High mass loading and additive-free prussian blue analogue based flexible electrodes for Na-ion supercapacitors

Supercapacitor electrodes often suffer from the low mass loading of active substances and the unsatisfactory ion/charge transport features due to the use of various additives. Exploring high mass loading and additive-free electrodes is of huge significance to develop advanced supercapacitors with commercial application prospects, which still remains challenging. Herein, high mass loading CoFe-prussian blue analogue (CoFe-PBA) electrodes are developed by a facile co-precipitation method using activated carbon cloth (ACC) as the flexible substrate. The homogeneous nanocube structure, large specific surface area (143.9 m² g^-1) and appropriate pore size distribution (3.4 nm) of the CoFe-PBA endow the as-prepared CoFe-PBA/ACC electrodes with low resistance and appealing ion diffusion characteristics. Typically, the high areal capacitance (1155.0 mF cm^-2 at 0.5 mA cm^-2) is obtained for high mass loading CoFe-PBA/ACC electrodes (9.7 mg cm^-2). Furthermore, symmetrical flexible supercapacitors (FSCs) are constructed using CoFe-PBA/ACC electrodes and Na₂SO₄/polyving alcohol (Na₂SO₄/PVA) gel electrolyte, achieving superior stability (85.6% capacitance retention after 5,000 cycles), maximum energy density of 33.8 μWh cm^-2 at 200.0 μW cm^-2 and promising mechanical flexibility. This work is expected to offer inspirations for the development of high mass loading and additive-free electrodes for FSCs.