Twist's Review #3 - Semiconductor for Water Splitting

Paper : A metal-free polymeric photocatalyst for hydrogen production from water under visible light

Water splitting, a method for producing hydrogen by ‘splitting water’, is a growing field or research and is one of the leading methods to produce clean hydrogen, also called green hydrogen. Green hydrogen is a terminology that describes hydrogen that has been produced, you’ve guessed it, with little to no carbon emissions. Research currently focuses on visible light water splitting processes, which is also what this paper presents but interestingly with a polymeric semiconductor.

The water splitting process in this paper uses graphitic carbon nitride (g-C3N4), a synthetic polymer, with several allotropes with g-C3N4 being the most stable one under regular conditions. The group synthesizes the polymer by heating cyanamide up to 873 K, which will the undergo thermal condensation. Different thermal condensation tempearatures allows for better tuning of the polymer’s electronic properties.

Essentially, the polymer was able to consistently produce hydrogen without any metal catalysts, with triethanolamine as a sacrifical electron donor, in powder form to maximize surface area. However, the amount of H2 produced differed between batches so the group added some Pt into the mix which helped reduce this variability while also improving hydrogen production by more than twice. It is also important to note that there is minimal reduction in production of H2 through the group’s method of producing hydrogen (72h with evacuation at every 24h mark).

Reference:
[1] X. Wang et al., “A metal-free polymeric photocatalyst for hydrogen production from water under visible light,” Nature Materials, vol. 8, no. 1, pp. 76–80, Nov. 2008, doi: https://doi.org/10.1038/nmat2317.

Water splitting was always an interest of mine as I thought it was really cool that we could produce hydrogen in such an interesting manner. Recent research works on using semicoductors to enable visible light water splitting as it is more practical to do the process in visible light (previously done in UV), and because semiconductors can fit into the visible light energy level requirement.

Now researchers have always surprised me, but this was a nice surprise. A ‘polymeric-semiconductor’, a semiconductor with polymer like mechanical characteristics, was used for the water splitting process. Furthermore it was not some complicated material, it is one with only two elements and it does not exactly require a metal catalyst, although obviously further studies have to be done to maximize the process with this material.