Advances in ink-jet printing of MnO2-nanosheet based pseudocapacitors

An overview of recent progress in the development of 2D manganese oxide nanosheet‐based pseudocapacitors is provided, with emphasis on underlying methods and strategies. 2D manganese oxide nanosheets are sheet‐like monocrystallites of ≈0.5 nm thickness and lateral dimensions of 50–5000 nm. MnO2 nanosheets are synthesized in the form of colloids, which can be readily utilized in wet‐chemical processes like ink‐jet printing. The synthetic strategies to make 2D δ‐MnO2 nanosheets by bottom‐up and top‐down approaches are discussed, and the relationship between the ionic defect structure of δ‐MnO2 nanosheets and their pseudocapacitance is explained. The basic principles and experimental challenges of ink‐jet printing of 2D materials at high resolution, and the development of 2D nanosheet‐based inks are discussed, with emphasis on δ‐MnO2, graphene, and graphene oxide. The fabrication and performance of δ‐MnO2 nanosheet derived pseudocapacitors, including ink‐jet printed flexible microsupercapacitors, is described. The relationship between the electrode thickness and layer architecture and the specific capacitance is explained.