Dr. Xudong Wang

Direct production of hydrogen fuel from water is of fundamental importance to alleviate the crisis that fossil resources confront nowadays. In this talk, I will discuss our recent development of 3D nanowire (NW) architectures for efficient photoelectrochemical (PEC) water splitting and the application of piezoelectric potential in water splitting  reactions.  Firstly, we developed a surface-reaction-limited pulsed chemical vapor deposition (SPCVD) technique that decouples the crystal growth from precursor vapor concentration, and thus successfully grew TiO₂ nanorods (NRs) inside dense Si NW arrays. Such high-density tree-like 3D NW architectures are ideal for high-performance PEC electrodes that offer high quality 1D conducting channels for rapid electron-hole separation and charge transport, as well as high surface areas for fast interfacial charge transfer and reactions. Dramatic increases of photocurrent and PEC efficiency were obtained when the 3D TiO₂ NR-Si NW architectures were applied as PEC anodes for water splitting. Secondly, through the PEC water splitting process, we demonstrated an effective strategy for engineering the barrier height of a heterogeneous semiconductor interface by piezoelectric polarization, known as the piezotronic effect. This discovery renders a new pathway for engineering the interface band structure without altering the interface structure or chemistry. At last, by straining a piezoelectric beam in water, we showed that piezoelectric potential can raise the energy of electrons at the surface of piezoelectric material (or electrode) to such a level that is sufficient to drive proton reduction reactions within its immediate vicinity. This provides a direct pathway for mechanical to chemical energy conversion - piezocatalysis. The   piezocatalytic efficiency was found to depend sensitively upon the over potential and the length of straining state. The results embolden a new and promising strategy for          mechanically tailoring interface energetics and chemistry.