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

Abstract

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 0.7 Sr 0.2 Ca 0.1 MnO 3 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 O 2 , 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.

Electronic and Structural Disorder of the Epitaxial La0.67Sr0.33MnO3 Surface

“…For applications such as electrochemistry correlated to the fundamental theoretical understanding of the complex oxide manganites, careful consideration of the surface morphology and electronic structure is important. Therefore, the results presented in this work of the disentanglement between the bulk and surface properties of LSMO make it a tantalizing model system to evaluate the relationship between the surface and bulk spin ordering in electrocatalysis. ,,, …”

“…Therefore, the results presented in this work of the disentanglement between the bulk and surface properties of LSMO make it a tantalizing model system to evaluate the relationship between the surface and bulk spin ordering in electrocatalysis. 9 , 10 , 54 , 55 …”

“…Therefore, the results presented in this work of the disentanglement between the bulk and surface properties of LSMO make it a tantalizing model system to evaluate the relationship between the surface and bulk spin ordering in electrocatalysis. 9,10,54,55 ■ METHODS PLD and RHEED. Thin films of La 0.67 Sr 0.33 MnO 3 were fabricated by using PLD and a stoichiometric target from SurfaceNet.…”

“…Doping the parent material LaMnO 3 with Sr in La 0.67 Sr 0.33 MnO 3 (LSMO) introduces insulator-to-metal and para-to-ferromagnetic transitions driven by a complex interplay of lattice structure, charge, and spin degrees of freedom. , LSMO possesses an advantageous Curie temperature of up to 370 K that potentially enables spin control at room temperature. The control of these properties is of interest in fundamental electrochemical studies , of manganites. LSMO has been used as a model catalyst to study the oxygen reduction and evolution reactions (ORR and OER, respectively) due to the tunability of the active manganese site and its promising bifunctional activity. − A recent experiment has shown that active strain can be used to regulate the activity of LSMO thin films in the OER .…”

“… 6 , 7 LSMO possesses an advantageous Curie temperature of up to 370 K 8 that potentially enables spin control at room temperature. The control of these properties is of interest in fundamental electrochemical studies 9 , 10 of manganites. LSMO has been used as a model catalyst to study the oxygen reduction and evolution reactions (ORR and OER, respectively) due to the tunability of the active manganese site and its promising bifunctional activity.…”