Electrodeposition of α‐ and β‐cobalt hydroxide thin films via dilute nitrate solution reduction

Abstract α‐ and β‐cobalt hydroxyde thin films were synthesized by cathodic electrodeposition on transparent conductive oxide (TCO) substrates, at 60 °C and 95 °C, respectively, using a very low concentration of Co(NO 3 ) 2 and an alkali nitrate supporting electrolyte. Localized cathodic electrochemical generation of hydroxyl species via the reduction of nitrate precursors led to the formation of well crystallized nanostructured films. Scanning Electron Microscopy and X‐ray diffraction confirmed the films were composed of vertically oriented nanoparticle platelets with the c ‐axis parallel to the substrate surface, and free of turbostratic disorder. UV/Vis spectra and thermal gravimetric analyses (TGA) indicated variation between the cobalt structures. Films deposited at 60 °C yielded a hydrotalcite‐like compound namely an “hydroxyl‐deficient” [Co(OH) 2– x (H 2 O) x ] x + with NO 3 – intercalated anion along with water molecules in the interlayer region. Those deposited at 95 °C yielded the brucite β‐Co(OH) 2 . (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)