Evolution of bismuth oxide catalysts during electrochemical CO2 reduction

Bismuth is a promising electrocatalyst for active and selective CO 2 electroreduction to formate.Herein, we investigated the evolution of various Bi-based catalysts (β-Bi 2 O 3 nanoparticles, BiOBr nanosheets, Bi 2 O 2 CO 3 nanosheets, and large α-Bi 2 O 3 and β-Bi 2 O 3 particles) during reaction.Apart from the α-Bi 2 O 3 particles, all the electrocatalysts reach the same Faradaic efficiency (93 ± 2%) and current density during potentiostatic operation, and their morphology changed to nanosheets.This change in morphology can be linked to the formation of Bi 2 O 2 CO 3 layers, which are prone to reduction to metallic Bi.The final phase and morphology depend on the size of the Bi precursor.Quasi-in situ XPS suggests that a Bi 2 O 2 CO 3 contribution persists on the surface even for the reduced catalysts.At a current density of 200 mA/cm 2 , all catalysts reduce to metallic Bi without forming a welldefined sheet morphology.Only for the Bi 2 O 3 nanoparticles can a FE above 90% be maintained.