Observation of NMR signals from samples with flat geometry: Application to in-situ analysis of a direct ethanol fuel cell

Most NMR samples are cylindrical, which is ideal for obtaining high-resolution NMR spectra, especially in superconducting magnets with a vertical bore. However, expanding NMR applicability to samples that are not necessarily cylindrical requires a new approach. In this study, we introduce a method for obtaining solution NMR signals from flat samples, such as flat containers or layered structures like a fuel cell. A flat rectangular NMR coil was developed for RF application and sensitive signal detection, while biplanar shim coils were designed using Bfieldtools and manufactured on multilayered printed circuit boards to improve NMR resolution. Water and ethanol molecules in flat rectangular and flat circular containers, as well as in a direct ethanol fuel cell, were observed with narrow NMR linewidths. We believe that our spectrometer design will enable NMR analysis of samples that need to be contained in flat structures and support in-situ analysis of various devices.