Solvent and substituent effects on UV-vis spectra and redox properties of zinc p-hydroxylphenylporphyrins

A series of zinc[Formula: see text]-hydroxylphenylporphyrins was synthesized and characterized by spectroscopic and electrochemical methods in four different nonaqueous solvents. The investigated compounds are represented as [([Formula: see text]-HOPh)[Formula: see text](ptBuPh)[Formula: see text]P]Zn, where P represents the dianion of a porphyrin, Ph represents a phenyl group, HO and [Formula: see text]Bu are para substituents on the meso-phenyl rings of the macrocycle and [Formula: see text] = 0–4. The four utilized nonaqueous solvents were dichloromethane (CH[Formula: see text]Cl[Formula: see text], NN-dimethylformamide (DMF), dimethylsulfoxide (DMSO) and pyridine (Py) which were selected on the basis of their coordinating capabilities. The UV-visible spectra and redox potentials of each porphyrin were analyzed both as a function of Hammett substituent constants for groups at the para-positions of the meso-phenyl rings and as a function of the Gutmann solvent donor number which is related to the coordinating ability of the solvent. Each porphyrin exhibits two reductions in CH[Formula: see text]Cl[Formula: see text], DMSO and Py while three reductions are observed in DMF, the additional reaction being due to a phlorin product generated in solution after formation of the porphyrin dianion. Two or three reversible oxidations were seen in CH[Formula: see text]Cl[Formula: see text], the exact number depending upon the specific porphyrin and the presence of [Formula: see text]-OH substituents at the meso-phenyl rings of the compound. The first two oxidations were assigned as involving the conjugated macrocycle and the third is associated with oxidation of the meso-HOPh group(s).

Polydopamine-Coated Manganese Complex/Graphene Nanocomposite for Enhanced Electrocatalytic Activity Towards Oxygen Reduction

Platinum electrodes are commonly used electrocatalysts for oxygen reduction reactions (ORR) in fuel cells. However, this material is not economical due to its high cost and scarcity. We prepared an Mn(III) catalyst supported on graphene and further coated with polydopamine, resulting in superior ORR activity compared to the uncoated PDA structures. During ORR, a peak potential at 0.433 V was recorded, which is a significant shift compared to the uncoated material's -0.303 V (both versus SHE). All the materials reduced oxygen in a wide pH range via a four-electron pathway. Rotating disk electrode and rotating ring disk electrode studies of the polydopamine-coated material revealed ORR occurring via 4.14 and 4.00 electrons, respectively. A rate constant of 6.33 × 10(6) mol(-1)s(-1) was observed for the polydopamine-coated material-over 4.5 times greater than the uncoated nanocomposite and superior to those reported for similar carbon-supported metal catalysts. Simply integrating an inexpensive bioinspired polymer coating onto the Mn-graphene nanocomposite increased ORR performance significantly, with a peak potential shift of over +730 mV. This indicates that the material can reduce oxygen at a higher rate but with lower energy usage, revealing its excellent potential as an ORR electrocatalyst in fuel cells.

An electrochemical bifunctional sensor for the detection of nitrite and hydrogen peroxide based on layer-by-layer multilayer films of cationic phthalocyanine cobalt(ii) and carbon nanotubes

Binder-free multilayer films composed of phthalocyanine and carbon nanotubes were constructed by the layer-by-layer electrostatic assembly and applied for the electrochemical detection of NO₂⁻ and H₂O₂.

Iron nanoparticles with a square pyramidal structure in mesoporous carbons as an effective catalyst toward oxygen reduction

FeAMC-1273, with more pyridinic-N and pyridinic-N–Fe for the creation of a square pyramidal planar geometry around iron, exhibits the best ORR activity.

Graphene supported non-precious metal-macrocycle catalysts for oxygen reduction reaction in fuel cells

Fuel cells are promising alternative energy devices owing to their high efficiency and eco-friendliness. While platinum is generally used as a catalyst for the oxygen reduction reaction (ORR) in a typical fuel cell, limited reserves and prohibitively high costs limit its future use. The development of non-precious and durable metal catalysts is being constantly conceived. Graphene has been widely used as a substrate for metal catalysts due to its unique properties, thus improving stability and ORR activities. In this feature, we present an overview on the electrochemical characteristics of graphene supported non-precious metal containing macrocycle catalysts that include metal porphyrin and phthalocyanine derivatives. Suggested research and future development directions are discussed.

Self-directedly assembled porphyrin thin films with high photoactivity

A highly photoactive porphyrin thin films were self-directedly assembled by using 5,10,15,20-tetra(4-hydroxyphenyl)porphyrin cobalt and γ-isocyanatopropyltriethoxysilane as the reactants.