This reactive metal oxide material for a two-step water-splitting cycle enables simple and sustainable production of hydrogen gas. The active material serves as a catalyst in the process, since it works in a cycle that regenerates the original material in the second half cycle. Along with applications in oil refining, fertilizer production, or food processing, hydrogen enables generation of clean electricity using fuel cells. Because the combustion of hydrogen produces water, the entire hydrogen production and utilization process would be clean and sustainable, if the energy to produce the hydrogen comes from a renewable energy source, such as solar energy. A thermochemical water-splitting cycle is well suited for produces hydrogen and oxygen from water and solar energy, but good performance requires high temperatures that differ during the two steps. Isothermal operation is difficult but would be much more energy-efficient.
Researchers at the University of Florida have discovered a unique material that drives a thermochemical water-splitting cycle at isothermal conditions to generate hydrogen. The mixed metal oxide allows an isothermal operation that is more energy-efficient than typical water-splitting processes, which cycle between different high temperatures for the two steps.
Production of hydrogen via efficient isothermal water-splitting using solar-powered heat sources
In the first step of the thermochemical water-splitting cycle, heat drives off oxygen gas from a metal oxide to yield an oxygen-deficient material. In the second step, superheated steam passes over the oxygen-deficient metal oxide, re-oxygenating the material and producing hydrogen gas. The cycle repeats with the two thermochemical steps operating at different high temperatures. This rare earth metal oxide retains water groups in its material matrix even at very high temperatures, allowing it to release hydrogen during both steps of the cycle. Therefore, a hydrogen production cycle can reliably operate at a high isothermal temperature for greater energy-efficiency. The amount of hydrogen released during the cycling is proportional to temperature.
