BACKGROUND OF THE INVENTION

The Lorentz force is the combination of the magnetic and electric forces acting on a moving charged particle (e.g., an electron in electrical systems; a cation or an anion in chemical systems) in electromagnetic fields. It plays a crucial role in electronic devices, electric motors, sensors, imaging, and biomedical applications. However, because Lorentz forces are typically considered to have a small effect on chemical reactions, it has not seen routine implementation in chemistry.

SUMMARY OF THE INVENTION

Here, a model to study the influence of a magnetic field in low-voltage (e.g., 0-10V) and high-voltage (e.g., plasma-driven, 1 -300kV) electrochemical processes is described. A combination of a magnetic field (either internally or externally applied) and an ionic current (e.g., generated during electrochemical reactions) generates flow of fluids in patterns (e.g., periodic circular motions around each electrode) that could improve mass transport around individual half-cells, as well as inhibiting the mixing between the cathodic product and the anodic product. This may lead to opportunities and applications such as ionic motors, new types of fuel cells, and improved yields, energy efficiency and production rate during electrochemical reactions, e.g., the chlor-alkali reaction.

In a first aspect, the disclosure provides a system for generating liquid motion having a first electrode, a second electrode, a reservoir housing a liquid electrolyte, and a magnet disposed to provide a magnetic field in the reservoir. The first and second electrodes are in electrical or ionic conduction with the liquid electrolyte.

In some embodiments, the system has a third electrode and a fourth electrode that are in electrical or ionic conduction with the liquid electrolyte.

In some embodiments, the system has an ionically conducting membrane separating a first region of the reservoir and a second region of the reservoir. The first electrode is in electrical or ionic conduction with the first region, and the second electrode is in electrical or ionic conduction with the second region.

In some embodiments, the system has a second reservoir in ionic conduction with the reservoir by a salt bridge.

In some embodiments, the system has a bipolar electrode in the liquid electrolyte.

In another aspect, the disclosure provides a method for generating liquid motion by providing a system described herein and causing an ionic current to flow between the first and second electrodes under a magnetic field. The resulting Lorentz forces, which are the sum of electrical and magnetic forces acting on a charged particle, generate liquid motion.

In some embodiments, the liquid motion results in a first region around the first electrode and a second region around the second electrode. In some embodiments, the method includes generating a concentration or temperature gradient between the first and second regions. In some embodiments, the liquid electrolyte is aqueous sodium chloride, and the reservoir has two fluid inlets and four fluid outlets. One fluid inlet and two fluid outlets are in fluid communication with each region.

In some embodiments, the method includes generating an electrical output.

In some embodiments, the system has a membrane, and the liquid motion removes passivation layers or otherwise defouls the membrane.

In some embodiments, the current is generated under low voltage. In some embodiments, the current is generated under high voltage.

In some embodiments, the liquid motion induces a mechanical output. In some embodiments, the mechanical output is a motion of a rotor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGs. 1 A and 1 B show the effect of Lorentz forces observed in low-voltage electrochemistry with a two- electrode setup and an external magnet placed underneath (B=0.4T at the electrode surfaces). FIG. 1 A shows experimental photographs of a water splitting experiment (at 2V, using Pt electrodes and a 500mM KNO3 aqueous solution as the electrolyte), with a drop of universal pH indicator added for visualizing chemical concentrations), and FIG. 1 B shows IR images during the water splitting experiment.

FIG. 2 shows experimental photographs of a low-voltage (2V) electrochemical experiment (running water splitting) with a four-electrode setup and an external magnet placed underneath (B=0.4T at the electrode surfaces).

FIG. 3 shows simulated two-dimensional maps of magneto-hydrodynamics in experimental systems studied. Electric field E (in which ionic current flows in the same direction), the external magnetic field B (e.g., with north-side of the magnet facing up, in the positive z-direction), and the resulting Lorentz forces F _L that lead to fluidic rotations were simulated in COMSOL Multiphysics software (using finite element analysis and the particle tracing module). The size of the arrows represents the magnitude of the depicted field or force (on a log scale). Parameters used include conductivity=4 S/m, relative permittivity = 81 , and relative permeability = 1 . Currently, E = v is assumed and a constant B = 0.4Twas used for simplifying the calculations. Movement of charged particles induced by such Lorentz forces was traced over time. The velocity of the particles is faster closer to the electrodes. The anode is to the left, and the cathode is to the right.

