MOF-derived 3D MnO2@graphene/CNT and Ag@graphene/CNT hybrid electrode materials for dual-ion selective pseudocapacitive deionization

Abstract

In the present study, an asymmetric pseudocapacitive deionization (PCDI) system was fabricated using redox-active electrode materials of three-dimensional (3D) MnO2@graphene/CNT (MGC) and Ag@graphene/CNT (AGC) as cathode and anode, respectively. The asymmetric PCDI system owns a dual-ion capture mechanism, resulting in a high desalination capacity. The 3D MGC and AGC active electrode materials have been derived through a facile two-step method. Initially, the Mn-BTC and Ag-BTC were in situ grown on the 3D r-GO/CNT structure through a hydrothermal process, yielding Mn-BTC@r-GO/CNT and Ag-BTC@r-GO/CNT hybrids. Subsequently, high-temperature annealing of these hybrids leads to respective MGC and AGC hybrid nanocomposites. Powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analysis facilities were used to investigate the structure and morphology of the as-prepared hybrid nanocomposites. The as-derived 3D MGC and AGC electrode materials exhibit the high specific capacitance of 496.4 and 206.6 F g−1, respectively, at 1 A g−1 using a 1 M NaCl solution. Furthermore, the MGC (cathode)//AGC (anode) electrode pairs-based PCDI system exhibits remarkable desalination performance with a high salt adsorption capacity of 62.4 mg g−1 and a charge efficiency of 95 % in 1000 ppm NaCl solution at 1.2 V.