Uniformly Dispersed Fe–N Active Centers on Hierarchical Carbon Electrode for High-Performance Capacitive Deionization: Plentiful Adsorption Sites and Conductive Electron Transfer

Abstract

Capacitive deionization (CDI) is a promising desalination technology to meet the growing demand for clean water resources. Carbon-based materials, as one of the most appealing electrode candidates for CDI, are still limited by low adsorption capacity and slow rates. Heteroatom doping of carbonaceous materials is considered a promising strategy for high-performance CDI desalination. Herein, hierarchically porous carbon with uniformly dispersed Fe–N active centers (FeNC) is fabricated by a one-step pyrolysis treatment from a Zn–Fe bimetal–organic framework. The systematic analysis demonstrated that the synergistic effect of the uniformly dispersed Fe and N increased the specific surface area and graphitization degree of the carbonaceous framework. Moreover, the electrochemical analysis confirmed that Fe intervention effectively increased the specific capacitance and reduced the charge-transfer resistance, ensuring a more desirable electrical double-layer capacitor (EDLC) behavior. As expected, FeNC exhibited an excellent electrosorption capacity of 28.88 mg g–1 and a faster rate (1.85 mg g–1 min–1). The results indicated that the introduction of trace Fe can not only modulate the structural properties of carbon materials to provide more accessible adsorption sites but also form Fe–N to accelerate electron transfer. This work provides a profound insight into the crucial role of Fe–N active centers in carbon-based CDI desalination.

Enhanced Capacitive Deionization Performance of Ti3C2Tx/C via Structural Modification Assisted by PMMA-Derived Carbon Spheres

“…The CDI cells are assembled by using m -Ti 3 C 2 T x , c -Ti 3 C 2 T x , a -Ti 3 C 2 T x , and Ti 3 C 2 T x /C electrodes as the cathode and an active carbon electrode as the anode for desalination performance testing. According to previous reports, the ion adsorption capacity of electrode materials in an asymmetric cell is generally different, and the commercially available activated carbon generally has low ion adsorption capacity. , Hence, to lower the effect of active carbon on the potential ion removal capacity of the prepared Ti 3 C 2 T x electrodes as much as possible, the mass of active carbon is deliberately loaded in excess of that of Ti 3 C 2 T x electrodes; in this work, the mass ratio is 5:1. Figure a shows the ion desorption capacity curves of m -Ti 3 C 2 T x , c -Ti 3 C 2 T x , a -Ti 3 C 2 T x , and Ti 3 C 2 T x /C electrodes in a 500 mg L –1 NaCl solution when the voltage is set to 1.2 V. The desalination rate of the Ti 3 C 2 T x electrodes is swift in the early stage, and Ti 3 C 2 T x electrodes essentially reach saturation after 4000 s. At this time, c -Ti 3 C 2 T x and a -Ti 3 C 2 T x only achieve a moderately improved desalination capacity of 15.17 and 14.77 mg g –1 , respectively, compared with m -Ti 3 C 2 T x (13.84 mg g –1 ) owing to the slightly increased specific surface area.…”

Effects of Potassium-Based Activating Agents on the Biochar Derived from Coconut Tree Husk for Enhancing the Surface Area and Supercapacitor Performance

“…The defect amount in the carbon material is ascribed to the intensity of the D band (disordered or defective graphite band), which is used for electrochemical reactions as an active site for ion adsorption. The G band (crystalline graphite band) reveals the graphene property of the carbon material, which helps improve the electrical conductivity …”