Enhanced Oxygen Reduction Reaction Performance Using Intermolecular Forces Coupled with More Exposed Molecular Orbitals of Triphenylamine in Co-porphyrin Electrocatalysts

Abstract

Triphenylamine (TPA) has often been used as a building block to construct functional organic materials yet is rarely employed in oxygen reduction reaction (ORR) due to its strong electron-donating ability. This versatile segment bears a three-dimensional spatial structure whose effect has not been fully explored in catalytic systems. To this end, five symmetric cobalt porphyrins with carbazole and TPA derivatives have been synthesized and their ORR performance has been evaluated in acid medium. It was found that all compounds produced mainly hydrogen peroxide in oxygen reduction, with CP1 attaching benzyl derivatives and XCP4 possessing TPA-carbazole substituents at the meso-position of porphyrin, showing similar but more positive ORR potential as compared to the other analogues. Importantly, XCP4 achieved the greatest response current and the largest electron transfer numbers and H 2 O 2 yields among the investigated molecules. Detailed electrochemical measurements suggested that the dipole-induced partial charges on the porphyrin in tandem with the more exposed molecular orbitals on TPA contributed to this enhancement, with the former attracting more protons to the affinity of reactive sites and the latter increasing the collision frequency between the electrocatalyst and H + in solution. This is the first attempt to integrate the intermolecular forces with more exposed molecular orbitals in altering the electrochemical process.

Promotion of Catalytic Oxygen Reduction Reactions: The Utility of Proton Management Substituents on Cobalt Porphyrins

“…The MO energies predicted in the DFT calculations for complexes with an O 2 axial ligand are consistent with this since a marked stabilization is predicted for the frontier MOs of CN-CoPor and AC-CoPor (Figure ). F-CoPor/C , which lacks a proton management substituent, exhibits poor ORR reactivity that is even lower than what has been reported for other cobalt porphyrins with electron-donating groups …”

Alkaline Metal Oxide Assisting the Ionothermal Method for Efficient Fe-NX/C Catalyst Preparation

“… Figure S3 shows the deconvolution of Fe 2p spectra of these catalysts. The peaks at around 710 and 714 eV can be denoted as the 2p 3/2 orbitals of the N-coordinated Fe­(II) and (III) species. ,− The other peaks at 713 and 725 eV correspond to the 2p 3/2 and 2p 1/2 orbitals of Fe­(III). Fe-N X can promote the initial oxygen adsorption and adsorption of reaction intermediates so as to improve the catalytic activity of ORR.…”

Improving Electrocatalytic Oxygen Reduction Activity and Selectivity with a Cobalt Corrole Appended with Multiple Positively Charged Proton Relay Sites

“…Molecular catalysts have the benefits of being used for the study of reaction mechanisms and structure–function relationships. − Recent efforts have led to the identification of a variety of coordination complexes of Mn, , Fe, − Co, − Ni, , and Cu − as active ORR catalysts. With the study of these complexes, valuable knowledge to improve the activity and selectivity of the 4e – ORR has been learned, including introducing hydrogen-bonding interactions, − providing rapid electron transfers, − using electron-donating axial ligands, ,, creating sterically protected O 2 -binding sites, − and making cooperative dinuclear sites. − In addition to these design strategies, it was demonstrated by Nocera, , Mayer, , Karlin, , Dey , and others that the efficient proton transfer facilitated by intramolecular proton relays can improve the selectivity for the 4e – ORR. Very recently, Warren and coworkers reported controlling the ORR selectivity by using positively charged groups, which are able to stabilize O 2 -bound intermediates through electrostatic interactions …”