Simultaneous electrodeposition of manganese oxide/poly(o-aminophenol) composites as electrode materials for aqueous electrochemical energy storage†

Developing novel electrode materials is crucial for the development of high-performance electrochemical energy storage devices. Here, a simultaneous electrodeposition method is developed to grow manganese oxide/poly(o-aminophenol) (MnO_x/PoAP) composites on a carbon paper substrate. The formed MnO_x/PoAP exhibits a crystalline Mn_1.92O₄ phase, and the surface of MnO_x/PoAP is rough. The electrochemical energy storage properties of the composites have been investigated, and the optimized MnO_x/PoAP can store charge as a battery-type electrode with a specific capacity of 100.88 mA h g⁻¹ at 1 A g⁻¹ in 2 M (NH₄)₂SO₄ and a specific capacity of 166.94 mA h g⁻¹ at 1 A g⁻¹ in 2 M KCl. Compared to the MnO_x and PoAP prepared using the same electrochemical method, the good charge storage performance of MnO_x/PoAP is mainly attributed to the increased number of active sites and more facile ion diffusion induced by the unique morphology. The charge storage mechanism has been investigated, and the redox processes of carbonyl/hydroxyl groups, amino/imino groups and Mn^3+/4+ are all involved in charge storage, along with the insertion and extraction of cations. When assembled as an aqueous electrochemical energy storage device with MnO_x/PoAP and a 2 M (NH₄)₂SO₄ solution, a specific capacity of 25.35 mA h g⁻¹ at 1 A g⁻¹ is achieved, along with a specific energy density of 57.24 W h kg⁻¹ at a specific power density of 1080 W kg⁻¹. In addition, the device also shows excellent cycling performance (86.02%) after 10 000 cycles. These indicate that forming composites of conducting polymers and inorganic nanostructures is a viable route to achieving high electrochemical energy storage performance.