Structural and electrochemical studies of Co oxide films formed by the sol-gel technique

Abstract

Two different types of Co oxide films, each having a distinct electrochemical signature correlated with the film drying temperature, were formed using the sol-gel (SG) technique. Two different states of gelation of the film precursor were also explored. Cyclic voltammograms, collected in alkaline solutions for the low temperature films, displayed two pairs of peaks corresponding to the Co(ll) to Co(lll) and Co(lll) to Co(IV) transitions, centered at 1.2 and 1.4 V, respectively, while the high temperature films underwent only the Co(lll) to Co(IV) redox process at 1.4 V. The charge densities obtained for the lower temperature films (particle sizes 2-10 nm in diameter) ranged between 40 and 70 mC/cm 2 ; charge densities for the higher temperature films (particle sizes of 5-40 nm), otherwise formed identically, were between 10 and 20 mC/cm 2. The more viscous Co oxide gels led to significantly higher charge densities than less viscous gels, as well as greater film stability during electrochemical cycling. Using a wide range of film characterization techniques, it was shown that Co oxide films formed at >180°C are composed mainly of C03O4 spinel, while films formed at <180°C consist predominantly of CoO.

Controlled vapor-phase synthesis of cobalt oxide nanomaterials with tuned composition and spatial organization

“…To this regard, actual challenging issues concern the devising and optimization of synthetic strategies towards high purity nanomaterials with specific features, opening new frontiers not only for understanding their fundamental properties, but also for developing new generation nanodevices with improved performances. [1][2][3][4][5][6] Nanostructured Co 3 O 4 , the most stable cobalt oxide with a spinel-type structure comprising both Co(II) and Co(III), is an important p-type semiconductor (direct optical bandgaps at z1.5 and 2.0 eV) 5,[7][8][9][10][11][12][13] for applications in secondary Li/O 2 cells, negative electrodes for Li-ion batteries and supercapacitors, 11,12,[14][15][16][17][18][19][20] as well as in field emitters, 6,16,21 heterogeneous catalysts, electrochromic devices, solar absorbers, solid-state sensors, 2,3,5,8,9,13,[17][18][19][22][23][24][25][26][27][28][29][30]…”

Construction and characterization of phenol-based sensor derived from colloidal chemistry

“…The sol precursors was deposited on a platinum (Pt) sputtered glass substrate, with surface area ranging between 0.1 and 0.5 cm 2 , by a dip coating procedure [51], where the substrate was immersed into the sol-gel precursor then withdrawn at a constant rate of 1.2-24 cm/min to vary the film thickness. The film was placed in a pre-heated oven at 50 • C and this temperature was maintained for 30 min to remove methanol.…”

Synthesis of Cobalt Oxides Thin Films Fractal Structures by Laser Chemical Vapor Deposition

“…Cobalt and cobalt oxides films have been synthesized by a variety of different methods including spray pyrolysis [11, 12], electron-beam evaporation [13], sol-gel technique [14, 15], and more recently chemical vapor deposition (CVD) [16]. In fact, CVD is the preferred method for direct deposition of thin films of metals on specific structures and substrates.…”

“…Cobalt oxides have attracted a considerable amount of attention in the recent years for extensive applications including electronics and sensing [ 1 , 2 ], catalysts [ 3 ], and biomedical devices [ 4 , 5 ] due to their superior properties, such as high saturation magnetization [ 6 , 7 ], stable catalytic activity [ 8 ], and excellent electrochemical performance [ 9 , 10 ]. Cobalt and cobalt oxides films have been synthesized by a variety of different methods including spray pyrolysis [ 11 , 12 ], electron-beam evaporation [ 13 ], sol-gel technique [ 14 , 15 ], and more recently chemical vapor deposition (CVD) [ 16 ]. In fact, CVD is the preferred method for direct deposition of thin films of metals on specific structures and substrates.…”