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Fe2O3is one of the most common anode materials beyond carbons but suffers from unsatisfactory capacity and poor stability, which are associated with the insufficient utilization of active material and the structural instability caused by the phase transformation. In this work, we report an effective strategy to overcome the above issues through electronic structure optimization by constructing delicately designed Fe2O3@VN core–shell structure. The Fe2O3@VN/CC exhibits a much higher areal capacity of 254.8 mC cm–2at 5 mA cm–2(corresponding to 318.5 mF cm–2, or 265.4 F g–1) than the individual VN (48 mC cm–2, or 60 mF cm–2) or Fe2O3/CC (93.36 mC cm–2, or 116.7 mF cm–2), along with enhanced stability. Moreover, the assembled asymmetric supercapacitor devices based on Fe2O3@VN/CC anode and RuO2/CC cathode show a high stack energy density of 0.5 mWh cm–3at a power density of 12.28 mW cm–3along with good stability (80% capacitance retention after 14000 cycles at 10 mA cm–2). This work not only establishes the Fe2O3@VN as a high-performance anode material but also suggests a general strategy to enhance the electrochemical performance of traditional anodes that suffer from low capacity (capacitance) and poor stability.

We report a versatile route for the preparation of metal phosphides using PH3plasma for supercapacitor applications. The high reactivity of plasma allows rapid and low temperature conversion of hydroxides into monometallic, bimetallic, or even more complex nanostructured phosphides. These same phosphides are much more difficult to synthesize by conventional methods. Further, we present a general strategy for significantly enhancing the electrochemical performance of monometallic phosphides by substituting extrinsic metal atoms. Using NiCoP as a demonstration, we show that the Co substitution into Ni2P not only effectively alters the electronic structure and improves the intrinsic reactivity and electrical conductivity, but also stabilizes Ni species when used as supercapacitor electrode materials. As a result, the NiCoP nanosheet electrodes achieve high electrochemical activity and good stability in 1M KOH electrolyte. More importantly, our assembled NiCoP nanoplates//graphene films asymmetric supercapacitor devices can deliver a high energy density of 32.9Whkg−1at a power density of 1301Wkg−1, along with outstanding cycling performance (83% capacity retention after 5000 cycles at 20Ag−1). This activity outperforms most of the NiCo-based materials and renders the NiCoP nanoplates a promising candidate for capacitive storage devices.