FIGs. 4A-4C show experimental studies of the sharp concentration gradient induced by Lorentz forces. FIG. 4A shows water splitting performed in aqueous electrolytes containing gelatin, with and without an applied magnetic field (B=0.4T). FIG. 4B shows real-time pH values experimentally tracked by an external pH probe using a continuous flow setup. FIG. 4C shows an l-t curve measured by a PalmSes4 potentiostat during a water splitting experiment with (either the “N” or the “S” side of the magnet facing up) vs. without (“NM”) an applied magnetic field.

FIGs. 5A-5C show examples of Lorentz-enabled applications. FIG. 5A shows an ionic motor developed based on Cu-Zn rechargeable cell with an applied magnetic field. Chemical inputs (different oxidation states) lead to mechanical outputs (specific rotational motions of a rotary element). FIG. 5B shows magneto-hydrodynamics in an electrophoresis-type setup, in which rotational motions in the non-redox cell with salt bridges allow an ionic current to flow through. FIG. 5C shows a scheme of objects rotating in opposite directions in a Maglev-electrochemical setup with an applied magnetic field and an ionic current (going from the anode to the cathode in the electrolyte, uniform in the z-direction).

FIG. 6A and 6B show images of Lorentz effects in high-voltage (plasma) electrochemistry. FIG. 6A shows simultaneous imaging (captured by a standard and an IR camera) of plasma experiments with an applied magnetic field, and FIG. 6B shows simultaneous imaging without an applied magnetic field.

FIGs. 7A-7C show schematics of applications related to electrochemical magneto-hydrodynamics. FIG. 7A shows ring electrodes and ring magnets, FIG 7B shows the effect of Lorentz forces on a bi-polar electrochemical system, and FIG. 7C shows the effect of Lorentz forces on galvanic cells (in both singlecell and double-cell configurations).

FIGs. 8A-8C show applications of the magneto-hydrodynamics. FIG. 8A shows a one-pot reaction and purification of the chlor-alkali process. On the left, a side-view of the electrochemical cell is shown along with the reactants and products of the process. Arrows indicate an idealized uniform magnetic field being applied; the direction of the magnetic field is arbitrary, but a magnetic field direction that is perpendicular to the ionic flow is preferred. On the right, the Lorentz forces can be visualized through the arrows. FIG. 8B shows a schematic of a setup in which coupling an applied magnetic field with an electrochemical cell can lead to both an electrical output and a mechanical output. An example use of this ionic motor-driven mechanical motion is driving propellers in air and under water. FIG. 8C shows that the charging and discharging process of an electrochemical cell (e.g., with an AC current) can generate alternating fluidic rotations under Lorentz effects.

FIGs. 9A-9B show schematics for systems utilizing a magnetic field in electrochemistry. FIG. 9A shows a traditional low-voltage (0-1 OV) electrochemical setup with two (top) or four (bottom) electrodes. FIG. 9B (top) shows a high-voltage (~10kV, plasma) electrochemical setup, in which spark discharges were generated at the air-liquid interface. FIG. 9B (bottom) shows model reactions such as water splitting with inert aqueous electrolytes.

FIG. 10 shows a schematic of a simulated ratio of magnetic field strengths of a neodymium 52 bar magnet (5cm x 5cm).

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a system for generating liquid motion using the combination of electric and magnetic forces acting on a charged species, e.g., using Lorentz forces. Without wishing to be bound by theory, Lorentz force F _L is the total force exerted on a charged species in an electric field E and a magnetic field B, as shown in equations 1 -3: K (1 ) (2) fi) (3) where q is the charge carried by the ionic species, and v is the velocity of the ionic species. The forces acting upon the charged species due to the combined electric and magnetic fields cause fluid movement, e.g., in rotation around an electrode. The direction of the magnetic force is orthogonal to both the direction of the magnetic field and the direction of the ionic current. When the north side of the magnet is facing up (e.g., aligned in parallel to the surface of electrodes), the direction of the magnetic field points in the positive z-direction (FIG. 3, bottom left), the ionic current (FIG. 3, top left) goes from the first electrode to the second electrode (in x-y planes), and the resulting Lorentz forces are along the axis of rotation (in x-y planes). Particles present higher velocity in the xy-plane near and between electrodes, because of the presence of higher electric fields.

