Spin-Modulated Oxygen Electrocatalysis

Abstract

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 − /H 2 O and triplet O 2 , 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.

Engineering the spin configuration of electrocatalysts for electrochemical renewable conversions

“…Thus, both energies contribute to the electrocatalytic activity. 30 The spin polarization effect is a common way to change the electron spin state of ferromagnetic (FM) coupled catalysts by adjusting the external magnetic fields. After the FM catalysts were polarized by an external magnetic field, the magnetic structure of the FM catalysts can be transformed from the multi-domain structures to single-domain counterparts.…”

Probing the evolution in catalytic graphitization of biomass-based materials for enduring energetic applications

“…Commonly used electrocatalysts include platinum (Pt), transition metal oxides, nitrides and carbon-based materials such as graphene and carbon nanotubes. 81,82 Researchers aim to improve the efficiency of electrocatalytic systems by designing catalysts with optimized activity and selectivity. As such, enhancing the durability and reducing the cost of electrocatalysts, especially for precious metals.…”

Modulation of the Phase Transformation of Fe2O3 for Enhanced Water Oxidation under a Magnetic Field

“…The OER process not only involves four consecutive proton-coupled electron transfers but also includes a transition of the spin states from the singlet state of the reactant OH – /H 2 O to the triplet product O 2 . − The O–O bond formed by the breakage of two water molecules must produce a paramagnetic triplet state of molecular oxygen through spin conservation . Therefore, the kinetics of triple oxygen formation can be effectively improved by modulating the electron spin polarization through an external magnetic field to align the spins of O–O in parallel, and also, theoretical studies have shown that the spin polarization on the surface of the activated catalysts may be beneficial to the parallel spin alignment of the oxygen atoms during the reaction process, thus improving the efficiency of the reaction process. ,, Garcés-Pineda used a magnetic field to modulate electron spin polarization for enhanced electrocatalytic water oxidation. The addition of an appropriate magnetic field (≤450 mT) to magnetic NiZnFe 4 O x catalysts significantly increased the current density and the intrinsic activity of the catalysts.…”