Electrocatalysis of hydrazine electrooxidation Part II. Adsorbed mixtures of water soluble sulfonated phthalocyanines

En este trabajo se informan las propiedades catalíticas de tetrasulfoftalocianinas de cobalto (CoTSF) y de hierro (Fe-TSF) co-adsorbidas sobre un electrodo de grafito. Los estudios voltamétricos demuestran que estos compuestos se adsorben sobre el electrodo dando cubrimientos similares a aquellos en que sólo se adsorbe un compuesto. Se examinó las propiedades electrocatalitícas de la mezcla de compuestos para la oxidación de hidracina y se encontró que estos catalizadores actúan en forma independiente, a juzgar por las pendientes obtenidas de curvas de Tafel

Mapping Transition Metal-MN4 Macrocyclic Complex Catalysts Performance for the Critical Reactivity Descriptors

There has been a significant progress towards the development of highly active and stable platinum group metal-free (PGM-free) electrocatalysts for the oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFC), promising a low-cost replacement for Pt group electrocatalysts. However, the success of such developments depends on the implementation of PGM-free electrocatalysts that are not only highly active but importantly, they also exhibit long-term durability under PEFC operating conditions. This manuscript is an overview of the current status of a specific, most advanced class of PGM-free electrocatalysts: transition metal-nitrogen-carbon (M-N-C) ORR catalysts. We present an overview for the understanding of catalysts’ performance descriptors for M-N-C materials

Redox Potentials as Reactivity Descriptors in Electrochemistry

A redox catalyst can be present in the solution phase or immobilized on the electrode surface. When the catalyst is present in the solution phase the process can proceed via inner- (with bond formation, chemical catalysis) or outer-sphere mechanisms (without bond formation, redox catalysis). For the latter, log k is linearly proportional to the redox potential of the catalysts, E°. In contrast, for inner-sphere catalyst, the values of k are much higher than those predicted by the redox potential of the catalyst. The behaviour of these catalysts when they are confined on the electrode surface is completely different. They all seem to work as inner-sphere catalysts where a crucial step is the formation of a bond between the active site and the target molecule. Plots of (log i)E versus E° give linear or volcano correlations. What is interesting in these volcano correlations is that the falling region corresponding to strong adsorption of intermediates to the active sites is not necessarily attributed to a gradual surface occupation of active sites by intermediates (Langmuir isotherm) but rather to a gradual decrease in the amount of M(II) active sites which are transformed into M(III)OH inactive sites due to the applied potential

Electrocatalytic Self-Assembled Nanoarchitectonics for Clean Energy Conversion Applications

The general trends in the construction of highly active electrode devices are focused on the science of materials. These are useful for developing 2D nanostructured electrodes, with well-defined active sites, which are excellent approaches for understanding the fundamentals of electrocatalytic reactions. Here we present an overview of the experimental self-assembled molecular catalyst configurations to develop excellent electrode materials containing molecular catalysts for energy conversion device applications. First, by applying well-known reactivity descriptors for electrocatalysis, nanoarchitectonics, and the self-assembled concept, we summarize the main molecular building blocks to achieve a technology system for arranging by a rational design, nanoscale structural units configuration that promotes electrocatalytic reactions such as oxygen reaction reduction (ORR) and water-splitting reactions. We focus the discussion on the MN4 molecular catalyst linked to electrode surfaces with the help of the axial blocks, bio-inspired self-assembled approaches such as biomimetic models of metalloenzymes active sites, and molybdenum sulfide clusters for hydrogen evolution reaction (HER). We briefly discuss the advantages of developing host-guest self-assembled molecular catalyst systems based on cyclodextrins anchored to electrodes to get well-defined active sites with local environment control

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

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 N2 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

Volcano correlations for the reactivity of surface-confined cobalt N4-macrocyclics for the electrocatalytic oxidation of 2-mercaptoacetate

