Artificial Photosynthesis

There is evidence to indicate that the earliest process of conventing sunlight into storable and usable energy (photosynthesis) began around 3.4 billion years ago on this planet. Over time, the bacteria that accomplished this changed the color range of light they absorbed from infrared into the visible spectrum and changed the waste output of their effort from sulphur to oxygen. They evolved from simple bacteria into algaes, then into plants, and then into more complex plants that live on land instead of in water. Humans are trying to reverse engineer this learning curve by applying the lessons of evolution to nano-components involved in photovoltaic technology.

Solar cell, heal thyself – [mit.edu]

Plants are good at doing what scientists and engineers have been struggling to do for decades: converting sunlight into stored energy, and doing so reliably day after day, year after year. Now some MIT scientists have succeeded in mimicking a key aspect of that process.

One of the problems with harvesting sunlight is that the sun’s rays can be highly destructive to many materials. Sunlight leads to a gradual degradation of many systems developed to harness it. But plants have adopted an interesting strategy to address this issue: They constantly break down their light-capturing molecules and reassemble them from scratch, so the basic structures that capture the sun’s energy are, in effect, always brand new.

That process has now been imitated by Michael Strano, the Charles and Hilda Roddey Associate Professor of Chemical Engineering, and his team of graduate students and researchers. They have created a novel set of self-assembling molecules that can turn sunlight into electricity; the molecules can be repeatedly broken down and then reassembled quickly, just by adding or removing an additional solution. Their paper on the work was published on Sept. 5 in Nature Chemistry.

Photosynthesis – Illuminating Alternatives for Solar Energy Research – [berkeley.edu]

A leaf may not look a whole lot like a solar panel, but the functional parallels between photovoltaic devices and the early, light-harvesting steps of photosynthesis are profound. Both processes begin with sunlight spilling into the atmosphere. That light, made up of a mixture of different wavelengths, shines onto a reactive surface—a leaf on a houseplant, say, or one of the PV panels encrusting the MLK Student Union.

Upon striking the reactive surface, a few units of solar energy (called photons), carried by light of just the right wavelength, are absorbed. This absorbed energy jolts loose an electron from the reactive surface, and the electron is then harnessed to do work. In a solar cell, it is diverted into a current of similarly liberated electrons, funneled through wires, and eventually used to power all manner of indispensable gadgets that blink and go beep. In photosynthesis, the loose electron instead interacts with a series of biological molecules, eventually driving the chemical synthesis of sugar. Plants and solar energy scientists therefore face a similar task: efficiently transforming light energy into a flow of electrons that can be harnessed to power downstream processes.

Scientists Mimic Chloroplasts – Meaning Solar Cells That Fix Themselves – [science20.com]

To imitate that process, Strano and his team, supported by grants from the MIT Energy Initiative and the Department of Energy, produced synthetic molecules called phospholipids that form discs; these discs provide structural support for other molecules that actually respond to light, in structures called reaction centers, which release electrons when struck by particles of light. The discs, carrying the reaction centers, are in a solution where they attach themselves spontaneously to carbon nanotubes — wire-like hollow tubes of carbon atoms that are a few billionths of a meter thick yet stronger than steel and capable of conducting electricity a thousand times better than copper. The nanotubes hold the phospholipid discs in a uniform alignment so that the reaction centers can all be exposed to sunlight at once, and they also act as wires to collect and channel the flow of electrons knocked loose by the reactive molecules.

The system Strano’s team produced is made up of seven different compounds, including the carbon nanotubes, the phospholipids, and the proteins that make up the reaction centers, which under the right conditions spontaneously assemble themselves into a light-harvesting structure that produces an electric current. Strano says he believes this sets a record for the complexity of a self-assembling system. When a surfactant — similar in principle to the chemicals that BP has sprayed into the Gulf of Mexico to break apart oil — is added to the mix, the seven components all come apart and form a soupy solution. Then, when the researchers removed the surfactant by pushing the solution through a membrane, the compounds spontaneously assembled once again into a perfectly formed, rejuvenated photocell.

Timeline of Photosynthesis on Earth – [scientificamerican.com]

Photosynthesis evolved early in Earth’s history. The rapidity of its emergence suggests it was no fluke and could arise on other worlds, too. As organisms released gases that changed the very lighting conditions on which they depended, they had to evolve new colors.

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