueous solution and the effect of initial chemical state of copper on C₂H₄ selectivity was investigated. We observed that C₂H₄ selectivity is highly improved when the initial chemical state of copper nanoparticles is Cu₂O compared to Cu/CuO_x with the faradaic efficiency is 55 % and 20 %, respectively at -1.05 V (vs. RHE). For the verification of the reason for improved activity, we conducted XANES experiment and TEM analysis in the middle of CO2 RR. We conclude that the subsurface oxygen enhance catalytic activity and stability for ethylene production.

Figure 1. TEM images of (A) cubic Cu₂O/C and (B) sphere Cu/CuO_x/C