System

The invention provides a system for generating liquid motion. The system includes a first electrode and a second electrode that are in electrical or ionic conduction with a liquid electrolyte in a reservoir. The system further includes a magnet that produces a magnetic field in the reservoir. Electrical or ionic conduction may be achieved by being in direct (e.g., immersed in the liquid electrolyte) or indirect contact (e.g., separated by a gap at high voltage or separated by one or more salt bridges). Electrodes are in electrical conduction when immersed directly in the liquid electrolyte or separate by a gap under high voltage. Electrodes are in ionic conduction when separated from the liquid electrolyte by one or more ionically conducting media, e.g., a salt bridge.

The system may include any number of additional electrodes, e.g., 3, 4, 5, 6, 7, 8, 9, 10, or more. The inclusion of additional electrodes allows for more complex liquid motions, as described herein. Electrodes may be of any suitable shape, such as rings, rods, sheets, meshes, or the like. Electrodes may or may not be connected to a load or voltage source (depending on whether the cell is galvanic or electrolytic or both). In one embodiment, the system includes a bipolar electrode unconnected to load or voltage source. For example, the addition of a bipolar electrode may change the electrical field within the cell and add additional reactive surfaces. This may potentially tune the magnetic field applied to the system. Bipolar electrodes may carry different magnetic properties that can contribute to different magnetic-field patterns. For example, a diamagnetic electrode (e.g., carbon) would alter the electrical field, but it would not interfere with the externally applied magnetic field; a paramagnetic electrode (e.g., platinum) or a ferromagnetic (e.g., iron) would alter both the electric field and the applied magnetic field. In some embodiments, electrodes may be a fan-shape bipolar electrode. In high voltage embodiments, the electrodes may be separated from the liquid electrolyte by a gas gap, e.g., air, nitrogen, argon, etc. High voltage electrodes may be constructed from materials such as tungsten, iron, copper, nickel chromium alloy, or the like.

Any electrode suitable for the liquid environment may be employed, e.g., inert under the voltage and chemical conditions. Such electrodes are known in the art. Examples include platinum, carbon electrodes, e.g., glassy carbon electrodes, carbon paper electrodes, carbon felt electrodes, or carbon nanotube electrodes., gold, silver, copper, nickel, and titanium. Electrodes may be of any suitable geometry or shape, e.g., disk, wire, plate, mesh, or ring. Combinations of shapes and materials may be employed in the systems of the invention. Electrodes may be micro, e.g., having an activation radius of radius of less than 200 pm, or macro, e.g., having an activation radius of greater than 200 pm.

The system has at least a reservoir housing a liquid electrolyte. In some embodiments, the system may have a plurality of reservoirs, e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10, or the like. Multiple reservoirs may be connected via a salt bridge that provides ionic conduction between the reservoirs. A salt bridge may include any material having a background material, e.g., polymer hydrogel, agar, or gelatin, and electrolytes, e.g., inorganic electrolytes (e.g., K ⁺ , Na ⁺ , Ch, NOs-, sulfate, or the like) and/or organic electrolytes (e.g., ionic liquids). In some embodiments, the background material may be a stable polymer hydrogel. For example, the background material may include agar or gelatin. The background material may include a gel that does not need chemical crosslinking for gelation. The background material may dissolve in a salt solution through heating, and gel by cooling back to room temperature. Electrodes may or may not be present in a reservoir in which the desired liquid motion occurs.

