The preparation of high specific-capacity pseudocapacitive transition-metal-oxide/hydroxide (TMH) materials into transparent micro-structure electrodes is a great challenge and has become the bottleneck restricting the performance of transparent flexible supercapacitors . Beyond that, extending the operating voltage window is an urgent need for improving energy density . Here, Co(OH) 2 nanosheets and amorphous FeOOH nanowires were prepared into transparent films through a simple and scalable bio-inspired method at the air-solution interface. Both nanostructures are enwrapped in graphene shells (Co@Gr-TFandFe@Gr-TF) for use as transparent asymmetric pseudocapacitive electrodes. The unique encapsulation structures (1) provide pseudocapacitive electrode materials, especially an amorphous FeOOH structure cathode, (2) build up rapid three-dimensional electron and ion transport pathways together with the underlying ITO layer, (3) alleviate the exfoliation and dissolution of the active materials into electrolyte, and (4) extend the potential window of the FeOOH cathode from −0.8 ∼ 0 V to −1.2 ∼ 0 V with minimal cycling stability degradation. The asymmetric transparent and flexible supercapacitor based on Co@Gr-TF//Fe@Gr-TF operated at 1.8 V exhibits good transparency (50.5% at 550 nm), high specific capacitance (25.5 mF cm −2 , one order higher than the maximum value reported for FFT-GP), and high energy density (1.04 mWh cm −3 , comparable to that of nontransparent devices) as well as a long cycle life (10 000 cycles) with high-capacity retention (83.5%).
Ningxiao Yuan,Lu Xu,Bo Xu,Jianhao Zhao,Jianhua Rong
Chitosan derivative-based self-healable hydrogels with enhanced mechanical properties are reported, which were prepared by polymerization of acrylic acid (AAc) in 2-hydroxypropyltrimethyl ammonium chloride chitosan (HACC) solution. The PAAc/HACC hydrogels exhibit tensile fracture stress as high as 3.31 MPa and a Young's modulus of 2.53 MPa. They can maintain their original shape after 30 repeated compression cycles under various strain conditions, with a compression stress of more than 60 MPa at 99% strain. The damaged PAAc/HACC hydrogels can heal together in the presence of a NaCl salt solution with a self-healing efficiency of up to 61%. In addition, the PAAc/HACC hydrogels have high ionic conductivity and can serve as electrolytes for supercapacitors. The analysis suggests that all these good properties of the PAAc/HACC hydrogels mainly result from their high-density dynamic ionic interactions structure.
Hua Tian,Kaixin Zhu,Wang Li,Lin Wang,Zhifeng Yu,Yuannan Lai,Yunyi He
Ni-Co layered double hydroxide (NCLDH) with nitrate anions as interlayer counter ions was obtained via an oxidation-induced anion intercalation process. The optimization on the tunable proportion between divalent and trivalent metal cations in NCLDH host layers is realized in the dependence on the regulation of the additive amount of hydrogen peroxide as an oxidizing agent. The increase of trivalent metal cations facilitates the intercalation of nitrate anions into the interlamellar region between NCLDH host layers. Importantly, the electrostatic interaction between NCLDH host layers and interlayer anions results in the formation of hierarchical flower-like morphologies towards the enhancement of specific surface areas. Moreover, the increase in number of interlayer nitrate anions expands effectively interplanar spacing between NCLDH host layers. Remarkably, this unique structure not only accelerates the diffusion process of active hydroxide anions in the bulk phase of LDH, but also strengthens the stability of the hierarchical structure during electrochemical reactions. The electrochemical evaluation shows that NCLDH-16 achieves a superior specific capacity of 802 C g −1 at a current density of 1 A g −1 with a capacity retention of 86.7% as the increase of current densities to 10 A g −1 . The NCLDH-16//AC hybrid supercapacitor delivers a maximum energy density of 37.6 Wh kg −1 at a power density of 800 W kg −1 as well as still retains 87.4% of the initial capacitance after 10 000 cycles, suggesting great potential in practical energy storage devices.
Nan Lu,Xi Zhang,Ruiqi Na,Wendi Ma,Chongyang Zhang,Yuchao Luo,Yongfeng Mu,Shuling Zhang,Guibin Wang
The synthesis of a nanocomposite gel polymer electrolytes (NGPEs) using Li + -functionalized SPEEK (SPEEK(Li)) nanofiber membrane as a matrix, cross-linked PVA as a gelled agent and LiClO 4 as an electrolytic salt for electric double layer capacitors (EDLCs) were reported in this work. Compared with conventional PVA based gel electrolyte, the “SO 3 − Li + ” functional groups and the pores structure of the SPEEK(Li) nanofiber membrane improves the ionic conductivity as well as mechanical stability , which made the prepared NGPEs exhibited a high ionic conductivity of 8.9 × 10 −3 S cm −1 at ambient temperature and a large voltage stability window range from 0 to 2.0 V. The fabricated symmetric EDLCs showed a specific capacitance of 146.96 F g −1 at a current density of 0.5 A g −1 , with a maximum energy density of 18.26 W h kg −1 . Meanwhile, the EDLCs showed outstanding cyclical stability of 98% specific capacitance retention after 3000 cycles GCD testing, all of these results indicated that the NGPEs should be appropriate to EDLCs and next-generation energy storage systems .
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