An Optical Study of Hydrogen Insertion in the Anodic Oxide of Vanadium.

This paper reports on an optical study of hydrogen insertion in the anodic oxide of vanadium. Ellipsometry is used to study the electrochromic processes which occur when anodically grown films of vanadium oxide are electrochemically reduced and subsequently reoxidized. Films up to 200 nm in thickness are grown by anodizing vanadium in acetic acid and acetone electrolytes. When the current is made cathodic, the outer surface of the V{sub 2}O{sub 5} film is reduced to H{sub 4}V{sub 2}O{sub 5}, and as coloring proceeds a phase boundary sweeps inward across the film toward the vanadium substrate. An optical inflection is observed when the phase boundary reaches the substrate, and no additional hydrogen is electrochemically bonded into the structure past this point.