Exploration of the Photocatalytic Cycle for Sacrificial Hydrogen Evolution by Conjugated Polymers Containing Heteroatoms

We analyze the photocatalytic activity of heteroatom containing linear conjugated polymers for sacrificial hydrogen evolution using a recently proposed photocatalytic cycle. We find that the thermodynamic barrier to electron transfer, relevant both in the presence and absence of noble metal co-catalysts, changes with polymer composition, reducing upon going from electron-rich to electron-poor polymers, and disappearing completely for the most electron-poor polymers in a water rich environment. We discuss how the latter is probably the reason why electron-poor polymers are generally more active for sacrificial hydrogen evolution than their electron-rich counterparts. We also study the barrier to hydrogen-hydrogen bond formation on the polymer rather than the co-catalyst and find that it too changes with composition but is always, at least for the polymer studied here, much larger than that experimentally reported for platinum. Therefore, it is expected that in the presence of any noble metal particles these will act as the site of hydrogen evolution.