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Identifying the proton donor in electrocatalytic hydrogen evolution by a model hydrogenase
Riley E Stein1, Ashlee E Wertz1, Peter J Moore1
1Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH, 43210, USA.
Summary
Identifying the proton donor is key for optimizing multi-electron transformations. This study on nickel-substituted rubredoxin (NiRd) suggests buffer-dependent proton transfer is not rate-limiting for hydrogen evolution, offering insights for catalyst design.
Area of Science:
- Biophysical Chemistry
- Electrocatalysis
- Bioinorganic Chemistry
Background:
- Proton transfer is fundamental to multi-electron transformations, but identifying the specific proton donor in aqueous solutions is challenging.
- Nickel-substituted rubredoxin (NiRd) is a model hydrogenase used for electrocatalytic hydrogen evolution, with prior studies indicating proton transfer in its rate-determining step.
Purpose of the Study:
- To identify the proton donor in the rate-determining step of NiRd electrocatalytic hydrogen evolution.
- To investigate the influence of buffer properties (pKa, concentration, pH) on NiRd catalytic activity.
- To extract intrinsic kinetic and thermodynamic parameters for NiRd catalysis.
Main Methods:
- Utilized a range of buffers with varying pKa values to probe proton donor identity.
- Investigated the effects of buffer concentration and pH on catalytic currents and turnover frequencies (TOF).
- Employed quantitative electrochemical simulations incorporating buffer information for parameter extraction.
Main Results:
- Intermolecular, buffer-dependent proton transfer was found not to be the rate-determining step under typical electrocatalytic conditions.
- Quantitative simulations enabled the determination of intrinsic thermodynamic and kinetic parameters.
- Mechanistic differences highlight the potential for controlling proton donors to modulate hydrogen-evolving catalyst activity.
Conclusions:
- The study clarifies the proton transfer mechanism in NiRd electrocatalysis, differentiating it from other hydrogen-evolving systems.
- Findings suggest that precise control over the proton donor can be a strategy for enhancing catalyst performance.
- This work provides a foundation for designing more efficient catalysts by understanding and manipulating proton transfer pathways.
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