Spin-Modulated Oxygen Electrocatalysis.

The electrocatalysis reactions involving oxygen, such as oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), play a critical role in energy storage/conversion applications, e.g., fuel cells, metal-air batteries, and electrochemical water splitting. The high kinetic energy barrier of the OER/ORR is highly associated with the spin state interconversion between singlet OH/HO and triplet O, which is influenced by the spin state and magnetism of catalysts. This Review summarizes recent progress and advances in understanding spin/magnetism-related effects in oxygen electrocatalysis to develop spin theory. It is demonstrated that the spin states (low, intermediate, and high spin) of magnetic transition metal catalysts (TMCs) can directly affect the reaction barriers of OER/ORR by tailoring the bonding of oxygen intermediates with TMCs. Besides, the spin states of TMCs can build a spin-selective channel to filter the electron spins required for the single/triplet interconversion of O species during OER/ORR. In this Review, we introduced many approaches to modulating spin state, for instance, altering the crystal field, oxidation state of active-site ions, and the morphology of TMCs. What's more, a magnetic field can drive the spin flip of magnetic ions to achieve the spin alignment (↑↑) (i.e., facilitating spin polarization), which will strengthen the spin selectivity for accelerating the filtration and transfer of the spins with the same direction for the generation and conversion of triplet ↑OO↑. Importantly, the origin of magnetic field enhancement on OER/ORR are deeply discussed, which provides a great vision for the magnetism-assisted catalysis. Finally, the challenges and perspectives for future development of spin/magnetism catalysis are presented. This Review is expected to highlight the significance of spin/magnetism theory in breaking the bottleneck of electrocatalysis field and promote the development of high-efficientcy electrocatalysts for practical applications.