Temperature effects on redox potentials and implications to semiconductor photocatalysis

摘要

Semiconductor photocatalysts facilitate solar energy conversions via reduction-oxidation (redox) reactions. This requires the bandgaps of semiconductors to straddle the redox potentials of half-reactions. Such inherent thermodynamic prerequisite greatly limits utilization of visible or near-IR light. Thus, controllable redox potentials are highly desirable to obtain favorable band alignment. Here a simple thermodynamic approach was proposed to quantitatively predict temperature dependent behavior of energetics of redox half-reactions. Distinguished trends were observed at a temperature range of 298.15-1500 K for representative photocatalytic processes: H2O splitting was relatively temperature insensitive than CO2 reduction and NH3 synthesis, and the shifts in negative or positive directions as a function of temperature depend on the Gibbs energy change of the reactions. Furthermore, thermodynamic and kinetic implications on photocatalysis were discussed based on band alignment and overpotential. Understanding those thermodynamic characteristics is important for prediction and manipulation of physiochemical properties for more efficient photocatalysis.