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Bipolar membranes consist of a layered ion-exchange structure composed of a cation selective membrane joined to an anion selective membrane. They are analogous to semiconductor p-n devices as both of them present current-voltage curves exhibiting similar rectification properties. In this article, we present some current-voltage curves obtained for different-bipolar membranes ate several temperatures. The results can be interpreted in terms of a simple model for ion transport and field-enhanced water dissociation previously developed. The mechanism responsible for water splitting is assumed to be a catalytic proton transfer reaction between the charged groups and the water at the membrane interface. The effects of temperature are taken into account by introducing an Arrhenius-type relationship for the dependence of the forward rate constant of the reaction on temperature. Finally, comparison between theory and experiments provides reasonable values for the parameters introduced in the theoretical model. The analysis aims at developing a better physical understanding of a process in which chemical reactions and transport phenomena are coupled in such a way that the potential technological applications depend strongly on this coupling.

Ammonia synthesis via the high‐temperature and high‐pressure Haber‐Bosch process is one of the most important chemical processes in the world. In spite of numerous attempts over the last 100 years, continuous Haber‐Bosch type ammonia synthesis at room‐temperature had not been possible, yet. We report the development of a mechanocatalytic system operating continuously at room‐temperature and at pressures down to 1 bar. With optimized experimental conditions, a cesium‐promoted iron catalyst was shown to produce ammonia at concentrations of more than 0.2 vol. % for over 50 hours.

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Mechanochemistry, as a synthesis tool for inorganic materials, became an ever-growing field in material chemistry. The direct energy transfer by collision of the educts with the milling media gives the possibility to design environmentalfriendly reactions. Nevertheless, the underlying process of energy transfer and hence the kinetics of mechanosynthesis remain unclear. Herein, we present in situ synchrotron X-ray diffraction studies coupled with pressure measurements performed during the formation of ZnS and the subsequent phase transition (PT) from the hexagonal to the cubic modification. Milling Zn and S 8 results in the sublimation of S 8 , observed by a sudden pressure increase. Simultaneously, the hexagonal metastable ZnS-modification (wurtzite) forms. Via detection of the pressure maximum, the exact start of the wurtzite formation can be determined. Immediately after the formation of wurtzite, the structural PT to the thermodynamic stable cubic modification sphalerite takes place. This PT can be described by the Prout-Tompkins equation for autocatalytic reactions, similar to thermally induced PT in sulfur vapor at high temperatures (T > 1133 K). The increase in the reactivity of the wurtzite formation is explained by the reaction in sulfur vapor and the induction of defect structures by the collisions with the milling media.