Flow NMR system development for real-time in situ multiple detection of direct methanol fuel cell exhausts

Abstract

Understanding the electrochemical reaction mechanisms of energy conversion and storage systems is essential for improving their performance. Nuclear magnetic resonance (NMR) spectroscopy is an excellent quantitative and qualitative analysis method for investigating electrochemical reactions. We developed in situ real-time 2H flow NMR spectroscopy using a toroid cavity detector to simultaneously acquire the spectra of the anode and cathode exhausts of a direct methanol fuel cell. We used deuterium-enriched methanol (CD3OH) as fuel in order to obtain background-free spectra. Besides HOD, the CD3OH crossed over from the anode was observed in the cathode exhaust. The amount of CO2 gas, which is impossible to detect with ex situ NMR spectroscopy, was proportional to the HOD amount and current generated during the cell operation at a given potential. Therefore, in situ real-time analysis enabled us to identify and quantify the anode and cathode exhaust chemical components, including the gaseous products, such as CO2, of a fuel cell. This explains differences in the fuel cell performance by identifying generated and consumed chemicals and their pathways in the cells at respective conditions. Hence, our results demonstrate that this in situ real-time flow NMR method is applicable to studying the reaction mechanism of various other liquid-flowing chemical reaction systems besides fuel cells. Furthermore, it may open a new door for designing advanced materials.