In Situ Electronic Probing of Photoconductive Trap States for the Catalytic Reduction of CO₂ by In₂O_3–xOH_y Nanorods

We use photoconductivity time, optical absorption, and electron quantum efficiency measurements under in situ reactant CO 2 + H 2 atmospheres to determine the role of surface trap states during photoreduction of CO 2 to CO using In 2 O 3– x OH y nanorods of varied annealing times. Photocurrent decay trends show an asymmetric energy distribution of surface barrier potentials with increased asymmetry from vacuum to CO 2 + H 2 . Urbach analysis shows crystalline disorder parameters of 0.35–0.40 under vacuum and 0.45–0.6 under CO 2 + H 2 . Quantum efficiency spectra show that under H 2 + CO 2 average tail state energies are similar to those under vacuum but with increased densities of photoconductive gap states. Photoelectro-paramagnetic-resonance measurements show the creation of new paramagnetic centers. Overall, enhanced activity is associated with a lower maximum barrier potential of 0.39 eV than that of 0.41 eV, lower average trap energies of 2.58 eV compared to 2.69 eV, with higher disorder due to increased surface state densities. These techniques pave the way for facile in situ probing of gas-phase photocatalysts, providing simple macrolevel understanding of adsorbed reactants on surface band bending, thus correlating to catalytic efficacy.