α-MnO2 composite with gold nanoparticles on carbon cloth modified with MOFs-derived porous carbon for flexible and activity-enhanced sodium-ion supercapacitors
Hanxue Zhao, Kaishuai Yang, Kailan Zhu, Mai Li, Wendong Xu, Waqar ul Hasan, Jiale Wang, Qinglin Deng, Jun Yu, Zhongyi Sun, Paul K. Chu
Abstract
Improving the catalytic activity of electrodes in a limited space is crucial to energy storage devices such as supercapacitors . Herein, the surface activity of the flexible electrode (Au-MnO 2 /CPCN@CC) is enhanced by combining gold particles (AuNPs) modified α-MnO 2 with conductive porous carbon nanoflakes (CPCN) derived from the metal-organic framework (MOF) on carbon cloth (CC). The Au-MnO 2 /CPCN@CC electrode exhibits a higher specific capacity of 503.7 F/g at 0.125 mA/cm 2 and retains 87.68% capacity after 10,000 cycles in 1 M Na 2 SO 4 , while the structure without AuNPs achieves 242.6 F/g and 61.07% capacity retention after 10,000 cycles. The high stability of Au-MnO 2 /CPCN@CC stems from the good pseudocapacitance ratio of 83.80% at 1 mV/s compared to 78.43% of MnO 2 /CPCN@CC and 40.88% of Au/CPCN@CC. The supercapacitor assembled with Au-MnO 2 /CPCN@CC as the positive electrode and activated carbon (AC) as the negative electrode in 1 M NaPF 6 shows an excellent power density of 79.96 W/kg at 71.48 Wh/kg as well as 81.93% capacitance retention after 10,000 cycles. Density-functional theory (DFT) calculations of Au-MnO 2 /CPCN composite reveal a sodium-ion adsorption energy of 3.744 eV and a large DOS near Fermi level. Hence, Au nanoparticles (AuNPs) and MOFs-derived CPCN lead to enhanced surface electron transport of MnO 2 and ultimately superior performance.