Electrochemical deposition of amorphous cobalt oxides for oxygen evolution catalysis

Mn-doped Co3O4 for acid, neutral and alkaline electrocatalytic oxygen evolution reaction

This work reports the application of Mn-doped Co3O4 oxides in the electrocatalytic oxygen evolution reaction (OER). The materials were characterized by structural, morphological, and electrochemical techniques. The oxides with higher Co : Mn molar ratio presented a lower electron transfer resistance, and consequently the most promising OER activities. Pure Co3O4 shows an overpotential at j = 10 mA cm-2 of 761, 490, and 240 mV, at pH 1, 7, and 14, respectively, and a high TOF of 1.01 × 10-1 s-1 at pH 14. Tafel slopes around 120 mV dec-1 at acidic pH and around 60 mV dec-1 at alkaline pH indicate different OER mechanisms. High stability for Co3O4 was achieved for up to 15 h in all pHs, and no change in the structure and morphology after the electrocatalysis was observed. The reported excellent OER activity of the Mn-Co oxides in a wide pH range is important to broaden the practical applicability in different electrolyte solutions.

Effects of A-site Cations in Quadruple Perovskite Ruthenates on Oxygen Evolution Catalysis in Acidic Aqueous Solutions

The quadruple perovskite ruthenate CaCu₃ Ru₄ O₁₂ is more active and stable than the benchmark catalyst RuO₂ in the oxygen evolution reaction (OER) in acidic aqueous solutions, where many oxide-based catalysts are dissolved. Studies on the crystal structures of quadruple perovskite ruthenates are rare, and the origin of OER activity or stability from a structural aspect has not been clarified in detail. This presents the need to study the effects of cations at the A site of quadruple perovskite ruthenates ACu₃ Ru₄ O₁₂ (A = Ca, Sr, La, Nd, and Ce) on the OER catalytic activity and stability in acidic aqueous solutions. CaCu₃ Ru₄ O₁₂ has the highest activity and stability among all quadruple perovskite samples. The type of cation at the A site changes the average Cu and Ru valence states, and the plot of OER activity versus the average Cu valence number shows a volcano-type relationship. In addition, stability increases with a decrease in Ru-O bond length. This research provides a good design principle for OER catalysts with high activity and stability in severely acidic aqueous solutions.

Electrodeposition of Cobalt Oxides on Carbon Nanotubes for Sensitive Bromhexine Sensing

We develop an electrochemical sensor for the determination of bromhexine hydrochloride (BHC), a widely use mucolytic drug. The sensor is prepared by electrodeposition of cobalt oxides (CoO_x) on a glassy carbon electrode modified with carboxylated single-walled carbon nanotubes (SWCNT). A synergistic effect between CoO_x and SWCNT is observed, leading to a significant improvement in the BHC electrooxidation current. Based on cyclic voltammetry studies at varying scan rates, we conclude that the electrochemical oxidation of BHC is under mixed diffusion–adsorption control. The proposed sensor allows the amperometric determination of BHC in a linear range of 10–500 µM with a low applied voltage of 0.75 V. The designed sensor provides reproducible measurements, is not affected by common interfering substances, and shows excellent performance for the analysis of BHC in pharmaceutical preparations.