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.