A novel in situ electrochemical NMR cell with a palisade gold film electrode

Abstract

In situ electrochemical nuclear magnetic resonance (EC-NMR) has attracted considerable attention because of its ability to directly observe real-time electrochemical processes. Therefore, minimizing the incompatibility between the electrochemical device and NMR detection has become an important challenge. A circular thin metal film deposited on the outer surface of a glass tube with a thickness considerably less than the metal skin depth is considered to be the ideal working electrode. In this study, we demonstrate that such a thin film electrode still has a great influence on the radio frequency field homogeneity in the detective zone of the NMR spectrometer probe and provide theoretical and experimental confirmation of its electromagnetic shielding. Furthermore, we propose a novel palisade gold film device to act as the working electrode. The NMR nutation behavior of protons shows that the uniformity of the radio frequency field is greatly improved, increasing the sensitivity in NMR detection. Another advantage of the proposed device is that an external reference standard adapted to the reaction compound can be inserted as a probe to determine the fluctuation of the physico-chemical environment and achieve high-accuracy quantitative NMR analysis. A three-chamber electrochemical device based on the palisade gold film design was successfully fabricated and the in situ electrochemical NMR performance was validated in a standard 5 mm NMR probe by acquiring voltammograms and high-resolution NMR spectra to characterize the electrochemically generated species. The evolution of in situ EC-NMR spectrum monitoring of the redox transformation between p-benzoquinone and hydroquinone demonstrates the ability of the EC-NMR device to simultaneously quantitatively determine the reactants and elucidate the reaction mechanism at the molecular level.

An NMR-compatible microfluidic platform enabling in situ electrochemistry

“…As expected from the analytical expressions given by Chen et al, 23 the thickest planar disk electrode showed the worst performance in terms of mass sensitivity -S rel = 86.4%. For all other structures except for the narrow channel sidewall configuration, the penalty to be paid in comparison with the electrode-free configuration, in terms of mass sensitivity, was <5%.…”

“…The challenge of introducing conductive structures for in situ electrochemical analyses with high-field NMR is reflected by there being only a few reports available. [38][39][40][41][42][43] Microfabrication introduces new opportunities. On one hand, ultra-thin metallic layers, which are NMR transparent, can be achieved by rather standard MEMS techniques.…”

“…Chen et al provided an analytical analysis of the field penetration inside a metallic cylinder. 23 According to their study, metallic layers thinner than 0.1% of the skin depth are transparent to the external RF field. In microsystems such as LOC devices, B 0 and B 1 perturbations are further exacerbated by the inherently smaller available real-estate.…”

In Situ Real-Time Quantitative Determination in Electrochemical Nuclear Magnetic Resonance Spectroscopy

“…To increase the RF field homogeneity in the volume of substances, we presented an original EC-qNMR cell with palisade structure of working electrode that was suited for routine operations in a modern high-frequency NMR spectrometer [ 23 ], as shown in Figure 1 . The homemade electrolytic cell was fabricated from several glass tubes with different outer diameters.…”

Desenvolvimento de um sensor de RMN (ímã e sonda) para aplicações espectroeletroquímicas

“…The reason why inductively coupled probes were chosen as a way to improve the performance of electrochemical reaction analysis by NMR is: first, because it is an approach that had not previously been tried for this application and; secondly, because most approaches to improve the quality of the coupling between electrochemistry and NMR focus on alterations to the electrochemical itself (3, 8-11, 14, 18, 69-84) and don't tend to focus on improvements to the NMR probe. Some solutions involve placing the electrodes outside the detection region (81)(82)(83)(84), using RF chokes (filters) (14,18,81,82), using nonmetallic electrodes such as carbon microfibers (81)(82)(83) or even metallic thin-films (11,70,71).…”