Abstract
A nano-porous Al/Au skeleton is constructed to effectively improve the utilization rate of the active MnO2 and the overall adhesion between the current collector and MnO2 in an electrodeposition system. The Al/Au current collector is prepared by first forming a nano-porous structure on the surface of Al foil through etching modification, and subsequently coating an ultra-thin Au layer onto the Al foil. The active MnO2 is electrodeposited on the Al/Au current collector to fabricate a novel Al/Au/MnO2 electrode. The nano-porous skeleton supports MnO2 to grow autonomously inside-out. The ultra-thin Au layer acts as a transition layer to improve the overall conductivity of the current collector (0.35 Ω m−1) and to improve the adhesion with MnO2 as well. Owing to the highly porous structure, the electrochemical properties of the electrode are greatly improved, as evidenced by a remarkable specific capacitance of 222.13 mF cm−2 at 0.2 mA cm−2 and excellent rate capability of 63% capacitance retention at 6.0 mA cm−2. Furthermore, the assembled solid-state symmetric supercapacitor exhibits a high energy density of 0.68 mW h cm−3, excellent cyclic stability (86.3% capacitance retention after 2000 cycles), and prominent flexibility.
Highlights
As an energy supply element, supercapacitors have attracted widespread attention because of their unique energy storage mechanism and the characteristics of low equivalent series resistance, instantaneous high current, and long service life.[1,2,3,4] Generally, there are two types of supercapacitors: electric double layer capacitors (EDLCs) formed by the reversible adsorption and desorption of ions and electrolytes, and pseudocapacitors formed by redox reaction and the Faraday charge– discharge process of active materials.[5]A typical supercapacitor is generally composed of active material and a current collector, electrolyte, and separator
Compared with the electrode prepared by pristine Al foil, the modi ed electrode exhibited superior electrochemical properties with a much higher speci c capacitance, enhanced rate capability and better cyclic stability
The excellent rate capability can be attributed to the nano-porous structure of metal/oxide electrode, in which nanoscale MnO2 grows along the internal pores and rough surface of highly conductive A3/Au current collector, allowing electrons to contact with electrolyte ions and efficiently to provide fast redox reaction even under a high current density
Summary
As an energy supply element, supercapacitors have attracted widespread attention because of their unique energy storage mechanism and the characteristics of low equivalent series resistance, instantaneous high current, and long service life.[1,2,3,4] Generally, there are two types of supercapacitors: electric double layer capacitors (EDLCs) formed by the reversible adsorption and desorption of ions and electrolytes, and pseudocapacitors formed by redox reaction and the Faraday charge– discharge process of active materials.[5]. Paper oriented NiO–TiO2 nanotube arrays electrode by electrochemically anodizing Ni–Ti alloy foils These methods were designed to prepare porous and high Sa current collectors for more active materials to grow, leading to improved speci c capacitance. Another factor worth considering is the adhesion between current collector and active materials, for which affects the electrochemical performance and cyclic stability of supercapacitors. Researchers usually grew carbon-based materials on Al current collector to form double layer supercapacitor, but the speci c capacitance of such electrodes only realized to $100 F gÀ1.13,14 In order to achieve a higher speci c capacitance, transition metal oxide MnO2 was chosen to grow onto the Al current collector to prepare pseudocapacitive capacitors in this work. Based on the Al/Au/MnO2 electrodes, the assembled symmetric solid-state supercapacitor presented excellent exibility, high energy and power density
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