Greater use of hydrogen as a renewable energy carrier rests on the ability to meet the U.S. Department of Energy’s (DOE’s) Hydrogen Energy Earthshot goal of cutting the cost by 80% to $1/kg in a decade. A solar power-based water splitting technology is being advanced at the U.S. National Renewable Energy Laboratory (NREL) to achieve this economic target.

Solar thermochemical hydrogen (STCH) production can be potentially more energy efficient than producing hydrogen via the commonly used electrolysis method. Electrolysis requires electricity to split water into hydrogen and oxygen while the STCH approach relies on a two-step chemical process. Metal oxides are exposed to temperatures greater than 1,400° C and then re-oxidized with steam at lower temperatures to produce hydrogen.

NREL research published in the journal Renewable Energy focuses on system-level design and techno-economic analyses for integrating possible materials into a solar-fuel platform and supporting the DOE HydroGEN program. The material discovery in the HydroGEN program involved machine learning, defect calculations and experiments to develop new perovskite materials. The researchers need to identify perovskites capable of handling the high temperatures required while hitting performance targets.

Electrolysis technologies are commercially available and the electricity required can be provided by photovoltaics (PV). The PV cells used, however, only capture a section of the solar spectrum. In contrast, the STCH platform uses the entire spectrum by means of a concentrated solar thermal power system to support the required chemical reaction with high efficiency.

This analytical approach will help researchers identify optimal materials for the STCH process.

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