(gentle music)
- This isn't a sculpture or a work of art,
but an important mineral known as bismuth.
In the past few decades,
this metal has slipped primarily under the radar.
It currently only has a few uses in everyday life,
and is mostly known for its brilliant colors
and crystals like these.
But in the years ahead,
bismuth could change the very meaning
of the word green in green energy.
(upbeat music)
People have known about bismuth for thousands of years,
but it was first identified as an element in 1753.
It was typically mined along with lead, copper, and tin
for use in things like cosmetics and paint.
It's a brittle, iridescent metal with a low melting point
and the ability to form beautiful geometric crystals
when melted and then slowly cooled.
Where bismuth is most widely known
is in the pharmaceutical industry.
You're probably familiar with this medicine
known as bismuth subsalicylate,
better known as Pepto Bismol.
Every dose of this antidiarrheal
contains up to a quarter gram of bismuth metal.
Now, ingesting a heavy metal isn't something we condone,
but this is where bismuth differs from other heavy metals.
It exists on the periodic table
in what's known as the poisoner's corridor,
hanging out with lead, mercury, thallium, and polonium,
but it's surprisingly safe to humans.
Even though it's surrounded by toxic elements,
it's totally benign,
which makes it not only safe to eat,
but fun to play with.
Here in a maker space on Staten Island,
we're going to try and grow some crystals
to see how they form.
Bismuth has a very low melting point
of just over 270 degrees celsius,
which makes the process relatively simple,
but also requires a bit of patience.
Here's how it works.
Heat the bismuth up in a pot,
skim off the impurities
or slag from the top,
and then wait for the crystals to form as it cools.
With a bit of luck,
you'll get something like this.
That's bonkers, look at that.
And you can see it's oxidizing now
so it's turning this purple color.
Neat, alien-like crystals aside,
bismuth also has some unique properties
that make it a valuable tool for researchers.
- What I think about is how do we combine bismuth
with other elements,
and in that sense,
the properties of bismuth that I'm mostly interested in
are its electronic properties, how the electrons
are arranged around the nucleus,
and if we look at that, bismuth has some
really interesting properties.
- Robert Hoye is a lecturer in materials
at Imperial College London.
He spoke with us about bismuth's electronic properties
and promising future applications.
Robert and his team are focused on creating
bismuth-based semi-conductors for use in
photovoltaics.
In the past ten years or so,
scientists have been looking into replacements
for silicon that are cheaper and more efficient.
Many have turned toward lead halide
and cadmium telluride solar cells,
both of which have electronic structures
that make them very good at absorbing sunlight.
But those materials are toxic or scarce,
and not very sustainable.
- The good thing about bismuth-based compounds
is that they are not toxic.
The precursors are not toxic,
the materials are not toxic,
and if it degrades within the field,
then it's not gonna harm the environment.
- For this same reason, bismuth has started
replacing lead in electronic solder,
fishing weights, shotgun shot, and even for water pipes
in people's homes.
It's been coined the green element for its ability
to replace lead in many applications,
and in doing so, reduce the possibility of lead
entering into ground or drinking water
when these things eventually end up in a landfill
years down the road.
Robert sees huge potential in bismuth-based photovoltaics
to one day be able to harvest light indoors
rather than outdoors.
While traditional photovoltaic cells rely heavily
on infrared light, the bismuth-based semiconductors
he's developing have a slightly wider band gap,
which determines how good a material is
at conducting electricity.
This allows the semi-conductors to absorb more visible
light, but prevents them from absorbing infrared light,
which might seem like a disadvantage,
but not to Robert.
- This apparent disadvantage can be turned into
a huge advantage if we take them indoors.
Having photovoltaics indoors is really important
because we have billions of these smart devices
which are autonomous, they're not connected to the wall,
and you have to power them somehow,
so if each of these smart devices has a photovoltaic,
then you can remotely power them.
So actually, the band gap for bismuth-based compounds
is exactly the right value.
We found that if you take bismuth-based compounds
indoors, you can increase the efficiency
by a factor of five.
- With everything from temperature sensors to alarm systems
to lighting systems in your home,
the internet of things could amount to billions
if not trillions of devices that could benefit
from indoor photovoltaics,
replacing the need for batteries
that rely on metals like lithium, cadmium, cobalt, and more.
- So you have a situation where you never have to
replace a battery ever again
using these bismuth-based semi-conductors
for indoor light harvesting.
- Never having to replace a battery in your home's devices
sounds like a dream.
The only question, is there enough bismuth to go around?
Bismuth is pretty rare.
It ranks 65th in elemental abundance
in the Earth's crust, less than point zero zero one percent.
But Robert's not super worried about that,
because a little bit of bismuth goes a long way.
- So we make what's called thin films,
which are layers of this material,
which are say five-hundredth to a micron thick.
In contrast to silicon,
for silicon you need quite a thick layer,
you need a lot of material.
You just need a small amount of bismuth,
and that's all you need to make this
device.
Even though bismuth isn't so widely used commercially
right now, there's enough bismuth in the world
right now to support the future of widespread
deployment of bismuth-based semi-conductors.
- So the next time you grab a bottle of Pepto Bismol,
take a moment to appreciate that the heavy metal
you're about to ingest
might one day help power all of your electronics.
- I am very excited about bismuth as a compound.
I think that they have huge potential for indoor
light harvesting
where really they could out-compete the existing materials
and provide a sustainable future.
- Hey everyone, thank you for watching.
Be sure to subscribe to our channel
for more videos like these,
and let us know in the comments below
if there are other materials you'd like us to check out.
Thanks.