Strain-Induced Magnetic Ordering Unlocks Spin-Conserved Catalysis in Lithium-Oxygen Batteries.

Layered 2D van der Waals materials, such as transition metal dichalcogenides, are promising for nanoscale spintronic and optoelectronic applications. Harnessing their full potential requires understanding both intrinsic transport and the dynamics of optically excited spin and charge carriers, particularly the transition between excited spin polarization and the conduction band's intrinsic spin texture. Here, we investigate the spin polarization of the conduction bands of bulk WSe_{2} using static and time-resolved spin-resolved photoemission spectroscopy, complemented by photocurrent calculations. Electron doping reveals the intrinsic spin polarization, while time-resolved measurements trace the evolution of excited spin carriers. We find that intervalley scattering is spin-conserving, with spin transport initially governed by photoexcited carriers and aligning with the intrinsic conduction band spin polarization after ∼150 fs.

One of the cruxes of developing high-performance lithium-oxygen batteries (LOBs) is the rational design and controllable synthesis of a promising cathode catalyst. High-entropy alloys (HEAs) have been considered as prospective catalytic materials for LOBs due to their adjustable composition and excellent catalytic performance. Herein, ∼50 nm PtFeCoNiCu HEA NPs with uniformly distributed elements embedded on few-layer reduced graphene oxide (PtFeCoNiCu@rGO) were successfully synthesized via a high-temperature annealing route. The LOBs with the PtFeCoNiCu@rGO cathode exhibited a high initial discharge capacity of 13 949 mA h g-1, a low overpotential of 0.77 V, and remarkable cycling stability over 148 cycles with a limited capacity of 500 mA h g-1 at 100 mA g-1. The dominant discharge product was Li2O2, and no by-products were detected. These excellent electrochemical performances arose from the combined effects of reduced graphene oxide (rGO) and HEA NPs. Reduced graphene oxide, with a large specific surface area and omnipresent pores with diverse size distribution, provided sufficient storage space for Li2O2 and facilitated transport channels for Li+ and O2, while the highly conductive HEA NPs, with optimized catalytic efficiency, further accelerated the kinetics of ORR/OER. This work presents a feasible alternative HEA-based catalyst design strategy for applicable LOBs.

The development of a high-energy-density lithium–oxygen (Li–O2) battery is mainly determined by highly efficient electrocatalysts with excellent activity and stability, facilitating reversible oxygen redox reactions. Engineering the electron spin state provides a novel strategy to enhance the electrocatalytic activity of electrode materials. In this work, sulfur vacancy-enriched spinel NiCo2S4 (Vs-NiCo2S4) with high spin polarization is designed as an effective electrocatalyst for high-performance Li–O2 batteries. Subtle lattice distortion is induced by sulfur vacancy in spinel Vs-NiCo2S4, which strongly contributes to the formation of high spin states of Co3+ (HS, t2g4eg2) from the low spin states of Co3+ (LS, t2g6eg0) at active octahedral sites. The electron transitions of Co3+ from low to high spin enable the increase of the spin polarization and produce abundant unpaired electrons in the 3d orbital of Co3+, enhancing the adsorption of oxygen intermediates and boosting the electron transfer process of oxygen redox reactions. Density functional theory calculations indicate that the spin magnetic moment of Co3+ in Vs-NiCo2S4 is raised in comparison to that in NiCo2S4, which improves the catalytic activity of the material via lowering the energy barrier for electron transfer. Experimentally, Vs-NiCo2S4-based Li–O2 batteries exhibit a large specific capacity of 8707.0 mAh g–1 and long cycling life of 487 h. Furthermore, in situ differential electrochemical mass spectrometry results show that the ratio of electron to oxygen during oxygen redox reactions is close to 2, demonstrating the favorable formation and decomposition of Li2O2 on Vs-NiCo2S4 in a Li–O2 battery. This work presents a powerful strategy to rationally design efficient electrocatalysts via spin engineering to boost oxygen redox reaction kinetics in Li–O2 batteries.

Spin-Enhanced C–C Coupling in CO ₂ Electroreduction with Oxide-Derived Copper

The oxygen evolution reaction (OER) is the bottleneck that limits the energy efficiency of water-splitting. The process involves four electrons’ transfer and the generation of triplet state O2 from singlet state species (OH- or H2O). Recently, explicit spin selection was described as a possible way to promote OER in alkaline conditions, but the specific spin-polarized kinetics remains unclear. Here, we report that by using ferromagnetic ordered catalysts as the spin polarizer for spin selection under a constant magnetic field, the OER can be enhanced. However, it does not applicable to non-ferromagnetic catalysts. We found that the spin polarization occurs at the first electron transfer step in OER, where coherent spin exchange happens between the ferromagnetic catalyst and the adsorbed oxygen species with fast kinetics, under the principle of spin angular momentum conservation. In the next three electron transfer steps, as the adsorbed O species adopt fixed spin direction, the OER electrons need to follow the Hund rule and Pauling exclusion principle, thus to carry out spin polarization spontaneously and finally lead to the generation of triplet state O2. Here, we showcase spin-polarized kinetics of oxygen evolution reaction, which gives references in the understanding and design of spin-dependent catalysts.

