Simultaneous Formation of CO and H₂O₂ from CO₂ and H₂O with a Ag–MnO_x/CaTiO₃ Photocatalyst

Carbon monoxide (CO) is an important feedstock for the chemical industry, and hydrogen peroxide (H2O2) is also an important chemical with versatile applications. Here, a photocatalytic system was discovered for the simultaneous production of CO and H2O2 from CO2 and H2O with both high activity and selectivity without any externally applied voltage and any consumption of chemical compounds, which was promoted by using a calcium titanate (CaTiO3) photocatalyst modified with a silver–manganese oxide (Ag–MnOx) dual cocatalyst. Although a Ag/CaTiO3(CTO) photocatalyst was reported to reduce CO2 with water to form CO and O2, the coexistence of MnOx species with silver nanoparticles (NPs) not only improved the CO formation rate more than 2 times with a selectivity of 76% but also changed the selectivity of the oxidative reaction and forms H2O2 instead of O2 with a high selectivity of 99%. The Ag NPs promoted the CO2 reduction to CO by the photoexcited electrons, and the Mn(III) oxide species deposited on the CaTiO3 surface contributed to the water oxidation to H2O2 by the positive holes in the aid of HCO3– as a reaction mediator. The produced CO is easily separated from the aqueous solution to the gas phase, and the H2O2 is stably stored in the aqueous HCO3– solution. This photocatalytic system can utilize the stable and ubiquitous molecules (CO2 and H2O) to produce reactive and useful molecules (CO and H2O2), concurrently, meaning that it can convert photoenergy to storable chemical energy to increase sustainability.