Unusual Activation Parameters, Electron and Nuclear Tunneling, Mechanisms of Charge Separation, Spin Exchange and Electron Transfer in Photosynthesis; Electron Transfer versus Proton Transfer at Electrodes and in Solution, Hydrogen Evolution, Quantum Effects, Classical and Semiclassical Calculations of Electron Transfer Rates

The development of more effective energy conversion processes is critical for global energy sustainability. The design of molecular electrocatalysts for the hydrogen evolution reaction is an important component of these efforts. Proton-coupled electron transfer (PCET) reactions, in which electron transfer is coupled to proton transfer, play an important role in these processes and can be enhanced by incorporating proton relays into the molecular electrocatalysts. Herein nickel porphyrin electrocatalysts with and without an internal proton relay are investigated to elucidate the hydrogen evolution mechanisms and thereby enable the design of more effective catalysts. Density functional theory calculations indicate that electrochemical reduction leads to dearomatization of the porphyrin conjugated system, thereby favoring protonation at the meso carbon of the porphyrin ring to produce a phlorin intermediate. A key step in the proposed mechanisms is a thermodynamically favorable PCET reaction composed of intramolecular electron transfer from the nickel to the porphyrin and proton transfer from a carboxylic acid hanging group or an external acid to the meso carbon of the porphyrin. The C–H bond of the active phlorin acts similarly to the more traditional metal-hydride by reacting with acid to produce H2. Support for the theoretically predicted mechanism is provided by the agreement between simulated and experimental cyclic voltammograms in weak and strong acid and by the detection of a phlorin intermediate through spectroelectrochemical measurements. These results suggest that phlorin species have the potential to perform unique chemistry that could prove useful in designing more effective electrocatalysts.

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Corrole–ferrocene and corrole–anthraquinone dyads: synthesis, spectroscopy and photochemistry

Physical Chemistry Chemical Physics ◽

10.1039/c5cp02565f ◽

2015 ◽

Vol 17 (40) ◽

pp. 26607-26620 ◽

Cited By ~ 17

Author(s):

Jaipal Kandhadi ◽

Venkatesh Yeduru ◽

Prakriti R. Bangal ◽

Lingamallu Giribabu

Keyword(s):

Electron Transfer ◽

Excited State ◽

Charge Separation ◽

Photoinduced Electron Transfer ◽

Charge Recombination ◽

Transfer Rates ◽

Donor Acceptor

Two different donor–acceptor systems based on corrole–ferrocene (Cor–Fc) and corrole–anthraquinone (Cor–AQ) have been designed and synthesized. Excited state properties of these dyads indicates intramolecular photoinduced electron transfer (PET) take place in these dyads and the electron-transfer rates (kET) was found to be ∼1011s−1. The charge separation (CS) and charge recombination (CR) are found to be identical.

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Proton transfer in microbial electrolysis cells

Sustainable Energy & Fuels ◽

10.1039/c7se00034k ◽

2017 ◽

Vol 1 (4) ◽

pp. 725-736 ◽

Cited By ~ 12

Author(s):

Abhijeet P. Borole ◽

Alex J. Lewis

Keyword(s):

Electron Transfer ◽

Proton Transfer ◽

Loading Rate ◽

Electrochemical Cells ◽

Transfer Rates ◽

Microbial Electrolysis Cells ◽

Time Control ◽

Electrolysis Cells ◽

Control Of Flow ◽

First Time

Proton transfer in microbial electrochemical cells is as important as electron transfer. This study quantifies proton transfer rates in MEC for the first time. Control of flow rate and loading rate allows improvement in proton transfer rates enabling hydrogen productivities >10 L per L per day.

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