2.3 Copper based
Copper is one of the few metals that can efficiently convert CO2 to hydrocarbons such as methane (CH4) and ethylene (C2H4), owing to the moderate adsorption energy of the *CO intermediate.[38,60-61] Because the electrocatalytic performance of Cu electrodes is usually determined by the Cu crystal facets, shape control of Cu nanoparticles (NPs) has been widely studied for desirable CO2RR selectivity.[62] Zhang et al. synthesized nanodefective Cu nanosheets using an electrochemical reduction method.[63] Cu nanosheet electrocatalysts with defects exhibited a better total current density, maximum ethylene FE of 83.2 % at −1.18 V vs. RHE without CO generation, and partial current density of up to 66.5 mA cm–2 at −1.48 V vs. RHE, which is much higher than those of its counterparts (Figure 2(F)–(H)). Such nanodefective structures promote ethylene production by enhancing the adsorption of intermediates and hydroxyl ions on the electrocatalyst.
Recently, simple approaches have been reported for fabricating ultrathin CuO nanoplate arrays through anodic oxidation for the conversion of CO2 to C2H4.[64]Benefitting from stable Cu/Cu2O interfaces, the catalyst exhibits remarkable C2H4 FE of 84.5 %, partial current densities of 92.5 mA cm−2 at −0.81 V vs. RHE, and high stability for 55 h. Yang et al. prepared one-dimensional ultrathin 5-fold twinned copper NWs for conversion of CO2 to methane.[65] Corresponding SEM and transmission electron microscopy (TEM) images revealed ultrathin NW structures with diameters of ~20 nm. Owing to its abundant edge sites, Cu NWs showed outstanding CH4selectivity with a maximum FECH4 up to 55 % at −1.25 V vs. RHE and selectivity.