Hybrid bimetallic phosphonates as cathode materials for miniaturized in-plane asymmetric supercapacitor device

The utilization of wearable electronic devices facilitates the development of smart and flexible technology as a superior energy storage device that minimizes the dimension of wearable devices. The simple vacuum filtration method was employed to fabricate the micro-supercapacitor device (MSC) using the as-synthesized bimetallic nickel cobalt phosphonate (NiCoNPO) on the PVDF membrane as substrate. Novel microporous bimetallic metal phosphonates (NiCoNPO, Ni2CoNPO, NiCo2NPO) have been synthesized in a hydrothermal reaction condition by varying the molar ratio (Ni1:Co1; Ni2:Co1; Ni1:Co2) of metal sources without any employment of templating agent. Among these, NiCoNPO exhibits the remarkable specific capacitance of 2308 F g⁻¹ at 1 mV s⁻¹ and long-term cyclic stability up to the 5000th cycle with 99.6 % capacity retention in the three-electrode system. In addition, the electrode material demonstrates an exceptional capacitance of 574 F g⁻¹ with stability (87.6 % retention) in a two-electrode system. Also, it displays excellent performance as a flexible MSC device with an areal capacitance of 123.5 mF cm⁻². Notably, the MSC demonstrates long-term stability up to the 5000th cycle with a capacity retention of 85.6 %, suggesting the electrode material has excellent mechanical flexibility and superior electrochemical performance.