Potential-Dependent Ionomer Rearrangement on the Pt Surface in Polymer Electrolyte Membrane Fuel Cells.

The interface between the catalyst and the ionomer in the catalyst layer of polymer electrolyte membrane fuel cells (PEMFCs) has been a subject of keen interest, but its effect on durability has not been fully understood due to the complexity of the catalyst layer structure. Herein, we utilize a Pt nanoparticle (NP) array electrode fabricated using a block copolymer template as the platform for a focused investigation of the interfacial change between the Nafion thin film and the Pt NP under a constant potential. A set of analyses for the electrodes treated with various potentials reveals that the Nafion thin film becomes densely packed at the intermediate potentials (0.4 and 0.7 V), indicating an increased ionomer-catalyst interaction due to the positive charges formed at the Pt surface at these potentials. Even for a practical PEMFC single cell, we demonstrate that the potential holding at the intermediate potentials increases ionomer adsorption to the Pt surface and the oxygen transport resistance, negatively impacting its power performance. This work provides fresh insight into the mechanism behind the performance fade in PEMFCs caused by potential-dependent ionomer rearrangement.

A chain extension method for apocarotenoids; lycopene and lycophyll syntheses.

The novel C5 benzothiazolyl (BT) sulfone containing an acetal group was prepared as a building block for the chain-extension of apocarotenoids. The double Julia-Kocienski olefination of the BT-sulfone with C10 2,7-dimethyl-2,4,6-octatrienedial and deprotection of the resulting acetal groups efficiently produced C20 crocetin dial. The higher homologues of C30 and C40 apocarotenoids were prepared from C20 crocetin dial by the repeated application of the Julia-Kocienski olefination of the C5 BT-sulfone and hydrolysis. The scopes of the Julia-Kocienski olefination in the total synthesis of carotenoid natural products were evaluated using the C10+C20+C10 coupling protocol. The olefination was sensitive to the steric factor and bulky C10 ß-cyclogeranyl BT-sulfone was not able to react with C20 crocetin dial, however, lycopene and lycophyll were efficiently produced by the Julia-Kocienski olefination of C10 geranyl BT-sulfone and hydroxygeranyl BT-sulfone, in which protection of the hydroxyl group was not necessary.

Sulfone-mediated syntheses of crocetin derivatives: regioselectivity of highly functionalized building blocks.

New C5 sulfone building blocks containing a masked polar end group have been devised for the efficient synthesis of carotenoids with polar termini. Chemoselectivity or the regiochemical issue of the highly functionalized units has been carefully addressed depending on the soft or hard nature of electrophiles. These building blocks have been successfully applied to the syntheses of crocetin derivatives, crocetin dial and the novel crocetin dinitrile.