Development of a novel metal hydride–air secondary battery

A laboratory metal hydride/air cell was evaluated. Charging was via a bifunctional air gas-diffusion electrode. Mixed nickel and cobalt oxides, supported on carbon black and activated carbon, were used as catalysts in this electrode. At 30mA cm⁻² in 6m KOH, the air electrode potentials were −0.2V (oxygen reduction) and +0.65V (oxygen evolution) vs Hg/HgO. The laboratory cell was cycled for 50 cycles at the C/2 rate (10mAcm⁻²). The average discharge/charge voltages of the cell were 0.65 and 1.6V, respectively. The initial capacity of the metal hydride electrode decreased by about 15% after 50 cycles.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

The effect of ink dilution and evaporation on the microstructures of catalyst layers in polymer electrolyte membrane fuel cells

The microstructures of catalyst layers (CLs) in proton exchange membrane fuel cells determine cell performance and durability. Delicate ink preparation processes and coating/drying processes affect the resulting microstructures including active sites, pore networks, ionomer networks and Pt/C networks. This paper reports our recent experimental observations of the effect of ink dilution and evaporation condition on the microstructures. The microstructures of dried ink droplets are presented and compared among different dilution ratios and different evaporation conditions in terms of the spatial distributions of Pt/C particles, ionomers, and pores. The method through which the microstructures are visualized is also introduced in this paper. It is observed that ink dilution ratio and evaporation condition can significantly alter resulting microstructure patterns through affecting viscosity and particle flow patterns during the evaporation. More concentrated solution makes catalyst inks less spread out on a substrate surface, leading to larger droplet height and larger contact angle. Ambient relative humidity has a significant impact on catalyst deposition patterns. Under low relative humidity condition, catalyst particles are concentrated both near the central and the periphery of the droplet; while under high relative humidity, the central part is uniform, and the particles move towards the edge of the deposition, forming a stripe-like structure. This indicates that ink dilution and evaporation is key to the CL microstructure formation and must be properly controlled in order to obtain the quality and consistency of the CLs in fabrication