Flexible sensors that monitor strain and temperature are vital for advancing wearable electronics and health monitoring systems. However, integrating these capabilities into a single flexible platform demands stable conductivity, mechanical flexibility, and tunable thermoresistive properties. Here, we present a CNT/ZnO/PDMS composite sensor that achieves both strain and temperature sensing independently. CNT/ZnO hybrid nanostructures, synthesized via hydrothermal method, were incorporated into a PDMS matrix at filler loadings of 0.5, 0.75, and 1 wt
Herein, we demonstrate an efficient valorization of rubber fruit shell waste (RFSW) as an abundant agricultural byproduct into activated carbon (AC) through a sequential multi-step KOH/CO2 activation. The RFSW-700 sample (synthesized at 700 °C) exhibits a large specific surface area exceeding 494 m2/g, high carbon content, a predominantly disordered carbon framework, and high proportion of graphitic ordering. The RFSW-700 achieves a specific capacitance of 229 F/g and delivers an energy density of 7.52 Wh/kg. The RFSW-700 electrode retains 88.8
Boron-doped reduced graphene oxides (B-rGO) were prepared by thermally treating GO with boric acid in argon at temperatures above 1300°C. Oxidized boron species formed at low temperatures progressively converted into substitutional BC3 above 1500°C, where they were incorporated into the sp² lattice. Boron also promoted the formation of closed-loop edge structures, thereby stabilizing high-energy open sites. Although substitutional boron atoms were incorporated into the sp2 framework, they induced localized distortions in both the lattice symmetry and the electronic environment. Accordingly, Raman spectra showed an intense D band and a suppressed G’ band, while XPS analysis revealed a reduced sp2/sp3 ratio, collectively indicating that boron functions as a defect in both optical and electronic terms. These BC3 dopants, particularly at looped edges, covalently linked graphene layers, increasing both the oxidation onset temperature and domain conductivity. Although edge looping increased interparticle resistance to some extent, B-rGO samples still exhibited higher overall conductivity than undoped rGO. Theoretical simulations further supported the mechanism, showing that substitutional boron at armchair edges enhanced peroxide ion adsorption through electron transfer. In contrast, looped-edge configurations exhibited weak peroxide binding, suggesting improved oxidation resistance through the reduced edge-reactivity. Taken together, these results reveal a direct link between boron doping, edge stabilization, and functional enhancement, and provide a strategy for designing high-performance carbon materials for energy and environmental applications.
Concerns over the environmental impact, supply chain vulnerability, and long-term availability of conventional lithium-ion battery (LIB) materials have intensified interest in sustainable alternatives. This review defines a fully sustainable battery as one in which all components are derived from renewable materials and produced through eco-friendly processes across their entire lifecycle, consistent with the ISO 14044:2006 LCA framework. The current state of partially sustainable batteries is evaluated against this definition through a critical review of recent advances in biomass-derived carbon anodes, organic cathode materials, biopolymer gel electrolytes, cellulose-based separators, bio-derived binders, and carbonaceous current collectors across lithium-ion, sodium-ion (SIB), and aqueous zinc-ion (ZIB) battery chemistries. Key findings include the cost and carbon footprint competitiveness of biomass-derived hard carbon anodes with synthetic graphite (1.72 kg−1 vs4.97 kg−1; 3.2 vs 25.1 kg CO₂-eq kg−1), the ionic conductivity competitiveness of biopolymer gel electrolytes with conventional liquid electrolytes (up to 11 mS cm−1), and the consistent superiority of cellulose-based separators over commercial polypropylene in thermal stability, electrolyte wettability, and biodegradability. This review makes an original contribution by identifying four challenges that prevent the integration of these components into a fully sustainable battery. The costs, sustainability, and lifecycle assessments of LIBs, SIBs, and ZIBs are comparatively evaluated using available LCA data, and prospects for sustainable battery recycling are assessed. Based on this analysis, five research directions are proposed, with SIBs and aqueous ZIBs identified as the most viable configurations for fully sustainable batteries given their compatibility with bio-derived materials and lower lifecycle environmental impact.
Three-dimensional vertical graphene (VG) possesses a high surface area and an edge-oriented architecture, making it a promising electrode material for electrochemical energy storage applications. In this study, nitrogen-doped VG (N-VG) films were synthesized via an in-situ microwave plasma process, and the effects of nitrogen doping and Cu substrate crystallinity on the structural, chemical, and electrochemical properties of VG were systematically investigated. The growth conditions for pristine VG in a CH4–H2 plasma were first optimized and used as a baseline for the nitrogen incorporation. The introduction of N2 during growth preserved the vertically oriented graphene morphology while inducing distinct changes in defect characteristics and bonding configurations. Raman spectroscopy revealed progressive increases in the ID/IG and ID′/IG ratios with increasing nitrogen incorporation, indicating enhanced defect density and localized bonding perturbations within the sp2 carbon lattice. X-ray photoelectron spectroscopy confirmed successful nitrogen incorporation, with graphitic (quaternary) N identified as the dominant bonding configuration. Electrochemical analyses using a PVA–H3PO4 gel electrolyte demonstrated that nitrogen doping, particularly when combined with a single-crystalline Cu substrate, reduced charge-transfer resistance and enhanced the charge accumulation behavior, leading to improved electric double-layer capacitor performance with excellent cycling stability. These results elucidate the role of in-situ nitrogen doping in modulating the defect characteristics and electronic structure of VG and provide insights into the structure–electrochemical property relationships of N-VG for use as an electrode material for solid-state electric double-layer capacitors (EDLCs).
