The In Situ Synthesis of Fe(OH)3 Film on Fe Foam as Efficient Anode of Alkaline Supercapacitor Based on a Promising Fe3+/Fe0 Energy Storage Mechanism

Abstract Herein, a simple in situ charge/discharge activation strategy is proposed to synthesize Fe(OH)3 film on Fe foam as an efficient anode of supercapacitors. The physical characteristics of electrodes are characterized and the electrochemical energy storage performances are investigated. Importantly, it is demonstrated the as‐synthesized Fe(OH)3@Fe foam electrode adopted a novel Fe 3+ /Fe 0 redox reaction mechanism for energy storage in alkaline electrolytes. Compared with previously reported Fe 3+ /Fe 2+ mechanisms, the Fe 3+ /Fe 0 redox couple shows a more promising application value (e.g., higher theoretical‐specific capacitance, excellent conductivity of its reduction state). As for supercapacitor anodes, the electrode achieves high areal capacitance of 5.55–3.94 F cm −2 at a current range of 20–200 mA cm −2 and shows good stability for high‐rate and long‐term cycling. The assembled single supercapacitor device gives a high energy density of 11.64–7.43 Wh m −2 at a power density of 157–1461 W m −2 . More importantly, the as‐adopted in situ activation strategy may also have potential value for synthesizing other transition metal oxide‐based products.