Scanty graphene-driven phase control and heteroatom functionalization of ZIF-67-derived CoP-draped N-doped carbon/graphene as a hybrid electrode for high-performance asymmetric supercapacitor

Zeolitic imidazolate framework (ZIF)-derived materials have been explored as promising electrode for energy storage, owing to their tunable composition, high porous structure, and heteroatom-based active sites. Herein, we report cobalt phosphide-draped N-doped carbon/graphene hybrid (CoP-NPC/GS) synthesized from ZIF-67 precursor via a single-step in-situ carbonization and phosphidation. The CoP-NPC/GS hybrid performed as a promising positive electrode with superior electrochemical performance - high capacitance (165 F g(-1) at 7 A g(-1) compared to 97 F g(-1) for CoP-NPC), enhanced rate capability, and promoted cycling stability (similar to 88% after 10,000 cycles). Excellent performance of the CoP-NPC/GS was derived from scanty graphene (2 wt%)-driven compositional variation, which promotes the redox-active CoP phase and higher nitrogen content offering enhanced electronic conductivity. Besides, CoP-NPC/GS performed well as a negative electrode, derived from double-layer capacitance of porous carbon, realizing a capacitance of similar to 71 F g(-1) at 1 A g(-1) but inferior to CoP-NPC, which was regulated by pyridinic nitrogen-induced pseudocapacitance. A fabricated CoP-NPC/GS parallel to CoP-NPC asymmetric device displayed an energy density of 10 Wh Kg(-1) at 700 W kg(-1), with excellent cyclability (similar to 100%) till 11,000 cycles. This study clarifies the role of scanty graphene on the phase control and heteroatom functionalization of phosphide-based electrode, beneficial for enhanced supercapacitive performance. (C) 2020 Elsevier Inc. All rights reserved.

Automated summary

ZIF-derived CoP-NPC/GS hybrid electrode exhibits superior electrochemical performance with high capacitance, enhanced rate capability, and stable cycling performance. The role of graphene in promoting redox-active CoP phase and enhanced electronic conductivity is key to the excellent performance of the electrode.