Intra-molecular proton transfer and hydrogen evolution mechanism in cobalt catalysts

Abstract

Hydrogen generation through catalytic water splitting is a promising strategy for solar energy storage and clean renewable energy generation. In most hydrogen evolution catalysts, external energetic costs to initiate the reaction are anti-correlated with the overall turnover frequency for the catalyst. This has been a limitation for designing more efficient catalysts that evolve hydrogen with both a high reactive rate and a low energetic cost. Here, we report the synthesis and characterization of cobalt-based (pyridine-diimine-dioime) catalysts for hydrogen evolution. A combination of theor. and exptl. anal. suggests that the complex can facilitate an intra-mol. proton transfer reaction from protonated pyridine to cobalt. This process produces CoIII hydride as the key intermediate for hydrogen evolution. Our calcns. indicate a significantly lower energetic barrier for hydrogen generation process with a CoII hydride intermediate compared to the corresponding CoIII hydride intermediate, suggesting that the CoII hydride is the key reactive species for hydrogen generation. Using these insights, we propose a strategy to decouple the anti-correlation between external energetic costs and the catalytic turnover frequency, which provides a promising design principle for more efficient hydrogen evolution catalysts.

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