Cobalt phthalocyanine can effectively convert CO2 or CO to methanol. However, this reaction is hampered by low selectivity (a methanol Faradaic efficiency of less than 40%) and poor understanding of the kinetics and mechanism. In this work, we use a mechanism-guided reaction design approach based on systematic kinetic studies to overcome these limitations. pH-dependent Tafel analysis and kinetic isotopic effect experiments explain that methanol production from CO electroreduction is pH independent and limited by the *CO hydrogenation to *CHO step with H2O as the major proton source. Proton donor comparisons show that bicarbonate can promote the reaction at its optimal concentration of 0.1 M and CO reaction order studies confirm a Henry type isotherm for CO adsorption on the catalyst surface. These mechanistic findings lead us to carry out CO reduction in a 0.1 M bicarbonate electrolyte, under 10 atm CO pressure and with a microporous layer on the electrode to enhance reactant transport. Our reaction achieves a high methanol Faradaic efficiency of 84% with a partial current density of more than 20 mA cm−2 at −0.98 V versus the reversible hydrogen electrode, making the electrochemical CO-to-methanol conversion a selective process viable for practical application.
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This work was supported by US National Science Foundation (grant no. CHE-2154724; mechanistic and kinetic studies) and the Yale Center for Natural Carbon Capture (performance and device work).
The authors declare no competing interests.
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Li, J., Shang, B., Gao, Y. et al. Mechanism-guided realization of selective carbon monoxide electroreduction to methanol. Nat. Synth (2023). https://doi.org/10.1038/s44160-023-00384-6
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