Mechanism-guided realization of selective carbon monoxide electroreduction to methanol

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. The electroreduction of CO to methanol catalysed by supported cobalt phthalocyanine molecules is hindered by low selectivity and poor mechanistic understanding. Here a mechanism-guided reaction based on systematic kinetic studies is used to achieve an improved methanol Faradaic efficiency of roughly 85%.