Mixed atomic-scale electronic configuration as a strategy to avoid cocatalyst utilization in photocatalysis by high-entropy oxides

TL;DR

This study demonstrates that high-entropy oxides with mixed electronic configurations can serve as effective photocatalysts for CO2 conversion and water splitting, eliminating the need for noble metal cocatalysts.

Contribution

It introduces a novel design strategy using heterogeneous electronic configurations in high-entropy oxides to replace cocatalysts in photocatalysis.

Findings

Successfully synthesized a new high-entropy oxide with mixed valence states.

The oxide catalyzed CO2 conversion and water splitting without cocatalysts.

Exhibited low bandgap and reduced electron-hole recombination.

Abstract

To enhance the activity of photocatalysts for hydrogen production and CO2 conversion, noble metal cocatalysts as electron traps and/or acceptors such as platinum or gold are usually utilized. This study hypothesizes that mixing elements with heterogeneous electronic configurations and diverse electronegativities can provide both acceptor and donor sites of electrons to avoid using cocatalysts. This hypothesis was examined in high-entropy oxides (HEOs), which show high flexibility for atomic-scale compositional changes by keeping their single-or dual-phase structure. A new highentropy oxide was designed and synthesized by mixing elements with an empty d orbital (titanium, zirconium, niobium and tantalum) and a fully occupied d orbital (gallium). The oxide, synthesized by high-pressure torsion followed by calcination, had two phases (88 wt% orthorhombic (Pbcn) and 12 wt% monoclinic (I2/m)) with an overall composition of TiZrNbTaGaO10.5. It exhibited UV and visible light absorbance with a low bandgap of 2.5 eV, low radiative electron-hole recombination and oxygen vacancy generation due to mixed valences of cations. It successfully acted as a photocatalyst for CO and CH4 production from CO2 conversion and hydrogen production from water splitting without cocatalyst addition. These findings confirm that introducing heterogeneous electronic configurations and electronegativities can be considered as a design criterion to avoid the need to use cocatalysts.