Beyond domain alignment: Revealing the effect of intrinsic magnetic order on electrochemical water splitting

TL;DR

This study demonstrates that intrinsic ferromagnetic order in La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ thin films enhances oxygen evolution reaction activity during water splitting, highlighting the role of magnetic properties in catalyst performance.

Contribution

It reveals that intrinsic magnetic order, modulated by temperature, influences catalytic activity, providing new insights into magnetic effects on electrochemical water splitting.

Findings

Ferromagnetic order enhances OER activity below Curie temperature.

External magnetic fields slightly increase current density, dependent on magnetic anisotropy.

No long-range magnetic order at the surface, indicating bulk magnetic order affects catalysis.

Abstract

To reach a long term viable green hydrogen economy, rational design of active oxygen evolution reaction (OER) catalysts is critical. An important hurdle in this reaction originates from the fact that the reactants are singlet molecules, whereas the oxygen molecule has a triplet ground state with parallel spin alignment, implying that magnetic order in the catalyst is essential. Accordingly, multiple experimentalists reported a positive effect of external magnetic fields on OER activity of ferromagnetic catalysts. However, it remains a challenge to investigate the influence of the intrinsic magnetic order on catalytic activity. Here, we tuned the intrinsic magnetic order of epitaxial La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ thin film model catalysts from ferro- to paramagnetic by changing the temperature in-situ during water electrolysis. Using this strategy, we show that ferromagnetic ordering below the Curie temperature enhances OER activity. Moreover, we show a slight current density enhancement upon application of an external magnetic field and find that the dependence of magnetic field direction correlates with the magnetic anisotropy in the catalyst film. Our work thus suggests that both the intrinsic magnetic order in La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ films and magnetic domain alignment increase their catalytic activity. We observe no long-range magnetic order at the catalytic surface, implying that the OER enhancement is connected to the magnetic order of the bulk catalyst. Combining the effects found with existing literature, we propose a unifying picture for the spin-polarized enhancement in magnetic oxide catalysts.