碳海绵上电化学沉积Fe_2O_3纳米片及其增强电容性能

设计高性能的可压缩电极是实现可压缩电容器器件的关键,碳海绵(CS)具有理想的压缩形变,但却受制于有限的容量。本工作以CS为可压缩基底,通过恒电流沉积及低温热处理技术,在CS骨架上均匀沉积了α-Fe_2O_3纳米片。复合电极中Fe_2O_3的负载量随沉积时间的延长逐渐增加,且在沉积16 h后达到饱和。系统地考察了CS-Fe_2O_3复合电极在不同压力下的可压缩性能,并在三电极体系中,通过循环伏安、恒电流充放电等方法研究了CS-Fe_2O_3复合电极在3.0mol·L~(-1)KOH电解液中的电容性能。结果表明,当复合电极CS-Fe_2O_3压缩率减小时,电极的内阻增大,比电容相应减小。CSFe_2O_3-12电极在电流密度为1 A·g~(-1)时的最大比电容为294 F·g~(-1),且经过10000次恒电流充放电后,电容量仍然能保持初始值的81%,是一种潜在的电化学性能稳定的可压缩超级电容器电极材料。

Growing Iron Oxide Nanosheets on Highly Compressible Carbon Sponge for Enhanced Capacitive Performance

Compressible supercapacitor is a promising flexible energy storage device in view of its excellent capacitive performance, which is recoverable at different compression states. The compressible electrode constitutes the core component that largely determines the performance of a compressible supercapacitor. Commercial polymer sponges are highly compressible materials because most of them are composed of elastic and interconnected polyurethane fibers. However, polymer sponges cannot be directly used as supercapacitor electrodes due to their non-conductive polymer framework. In contrast, carbon sponge (CS) derived from melamine sponge has superior compressible property and exhibits substantially improved conductivity compared to commercial polymer sponge. However, the low specific surface area of CS leads to low specific capacitance, which severely limits its application as compressible supercapacitor electrodes. Currently, pseudocapacitive materials are grown on the conductive CS framework to form hybrid electrodes with improved specific capacitance. Among various pseudocapacitive electrode, iron oxides have attracted considerable attentions due to their natural abundance, high theoretical specific capacitance, and negative working potential. Moreover, the much higher specific capacitance than that of carbon electrodes makes iron oxides one of promising negative candidates for configuring an asymmetric supercapacitor. Herein we report the successful growth of α-Fe₂O₃ nanosheets on CS by electrodeposition followed by low-temperature thermal annealing. The α-Fe₂O₃ on CS displays typical nanosheet morphology with mass loading ranging from 3.4 to 6.7 mg·cm^-3 that can be facilely controlled by extending the deposition time from 4 to 16 h. The CS-Fe₂O₃ electrode retains 90% of its geometric height even after manual compression for 100 cycles. Moreover, the CS-Fe₂O₃ can withstand 60% strain even at Fe₂O₃ mass loading as high as 6.5 mg·cm^-3. The performance of the CS-Fe₂O₃ electrode at different strains was systematically investigated in 3.0 mol·L^-1 KOH aqueous electrolyte by cyclic voltammetry (CV), galvanostatic charge-discharge, and electrochemical impedance spectroscopy (EIS) in a three-electrode system. Our results show that the CS-Fe₂O₃ composite electrode produces lower specific capacitance at lower strain. The EIS characterization and IR drop results indicate that this is due to the larger internal resistance arising from looser contact of electrode with the current collector and longer ion diffusion length. Particularly, the CS-Fe₂O₃-12 electrode delivers a maximum specific capacitance of 294 F·g^-1 at a current density of 1.0 A·g^-1, 1.7-times higher than that of CS substrate. Assuming that the specific capacitance of CS-Fe₂O₃-12 is derived from the double-layer capacitance of CS and the pseudocapacitance of Fe₂O₃, the capacitance of Fe₂O₃ nanosheets in the hybrid is calculated to be as high as 421 F·g^-1, much higher than most of recently reported results, showing that the sheet-like structure with more exposed active sites and short ion pathways could dramatically improve the utilization efficiency of the electrode for reversible faradaic reactions. More importantly, the CS-Fe₂O₃-12 electrode retains 87% of its initial capacitance after continuous charge-discharge at 5.0 A·g^-1 for 10000 cycles, showing promising application as a stable and compressible supercapacitor electrode.