Fe3O4/MnO2 co-doping phenolic resin porous carbon for high performance supercapacitors

•A series of PR-Fe@MnO2 - X (X = 0, 0.5, 1, 1.5, 2) nanosheet structure was synthesized through one-step carbonization method.•PR-Fe@MnO2 −1.5 exhibited a large specific surface area and a specific capacitance.•These experimental results were consistent with the DFT calculations predictions. Thus, the excellent electrochemical property of PR-Fe@MnO2 composite made it an encouraging electrode material for practical applications like charge storage and in other pseudocapacitors. Using phenolic resin (PR) as a carbon source, potassium ferrate (K2FeO4) and manganese acetate (Mn(CH3COO)2·4H2O) as the dopants, a one-step carbonization method was used to prepare a series of Fe3O4 and MnO2 co-doped composites, which are denoted as PR-Fe@MnO2. During high-temperature carbonization (800 °C), partially amorphous carbon forms a multi-layer graphene structure, making PR-Fe@MnO2 exhibit a high degree of graphitization. After doping, the transition metal Mn was investigated theoretically by performing density functional theory calculations. The results confirmed that doping of moderate Mn ions in the PR-Fe lattice improved the interactions between OH− in the electrolyte and Mn metal center, consequently, the electrical conductivity (19%) of the electrode according to the equivalent series resistance (Rs). The Mn composition also increased the specific area for more electroactive sites and reduced the charge transfer resistance (decreased by 27.7%). As a result, PR-Fe@MnO2–1.5 had the highest specific capacitance of 601 F/g at 1.0 A/g and superior cycling stability (capacitance retention of 97.8% after 10,000 cycles). Furthermore, the assembled PR-Fe@MnO2–1.5//PR-Fe@MnO2–1.5 symmetric supercapacitor provided a specific energy density of 25.7 Wh/kg at a power density of 384.9 W/kg. Construction of PR-Fe@MnO2–1.5 composite and its application in symmetric supercapacitor. [Display omitted]