In Situ Study of the Magnetoelectrolysis Phenomenon during Copper Electrodeposition Using Time Domain NMR Relaxometry

Abstract

Although the effect of magnetic field (B) on electrochemical reactions (magnetoelectrolysis phenomenon) has been long known, it has not been considered in electrochemical reactions analyzed in situ by magnetic resonance methods, such as nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), and magnetic resonance imaging (MRI), which are intrinsically performed in the presence of B. In this report, the effect of B on the copper electrodeposition reaction, measured by a low-field (0.23 T) NMR spectrometer, was demonstrated. As expected, an enhancement in the reaction rate in comparison to the ex situ electrodeposition reaction was observed. Such enhancement was not dependent on electrodes/magnetic field orientations. Parallel and perpendicular orientations showed similar electrodeposition rates, which is explained by the cyclotron flows generated by distortions in electric and magnetic field lines near the electrode and the electrode edge. Therefore, NMR spectroscopy is not a passive analytical method, as assumed in preceding in situ spectroelectrochemical studies. Although the magnetoelectrolysis phenomenon demonstrated in this report used a paramagnetic ion, it can also be observed for diamagnetic species, since the magnetoelectrolysis phenomenon is independent of the nature of the species. Consequently, similar convection effects may occur in other electrochemical nuclear magnetic resonance (EC-NMR) experiments, such as the electrochemical reaction of organic molecules, as well as in electrocatalysis/fuel cells, lithium-ion batteries, and experiments that use electrochemical electron paramagnetic resonance (EC-EPR) and electrochemical magnetic resonance imaging (EC-MRI).

Measuring the solubility product constant of paramagnetic cations using time-domain nuclear magnetic resonance relaxometry

“…Recently, we used the CPMG sequence and the T 2 values to measure the Cu 2+ concentration in situ during electrodeposition reactions [11][12][13].…”

Monitoring Electrochemical Reactions in Situ with Low Field NMR: A Mini-Review

“…In 2014, Gomes et al [8] used a similar system to that used by Nunes et al in 2012 and observed that the reaction rate of the Cu 2+ electrodeposition reaction monitored in situ by TD NMR was faster than the same reaction performed ex situ ( Figure 5). The results showed that after 1 h of reaction 40% of the copper ions had been deposited on the electrode surface when the reaction was performed in situ, which is a 48% increase in copper deposition when compared to the 27% that was deposited when the reaction was performed ex situ ( Figure 5).…”

“…The linear relationship between the relaxation rate (1 T 2 ) and the concentration of paramagnetic ions has been exploited to quantify paramagnetic ions in solutions, to calculate K SP values [23], to study coordination complexes with paramagnetic ions as ligands [24] and also to monitor electrochemical reactions in situ [8,9].…”

“…In practice, however, even if at a macroscopic level j and B are parallel, the electrode surface as well as its edges create local distortions to the electric field which results in there being regions where j and B are no longer parallel and thus F B will be minimum, but not zero, as explained Monzon et al in 2015 [13], who call this particular effect micro-magnetohydrodynamic effect. Gomes et al (2014) [8] also discuss the reason for why the reaction rate remains unaltered despite an apparent parallel orientation between B and j ( Figure 5). They explain this result in terms of the effect of the edges of the electrode and gas bubbles that form on its surface during the reaction, which locally alter the electric field, therefore preventing F B from being zero.…”

“…The instruments used for these analyses are normally based on permanent magnets which produce a magnetic field intensity usually below 0.6 T (25 MHz for 1 H) with a low homogeneity (above 100 ppm) which means that the relevant information can only be extracted from the intensity of the free induction decay signal (FID), the spin echo or by measuring the relaxation times T 1 and/or T 2 or the diffusion coefficient of the sample. In this review we show the application of time domain NMR (TD NMR-also known as low-field NMR) to an increasingly popular research field which is the in situ monitoring of electrochemical reactions (EC-NMR) [7][8][9]. The first published paper which detailed the use of TD NMR for such an application was published as recently as 2010 [10] (which is a 40 year delay from the first paper detailing the use of high-field NMR for the same application [11]).…”