A homologous strategy to parallelly construct doped MOFs-derived electrodes for flexible solid-state hybrid supercapacitors

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Abstract
Developing efficient and cost-effective electrode materials is of essential significance to advance various energy storage technologies, among which flexible supercapacitors hold great promise to meet the growing popularity of wearable electronics. Herein, we report a homologous strategy to parallelly synthesize phosphorus-doped ZnCo2O4 (P-ZnCo2O4@NCC) and nitrogen-doped carbon (NC@NCC) both derived from ZnCo-metal-organic frameworks (MOFs) precursors in-situ grown on dopamine-modified carbon cloth (NCC) as conductive substrates. Impressively, the as-obtained P-ZnCo2O4@NCC can achieve a high specific capacitance of 2702.2 mF·cm−2 at 1 mA·cm−2 with the capacitance retention rate exceeding 70.6% at 10 mA·cm−2, demonstrating the outstanding rate capability. Moreover, flexible solid-state hybrid supercapacitors, using P-ZnCo2O4@NCC as positive electrode and NC@NCC as negative electrode, are assembled with poly(vinyl alcohol) (PVA)/KOH as the gel electrolyte, which deliver the energy density of 11.9 mWh·cm−3 when the power density reaches up to 47.3 mW·cm−3. In addition, 85.15% of the initial specific capacitance is maintained after 5000 continuous cycles and no obvious capacitance decay is observed under different bending conditions, revealing the excellent cycling stability and flexibility. As a proof-of-concept demonstration, two as-assembled hybrid supercapacitors connected in series can light up a red light-emitting diode (LED) under the bending angle of 180°, heralding the feasibility for broad practical applications.

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