Electrodeposition of Tin-Based Electrocatalysts with Different Surface Tin Species Distributions for Electrochemical Reduction of CO2 to HCOOH

Tin-based electrocatalysts with different tin species distributions were deposited on the carbon paper substrate by three electrodeposition methods and applied to the selective electroreduction of carbon dioxide to formic acid. Among them, the electrocatalysts prepared using unipolar pulse electrodeposition (UPED) method exhibited the maximum HCOOH faradaic efficiency of 89% at -1.7 V (vs Ag/AgCl) with a current density of 6.0 mA cm(-2) and long-term stability in the 0.1 M CO2- saturated KHCO3 solution. Moreover, the effects of surface oxides species on the performance of tin-based electrocatalysts were systematically investigated via density functional theory (DFT) calculations. The calculation results indicated that both metal tin and tin oxides had excellent catalytic ability for the electrochemical reduction of CO, to HCOOH. Specifically, the tetravalent tin (Sn4+) and divalent tin (Sn2+) species can reduce the overpotential and improve the HCOOH selectivity, respectively. In addition, we found that the tin oxides/metal tin interface can suppress the evolution of H-2, but we observed no obvious effect on the formations of HCOOH and CO. Thus, the actual CO, catalytic electroreduction process should be synergistically controlled by the complex surface oxide species on the tin-based electrocatalysts.