Scientists at the Max Planck Institute of Colloids and Interfaces realize an artificial light driven ion pump

The first artificial light-driven ion pump that can pump ions uphill against a concentration gradient of more than 5000 was reported in Nat. Commun. 10, 74 (2019).

 

January 24, 2019

One of the first approaches of nature to convert solar energy into chemical energy is by using light to pump ions or protons. Scientists at the Max Planck Institute of Colloids and Interfaces in Potsdam have developed an artificial light-driven ions pump for photoelectric energy conversion now. According to their findings, the carbon nitride nanotube membrane based artificial ion pump can drive ions thermodynamically uphill against concentration gradients by ordinary light illumination. This efficiency has not been possible before and is comparable to biological ion pumps.

Ion pump and solar energy conversion process by bacteriorhodopsin.

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In nature solar energy conversion in some archaea, such as Halobacterium halobium, has much in common with its analogue of photosynthesis in green plants but it is simpler and better understood. These microorganisms can pump protons transport across the membrane by absorbing sunlight and converting it into electronic excitated states. This is generating an osmotic and charge imbalance that in turn powers the synthesis of adenosine triphosphate (ATP) in a molecular machine. From a technological angle, the process of light triggered electrochemical gradients build-up by ion pumps is an energy conversion process.

Researchers from the Max Planck Institute of Colloids and Interfaces in Potsdam and the Technical Institute of Physics and Chemistry of the Chinese Academy of Sciences have now developed an artificial ion pump system based on a commercial membrane to realize the ion pump and energy conversion process in vitro. The cylindrical nanochannels of the membrane were therefore coated with carbon nitride to form nanotubes.

The researchers confirmed that this membrane converts light into an osmotic potential worth a sustained open circuit voltage of 550 mV and a current density of 2.4 μA/cm2. The light conversion process rather efficiently generates electroosmotic energy without any cables or complicated devices as for instance needed in solar cells. The set-up can be further scaled up through series and parallel circuits of multiple membranes up to very high potentials.

"The separation of electrons and holes in membrane under illumination results in a transmembrane potential, which is the base of the pumping and energy conversion phenomenon.” explained by Dr. Kai Xiao, main author of the study and being as an Alexander von Humboldt Fellow at the Max Planck Institute of Colloids and Interfaces. "In our future research we expect performance increase by orders of magnitudes just by lowering the length of the nanotubes as well as the diameters to the sizes of protein pumps. In comparison with the previously reported methods to harvest light energy, the described approach is rather cheap, very stable, universal and highly efficient."

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