An in-depth investigation of BaO2/BaO redox oxides for reversible solar thermochemical energy storage

Abstract

An in-depth investigation of the BaO2/BaO redox couple for reversible solar thermochemical energy storage has been performed. Beyond improving the cyclability and energy storage density of the material, an additional objective of this work is to better understand inconsistencies in the literature surrounding this chemistry. Sintering of BaO2/BaO is a hindrance for practical high temperature energy storage. MgO-stabilized BaO-based materials were synthesized by co-precipitation methods and investigated for improving the longevity and reactivity of the redox materials. The effect of the calcination environment during synthesis on sample purity was evaluated. Energy storage capacity and stability of commercial BaO2 and BaO2 made by co-precipitation methods were compared over 25 consecutive redox cycles. The effect of different amounts of MgO was studied, and it was discovered that with increasing amounts of MgO, the stability and reactivity of BaO2 increases while the energy storage density decreases. 15 wt% MgO/BaO2 exhibits the greatest stable weight gain/loss with a value of 6.62% (estimated 338 kJ/kg). A BaO2/MgO sample with 33 wt% MgO shows good storage capacity with weight gain/loss at 5.65% (corresponds to approximately 290 kJ/kg) over 200 redox cycles.