Electrocatalysis of molecular oxygen reduction reaction at liquid-liquid interface and DFT computational study of proton
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ORIGINAL PAPER
Electrocatalysis of molecular oxygen reduction reaction at liquid-liquid interface and DFT computational study of proton transfer from the conjugate acid of 2,2′-dipyridylamineto oxygen Fatemeh Soleymani-Bonoti 1,2 Received: 28 August 2020 / Accepted: 8 November 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract In this study, the catalytic effect of 2,2′-dipyridylamine (DPA) on the reduction of oxygen (O2) at the polarized water/1,2dichloroethane (DCE) interface was investigated. Ferrocene (Fc) and tetrathiafulvalene (TTF) were weak electron donors used in this study. Slow reduction of O2 at the interface containing Fc and TTF was significantly accelerated upon the addition of DPA. Voltammetry and biphasic shake flask experiments revealed that DPA acts as a proton ionophore to transfer protons between the aqueous and organic phases. The PA, GB, and pKa values of all possible conjugate acids of DPA were calculated. Then, a mechanism was suggested to explain the interaction between protonated DPA and oxygen molecular. The mechanism was computationally analyzed by using density functional theory (DFT). Furthermore, DFT calculations at the B3LYP/6-31G** level of theory showed that the conjugate acid species of DPA transfer proton to O2 at the interface. The results show that DPAH2+ and DPA-H1+ are the best species to transfer proton to molecular oxygen. Keywords Oxygen reduction reaction . Liquid/liquid interface . Density functional theory . Biphasic shake flask experiments . Voltammetry
Introduction Amines as derivatives of ammonia are weak bases with pKb values in the range of 4 to 6. The unpaired electron density around the nitrogen atom makes amines enable to receive proton from proton sources and transfer it to proton acceptors [1, 2]. Reduction of molecular oxygen to peroxide or water is of interest from different stand points [3]. Oxygen reduction reaction (ORR) is significantly important for chemical and biological processes [4] such as biological respiration and fuel cells [5–7]. The thermodynamically favorable ORR has a slow kinetics which necessitates the use of catalysts. ORR can be performed on surfaces such as biological membranes [8], solid electrodes [9], and the interface between two immiscible electrolyte solutions (ITIES) [10, 11]. * Fatemeh Soleymani-Bonoti [email protected] 1
Department of Chemistry, Faculty of Science, University of Jundishapur, Dezful, Iran
2
Department of Chemistry, Faculty of Science, University of Zanjan, Zanjan 45371-38791, Iran
ITIES provides a reproducible platform to study electrocatalysis reactions such as ORR [10, 12, 13]. At liquid/ liquid interfaces, ORR is a proton-coupled electron transfer (PCET) which supply protons and electrons from the aqueous and organic phases, respectively [10, 12, 14]. The catalytic effects of various catalysts such as metallic phthalocyanine [15, 16], metallicporphyrins [17], oxidative resistant complex [18], dodecylaniline [1], and free base monomeric porphyrin [15, 19] on the ORR by orga
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