Polymorphic Phase Engineered Structures (PPES) for PEC Energy Conversion

Photoelectrochemical (PEC) energy transformation systems have been a highly effective pathway in producing easier, cheaper, and more sustainable hydrogen energy that solve the current pressing energy and environmental challenges. Great effort has been made to develop a feasible PEC system that can improve the solar to hydrogen (STH) efficiency for practical applications. However, such progress is not viable yet due to the lack of suitable materials that should overcome some stringent requirements: (i) appropriate band-edge locations, (ii) low overpotential and cost, (iii) highly durable and stable under harsh conditions, (iv) excellent photoinduced electron-hole separation and migration to the active sites, and (v) ability to adjust a broad range of solar spectrum absorption. Polymorphic phase-engineered structures (PPES) materials possess unique electronic and optoelectronic properties that can be ideal for PEC devices for efficient energy conversion, including hydrogen production from overall water splitting and nitrogen reduction to ammonia, as discussed in this chapter.