Nitrite electro-oxidation mediated by Co(II)-[tetra(4-aminophenyl)porphyrin]-modified electrodes: behavior as an amperometric sensor

Electro-Reduction of Molecular Oxygen Mediated by a Cobalt(II)octaethylporphyrin System onto Oxidized Glassy Carbon/Oxidized Graphene Substrate

The oxygen reduction reaction (ORR) is the most important reaction in life processes and in energy transformation. The following work presents the design of a new electrode which is composed by deposited cobalt octaethylporphyrin onto glassy carbon and graphene, where both carbonaceous materials have been electrochemically oxidized prior to the porphyrin deposition. The novel generated system is stable and has an electrocatalytic effect towards the oxygen reduction reaction, as a result of the significant overpotential shift in comparison to the unmodified electrode and to the electrodes used as target. Kinetic studies corroborate that the system is capable of reducing molecular oxygen via four electrons, with a Tafel slope value of 60 mV per decade. The systems were morphologically characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM) Electrochemical impedance spectroscopy studies showed that the electrode previously oxidized and modified with cobalt porphyrin is the system that possesses lower resistance to charge transfer and higher capacitance.

Synthesis of novel porphyrin and chlorin phosphonic acids and their immobilization on metal oxides

In this study an easy and flexible access to porphyrin and chlorin phosphonic acids is presented. Novel types of phosphonic acid terminated porphyrins and chlorins were synthesized starting from commercially available red blood pigment hemin chloride. Phosphonic acid groups were linked to the porphyrinoids by amide coupling via appropriate spacer moieties. Self-assembled monolayers of the synthesized phosphonates on mesoporous TiO2 electrodes of approximately 3 μm thickness were formed. Surface concentrations in a range of 1 to 4 × 10-8 mol.cm-2 could be determined by UV-vis spectroscopy.

Metal insertion into phosphonic acid terminated porphyrins immobilized on TiO2 electrodes

In this study an easy access for modification of properties of porphyrin covered TiO2 electrodes by post-assembling metal insertion was investigated. Therefore a new type of phosphonic acid terminated porphyrin was synthesized and immobilized on mesoporous TiO2 electrodes by self-assembling. Surface concentrations in a range of 1.5–3.3 × 10-8 mol.cm-2, based on the geometric area, were obtained by two independent techniques, UV-vis and cyclic voltammetry. Co(II) , Zn(II) , Pd(II) and Mn(III) ions could be inserted into the immobilized porphyrin by exposing the electrode to a boiling solution of metal chloride in methanol. The electrode surface was characterized by UV-vis spectroscopy and cyclic voltammetry before and after metal insertion. The electrocatalytic activity towards the reduction of molecular oxygen in acidic solution was examined, further confirming metal insertion into immobilized porphyrin monolayer.