Efficient Hybrid Capacitive Deionization Device with High Operating Voltage Based on Layered Sodium Manganese Oxide

Abstract

This study aims to synthesize sodium manganese oxide through a single-step hydrothermal method, enabling precise temperature control for manipulating the structure, composition, morphology, and sodium storage performance of the products. The synthesized Na 0.55 Mn 2 O 4 •1.5H 2 O demonstrated a stable two-dimensional nanosheet structure and a significantly large specific surface area when prepared at a temperature of 180 °C. Under constant current charge−discharge conditions in a neutral solution, the material exhibited a specific capacitance of 184.3 F/g. By utilizing Na 0.55 Mn 2 O 4 •1.5H 2 O as the positive electrode and self-made pine bark biomass-activated carbon as the negative electrode in a Na 0.55 Mn 2 O 4 •1.5H 2 O|PBC-3 hybrid capacitor (HC), an optimized positive-to-negative electrode mass ratio of 1:3 resulted in the best overall performance. Notably, the system operated at a high voltage (1.5 V) without the requirement for ion-selective membranes. In a 1000 ppm NaCl solution, the system displayed an impressive desalination capacity of 44.8 mg/g and a desalination rate of 0.064 mg/g/s. At a higher removal rate of 0.095 mg/g/s, the system achieved a desalination capacity of 32.53 mg/g. Comparative analysis of comparable hybrid capacitive deionization devices revealed that the Na 0.55 Mn 2 O 4 •1.5H 2 O|PBC-3 HC displayed a high operating voltage and superior desalination performance. Moreover, these findings enhance the feasibility of using HCDI technology in large-scale water treatment systems.