Reservoirs may be macrofluidic or microfluidic. Microfluidic reservoirs may have a volume of about 0.1 pL to about 100 pL, e.g., about 0.1 pL to about 1 pL (e.g., about 0.1 pL, about 0.2 pL. about 0.3 pL, about 0.4 pL, about 0.5 pL, about 0.6 pL, about 0.7 pL, about 0.8 pL, about 0.9 pL, or about 1 pL), about 1 pL to about 100 pL (e.g., about 1 pL, about 10 pL, about 20 pL, about 30 pL, about 40 pL, about 50 pL, about 60 pL, about 70 pL, about 80 pL, about 90 pL, or about 100 pL), about 0.1 pL to about 10 pL, or about 10 pL to about 100 pL. Macrofluidic reservoirs may have a volume of about 100 pL to about 100,000 L, e.g., about 100 pL to about 1 mL (e.g., about 100 pL, about 200 pL. about 300 pL, about 400 pL, about 500 pL, about 600 pL, about 700 pL, about 800 pL, about 900 pL, or about 1 mL), about 1 mL to about 10 mL, (e.g., about 1 mL, about 2 mL, about 3 mL, about 4 mL, about 5 mL, about 6 mL, about 7, mL, about 8 mL, about 9 mL, or about 10 mL), about 1 mL to about 1 L (e.g., about 1 mL, about 100 mL, about 200 mL, about 300 mL, about 400 mL, about 500 mL, about 600 mL, about 700 mL, about 800 mL, about 900 mL, or about 1 L), about 1 L to about 100 L (e.g., about 1 L, about 20 L. about 30 L, about 40 L, about 50 L, about 60 L, about 70 L, about 80 L, about 90 L, or about 100 L), or about 100 L to about 100,000 L (e.g., about 100 L, about 1 ,000 L, about 10,000 L, or about 100,000 L).

A reservoir may include multiple regions separated by a membrane or other ionically conducting barrier. Each region is typically in electrical or ionic conduction with an electrode. Suitable barriers and membranes are known in the art. Membranes may be a porous media membrane or an ion-exchange membrane. A porous media membrane may include unglazed porcelain or porous sintered glass, woven fabrics made of cloth, fiberglass, nylon, polyethylene terephthalate, and microporous rubber or microporous plastic sheets of polyethylene, polyvinyl chloride (PVC), or polytetrafluoroethylene (PTFE). Ion exchange membranes may be thin sheets of polymers containing sulphonic acid or carboxylic acid groups for cation exchange membranes and amine groups for anion exchange membranes. In some embodiments, ion exchange membranes may include polystyrene cross linked with divinyl benzene, in which suitable groups are linked to the membrane for ion exchange. In some embodiments, ion exchange membranes may be chemically inert perfluoro type membranes or a metal diaphragm. In some embodiments, ion exchange membranes may include refractory materials such as p-alumina or Nascion.

Any suitable magnet may be employed. The magnet may be a permanent magnet or an electromagnet. In some embodiments, the magnet may be a permanent bar magnet placed above, below, or to the side of the reservoir. Exemplary magnetic field strengths are about 0.01 T to about 10 T, e.g., about 0.01 T to about 1 T (e.g., about 0.01 T, about 0.05 T, about 0.1 T, about 0.15 T, about 0.2 T, about 0.25 T, about 0.3 T, about 0.35 T, about 0.4 T, about 0.45 T, about 0.5 T, about 0.55 T, about 0.6 T, about 0.65 T, about 0.7 T, about 0.75 T, about 0.8 T, about 0.85 T, about 0.9 T, about 0.95 T, or about 0.1 T), or about 1 T to about 10 T (e.g., about 1 T, about 2 T, about 3 T, about 4 T, about 5 T, about 6 T, about 7 T, about 8 T, about 9 T, or about 10 T). The magnetic field strength may be about 0.2 T to about 0.5 T (e.g., about 0.2 T, about 0.3 T, about 0.4 T, or about 0.5 T).

The magnet may apply a near-uniform magnetic field, which has a negligible B _xy , and a near constant B _z , to the reservoir. Multiple magnets may be employed. For example, 1 -20 magnets may be employed with a single reservoir. Multiple magnets may or may not have the same strength, shape, or polarity facing the reservoir. Magnets may be of any suitable shape, e.g., bar or ring. In some embodiments, the magnet may be a ring magnet. In some embodiments, magnets may be selected from one or more categories including permanent magnets, temporary magnets, and electromagnets. In some embodiments, multiple categories of magnets may be employed. In some embodiments, multiple categories may or may not have the same strength, shape, or polarity facing the reservoir.

