Mg-Doped Porous Ca-Fe Microsphere as Bifunctional Oxygen Carriers for Chemical-Looping Hydrogen Production

Abstract

Sintering-induced deactivation remains a critical bottleneck for Ca-Fe oxygen carriers in chemical-looping hydrogen production. To address this, we developed Mg-doped porous Ca-Fe microspheres via a one-pot hydrothermal-carbon templating strategy. Our investigation reveals that moderate Mg doping facilitates the formation of highly dispersed MgO inert spacers. Acting as physical barriers, these MgO species effectively impede high-temperature particle growth and agglomeration, thereby preserving a robust, dense, and uniformly porous microsphere architecture with a high specific surface area (44.1 m2·g-1 for Mg5). This unique structural advantage provides more enhances gas diffusion channels and significantly enhances the accessibility of active sites. Consequently, the optimal Mg5 sample (with an actual Mg loading of 1.66 wt%) exhibits superior performance, achieving a hydrogen yield 16.60% higher than the undoped counterpart and 34.61% higher than the mechanical mixture, alongside effective in-situ CO2 capture capacity. Furthermore, the material demonstrates good cyclic durability over 23 redox cycles, attributed to the structural integrity of the porous microspheres maintained by MgO. This study elucidates that the inert-phase physical barrier constructed via moderate Mg doping effectively stabilizes the porous microsphere, which is pivotal for sustaining high hydrogen production, offering a structure-oriented design strategy for developing durable bifunctional Ca-Fe oxygen carriers.