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The ability to accurately predict the solvation free energies of ionic species using the appropriate thermodynamic cycle is of great importance in many areas of chemistry and biochemistry. To improve the accuracy of calculating solvation free energies, we devised a hybrid clustercontinuum approach, where explicit solvent molecules are added to the traditionally employed continuum model. Our computational workflow consists of the following steps: First, the minimum number of explicit water molecules beyond which additional water molecules no longer improve the accuracy of the cluster-continuum model is carefully established. Next, the convergence values for fully relaxed molecular configurations are compared with those obtained by sampling thermally disordered configurations using single-point calculations. We find that the dielectric constant does not have a significant influence on the solvation free energy, while accounting for the placement of a counterion is necessary for the accurate calculation of the solvation free energy.

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The two‐electron pathway to form hydrogen peroxide (H2O2) is undesirable for the oxygen reduction reaction (ORR) in iron and nitrogen doped carbon (Fe–N–C) material as it not only lowers the catalytic efficiency but also impairs the catalyst durability. In this study, a relay catalysis pathway is designed to minimize the two‐electron selectivity of Fe–N–C catalyst. Such a design is achieved by introducing two other sites, that is, MnN4 site and α‐Fe(110) face. A combination of transmission electron microscopy image and X‐ray absorption spectra verify the three site formation. Electrochemical test coupled with post‐treatment confirm the improvement of MnN4 site and α‐Fe(110) face on catalyst performance. Theoretical calculation proposes a relay catalysis pathway of three sites, that is, H2O2 released from the FeN4 site migrates to the MnN4 site or α‐Fe(110) face, on which the captive H2O2 is further reduced to H2O. The relay catalysis pathway positioned the as‐prepared catalyst among the best ORR catalysts in both aqueous electrode and alkaline direct methanol fuel cell test. This study examples an interesting relay catalysis pathway of multi‐sites for the ORR, which offers insights into the design of efficient electrocatalysts for fuel cells or beyond.

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The surface tension components and parameters for nine naturally occurring colloidal-sized volcanic ash samples were determined by thin-layer wicking. These materials include rhyolites, trachytes, phonolites, and an andesite, and were collected from deposits in California, Arizona, Italy and Martinique. The samples are principally volcanic glass (with minor amounts of mixed materials of various compositions) with silica contents ranging (average values) from 74% (rhyolite) to 57% (andesite). The surface tension components were determined by means of thinlayer wicking to provide contact angles which were used to solve the Yeung-Dupre equation. The Lifshitz-van der Waals component of the surface tension, 'Y LW , for these ash samples varies between 26.6 mJ/m 2and 38.7 ml/m''. The Lewis acid parameter, 'Y Ill , values are small with values ranging from 0 mJ/m 2to 1.8 ml/rn", while the Lewis base parameter, 'Y e , values varied between 15.6 mJ/m 2and 45.6 mJ/m 2. Of the nine samples, five were hydrophobic and the other four were hydrophilic. The hydrophobic ashes were produced by eruptions with a dominantly 223 Copyright 0 1997 by Marcel Dekker, Inc. 224 LI ET AL.magmatic rupture mechanism: pyroclastic flow, nuee ardente, ash cloud surge. The hydrophilic ashes were generated by a strong hydromagmatic mechanism and most formed accretionary lapilli. The <:-potential values were determined from the electrophoretic mobility, and varied between -32.1 mV and -55.2 mY. Utilizing the surface tension values and the <:-potential, an extended DLVO-type (XDLVO) calculation of the free energy of interaction versus distance, including the Lewis acid-base contribution, between 1 I'm spherical particles, showed that for the five hydrophobic ash samples there is a net attraction between particles in the presence of water, and for the four hydrophilic samples there is a strong net repulsion between particles. Assuming that the stability of an ash deposit (in the presence of water) on an inclined slope is related to the forces acting between neighboring ash particles, those deposits with repulsive interparticle forces would be more mechanically unstable and pose a risk of forming mud flows on remobilization.

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