Water-Mediated ElectroHydrogenation of CO2at Near-Equilibrium Potential by Carbon Nanotubes/Cerium Dioxide Nanohybrids

The combination of multiwalled carbon nanotubes (MWCNTs) with undoped CeO2 nanoparticles (NPs) is effective for the direct electrocatalytic reduction of CO2 to formic acid (FA) at acidic pH (0.1 M HNO3), at overpotential as low as η = -0.02 V (vs RHE) with Faradic efficiency (FE) up to 65%. Ex situ and operando evidence identifies nonstoichiometric Ce4+/3+O2-x reduced sites as essential for the selective CO2 reduction reaction (CO2RR). The MWCNT-mediated electrochemical reduction of the CeO2 NPs offers a definite advantage with respect to the generally adopted thermochemical cycles (800-1500 °C) or deep hydrogenation pretreatments, thus presenting an interesting perspective for the engineering of CeO2 electrocatalysts.