Free-Standing Co(OH)₂/Prussian Blue Analogue Nanostructured Electrodes for Flexible Na-Ion Supercapacitors with an Ultrawide Potential Window

The low energy density of flexible supercapacitors (FSCs) limits their practical applications, which can be improved by enhancing their specific capacitance or potential window. Herein, uniform Co(OH)2 nanosheets are grown on activated carbon cloth (CC) by electrodeposition, which are subsequently embedded with Prussian blue analogue (PBA) nanocubes by the ion-exchange, obtaining Co(OH)2/PBA/CC electrodes. The uniform distribution and tight interfacial contact between Co(OH)2 and PBA on CC result in low resistance and high specific capacitance (1175.7 mF cm–2 at 1 mA cm–2). Notably, the asymmetric FSCs (Co(OH)2/PBA/CC//activated carbon/CC) exhibit an ultrawide potential window of 2.1 V and thus yield a high energy density of 0.4 mWh cm–2 at a power density of 1.5 mW cm–2. In addition, the FSCs exhibit excellent mechanical strength and flexibility with 87.1% capacitance retention after 10,000 cycles. This work can provide inspiration for the development of robust Na-ion FSCs with an ultrawide potential window and high energy density.