Photoelectrochemical H₂ Production Coupled With Glycerol Selective Oxidation To Dihydroxyacetone

The selective oxidation of glycerol to dihydroxyacetone（DHA）is an important route to achieve glycerol upgrading.Although traditional catalytic methods（such as enzyme catalysis and thermocatalysis）can achieve high DHA selectivity and yield,these methods usually require harsh reaction conditions,precious metal catalysts and additional oxidants.The solar-driven photoelectrocatalytic（PEC）technology can realize the selective oxidation of glycerol at room temperature and atmospheric pressure,and coupled with cathodic hydrogen production,providing a green and efficient approach for the glycerol oxidation to produce DHA.However,the current researches for PEC glycerol oxidation to DHA still suffer from the low DHA selectivity（<60%）and slow reaction rate.In addition,the reaction mechanism of PEC glycerol oxidation to DHA is still not clear.In view of the above-mentioned problems,this thesis focus on the construction of two types of compound photoanodes to realize the regulation of the adsorption state of glycerol molecules and the self-oxidation capacity of the catalyst,thereby achieving the improvement of the selectivity and reaction rate of PEC glycerol oxidation to DHA.In addition,the reaction mechanism of PEC glycerol oxidation to DHA has also been revealed by various characterization methods.The main research contents and conclusions of the paper are as follows:（1）Bi₂O₃/Ti O₂ photoanode was prepared by supporting Bi₂O₃nanoparticles on the surface of Ti O₂ nanorods with hydrothermal and electrodeposition methods.Under the experimental conditions of 1.0 V vs.RHE reaction voltage and p H=2,the selectivity of DHA over Bi₂O₃/Ti O₂ reached75.4%with Faradaic efficiency of 62.2%,which is the highest value in the reported works for PEC glycerol oxidation to DHA in literature.Based on a series of photoelectrochemical test methods,we proved that the recombination of Bi₂O₃ and Ti O₂ can form a p-n heterojunction,which can accelerate the separation of photogenerated carriers and improve the utilization rate of photogenerated holes,thereby improving the activity of glycerol oxidation.The mechanism of Bi₂O₃ promoting the oxidation of glycerol PEC to DHA was further revealed by in-situ infrared,electron paramagnetic resonance spectroscopy,free radical trapping experiments,isotope labeling and fluorescence spectroscopy experiments.It is demonstrated that Bi₂O₃ can promote the preferential adsorption of the secondary hydroxyl groups of glycerol,while promoting the desorption of DHA on the photoanode surface,which can realize the selective oxidation of glycerol.（2）To realize the regulation of the self-oxidation ability of the catalyst and expand the types of photoanode materials suitable for glycerol oxidation,a Zn In₂S₄/Ti O₂ composite photoanode was prepared by a two-step hydrothermal method.Under the experimental conditions of 1.0 V vs.RHE reaction voltage,p H=2,the selectivity of DHA over Zn In₂S₄/Ti O₂ reached 72%.UV-visible light diffuse reflection and electrochemical impedance results proved that the composite of Ti O₂ and Zn In₂S₄ can expand the light absorption range of the photoanode,promoting the directional movement of photogenerated carriers and and improving the photocatalytic glycerol oxidation reaction activity.The mechanism of Zn In₂S₄/Ti O₂ to promote the selective oxidation of glycerol to DHA was analyzed by experimental phenomena,and it was proved that the recombination of wide and narrow band gap materials accelerated the separation of photogenerated carriers,and the photogenerated holes were transferred to Zn In₂S₄ with a corrected valence band.The mild oxidative power enables the highly selective generation of DHA.