Toshiko Miura

DFT Method Estimation of Standard Redox Potential of Metal Ions and Metal Complexes.

The DFT method calculation was carried out to evaluate standard redox potential (SRP) for metal-to-metal cation and metal-to-metal complex systems. With the Born-Haber cycle, standard redox potential was composed of the cohesive energy, ionization energy, and solvation energy. The ligand exchange energy was added in case of metal complex. The solvent effects were incorporated by the self-consistent reaction field theory at the level of the polarized continuum model (PCM). At the highest level of calculations, the geometry optimization and harmonic frequency analysis were evaluated under the PCM. Utilizing experimental values of the cohesive energy of metals, the standard deviations between the calculated and experimental SRP values were 0.20-0.27 V depending on the calculation levels and basis sets used. For three Ag complexes with CN(-), S2O3(2-), and NH3 ligands, the discrepancy was within 0.3 V.

DFT Study of Oxygen Reduction Reaction on N-substituted Carbon Electrodes. Adsorption

Carbon alloys attract attention as metal-free cathode catalysts. Mechanisms of oxygen reduction reactions are investigated using the DFT calculations and molecular models such as N-substituted coronene, circum pyrene, and corannulene. The overall oxygen reduction reaction (ORR) is decomposed into five elementary reactions. Adsorption of O2 is important as the first step of reduction, and it depends strongly on the spin density on C atoms, introduced by the N atom. Secondly the peripheral C atoms have an advantage due to the rehybridization freedom to the sp3 configuration. Based on the reversible electrode potential (REP) for each elementary reaction, the overpotential is expected for the first reduction of O2 to OOH and the final reduction of OH to H2O. These features indicate that N-substituted carbon electrode resembles Pt electrode compared to other less active metals, such as Au.