MOF-Derived Hollow Heterostructure MnCo2O4@Co9S8 Nanocages as a High-Performance Bifunctional Electrode for Water Electrolysis and Flexible Supercapacitor

Bifunctional electrodes with high electrochemical activity for oxygen evolution reaction (OER) and capacitance characteristics are essential for overall water-splitting devices and supercapacitors. Here, the S-etched Co/Mn-metal–organic frameworks (Co/Mn-MOF) derivative (MnCo2O4@Co9S8-10) electrode with dodecahedral hollow heterostructure was prepared by a vulcanization strategy, which greatly improves the bifunctional activity of the electrode. Specifically, the OER requires low overpotentials of 297 and 340 mV to provide current densities of 100 and 500 mA cm–2, respectively, and it remained stable in alkaline electrolyte for 300 h using a high current cycle test. The activity of the overall water-splitting electrolyzer did not decrease significantly even in alkaline simulated seawater, which means that it has a resistance to chlorine corrosion. In terms of capacitive performance, the MnCo2O4@Co9S8-10 electrode shows a specific capacitance of 1555.43 F g–1 at 0.5 A g–1. The assembled MnCo2O4@Co9S8-10//AC battery–supercapacitor hybrid (BSH) has a high energy density of 154.18 W h kg–1 at 388.69 W kg–1 power density, and the capacitance retention rate is still as high as 93.4% after 50,000 cycles. The self-assembled flexible solid-state battery successfully lights up the LED board. These results demonstrate the wide applicability of the high-performance bifunctional MnCo2O4@Co9S8-10 electrode in supercapacitors, wearable electronic devices, water splitting, and even seawater electrolysis devices and reveal promising prospects with important implications for energy storage and hydrogen economy.