Enhanced oxygen transfer rate of chemical looping combustion through lattice expansion on CuMn₂O₄ oxygen carrier

This study applied the lattice expansion strategy to enhance the performance of the CuMn2O4 oxygen carrier. The lattice-expanded oxygen carrier was developed using sulfurization and re-oxidation processes. The lattice of re-oxidized CuMn2O4 (CuMn2O3.5S0.5) did not shrink to the original lattice and maintained the expanded structure because of the residual sulfur in the CuMn2O4. Density functional theory calculations predicted that the lattice expansion accelerates the CH4 oxidation kinetics on the surface and the oxygen mobility in the oxygen carrier. As a result, the oxygen transfer rate was expected to be accelerated. Experimental analysis confirmed the predicted enhancement. The comprehensive characteristic analysis revealed notable variations in the lattice structure and oxidation state between lattice-expanded CuMn2O4 and pristine CuMn2O4 because of the enhanced oxygen transfer rate, as confirmed by temperature-programmed analysis. The chemical looping combustion test showed that the oxygen transfer rate of lattice-expanded CuMn2O4 was 1.6 times higher than that of pristine CuMn2O4. The simulation predicted an enhanced oxygen transfer rate of the oxygen carrier. Based on the results, the strategy of lattice expansion could be a universal approach to enhance the oxygen transfer rate and improve the overall performance of the oxygen carrier.