Synthesis of Carbon-modified Rod-like Nickel-cobalt Phosphides with Enhanced Energy-storage Performance for Supercapacitors

The use of metal-organic frameworks (MOFs) as precursors has garnered growing recognition due to their appeal in synthesizing carbon/transition-metal phosphide composites. Here, we report the synthesis of carbon-modified rod-like nickelcobalt phosphide (NiCoP-N) and nickel-cobalt phosphide (NiCoP-A) through a low-temperature in situ phosphorization process using NiCo-MOF-74 as the precursor, with the annealing atmosphere serving as the key variable. The characterization revealed that compared with NiCoP-A, NiCoP-N possesses the boosted specific surface area, improved dispersion, and enhanced charge transport capability. Benefiting from these advantages, NiCoP-N delivers excellent rate performance and capacity retention. Remarkably, the optimized Ni 2 Co 1 P-N electrode achieves a gravimetric capacitance of 898 F g -1 at 1 A g -1 , with 78.4% of this value maintained under 20 A g -1 , significantly outperforming NiCoP-A, which retains only 41.5%. With 2000 cycles, Ni 2 Co 1 P-N maintains a mass-specific capacitance of 524.8 F g -1 , while Ni 2 Co 1 P-A decreases to 230.4 F g -1 . Additionally, an asymmetric supercapacitor assembled from Ni2Co1P-N and activated carbon can offer an energy density of 27.2 Wh kg -1 under 750 W kg -1 , and hold 100% of its initial specific capacitance following 5000 cycles at 20 A g -1 , confirming its excellent long-term durability.