Oxygen reduction at negatively charged iron porphyrins heat-treated and bridged by alkaline-earth metal ions

Energy-Related Small Molecule Activation Reactions: Oxygen Reduction and Hydrogen and Oxygen Evolution Reactions Catalyzed by Porphyrin- and Corrole-Based Systems

Globally increasing energy demands and environmental concerns related to the use of fossil fuels have stimulated extensive research to identify new energy systems and economies that are sustainable, clean, low cost, and environmentally benign. Hydrogen generation from solar-driven water splitting is a promising strategy to store solar energy in chemical bonds. The subsequent combustion of hydrogen in fuel cells produces electric energy, and the only exhaust is water. These two reactions compose an ideal process to provide clean and sustainable energy. In such a process, a hydrogen evolution reaction (HER), an oxygen evolution reaction (OER) during water splitting, and an oxygen reduction reaction (ORR) as a fuel cell cathodic reaction are key steps that affect the efficiency of the overall energy conversion. Catalysts play key roles in this process by improving the kinetics of these reactions. Porphyrin-based and corrole-based systems are versatile and can efficiently catalyze the ORR, OER, and HER. Because of the significance of energy-related small molecule activation, this review covers recent progress in hydrogen evolution, oxygen evolution, and oxygen reduction reactions catalyzed by porphyrins and corroles.

Dioxygen reduction catalyzed by substituted iron tetraphenylporphyrins in acidic media

Five iron tetraphenylporphyrins including the (TPP)FeCl and its derivatives which contain electron-withdrawing or electron-donating substituents on the meso-phenyl rings of the porphyrin macrocycle were examined as catalysts for the electoreduction of dioxygen in 1.0 M HClO4. The investigated compounds are represented as ( T p RPP ) FeCl , where T p RPP is the dianion of the para-substituted tetraphenylporphyrin and R = NEt2, OMe , H , Br or CF3. Cyclic voltammetry and linear sweep voltammetry at a rotating disk electrode (RDE) or a rotating ring disk electrode (RRDE) were utilized to examine the catalytic activity of the compounds. The number of electrons transferred and the percentage of H2O2produced as the product of O2electroreduction were calculated. The investigated iron porphyrins containing electron-withdrawing substituents ( R = Br and CF3) were shown to be more efficient catalysts for O2reduction than the compounds having electron-donating groups ( R = NEt2and OMe ) on the four phenyl rings of the porphyrin macrocycle.