The process of copper oxidation has been thoroughly studied for many years, yielding a significant understanding of its kinetics and chemistry. However, the possible roles of surface spin polarization in important issues such as oxidation rates have not been widely explored despite the triplet nature of molecular oxygen. Here, we investigate the spin-dependent oxidation of copper films by triplet O2, exploiting engineered ferromagnetic substrates to impose controlled surface spin polarization. Three sample architectures that enable comparison between spin-polarized and nonpolarized surfaces were implemented to enable direct comparison between regions of varying spin polarization on the same sample. Combining various surface-sensitive techniques, including atomic force microscopy, Kelvin probe force microscopy, ellipsometry, and magneto-optical Kerr effect, we followed oxide growth kinetics and electronic property changes over time scales from minutes to weeks. Our results demonstrate that spin-polarized surfaces exhibit a significant acceleration in copper oxide formation compared with less polarized regions. The difference appears to be driven by a preference toward the formation of cupric oxide (CuO), the second oxidation state of copper, over cuprous oxide (Cu2O), the first oxidation state. We suggest that the results are related to the different magnetic properties of each oxide. Our data also reveal that the CuO oxidation phase propagates from the Cu film edges toward the center of the sample. These findings provide direct evidence of the surface-spin influence on metal oxidation kinetics and support the notion that spin polarization can induce a lower activation energy barrier for electron transfer between metal to triplet O2. Beyond advancing the fundamental understanding of corrosion chemistry, this spin-dependent control of surface reactivity opens potential avenues for tailored catalyst design, spintronic device stability, and corrosion mitigation strategies.

Transport properties of normal and ferromagnetic atomic-size constrictions with superconducting electrodes

Lithium-oxygen (Li-O2) batteries have attracted significant attention due to their ultrahigh theoretical energy density, but are obstructed by the sluggish reaction kinetics at the cathode and high overpotential. Our previous researches have proved that energy fields such as light, force, and heat are effective strategies to improve the reaction kinetics of Li-O2 batteries. Herein, we proposed a novel magnetic field-assisted Li-O2 batteries via a spin polarization strategy. By doping magnetic Mn2+ ions with spin polarization characteristics into CsPbBr3 (Mn-CsPbBr3) perovskite, a magnetic field-responsive cathode was designed and prepared. The incorporation of Mn2+ ions drives the charge redistribution and spin polarization of CsPbBr3, which remarkably improve the carrier separation efficiency and the oxygen species adsorption energy. TheIncreased spin-polarization of the magnetic elements by Zeeman effect in an external magnetic field results in the enhanced oxygen reduction and evolution reaction. In the magnetic field, a low overpotential of 0.40V was obtained for Li-O2 batteries with Mn-CsPbBr3 cathodes, demonstrating an ultralow overpotential of 0.12V and an ultrahigh energy efficiency of 96.3% with the further illumination. The introduction of magnetic fields into the Li-O2 battery system provides a new avenue for improving the reaction kinetics of rechargeable Li-O2 battery.

Green synthesis of highly reduced graphene oxide by compressed hydrogen gas towards energy storage devices

Magnetic properties and spin polarization of Co 2Mn(Si xSn 1− x) alloys containing two L2 1 phases

Three-dimensional reticular material NiO/Ni-graphene foam as cathode catalyst for high capacity lithium-oxygen battery

The oxygen evolution reaction (OER) is the bottleneck that limits the energy efficiency of water-splitting. The process involves four electrons’ transfer and the generation of triplet state O2 from singlet state species (OH- or H2O). Recently, explicit spin selection was described as a possible way to promote OER in alkaline conditions, but the specific spin-polarized kinetics remains unclear. Here, we report that by using ferromagnetic ordered catalysts as the spin polarizer for spin selection under a constant magnetic field, the OER can be enhanced. However, it does not applicable to non-ferromagnetic catalysts. We found that the spin polarization occurs at the first electron transfer step in OER, where coherent spin exchange happens between the ferromagnetic catalyst and the adsorbed oxygen species with fast kinetics, under the principle of spin angular momentum conservation. In the next three electron transfer steps, as the adsorbed O species adopt fixed spin direction, the OER electrons need to follow the Hund rule and Pauling exclusion principle, thus to carry out spin polarization spontaneously and finally lead to the generation of triplet state O2. Here, we showcase spin-polarized kinetics of oxygen evolution reaction, which gives references in the understanding and design of spin-dependent catalysts.

