Magnetoelectrochemistry

The Magneto electrochemistry is a research area in which the effects of magnetic fields on electrochemical processes are investigated. The most important sub-area is magnetoelectrolysis , the use of magnetic fields in electrolysis . Possible applications of the effects are improved processes in electroplating or water electrolysis . Magnetoelectrochemistry as a combination of electrochemistry and magnetic fields also has overlaps with magnetochemistry , but especially with magnetohydrodynamics . The most important effect of the magnetic field on the electrochemical processes concerns the movement of the ions in the solution.

Effects of the magnetic field

When a current flows, the dissolved ions ( cations and anions ) move through the electrolyte . A magnetic field leads to a force (the Lorentz force in the narrower sense) on the moving charge carriers. The total force acting on an ion moving with speed is the Lorentz force in the broader sense: ${\displaystyle {\vec {B}}}$ ${\displaystyle {\vec {F_{\text{B}}}}}$ ${\displaystyle {\vec {v}}}$ ${\displaystyle {\vec {F}}}$

${\displaystyle {\vec {F}}={\vec {F_{\text{E}}}}+{\vec {F_{\text{B}}}}=q{\vec {E}}+q{\vec {v}}\times {\vec {B}}}$,

wherein the charge q of the ion by its charge number z and the elementary charge e is given: . Accordingly, the magnitude of the force is proportional to the magnetic field or, more precisely, to the component of the field perpendicular to the direction of the current. The additional shifting of the charges creates a voltage, this is the Hall effect . The movement component of the ions caused by the magnetic field perpendicular to the direction of current and to the magnetic field according to the three-finger rule leads to convection of the electrolyte parallel to the electrode surface. This circulation of the solution leads to a reduction in the size of the diffusion layer and therefore enables higher current densities with the same voltages. The limiting current density is proportional to with the electrolyte concentration c . ${\displaystyle q=z{\text{e}}}$ ${\displaystyle {\vec {F_{\text{B}}}}}$ ${\displaystyle c^{4/3}B^{1/3}}$

The convection currents in the electrolyte caused by the magnetic field are comparable to those caused by differences in density or by gentle stirring. You can change the shape of dendritic deposits significantly. They do not appear in a viscous electrolyte.

Possible applications

Compared to electrolysis without an additional magnetic field, magnetoelectrolysis promises improved ionic transport and thus higher current densities and greater deposition rates. The production of structured surfaces is also possible, as well as an improvement in the deposition of complex geometries, e.g. B. by filling in wells.

research

Magnetoelectrolysis is being researched e.g. B. in Germany in Bochum, Dresden and Saarbrücken, in Europe especially in Dublin.

Historical

The first experiments on magnetoelectrochemistry were carried out by Michael Faraday - albeit without conclusive results. The first publications on measurements of the Hall effect in electrolytes were made from 1896 and in the following two decades. However, the experiments suffered from various difficulties, so that reliable determinations were only possible later. Extensive research into magnetoelectrolysis began in 1974.

Alternatives to magnetoelectrochemistry

The speed of electrolytic metal deposition can also be greatly increased by vigorous stirring. In many cases this is easier or more effective than applying a strong magnetic field. By means of suitable conditions such as a high current density, gas bubble stirring can be achieved through simultaneous evolution of hydrogen. If a pump and suitable nozzles are used, the separation can be intensified at specific points, as in magnetoelectrolysis. The arrangement and shape of the counter electrode can also serve to vary the current density locally in a targeted manner; this is z. B. is also used in the opposite case, the dissolution during electrochemical lowering . Furthermore, by an insulating coating, e.g. B. by masking, the deposition can be prevented there.

