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 La0.67Sr0.33MnO3 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 La0.67Sr0.33MnO3 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.

中文翻译：

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内禀磁序对电化学水分解的影响

为了实现长期可行的绿色氢经济，合理设计活性析氧反应（OER）催化剂至关重要。该反应的一个重要障碍源于反应物是单线态分子，而氧分子具有具有平行自旋排列的三线态基态，这意味着催化剂中的磁序至关重要。因此，多名实验者报告了外部磁场对铁磁催化剂的 OER 活性的积极影响。然而，研究固有磁序对催化活性的影响仍然是一个挑战。在这里，我们通过改变水电解过程中的原位温度，将外延 La0.67Sr0.33MnO3 薄膜模型催化剂的固有磁序从铁磁性调整为顺磁性。使用这种策略，我们表明低于居里温度的铁磁有序性增强了 OER 活性。此外，我们在施加外部磁场时表现出轻微的电流密度增强，并发现磁场方向的依赖性与催化剂膜中的磁各向异性相关。因此，我们的工作表明 La0.67Sr0.33MnO3 薄膜中的固有磁序和磁畴排列都会增加其催化活性。我们在催化表面没有观察到长程磁序，这意味着 OER 增强与本体催化剂的磁序有关。结合现有文献中发现的效应，我们提出了磁性氧化物催化剂中自旋极化增强的统一图景。