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Hexagonal Prism Arrays Constructed by Ultrathin Porous Nanoflakes of Carbon Doped Mixed-Valance Co-Mn-Fe Phosphides for Ultrahigh Areal Capacitance and Remarkable Cycling Stability

Abstract

One of the challenges with supercapacitors is achieving ultrahigh specific capacitance by maximizing utilization of active materials while assuring their cycling stability. Herein, we report a significant advance toward the design and fabrication of novel hierarchical hexagonal prism arrays constructed by carbon doped mixed-valance Co-Mn-Fe multi-metallic phosphides ultrathin porous nanoflakes via ion-induced growth of precursor followed by phosphorization. Each hexagonal prism features a architecture consisting of six symmetrically distributed and interlaced nanoflakes with a thicknesses of ~15 nm and many pores of ~10 nm in diameter. New insights into that Fe2+ induced anisotropic growth of Co-Mn oxide hydroxides and partial conversion of Co2+ into Co3+ leading to enhanced electrical conductivity are proposed. Such Co-Fe-Mn phosphides electrode shows a specific areal capacitance reaching 5.06 F cm-2 (at 2 A cm-2), much higher than those for bimetallic phosphides. The high areal capacitance is attributed to the unique architecture lowering flow resistance of the electrolyte wetting, richness in mixed-valances of metals and active sites/interfaces, and enhanced electrical conductivity. The carbon doping substantially improves the cycling stability because it effectively buffers the strain/volume expansion during fast Faradaic reactions. Especially even at a high current density of 20 mA cm2, 100% capacitance retention was achieved after 5000 cycles. An asymmetric device based on such electrode delivers a higher energy density of 53.2 Wh kg-1 (at 399.7 W kg-1) than many previously reported values.

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Publication details

The article was received on 06 Dec 2018, accepted on 31 Jan 2019 and first published on 31 Jan 2019


Article type: Communication
DOI: 10.1039/C8TA11763B
Citation: J. Mater. Chem. A, 2019, Accepted Manuscript

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    Hexagonal Prism Arrays Constructed by Ultrathin Porous Nanoflakes of Carbon Doped Mixed-Valance Co-Mn-Fe Phosphides for Ultrahigh Areal Capacitance and Remarkable Cycling Stability

    R. Niu, G. Wang, Y. Ding, S. Tang, X. Hu and J. Zhu, J. Mater. Chem. A, 2019, Accepted Manuscript , DOI: 10.1039/C8TA11763B

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