Layered Manganese Oxides as Electrodes for Water Desalination via Hybrid Capacitive Deionization

This work explores the ion removal performance of Na-birnessite and Mg-buserite during extended cycling in NaCl and MgCl2 solutions in a hybrid capacitive deionization (HCDI) cell. These two layered manganese oxides (LMOs) contain two-dimensional diffusion pathways and thus present the potential for enhanced ion diffusion and higher performance in HCDI. Correlation between stabilizing ions and ions removed from solution are investigated. In NaCl solution, Mg-buserite shows the largest ion removal capacity of 37.2 mg g(-1) while the reverse is true in MgCl2 solution, where Na-birnessite delivers a capacity of 50.2 mg g(-1). Furthermore, ex-situ XRD after 200 cycles revealed the changes in the structures of the two materials after repeated ion removal-ion release. These results demonstrate that materials with two-dimensional crystal structures can demonstrate high capacities in HCDI and show that interlayer content and spacing can dramatically impact material stability in electrochemical water desalination.