Any suitable liquid electrolyte may be employed, e.g., an aqueous electrolyte or an organic electrolyte (e.g., ionic liquids with or without molecular solvents). The liquid electrolyte may include ions suitable for ionic conduction. The electrolyte may also include other dissolved or suspended species, e.g., to react electrochemically. Solid and gaseous reactants may also be present and in contact with the liquid electrolyte. In some embodiments, ion concentrations may range from about 0.1 mM to about 20 M, e.g., about 0.1 mM to about 1 M (e.g., about 0.1 mM, about 0.2 mM, about 0.3 mM, about 0.4 mM, about 0.5 mM, about 0.6 mM, about 0.7 mM, about 0.8 mM, about 0.9 mM, about 1 M), or about 1 M to about 20 M (e.g., about 1 M, about 2 M, about 3 M, about 4 M, about 5 M, about 6 M, about 7 M, about 8 M, about 9 M, about 10 M, about 11 M, about 12 M, about 13 M, about 14 M, about 15 M, about 16 M, about 17 M, about 18 M, about 19 M, or about 20 M). Alternatively, ion concentration may range up to saturation.

The system may include additional components to carry out a specified purpose. For example, systems may include a component, such as a rotor, to convert the liquid motion into mechanical energy. The system may include multiple components, e.g., multiple rotors, to convert the liquid motion into mechanical energy. In these embodiments, the rotors can rotate in the same or opposite directions. In another example, the system includes inlets and outlets for liquids and/or gases. Additionally, a voltage source may be present in the system. In some embodiments, additional electrical conductors (e.g., bipolar electrodes) or ionic conductors (e.g., salt bridges) may be applied, as described herein.

Methods

The invention provides a method for generating liquid motion using the systems described herein. The motion may be used for any suitable purpose. For example, the motion may be used in liquid transport, liquid mixing, creation of chemical or temperature gradients, creation of mechanical energy, chemical isolation, enhancement of electrochemical reaction, and removal or passivating layers on an electrode or membrane or otherwise defouling and electrode or membrane.

The present invention can be employed in both low-voltage (e.g., 0-1 OV) and high-voltage (e.g., 1 -40 kV, plasma-driven) electrochemical cells. Based on the Lorentz effect in electrochemical systems and its resulting magneto-hydrodynamics, sharp concentration gradients and temperature gradients can be created in liquid electrolytes. Specific fluidic motions (as a result of moving ionic species in the electrochemical field crossing an external magnetic field) can directly lead to mechanical outputs without an electrical interface. Such movements may also be used to isolate chemical species in defined regions, to mix liquids, and to transport liquids in the system, e.g., as a microfluidic pump. The fluid movement may also be used to remove passivating layers or otherwise defoul membranes or electrodes, e.g., by sweeping away bubbles or debris. In some embodiments, the fluid movement can prevent the passivation of electrode surfaces, improve mixing within the region around individual electrodes, induce chemical separation between the two electrodes, and/or prevent cross-contamination between the cathodic products and the anodic products. The invention may also be used to create complex chemical concentration patterns in an analog format. When used in synthesis, the methods also sustain the electrochemical current and therefore increasing the production rate, improve the homogeneity of ionic currents and therefore increasing the production yields, and either eliminate the need for a membrane or extend the lifetime of a membrane, therefore reducing costs. For example, the creation of defined fluidic regions also allows for chemical reactions without the need for membranes, e.g., in a battery or other chemical process, such as the chlor-alkali process. The invention further provides ionic motors that utilize the electrochemical potential (from a chemical source) as the energy input, and these ionic motors output either or both electrical power (in either DC or AC format) and mechanical power (e.g., ionic-motor driven propellers in air or under water). In another embodiment, an array of electrodes may be employed to generate a plurality of regions in which the same or different chemical reactions or analyses may be carried out. For example, a single liquid, e.g., a sample, may be introduced into a reservoir with a plurality of electrodes. A region sets up around each electrode, and each region may be exposed to different reagents.

In some embodiments, magneto-hydrodynamics may require a substantial amount of electrochemical current, e.g., I>1 OOpA, if B=0.1 -0.4T because the current J directly correlates to the velocity of ionic species in the electrolyte, according to eq. 4:

J = qt Ci Vt (4) where qcation^ , q _an ion =-1 , and it is assumed that the concentration cot cations and anions are equal and homogenous across the electrolyte. As such, ions that are moving slowly, as reflected by the low current, may require a strong magnetic field B to generate a high-enough magnetic force F _B , to overcome fluidic inertia and result an observable magneto-hydrodynamic effect.

