The preparation and characterisation of H1-e palladium films with a regular hexagonal nanostructure formed by electrochemical deposition from lyotropic liquid crystalline phases

Abstract

The hexagonal (H₁) lyotropic liquid crystalline phases of C₁₆EO₈ (octaethyleneglycol monohexadecyl ether) and Brij® 56 non-ionic surfactants have been used to template the electrochemical deposition of nanostructured palladium films. The resulting H₁-e palladium films were characterised by SEM, TEM and X-ray. The films contain regular hexagonal arrays of cylindrical pores separated by palladium walls with a centre to centre distance of 5.8 nm. Electrochemical studies show that these films have very high surface areas of the order of 91 m² g⁻¹. Studies of the hydrogen evolution reaction on these H₁-e palladium films in acid show that the formation of adsorbed hydrogen can be readily distinguished because of the high surface area to volume ratio of the films (of the order of 10⁷ cm² cm⁻³). Hydrogen insertion into the palladium films is fast and the formation of both the α and β-hydride phases is observed in the voltammetry at potentials which are similar to those reported for bulk palladium. The electrodes are stable towards repeated cycling to form the β-hydride phase showing that the hydrogen insertion and concomitant lattice expansion does not destroy the H₁ nanostructure.