Grain Refinement and Porous Architecture Boost Charge Transport and Rate Kinetics in MOF-Derived CoP@C for Battery-Type Hybrid Supercapacitors with Improved Power and Durability
Hongna Xing, Luyao Wang, Juan Feng, Yanan Liu, Weijun He, Yan Zong, Xinghua Li, Xiuhong Zhu, Xinliang Zheng
Abstract
Metal phosphides have emerged as competitive candidates for supercapacitors owing to their metallic conductivity and ultrahigh theoretical capacitance. Nevertheless, their practical implementation is hindered by sluggish reaction kinetics and structural degradation during cycling. Herein, we propose a synergistic strategy integrating grain refinement and hierarchical porosity design through pyrolysis of ZIF-67, fabricating structurally optimized Co 3 O 4 @C and CoP@C electrode materials. The carbon skeleton inherits the hierarchical porous polyhedral structure of ZIF-67, while the confinement effect of the carbon matrix ensures the formation of ultrasmall Co 3 O 4 /CoP nanoparticles. This architecture offers dual advantages: (1) interconnected carbon channels facilitate rapid ion/charge transport, and (2) ultrasmall nanoparticles maximize active sites for redox reactions. Notably, the CoP@C electrode delivers remarkable areal capacitance (343.1 mC cm –2 /902.0 mF cm –2 at 1 mA cm –2 ) and rate retention (87.8% at 10 mA cm –2 ), surpassing the Co 3 O 4 @C counterpart by 1.5-fold and 1.2-fold, respectively. Advanced Amplitude modulation-Kelvin probe force microscopy (AM-KPFM) analysis reveals that CoP@C possesses a reduced surface potential (ΔΨ = 11.6 mV) in CoP@C compared to that in Co 3 O 4 @C (20.5 mV), displaying faster interfacial charge transfer kinetics. Density functional theory (DFT) calculations further elucidate interfacial electron redistribution, where electron donation from carbon to Co 3 O 4 or CoP. CoP@C behaves with a lower work function (4.8 eV) and closer d-band center positions (−1.47 eV vs Fermi level) than Co 3 O 4 @C (5.4, −1.67 eV), thereby optimizing the adsorption energetics of electrolyte ions and reducing charge transfer resistance. Assembled asymmetric supercapacitors (CoP@C//AC) achieve a high energy density of 46.8 Wh kg –1 at 1696.7 W kg –1, with ultralong cyclability (91.3% retention after 10,000 cycles), surpassing most reported metal phosphide-based devices. This work highlights the synergy between grain refinement and porous architecture engineering in enhancing charge transport and rate kinetics, providing a viable strategy to improve the power density and cycling stability of metal phosphide-based electrodes for advanced energy storage devices.