A comparative differential electrochemical mass spectrometry (DEMS) study towards the CO2 reduction on Pd, Cu, and Sn -based electrocatalyst

Abstract The electrocatalytic reduction of CO2 (CO2RR) on carbon-supported palladium-based (Pd/C, Pd-Cu2O/C, Pd-SnO2/C) and non-precious metal oxides (Cu2O/C and SnOX/C) was investigated through physicochemical and electrochemical measurements. The formation of a solid solution in the bimetallic Pd-based compounds was confirmed by a contraction of the Pd unit cell volume, measurements of the TEM interplanar distance, and cyclic voltammetry characterization. Pd-based electrocatalysts presented smaller crystallite sizes (9 nm–18 nm) than Cu2O/C and SnOX/C (62 nm and 82 nm, respectively). Pd/C, Pd-Cu2O/C, and Pd-SnO2/C showed the highest electrochemical activity to perform the CO2RR due to a lower overpotential value compared to Cu2O/C and SnOX/C. The Tafel plots during CO2RR revealed a small slope in the region of lower overpotentials for the Pd-based electrocatalysts (less than 52 mV dec-1), which indicates a better kinetic compared to Cu2O/C and SnOX/C (165 and 193 mV dec-1, respectively). SnOX presented the highest selectivity toward HER instead of CO2 reduction. DEMS measurements allowed the determination of the selectivity for the electrocatalysts to produce specific CO2 reaction products. Pd-based materials are suitable to perform the CO2RR since bimetallic electrocatalyst (Pd-Cu2O/C and Pd-SnO2/C) generates CO, formic acid, and CH4 as reaction products. At the same time, Pd/C produced CO and H2. On the other hand, Cu2O presented lower electrochemical activity than Pd-based materials, with CO as the main reaction product. The low overpotential and the faradic vs. ionic current profiles showed that SnOX/C could be classified as a promising material for hydrogen production in the presence of CO2.