Inkjet-Printed Transparent Asymmetric Microsupercapacitors with Mesoporous NiCo₂O₄ and Mn₂O₃ Electrodes

In order to cater to the energy needs of emerging portable and wearable electronics, the demand for reliable, environmentally friendly, transparent, and high-performance microsupercapacitors (MSCs) is rapidly increasing. In this context, a cost-effective, substrate-independent, and high-throughput fabrication process, such as printing, can be ideally suitable to accommodate the large volume demand of such energy storage devices. Within the electrode materials of choice, the pseudocapacitive oxides can offer a combination of high optical transparency and large specific capacitance. In this study, large surface-to-volume ratio oxide electrodes based on transparent and high capacitance NiCo 2 O 4 have been fabricated using a commercial inkjet printing method and electrochemically characterized to demonstrate a record gravimetric specific capacitance of 4122 F g –1 (1649 C g –1 ) at a specific current of 1 A g –1 . Here, the high-surface-area mesoporous NiCo 2 O 4 electrodes have been realized by mimicking the evaporation-induced self-assembly technique using a soft templating agent, Pluronic F127. Next, inkjet-printed, transparent asymmetric MSCs are realized with a single-step annealing routine with mesoporous NiCo 2 O 4 as the cathode and mesoporous Mn 2 O 3 as the anode material. These MSCs have shown a promising specific gravimetric capacitance of 318 F g –1 at a voltage scan rate of 2 mV s –1, and in addition, they have demonstrated an excellent gravimetric energy density and a power density of 165 W h kg –1 and 475 kW kg –1 at a constant current of 1 and 500 A g –1, respectively. Furthermore, the printed asymmetric MSCs have also demonstrated optical transparency >90% at the wavelength of 550 nm, thereby validating their potential to be used in transparent electronic and optoelectronic applications.