CHAPTER 8: Hierarchical Nanostructures for Photo-Electro-Chemical Cells

A photo-electro-chemical (PEC) cell is a device that directly generates electrical energy (photovoltaics) and converts solar energy into chemical fuels such as hydrogen (water splitting). Hierarchical structures have been adopted as photoelectrodes in PEC cells to increase the efficiency significantly. Hierarchical structures provide a substantially increased surface area enabling higher light harvesting while allowing a longer effective path for the photons to be absorbed in the photoelectrodes by intense scattering and trapping enhancement. Moreover, their large surface area boosts the chemical reactions and enhances diffusion of chemical species into the interfaces and surfaces in PEC cells. Hierarchical structures, made by hybridizing two or more different materials, provide additional functionality. For example, integrating materials of different band structures enables the absorption of photon energy over a broader range as well as each semiconductor conducting the individual half reactions with effective charge separation in water splitting PEC cells. This chapter focuses on several pathways to synthesize hierarchical nanostructures for PEC cells and their applications in photovoltaics and water splitting for fuel generation.