Magnetic Field-Enhanced Oxygen Evolution Reaction via the Tuneability of Spin Polarization in a Half-Metal Catalyst

The magnetic field response of an electrochemistry process, such as the oxygen evolution reaction (OER), provides not only a strategy for enhanced catalytic activity by applying an external field but also a platform for revealing the functionality of the multiple degrees of freedom of the catalyst. However, the mechanism of the magnetic field tuneable OER is controversial. The strong correlation between the d and p orbitals of transition metal and oxygen still puzzles the dominant role of spin in an OER process. Here in this study, we have employed the manganite La_0.7Sr_0.2Ca_0.1MnO₃ as the ferromagnetic OER catalyst, which has a ferromagnetic/paramagnetic transition (T_C) around the room temperature. It is found that the overpotential can be reduced by ∼18% after applying a 5 kOe magnetic field. Furthermore, this magnetic field can trigger a further improvement of the OER performance, and it demonstrates a strong temperature dependence which is incongruent with its magnetoresistive behavior. So our experiments suggest that the observed magnetic response originates dominantly from the triplet state of the O₂, where the spin-polarized d and oxygen p orbitals lower the Gibbs free energy for every reaction step in OER. This study offers experimental evidence on comprehending the spin degree in the OER process, meanwhile benefiting the further design and engineering of the promising magnetic electrochemistry catalysts.