The ‘power-to-hydrogen’ strategy aims at splitting water into O2 and H2 via the oxygen and hydrogen evolution reactions. The complex four-step oxygen evolution reaction (OER) limits the overall efficiency of hydrogen production. An important reason of the low efficiency is that the production of ground-state (triplet) O2 is a spin-forbidden reaction: in fact, the reactants, OH- or H2O, are diamagnetic, but the final product, O2, is a paramagnetic molecule. Recently, this was well-recognized theoretically1 and the use of spin selective catalysts was described as a possible way to promote the OER.2 . However, it remains complex to understand and exploit intrinsic and extrinsic magnetic features to enhance catalytic performance. Here, we investigate the role of magnetic moments in individual active sites in the catalyst surface layer and the role of spin order in ferromagnetic vs. paramagnetic catalysts, focussing on perovskite oxides.First, we investigated the role of Ni magnetic moment in the the (001), (110) and (111) facet of LaNiO3 electrocatalysts, which we studied using electrochemical measurements, X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and density functional theory (DFT+U) calculations.3 The results show a facet-dependent activity, where the (111) overpotential is ~60 mV lower as compared to the other facets. Closer investigation of the (001) and (111) facets reveals a surface transformation to a oxyhydroxide-like NiOO with edge-sharing octahedra,4 and we observed that the transformed surface is thicker for (111) than for (001).3 The detailed DFT+U analysis reveals important distinctions that give rise to the increased activity: the transformed LaNiO3 (111) surface exhibits a better match to the underlying perovskite layer. Moreover, protonation induces reduced Ni3+ with a finite magnetic moment. A moderate Jahn-Teller distortion enables a favorable binding of reaction intermediates. In contrast, the structural mismatch to the underlying LaNiO3(001)-substrate leads to a strong distortion of the transformed layer for this orientation and a weak binding of *O and ultimately to a different potential determining step (PDS), *OH→*O, compared to *O→*OOH for the transformed LaNiO3(111) surface.Second, we experimentally demonstrate the effect of intrinsic magnetic order on the OER on catalytic performance. Thin films of La0.67Sr0.33MnO3 grown by pulsed laser deposition with appropriate magnetic and electronic properties were chosen as well-defined model systems. Using the ferromagnetic to paramagnetic transition at the Curie temperature in these ferromagnetic perovskite oxides, the magnetic order of the catalysts were switched in situ during the OER by changing the temperature. For ferromagnetic films, the decrease in current density with decreasing temperature, induced by the reduction of thermal energy, was suppressed for temperatures below the Curie temperature, indicating that the presence of ferromagnetic ordering below Curie temperature enhances OER activity. This claim is further supported by an enhancement of OER activity for the same ferromagnetic film upon alignment of magnetic domains with an external magnetic field. All in all, our results reveal that the spin state, intrinsic spin order, and extrinsic magnetic fields are decisive for the OER activity. Biz, C., Fianchini, M. & Gracia, J. Strongly Correlated Electrons in Catalysis: Focus on Quantum Exchange. ACS Catal 11, 14249–14261 (2021).Sun, Y. et al. Spin‐Related Electron Transfer and Orbital Interactions in Oxygen Electrocatalysis. Advanced Materials 32, 2003297 (2020).Füngerlings, A. et al. Crystal-facet-dependent surface transformation dictates the oxygen evolution reaction activity in lanthanum nickelate. in preparation (2023).Baeumer, C. et al. Tuning electrochemically driven surface transformation in atomically flat LaNiO3 thin films for enhanced water electrolysis. Nat Mater 20, 674–682 (2021).

Electron spin polarization enhances the kinetics of the oxygen evolution reaction (OER), a rate-limiting step that restricts the energy efficiency of water splitting. Here, a dual-channel spin-regulated strategy combining chiral-induced spin selectivity (CISS) and external magnetic field (MH)-induced spin polarization synergistically reduces the overpotential and enhances durability in spinel-based ferromagnetic materials. Chiral molecule-modified CoFe2O4 under MH (CFO-L-M) achieves a 90 mV reduction in overpotential compared to unmodified CFO, which is primarily ascribed to the synergistic "1 + 1 > 2" effect arising from the dual-spin channel mechanism. Theoretical calculations show that surface spin states critically influence adsorbate binding, with spin selectivity and polarization being activated during the first electron transfer step, ultimately producing triplet O2. This study elucidates spin-related OER kinetics, offering a foundation for designing advanced spin-dependent electrocatalysts.

CuFeSb is isostructural to the ferro-pnictide and chalcogenide superconductors and it is one of the few materials in the family that are known to stabilize in a ferromagnetic ground state. Majority of the members of this family are either superconductors or antiferromagnets. Therefore, CuFeSb may be used as an ideal source of spin polarized current in spin-transport devices involving pnictide and the chalcogenide superconductors. However, for that the Fermi surface of CuFeSb needs to be sufficiently spin polarized. In this paper we report direct measurement of transport spin polarization in CuFeSb by spin-resolved Andreev reflection spectroscopy. From a number of measurements using multiple superconducting tips we found that the intrinsic transport spin polarization in CuFeSb is high (∼47%). In order to understand the unique ground state of CuFeSb and the origin of large spin polarization at the Fermi level, we have evaluated the spin-polarized band structure of CuFeSb through first principles calculations. Apart from supporting the observed 47% transport spin polarization, such calculations also indicate that the Sb-Fe-Sb angles and the height of Sb from the Fe plane are strikingly different for CuFeSb than the equivalent parameters in other members of the same family thereby explaining the origin of the unique ground state of CuFeSb.