Determining the Effect of Cation (Ti/Zr) Doping in Bismuth Oxide for Electrochemical CO2 Reduction to Formic Acid: A DFT Study

First-principles-based density functional theory (DFT) calculations were used to explore the electrochemical CO2 reduction (ECR) activity of cation-doped Bi2O3. We studied the ECR reaction over pure and doped Bi2O3 (100) surfaces and demonstrated Gibbs free energy diagrams of HCOOH formation via COOH and HCOO pathways. Compared with pure bismuth oxide, doping can alter the rate-determining step and reduce the Gibbs free energy from 2.98 to 0.11 eV. The CO2 reduction activity was found to be most productive on the TiZr–Bi2O3 surface with onset potentials of −0.23 and 0.55 V via the COOH and HCOO pathways, respectively. The probability of CO formation through the ECR reaction was also investigated using Gibbs free energy calculations, and it was found that Bi2O3, Ti–Bi2O3, Zr–Bi2O3, and TiZr–Bi2O3 displayed insufficient ECR activity to produce CO. We also compared the selectivity of the ECR reaction and the hydrogen evolution reaction (HER) to demonstrate the practicality of the electrocatalysts.