Strongly coupled polypyrrole/molybdenum oxide hybrid films via electrochemical layer-by-layer assembly for pseudocapacitors

There is an ever increasing demand for advanced electrode materials with well-defined micro-nanostructures for supercapacitors. Both polypyrrole (PPy) and molybdenum oxide (MoOx) are promising candidates for capacitive applications, yet each has limitations. Here, a facile electrochemical method capable of assembling strongly coupled layer-by-layer (LbL) PPy/MoOx hybrid films on a 3D exfoliated graphite current collector is demonstrated. The strong interlayer interaction between PPy and MoOx was studied. The spectroscopy results indicate that the protonation level of PPy is enhanced and the valence state of Mo in MoOx is reduced, which synergistically improve the charge transfer kinetics of the composites. LbL-PPy/MoOx achieves a high specific capacitance of 398 F g(-1) and good cycling stability. The quantitative calculation suggests that the strong coupling effect contributes more than 50% of the total capacitance at a fast discharge rate (e.g., 20 A g(-1)). A 2.2 V asymmetric capacitor using LbL-PPy/MoOx as the anode can deliver a high energy density of 72.7 W h kg(-1) at a power density of 343 W kg(-1). Our findings disclose the interfacial interaction between PPy and MoOx in the composite materials and could open up new opportunities for the fabrication of other composite materials with enhanced interactions, leading to great development in a plethora of applications.