Artificial photosynthesis produces 'green methane'

A new device shows promising results in its ability to convert CO2 and water into useful fuels.

Photo by Maros Misove on Unsplash
  • Artificial photosynthesis devices have long been touted as a way to remove carbon dioxide from the atmosphere and turn it into useful products.
  • New research describes a highly efficient and cheap device that could be used to turn waste carbon dioxide into methane.
  • Natural gas, which mainly consists of methane, is a cleaner fuel than coal and has been characterized as a "bridge fuel" prior to transitioning to renewable energy sources, but not everyone thinks it's a good idea to burn yet more hydrocarbons.


A great many human inventions are inspired by nature. Velcro, for instance, was inspired by the hooked barbs of thistle, sonar was inspired by bats and dolphins, and flight was, of course, inspired by birds. To solve climate change, arguably the world's most pressing challenge, we've once again turned to nature for solutions.

That's why researchers have been working on building devices modeled on plant life's ability to photosynthesize CO2 and water and, using sunlight as an energy source, transform these molecules into carbohydrates and oxygen.

The field of artificial photosynthesis has long looked into how best to implement and adapt this process for our own needs. Now, recent research has uncovered a cheap and efficient means of photosynthesizing useful fuel out of waste CO2 and water.

Scalable and efficient

Artificial photosynthesis

An electron microscope image shows the semiconductor nanowires. These deliver electrons to metal nanoparticles, which turn carbon dioxide and water into methane.

Baowen Zhou

The new method, described in Proceedings of the National Academy of Sciences, uses solar power to produce methane, which can be used as natural gas.

In the context of climate change, many environmentalists are probably groaning over the idea that the production and burning of yet more greenhouse gases should be portrayed as a good thing, but it's important to remember the practical benefits of devices such as this. Attached to the smokestacks of power plants, this artificial photosynthesis device can capture CO2 that would otherwise pollute the atmosphere and transform it into a far more efficient fuel that remains carbon neutral — so-called "green" methane.

Since our current infrastructure already supports the use of hydrocarbons for fuel, implementing tools such as these is an important first step to transitioning towards a more advanced but as-of-yet incomplete renewable energy infrastructure.

"Thirty percent of the energy in the U.S. comes from natural gas," said co-author Zetian Mi in a statement. "If we can generate green methane, it's a big deal."

Most importantly, the device makes use of low-cost and easily manufactured components, meaning that it will be scalable. The fatal flaw of many magic bullet climate change solutions is that they are expensive or difficult to make and implement, preventing them from being used at the scale necessary to combat climate change.

The device itself can be characterized as a solar panel studded with nanoparticles of iron and copper. The copper and iron nanoparticles hang onto molecules of CO2 and H2O by their carbon and hydrogen atoms. Using the sun's energy or an electrical current, the bonds between atoms in the CO2 and H2O are broken down, enabling the water's hydrogen atoms to connect to the carbon dioxide's carbon atom. The end result is one carbon atom bonded with four hydrogen atoms — methane. What's more, the new device does this work far more efficiently than other artificial photosynthesis systems.

"Previous artificial photosynthesis devices often operate at a small fraction of the maximum current density of a silicon device, whereas here we operate at 80 or 90 percent of the theoretical maximum using industry-ready materials and earth abundant catalysts," said Baowen Zhou, a postdoctoral researcher on this project.

Methane is merely one of the more useful products this device can produce; it can also be configured to produce syngas — a fuel consisting of hydrogen, carbon monoxide, and some carbon dioxide — or formic acid, which is used as a preservative in livestock feed.

A bridge too far?

The use of natural gas is on the rise in the U.S., but not everybody sees this as a positive. It's a cleaner fuel than coal, for instance, or diesel. It's been characterized as a bridge fuel that economies can lean on while waiting for the renewable energy sector to mature. Then again, its advantages make it awfully attractive, so much so that critics claim we may pay too much attention to it when we ought to be pivoting to renewable energy in a more focused fashion.

Nearly everyone (except for certain politicians and industry leaders) are on the same page regarding the ultimate fate of the world's energy sources — renewable energy like solar and wind power are going to be the main way we generate power in the future. In the meantime, however, the next-best thing is to implement CO2-scrubbing technology like the artificial photosynthesis device described in this article. Burning natural gas that we've sucked out of the Earth will certainly trash the atmosphere, but converting existing emissions into carbon-neutral fuels is far more practical, regardless of whether natural gas should be considered a bridge fuel or a barrier.

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Photos: Courtesy of Let Grow
Sponsored by Charles Koch Foundation
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New research establishes an unexpected connection.

Reactive oxygen species (ROS) accumulate in the gut of sleep-deprived fruit flies, one (left), seven (center) and ten (right) days without sleep.

