Nickel nanoparticles modified MnO nanosheet arrays for high-performance supercapacitor with long-lasting and sustainable capacitance increase

Abstract Rational design of binder-free electrode materials with good electronic conductivity, high specific capacitance and long cyclic stability is of great interest for high-performance pseudocapacitors. Herein, an etching-induced co-precipitation approach coupled with reduction and dehydration is developed, through which the Ni-modified MnO (Ni/MnO) nanosheet arrays can be successfully grown on Ni foam and directly used as binder-free electrode for pseudocapacitors. During the synthesis, the nickel foam acts as not only conductive substrate but also nickel source for the growth of the composite nanosheet arrays. With the introduction of Ni nanoparticles, the conduction of the electrons is efficiently promoted. Meanwhile, the porous structure of the Ni/MnO nanosheet arrays gives rise to the larger contact area between the active material and the electrolyte. Furthermore, the Ni nanoparticles on the MnO nanosheets and the Ni substrate can both participate in the electrochemical charge storage processes, which exerts extra positive effects on the improvement of the capacitance for the composite material. As a result, the as-prepared Ni/MnO nanosheet arrays electrode demonstrates excellent electrochemical performances with high specific capacitance achieved. More strikingly, a long-lasting and sustainable capacitance increase upon cycling is observed, which is systematically investigated and discussed. Overall, this work provides a facile and effective method to fabricate composite pseudocapacitive material with a hierarchical structure, which may open a promising direction for high-performance pseudocapacitors.