Water Splitting:
The inevitable depletion of fossil fuels and the environmental impact of their combustion have developed renewable energy research programs. Hydrogen is an exciting alternative to the primary fossil fuels, coal, crude oil, natural gas, and their derivatives. The significant advantage of hydrogen is that it reacts with oxygen, either by combustion or in fuel cells, to give energy, and the only product is water. Using solar energy to split water is the cleanest way to generate hydrogen fuel. There are several approaches to split water using solar energy, among which our research focuses on solar thermochemical hydrogen (STCH) production and Photocatalytic Water Splitting.
Solar Thermochemical Water Splitting (STCH):
Solar thermochemical water splitting has attracted considerable attention in recent years. In this process, the energy of the entire solar spectrum can be used to split water and produce H2 fuel. In an STCH process, concentrated solar radiation is used to liberate oxygen from an oxide (MnOm) and reduce metal cations through a high-temperature (TH > 1400 °C) endothermic reaction. Then, in a subsequent exothermic reaction occurring at lower temperatures (TL ≈ 800 °C), the metal cation is oxidized again by taking oxygen from H2O, which produces H2 gas. The following schematic figure can summarize the two-step process. In this process, to achieve a high fuel production efficiency, we require materials with an enthalpy of reduction larger than ~ 2 eV and high reduction entropy. Among the tested metal oxides, Ceria (CeO2) has proved to be a leading candidate; however, CeO2 suffers from its large enthalpy of reduction, leading to a low fuel production efficiency. In our group, we present a novel strategy to search for high-efficiency and experimentally viable oxides for STCH applications.
Photocatalytic Water Splitting:
Photocatalytic water splitting is another promising way to split water and generate hydrogen. In this process, sunlight shines on a semiconducting material. It excites electrons to higher energy states and forms pairs of electrons and holes. Then the excited electrons reduce H2O to H2, and the holes oxidize water to O2. The following schematic figure shows the Photocatalytic water splitting process. The efficiency of a photocatalytic process depends on the characteristics of semiconductors used as the light absorber, such as light-harvesting, charge separation, charge transport. In our group, we explore new materials and propose a design strategy for efficient photocatalytic materials. Our findings will help guide experiments to the search for better photocatalytic water splitters.