Image source: Vaccaro et al, 2020/Harvard Medical School
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  • Surprisingly, the direct cause seems to be a buildup of Reactive Oxygen Species in the gut produced by sleeplessness.
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We don't have to tell you what it feels like when you don't get enough sleep. A night or two of that can be miserable; long-term sleeplessness is out-and-out debilitating. Though we know from personal experience that we need sleep — our cognitive, metabolic, cardiovascular, and immune functioning depend on it — a lack of it does more than just make you feel like you want to die. It can actually kill you, according to study of rats published in 1989. But why?

A new study answers that question, and in an unexpected way. It appears that the sleeplessness/death connection has nothing to do with the brain or nervous system as many have assumed — it happens in your gut. Equally amazing, the study's authors were able to reverse the ill effects with antioxidants.

The study, from researchers at Harvard Medical School (HMS), is published in the journal Cell.

An unexpected culprit

The new research examines the mechanisms at play in sleep-deprived fruit flies and in mice — long-term sleep-deprivation experiments with humans are considered ethically iffy.

What the scientists found is that death from sleep deprivation is always preceded by a buildup of Reactive Oxygen Species (ROS) in the gut. These are not, as their name implies, living organisms. ROS are reactive molecules that are part of the immune system's response to invading microbes, and recent research suggests they're paradoxically key players in normal cell signal transduction and cell cycling as well. However, having an excess of ROS leads to oxidative stress, which is linked to "macromolecular damage and is implicated in various disease states such as atherosclerosis, diabetes, cancer, neurodegeneration, and aging." To prevent this, cellular defenses typically maintain a balance between ROS production and removal.

"We took an unbiased approach and searched throughout the body for indicators of damage from sleep deprivation," says senior study author Dragana Rogulja, admitting, "We were surprised to find it was the gut that plays a key role in causing death." The accumulation occurred in both sleep-deprived fruit flies and mice.

"Even more surprising," Rogulja recalls, "we found that premature death could be prevented. Each morning, we would all gather around to look at the flies, with disbelief to be honest. What we saw is that every time we could neutralize ROS in the gut, we could rescue the flies." Fruit flies given any of 11 antioxidant compounds — including melatonin, lipoic acid and NAD — that neutralize ROS buildups remained active and lived a normal length of time in spite of sleep deprivation. (The researchers note that these antioxidants did not extend the lifespans of non-sleep deprived control subjects.)

fly with thought bubble that says "What? I'm awake!"

Image source: Tomasz Klejdysz/Shutterstock/Big Think

The experiments

The study's tests were managed by co-first authors Alexandra Vaccaro and Yosef Kaplan Dor, both research fellows at HMS.

You may wonder how you compel a fruit fly to sleep, or for that matter, how you keep one awake. The researchers ascertained that fruit flies doze off in response to being shaken, and thus were the control subjects induced to snooze in their individual, warmed tubes. Each subject occupied its own 29 °C (84F) tube.

For their sleepless cohort, fruit flies were genetically manipulated to express a heat-sensitive protein in specific neurons. These neurons are known to suppress sleep, and did so — the fruit flies' activity levels, or lack thereof, were tracked using infrared beams.

Starting at Day 10 of sleep deprivation, fruit flies began dying, with all of them dead by Day 20. Control flies lived up to 40 days.

The scientists sought out markers that would indicate cell damage in their sleepless subjects. They saw no difference in brain tissue and elsewhere between the well-rested and sleep-deprived fruit flies, with the exception of one fruit fly.

However, in the guts of sleep-deprived fruit flies was a massive accumulation of ROS, which peaked around Day 10. Says Vaccaro, "We found that sleep-deprived flies were dying at the same pace, every time, and when we looked at markers of cell damage and death, the one tissue that really stood out was the gut." She adds, "I remember when we did the first experiment, you could immediately tell under the microscope that there was a striking difference. That almost never happens in lab research."

The experiments were repeated with mice who were gently kept awake for five days. Again, ROS built up over time in their small and large intestines but nowhere else.

As noted above, the administering of antioxidants alleviated the effect of the ROS buildup. In addition, flies that were modified to overproduce gut antioxidant enzymes were found to be immune to the damaging effects of sleep deprivation.

The research leaves some important questions unanswered. Says Kaplan Dor, "We still don't know why sleep loss causes ROS accumulation in the gut, and why this is lethal." He hypothesizes, "Sleep deprivation could directly affect the gut, but the trigger may also originate in the brain. Similarly, death could be due to damage in the gut or because high levels of ROS have systemic effects, or some combination of these."

The HMS researchers are now investigating the chemical pathways by which sleep-deprivation triggers the ROS buildup, and the means by which the ROS wreak cell havoc.

"We need to understand the biology of how sleep deprivation damages the body so that we can find ways to prevent this harm," says Rogulja.

Referring to the value of this study to humans, she notes,"So many of us are chronically sleep deprived. Even if we know staying up late every night is bad, we still do it. We believe we've identified a central issue that, when eliminated, allows for survival without sleep, at least in fruit flies."

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