We have investigated the electrocatalytic activity of several substituted and unsubstituted cobalt–phthalocyanines of substituted tetraphenyl porphyrins and of vitamin B12, for the electro-oxidation of 2-mercaptoacetate, with the complexes pre-adsorbed on a pyrolytic graphite electrode. Several N4-macrocyclic were used to have a wide variety of Co(II)/(I) formal potentials. The electrocatalytic activity, measured as current at constant potential, increases with the Co(II)/(I) redox potential for porphyrins as Co–pentafluorotetraphenylporphyrin larger than Co–tetrasulfonatotetraphenylporphyrin larger than Co-2,2′,2″,2‴tetra-aminotetraphenylporphyrin and decreases for cobalt phthalocyanines as Co-3,4-octaethylhexyloxyphthalocyanine > Co–octamethoxyphthalocyanine > Co–tetranitrophthalocyanine Co–tetraaminophthalocyanine > Co–unsubstituted phthalocyanine > Co–tetrasulfonatophthalocyanine > Co–perfluorinated phthalocyanine. Vitamin B12 exhibits the maximum activity. A correlation of log I (at constant potential) versus the Co(II)/(I) formal potential of the catalysts gives a volcano curve. This clearly shows that the search for better catalysts for this reaction point to those N4-macrocyclic complexes with Co(II)/(I) formal potentials close to −0.84 V versus SCE, which correspond to an optimum situation for the interaction of the thiol with the active site

Tuning the redox properties of metalloporphyrin-and metallophthalocyanine-based molecular electrodes for the highest electrocatalytic activity in the oxidation of thiols

In this work we discuss different approaches for achieving electrodes modified with N4 macrocyclic complexes for the catalysis of the electrochemical oxidation of thiols. These approaches involve adsorption, electropolymerization and molecular anchoring using self assembled monolayers. We also discuss the parameters that determine the reactivity of these complexes. Catalytic activity is associated with the nature of the central metal, redox potentials and Hammett parameters of substituents on the ligand. Correlations between catalytic activity (log i at constant E) and the redox potential of catalysts for complexes of Cr, Mn, Fe, Co, Ni and Cu are linear with an increase of activity for more positive redox potentials. For a great variety complexes bearing the same metal center (Co) correlations between log i and Eo′ of the Co(II)/Co(I) couple have the shape of an unsymmetric volcano. This indicates that the potential of the Co(II)/Co(I) couple can be tuned using the appropiate ligand to achieve maximum catalytic activity. Maximum activity probably corresponds to a ΔG of adsorption of the thiol on the Co center equal to zero, and to a coverage of active sites by the thiol equal to 0.5

ARIA digital anamorphosis: Digital transformation of health and care in airway diseases from research to practice

Digital anamorphosis is used to define a distorted image of health and care that may be viewed correctly using digital tools and strategies. MASK digital anamorphosis represents the process used by MASK to develop the digital transformation of health and care in rhinitis. It strengthens the ARIA change management strategy in the prevention and management of airway disease. The MASK strategy is based on validated digital tools. Using the MASK digital tool and the CARAT online enhanced clinical framework, solutions for practical steps of digital enhancement of care are proposed

Strategies to improve the catalytic activity and stability of bioinspired Cu molecular catalysts for the ORR

The oxygen reduction reaction (ORR) is essential for energy conversion devices such as fuel cells and metal-air batteries. The use of expensive and scarce noble metal materials to catalyze the ORR is a limitation for the massification of these energy conversion technologies. Copper molecular catalysts that mimic the active sites of metalloenzymes such as laccase are under continuous development. In this minireview, we present the strategies to increase the activity and stability of the copper catalysts for the ORR. The flexibility, lability, and electronic character of the ligands are crucial to promote the ORR. In addition, the use of polymers as backbone for multicopper catalysts and the synthesis of copper carbon-based pyrolyzed catalysts present remarkable results with promissory applicationsThis work has been supported by FONDECYT 11221073, FONDECYT 1221798, FONDECYT Postdoctoral Project 3170330 and Anillo Project ACT-19217