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Reaction Parameters Influencing Cobalt Hydride Formation Kinetics: Implications for Benchmarking H(2)-Evolution
Noémie Elgrishi1, Daniel A Kurtz1, Jillian L Dempsey1
1Department of Chemistry, University of North Carolina , Chapel Hill, North Carolina 27599-3290, United States.
Benchmarking hydrogen evolution catalysts requires understanding factors beyond acid strength. This study shows acid choice and steric bulk significantly impact hydride formation kinetics, revealing complex catalyst performance drivers.
Area of Science:
- Electrochemistry
- Catalysis
- Physical Chemistry
Background:
- Benchmarking hydrogen evolution catalysts is crucial for advancing renewable energy technologies.
- Catalyst activity is often simplified to overpotential, neglecting other influential factors.
- Understanding the role of the acid medium is vital for accurate catalyst evaluation.
Purpose of the Study:
- To investigate the influence of acid choice on the kinetics of hydride formation in a cobalt hydride complex.
- To explore factors beyond acid dissociation constant (pKa) that affect catalyst performance.
- To elucidate the complex interplay between acid properties and catalytic reaction rates.
Main Methods:
- Studied a stable cobalt hydride complex.
- Analyzed the kinetics of hydride formation using varying acids.
- Correlated acid properties (pKa, steric bulk) with observed reaction rate constants.
Main Results:
- A linear free energy relationship was observed between acid pKa and second-order rate constants for weaker acids.
- Stronger acids did not show a correlation between increased pKa and enhanced rate constants.
- Steric bulk of the acid significantly influenced the rate constants of hydride formation.
Conclusions:
- Acid choice impacts hydrogen evolution catalyst kinetics through mechanisms beyond simple acid strength (pKa).
- Steric hindrance around the acidic proton is a critical factor affecting catalytic rates.
- Accurate benchmarking of catalysts necessitates considering a broader range of chemical and physical factors.
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