Formation of lattice-dislocated bismuth nanowires on copper foam for enhanced electrocatalytic CO2 reduction at low overpotential

Metallic bismuth (Bi) is an electrocatalyst that promotes CO2 reduction to formate. However, a substantial overpotential is needed to achieve a high formate faradaic efficiency along with a large catalytic current density, and this hinders its practical application. In this work, a facile strategy has been developed to obtain lattice-dislocated Bi nanowires on copper foam (Cu foam@BiNW) through in situ electrochemical transformation of an electroless plated Bi film on copper foam after thermal treatment in air. The Cu foam@BiNW is found to be a highly active electrocatalyst for CO2 reduction to formate at a low overpotential, reaching a faradaic efficiency for formate (FEformate) of 95% and a formate partial current density of approximate to 15 mA cm(-2) at -0.69 V vs. RHE. High FEformate values of above 93% were also maintained over a potential range from -0.69 V to -0.99 V vs. RHE. A Fourier transformed ac voltammetric study revealed that unlike other Bi materials, the rate determining step for CO2 reduction on the Cu foam@BiNW electrode is the reduction of protonated CO2- radical anion, which indicates the presence of new catalytic active sites on the BiNWs. The high CO2 reduction activity of the Cu foam@BiNW electrode is attributed to the high intrinsic activity arising from the presence of crystal lattice dislocations on the twisted Bi nanowires and the large catalytic surface area associated with the porous structure. This work demonstrates the use of crystal defect engineering to improve the efficiency of electrocatalytic CO2 reduction on Bi metal.