Experimental evaluation and energy analysis of a two-step water splitting thermochemical cycle for solar hydrogen production based on La0.8Sr0.2CoO3-δ perovskite

Abstract

A study of the hydrogen production by thermochemical water splitting with a commercial perovskite La0.8Sr0.2CoO3-d(denoted as LSC) under different temperature conditions is presented. The experiments revealed that high operational temperatures for the thermal reduction step (>1000 C) implied a decrease in the hydrogen production with each consecutive cycle due to the formation of segregated phases of Co3O4. On the other hand, the experiments at lower thermal reduction operational temperatures indicated that the material had a stable behaviour with a hydrogen production of 15.8 cm3 STP/gmaterial$cycle during 20 consecutive cycles at 1000 C, being negligible at 800 C. This results comparable or even higher than the maximum values reported in literature for other perovskites (9.80 e10.50 STP/gmaterial$cycle), but at considerable lower temperatures in the reduction step of the thermochemical cycle for the water splitting (1000 vs 1300e1400 C). The LSC keeps the perovskite type structure after each thermochemical cycle, ensuring a stable and constant H2 production. An energy and exergy evaluation of the cycle led to values of solar to fuel efficiency and exergy efficiency of 0.67 and 0.36 (as a percentage of 1), respectively, which are higher than those reported for other metal oxides redox pairs commonly found in the literature, being the reduction temperature remarkably lower. These facts point out to the LSC perovskite as a promising material for full-scale applications of solar hydrogen production with good cyclability and compatible with current concentrating solar power technology.