CoOx ceramics synthesized by a facile and rapid combustion method and its application for thermochemical energy storage

Abstract

Cobalt-based ceramics is one of the most promising candidates for thermochemical energy storage. In this paper, a novel cigarette butts assisted combustion synthesis method was proposed to synthesize nano-CoOx ceramics used for thermochemical energy storage. For this method, cigarette butts were selected as solid fuels. The cigarette butts were impregnated in cobalt nitrate solution, and the cobalt nitrate solution was absorbed, filled and dispersed uniformly in the cigarette butts. The wet cigarette butts were directly burned, and two combustion modes (smoldering and flaming) were considered. After the wet impregnated cigarette butts burned out, nano-CoOx was obtained. The commercial and sol-gel method prepared CoOx was also tested for comparison. Based on the characterization results, the CoOx obtained from the combustion synthesis method was a mixture of Co3O4 and CoO. In addition, CoOx synthesized in the smoldering combustion process (S250) had the highest BET specific surface area and better performance on thermochemical energy storage. The conversion rate was kept above 97% and the oxidation rate could maintain at a stable and higher value (∼175 μmol/min/g) after 30 cycles. For S250, the onset temperature gap between heat charging and discharging was the smallest (15.9 °C), suggesting that S250 could charge and discharge quickly and kept a complete reversibility in multiple cycles. The heat loss of S250 was the smallest and its heat grade was the highest. As a whole, direct combustion of the wet impregnated cigarette butts could be a feasible and rapid method to synthesize nano-CoOx ceramics, which exhibited superior performance on thermochemical energy storage.