Abstract
Hybrids of low-symmetry (disordered) mesoporous titanium dioxide modified with different weight ratios of cobalt oxide nanoparticles (Co3O4(x)/lsm-TiO2) are prepared using a one-pot self-assembly surfactant template. The physicochemical characterization of Co3O4(x)/lsm-TiO2 hybrids by scanning and transmission electron microscopy, X-ray diffraction, N2 adsorption–desorption isotherms, and X-ray photoelectron spectroscopy confirm the successful incorporation of cobalt oxide nanoparticles (2–3 nm in diameter) with preservation of the highly mesoporous structure of titanium dioxide substrate. Among these mesoporous hybrids, the ~3.0 wt.% Co3O4/lsm-TiO2 exhibits the best performance toward both the oxygen evolution (OER) and reduction (ORR) reactions in alkaline solution. For the OER, the hybrid shows oxidation overpotential of 348 mV at 10 mA cm−2, a turnover frequency (TOF) of 0.034 s−1, a Tafel slope of 54 mV dec−1, and mass activity of 42.0 A g−1 at 370 mV. While for ORR, an onset potential of 0.84 V vs. RHE and OER/ORR overpotential gap (ΔE) of 0.92 V are achieved which is significantly lower than that of commercial Pt/C, hexagonal mesoporous, and bulk titanium dioxide analogous. The Co3O4/lsm-TiO2 hybrid demonstrates significantly higher long-term durability than IrO2. Apparently, such catalytic activity performance originates from the synergetic effect between Co3O4 and TiO2 substrate, in addition to higher charge carrier density and the presence of disordered mesopores which provide short ions diffusion path during the electrocatalytic process.
Highlights
The fabrication of effective, highly stable and multi-functional electrocatalysts for oxygen evolution (OER) and reduction (ORR) reactions is in high demand for the commercialization of rechargeable metal–air and Li-ion batteries [1,2,3], fuel cells [4], and water splitting [5] applications
These results prove that the introduction of Co an enriched quantity of surface O vacancies in the form of metal–OH bonds
We have demonstrated the synthesis of highly active bifunctional OER/ORR hybrids of cobalt oxide-doped low-symmetry mesoporous titanium oxide (Co3 O4 (x)/lsm-TiO2 ) catalysts via the self-assembly surfactant template method
Summary
The fabrication of effective, highly stable and multi-functional electrocatalysts for oxygen evolution (OER) and reduction (ORR) reactions is in high demand for the commercialization of rechargeable metal–air and Li-ion batteries [1,2,3], fuel cells [4], and water splitting [5] applications. The development of highly efficient, stable and dual-functional electrocatalysts for the oxygen evolution (4OH− →O2 + 2H2 O + 4e− ) and reduction reactions (O2 + 2H2 O + 4e− → 4OH− ) has attracted the interest of scientific researchers, as well as industrial R&D centers. The development of highly effective, inexpensive, and bifunctional (active for both the ORR and the OER) electrocatalysts is important for the development of renewable energy technologies. Ru-based materials, while the Pt-group materials are the most active electrocatalysts for the ORR [9,10].
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