Full Spectrum Solar Energy Water Splitting for Storable Fuel Generation

Jeff Chou, Yu Wang, S.G. Kim

This proposal aims to develop technologies enabling a “Water Splitting System utilizing Full Spectrum Solar Energy.” The direct conversion of solar energy to storable chemical fuels which have much higher power and energy density compared to solar-thermal or photovoltaic conversion methods can circumvent the biggest challenge of harvesting intermittent solar energy: no solution for grid-scale electrical energy storage. One promising solar-to-fuel conversion method is the photosynthesis of hydrogen fuel directly from water, specifically from seawater or other abundant untreated sources. However, the performance and efficiency of wide bandgap oxide-based (such as TiO2) photocatalytic systems available at the present time has been seriously limited. This is mainly due to the poor absorption of visible light to wide bandgap oxides, resulting in much less than 10% solar-to-fuel efficiency, which is regarded as the threshold for the cost effectiveness of this technology. We propose to develop a novel optical nanostructured photoelectrode/catalyst, which will solve this limitation that currently plague the energy conversion efficiency of water splitting. We will develop metallic photonic crystals (MPhC) where cavity resonances convert most photons of the entire visible solar spectrum into hot electrons, which will then be transferred to oxide layers to catalyze H2 evolution at the interface between the catalytic oxide thin film and the electrolyte. In order to prove the key idea and implement it into a working device, we will also study and model the photon absorption and hot electrons transport across the interfaces and optimize the design of the system and the semiconductor catalysts. Successful outcome will enable important low-cost and massively scalable technologies to address the ever-growing energy problem.