Bifunctional Microwave-Assisted Molybdenum-Complex Carbon Sponge Production for Supercapacitor and Water-Splitting Applications

The synthesis of dual-function molybdenum (Mo)-complex carbonous sponges is reported for elucidating their utilization as positive and negative electrodes in electrochemical devices and their applicability to the active oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in electrocatalytic devices. Molybdenum (Mo)-coordinated polyvinyl alcohol gel is converted into a porous Mo-complex nitrogen-rich carbonous sponge (MNCS) via microwave and low-temperature-annealing processes as a positive electrode. This MNCS was further thermally treated at a higher temperature to prepare a more carbonized Mo-complex N-doped carbon sponge (cMNCS) as a negative electrode. Both sponges were lightweight and porous and exhibited excellent specific capacitances of 562 F g^-1 as a positive MNCS electrode and 937 F g^-1 as a negative cMNCS electrode. The asymmetric supercapacitor assembled using them reveals a power density of 887.5 W kg^-1 at an energy density of 36 Wh kg^-1, in addition to a retention rate of >95% after 5000 cycles. We furthermore demonstrate the electrocatalytic capabilities of these materials with overpotentials of -170 and -220 mV for the HER and 1.70 and 1.53 V for the OER at a current density of 10 mA cm^-2 using a water-splitting electrocatalyzer.

Highly Compressible Carbon Sponge Supercapacitor Electrode with Enhanced Performance by Growing Nickel-Cobalt Sulfide Nanosheets

The development of compressible supercapacitor highly relies on the innovative design of electrode materials with both superior compression property and high capacitive performance. This work reports a highly compressible supercapacitor electrode which is prepared by growing electroactive NiCo₂S₄ (NCS) nanosheets on the compressible carbon sponge (CS). The strong adhesion of the metallic conductive NCS nanosheets to the highly porous carbon scaffolds enable the CS-NCS composite electrode to exhibit an enhanced conductivity and ideal structural integrity during repeated compression-release cycles. Accordingly, the CS-NCS composite electrode delivers a specific capacitance of 1093 F g^-1 at 0.5 A g^-1 and remarkable rate performance with 91% capacitance retention in the range of 0.5-20 A g^-1. Capacitance performance under the strain of 60% shows that the incorporation of NCS nanosheets in CS scaffolds leads to over five times enhancement in gravimetric capacitance and 17 times enhancement in volumetric capacitance. These performances enable the CS-NCS composite to be one of the promising candidates for potential applications in compressible electrochemical energy storage devices.