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

Funding Information: This work was supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico (BR) - CNPq [PQ-2/2018: 313831/2018-1], Fundação Carlos Chagas de Amparo à Pesquisa do Estado do Rio de Janeiro - FAPERJ [JCNE 2018: E-26/203.023/2018; Apoio às Universidades Estaduais: E-26/010.101141/2018; Projetos Temáticos: SEI-260003/001198/2020; PD10 2020: E-26/290.125/2020 post-doctoral Scholarship], and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) [Finance Code 001]. The authors would like to acknowledge NANOFAB/UERJ for the SEM measurements, LCM/CAIPE-UFF for the Raman analyses, G2E-UFF for the RDE electrode, LACES-UFRJ for the thermogravimetric analysis, Multiuser Laboratory of Pontal at the Federal University of Uberlândia for the ASAP analyses (FINEP/2013 INFR13 01.13.0371.00), and LCS/LNNano-CNPEM for the use of AFM in its open facilities. Funding Information: This work was supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico (BR) – CNPq [PQ-2/2018: 313831/2018-1], Fundação Carlos Chagas de Amparo à Pesquisa do Estado do Rio de Janeiro – FAPERJ [JCNE 2018: E-26/203.023/2018; Apoio às Universidades Estaduais: E-26/010.101141/2018; Projetos Temáticos: SEI-260003/001198/2020; PD10 2020: E-26/290.125/2020 post-doctoral Scholarship], and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) [Finance Code 001]. The authors would like to acknowledge NANOFAB/UERJ for the SEM measurements, LCM/CAIPE-UFF for the Raman analyses, G2E-UFF for the RDE electrode, LACES-UFRJ for the thermogravimetric analysis, Multiuser Laboratory of Pontal at the Federal University of Uberlândia for the ASAP analyses (FINEP/2013 INFR13 01.13.0371.00), and LCS/LNNano-CNPEM for the use of AFM in its open facilities. Publisher Copyright: © 2022 The Royal Society of Chemistry.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.publishersversionpublishe

Uso de equações lineares na determinação dos parâmetros de Michaelis-Menten

The Michaelis-Menten equation is used in many biochemical and bioinorganic kinetic studies involving homogeneous catalysis. Otherwise, it is known that determination of Michaelis-Menten parameters K M, Vmax, and k cat by the well-known Lineweaver-Burk double reciprocal linear equation does not produce the best values for these parameters. In this paper we present a discussion on different linear equations which can be used to calculate these parameters and we compare their results with the values obtained by the more reliable nonlinear least-square fit

Synthesis and Characterization of Cobalt(III), Nickel(II) and Copper(II) Mononuclear Complexes with the Ligand 1,3-bis[(2-aminoethyl)amino]-2-propanol and Their Catalase-Like Activity

<div><p>In this work, we present the synthesis and characterization of two new mononuclear complexes with the ligand 1,3-bis[(2-aminoethyl)amino]-2-propanol (HL), [Co(L)(H₂O)](ClO₄)₂ (1), [Ni(HL)](ClO₄)₂ (2), as well as the known complex [Cu(HL)](ClO₄)₂ (3) for comparison. Their abilities to catalyze the dismutation of H₂O₂ and the oxidation of cyclohexane were investigated. The complexes were characterized by X-ray diffraction, elemental analysis, electronic and infrared spectroscopy, cyclic voltammetry, electrospray ionization mass spectrometry (ESI-MS) and conductivity measurements. The X-ray structures showed that the nickel (2) and copper (3) complexes are tetracoordinated, with the metal ion bound to the nitrogen atoms of the ligand. On the other hand, the cobalt complex (1) is hexacoordinated, possessing additional bonds to the alkoxo group of the ligand and to a water molecule. Neither of the complexes was able to catalyze the oxidation of cyclohexane, but all of them exhibited catalase-like activity, following Michaelis-Menten kinetics, which suggest resemblance with the catalase natural enzymes. The catalytic activity followed the order: [Ni(HL)](ClO₄)₂ (2) > [Cu(HL)](ClO₄)₂ (3) > [Co(L)(H₂O)](ClO₄)₂ (1). As far as we know, this is the first description of a nickel complex presenting a significant catalase-like activity.</p></div

Cyclic voltammogram of [Co(L)(H₂O)](ClO₄)₂, in water.

<p>K₃[Fe(CN)₆] (<i>E</i>_1/2 = 0,254 V <i>versus</i> Ag/AgCl; Δ<i>E</i> = 347 mV) was used as internal standard. Inlet: voltammograms at 25 mV s^-1.</p

Initial rate (<i>v</i>₀) of O₂ evolution as a function of initial H₂O₂ concentration.

<p>Experimental data (square); Nonlinear Least Square fitting using Michaelis-Menten equation (continuous line). (A) [Co(L)(H₂O)](ClO₄)₂; (B) [Ni(HL)](ClO₄)₂; (C) [Cu(HL)](ClO₄)₂. [complex] = 3.0×10⁻³ mol dm^-3.</p

Selected bonds lengths (Å) and bond angles (°) for [Ni(HL)](ClO₄)₂.

<p>Selected bonds lengths (Å) and bond angles (°) for [Ni(HL)](ClO₄)₂.</p

Cyclic voltammetry data for the complexes.

<p>^a: <i>E</i>_pc is given instead of <i>E</i>_1/2</p><p>^b: <i>E</i>_pa is given instead of <i>E</i>_1/2.</p><p>Cyclic voltammetry data for the complexes.</p