UV-Light-Driven Oxygen Pumping in a High-Temperature Solid Oxide Photoelectrochemical Cell

Thermochemical energy conversion based on high-temperature materials is a third approach and generally employs two step processes with oxygen release (i.e., a reduction reaction) at high temperature and chemical water splitting at lower temperatures. [ 13–17 ] Interestingly, only very few activities aim at a combination of high temperatures and photoelectrochemical energy storage. In a theoretical paper, a solid-state electrochemical cell was suggested for splitting of steam at high temperatures by solar radiation. [ 18 ] Such a high-temperature cell running on steam may avoid stability problems of photoactive materials in liquid water, can exploit the reduced theoretical energy input required for water splitting at higher temperatures, and does not suffer from problems due to heating in case of high solar energy intensity. However, to the best of the authors’ knowledge, experimental realization of solid electrolyte-based (photo-) electrochemical cells for photon-driven steam electrolysis has not been reported yet. The scope of this paper is to experimentally demonstrate the feasibility of a high-temperature solid-state photoelectrochemical cell (SOPEC). The multilayer cell used consists of a sequence of different oxides, some being active in terms of photovoltaics and some using the voltage to chemically store energy. At operating temperatures between 400 and 500 °C UV light-induced open circuit voltages as high as 900 mV are directly transferred into chemical energy via oxygen pumping from low to high oxygen partial pressure. The experiments show that solid-state photoelectrochemical cells can indeed be realized and that improved cells for water splitting and thus hydrogen production are feasible.