Spin Polarized Electron Dynamics Enhance Water Splitting Efficiency by Yttrium Iron Garnet Photoanodes: A New Platform for Spin Selective Photocatalysis

Abstract

This work presents a detailed spectroscopic and kinetic comparison of yttrium iron garnet (Y3Fe5O12, YIG) and hematite (α-Fe2O3) for photocatalytic water splitting. Despite similar electronic structures, YIG significantly outperforms hematite as a water oxidation catalyst, displaying nearly an order of magnitude increase in photocurrent density and a factor of two increase in Faradaic efficiency. Probing the charge and spin dynamics by ultrafast, surface-sensitive XUV spectroscopy reveals that the enhanced performance arises from 1) reduced polaron formation in YIG compared to hematite and 2) an intrinsic spin polarization of catalytic photocurrents in YIG. Linear XUV measurements show a significant reduction in the formation of surface electron polarons in YIG compared to hematite due to site-dependent electron-phonon coupling in YIG leading to spin-polarized currents upon photoexcitation. Direct observation of surface spin accumulation with chemical state resolution at the Fe M2,3 and O L1 edges using XUV magnetic circular dichroism provides a detailed picture of the spin-polarized electron dynamics. Together, these results point to YIG as a new platform for highly efficient, spin-selective photocatalysis.