Self-acceleration effect of Mn/Ce-modified carbide slag in CO2 absorption for CaO/CaCO3 energy storage

Abstract

Carbide slag, a solid waste from the chlor-alkali industry, can be used for CO₂ capture and energy storage. Herein, the cyclic reaction activity of Mn/Ce-modified carbide slag under energy storage conditions was studied. The Mn/Ce-modified carbide slag shows energy storage density over 2100 kJ/kg and CO₂ absorption capacity of 0.52 g CO₂/g sorbent after 30 cycles. Notably, both carbonation and calcination rates are accelerated with the number of cycles. This self-acceleration effect is related to the evolution of oxygen vacancy concentration and texture structure of Mn/Ce-modified carbide slag during the cycles. In the cycles, CaMnO₃ in the Mn/Ce-modified carbide slag reacts with the formed CaCO₃ in the carbonation stage to produce more Ca₂MnO₄. The formation of Ca₂MnO₄ increases oxygen vacancies in the Mn/Ce-modified carbide slag, significantly enhancing its CO₂ adsorption capacity. Thus, the release of the increased CO₂ in the calcination stage generates more pores in the 10–100 nm diameter range in the modified carbide slag, facilitating rapid carbonation. Thus, the Mn/Ce-modified carbide slag exhibits good prospect for CaO/CaCO₃ thermochemical energy storage.