Buffer-Induced Electrocatalytic Hydrogen Evolution by a Cobalt Pentadentate Complex in Water.

Area of Science:

• Catalysis and Reaction Mechanisms
• Electrochemistry and Energy Conversion
• Inorganic Chemistry

Background:

• Proton transfer dynamics in water splitting are complex due to multiple proton donors, hindering reaction kinetics.
• Understanding buffer effects is crucial for optimizing catalytic hydrogen evolution reactions.

Purpose of the Study:

• To investigate how buffer acid dissociation exponent (pKa) and concentration influence the catalytic performance of a Cobalt(III) complex for hydrogen evolution.
• To elucidate the mechanism of buffer-mediated proton transfer in catalytic water splitting.

Main Methods:

• Electrochemical catalytic studies using a Cobalt(III) complex.
• Systematic variation of buffer pKa and concentration.
• Analysis of reaction kinetics and linear free energy relationships.

Main Results:

• Buffer addition enhances the catalytic rate of hydrogen evolution.
• 2-(N-morpholino)ethanesulfonic acid (MES) showed the highest catalytic current.
• A linear free energy relationship confirmed a Brønsted-type mechanism, indicating proton delivery as the rate-limiting step.
• Higher buffer concentrations led to inhibition, suggesting buffer-cobalt binding.

Conclusions:

• Buffer identity and concentration are critical parameters for optimizing proton-dependent catalytic reactions.
• The study provides insights into the role of buffers in facilitating proton transfer for hydrogen evolution.
• Buffer-substrate interactions can influence catalytic efficiency, necessitating careful optimization.