An electrochemical cell for in operando 13C nuclear magnetic resonance investigations of carbon dioxide/carbonate processes in aqueous solution.

Sven Jovanovic,Michael Schatz,P. Philipp M. Schleker,Peter Jakes,Matthias Streun,Josef Granwehr,Rüdiger-A. Eichel,Steffen Merz

doi:10.5194/mr-2-265-2021

Abstract

In operando nuclear magnetic resonance (NMR) spectroscopy is one method for the online investigation of electrochemical systems and reactions. It allows for real-time observations of the formation of products and intermediates, and it grants insights into the interactions of substrates and catalysts. An in operando NMR setup for the investigation of the electrolytic reduction of at silver electrodes has been developed. The electrolysis cell consists of a three-electrode setup using a working electrode of pristine silver, a chlorinated silver wire as the reference electrode, and a graphite counter electrode. The setup can be adjusted for the use of different electrode materials and fits inside a 5 mm NMR tube. Additionally, a shielding setup was employed to minimize noise caused by interference of external radio frequency (RF) waves with the conductive components of the setup. The electrochemical performance of the in operando electrolysis setup is compared with a standard electrolysis cell. The small cell geometry impedes the release of gaseous products, and thus it is primarily suited for current densities below 1 mA cm. The effect of conductive components on CNMR experiments was studied using a -saturated solution of aqueous bicarbonate electrolyte. Despite the field distortions caused by the electrodes, a proper shimming could be attained, and line widths of ca. 1 Hz were achieved. This enables investigations in the sub-Hertz range by NMR spectroscopy. High-resolution CNMR and relaxation time measurements proved to be sensitive to changes in the sample. It was found that the dynamics of the bicarbonate electrolyte varies not only due to interactions with the silver electrode, which leads to the formation of an electrical double layer and catalyzes the exchange reaction between and , but also due to interactions with the electrochemical setup. This highlights the necessity of a step-by-step experiment design for a mechanistic understanding of processes occurring during electrochemical reduction.

Highlights

The anthropologically driven atmospheric CO2 increase is considered one of the major contributions to global warming (Hansen et al, 2008)
The potentials observed for both the in operando and the bulk cell are within the range reported in the literature, as the values depend on the properties of the catalyst and the electrolysis cell
This study presented a setup for the in operando nuclear magnetic resonance (NMR) study of the electrochemical CO2 reduction, designed to observe changes in molecular dynamics in proximity to the working electrode

Summary

Introduction

The anthropologically driven atmospheric CO2 increase is considered one of the major contributions to global warming (Hansen et al, 2008). A decline in anthropological CO2 emissions is seen as improbable due to socio-economic factors (Grundmann, 2016). One promising method in terms of cost and variability is the electrolytic reduction of CO2, usually performed in an aqueous bicarbonate electrolyte solution (Haas et al, 2018). Depending on the metal electrode, CO2 electrolysis yields a number of products, e.g., formate, hydrocarbons, alcohols, and carbon monoxide (Hori, 2008; Haas et al, 2018). CO, which is a versatile educt for the chemical industry, e.g., as feedstock for the Fischer–Tropsch process, is obtained by using silver or gold electrodes (Hernández et al, 2017)

Methods

Results

Conclusion