Photocatalytic Co₂ Reduction Of BaCeO₃

For the advantages of stability, ready availability, and high energy density (about 33 GJ/m3 for gasoline), hydrocarbon fuels have been considered as one of the most important sources of energy. Unfortunately, due to the long-term excess consumption, the hydrocarbon fuels have been dangerously depleted. Also, hydrocarbon fuels combustion has caused the environmental pollution, including the rise in atmospheric CO2 concentration and other unforeseen and potentially severe consequences. In order to solve the energy crisis which threatened the survival and development of human, the clean energies (including solar energy, tidal energy, geothermal energy) become the topic for modern scientific research. Sunlight has the potential to solve the energy crisis if some efficient systems can be developed in capturing solar energy. The researches on the storing solar energy through water splitting with the help of photocatalyst (or photoelectrode) and the photocatalytic conversion of CO2 into hydrocarbon fuels driven by solar energy, offered the intriguing possibility of achieving solar fuels compatible with current energy infrastructure perfectly and slowed the increase of atmospheric CO2 concentration. In this process, CO2 and H2O generated by hydrocarbon fuels become the raw materials to produce hydrocarbon fuels, which would partly advance us into a carbon-neutral renewable energy cycle.Recently, a series of perovskite-type oxides semiconductor photocatalysts with wide band gap have been studied for photocatalytic CO2 reduction. The good photocatalytic activities of the photocatalysts such as SrTiO3 (with Pt as cocatalyst), BaZrO3, MNbO3 (M=K, Na, Li, Cu; with or without Pt cocatalyst), and AgTaO3 have been proved. However, these studies were mainly focused on the perovskite-type oxides with d orbitals. Little attentions had been paid on the photocatalysts whose conduction band is dominated by the 4f electronic configuration. The BaCeO3 was selected to continue our studies, since it exhibited photocatalytic water reduction in our previous report. As we all know the 4f electron orbital was buried deep in the 5s25p6 electron shell, which was filled with 8e.For the shielding effects, the degree of orbital splitting caused by crystalline field should be greatly reduced compared to that of the d orbital. Based on the density functional theory calculations results and the partial density of states (PDOS), no obvious orbital splitting in Ce 4f could be observed. Then we needn’t consider a series of questions caused by the introduction of the impurity level, such as the change of band gap, the generation of harmful defects and the formation of recombination centers. The BaCeO3 were found to exhibit appreciable proton conduction at high temperature and chemical stability, which may provide a possibility for electron transport. The BaCeO3 have been reported as a photocatalyst for the performance on the water splitting in our group.The process of photocatalytic CO2 reduction was similar to water splitting. In addition to the selective adsorption of vapour and the potential of water oxidation, the materials applied to reduction CO2 should meet the required that, fairly good adsorption of CO2, desorption of CH4 and less negative reduction potential than water splitting. It means that the materials must own a wide band gap. To the best of our knowledge, no result has been reported about the photocatalytic CO2 reduction of BaCeO3 under UV light irradiation. Considering the BaCeO3 has an appropriate band gap for CO2 reduction, it is important to investigate the photocatalytic activities of BaCeO3 with the assistance of cocatalysts. In this study, a series of BaCeO3 samples were synthesized by two methods and characterized by X-ray diffraction, BET surface area, UV-vis diffuse reflectance spectra, SEM and TEM observations. And the photocatalytic activities of BaCeO3 in CO2 reduction under UV irradiation have been investigated in detail.