Mechanism-Guided Kinetic Analysis of Electrocatalytic Proton Reduction Mediated by a Cobalt Catalyst Bearing a Pendant Basic Site

Amtawong, Jaruwan; Montgomery, Charlotte L.; Bein, Gabriella P.; Raithel, Austin L.; Hamann, Thomas W.; Chen, Chun-Hsing; Dempsey, Jillian L.

doi:10.1021/jacs.3c10408

Mechanism-Guided Kinetic Analysis of Electrocatalytic Proton Reduction Mediated by a Cobalt Catalyst Bearing a Pendant Basic Site

Journal Article · Sun Feb 04 23:00:00 EST 2024 · Journal of the American Chemical Society

DOI:https://doi.org/10.1021/jacs.3c10408· OSTI ID:2333086

Amtawong, Jaruwan ^[1]; Montgomery, Charlotte L. ^[2]; ^[2]; Raithel, Austin L. ^[3]; ^[3]; ^[2]; ^[2]

University of North Carolina at Chapel Hill, NC (United States); University of North Carolina at Chapel Hill
University of North Carolina at Chapel Hill, NC (United States)
Michigan State University, East Lansing, MI (United States)

Cobalt polypyridyl complexes stand out as efficient catalysts for electrochemical proton reduction, but investigations into their operating mechanisms, with broad-reaching implications in catalyst design, have been limited. Herein, we investigate the catalytic activity of a cobalt(II) polypyridyl complex bearing a pendant pyridyl base with a series of organic acids spanning 20 pKa units in acetonitrile. Structural analysis, as well as electrochemical studies, reveals that the Co(III) hydride intermediate is formed through reduction of the Co(II) catalyst followed by direct metal protonation in the initial EC step despite the presence of the pendant base, which is commonly thought of as a more kinetically accessible protonation site. Protonation of the pendant base occurs after the Co(III) hydride intermediate is further reduced in the overall ECEC pathway. Additionally, when the acid used is sufficiently strong, the Co(II) catalyst can be protonated, and the Co(III) hydride can react directly with acid to release H₂. With thorough mechanistic understanding, the appropriate electroanalytical methods were identified to extract rate constants for the elementary steps over a range of conditions. Thermodynamic square schemes relating catalytic intermediates proposed in the three electrocatalytic HER mechanisms were constructed. Furthermore, these findings reveal a full description of the HER electrocatalysis mediated by this molecular system and provide insights into strategies to improve synthetic fuel-forming catalysts operative through metal hydride intermediates.

View Accepted Manuscript (DOE)

Research Organization:: University of North Carolina at Chapel Hill, NC (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF)

Grant/Contract Number:: SC0015303; SC0017342; SC0021173

OSTI ID:: 2333086

Alternate ID(s):: OSTI ID: 2461613

Journal Information:: Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 6 Vol. 146; ISSN 0002-7863

Publisher:: American Chemical Society (ACS)Copyright Statement

Country of Publication:: United States

Language:: English

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Mechanism-Guided Kinetic Analysis of Electrocatalytic Proton Reduction Mediated by a Cobalt Catalyst Bearing a Pendant Basic Site

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