Isothermal Water Splitting

Abstract

The potential of solar radiation as an infinite resource of renewable energy is widely recognized. The challenge is to convert it as efficiently as possible into useful energy forms such as hydrogen or liquid carbonaceous fuels. Thermochemical cycles are a number of consecutive chemical reactions (≥2) that lower the maximum temperature compared to a single chemical reaction. Typical temperatures for these cycles to reach full conversion range from 800°C to 2000°C. The necessary solar heat can be generated by concentrating optics that direct the solar radiation on a single point—in solar towers or central receiver systems. To use the solar power efficiently and economically, losses must be minimized, with major factors being the minimization of re-radiation and the reduction of gases that are used to transport the reactant. As pointed out by Muhich et al. (1) on page 540 of this issue, a particularly important factor in this respect is the minimization of temperature differences between reaction steps. However, the necessary temperatures are high, and it has yet to be proven that the materials and components are stable over a long time to make the processes economically attractive.