In some embodiments, the high-voltage set up may amplify the Lorentz effect because of the greater electrochemical current, orders of magnitude higher, e.g., 5-100A, than low-voltage electrochemical processes, e.g., pA-mA. In low-voltage electrochemical process embodiments, the required magnetic field to achieve the Lorentz effect may be lower when the current is higher

In some embodiments, the electrodes may be surrounded by one or more atmospheres, e.g., Ar, N2, He, or the like. For example, the electrodes may be in an H2 atmosphere for fuel cell applications.

EXAMPLES

Example 1 :

Referring now to FIGs. 9A-9B, a neodymium 52 bar magnet (5cm x 5cm) was used for each experiment. The magnet was placed directly under the electrochemical cell (the center of the magnet is in line with the center between the cathode and the anode). According to experimental measurements, B = 0.4 T when the distance of separation = 5 mm between the surface of the electrode and the top surface of the magnet.

In a low-voltage electrochemical setup (FIG. 9A), platinum electrodes (with an inert Teflon shell wrapped around (dsheii = 8mm) and an active electrode surface at the bottom (dpt= 2mm)) were used as both the cathode and the anode. The distance between the surface of the liquid electrolyte and the surface of Pt was 2 mm. The distance between the surface of Pt and the surface of the magnet placed underneath the setup was 5 mm.

In the two-electrode setup, the distance between the center of the cathode and the center of the anode was 1 .5 cm. In the four-electrode setup, the distance between the center of the cathode and the center of the anode was 2.0 cm. In both low-V setups, a Ag/AgCI reference electrode was placed near the edge of the electrochemical cell to minimize its interference on fluid dynamics (as it is a physical obstacle immersed in the fluid). 2 V was applied to an aqueous solution of inert electrolytes (e.g., 0.5 M KNO3) for water to react (FIG. 9B, right). For every two moles of electrons transmitted, one mole of hydrogen and two moles of hydroxide anions were produced at the cathode; half mole of oxygen and two moles of protons were produced at the anode. The value of pH near the cathode increases, whereas the value of pH near the anode decreases over time.

In the high-voltage (plasma) electrochemical setup (FIG. 9B), tungsten electrodes (d = 2.4mm) were used as both the cathode and the anode. The horizontal distance between the electrodes was set at 2.5 cm, and the vertical distance between the electrode tip and the aqueous electrolyte was set at 2 mm. The distance between the surface of the liquid and the surface of the magnet was 5 mm. 10 kV was applied between the electrodes, generating a negative discharge at the cathode and a positive discharge at the anode. Instead of discharging from the cathode to the anode directly through air (which has a conductivity of ~10' ¹⁰ S/cm), electrical discharge went through the liquid electrolyte (which has a higher conductivity of ~10' ³ S/cm) with plasma-driven electrochemical reactions happening at the air-liquid interface.

Specifically, the negative plasma (generated at the cathode) would induce reduction reactions at the airliquid interface underneath of the cathode, and the positive plasma (generated at the anode) would induce oxidation reactions at the liquid-air interface underneath of the anode.

FIG. 10 shows a 2D map of simulated ratio between the magnetic field strength in the z- (vertical) and x- (horizontal) directions. At the top of the magnet, B _z is dominant at the center (+/- 5mm) with a B _z /B _x ratio of over 10. However, as distance from the center in the x-y plane occurred, B _z decreases and B _x (and By) increases to the same order of magnitude near the edge of the magnet (+/- 25mm).

Example 2:

We designed a simple two-electrode setup (FIG. 1 A) to explore the effect of an external magnetic field on an electrolytic cell. A permanent bar magnet was placed underneath the cell, applying a near-uniform magnetic field (with a negligible B _xy and a near-constant B _z throughout the cell) to the electrochemical system. (See Example for details.)

Water splitting was used as a model reaction to study Lorentz effects on electrochemical systems. Experimental results show that, when the magnet’s south side is facing up (i.e. , magnetic field lines pointing down in the z-direction) while the voltage is on, the liquid electrolyte rotates clockwise around the cathode but counter-clockwise around the anode in the x-y plane. When either the polarity of the magnet was flipped (i.e., north facing up instead) or the applied voltage was flipped (i.e., anode on the left and cathode on the right instead), fluidic rotational directions flipped accordingly. These rotational directions were confirmed by using tracer particles (6pm latex microspheres) and by videoing using an IR camera (FIG. 1 B).

Surprisingly, a chemical concentration “interface” (in the case of water splitting, a sharp [H ⁺ ] gradient observed via pH indication) emerged over time between the cathode and the anode with an “interface” observed in the y-z plane (FIG. 1 A) driven by magneto-hydrodynamics.

