Hierarchical nanostructures for photo-electro-chemical cells

Abstract

The photoelectrode is the main component of the PEC cell that absorbs incident photons to generate electron-hole pairs and generates either electricity directly or chemical fuel by redox reactions. Adopting hierarchical structure photoelectrodes by structural reconfiguration of the same material and/or integrating two or more materials provides a promising route to achieve significant enhancement of PEC cell efficiency. Several approaches to fabricate the hierarchical structure via either developing a new method or combining conventional processes have been reported. A high density of hierarchical branches with a much smaller diameter increases the roughness factor dramatically and also provides longer effective pathways for photon absorption in the photoelectrode by enhanced light scattering and trapping, thereby resulting in better photoconversion efficiency. Moreover, the large contact area of the interface between the electrode and electrolyte boosts chemical reactions and diffusion of chemical species. Particularly promising is the hybridization of two or more different materials. Integrating materials having distinct band structures broadens the absorption spectrum and leads to effective charge separation and collection, enabling a wider selection of materials for the water splitting PEC cell configuration without external bias. © 2015 The Royal Society of Chemistry.