In Situ NMR Spectroelectrochemistry of Higher Sensitivity by Large Scale Electrodes

Abstract

The combination of NMR spectroscopy and electrochemistry provides an in situ method to measure structural changes of the redox components in an electrochemical reaction by proton NMR experiments. As the use of metal thin film radio frequency (RF) transparent electrodes in NMR spectroelectrochemical studies is limited by layer thickness and electrodes size, we present a new spectroelectrochemical NMR cell design consisting of nearly metal free symmetrically arranged large scale carbon fiber electrodes. Due to the advantages of modern NMR spectroscopy, a cell rotation is not necessary for high resolution measurements. This makes the presented cell for in situ spectroelectrochemical NMR measurements easy to prepare. The cell design is universal for a large variety of NMR spectrometers and frequencies used for detection of different nuclei. The feasibility of this new in situ NMR spectroelectrochemical cell is demonstrated in a detailed study of the electrochemical behavior of p-benzoquinone in different aqueous solutions.

Design and applications of an in situ electrochemical NMR cell

“…Probe performance: studies of 1,4-benzoquinone 1,4-Benzoquinone was chosen to study because it is easy to work with and has been well-studied electrochemically both in aqueous [18][19][20][21] and non-aqueous [22][23][24] solutions. The evolution of NMR spectra with time upon the reduction to hydroquinone has also been reported [4,11,12,14]. However, no simultaneous electrochemical data along with NMR spectra on benzoquinone have been presented.…”

“…The H 2 SO 4 solvent provides sufficient proton donors required for the reaction. This well-studied reaction [4,11,12,14,[18][19][20][21] was selected in order to evaluate the function of the ECNMR cell. The NMR spectra of the four phenyl protons in benzoquinone and hydroquinone are similar.…”

“…However, both gold film systems [12,13] used a 10 mm or larger size NMR tubes. Very recently, Dunsch et al [14] used large scale carbon fibers for both working and counter electrodes. The metal-free electrodes were unique in producing an enhanced homogeneity of the NMR magnetic field.…”

A combination of in situ ESR and in situ NMR spectroelectrochemistry for mechanistic studies of electrode reactions: the case of p‐benzoquinone

“…The experimental details of this NMR spectroelectrochemical method as well as the special cell design for this in situ method have been described elsewhere. [7] The p-benzoquinone and p-hydroquinone were dissolved at a concentration of 0.1 mol/l in water or in deuterated water for the NMR experiments. The water was distilled two times to remove any impurities.…”

“…Symmetrically arranged carbon fibre electrodes provide a well-controlled working electrode system of large scale thus making in situ NMR spectroelectrochemistry sensitive. [7] Here we present a study of a model redox reaction of the combination of both the in situ NMR and in situ ESR spectroelectrochemistry to describe all intermediate and final paramagnetic and diamagnetic structures for the determination of a reaction mechanism in the electrode reactions of a model redox system.…”