Quantifying local pH changes in carbonate electrolyte during copper-catalysed CO 2 electroreduction using in operando 13C NMR

Abstract

The electrochemical carbon dioxide reduction on copper attracted considerable attention within the last decade, since Cu is the only elemental transition metal that catalyses the formation of short-chain hydrocarbons and alcohols. Research in this field is mainly focused on understanding the reaction mechanism in terms of adsorbates and intermediates. Furthermore, dynamic changes in the micro-environment of the catalyst, i.e. local pH and CO 2 concentration values, play an equivalently important role in the selectivity of product formation. In this study, we present an in operando13C nuclear magnetic resonance technique that enables the simultaneous measurement of pH and CO 2 concentration in electrode vicinity during electroreduction. The influence of applied potential and buffer capacity of the electrolyte on the formation of formate is demonstrated. Theoretical considerations are confirmed experimentally and the importance of the interplay between catalyst and electrolyte is emphasised.