Introduction
Hydrogen utilization is a promising alternative to fossil fuels where molecular, metal-based catalysts represent a sustainable opportunity. However, many molecular catalysts require rare metals or organic solvents, reducing their sustainable potential.
Cobaloxime is a molecular catalyst containing the globally available metal, cobalt, but its low solubility and stability has hindered its broader application. In a study from 2024, Berglund et al. sought to address this challenge by designing a de novo artificial enzyme for hydrogen production.
The researchers engineered a 65-amino acid protein consisting of three alpha-helices and covalently linked cobaloxime to a cysteine residue. This would effectively solubilize cobaloxime, but also partially bury it within the protein scaffold, potentially reducing the efficacy of hydrogen production from the artificial enzyme compared with free cobaloxime.
Laboratory Setup
The researchers quantified the Hydrogen Evolution Reaction (HER) of the artificial enzyme and compared it to free cobaloxime. Both catalysts were placed in sealed vials with septum closures to prevent gas exchange with the atmosphere, and hydrogen production was initiated either photocatalytically or chemically.
For the photocatalytic HER, the artificial enzyme and free cobaloxime were illuminated in the presence of [Ru(bpy)3]2+ and ascorbic acid as an electron donor.
A Unisense H2 Microsensor in a piercing needle (H2-NPLR) was inserted through the septum and submerged in the solution (Figure 1). Once HER was triggered, the microsensor continuously monitored hydrogen levels in real time.
Results and Conclusion
Under photocatalytic conditions, the artificial enzyme exhibited a rapid initial increase in hydrogen production, reaching a peak concentration of approximately 49 μM per μM catalyst (Figure 2). Free cobaloxime showed a similar trend but achieved a higher maximum hydrogen concentration of 62 μM per μM catalyst.
Consequently, the hydrogen production of the artificial enzyme corresponds to 80% of the hydrogen production of free cobaloxime, indicating a slightly reduced catalytic efficiency when cobaloxime was embedded in the protein scaffold. The researchers thereby demonstrated the potential of using artificial enzymes for hydrogen production.
The Unisense H2 Microsensor enabled continuous, realtime measurements of dissolved hydrogen throughout the illumination period. Its piercing needle design allowed insertion into the sealed vials while avoiding gas exchange with the atmosphere.
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