The latest generation flexible devices feature materials that are conductive, highly stretchable, and transparent to meet the requirements of a reliable performance. However, the existing conductors are mostly electronic conductors, which cannot satisfy these high-performance challenges. A robust hydrogel ionic conductor was rapidly fabricated with a facile one-pot approach by employing bioinspired agar with a physically cross-linked network, polyacrylamide (PAM) with a photoinitiated cross-linked network under appropriate UV intensity, and Li+ as conductive ions. The resulting Li+/agar/PAM ionic double-network hydrogels could be fabricated into various shapes through injection. The unique ionic hydrogel showed a remarkable stretchability with over 1600% extension, high tension/compression strength (0.22 MPa/3.5 MPa), and toughness (2.2 MJ/m3). Furthermore, it was demonstrated to possess dual sensory capabilities through the combination of both temperature and mechanical deformation. This hydrogel ionic conductor exhibited high stretching sensitivity with a gauge factor of 1.8 at strain 1100% and bending sensitivity in a broad angle range of 30–150°, respectively. Such highly optical transparency and elasticity endow the hydrogel-phosphor composites with promising luminescent properties. The multifunctional ionic hydrogel can be used as soft conductors for application in flexible devices such as ionic skin for wearable sensors and luminescence display.

The artificial skin-like stretchable ionic sensor device usually requires a synergistic effect of reliable adhesion between human machine interface, reasonable mechanical strength, and visually displayable transparency. A plant-inspired zwitterionic hydrogel was prepared through rapid UV initiation in the existence of cellulose nanocrystals as physically crosslinker and reinforcing agent. The resulting transparent zwitterionic nanocomposite hydrogel successfully brings the synergistic advantages of robust adhesive strength between diversified substrates such as skins, plastics, glass, and steels with remarkable mechanical properties of a superior stretchability over 1000% strain, a mechanical tensile strength up to 0.61 MPa, and compressive strength up to 7.5 MPa, manifesting in superior ionic transport performance, simultaneously. Furthermore, the zwitterionic nanocomposite hydrogel was fabricated as a wearable compliant stretchable pressure–strain sensor in the modality of the skin-adhesive patch to be sensitive to human motion such as finger touch and speech recognition for personal healthcare of patient sensory rebuilding and physiological data acquisition. It maintains compressive cycling sensibility at diverse pressure during 0.5, 1.0, and 1.5 Hz, respectively. The multifunctional zwitterionic nanocomposite hydrogel could also be assembled into flexible electrical devices such as luminescent display and information transfer between human and robot communication for mechanosensory electronics and artificial intelligence.

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Employing polytetrafluoroethylene (PTFE)-treated carbon fiber paper (CFP) as the substrate of the gas diffusion layer (GDL) is a common practice to improve water management in proton exchange membrane fuel cells (PEMFCs), but the resulting increase in electrical and thermal resistance is a critical problem that restricts the performance output of PEMFCs. Hence, studying the mechanism and prediction model for both the electrical and thermal conductivity in CFP is essential. This work established a mathematical graph theory model for CFP electrical and thermal conductivity prediction based on the observation and abstraction of the CFP characteristic structures. For the PTFE-treated CFP, the electrical and thermal conductivity of CFP can be effectively increased by optimizing the PTFE distribution in CFP. A "filter net effect" mechanism was proposed to reasonably explain PTFE distribution's influence on the CFP performance. Finally, the equivalent effect of multiple factors on conductivity was revealed using contour maps, which provides inspiration for further reducing the electrical and thermal resistance in CFP.

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