3 years ago

High-Performance Wearable Micro-Supercapacitors Based on Microfluidic-Directed Nitrogen-Doped Graphene Fiber Electrodes

High-Performance Wearable Micro-Supercapacitors Based on Microfluidic-Directed Nitrogen-Doped Graphene Fiber Electrodes
Xingjiang Wu, Ziyi Yu, Pengfeng Tan, Guan Wu, Su Chen, Lu Peng, Cai-Feng Wang, Wei Chen, Hengyang Cheng
Fiber-shaped micro-supercapacitors (micro-SCs) have attracted enormous interest in wearable electronics due to high flexibility and weavability. However, they usually present a low energy density because of inhomogeneity and less pores. Here, we demonstrate a microfluidic-directed strategy to synthesize homogeneous nitrogen-doped porous graphene fibers. The porous fibers-based micro-SCs utilize solid-state phosphoric acid/polyvinyl alcohol (H3PO4/PVA) and 1-ethyl-3-methylimidazolium tetrafluoroborate/poly(vinylidenefluoride-co-hexafluoropropylene) (EMIBF4/PVDF-HFP) electrolytes, which show significant improvements in electrochemical performances. Ultralarge capacitance (1132 mF cm−2), high cycling-stability, and long-term bending-durability are achieved based on H3PO4/PVA. Additionally, high energy densities of 95.7–46.9 µWh cm−2 at power densities of 1.5–15 W cm−2 are obtained in EMIBF4/PVDF-HFP. The key to higher performances stems from microfluidic-controlled fibers with a uniformly porous network, large specific surface area (388.6 m2 g−1), optimal pyridinic nitrogen (2.44%), and high electric conductivity (30785 S m−1) for faster ion diffusion and flooding accommodation. By taking advantage of these remarkable merits, this study integrates micro-SCs into flexible and fabric substrates to power audio–visual electronics. The main aim is to clarify the important role of microfluidic techniques toward the architecture of electrodes and promote development of wearable electronics. Novel fiber-shaped micro-supercapacitors are based on nitrogen-doped porous graphene fibers via a microfluidic technique. Owing to the microfluidic technique creating a uniform environment for fiber production, the fibers present a uniform porous network, large specific surface area, high electrical conductivity, and optimal nitrogen-active sites, which endow micro-supercapacitors higher electrochemical performance to successfully power audio–visual electronics.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/adfm.201702493

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