Spin-selected electron transfer in liquid-solid contact electrification

Electron transfer has been proven the dominant charge carrier during contact electrification at the liquid-solid interface. However, the effect of electron spin in contact electrification remains to be investigated. This study examines the charge transfer between different liquids and ferrimagnetic solids in a magnetic field, focusing on the contribution of O₂ molecules to the liquid-solid contact electrification. The findings reveal that magnetic fields promote electron transfer at the O₂-containing liquid-solid interfaces. Moreover, magnetic field-induced electron transfer increases at higher O₂ concentrations in the liquids and decreases at elevated temperatures. The results indicate spin-selected electron transfer at liquid-solid interface. External magnetic fields can modulate the spin conversion of the radical pairs at the O₂-containing liquid and ferrimagnetic solid interfaces due to the Zeeman interaction, promoting electron transfer. A spin-selected electron transfer model for liquid-solid contact electrification is further proposed based on the radical pair mechanism, in which the HO₂ molecules and the free unpaired electrons from the ferrimagnetic solids are considered radical pairs. The spin conversion of the [HO₂• •e^-] pairs is affected by magnetic fields, rendering the electron transfer magnetic field-sensitive.