A method of preparing an array of vertically aligned carbon nanotubes for use in catalytic electrodes for fuel cell or electrolytic cell, comprising: providing an array of vertically aligned carbon nanotubes obtained by a gas phase growth process in which the precursor of a carbon nanotube growth catalyst is added continuously to the feed gas; and depositing a plurality of platinum nanodots onto the outer surface of said vertically aligned carbon nanotubes by using a gas phase deposition process such as ALD. The ALD process advantageously uses a platinum source gas which is Pt(PF.sub.3).sub.4. The nanodots can be protected by nanocaging.

Catalyst material comprising nanoparticles dispersed within a metal oxide layer, the metal oxide layer comprises metal oxide comprising at least one metal cation, wherein the nanoparticles comprise Pt, wherein the nanoparticles comprise less than 10 atom % of oxygen, and wherein the metal oxide layer has an average thickness not greater than 50 nanometers. The catalyst material comprising nanoparticles dispersed within a metal oxide layer can be converted, for example, to nanoporous catalyst layer comprising nanoparticles fused together, wherein the nanoparticles comprise Pt, wherein the nanoparticles comprise less than 10 atom % of oxygen, and wherein the layer has an average thickness not greater than 50 nanometers. The nanoporous catalyst layer is useful, for example, in fuel cell membrane electrode assemblies.