Heterostructured polypyrrole/hybrid iron oxide composite film as highly stable anode for pseudocapacitors

Abstract Pseudocapacitive iron oxide materials own high theoretical capacitance as desirable anode materials for electrochemical energy storage. The poor electrical conductivity and sluggish ion diffusion kinetics of iron oxides are the two main obstacles that hinder their practical application. In this work, a simple and fast electrodeposition method to fabricate composite film of polypyrrole (PPy) and hybrid iron oxide (FeOx) on a 3D exfoliated graphite (EG) current collector is demonstrated. The experimental results suggest that the valence state of Fe in FeOx decreases obviously during the concurrent electrodeposition, which effectively regulates the electronic transmission and formed heterostructured PPy-FeOx iron oxide. The hybrid iron oxide (Fe2O3 and Fe3O4) phase interface synergistically improves the pseudocapacitance of the composite film. The as-prepared PPy-FeOx composite film exhibits a high areal capacitance of 2.0 F cm−2 at 1 mA cm−2 and ultrahigh cycling stability (105.6% capacitance retention after 10 000 charge/discharge cycles). The assembled asymmetric capacitor (ASC) based on PPy-FeOx can deliver a volumetric energy density of 3.44 mWh cm−3 at a power density of 6.72 mW cm−3. This work offers a new strategy for the concurrent electrodeposition of conducting polymers and metal oxides with strong interactions, leading to great development in energy storage applications.