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 (CuMn₂O_3.5S_0.5) 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.