Black indium oxide a photothermal CO ₂ hydrogenation catalyst

Abstract

Nanostructured forms of stoichiometric In ₂O ₃ are proving to be efficacious catalysts for the gas-phase hydrogenation of CO ₂. These conversions can be facilitated using either heat or light; however, until now, the limited optical absorption intensity evidenced by the pale-yellow color of In ₂O ₃ has prevented the use of both together. To take advantage of the heat and light content of solar energy, it would be advantageous to make indium oxide black. Herein, we present a synthetic route to tune the color of In ₂O ₃ to pitch black by controlling its degree of non-stoichiometry. Black indium oxide comprises amorphous non-stoichiometric domains of In ₂O _3-x on a core of crystalline stoichiometric In ₂O ₃, and has 100% selectivity towards the hydrogenation of CO ₂ to CO with a turnover frequency of 2.44 s ⁻¹.

Abstract

The utilization of white-colored, wide-bandgap CO ₂ hydrogenation photocatalysts has been hindered by their limited light-harvesting ability. By making stoichiometric white indium oxide non-stoichiometric and black, it is transformed from a highly inactive to a highly active photothermal catalyst.