Augmenting the Performance of Hydrogenase for Aerobic Photocatalytic Hydrogen Evolution via Solvent Tuning

Abstract

This work showcases the performance of [NiFeSe] hydrogenase from Desulfomicrobium baculatum for solar‐driven hydrogen generation in a variety of organic‐based deep eutectic solvents. Despite its well‐known sensitivity towards air and organic solvents, the hydrogenase shows remarkable performance under an aerobic atmosphere in these solvents when paired with a TiO2 photocatalyst. Tuning the water content further increases hydrogen evolution activity to a TOF of 60±3 s−1 and quantum yield to 2.3±0.4 % under aerobic conditions, compared to a TOF of 4 s−1 in a purely aqueous solvent. Contrary to common belief, this work therefore demonstrates that placing natural hydrogenases into non‐natural environments can enhance their intrinsic activity beyond their natural performance, paving the way for full water splitting using hydrogenases.

Avoiding Oxygen Removal for Photochemical Reactions – towards Water as the Solvent

“…The current understanding of local effects on photochemical reactions is underdeveloped and further unexplored supramolecular effects on photochemical reactivity could pave the way for the development of new reactions. [8] Figure 7. Peptide assembly into microrods and upconversion process in the presence of oxygen in water.…”

“…[30] The oxygen sensitive enzyme [NiFeSe] hydrogenase can be applied for solar driven hydrogen production in combination with a TiO 2 photocatalyst (Figure 6). [8] [NiFeSe] hydrogenase can function in pure water, but the activity was drastically improved by adding an eutectic solvent under aerobic conditions. The significant increase in activity was demonstrated by comparing the turn over frequency (TOF) of 4 s À 1 in pure water to a TOF of ca.…”

“…The compromise between oxygen tolerance and photoreactivity was found at 60 % aqueous glyceline. [8]…”

“…Interestingly, water as the solvent inherently contains low amounts of oxygen [4] and combined with supramolecular containers or networks can result in a significant oxygen tolerance observed for certain oxygen sensitive intermediates such as triplet states. [5][6][7][8][9] Supramolecular structures have the potential to not only shield the photoreaction from oxygen interference but also facilitate the organization of reactants, leading to enhanced reaction rates and selectivity. [6,10,11] An additional advantage of performing reactions in water is that it is considered a sustainable and safe solvent to use.…”

“…Figure 6. Reaction design of an TiO 2 -hydrogenase based photocatalyst in deep eutectic solvents that cause oxygen tolerance under aerobic conditions [8]. …”