Ordered mesoporous/microporous carbon was synthesized from sucrose. The carbon was oxidized and modified with urea at 600, 800, and 950 °C. The obtained carbons differed in the pore size distributions in the meso- and micropore ranges. The carbons, after an extensive surface characterization, were used as ORR catalysts in a KOH electrolyte. Kinetic current densities and n reached 12.5 mA cm–2 and 3.94, respectively. The results suggested that small micropores increased the efficiency of ORR. The density of surface oxygen in mesopores had also a positive effect on ORR by increasing the hydrophilicity and the electrochemically active surface area (ECSA) and, thus, the accessibility of oxygen dissolved in the electrolyte to the pores of the highest adsorption potential. From the viewpoint of the number of electron transfers, current density, and onset potential, the carbons with small pore sizes and with only traces of nitrogen performed equally, or even better, in ORR process as those containing the catalytic nitrogen sites.

BACKGROUND The effect of framework topology on the guest‐induced flexibility of several crystalline zeolitic imidazolate frameworks (ZIF‐7, ZIF‐9, ZIF‐11 and ZIF‐12) was investigated via analysis of experimental nitrogen (N2), carbon dioxide (CO2) and argon (Ar) isotherms at 77 K (N2 and Ar) and 273 K (CO2) for gas pressures up to 0.13 MPa. RESULTS The experimental isotherms of these frameworks were analysed in order to investigate their structural flexibility using gases with kinetic diameters equal to or larger than the diameters of their static pore apertures. The results of gas sorption measurements indicate guest‐induced phase changes for ZIF‐7 and ZIF‐9 (SOD topologies). ZIF‐12 (RHO topology) also shows uptake for gases, despite its pore‐limiting diameter being smaller than the kinetic diameters of the adsorbed molecules. CONCLUSIONS This work highlights the ability of ZIFs with different framework topologies to change their structure and increase their pore aperture upon interaction with certain gases. These findings are key in the development of more selective ZIF‐based materials for important industrial applications including low‐energy gas separations, catalytic nanoreactors and sensor technology. © 2019 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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The dual site-bond model (SBM) to describe heterogeneous surfaces with different energetic topographies is reviewed and applied to the study of molecular processes on solid surfaces such as adsorption, surface diffusion, reactions, and diffusion limited aggregation. It is found that all these processes are strongly affected by the energetic topography, and the observed behaviors are discussed.