Susumu Yamaguchi

Anion Conductive Block Poly(arylene ether)s: Synthesis, Properties, and Application in Alkaline Fuel Cells

Anion conductive aromatic multiblock copolymers, poly(arylene ether)s containing quaternized ammonio-substituted fluorene groups, were synthesized via block copolycondensation of fluorene-containing (later hydrophilic) oligomers and linear hydrophobic oligomers, chloromethylation, quaternization, and ion-exchange reactions. The ammonio groups were selectively introduced onto the fluorene-containing units. The quaternized multiblock copolymers (QPEs) produced ductile, transparent membranes. A well-controlled multiblock structure was responsible for the developed hydrophobic/hydrophilic phase separation and interconnected ion transporting pathway, as confirmed by scanning transmission electron microscopic (STEM) observation. The ionomer membranes showed considerably higher hydroxide ion conductivities, up to 144 mS/cm at 80 °C, than those of existing anion conductive ionomer membranes. The durabilities of the QPE membranes were evaluated under severe, accelerated-aging conditions, and minor degradation was recognized by (1)H NMR spectra. The QPE membrane retained high conductivity in hot water at 80 °C for 5000 h. A noble metal-free direct hydrazine fuel cell was operated with the QPE membrane at 80 °C. The maximum power density, 297 mW/cm(2), was achieved at a current density of 826 mA/cm(2).

Study of Anode Catalysts and Fuel Concentration on Direct Hydrazine Alkaline Anion-Exchange Membrane Fuel Cells

A platinum-free fuel cell using liquid hydrazine hydrate (N 2 H 4 ·H 2 O) as the fuel and comprised of a cobalt or nickel anode and a cobalt cathode exhibits high performance. In this study, the fuel cell performances using nickel, cobalt, and platinum as anode catalysts are evaluated and compared. It is found that fuel cell performance in the case of nickel and cobalt is higher than that in the case of platinum. Further, anodic reactions are discussed by comparing the hydrazine consumption and ammonia generation when cobalt and nickel are used as anode catalyst. Cobalt exhibits a higher rate of decomposition than nickel. Nickel is found to be the most suitable anode catalyst among the above mentioned anode catalysts for this fuel cell. The influence of hydrazine hydrate and KOH concentrations in the fuel on cell performance is also discussed. Cell performance is the highest at a hydrazine hydrate concentration of 4 M and a KOH concentration of 1 M. The maximum power density of the alkaline anion-exchange membrane fuel cell, comprised of a nickel anode and a Co-PPY-C (cobalt polypyrrole carbon) cathode, is 617 mW cm -2 .

Adsorption of Carbohydrazide on Au(111) and Au 3 Ni(111) Surfaces

Carbohydrazide (CH6N4O) is a potential substitute to hydrazine in fuel cell applications. This paper presents a theoretical study on the adsorption of carbohydrazide on Au(111) and Au3Ni(111) surfaces using first principles calculations based on density functional theory. Results show that without van der Waals correction in the calculations, carbohydrazide weakly physisorbs on Au(111), corroborating the experimentally observed high overpotential requirement for carbohydrazide oxidation on Au catalyst. An enhanced reactivity is observed by alloying Au with Ni due to the emergence of a localized d-band near the Fermi level that interacts strongly with the HOMO of carbohydrazide. On Au3Ni(111), a N–Ni bond between carbohydrazide and the surface is formed, characterized by the hybridization of N–pz and Ni–dzz states. These results pose insights into the use of 3d transition metals as alloying components in enhancing the reactivity of Au catalyst for carbohydrazide oxidation.Graphical Abstract