Hydrogen evolution by polymer photocatalysts; a possible photocatalytic cycle

Zwijnenburg

2021

Preprint

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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.

Section: Hydrogen Formation Barrierscontrasting

confidence: 64%

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

Zwijnenburg

2021

Preprint

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“…[39][40] Polymers can also potentially act as a catalyst for proton reduction themselves but in the presence of palladium or platinum nanoparticles the activity of those will very likely outcompete any inherent catalytic activity of the polymer. 41 In contrast, TEA oxidation most likely is not catalytic, and probably takes the form of two sequential out-of-sphere electron-transfer steps between the polymer and TEA. First TEA gets oxidised to TEA + , which after deprotonation, gets oxidised in the second electron-transfer step to diethylamine and acetaldehyde, the expected 2electron oxidation products.…”

Section: Resultsmentioning

confidence: 99%

The potential scarcity, or not, of polymeric overall water splitting photocatalysts

Saunders

Sprick

et al. 2021

Preprint

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We perform a high-throughput computational screening of a set of 3240 conjugated alternating binary co-polymers and homo-polymers, in which we predict their ability to drive sacrificial hydrogen evolution and overall water splitting when illuminated with visible light. We use the outcome of this screening to analyse how common the ability to drive either reaction is for conjugated polymers loaded with suitable co-catalysts, and to suggest promising (co-)monomers for polymeric overall water splitting catalysts.

“…Regardless, most of the materials considered, or at least the corresponding polymers, are experimentally not known to oxidize H 2 O to either OH • or O 2 . However, Prentice et al., [ 101 ] show that in principle this mechanism should be easily extendable to the oxidation of a SED such as TEA instead of water.…”

Section: Predictions For Homolytic Exciton Dissociation Mechanismmentioning

confidence: 99%

“…[ 102,103 ] Finally, Prentice et al. [ 101 ] studied the barrier for hydrogen evolution in the case of poly( p‐ phenylene) using a similar computational set‐up as Pati et al., predicting a barrier of 0.79 eV, see Figure 4B, suggesting again that the route toward activity does not necessarily involve heteroatoms.…”

Section: Predictions For Heterolytic Exciton Dissociation Mechanismmentioning

confidence: 99%

“…[97,98] Adsorbing a hydrogen atom on one of the two nitrogen atoms of the fused selenium containing BT unit was predicted to be especially favorable with a predicted ΔG H of 0.02 eV, very close to the optimum value of 0 and very similar to that predicted for platinum. Adsorption of hydrogen on carbon atoms was recently studied by Prentice et al, [101] who reported a value of 1.2 eV for adsorption on aromatic −C[H]− carbons atoms in the case of poly(p-phenylene). While the latter value is larger than that predicted for most heteroatom containing systems discussed above, it is similar enough to suggest that also non-heteroatom sites are worth considering.…”

Section: Hydrogen (And Oxygen) Bond Formationmentioning

confidence: 99%

See 1 more Smart Citation

The Role of Computational Chemistry in Discovering and Understanding Organic Photocatalysts for Renewable Fuel Synthesis

Advanced Energy Materials

Zwijnenburg

2021

Self Cite

In this review the role computational chemistry plays in helping to rationalize the ability of organic materials, such as conjugated polymers, to drive photocatalytic water splitting and CO2 reduction, and the discovery of new organic photocatalysts, is reviewed. The ways in which organic photocatalysts differ from their inorganic counterparts, the mechanism by which such materials, when illuminated, reduce protons or CO2 and oxidize water or sacrificial donors, and how this can be studied using computational methods, as well as the high‐throughput virtual screening of organic materials as photocatalysts, are discussed. Finally, the current opportunities and challenges associated with studying photocatalysts computationally, are examined.