Photosynthesis is, arguably, the most important biological process there has ever been.
Aside from simply creating the climatic conditions that made multicellular life
possible, photosynthesizing organisms continue to graciously provide our planet with the oxygen
that basically everything needs to live. And, yet, scientists are looking for ways
to make photosynthesis even better. And if they crack it, we could use
photosynthesis to power stuff like cars!
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You might remember the equation for photosynthesis from your freshman biology class. The process is
relatively simple: basically, plants take in sunlight, water, and carbon dioxide and
turn that into oxygen and stored energy in the form of glucose.
And while it’s the foundation for virtually all life on earth, photosynthesis is surprisingly
inefficient. Plants are only able to store about one percent of all the
energy they receive from the sun. But researchers know they can do better
than that. So for decades they’ve been trying to create artificial forms of photosynthesis
in order to power our whole world. Now you might be thinking, “but isn’t
that just a solar panel?” Well, yes and also no.
Solar panels soak up the sun’s rays to generate electricity, which is an immediate energy
source resulting from the flow of charged particles, photosynthesis makes something
that stores energy. So, think the difference between electricity
and something like gasoline. Gasoline stores energy within
its chemical bonds, and then releases that energy when it gets ignited,
and takes up very little space to do so. And while generating solar electricity is
able to power our homes and cars, it can’t always substitute for combustible fuels,
which provide an unbeatable combination of power and compactness.
Roughly 40% of global transportation is incapable of being electrified.
I mean, you’d need a pretty big battery to get a Boeing 747 off the ground.
So while solar panels generate electricity, the goal of artificial photosynthesis is to
use solar energy to produce usable fuel, which is done by splitting apart water molecules,
just like plants do. This basic design for
artificial photosynthesis has existed since 1998. And even back then,
it was way more efficient than nature’s version. However, in basically all the designs we’ve ever
had for the process, it can either be durable, efficient, or cheap, but never all three at once.
Which is a big part of why we haven’t been using artificial photosynthesis much so far.
But if we do manage to make the process cheap and efficient, what could it be used for?
Well, one type of fuel that researchers want to make is hydrogen, which burns cleanly,
is zero-carbon, and could be used to power future combustion engines or fuel cells.
However, hydrogen gas is pretty scarce, and is still mostly derived from fossil fuels.
But, we can make hydrogen fuel using a system called an artificial leaf. These
pseudo-leaves utilize a design that features two electrodes immersed in
a water-based solution, called an electrolyte. The electrodes each gather energy from sunlight,
and use that energy to split the water into hydrogen and oxygen.
This is a tricky process, not only generating the gasses, but keeping them separate from
each other. Hydrogen gas is very flammable, and can full-on explode in the presence of oxygen.
But the biggest problem often involves that liquid electrolyte we discussed earlier. That’s because
water has a tendency to corrode the electrodes. And as you might imagine, that’s not great for
the performance of electrodes. Most devices that used these liquid electrolytes could only function
for less than a day before their electrodes would completely corrode and need replacement.
But in 2018, researchers at the Joint Center for Artificial Photosynthesis in
California made a major breakthrough for keeping their equipment in tip-top shape.
Very basically, they used a solid electrolyte instead of the usual liquid kind, and only
fed water vapor into the system. Without liquid electrolyte, the risk of corrosion went way down.
Doing so minimized moisture exposure while still allowing sunlight to be harvested,
making the resulting system capable of 100 continuous hours of hydrogen production.
But hydrogen and oxygen aren’t the only things we can make with artificial photosynthesis.
Researchers can also make methane. Methane is the primary component
in natural gas, and the same greenhouse vapor that gives cows a bad reputation.
Methane is a pretty potent greenhouse gas, but it also has major potential as an
energy-dense fuel source. And instead of harvesting this methane
from bovine burps, we could be making it from carbon dioxide, water, and sunlight.
While natural photosynthesis results in molecules called carbohydrates, methane is a hydrocarbon,
which is a whole different kind of molecule. And making it involves a major, difficult
reengineering of nature’s formula. But in late 2022, researchers at the
University of Chicago announced they had created a novel system that signals a big step towards
realizing this technology on a larger scale. Their design utilized what’s called a
metal-organic framework, or MOF. Which is basically a bunch of
metal ions held together by organic molecules. After adding amino acids to the MOFs, the team
found these compounds were really efficient at both splitting water and augmenting CO2 molecules,
rearranging them into methane. Like ten times more efficient than any previous model.
These are only a couple examples of the work currently being done
to take a leaf out of Mother Nature’s book . And while it may be a while before we’re cooking
with green methane or filling our tanks with solar fuel, artificial photosynthesis could be
a key part of getting the world to become carbon neutral and slowing down the climate crisis.
So thank you to all the plants out there for giving us the blue print,
or maybe the green print? I don’t know.
And thank you for watching this episode of SciShow.
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