Magnetic-field-controlled counterion migration within polyionic liquid micropores enables nano-energy harvest

Efficient separation of positive and negative charges is essential for developing high-performance nanogenerators. In this article, we describe a method that was not previously demonstrated to separate charges which enables us to fabricate a magnetic energy harvesting device. The magnetic field induces the migration of the mobile magnetic counterions (Dy(NO₃)₄^-) which establishes anion gradients within a layer of polyionic liquid micropores (PLM). The PLM is covalently cross-linked on which the positive charges are fixed on the matrix, that is, immobile. In a device with a structure of Au/dielectric//mag-PLM//dielectric/Au, the charge gradient is subsequently transformed into the output voltage through electrostatic induction. Removing the magnetic field leads to the backflow of magnetic anions which produces a voltage with a similar magnitude but reversed polarity. The parameters in fabricating the magnetic PLM such as photoinitiator concentration, UV irradiation time, water treatment time, and temperature are found to dramatically influence the size of micropores and the effective concentration of magnetic anions. Under optimized conditions, an output voltage with an amplitude of approximately 4 V is finally achieved. We expect this new method could find practical applications in further improving the output performance.