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Abstract A simple hydrothermal method is developed for the growth of NiCo 2 O 4 nano-needle arrays on a filter paper carbon (FC) substrate for use as a high performance electrode for supercapacitors. The as-synthesized NiCo 2 O 4 /C composites exhibited high specific capacitance (995.2 F g−1 at a current density of 10 A g−1) and excellent cycling performance (no capacitance loss after 3000 cycles). The 3D framework of the FC substrate not only prevents the aggregation of NiCo 2 O 4 nanoparticles, but also improves its electrical conductivity, thus leading to excellent electrochemical performance. Moreover, an asymmetric supercapacitor was assembled by using the NiCo 2 O 4 /C composites and activated carbon as the positive and negative electrode, respectively, and provided a maximum energy density of 20.87 Wh kg−1 at a power density of 374.6 W kg−1 and a maximum power density of 7.48 kW kg−1 at an energy density of 11.43 Wh kg−1 within a potential window of 0–1.5 V, demonstrating the potential of the composites for use in high performance energy storage systems. Highlights • Filter paper derived carbon (FC)/NiCo 2 O 4 was prepared by hydrothermal method. • The FC with open channels increased the electron and ion transport rates. • The FC-based supercapacitor exhibited good capacity and cycling stability. [ABSTRACT FROM AUTHOR]

Abstract: To mitigate the mass transfer limitations of a highly viscous room temperature ionic liquid (RTIL) electrolyte, systematic characterizations of viscosity, ionic conductivity, apparent triiodide diffusion coefficient and photovoltaic response of an alternative cost-effective and highly conductive binary RTIL mixture of 1-ethyl-3-methylimidazolium trifluoroacetate (EMIATF) and 1-methyl-3-propylimidazolium iodide (PMII) were investigated. An emphasis was placed on the dynamics of electron transport and charge recombination processes; specifically, a focus was placed on the effective electron diffusion length and charge collection efficiency in the devices. Notably, the introduction of perfluorinated anions, with a strong delocalization of the negative charge over the anion backbone, was able to weaken the hydrogen bonding with the imidazolium cations and, thus, decrease the viscosity and increase the ionic conductivity of the electrolyte. A sealed device that employed the binary RTIL achieved an overall conversion efficiency of 5.22% under irradiation of 100mWcm−2, which increased the value by 30% compared to a device with a blank PMII-based RTIL electrolyte. Electrochemical impedance spectroscopy and intensity-modulated photovoltage/photocurrent spectroscopy analysis revealed that employment of this alternative binary RTIL electrolyte system was able to significantly decrease the diffusion resistance of triiodide species in the electrolyte and retard the charge recombination between the injected electrons with triiodide anions in the electrolyte, thus improving the effective electron diffusion length and charge collection efficiency in the device. The charge collection efficiency was certified to be the dominant parameter governing the short-circuit photocurrent density and the overall conversion efficiency of devices with RTIL electrolyte. [Copyright &y& Elsevier]