Real-time Detection of Acetaldehyde in Electrochemical CO Reduction on Cu Single Crystals

Abstract

Copper is known to be versatile in producing various products from CO2 reduction (eCO2RR), and the product preference is dependent on reaction environments. Literature have reported alkaline electrolytes favor acetate production, and proposed hypotheses on the reaction pathway accordingly. Our work shows acetate can additionally come from the non-faradaic chemical oxidation of acetaldehyde in alkaline environments, which occurs quite rapidly in comparison to typical measurement times. This adds uncertainty into both acetaldehyde and acetate production. With an electrochemistry-mass spectrometry combined (EC-MS) system, we present real-time detection of acetaldehyde as a function of applied potential on single crystal Cu electrodes during electrochemical CO reduction (eCORR). In 0.1M KOH, the (100) and (211) facets had an acetaldehyde production onset of -0.35 V vs. RHE, whereas (111) and (110) exhibited no detectable acetaldehyde production up to -0.6 V vs. RHE. Moreover, the quantified acetaldehyde-to-ethylene production ratio provides insightful information on the acetaldehyde-to-ethylene bifurcation point in eCO2RR, and thus help understand the reaction pathways.