The electrocatalytic reduction of CO2 with In is severely hindered by its complex multi-electron reaction pathway for C2 products and the high reaction overpotential. Polyoxometalates (POM) with the ability to transport and store electrons and protons have great potential to overcome these limitations. The Keggin-type POM [SiW9V3O40](7-) (SiW9V3) and metal indium were selected to build the electrocatalytic CO2 reduction system. It overcomed the low selectivity limitation of In for C2 products, converting CO2 to acetic acid over formic acid with an onset potential of -1.0 V vs. Ag/AgCl. The Faradaic efficiency for the production of acetate was up to 96.5% at -1.15 V vs. Ag/AgCl (-0.71 V vs. RHE) with nearly 96% selectivity. The electrochemical experimental studies and XPS spectra reveal that the V-center in SiW9V3 primarily facilitates the conversion of CO2 into acetate and formate. (C) 2019 Elsevier Inc. All rights reserved.