Towards Watt-scale hydroelectric energy harvesting by Ti₃C₂T_X -based transpiration-driven electrokinetic power generators

Nano-hydroelectric technology utilizes hydraulic flow through electronically conducting nanomaterials to generate electricity in a simple, renewable, ubiquitous, and environmentally friendly manner. To date, several designs of nano-hydroelectric devices have been devised to maximize the electrokinetic interactions between water molecules and nanomaterials. However, the reported power generation of the state-of-the-art nano-hydroelectric generators is not sufficient for practical use, as tens of thousands of units were required to operate low-power electronics on a mW scale. Here, we utilize titanium carbide (Ti3C2Tx) MXene nanosheets, which have advantageous properties including metal-like conductivity and hydrophilicity, to facilitate the electrokinetic conversion of the transpiration-driven electrokinetic power generator (TEPG) with a remarkably improved energy generation efficiency compared to that of carbon-based TEPG. The Ti3C2Tx MXene-based TEPG delivered a high pseudo-streaming current of 120 μA by the fast capillary flow promoted by MXene sheets coated on cotton fabric. The strong cationic affinity of Ti3C2Tx enables the generator to achieve an output of 0.68 V and 2.73 mA when NaCl solution is applied. Moreover, incorporation of a conducting polymer (i.e., Ti3C2Tx/polyaniline composite) enhanced the ionic diffusivity while maintaining the electrical network of Ti3C2Tx. The optimized Ti3C2Tx/polyaniline composite TEPG generated a maximum voltage of 0.54 V, a current of 8.2 mA, and a specific power density of 30.9 mW cm-3, which was sufficient to successfully charge a commercial Li-ion battery as well as low-power electronics and devices with a volume of 6.72 cm3.