High-Performance Capacitive Deionization via Manganese OxideCoated, Vertically Aligned Carbon Nanotube

Discovering electrode materials with exceptional capacitance, an indicator of the ability of a material to hold charge, is critical for developing capacitive deionization devices for water desalination. Maganese oxides (MnOx) have shown promise as capacitive electrode materials, but they exhibit a trade-off in which a higher loading of the active MnOx comes at the cost of lower conductivity. To address this challenge and achieve high salt adsorption, we fabricated electrodes comprising vertically aligned core shell nanostructures using atomic layer deposition (ALD) to coat thin films of MnOx onto vertically aligned carbon nanotubes (VACNTs). The inherently hierarchical, anisotropic, three-dimensional macroporous structure of VACNTs and the tunable coating, a hallmark of ALD, enabled co-optimization of the hybrid material's specific capacitance with respect to mass and geometric area. The specific capacitance was optimized in this study to 215 +/- 7 F/g and 1.1 +/- 0.1 F/cm(2) in a 1 M NaC1 electrolyte at a scan rate of 5 mV/s. This material exhibited a remarkable sodium ion adsorption capacity of 490 +/- 30 mu mol of Na/g of material (2-fold higher than that of pristine VACNTs) at a functioning voltage of 1.2 V, which may ultimately enable expanded desalination applications of capacitive deionization.