Electron Spin-Dependent Electrocatalysis for the Oxygen Reduction Reaction in a Chiro-Self-Assembled Iron Phthalocyanine Device

The chiral-induced spin selectivity effect (CISS) is a breakthrough phenomenon that has revolutionized the field of electrocatalysis. We report the first study on the electron spin-dependent electrocatalysis for the oxygen reduction reaction, ORR, using iron phthalocyanine, FePc, a well-known molecular catalyst for this reaction. The FePc complex belongs to the non-precious catalysts group, whose active site, FeN4, emulates catalytic centers of biocatalysts such as Cytochrome c. This study presents an experimental platform involving FePc self-assembled to a gold electrode surface using chiral peptides (L and D enantiomers), i.e., chiro-self-assembled FePc systems (CSAFePc). The chiral peptides behave as spin filters axial ligands of the FePc. One of the main findings is that the peptides ' handedness and length in CSAFePc can optimize the kinetics and thermodynamic factors governing ORR. Moreover, the D-enantiomer promotes the highest electrocatalytic activity of FePc for ORR, shifting the onset potential up to 1.01 V vs. RHE in an alkaline medium, a potential close to the reversible potential of the O2/H2O couple. Therefore, this work has exciting implications for developing highly efficient and bioinspired catalysts, considering that, in biological organisms, biocatalysts that promote O2 reduction to water comprise L-enantiomers. The electrocatalytic activity of iron phthalocyanine (FePc) for the oxygen reduction reaction (ORR) was highly increased by promoting the chiral-induced spin selectivity effect on FePc axially coordinated by chiral-peptides (L and D enantiomers). By adjusting the peptides ' handedness and length (chiral C number), the kinetics and thermodynamic factors governing ORR were optimized for developing highly efficient catalysts.image

Automated summary

This study demonstrates that the chiral-induced spin selectivity effect can greatly enhance the electrocatalytic activity of iron phthalocyanine for the oxygen reduction reaction. By using chiral peptides to assemble FePc on a gold electrode surface, the handedness and length of the peptides can optimize the kinetics and thermodynamics of ORR. The D-enantiomer shows the highest electrocatalytic activity, shifting the onset potential close to the reversible potential of the O2/H2O couple.