Cobalt carbonate hydroxide hydrate nanowire array modified by sulfur doping for aqueous asymmetric supercapacitors

Cobalt carbonate hydroxide hydrate (CCHH) is usually used as precursor for cobalt oxides yet its intrinsic potential for supercapacitors is usually ignored owing to its poor conductivity and low practical capacitance. In this work, low-content sulfur doping in CCHH hierarchical nanowire array grown on nickel foam (CCHH/NF) greatly improves its conductivity while preserving its unique micromorphology. Accordingly, the obtained Co3S4-CCHH/NF electrode delivers a high specific capacitance of 2.10 F cm−2 at 12.5 mA cm−2 (∼6 times the CCHH/NF). Furthermore, due to the synergistic effect of the CCHH and S elements, a unique micromorphology reconstruction transforms the nanowire array to a porous nanosheet net structure. The newly formed structure provides more electroactive sites, thus further increasing the specific capacitance from 2.10 to 3.95 F cm−2 at 12.5 mA cm−2. Although the huge volume expansion accompanied with the micromorphology reconstruction also weakens the contact between the active material and NF which results in capacitance decay, the preponderance of the enhanced electroactive sites gives rise to an excellent cycling stability of the Co3S4-CCHH/NF by maintaining 165.9% of the initial capacitance after 11,000 cycles. When coupled with a conductive carbon cloth (CC) anode, the Co3S4-CCHH/NF//CC aqueous asymmetric supercapacitor also holds outstanding cycling performance (142.6% of the initial capacitance after 20,000 cycles). This work provides a facile and promising method to obtain high-performance Co-based electrodes for aqueous supercapacitors.