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Saturday, 22 June 2019

Discovered rocks that generate electricity in the sunlight

Photovoltaic conversion may be widely spread on the surface of the Earth, through rocky coatings of iron and manganese. [Image: Anhuai Lu and Yan Li.]

Photocurrent on rocks

Researchers have found the first evidence of photocurrent - light-induced electrical currents - occurring naturally in inorganic minerals.

We know a lot about the organic photoelectric systems present in nature, since they form the basis of photosynthesis. But so far, virtually nothing has been known about non-biological systems that turn light into electricity.

Anhuai Lu of Peking University in China suspected rock crusts could be a photoelectric material because many of them contain iron and manganese that have been used in man-made photocurrent systems.

Photoelectric materials are materials that generate electricity when exposed to light, such as those used to make solar cells.

In order to confirm his hypothesis, the researcher placed sensors on samples of rocks collected from the desert that had a rich crust in these minerals, and then placed them in the sunlight. He did the same with rocks of the same type that did not have a crust, such as control.

The phenomenon must play a role in biogeochemical processes, which should be studied from now on. [Image: Anhuai Lu et al. - 10.1073 / pp.1902473116]

The coatings responded to light by releasing electrons, resulting in an electric current flow. And the thing works as if there was a switch - when the sunlight shines, the material releases electrons, when the sunlight is blocked, it stops releasing electrons. The naked rocks had no electrical activity.


A careful analysis of the rock coatings revealed that these coverings mainly consist of iron (Fe) and manganese oxides (Mn), forming crystals of minerals such as birnessite, hematite and goethite.

Researchers note that some areas of the Earth have vast expanses of rocks covered or inlaid with these minerals, all presumably generating electricity.

They do not yet know what impact this may be having, but they theorize that the phenomenon probably plays a role in some biogeochemical processes, a kind of "minerosynthesis," similar in some respects to the biological photoelectric systems on which photosynthesis is based.


Photoelectric conversion on Earth's surface via widespread Fe- and Mn-mineral coatings

Anhuai Lu, Yan Li, Hongrui Ding, Xiaoming Xu, Yanzhang Li, Guiping Ren, Jing Liang, Yuwei Liu, Hao Hong, Ning Chen, Shengqi Chu, Feifei Liu, Yan Li, Haoran Wang, Cong Ding, Changqiu Wang, Yong Lai, Juan Liu, Jeffrey Dick, Kaihui Liu, Michael F. Hochella Jr.

Proceedings of the National Academy of Sciences 

DOI: 10.1073 / pnas.1902473116

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