Structure, magnetic behavior and OER activity of CoFe2O4 powders obtained using agar-agar from red seaweed (Rhodophyta)

• Published in: Materials chemistry and physics 2019-11, Vol.237, p.121847, Article 121847
• Main Authors: Ferreira, Luciena S., Silva, Thayse R., Santos, Jakeline R.D., Silva, Vinícius D., Raimundo, Rafael A., Morales, Marco A., Macedo, Daniel A.
• Format: Article
• Language: English
• Subjects: Agar; Agar-agar; Anisotropy; Carrier transport; Charge transport; Cobalt ferrites; CoFe2O4; Current carriers; Electrocatalysts; Energy conversion; Ferrimagnetism; Gelatin; Green synthesis; Magnetic measurement; Magnetic properties; Mossbauer spectroscopy; Oxygen evolution reaction; Oxygen evolution reactions; Performance assessment; Seaweeds; Sol-gel processes; Water splitting
• ISSN: 0254-0584; 1879-3312
• DOI: 10.1016/j.matchemphys.2019.121847

This work is the first report on the synthesis of cobalt ferrite (CoFe2O4) powders by a proteic sol-gel green method that uses agar-agar from red seaweed (Rhodophyta). CoFe2O4 is also prepared using flavorless gelatin for the sake of comparison. The as-prepared powders are calcined at 1073 K and characterized by XRD, FESEM, Mössbauer spectroscopy (MS), and DC magnetometry. Electrodes made of CoFe2O4 powders were also investigated as electrocatalysts for the oxygen evolution reaction (OER), a reaction of high importance to produce pure H2 through water splitting. The material obtained with agar-agar showed a particle size of 176 nm and effective magnetocrystalline anisotropy of 5.8× 107 erg/cm3 (against 74 nm and 5.7 × 107 erg/cm3 for the gelatin-based sample). Magnetic assessment at 5 K showed a ferrimagnetic behavior for both samples. As an OER electrocatalyst, CoFe2O4 obtained with agar-agar attains an overpotential of 360 mV vs. RHE to generate 10 mA cm−2, a Tafel slope of 69.2 mV dec−1 and a turnover frequency (TOF) of 8.8 × 10−2 s−1 (against 435 mV vs. RHE, 126.3 mV dec−1 and 1.9 × 10−3 s−1 for the gelatin-based sample). The electrocatalytic performance towards OER can be explained by differences in mass and charge carrier transport processes influenced by microstructural features. The performance assessment of the cobalt ferrite (CoFe2O4) powders herein synthesized by sol-gel green methods shows their potential for using in energy conversion applications. [Display omitted] •Synthesis of CoFe2O4 powders using agar-agar from red seaweed (Rhodophyta).•Cation site occupancy by Rietveld refinement and Mössbauer spectroscopy.•Mössbauer and magnetic studies of CoFe2O4 at T ≤ 12 K.•CoFe2O4 as electrocatalyst for OER in alkaline medium.