Elucidation of the mechanism of melamine adsorption on Pt(111) surface via density functional theory calculations.

The oxygen reduction reaction (ORR) activity of Pt catalysts in polymer electrolyte fuel cells (PEFCs) should be enhanced to reduce Pt usage. The adsorption of heteroaromatic ring compounds such as melamine on the Pt surface can enhance its catalytic activity. However, melamine adsorption on Pt and the consequent ORR enhancement mechanism remain unclear. In this study, we performed density functional theory calculations to determine the adsorption structures of melamine/Pt(111). Melamine was coordinated to Pt via two N lone pairs on NH2 and N- in the triazine ring, resulting in a chemisorption structure with slight electron transfer. Four types of adsorption structures were identified: three-point adsorption (two amino groups and a triazine ring: Type A), two-point adsorption (one amino group and a triazine ring: Type B), two-point adsorption (two amino groups: Type C), and one-point adsorption (one amino group: Type D). The most stable structure was Type B. However, multiple intermediate structures were formed owing to the conformational changes from the most stable to other stable adsorption structures. The resonance structures of the adsorbed melamine stabilise the adsorption, as increased resonance allows for more electron delocalisation. In addition, the lone-pair orbital of the amino group in the adsorbed melamine acquires the characteristics of an sp3 hybrid orbital, which prevents horizontal adsorption on the Pt surface. We believe that understanding these adsorption mechanisms will help in the molecular design of organic molecule-decorated Pt catalysts and will lead to the reduction of Pt usage in PEFCs.

Characterization of a Rh(III) porphyrin-CO complex: its structure and reactivity with an electron acceptor.

To analyse the electrocatalytic oxidation of carbon monoxide by Rh porphyrins, we isolated a CO-adduct of Rh octaethylporphyrin, and examined its properties and reactivity by IR, NMR, and X-ray crystallographic analyses. The results indicate that the CO adduct of Rh octaethylporphyrin is vulnerable to nucleophilic attack by H2O. The CO-adduct was easily oxidized by an electron acceptor (1,4-naphthoquinone) to generate CO2. This indicates that CO is sufficiently activated in the CO complex of Rh octaethylporphyrin to reduce an electron acceptor. This mechanism is in contrast to that for the CO oxidation by Pt-based electrocatalysts.

Electrochemical reduction of dioxygen by copper complexes with pyridylalkylamine ligands dissolved in aqueous buffer solution: the relationship between activity and redox potential.

The Cu(II)/Cu(I) redox properties and electrochemical O2 reduction activity of a series of Cu(II)-complexes with pyridylalkylamine ligands were investigated in a neutral buffer solution. The relationship between Cu(II)/Cu(I) redox properties and O2 reduction activity was clearly demonstrated by voltammetric analyses.

Direct electron transfer to a metagenome-derived laccase fused to affinity tags near the electroactive copper site.

We demonstrate the efficient direct electron transfer (DET) from an electrode to an engineered laccase isolated from a metagenome. The enzyme has a unique homotrimeric architecture with a two-domain-type laccase subunit. The recombinant laccase-modified mesoporous carbon electrode exhibits an effective catalytic current for oxygen reduction, which depends on the affinity tags attached near the electroactive Cu site of the enzyme. We also investigated the effect of the affinity tags on the orientation of the enzyme on functional thiol-modified Au electrodes. The results suggest that a poly-histidine tag (His-tag) functions as an anchor to control the orientation of the enzyme to enhance the current density of the DET-type bioelectrocatalysis.