Electrocatalytic oxidation of hydrazine in alkaline media promoted by iron tetrapyridinoporphyrazine adsorbed on graphite surface

Abstract

A oxidação eletrocatalítica de hidrazina foi estudada sobre um eletrodo de grafite pirolítico ordinário modificado com tetrapiridinoporfirazina de ferro (FeTPyPz) com as técnicas de voltametria cíclica e de eletrodo de disco rotatório. Análise dos voltamogramas registrados a diferentes velocidades de varredura do potencial e das curvas de polarização para diferentes velocidades de rotação do eletrodo mostraram que a reação de eletroxidação de hidrazina sobre FeTPyPz processa-se de acordo com um mecanismo envolvendo 4 elétrons e com a formação de N 2 como principal produto. Os parâmetros cinéticos sugerem que a segunda etapa de transferência de carga é a etapa determinante da velocidade da reação. A atividade eletrocatalítica do complexo FeTPyPz depende do potencial formal do processo redox Fe(II)/Fe(I), que apresentou bom ajuste num gráfico do tipo vulcano formado por diferentes ftalocianinas de ferro, indicando que este potencial formal é um bom indicador da reatividade destes complexos.The electrocatalytic oxidation of hydrazine was studied using an ordinary pyrolytic graphite electrode modified with iron tetrapyridinoporphyrazine complex (FeTPyPz), employing cyclic voltammetry and rotating disk electrode techniques. Analyses of the voltammograms recorded at different potential scan rates and the polarization curves at different electrode rotation rates showed that the reaction of electrooxidation of hydrazine on FeTPyPz occurs via 4-electrons with the formation of N 2 as main product. The kinetic parameters suggest that the second electron transfer step is rate controlling. The activity of FeTPyPz depends on its Fe(II)/Fe(I) formal potential and fits well in a volcano plot that includes several iron phthalocyanines, indicating that such formal potential is a good reactivity index for these complexes.Keywords: hydrazine oxidation, modified graphite electrode, iron tetrapyridinoporphyrazine, volcano plot IntroductionThe study of chemically modified electrodes has attracted considerable interest in the last decades as researchers attempt to exert more control over the chemical nature of the electrode surface. Molecules of known reactivity are then incorporated or confined on the electrode surface, acting as mediators for electron transfer reactions. Applications include electrocatalysis, electroanalysis, sensors and biosensors, as well as in electrochemical detection systems used in flow-injection analysis or high performance liquid chromatography. One applicability of these electrodes refers to the oxidation and detection of hydrazine, an important chemical compound used in jet and rocket fuels and in the production of agricultural and textile chemicals, drugs, explosives, photographic developers, blowing agents used in the manufacture of foam rubber, and in the prevention of rusting in boilers and nuclear reactors. 31 Furthermore, the detection of hydrazine and its derivatives is very important in pharmacology due to the recognition as carcinogenic and hepatotoxic substances. 31,32 In order to reduce the typi...

Metallophthalocyanine-based molecular materials as catalysts for electrochemical reactions

“…This illustrates again the concept "tuning" the redox potential of the catalyst to a desired value, using appropriate groups on the phthalocyanine ligand to obtain the highest activity. It is important to point out here that macrocyclic complexes that are not phthalocyanines do fit in this volcano correlation indicating that the redox potential of the cata- lyst is a good reactivity index and seems to be independent of the nature of the ligand in the complex [85,475].…”

Electrode modification using iron metallophthalocyanine through click chemistry and axial ligation with pyridine

“…A clear oxidation process was visible at À0.2 V, on both the anodic and cathodic scans. The electrocatalytic oxidation of hydrazine at or near this potential (À0.2 V) has been shown with CoPc [2,53,54], as well as FePc [55][56][57]. The electro-oxidation on both scans has been attributed in a similar study to the regeneration or reformation of the active catalyst that oxidises hydrazine [58] -the Fe(II)Pc species in this case.…”

“…It has also been observed with substituted FePc sensors [55]. A number of studies confirming the relationship between the potential of the metal process and the potential of hydrazine electrocatalysis have been done, proving the involvement of the Fe II/ Fe I couple of the FePc [40][41][42][55][56][57]. Zagal and co-workers [40][41][42] have suggested the following mechanism for the oxidation of hydrazine on MPc modified electrodes (equations 1-3):…”

Electrochemical properties of metallated porphyrazines possessing isophthaloxybutylsulfanyl substituents: Application in the electrocatalytic oxidation of hydrazine

“…The catalytic oxidation of hydrazine through the use of various porphyrinoids has been mainly carried out in strong alkaline conditions [24][25][26]; whereas, the properties of such macrocycles in a neutral pH have been rarely studied [27]. Moreover, Pzs have up until now hardly been studied in the application in electrocatalysis or electrochemical sensors [24].…”

“…Moreover, Pzs have up until now hardly been studied in the application in electrocatalysis or electrochemical sensors [24].…”