As the level of deployment and utilization of renewable energy sources, including wind and solar, continues to rise, large-scale, long-term energy storage technologies that could accommodate weekly and seasonally energy fluctuations will play a significant role in the overall deployment of renewable energies in the future. Storing renewable electrons, using either electrochemical or photoelectrochemical processes, in the form of chemical bonds, e.g., fuels, has the potential to meet the long-term, terra-watt scale energy storage challenge. Renewable hydrogen, in particular, is a centerpiece for renewable fuel production and deep de-carbonization of multiple sectors in our society. Cost-competitive renewable hydrogen can be directly used in the transportation sector for fuel cell cars, in the electric grid sector for electricity firming and load balancing and in the industry sector for metal refineries or biomass upgrading. In addition, coupling with the carbon and nitrogen cycles, renewable hydrogen can be readily processed with known and well-established thermal-chemical processes to generate hydrocarbon fuels and ammonia.

Xiang's research team, as part of the DOE HydroGEN Benchmarking project, is working on Protocols and Best Practice documents on advanced water-splitting technologies, including high/low temperature electrolysis (LTE/HTE), photoelectrochemical (PEC) and solar thermochemical (STCH) waters splitting. The Benchmarking team also hosts annual HydroGEN Workshop and bring together research community from four advanced water-splitting pathways to review and discuss roadmaps, techno-economic analysis and deployment of renewable hydrogen productions. Xiang's research team, as part of the Joint Center for Artificial Photosynthesis (JCAP), has designed and developed a portfolio of fully integrated, high efficiency solar-hydrogen cells with many unique attributes. Under DOE-SBIR Phase-I and Phase-II projects, as well as working with multiple industry partners, including Tetramer Technologies and SoCalGas, Xiang's research team continues to work on materials and devices for stable, scalable and cost-competitive generation of H2 directly from sunlight.