Synergy of VN and Fe2O3 Enables High Performance Anodes for Asymmetric Supercapacitors.

Fe2O3 is 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-2 at 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-3 at a power density of 12.28 mW cm-3 along 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.

Plasma-Assisted Synthesis of NiCoP for Efficient Overall Water Splitting.

Efficient water splitting requires highly active, earth-abundant, and robust catalysts. Monometallic phosphides such as Ni2P have been shown to be active toward water splitting. Our theoretical analysis has suggested that their performance can be further enhanced by substitution with extrinsic metals, though very little work has been conducted in this area. Here we present for the first time a novel PH3 plasma-assisted approach to convert NiCo hydroxides into ternary NiCoP. The obtained NiCoP nanostructure supported on Ni foam shows superior catalytic activity toward the hydrogen evolution reaction (HER) with a low overpotential of 32 mV at -10 mA cm-2 in alkaline media. Moreover, it is also capable of catalyzing the oxygen evolution reaction (OER) with high efficiency though the real active sites are surface oxides in situ formed during the catalysis. Specifically, a current density of 10 mA cm-2 is achieved at overpotential of 280 mV. These overpotentials are among the best reported values for non-noble metal catalysts. Most importantly, when used as both the cathode and anode for overall water splitting, a current density of 10 mA cm-2 is achieved at a cell voltage as low as 1.58 V, making NiCoP among the most efficient earth-abundant catalysts for water splitting. Moreover, our new synthetic approach can serve as a versatile route to synthesize various bimetallic or even more complex phosphides for various applications.