Cobalt compounds are intensely explored as efficient catalysts for the oxygen evolution reaction (OER). Since vitamin B12 is a soluble cobalt compound with high enzymatic activity, evaluating its OER activity is of relevance for biomimetic catalyst research. In this work, the temporal evolution of a homogenous vitamin B12 catalyst in the early stages of OER was investigated by an advanced combination of in situ electrochemical liquid transmission electron microscopy (EC-LTEM), in situ UVvis spectroelectrochemistry, and extended X-ray absorption fine structure (EXAFS) methods. For the first time, we provided direct evidence of diffuse layer dynamics on the working electrode interface. The results suggested that the formation of cobalt oxyphosphate nanoparticles on the working electrode interface and in the presence of phosphate buffer is the initial stage of the catalytic pathway. Computational results confirmed that the ligand oxidation pathway could occur at potentials below the OER thermodynamic barrier (1.23 V vs reversible hydrogen electrode (RHE)), which leads to a Co ion leaching into the electrolyte. This study showed that investigation of the apparent molecular mechanisms of OER with metal complexes requires careful analyses. We illustrate the high precision and sensitivity of EC-LTEM under operational conditions to monitor heterogeneous catalysts generated during OER and to evaluate their actual roles in the catalytic process.

No abstract

Ferritin is a protein (ca. 12 nm) with a central pocket of 6 nm diameter, and hydrated iron oxide stored in this central cavity of this protein. The protein shell has a complicated structure with 24 subunits. Transmission electron microscopy images of ferritin showed nanosized iron oxides (ca. 4–6 nm) in the protein structure. In high-resolution transmission electron microscopy images of the iron core, d-spacings of 2.5–2.6 Å were observed, which is corresponded to d-spacings of ferrihydrite crystal structure. Our experiments showed that at pH 11, the modified electrode by this biomolecule is active for water oxidation (turnover frequency: 0.001 s −1 at 1.7 V). Using affected by bacteria, we showed that Fe ions in the structure of ferritin are critical for water oxidation.

No abstract

All studies on oxygen-evolutionr eaction by Mn oxides in the presence of cerium(IV)a mmonium nitrate (CAN) have been so far carriedo ut by synthesizing Mn oxides in the first step. And then, followed by the investigation of the Mn oxides in the presence of oxidants for oxygen-evolution reaction (OER). This paperp resents ac ase study of an ew and promising strategy for in situ catalyst synthesis by the adding Mn II to either CAN or KMnO 4 /CAN solution, resulting in the formationo fM n-based catalysts for OER. The catalysts were characterized by scanning electron microscopy,e nergy-dispersive spectroscopy,t ransmission electron microscopy,X-ray diffraction, Fourier transform infrared spectroscopy,X-ray absorption spectroscopy,a nd Xray photoelectron spectroscopy. Both compounds contained nano-sized particlest hat catalyzed OER in the presenceo f CAN. The turnover frequencies for both catalysts were 0.02 (mmol O 2 /mol Mn •s).