STEP chemistry: A fundamental insight into solar thermal electrochemical process

Highlights: • A fundamental insight into STEP chemistry was demonstrated firstly and systematically. • A mechanism of the construction of the STEP chemistry is schematized and explained. • A coupled combination of the STEP chemistry is formulated and established. • Efficiency of the solar utilization is enhanced by the optimization conditions. - Abstract: A fundamental principle in the culture of solar utilization has historically been to pursue the "Best Efficiency" and "Lowest Cost", but currently the "Most Diversity" to opening new applications. To find innovative solutions for the realization of these goals, a new technology must meet the needs of the original photochemistry, as well as the electrochemical and thermochemical aspects. The STEP (Solar Thermal Electrochemical Process) was established as a comprehensive solar photo-thermo-electrochemical process to utilize solar energy for chemical reactions. To date, this has included STEP chemistries with high solar efficiency for generating hydrogen fuels, splitting carbon dioxide to generate fuels and graphite, separating iron metal from hematite ore, production of lime from limestone, production of bleach, wastewater treatment, organic synthesis and other useful chemistries. In this paper, we report a fundamental study of STEP chemistry in terms of the model, theory and practices of the existing applications. Fundamental insight was systematically demonstrated for STEP chemistry with high efficiency of solar utilization and chemical reaction. A mechanism for the overall construction and coupled combination of the STEP chemistry was developed and established in detail. The fundamentals of STEP chemistry include two aspects: improved solar utilization by enhancement of conversion efficiency, and adjustment of both the thermodynamics and kinetics of the reaction chemical reaction. The high overall solar efficiency can be achieved by the synergistically coupled combination of the solar utilization and chemical reaction to provide a total solution to the challenges of the energy and chemical industries.