Public Research Seminar by Advanced Materials Thrust, Function Hub, HKUST(GZ)  - Thermodynamic and kinetic challenges of (photo)electrochemical oxidations on metal oxides

Photoelectrochemical (PEC) oxidation is one of the most challenging reactions for solar-driven chemical syntheses due to its unfavourably slow kinetics. Although water oxidation has been identified as the key limiting step for the overall water splitting, the underlying mechanism of other oxidations (e.g. organic compounds) using metal oxides is still ambiguous. For example, the selectivity of aldehyde formation from alcohol oxidation varies with the oxide material – hematite showed an excellent selectivity whilst titania showed opposite, despite the strong oxidation power in both materials and the reductive nature of aldehyde, thus confusing the material selection and design.

My talk will primarily focus upon the underlying kinetics of alcohol oxidation on hematite and titania surfaces, and its aldehyde overoxidation using operando time-resolved absorption spectroscopies. The kinetic competition of alcohol oxidation and aldehyde oxidation will be elucidated based upon its reaction pathway correlated with its valence band potential. The ambiguity of selectivity control over these two oxides will be uncovered by comparing their activation energies (i.e. catalysis) which determines the reaction pathway in a kinetically competing condition. These results will further be extended to water purification using PEC oxidation with particular focus upon the thermodynamic and kinetic requirements for mineralisation vs decolouration of PEC organic oxidations. In parallel with PEC methods, the kinetic impact of electrochemical oxidation of water using nickel derived oxide materials will be briefly discussed to extend the kinetics challenge to a more universal scope.