A sustainable synthesis of mesoporous Mn _{1− x} Ni _x Co ₂ O ₄ nanoparticles: exploring calcination effects on supercapacitor performance

The current work presents the sustainable, calcination-free synthesis of Mn_1-xNi_xCo₂O₄ (MNCO) nanoparticles via a co-precipitation method. This approach eliminates the need for high-temperature calcination, making the process energy-efficient, time-saving, and cost-effective, without compromising the electrochemical performance. The phase of synthesized samples was confirmed via XRD analysis, and the effects of calcination on their electrochemical properties were further studied. Our findings indicate that calcination negatively affects the electrochemical performance of these nanoparticles. Specifically, uncalcined MNCO1 (Mn_0.9Ni_0.1Co₂O₄) demonstrated superior electrochemical performance, achieving a specific capacitance of 559 F g^-1 at 0.5 A g^-1 and excellent cycling stability, retaining 97.29% of its capacitance after 10 000 cycles at 10 A g^-1. These outstanding properties are attributed to its mesoporous pore size distribution and high surface area (73 m² g^-1). An asymmetric supercapacitor (ASC) was assembled using uncalcined MNCO1, activated carbon and PVA/KOH gel as the cathode, anode and electrolyte, respectively. This device demonstrated energy and power densities of 54 Wh kg^-1 and 20 kW kg^-1, respectively. After 20 000 cycles at 3 A g^-1, the supercapacitor exhibited 81.81% capacitance retention with a remarkable coulombic efficiency of 99.96%. The above results are better among asymmetric supercapacitors reported so far. Furthermore, connecting two devices in series successfully powered three green LEDs for more than 4 minutes.