Membrane generates electricity from water

Ars Technica said:

It's possible to generate energy using nothing but the difference between fresh and salt water. When fresh and salt water are separated by a membrane that blocks the passage of certain ions, there is a force that drives the freshwater into the salt water to even out the salt concentration. That force can be harvested to produce energy, an approach termed "osmotic power."

But the generation of osmotic power is highly dependent on how quickly ions can cross the membrane—the thicker (and more robust) the membrane, the slower the ions will flow. Theoretically, the most efficient osmotic power generation would come from an atomically thin membrane layer. But can this theoretical system be achieved here in reality?

Recently, scientists answered that question using atomically thin membranes composed of molybdenum-disulfide (MoS2). In the paper that resulted, they describe a two-dimensional MoS2 membrane containing a single nanopore, which was used to separate reservoirs containing two solutions with different concentrations of salt in order to generate osmotic power.

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How much power can we actually generate from this type of system? The scientists did calculations modeling a single-atom-thick MoS2 membrane with 30 percent of its surface containing 10nm pores. The results suggest that with the right salt gradient, you could get a power density of 106 W/m2. For comparison, the amount of energy we get from the Sun maxes out at about 1,000 W/m2.

That high power density suggests that MoS2 membranes have some serious potential as a source of renewable energy. While it would be very difficult to scale up an atomically thin membrane, there's still the possibility of using it to harvest a small bit of energy for electronic devices.

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