Graduate Student Christian Guzman

"Conjugated Polymer/Metal Cocatalysts for Photocatalytic Water Splitting"

It is widely accepted that CO2 produced from human energy consumption is the leading cause of global warming, which threatens to upset the environmental balance of the Earth. Hydrogen gas (H2) offers a clean alternative to fossil fuels because it produces only water as a combustion product. Currently, H2 is industrially produced by steam reformation, which involves the reaction of methane with high pressure steam. Unfortunately, the steam reformation process requires a large amount of energy and forms CO2 as a byproduct.

CO2 evolution in the H2 production process can be eliminated by electrochemical water splitting which results in H2 and O2 as sole products. This process, while clean, is an endergonic process requiring the input of energy. Use of a photocatalyst can provide the required energy input to drive the water splitting reaction and thereby enables the production of H2 with no CO2 production. As it turns out, Nature has already developed a method to utilize photons for water splitting in the photosynthetic process. Chlorophyll structures contain a porphyrin ring which serves as a starting structure for human-designed photocatalysts.

While molecular porphyrins are capable of photocatalysis, the isolated ring system does not facilitate charge separation well which leads to low hydrogen evolution rates. Incorporating the porphyrin moiety into conjugated polymer structures increases electron delocalization and leads to increased efficiency. In this presentation, I will discuss two polyporphyrin1,2 structures and one polypyrrole3 structure that have been examined for their photocatalytic hydrogen evolution efficiency with and without metal cocatalysts.

References
(1) Zhao, X.; Zhang, X.; Liang, Y.; Hu, Z.; Huang, F. Porphyrin-Based Conjugated Polyelectrolytes for Efficient Photocatalytic Hydrogen Evolution. Macromolecules 2021, 54 (10), 4902–4909. https://doi.org/10.1021/acs.macromol.1c00489.
(2) Chen, Z.; Wang, J.; Zhang, S.; Zhang, Y.; Zhang, J.; Li, R.; Peng, T. Porphyrin-Based Conjugated Polymers as Intrinsic Semiconducting Photocatalysts for Robust H2 Generation under Visible Light. ACS Appl Energy Mater 2019, 2 (8), 5665–5676. https://doi.org/10.1021/acsaem.9b00811.
(3) Yuan, X.; Dragoe, D.; Beaunier, P.; Uribe, D. B.; Ramos, L.; Méndez-Medrano, M. G.; Remita, H. Polypyrrole Nanostructures Modified with Mono- And Bimetallic Nanoparticles for Photocatalytic H2 Generation. J Mater Chem A Mater 2020, 8 (1), 268–277. https://doi.org/10.1039/c9ta11088g.