Electrodeposition of epitaxial Co(OH)2 on gold and conversion to epitaxial CoOOH and Co3O4

An electrodeposition method for growing epitaxial Co(OH)(2) films on single crystalline gold (111), (100), and (110) substrates is described. The films were grown by electrochemical reduction of [Co(en)(3)](3+) in an alkaline electrolyte. The Co(OH)(2) grew with a [0001] out-of-plane orientation on all the gold crystal orientations. The in-plane orientation follows the symmetry of the gold (111), (100), and (110) substrates. The Co(OH)(2) can be converted to CoOOH by electrochemical oxidation in 1 M KOH at 95 degrees C, and after conversion remains epitaxial with a [0001] out-of-plane orientation. The CoOOH film can be further converted to epitaxial Co3O4 with a [111] out-of-plane orientation by decomposition of the CoOOH film in air at 300 degrees C. This synthesis method allows for a simple fabrication of epitaxial catalysts and could be useful to probe the catalytic activity of specific crystal planes.