Decorating N-doped carbon-coated cobalt phosphide nanoparticles onto N-doped carbon nanotubes for high-performance supercapacitors and efficient methanol electro-oxidation

Cobalt phosphide (CoP) has become a promising electrode material for supercapacitors and methanol electro-oxidation due to its high electrical conductivity and and multiple oxidation states. However, the insufficient electroactive sites and large volume changes restrict its electrochemical performance. Herein, a novel CoP/carbon nanocomposite electrode material is designed and synthesized by decorating N-doped carbon (NC) coated CoP nanoparticles onto N-doped carbon nanotubes (N-CNTs). N-CNTs serve as support to grow CoP nanoparticles, which effectively reduces the sizes and aggregation of CoP nanoparticles and provides more electroactive sites. Density function theory calculation results confirm that the coating of NC on CoP nanoparticles increases the electrical conductivity of CoP by transferring electrons from NC to CoP. Meanwhile, a built-in electrical field is formed at the CoP/NC interface, resulting in higher electron/ion transfer efficiency as well as easier surface OH – adsorption. Moreover, the flexible NC shell and N-CNTs supports together effectively withstand the mechanical stress and buffer volume changes of CoP during the charge/discharge processes. Therefore, the obtained N-CNTs@CoP@NC nanocomposite electrode demonstrates high specific capacities (1003 and 621C g −1 at 1 and 10 A g −1 , respectively) and good cycling performance (91.2 % retention of initial capacity after 10,000 cycles at 5 A g −1 ). Furthermore, it also shows a current density of up to 281 mA cm −2   at a scan rate of 10 mV s −1   with 92.4 % retention of initial current density in 1 M KOH with 0.5 M methanol. These results highlight a feasible strategy for improving practical capacities and cyclic stability of CoP-based electrode materials by integrating nanostructured CoP with one/two-dimensional carbon materials.