The design and synthesis of high-performance, environmentally friendly, and economical electrode materials are essential for the development of energy-efficient capacitive deionization (CDI) technologies. As a strategy to turn waste into resource, abundant and low-cost sludge biomass materials are promising candidates for the preparation of CDI electrodes. In this work, a series of iron-containing dyeing sludge-derived biochar with different iron compounds were successfully prepared by direct pyrolysis followed by chemical modification treatment, and applied them as hybrid capacitive deionization (HCDI) cathodes for the first time. The ion adsorption capacity of HCDI electrode is up to 78.76 mg g-1 in 500 mg L-1 NaCl solution at 1.2 V and stable regeneration performance over 50 cycles. XPS measurements reveal that the storage mechanism of ions is a pseudocapacitance effect induced by the Fe2+/Fe3+ redox couple, enabling reversible and fast ion storage. The enhanced HCDI performance is ascribed to the well dispersed iron compounds active sites, rich pore structure and superior hydro-philicity. This work offers a promising strategy for the synthesis of high-performance HCDI electrode materials from sludge biomass, and demonstrates the superior pseudocapacitive performance of Fe2+/Fe3+ redox couple.