Individual evidence

1. ↑ ^{a b c} Sascha Mühlenhoff: Analysis of convective transport processes during magnetoelectrolysis . Dissertation from the Faculty of Mechanical Engineering at the Technical University of Dresden. Dresden July 2012, DNB  1067732519 , urn : nbn: de: bsz: 14-qucosa-91957 .
2. ↑ Ming-Yuan Lin, Lih-Wu Hourng, Chan-Wei Kuo: The effect of magnetic force on hydrogen production efficiency in water electrolysis . 10th International Conference on Clean Energy 2010. In: International Journal of Hydrogen Energy . tape 37 , no. 2 . Elsevier, January 2012, ISSN  0360-3199 , p. 1311–1320 , doi : 10.1016 / j.ijhydene.2011.10.024 (English): “as a magnetic field is added, the electrolysis efficiency is enhanced”
3. ↑ ^{a b c d} J. Michael D. Coey: Magnetoelectrochemistry . In: European Physical Society, EDP Sciences (Ed.): Europhysics News . Magnetism. tape 34 , no. 6 , November 2003, ISSN  0531-7479 , p. 246–248 , doi : 10.1051 / epn: 2003615 (English, europhysicsnews.org [PDF; 513 kB ; retrieved on November 30, 2016] good introductory review): “At present it seems that all the various effects of magnetic fields in electrochemistry are somehow related to mass transport.”
4. ↑ ^{a b} RA eating, Leonard JJ Janssen: Applications of magnetoelectrolysis . Reviews of Applied Electrochemistry 38. In: Journal of Applied Electrochemistry . tape 25 , no. 1 . Springer, 1995, ISSN  1572-8838 , p. 1–5 , doi : 10.1007 / BF00251257 (English, tue.nl [PDF; 549 kB ; accessed on November 30, 2016] short review article on possible applications): “Improved mass transfer in cells, better deposit quality”
5. ↑ ^{a b} Magnetic Electrochemistry. In: School of Physics, Magnetism and Spin Electronics Group, Research. Trinity College Dublin, the University of Dublin, accessed on December 2, 2016 (English, beautiful examples for the effects of a magnetic field): "A uniform magnetic field has a dramatic influence on the morphology of fractal electrodeposits grown in a thin flat cell."  
6. ^ Peter Dunne, J. Michael D. Coey: Patterning metallic electrodeposits with magnet arrays . In: American Physical Society (ed.): Physical Review B . condensed matter and materials physics. tape 85 , no. 22 , June 12, 2012, ISSN  2469-9969 , 224411, doi : 10.1103 / PhysRevB.85.224411 (English, online at the TARA document server of Trinity College [PDF; 9.3 MB ; retrieved on November 30, 2016]): “Magnetic fields [...] can be used to structure electrodeposits of both paramagnetic and diamagnetic ions, in patterns reflecting the magnetic field near the cathode”
7. ↑ ^{a b} M. Weinmann, A. Jung, Harald Natter: Magnetic field-assisted electroforming of complex geometries . In: Journal of Solid State Electrochemistry . tape 17 , no. 10 . Springer, 2013, ISSN  1432-8488 , p. 2721–2729 , doi : 10.1007 / s10008-013-2172-6 : "enhance the deposition of nickel on complex 3D geometries"
8. ↑ ^{a b} Martin Weinmann: Electrochemical generation of three-dimensional structures . Dissertation to obtain the degree of Doctor of Engineering. Saarbrücken 2015, DNB  1064868541 , urn : nbn: de: bsz: 291-scidok-59811 : "By superimposing magnetic fields, it was possible to achieve an increased wall thickness for particularly critical component geometries and thus reduce the component thickness overall, which resulted in a better energy balance with a simultaneously extended service life. "
9. ↑ Kristina Tschulik: Magneto-electrochemistry. In: Research Micro- / Nano-Electrochemistry, Electrocatalysis & Functional Materials. Ruhr University Bochum, accessed on February 23, 2018 .  
10. ↑ Tom Weier, Gerd Mutschke: Magnetic control of mass transfer and convection in electrochemical processes. Investigations into the use of MHD processes in electrochemistry, magnetoelectrochemistry / magnetoelectrochemistry. (No longer available online.) In: Magnetohydrodynamics Department, Research Topics. Helmholtz-Zentrum Dresden-Rossendorf, November 9, 2016, archived from the original on December 3, 2016 ; accessed on December 2, 2016 (English): "improving the uniformity of deposits, thus saving energy and material" Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.   
11. ↑ ^{a b c d} Thomas Z. Fahidy: Magnetoelectrolysis . Reviews of Applied Electrochemistry 8. In: Journal of Applied Electrochemistry . tape 13 , no. 5 . Chapman and Hall, Springer, September 1983, ISSN  1572-8838 , pp. 553–563 , doi : 10.1007 / BF00617811 (English, abstract online [PDF; 963 kB ; retrieved on November 30, 2016] Review article with an overview of previous work): “The major practical advantage of electrolysis in magnetic fields is the attainment of large mass transport rates”