Electrochemical characteristics of flexible open-cell supercapacitors employing different electrolyte types: KOH and ionic liquid

A carbonate hydroxide compound with substantial wettability was deposited on a porous Ni foam substrate, employing the Ni-based chemical precursor by a facile hydrothermal method. The resulting Ni₂(CO₃)(OH)₂ electrode exhibits a nanowire structure characterized by a significant surface area. These electrodes represent highly promising materials for faradaic capacitors. They demonstrate high wettability on the electrode surface, facilitating charge and discharge processes on the electrode surface through redox reactions. A flexible hybrid open-cell supercapacitor, designed to operate at 1.5 V, was constructed with the Ni₂(CO₃)(OH)₂ electrode as the positive terminal and graphene as the negative terminal, employing two distinct electrolytes (KOH and ionic liquid named MPPyFSI with 1-Methyl-1-propylpyrrolidinium Bis(fluorosulfonyl)imide structure). The open-cell devices, fabricated with 6 M KOH and MPPyFSI electrolyte, exhibit high energy densities of 39.6 and 24.8 Wh kg⁻¹ and power densities of 1752.1 and 2908.5 W kg⁻¹ at current densities of 2 A g⁻¹, respectively. Furthermore, the energy storage devices utilizing aqueous KOH and MPPyFSI demonstrate excellent stability, maintaining 73.4 and 87.1% of their specific capacity after 5,000 charge/discharge cycles. The mechanical properties of the flexible open-cell device were characterized, and the electrochemical values corresponding to the banding angle of the device were measured.