While ice exhibits flexoelectricity – electrical polarization under non-uniform deformation – pure ice's low flexoelectric coefficient (around 10^-10 nC/m) limits its potential for energy harvesting. Significantly enhancing this coefficient is therefore crucial for harnessing ice energy.

A research team led by Professor Shen Shengping at Xi'an Jiaotong University (XJTU) has discovered an ingenious method to boost electricity generation from ice: adding salt. This approach, detailed in a recent Nature Materials publication, involves salt ions migrating along grain boundaries when the ice is bent, generating an electric current.

This not only advances ice energy research but also offers new insights into the electrical activity of icy ocean worlds like Europa.

Experiments revealed that as saltwater freezes, the "salting-out" effect forces salt ions to the ice crystal boundaries, forming a nanometer-scale, quasi-liquid brine layer. As a result, salt ice remains solid overall while developing a continuous 3D network for ion transport within.

When ice bends, it squeezes brine from the compressed area to the tensioned area along the grain boundaries, much like water being squeezed from a sponge. This movement, driven by the interfacial double layer, carries a net charge and generates an electric current that the team has called the "streaming flexoelectric effect".

To confirm this mechanism, the team created ice beams with varying salt concentrations and conducted flexoelectric tests using a standard three-point bending setup. Results showed a dramatic increase in the equivalent flexoelectric coefficient with higher salinity, reaching values roughly three orders of magnitude greater than pure ice.

Based on these findings, the team developed a theoretical model that captures the mechanical-electrical-chemical coupling and derived an analytical expression for the coefficient.