Photocatalysis, Photoelectrochemical and Photoassisted-Electrochemical Systems for Light Energy Conversion
Photocatalysis is a solar energy conversion process, extensively investigated for both environmental remediation (airborne and water treatment) and energy generation (H2 generation). Novel semiconductor photocatalysts have been developed and studied for many decades. Interest in understanding and developing semiconductor photocatalysts was geared by Fujishima and Honda's observation in 1972 that simultaneous oxidation and reduction of water into O2 and H2 occur upon UV illumination of a TiO2 electrode in aide of a small electrochemical bias. This significant discovery, to a great extent, prompted and directed extensive research on the production of hydrogen from water and/or other media as an alternate source of clean energy using sunlight.
It is the primary photochemical processes occuring at the surface of an illuminated semiconductor that form the basis for photocatalytic and photoelectrocatalytic applications. A semiconductor photocatalyst has two series of energetically closely spaced energy levels that form the valence and conduction bands. The magnitude of the difference between the electrons-populated valence band and the almost vacant conduction band is termed the energy band gap of a semiconductor. Band gap energy governs the wavelength of light required to excite the semiconductor upon illumination. Ideally, excited charges generated upon illumination should initiate interfacial electron transfer or chemical reactions to its adsorbate, reactant, or the surface-bound hydroxyl group.
We are dedicated to explore the fundamental understanding in these excited charge-induced reactions: water splitting, hydrogen generation, and charge storage (solar battery). Various strategies from materials nanostructuring to system engineering are adopted to investigate the scientific phenomena and boost the light energy conversion and utilization.
Suspension-type nanoparticulate photocatalytic water splitting
(i) Reactor design for scalable reaction;
(ii) Development of Z-scheme artificial photosynthesis using oxide powder;
(iii) Band-structural modulation of oxide semiconductor
Photoelectrochemical water splitting
(i) Scalable thin film fabrication methods;
(ii) Liquid-solid interface at photoelectrodes;
(iii) Charge transportation under illuminated electrochemical system.
Electrochemical carbon dioxide reduction or conversion assisted with light
(i) CO2 adsorption-reduction/conversion mechanistic pathways;
(ii) Development of low cost earth-abundant electrode materials.
Other photocatalytic reactions for energy and environmental applications
For examples, (i) NOx degradation and (ii) ammonia decomposition (for hydrogen generation)