Quantifying local pH changes in carbonate electrolyte during copper-catalysed CO2 electroreduction using in operando 13C NMR
The electrochemical reduction of CO2 is a promising energy storage alternative, that could not only stabilise fluctuations of the renewable energies but at the same time consume CO2 from the atmosphere or industrial waste streams. Among elemental metal catalysts, copper has the unique ability to catalyse significant amounts of various short-chain hydrocarbons, some of which can be used as fuels or base chemicals. However, the reaction mechanisms towards these products are not fully understood yet and are strongly influenced by local reaction conditions at the copper working electrode.
We herein present an in operando 13C Nuclear Magnetic Resonance (NMR) method for the determination of local concentrations as well as pH values in the vicinity of the working electrode. Local pH values are derived from the pH-dependent equilibrium between CO2 and the carbonate species in a KHCO3 electrolyte solution. Variations in applied potential and buffer capacity are investigated and interrelated to product selectivity. The experimental results are in accordance with theoretical considerations.