The oxygen reduction reaction is an important step in the production of fuel cells, determining their efficiency and general use. However, the slow kinetics of the ORR, especially at the cathode, poses challenges due to the slow and energetic four-electron process. Efforts have been focused on the development of platinum-based catalysts with improved activity and stability.
One way is to alloy platinum with transition metals, which succeeds in lowering the energy level of the antibonding orbital and increasing the intrinsic activity of platinum.
Recent research has revealed that electrons not only carry charge but also have spin, which plays an important role in catalytic reactions. The transformation of oxygen molecules during the ORR involves a change in the spin state, which is important considering the interplay between local spins and electron magnetic interactions.
The spin effect in electrocatalytic reactions, especially those involving spin-flipping, remains poorly understood. Therefore, exploring the spin regulation of catalysts by involving dominant magnetism has become an interesting method for optimizing electron transfer and adsorption energy for local intermediates.
In this study, the researchers successfully incorporated gadolinium (Gd), a rare earth element, into the platinum lattice to make Pt.2Gd intermetallic alloy. Gadolinium has an intrinsic high spin density due to its half-filled 4f orbitals, resulting in a natural magnetic moment.
The alloy exhibits a unique intrinsic spin reconfiguration, which affects the kinetics of the ORR. The experimental results revealed that Pt2The Gd alloy exhibits remarkable electroactivity, including a high mass activity of 1.5 A·mgPt-1 and a half-wave potential of 0.95 V in an acid electrolyte environment. In addition, it exhibits superior stability compared to conventional platinum/carbon (Pt/C) catalysts.
Through density functional theory (DFT) calculations, the researchers unraveled the modulation of the Pt-5d orbitals induced by spin reconfiguration caused by mixing with Gd. The complementary spin polarization between Gd and Pt optimizes the electronic structure of Pt, leading to better adsorption of the oxygen intermediate.
In addition, the spin shielding effect of the Gd-4f orbitals balances the spin polarizations of the Pt-5d, which enhances the reduction capability of the Pt sites. This unique interplay between Pt and Gd resulted in a significant reduction of the energy barrier for the rate-determining step, which contributed to the superior ORR performance observed with Pt.2Gd alloy.
The successful synthesis of rare earth-platinum intermetallic alloys based on metal-organic framework structures not only overcomes the chemical potential difference between the single atom rare earth elements and Pt but also experimentally confirmed the spin state-performance dependence for the ORR process.
This work opens new avenues to understand spin modulation and its profound influence on electrocatalysis. The findings offer important references for the design and development of novel electrocatalysts using the spin modulation strategy, promising improved ORR activity and catalytic performance.
The discovery of the intrinsic spin shielding effect of platinum-rare earth alloys, especially Pt2Gd intermetallic alloy, has given a significant breakthrough in electrocatalysis. By elucidating the interplay between spin configurations and catalytic activity, researchers are advancing our understanding of spin modulation strategies for optimizing electrocatalytic processes.
This work paves the way for the design of new catalysts and holds great potential for the development of highly efficient PEMFCs, contributing to the search for sustainable energy solutions.
The work is published in the journal National Science Review.
More information:
Siyuan Zhu et al, Intrinsic Spin Shielding Effect of Platinum–Rare Earth Alloy Increases Oxygen Reduction Activity, National Science Review (2023). DOI: 10.1093/nsr/nwad162
Provided by Science China Press
Citation: New study reveals remarkable impact of intrinsic spin shielding in platinum-rare earth alloys on electrocatalysis (2023, July 24) retrieved on July 24, 2023 from https://phys.org/news/2023-07-reveals-remarkable-impact-intrinsic-shielding.html
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