When the voltage was first turned on, initial fluidic accelerations (caused by Lorentz forces) were captured by an IR camera (FIG. 1 B). A temperature interface in the y-z plane emerged within the first 2s and sustained throughout the experiment with the presence of an external magnetic field. Interestingly, a temperature interface was observed at the same position as the concentration interface. The reaction vessel was heated over time because of the redox production (at the electrode surfaces) and the exothermic dissolution of the products (in the case of water splitting, OH- at the cathode and H ⁺ at the anode).

Example 3:

To demonstrate the reliability of our experimental system with tunable electrochemical and magnetic fields that can lead to interesting interfacial patterns and applications, the same water splitting experiment as in Example 2 on a four-electrode setup was performed (FIG. 2). Details and dimensions of the electrochemical cell are discussed in Example 1 . Experimental results show that the direction of fluidic motions observed in the four-electrode setup are consistent with observations from the simple two-electrode setup. When the magnet’s south side is facing up, the electrolyte rotates clockwise around the cathode but counter-clockwise around the anode.

This array of clockwise- and counterclockwise-vortices led to a chess-like pattern made of distinct regions of different chemical concentrations. These results may be an example of how one could engineer complex fields (either electrochemical or magnetic) that lead to desired chemical (and potentially thermal) patterns.

These 2D-planar interfaces (of concentration and temperature) only emerged with an applied magnetic field. Upon removal (or without the presence) of the external magnet, these interfaces became visually vague and geometrically less-well defined. Both the concentration difference and the temperature difference depleted over time through diffusion and reaction (e.g., acid-base neutralization).

Example 4:

Simulation of the magnetic field around the magnet (FIG. 10) shows that, based on our current setup, the electrochemical cell primarily experiences B _z . However, the magnetic field is not uniform (e.g., decreasing B _z in the positive z-direction; decreasing B _z /B _x as ions move away from the z-axis, across the x-y plane).

Based on calculations, the electric force F _E is orders of magnitude lower than the magnetic force F _B in this electrochemical cell. The Lorentz force F _L therefore approximates to the direction and the magnitude of F _B . These Lorentz forces exerted on ionic species led to an acceleration, based on F=ma, and ultimately to the vortex-like moving trajectories of the bulk fluid.

In FIG. 3 (bottom right), charged particles were added to the simulated system (with Lorentz forces), and movement was tracked over time. Results show that, in such conditions, charged species would perform a circular motion around the electrode - as seen experimentally. The simulation allows us to visualize that particles present higher velocity in the xy-plane near and between electrodes, due to the presence of higher electric fields. The agreement between simulated and experimental data allows us to better understand the physics of the studied magneto-hydrodynamics and quickly explore different setups.

Our experimental observations from using water splitting as a model reaction should apply to all electrochemical systems and reactions (e.g., electrolytic cells, galvanic cells, electrochemical systems connected by salt bridges, high-voltage electrochemical setups etc.).

Example 5:

To investigate the degree of chemical separation achieved by our experimental setup, pH measurements were conducted, the size of the concentration “interface” was imaged, and the current profile was measured over time with and without an applied magnet in our model system (i.e., water splitting) as shown in FIGs. 4A-4B.

Results show concentration “interfaces” (with a sharp concentration gradient over a small distance of <1 mm) formed in the electrolyte solution (FIG. 4A), as a result of Lorentz effects (i.e., electrochemical magneto-hydrodynamics). Experimental measurements show that Lorentz forces can enhance the concentration difference (between LHS and the RHS of the cell) by three orders of magnitude within 4 mins (FIG. 4B). Chemical separation and homogenous mixing (around individual electrodes) are important functions of our system that can be directly applied to one-pot reaction and purification processes, such as improving the energy efficiency and reducing the cost of chlor-alkali reaction.

In addition to chemical separation, experimental results were obtained (FIGs. 5A-5C) that demonstrate the potential of a range of applications, such as ionic motors that convert chemical inputs into mechanical outputs without the need of an electrical interface (FIG. 5A) and non-reactive magneto-hydrodynamics induced by a non-redox ionic flow using a setup that is similar to electrophoresis (FIG. 5B). This is also useful for electrochemical separations; and a combination of magnetic levitation with electrochemistry leads to controlled rotations of objects levitated based on density, which is useful as a non-contact method for 3D assembly (FIG. 5C).

