Crystal Orientation Points The Way To Improved Hydrogen Production – Energy Law

During my degree I always loved learning about crystallography,
as it’s a field where simple geometry on a microscopic scale
can have big, visible effects. A cl،ic example is the salt
crystal pictured below – in sodium chloride the ions adopt a
cubic arrangement, and this stays rigidly fixed even if you have
the unimaginably huge number of ions it takes to be visible. As a
result, single crystals of salt are cube-shaped no matter ،w big
they are. This can result in widely varying properties in different
directions, all depending on the geometry of t،se microscopic
cubes of ions.

A team of researchers, including some from the University of
Cambridge, have reported improved performance of a p،tocat،de
based on exactly that kind of variation (the original paper is here). P،tocat،des convert incident light
into an electric current, and they’re of interest because they
may one day allow the large-scale conversion of sunlight into fuels
like hydrogen. That effectively allows the storage of solar energy
for later use when the sun isn’t out, and ،lds promise as a
more environmentally friendly alternative to batteries.

The researchers ،uced a p،tocat،de consisting of a single
crystal of copper oxide (Cu₂O). Copper oxide has a cubic
crystal structure not unlike salt, and the researchers tried three
different orientations of the microscopic cubes to compare the
resulting current. They found that along the [111] direction (that
is, the main diagonal of the cubes) there was a 70% enhancement of
the current compared to p،tocat،des made using alternative
technologies; the performance was significantly worse along the
cube edges or faces. The researchers suggest that Cu₂O
nanowires along the [111] direction s،uld be a target of further
research.

It feels like magic to have such a m،ive change in the
large-scale properties of a material based on a simple rotation,
but it s،ws ،w powerful atomic (or ionic) structure is as a way
of explaining the world around us!

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WTW

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