Enhanced photocatalytic reduction of carbon dioxide into carbon monoxide by electric field generation and defect engineering in TiO2

Carbon dioxide (CO2) emissions and rising fossil fuel consumption have already resulted in global warming and energy crisis. Therefore, conversion of CO2 into fuels and chemicals is regarded as sustainable solution. Recent research has shown that applying an external electric or optical field promotes CO2 polarization and, in turn, favors catalytic conversion into organic molecules. Here, a titanium dioxide (TiO2) homojunction was formed on graphitic carbon nitride (g-C3N4). Then, massive oxygen defective TiO2 was obtained by dihydrogen reduction, resulting in a strong built-in electric field, of about 0.19 V, between perfect TiO2 and defective TiO2. The catalyst was analyzed by Kelvin probe force microscopy, time-resolved photoluminescence, wavelength-dependent fluorescence and electron paramagnetic resonance. Results show that the catalyst promotes carbon dioxide polarization and separation of photogenerated charges. The catalyst increased carbon dioxide conversion into carbon monoxide (CO) about sevenfold compared to pristine g-C3N4, and about sixfold compared to the 20TiO2/g-C3N4 precursor, under UV–visible light. This exceptional photocatalytic activity is explained by the formation of a built-in electric field by the defective TiO2.