Toward Low-Cost and Sustainable Supercapacitor Electrode Processing: Simultaneous Carbon Grafting and Coating of Mixed-Valence Metal Oxides by Fast Annealing

There is a rapid market growth for supercapacitors and batteries based on new materials and production strategies that minimize their cost, end-of-life environmental impact, and waste management. Herein, mixed-valence iron oxide (FeO(x)) and manganese oxide (Mn(3)O(4)) and FeO(x)-carbon black (FeO(x)-CB) electrodes with excellent pseudocapacitive behavior in 1 M Na(2)SO(4) are produced by a one-step thermal annealing. Due to the in situ grafted carbon black, the FeO(x)-CB shows a high pseudocapacitance of 408 mF cm(−2) (or 128 F g(−1)), and Mn(3)O(4) after activation shows high pseudocapacitance of 480 mF cm(−2) (192 F g(−1)). The asymmetric supercapacitor based on FeO(x)-CB and activated-Mn(3)O(4) shows a capacitance of 260 mF cm(−2) at 100 mHz and a cycling stability of 97.4% over 800 cycles. Furthermore, due to its facile redox reactions, the supercapacitor can be voltammetrically cycled up to a high rate of 2,000 mV s(−1) without a significant distortion of the voltammograms. Overall, our data indicate the feasibility of developing high-performance supercapacitors based on mixed-valence iron and manganese oxide electrodes in a single step.