Protic ionic liquid and ionic melts were prepared from the combination of methanesulfonic acid (CH 3 SO 3 H) and 1H-1,2,4-triazole (C 2 H 3 N 3) at various molar ratios. The thermal properties, crystal structure, acid-base interactions, ionic conductivity, proton conduction behavior and electrochemical stability of the system were studied. The equimolar composition, 1,2,4-triazolium methanesulfonate (C 2 H 4 N 3 + $CH 3 SO 3 À (1)), was a proton transfer salt with a melting point of around 134 C. Single crystal and powder XRD data, as well as TGA results, revealed that the base-rich region was a mixture of 1 and 1H-1,2,4-triazole. Infrared analysis and single crystal data suggested that the C 2 H 3 N 3-CH 3 SO 3 H system exists in a strongly hydrogen-bonded network. Systematic investigation of the ionic conductivity showed that the ionic conductivity reached local maxima at the compositions of [C 2 H 3 N 3 ]/[CH 3 SO 3 H] ¼ 10/90 and 80/20, respectively, while it exhibited a local minimum at the equimolar composition. The temperature dependence of the ionic conductivity was found to obey the Vogel-Fulcher-Tamman (VFT) equation. The fitting of the conductivity data to the VFT equation showed that the carrier ion concentration versus the mole fraction of 1H-1,2,4-triazole exhibited a volcano shape. In addition, the C 2 H 3 N 3-CH 3 SO 3 H system showed adequate electrochemical stability under PEMFC conditions as measured by linear sweep voltammetry. The relatively high ionic conductivity, wide electrochemical window and good thermal stability demonstrated that the C 2 H 3 N 3-CH 3 SO 3 H system is a suitable candidate for high temperature PEMFC electrolytes.

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Advanced organic bioelectronics enable smooth fusion between modern electronics and biological systems for better physiological monitoring and pathological examinations. Photon-regulated bioelectronics are especially desirable due to the non-contact impact, remote-control, and even selfpowered operation. However, few studies have addressed the advanced photon-enabled organic photoelectrochemical transistor (OPECT) biosensors capable of operation at zero gate bias. Here, on the basis of a hydrogel/graphene oxide hybrid (denoted as HGH), a multifunctional HGH-gated OPECT biosensor is presented, which is exemplified by Ca 2+ -triggered gelation on the CdS quantum dot (QD) photoelectrode linking with a sandwich immunoassay toward human IgG as the model target. Gelation of HGH on the CdS QD gate electrode can not only inhibit the interfacial mass transfer on the gate/ electrolyte interface, but also significantly block the light absorption of CdS QDs, leading to the corresponding change of the channel currents of OPECT device. At zero gate bias, this OPECT biosensor exhibits high gain in response to light and good analytical performance for human IgG with a detection limit of 50 fg mL -1 . Given the numerous intelligent hydrogel materials and their potential interactions with light, this work unveils a general platform for developing a new class of hydrogel-gated OPECT bioelectronics and beyond.