Abstract
In the study reported herein, glovebox-protected X-ray photoelectron spectroscopy (XPS) and in situ Hall charge carrier measurements provide new insights into the surface physical chemistry of gaseous H2, CO2, and H2+CO2 combined with nanostructured In2O(3−x)(OH)y nanorods, which ensue under photochemical and thermochemical operating conditions. Heterolytic dissociation of H2 in H2-only atmosphere appears to occur mainly under dark and ambient temperature conditions, while the greatest amount of OH shoulder expansion in H2+CO2 atmosphere appears to mainly occur under photoilluminated conditions. These results correlate with those of the Hall measurements, which show that the prevalence of homolytic over heterolytic dissociation at increasing temperatures leads to a steeper rate of increase in carrier concentrations; and that H2 adsorption is more prevalent than CO2 in H2+CO2 photoillumination conditions.
Highlights
Photocatalysts are useful tools in the reduction of CO2 under solar radiation to generate sustainable fuels [1,2,3]
The X-ray photoelectron spectroscopy (XPS) O1s core-level binding energies of In2 O(3−x) (OH)y nanorods in a vacuum can be resolved into four peaks, assigned to lattice oxide around ~529.5 eV, oxygen vacancy ~530.5 eV, hydroxide ~532 eV, and protonated OH groups at
The effective positive charge of the proton bonded to the oxide site of the hydroxide causes the O1s ionization potentials to shift to higher energy than the lattice oxide, while the protonated OH species (H+ OH) (14% of total species) arising from ambient moisture during synthesis preparation [18,19] causes a positive shift for some of the OH groups, which all result in a broad OH shoulder
Summary
Photocatalysts are useful tools in the reduction of CO2 under solar radiation to generate sustainable fuels [1,2,3]. By controlling the thermal profile used for the dehydroxylation of the In(OH) precursor, a partially dehydroxylated indium oxide hydroxide is obtained, in which the bixbyite structure is retained [4,5,6,7,8]. By quantifying the amount of water eliminated from the lattice of In(OH) by thermal gravimetric analysis, the stoichiometry of the oxide and hydroxide groups in the obtained material can be established according to the balanced reaction equation, with the following intermediate stochiometric composition: reaction [11]: CO2 + H2 → CO + H2 O. Depending on the ratio of H2 to CO2 pressure fraction, the selectivity of the RWGS can range from CH4 to CO or CH3 OH. The main product of the 1:1 pressure
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