Developing new concepts to design noble-metal-free catalysts is necessary to achieve the hydrogen economy and reduce global CO2 emissions. Here, we provide novel insights into the design of catalysts with internal magnetic fields by investigating the relationship between the hydrogen evolution reaction (HER) and the Slater-Pauling rule. This rule states that adding an element to a metal reduces the alloy's saturation magnetization by an amount proportional to the number of valence electrons outside the d shell of the added element. We observed that rapid hydrogen evolution occurred when the magnetic moment of the catalyst was high, as predicted by the Slater-Pauling rule. Numerical simulation of the dipole interaction revealed a critical distance, r C, at which the proton trajectory changes from a Brownian random walk to a close-approach orbit towards the ferromagnetic catalyst. The calculated r C was proportional to the magnetic moment, consistent with the experimental data. Interestingly, r C was proportional to the number of protons contributing to the HER and accurately reflected the migration length for the proton dissociation and hydration and the O-H bond length in water. The magnetic dipole interaction between the nuclear spin of the proton and the electronic spin of the magnetic catalyst is verified for the first time. The findings of this study will open a new direction in catalyst design aided by an internal magnetic field.
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