Investigating electrochemical behavior of cobalt pentacyano(methylaniline)ferrate(II) in various aqueous electrolytes for supercapacitor application

Electrolytes play a significant role in improving the stability and specific capacity of supercapacitors; however, they have gained less attention compared to the designing of electrode materials. This study presents the supercapacitor application of novel Prussian blue analog (PBA)-based fabricated electrodes in different electrolytes. PBA was derived by the ligand substitution of sodium pentacyanonitrosyl ferrate(iii) dihydrate followed by precipitation with cobalt salt to yield cobalt pentacyano(methylaniline)ferrate(ii) (CoPCF). The fabricated electrode exhibited specific capacity of 390, 233, 175, and 83 mA h g(-1) in 3 M KOH, 1 M NaOH, 1 M LiOH, and 1 M KNO3 at 1 A g(-1) with capacity retention of 88.80%, 89.95%, 92.42%, and 90.80%, respectively, after 1000 continuous charge-discharge cycles. Furthermore, a solid-state asymmetric supercapacitor (ASC) device was fabricated using a PVA/KOH polymer gel electrolyte that exhibited a specific capacity of 56 mA h g(-1) with a specific energy density of 71 W h kg(-1) and a specific power density of 2560 W kg(-1) at a current density of 1 A g(-1), with excellent capacity retention of 93% over 2000 continuous (dis)charge cycles. These results demonstrated that the introduction of organic ligands in the framework of PBAs along with the selection of the right electrolyte is an effective strategy in the development of high-capacity and stable supercapacitor electrodes.