Direct electrosynthesis of hydrogen peroxide (H2O2) by oxygen reduction is a green and safe strategy to replace the traditional anthraquinone process. Herein, we have designed a two-dimensional redox-active cationic covalent triazine network to be used directly as a cost-effective metal-free electrocatalyst for the oxygen reduction reaction (ORR) to form H2O2. Such a dicationic 2D polymer possesses a porous structure with pore diameters of 2-10 nm and a total N content of 13.3 wt%. The electron paramagnetic resonance experiment confirms the reduction of a viologen-based polymer to radical cations and the subsequent generation of superoxygen radicals. The radical characteristics and high N content within this polymer are the essential for the efficient ORR via a two-electron pathway. As a result, the present electrocatalyst exhibits a high ORR activity and excellent H2O2 selectivity (∼85%), thus providing a feasible possibility of designing highly selective metal-free electrocatalysts for electrocatalytic production of H2O2 from O2.

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Diffusion and sorption of U(VI) in compacted bentonite were studied using a capillary method. The experiments were carried out at room temperature in 0.1 M NaClO 4 solutions at pH 7.0 ± 0.1. Effects of contact time, solution concentration and bentonite bulk density on diffusion were also investigated. The results fit the Fick's second law very well and are in good agreement with the literature data for similar bentonite dry densities [3]. The K d values from capillary method are in most cases lower than those from batch experiments. The interlaminary space of the compacted bentonite contributes significantly to the sorption of uranium. The apparent diffusion coefficient D a of diffusion derived from the experiments are used to simulate its diffusion in compacted bentonite and the results indicate that several meters of compacted bentonite is enough to prevent the diffusion of from the repository to the environment.