Spin-dependent electrocatalysis with Gadolinium and external magnetic field.In some experimental setups, an external constant magnetic field is applied to the electrolyzer.
The gadolinium ions in the catalyst structure align their spins under the influence of the external field. This creates a "spin filter" on the electrode surface.
Since the oxygen molecule in its stable state is a triplet (its electrons have parallel spins), a catalyst with ordered gadolinium spins "forces" the outgoing electrons to also have the desired orientation. This prevents the formation of byproducts (such as singlet oxygen or hydrogen peroxide) and accelerates the oxygen gas evolution reaction by tens of percent.
Spin activation in alkaline electrolysis to increase oxygen yield:Nanostructured catalysts doped with gadolinium are used for low-temperature water splitting. As in high-temperature systems, the gadolinium's gigantic magnetic moment is critical here. When an external magnetic field of 0.1–0.5 T is applied to the electrolyzer, gadolinium ions on the electrode surface polarize the electron spins. This facilitates the transition of water molecules to the triplet state of molecular oxygen, reducing the reaction overpotential. Bimetallic nanoparticles with gadolinium exhibit ultra-low reaction onset potentials, comparable to platinum catalysts.
The problem of triplet oxygen in alkaline electrolysis:In an alkaline medium, water molecules must be converted into molecular oxygen during electrolysis. The main difficulty is that the initial hydroxyl ions are in the singlet state (electron spins are paired/opposite). Molecular oxygen in the ground state is a triplet (two unpaired electrons with parallel spins). The transition from singlet to triplet is quantum forbidden or hindered, which creates a high "overpotential" (excessive energy consumption) at the anode.
Gadolinium has the highest magnetic moment among stable elements (seven unpaired electrons). Spin alignment occurs in the gadolinium catalyst structure, as gadolinium ions, under the influence of an external magnetic field (or due to internal magnetic ordering in the nanoparticles), create a powerful local field.
When an OH ion is adsorbed on the active site of the catalyst near gadolinium, the strong magnetic interaction of Gd3+ forces the oxygen electrons to orient themselves in a specific manner. This "prepares" the electrons for the transition to the triplet state even before the O-O bond is formed. To achieve this effect, an external magnetic field of approximately 0.1–0.5 T is applied to alkaline electrolyzers. This field aligns the magnetic moments of the Gd3+ ions in one direction, transforming the electrode surface into a "spin bridge." Because the electron spins are already polarized, the recombination of *O and *OH radicals into an O2 molecule occurs almost instantaneously. The activation energy decreases, and the reaction proceeds significantly faster.
The use of gadolinium in alkaline electrolysis cells reduces overvoltage by 50–100 mV, thereby increasing current density by 20–40% while maintaining the same voltage. Furthermore, adding a small amount of gadolinium to standard nickel or iron allows them to compete in efficiency with expensive catalysts based on precious metals such as iridium or ruthenium.
Gadolinium in Hydrogen Evolution Catalysts:Gadolinium is most often incorporated into a matrix of transition metals (Ni, Co, Fe) or their oxides.
Gd3+ ions have a large ionic radius and a specific electron configuration. When incorporated into the nickel lattice, they cause localized deformation of the structure and redistribution of electron density on adjacent nickel atoms. This optimizes the metal-hydrogen bond energy. While pure nickel binds hydrogen too strongly, hindering its desorption as H2 gas, the presence of gadolinium weakens this bond.
The hydrogen evolution reaction at the cathode consists of two stages:
- Proton adsorption
- Combination of two hydrogen atoms into a molecule
To form a stable H2 molecule, the electrons of the two hydrogen atoms must have opposite spins (singlet state). The strong local magnetic field of the Gd3+ ion acts as a "quantum dispatcher." It promotes rapid spin reorientation of adsorbed hydrogen atoms. This accelerates their recombination and detachment from the electrode surface as gas bubbles.
Gadolinium combined with cerium oxide as a hydrogen evolution catalyst:Ceria provides a high concentration of oxygen vacancies, while gadolinium creates active magnetic centers.
Studies show that at the interface between Gd and CeO2, the activation barrier for bond cleavage in water molecules is reduced by almost half. Gadolinium "pulls" hydroxyl groups toward itself, releasing hydrogen for further reduction.
Although the spin effect is more pronounced during oxygen evolution, an external field can be used in electrolysis to accelerate hydrogen evolution at the cathode. The magnetic field interacts with ions in the electrolyte, creating localized microcurrents (Lorentz forces). This helps to more quickly remove hydrogen bubbles from the catalyst surface, preventing clogging of the active centers.
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Topic: Energy from electron spin (Read 54033 times)
