MnO₂-deposited lignin-based carbon fiber (MnO₂-LCF) mats are fabricated for supercapacitor applications. LCF mats are produced from alkali lignin via electrospinning followed by stabilization and carbonization. The carbonization process is carried out at 800, 900, and 1000 °C, and the corresponding mats are denoted as MnO₂-LCF-800, MnO₂-LCF-900, and MnO₂-LCF-1000, respectively. The LCF mats are immersed in a KMnO₄ solution at room temperature for 72 h to obtain MnO₂-LCF mats. The scanning electron microscopy and X-ray diffraction analysis confirm the deposition of MnO₂ on the LCFs. The Brunauer–Emmett–Teller analysis, X-ray spectroscopy, and Raman spectroscopy reveal that MnO₂-LCF-800 mat possesses a large number of mesopores and Mn vacancies as compared to MnO₂-LCF-900 mat and MnO₂-LCF-1000 mat. Consequently, MnO₂-LCF-800 mat possesses the best electrochemical properties with a specific capacitance of 131.28 F∙g⁻¹, an energy density of 14.77 Wh∙kg⁻¹, and a power density of 135.01 W∙kg⁻¹ at a specific current of 0.3 A∙g⁻¹. Hence, MnO₂-LCF-800 mat shows high potential to be used as a high-performance supercapacitor.

Shaddock peel, a crop by-product mainly composed of cellulose, hemicellulose, lignin, and pectin, was developed as a flexible sensitive material for detecting environmental external pressure. Firstly, a natural carbon framework (C-SPF) with high conductivity was prepared using hydrothermal treatment followed by carbonization. Then, the PDMS elastomer was coated on the C-SPF instead of dense filling to convert the brittle C-SPF into elastic porous materials (M-SPF). Benefiting from the large deformation space of the porous framework and the stable interactions between PDMS and C-SPF, M-SPF exhibited ultrahigh coercibility (up to 99.0% strain) and high elasticity (99.4% height retention for 10 000 cycles at 50.0% strain). The M-SPF-based pressure sensor also exhibited a quick response (loading and unloading times were 20 ms and 30 ms), high sensitivity (63.4 kPa⁻¹), wide working range (from 0 to 800 kPa), and stable stress-electric current response (10 000 cycles). These advantages open a door to a variety of applications, such as flexible wearable devices, which demonstrated human physiological signal monitoring. The low cost, simple design and portable use of piezoresistive sensors highlight the potential application of the crop by-product shaddock peel as a high-value material.