Synergistic effects in silver-indium electrocatalysts for carbon dioxide reduction

- Bulk Ag-In, and In2O3- and In(OH)3-supported Ag electrocatalysts were studied.
- Near-surface In enrichment in bulk Ag-In alloys results in a similar behavior to In.
- In(OH)3 and In2O3 supports enhance the selectivity for CO at low overpotential.
- In(OH)3 is stable under eCO2RR reactions, while In2O3 suffers reduction.
- Ag on a P25 TiO2-In(OH)3 support shows parallel gains in activity and selectivity.

The emergence of synergistic effects in multicomponent systems opens new opportunities to design improved catalysts for the electrochemical CO2 reduction reaction (eCO2RR). Targeting the selective formation of CO, we have evaluated a comprehensive set of silver-indium electrocatalysts with different architectures, ranging from bulk intermetallic compounds to Ag nanoparticles supported on In2O3 and In(OH)3. This approach allowed the design of a supported electrocatalyst with maximized performance. Despite very different bulk compositions, XPS analyses on Ag-In alloy electrodes revealed a near-surface indium enrichment, leading to a comparatively poor electrocatalytic performance. In contrast, the presence of oxidized indium deposits on the surface of bulk silver had a positive effect on the selectivity for CO at moderate overpotential. Based on these findings, we studied the interactions between silver and oxidic indium phases by preparing sets of In2O3- and In(OH)3-supported Ag catalysts, which were characterized with XRD, N2 sorption, H2-TPR, CO2-TPD, STEM and EDX. With respect to the pristine supports and to similarly prepared Ag catalysts on carbon black, these nanostructured systems exhibited an enhanced current efficiency for CO at moderate overpotential, evidencing a synergistic effect between the metal nanoparticles and the supports. This effect was particularly marked at higher Ag loadings and with In(OH)3 as support which, unlike In2O3, was stable against reduction under eCO2RR conditions. As a final step, the selectivity enhancement achieved in Ag/In(OH)3 was combined with the known activity-promoting role of P25 TiO2 by depositing Ag on a composite support. The Ag/In(OH)3-TiO2 catalyst showed concurrent gains in selectivity and activity for CO. The findings highlight the potential of stable metal (hydr)oxide supports to act as promoters in the eCO2RR and the importance of the structural configuration in multicomponent electrocatalysts.

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