Direct Deposition of Amorphous Cobalt-Vanadium Mixed Oxide Films for Electrocatalytic Water Oxidation.

ABSTRACT: Efficiency of water oxidation catalysts in terms of overpotential, current density, and voltage stability over time with facile methods of their fabrication remains a key challenge in developing competent mechanisms of storing energy in the form of green hydrogen fuels. In this work, a rapid one-step aerosol-assisted chemical vapor deposition (AACVD) method is employed to synthesize amorphous and highly active cobalt-vanadium mixed oxide catalysts (CoVO_x) directly over fluorine-doped tin oxide (FTO) substrates. Morphological and structural characterizations made by field emission scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy techniques revealed the formation of pure-phase amorphous films with a gradual variation of topography as a function of deposition time. Of these films, the most active film (CoVO_x-20) was obtained in 20 min deposition, showing a spongy networking of interwoven nanofibers with a homogeneous distribution of 3-4 nm pores, achieving an overpotential of 308 mV at 10 mA/cm² current density. A much higher current density of 175 mA/cm² could be achieved just at 380 mV of overpotential with Tafel slope as low as 62 mV/dec for this whole range while exhibiting long-term stability. Mass activity, electrochemical impedance spectroscopy data, and the estimation of electrochemically active surface area all endorsed this high catalytic performance of CoVO_x-20, which is unprecedented for a low-cost, upscalable, and relatively less conductive substrate such as FTO used here. Our findings, thus, not only highlight the benefits of using AACVD in preparing two-dimensional amorphous catalysts but also prove the high efficiency of CoVO_x materials thus obtained, as outlined in a plausible reaction mechanism.

SUBMITTER: Ehsan MA 

PROVIDER: S-EPMC6682157 | biostudies-literature | 2019 Jul

REPOSITORIES: biostudies-literature