Streaming flexoelectricity in saline ice

Despite 10% of the Earth’s surface being covered by ice, ice power remains untapped. Although ice is known to generate electricity upon bending via flexoelectricity1, the generated electric polarization per curvature, that is, the flexoelectric coefficient, is too small (~1–10 nC m−1) to be utilized for electromechanical devices. Here we demonstrate that doping ice with NaCl can enhance its flexoelectric coefficient 1,000-fold, to ~1–10 μC m−1. We find that this enhancement is due to the bending-induced streaming current along ice grain boundaries. On the basis of this mechanism, we fabricated flexural devices with an effective piezoelectric coefficient of ~4,000 pC N−1, which is comparable to that of the best piezoelectric materials. The high flexoelectricity of saline ice brings the vision of harnessing ice power one step closer to reality, and may also be relevant to the electrical activity of ice-covered terrestrial regions and icy ocean worlds such as Europa or Enceladus. In addition, the model for coupling between strain gradients and streaming currents is not limited to ice and provides a general framework for extracting electromechanical activity from liquid-infused porous solids. By doping ice with NaCl, it is shown that a flexoelectric coefficient of up to 10 μC m−1 is generated, enabling effective piezoelectric coefficients that are comparable to those of ceramics. This arises from the streaming current of quasi-liquid flow through grain boundaries from one side of the sample to the other.