Sulfonic Acid Functionalization-Boosted Ultrafast, Durable, and Selective Four-Electron Oxygen Reduction Reaction: Evidenced by EC-SHINERS and DFT Studies

Abstract

Hydroperoxyl intermediate is a vital component in the mechanism of electrochemical oxygen reduction reaction (ORR) and several other important chemical reactions. The selectivity and kinetics of ORR are controlled by the energetics of *OOH intermediate (* represents the active site). The present work integrates iron phthalocyanine (FePc) with sulfonic acid-functionalized multiwalled carbon nanotubes (MWCNTs-SO 3 H). The resulting composite (FePc@MWCNTs-SO 3 H) demonstrates significantly improved kinetics and higher four-electron selectivity for the electrochemical reduction of oxygen compared to its counterpart without functionalization (FePc@MWCNTs) in alkaline, neutral, and acidic media. Based on the in situ electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy (EC-SHINERS) results and DFT calculations, it is proposed that sulfonate groups are involved in the water-assisted hydrogen-bonding interaction with the FeOOH intermediate. This interaction causes a substantial increase in selectivity and kinetics of ORR. Apart from the ORR, the findings of the current work strongly recommend that the functional groups on carbon support can be manipulated to get improved kinetics and selectivity of several important chemical transformations.

Co(II) Porphyrin-MWCNT Nanoconjugate as an Efficient and Durable Electrocatalyst for Oxygen Reduction Reaction

“…However, after a similar treatment, the Pt-C shows a significant decrease (11.5%) in the current density, as reported recently. 50 This result suggests that the GC/nanoconjugate electrode is highly stable during the ORR for a long period of time, and therefore, this material could be a promising candidate for the cathode material in fuel cells to replace the expensive Pt-C.…”

Enhanced Four‐Electron Selective Oxygen Reduction Reaction at Carbon‐Nanotube‐Supported Sulfonic‐Acid‐Functionalized Copper Phthalocyanine

“…The Tafel slopes measured for GC RDE /MWCNTs, GC RDE /MWCNTs‐CuPc‐SO 3 − , GC RDE /NMWCNTs, and GC RDE /NMWCNTs‐CuPc‐SO 3 − in 0.1 M HClO 4 at a sweep rate 10 mV/s and a rotation rate 1600 rpm are found to be 294, 285, 276, and 222 mV/dec (Figure S10). Based on these values, GC RDE /NMWCNTs‐CuPc‐SO 3 − shows high catalytic activity for the ORR as it exhibits the lowest slope [77] …”

“…Based on these values, GC RDE / NMWCNTs-CuPc-SO 3 À shows high catalytic activity for the ORR as it exhibits the lowest slope. [77] During the oxygen reduction process, initially, the O 2 molecules diffuse from the bulk to the electrode-electrolyte interface. There it gets attached to the catalytic site and participates in the proton-coupled electron transfer reaction.…”

π-Extended nonplanar cobalt porphyrins immobilized on MWCNTs as efficient electrocatalysts for selective oxygen reduction reaction

“…However, it is expensive and has certain stability and selectivity issues. 12 The 4e À selective ORR is desired in fuel cells. Bond breaking in the A-O-O-H* intermediate (where A represents the active site) depends upon the nature of the active site.…”

“…Several approaches have been explored to achieve the efficient and highly selective 4e À ORR. [11][12][13][14][15][16][17][18][19] Macrocyclic cobalt complexes exhibit reliable ORR catalytic activity. 15,20 For the past two decades, planar porphyrins have been utilized as electron donors to interact with MWCNTs.…”