Researchers from China discovered that dragging a droplet of salt water on graphene generates a small voltage difference. The researchers found a linear relationship between the velocity and the generated electricity - the faster you drag the droplet, the higher the voltage.
The researchers explain that the charge distribution on the sides of the droplet is redistributed symmetrically on both sides when the droplet is not moving. But when you move it, the distribution becomes unbalanced and electrons are desorbed from the graphene at one end of the droplet and are adsorbed into the graphene at another end. This results in a large potential on one side of the droplet and generates a measurable voltage across its length.
The researchers then used a copper chloride droplet, and found that by tilting the graphene and allowing the droplet to flow, you can generate aboue 30 mV. This means that graphene can be used as a way to harvest energy from flowing water, and maybe even be scaled up for energy generation.