Layered hydrated-titanium-oxide-laden reduced graphene oxide composite as a high-performance negative electrode for selective extraction of Li via membrane capacitive deionization.

In this work, we initially prepared layered lithium titanate (LiTiO) using a solid-state reaction. Then Li of LiTiO were acid-eluded with Hydrochloric acid to obtain hydrated titanium oxide (HTiO). Different weight percentages (50%, 60%, 70%, 80%, and 90%) of the as-prepared HTiO were deposited on a conductive reduced graphene oxide (rGO) matrix to obtain a series of rGO/ HTiO composites. Of the prepared composites, rGO/HTiO-60% showed excellent current density, high specific capacitance, and rapid ion diffusion. An asymmetric MCDI (membrane capacitive deionization) cell fabricated with activated carbon as the anode and rGO/HTiO-60% as the cathode displayed outstanding Li electrosorption capacity (13.67 mg g) with a mean removal rate of 0.40 mg g min in a 10 mM LiCl aqueous solution at 1.8 V. More importantly, the rGO/HTiO-60% composite electrode exhibited exceptional Li selectivity, superior cyclic stability up to 100,000 s, and a Li sorption capacity retention of 96.32% after 50 adsorption/desorption cycles. The excellent Li extraction obtained by MCDI using the rGO/HTiO-60% negative electrode was putatively attributed to: (i) ion exchange between Li and H of HTiO; (ii) the presence of narrow lattice spaces in HTiO suitable for selective Li capture; (iii) capture of Li by isolated and hydrogen-bonded hydroxyl groups of HTiO; and (iv) enhanced interfacial contact and transfer of large numbers of Li ions from the electrolyte to HTiO achieved by compositing HTiO with a highly conductive rGO matrix.