P/C collaborative optimization strategy to enhance electrochemical performance of CoO electrode

Transition metal phosphides are emerging as promising electrode materials for energy storage devices because of their higher activity than the oxides counterparts. However, they usually converse to metal hydroxides fast and the P element is depleted during cycles. Here, we report a collaborative optimization strategy by a simple one-step CVD method to address this issue. A synergistic effect between the phosphorization and carbonization significantly enhancing the electrochemical performance of the cobalt oxides is found. The carbonization increases the P content in the sample and the produced carbon layer serving as a protection shell slows the loss of P elements during repeated charging and discharging process. While the phosphorization induces the formation of abundant pores in the carbon layer which is favorable for the electrolyte ions entering into inner active material. Accordingly, the obtained CoO-P/C sample shows high specific capacitance (5 F cm−2 at 10 mA cm−2), excellent rate capability and cyclic stability with 88.6% retention after 5000 cycles at 30 mA cm−2, much better than the samples only treated with P or C modification. In addition, the asymmetric supercapacitor assembled by CoO-P/C and carbon cloth (CC) delivered an energy density of 0.24 mWh cm−2 at a power density of 9.16 mW cm−2, and extraordinary cyclic performance by preserving 181.48% of the initial specific capacitance after 20,000 cycles at 30 mA cm−2. This work provides a simple P/C collaborative optimization strategy to improve the electrochemical performance of metal oxides electrodes.