Ze Li

In this work, poplar veneer (PV) rotary-cut from fast-growing polar was delignified to prepare flexible transparent poplar veneer (TPV). Lignin was gradually removed from the PV and then epoxy resin filled into the delignified PV. The study mainly concerns the effect of lignin content on microstructure, light transmittance, haze, tensile strength, and thermal stability of the PVs impregnated with epoxy resin. The results indicate that the lignin could be removed completely from the PV when the delignification time was around 8 h, which was proved by FTIR spectra and chemical component detection. Moreover, according to SEM observation and XRD testing, the porosity and crystallinity of the PVs were gradually increased with the removal of lignin. Also, the optical properties measurement indicated that the light transmittance and haze of the TPVs gradually increased, and the thermal stability also became more stable as shown by thermogravimetric analysis (TG). However, the tensile strength of the TPVs declined due to the removal of lignin. Among them, TPV₈ exhibited excellent optical properties, thermal stability, and tensile strength. Consequently, it has great potential to be used as a substrate in photovoltaics, solar cells, smart windows, etc.

With the rapid development of portable and wearable electronic devices, self-supporting flexible supercapacitors have attracted much attention, and higher requirements have been put forward for the electrode of the device, that is, it is necessary to have good mechanical properties while satisfying excellent electrochemical performance. In this work, a facile method was invented to obtain excellent self-supported flexible electrode materials with high mechanical properties and outstanding electrochemical performance by combining cellulose nanofibrils (CNFs) and reduced graphene oxide (RGO). We focused on the effect of the ratio of the addition of CNFs and the formation process of the film on the electrochemical and mechanical properties. The results show that the CNFs/RGO₁₂ (where the ratio of CNFs to GO is 1:2) film displayed outstanding comprehensive properties; its tensile strength and conductivity were up to 83 MPa and 202.94 S/m, respectively, and its C_A value was as high as 146 mF cm⁻² under the current density of 5 mA cm⁻². Furthermore, the initial retention rate of the specific capacitance was about 83.7% when recycled 2000 times; moreover, its capacitance did not change much after perpendicular bending 200 times. Therefore, the films prepared by this study have great potential in the field of flexible supercapacitors.

In this research, flexible transparent supercapacitor electrode materials were fabricated using cellulose nanofibrils (CNFs) and reduced graphene oxide (RGO) via a layer‐by‐layer (LbL) self‐assembly method. First, a transparent film was obtained by vacuum filtration of a CNF suspension, which was isolated from bamboo materials using a combination of 2,2,6,6‐tetramethylpiperidin‐1‐oxyl radical catalytic oxidation and ultrasonic treatment. Subsequently, graphene oxide (GO) was deposited on the surface of the CNF film using Cu²⁺ as a cross‐linking agent via the LbL self‐assembly technique and then was reduced by L‐ascorbic acid under mild reaction conditions. The degree of reduction of the GO on the CNF film surface was investigated by X‐ray photoelectron spectroscopy (XPS), Raman spectroscopy (Raman), and Fourier transform infrared spectroscopy (FT‐IR); concurrently, the effect of the number of self‐assembly times on the transparency, mechanical properties, and conductivity was also evaluated. The XPS, Raman, and FT‐IR spectral analyses proved that the CNFs/GO composite films were successfully reduced to CNFs/RGO composite films, of which the transparency and mechanical properties decreased with the increase in the number of self‐assembly times, while the conductivity remarkably raised. Based on the analysis of the results, the CNFs/RGO composite film obtained after 18 self‐assembly cycles exhibited excellent transparency, good tensile strength, and a high conductivity. Therefore, the CNFs/RGO composite film was selected to fabricate a supercapacitor electrode material, and the obtained supercapacitor displayed excellent electrochemical properties, in which the areal specific capacitance was 2.25 mF cm⁻² at a current density of 0.01 mA cm⁻² and the capacitance retention reached 97.3% after 1500 cycles. The presented strategy provides a good reference for the development of transparent and portable energy storage devices.