(Invited) Evidence for Magnetic Effects on Electron Transfer

Electron transfer events are commonly considered in light of the transfer of charge. But, electrons also have properties of spin. Here, various systems are evaluated for impact of spin on rates of electron transfer. Literature and experimental data are considered. Electron spins interact with magnetic fields. In our experimental studies, magnetic microparticles are introduced to the electrode surface. From the literature, correlations between measured parameters and magnetic properties of electrodes and electroactive species are presented. This includes rate constants for heterogeneous and homogeneous electron transfer. From laboratory studies with micromagnets held to the electrode with a Nafion coating, impacts on homogeneous and heterogeneous electron transfer are found. For transition metal complexes such as M(bpy)₃z+ present at near contact in Nafion, electron hopping rates are measured as self exchange rates, k₁₁. When compared to simple Nafion films, rates of electron electron hopping are enhanced in the presence of magnets; effects scale with the number of spin (unpaired electrons) involved in the reaction. Temperature studies chart variation in the energy of activation (reorganization energy) and the pre-exponential factor. For adsorbate reactions, magnetic effects are substantial for reactions such as CO oxidation and hydride formation on palladium. Rates are enhanced > 100 fold. Hydrogen evolution reaction (HER) rates for poorly electrocatalytic electrodes are enhanced substantially on introduction of micromagnets. Because transfer of electrons requires transfer of both charge and spin, electron transfer rates can be slowed when rates of spin transfer are slow. Facilitating rates of spin transfer as by introduction of micromagnets increases rates of electron transfer reactions.