Zeolitic Imidazolate Framework-Derived Ru/RuO2–Co3O4 Catalyst for Methanol Oxidation Reaction in Alkaline Media

Abstract

The present study explores the possibility of a hybrid nanostructure of ruthenium (Ru) and cobalt oxide (Co₃O₄) for effective methanol oxidation reaction (MOR) in alkaline media. The spherical Ru/RuO₂ nanoparticle, uniformly dispersed in zeolitic Co₃O₄ derived from its ZIF-67 precursor, showed significant activity in MOR process. The duly characterized material exhibited a maximum current density of 131 mAcm⁻² with an onset potential of ∼1.07 V vs RHE (reversible hydrogen electrode). Under the electrocatalytic condition, the material exhibited stability up to 500 cycles of 12 h without substantial loss in current density. A comparative study showed that incorporation of Ru/RuO₂ into zeolitic spinel Co₃O₄ altered the activity in the MOR process. The catalyst had a good methanol (CH₃OH) concentration tolerance up to 2.5 M in alkaline media. A diffusion-controlled MOR process was indicated by the linear dependency of the current density against the square root of the scan rate. It was predicted that the temperature influenced the MOR process, and the apparent activation energy, E_a(app), calculated from the Arrhenius plot, was 27.45 kJmol⁻¹. The mechanism of the MOR was studied by using the density functional theory (DFT) calculation, and it was supported experimentally through the FTIR (Fourier transform infrared) and Raman analysis. DFT suggested for the engagement of both cobalt (Co) and Ruthenium (Ru) in the catalytic cycle. FTIR study showed that Ru nanoparticles get poisoned through CO (carbon monoxide) adsorption after 100 cycles and retard the activity after 12 h. On the other hand, the Raman study predicted that the Co₃O₄ surface gets hydroxylated, forming ─CoOOH (cobalt oxyhydroxide) species that participated in the deprotonation of CH₃OH with the assistance of Ru/RuO₂ nanoparticles.