Porous carbon-MnO2 heterostructures for high energy density aqueous ammonium-ion asymmetric supercapacitors

Aqueous ammonium-ion (NH 4 + ) is gaining attention as a viable energy storage option due to the use of NH 4 + as the charge carrier, offering advantages of resource abundance, safety, fast diffusion, and a unique storage mechanism. Despite these benefits, the development of storage devices with NH 4 + as the charge carrier are still in the early stages, highlighting the crucial need to explore suitable electrode materials for the production of high-performance devices. In this study, broken porous carbon nanocages (BPCs) serve as the support structure to form a heterostructure with δ-MnO 2 nanosheets (MnO 2 -BPCs) grown onto them, building aqueous NH 4 + asymmetric supercapacitors (ASCs). Both MnO 2 -BPCs and BPCs act as host materials for storing aqueous NH 4 + , exhibiting high specific capacitance and long cycling durability. The assembled NH 4 + ASCs present good capacitive performance, with a large specific capacitance of 223 F g −1 and capacitance preservation of 91.4 % over 10,000 cycles. The high energy density achieved by NH 4 + ASCs is crucial for advanced energy storage thanks to their elevated specific capacitance and broad operating voltage. The balanced capacitive performance of the positive and negative electrodes is essential in enhancing the energy storage capabilities of NH 4 + ASCs. This work provides a straightforward method for creating porous carbon-MnO 2 heterostructures for NH 4 + storage and paves the way for designing aqueous NH 4 + -based sustainable energy storage systems (SESSs) for capacitive energy storage.