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Layered Manganese and aluminum double hydroxides (Mn-Al LDH) were electrochemically synthesized on a Ni, or a Pt substrate by galvanostatic electrochemical reduction of Mn(NO 3 ) 2 and Al(NO 3 ) 3 aqueous solutions mixtures. The obtained XRD data indicated that the interlayer spacing of the Mn-Al LDH was 0.87 nm and was in good agreement with that reported for NO 3 /Mn-Al LDH. The contents of trivalent cation, Al 3+ , in the products were almost identical to those in the corresponding electrolyte solutions. During electrochemical oxidation and reduction of NO 3 /Mn-Al LDH precipitated from a Mn(NO 3 ) 2 and Al(NO 3 ) 3 aqueous solutions 3:1 mixture in a 2 mol dm −3 KOH solution, Al contents in the NO 3 /Mn-Al LDH deviated products decreased by ca. 0.2. Although the dissolution of Al 3+ in the LDHs occurred at the first electrochemical oxidation in a 2 mol dm −3 KOH solution, reversible redox peaks were observed at around −0.2 V vs. Hg/HgO after 2nd cycle of CVs.

We developed a novel solid-state electrochemical cell for modeling triple-phase boundary of polymer electrolyte fuel cells and investigated oxygen reduction reaction (ORR) activity and durability of Pt/C catalysts using the cell. ORR current was depended on relative humidity as well as the thickness of coated Nafion layer on the model electrode. We also conducted the theoretical calculation and clarified that ORR current in the model TPB region is not restricted by oxygen diffusion but by an ohmic drop due to proton migration in the coated Nafion layer on the model electrode.Durability test of Pt/C catalysts in the model TPB region was carried out under oxygen atmosphere. After the test, aggregation and somewhat larger Pt particles were observed on the model electrode at which electrode potential would reach to be open circuit potential, i.e., low overpotential region, under oxygen atmosphere.