The emergence of synergistic effects in multicomponent systems opens new opportunities to design improved catalysts for the electrochemical CO2 reduction reaction (eCO(2)RR). 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 In203- and In(OH)(3)-supported Ag catalysts, which were characterized with XRD, N-2 sorption, H-2-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 In203, was stable against reduction under eCO(2)RR conditions. As a final step, the selectivity enhancement achieved in Agiln(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 eCO(2)RR and the importance of the structural configuration in multicomponent electrocatalysts. (C) 2015 Elsevier Inc. All rights reserved.