Post‐synthetic Metalation on the Ionic TiO2 Surface to Enhance Metal‐CO2 Interaction During Photochemical CO2 Reduction

Abstract During the photochemical CO 2 reduction reaction, CO 2 adsorption on the catalyst's surface is a crucial step where the binding mode of the [metal‐CO 2 ] adduct directs the product selectivity and efficiency. Herein, an ionic TiO 2 nanostructure stabilized by polyoxometalates (POM), ([POM] x @TiO 2 ), is prepared and the sodium counter ions present on the surface to balance the POMs’ charge are replaced with copper(II) ions, (Cu x [POM]@TiO 2 ). The microscopic and spectroscopic studies affirm the copper exchange without altering the TiO 2 core and weak coordination of copper (II) ions to the POMs’ surface. Band structure analysis suggests the photo‐harvesting efficiency of the TiO 2 core with the conduction band edge higher than the reduction potential of Cu II/I and multi‐electron CO 2 reduction potentials. Photochemical CO 2 reduction with Cu x [POM]@TiO 2 results in 30 μmol g cat. −1 CO (79 %) and 8 μmol g cat −1 of CH 4 (21 %). Quasi‐in‐situ Raman study provides evidence in support of CO 2 adsorption on the Cu x [POM]@TiO 2 surface. 13 C and D 2 O labeling studies affirm the {Cu‐[CO 2 ] − } adduct formation. Despite the photo‐harvesting ability of Na x [POM]@TiO 2 itself, the poor CO 2 adsorption ability of sodium ions highlights the crucial role of copper ion CO 2 photo‐reduction. Characterization of the {M‐[η 2 ‐CO 2 ] − } species via surface tuning validates the CO 2 activation and photochemical reduction pathway proposed earlier.