Abstract
Hierarchically ordered structures with low tortuosity, excellent mechanical flexibility, high optical transparency, and outstanding electrical conductivity are critically important in developing flexible transparent supercapacitor electrodes for innovative applications in electronics and displays. Here a CVD process is employed to fabricate leaf-skeleton inspired electrodes, which are reticulated monolithic networks consisting of carbon nanostructures serving as a 3D spongy core and graphene-based films as a protective/conductive shell. The network electrodes show optical transmittance of 85–88%, an electrical sheet resistance of ~1.8 Ω/sq, and an areal capacitance of 7.06 mF cm−2 (at 0.78 mA cm−2 in a three-electrode cell) in Na2SO4 aqueous electrolyte. Flexible transparent and symmetric supercapacitors, based on PVA/H3PO4 gel and the network electrodes, possess a stable working voltage of 1.6 V, energy and power density of 0.068 μWh cm−2 and 47.08 μW cm−2 at an optical transparency of ~80%, and no capacitance loss over 30,000 flat-bend-release cycles.
Highlights
Ordered structures with low tortuosity, excellent mechanical flexibility, high optical transparency, and outstanding electrical conductivity are critically important in developing flexible transparent supercapacitor electrodes for innovative applications in electronics and displays
A common approach to construct flexible transparent SC electrodes is the deposition of active materials onto flexible transparent conductive electrodes (TCEs) with rigorous attention paid to adjustment of mass loading in order to achieve highest areal capacitance at lowest deterioration in optical transmittance[1,3]
It is worth noting that such volume alterations after few thousand charge/discharge cycles could lead to dissolution and fragmentation of MnO2 into colored, segregated nanoparticles[9,10]; optical transparency of MnO2based SCs should be seriously deliberated if severe conditions, such as long time operation under flexed states are employed
Summary
Ordered structures with low tortuosity, excellent mechanical flexibility, high optical transparency, and outstanding electrical conductivity are critically important in developing flexible transparent supercapacitor electrodes for innovative applications in electronics and displays. The leaf-skeleton mimicked and core–shell (LSMCS) electrodes, regarded as a bioinspired microfluidic network, could provide interconnected channels for electrolyte ions transporting throughout and contacting entirely with the 3D spongy carbon core and interior/ exterior surfaces of the graphene shell (in a similar way as nutrients delivering within skeleton networks of plant leaves), that is, ion-accessible surface areas of active materials are optimized[27,28].
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