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

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.