Example 6:

A high-voltage setup (FIGs. 6A-6B), in which 10kV was applied between two tungsten electrodes was performed. Spark discharges were generated between the solid electrode and the aqueous electrolyte through an air gap, inducing an ionic current passing through the liquid phase. See Example 1 for details.

Experimental results show that, with an applied magnetic field (FIG. 6A), rotational motions were observed in the liquid phase as soon as plasma was turned on. Specifically, when the south side of the magnet is facing up, the liquid rotates clockwise around the cathode and counter-clockwise around the anode. A concentration interface (with pH>12 near the cathode and pH<2 near the anode) was observed within seconds of electrical discharge.

Control experiments without any applied magnetic field (FIG. 6B) show that the fluidic motion was rather random, created by the plasma plunging through the air-liquid interfaces underneath of the two electrodes. Heat (transferred from the plasma to the electrolyte) was less well dissipated (in the case of no magnet and no fluidic rotations) compared to the Lorentz experiment (in the case of having magnetohydrodynamics and fluidic rotations).

Note that observable magneto-hydrodynamics require a substantial amount of electrochemical current (e.g., I>1 OOpA, if B=0.1 -0.4T). This is because the current J directly correlates to the velocity of ionic species in the electrolyte, according to eq. 4, described above, where q _ca tion^ , q _an ion =-1 , and it was assumed that the concentration cof cations and anions are equal and homogenous across the electrolyte.

Based on equation 3 discussed previously, if ions were moving slowly (as reflected by the low current), a strong magnetic field B is required to generate a high-enough magnetic force F _B to overcome fluidic inertia and result in an observable magneto-hydrodynamic effect.

One advantage of the high-voltage system is its amplified Lorentz effect. This is because its electrochemical current is orders of magnitude higher (e.g., 5-100A) than low-voltage electrochemical processes (e.g., pA-mA). Based on eq. 4 discussed above, ionic species move at higher velocities in plasma-driven electrochemical systems. Additionally, ionic species move at higher velocities in high- voltage electrochemical systems, which have lower viscosity and lower collision frequency compared to low-voltage electrochemical systems. Even a weak magnetic field (~pT) may lead to experimentally observable effects such as the resulting fluid hydrodynamics, concentration gradients, and thermal gradients.

Being completely non-contact is another advantage of the high-voltage setup. Both electrodes are in the gas phase, an air gap away from the liquid electrolyte, and the magnet is placed on the outside of the electrochemical cell. This eliminates possible interference on the magneto-hydrodynamics from any physical obstacle in the fluid, the accumulation of bubbles, or the passivation of electrodes.

Note that the current plasma experiments were done in air (composed of -80% N2 and -20% O2), in which both N2 and O2 can be ionized and contribute to redox reactions in the gas phase. Different atmospheres may be employed, e.g., using Ar to eliminate side reactions in the gas phase or using H2 for fuel cell applications.

Example 7:

We can tune fluid dynamics to generate complex patterns by using electrodes and magnets of various shapes. Simulations of different electro-magnetic fields and corresponding Lorentz forces can be used to predict experimental designs. FIG. 7A (left) shows magnetic field lines of a ring magnet and FIG. 7A (right) shows an experimental setup that contains a ring electrode, as an example that could lead to complex fluid dynamics. Within the x-y (horizontal) plane, the magnetic field direction flips from pointing downwards within the inner circle of the ring magnet to pointing upwards between the inner and outer circle of the ring magnet. This radial change in magnetic field direction can lead to interesting fluidic behaviors (and chemical concentration patterns in an analog format, rather than digital, as observed in our current experimental systems) as ions are moving radially across from one electrode to another. Preliminary experiment shows that it is possible to generate a radial electrical field by having a rod-shape electrode inserted at the center of a ring-shape electrode (FIG. 7A, right).

A system of investigating the effect of Lorentz forces on bi-polar electrochemistry was also designed (FIG. 7B), which is complementary to the direction of generating complex patterns of fluidic flow and chemical concentration gradients. The addition of a bipolar electrode changes the electrical field within the cell, adds additional reactive surfaces, and can potentially tune the magnetic field applied to the system. Bipolar electrodes may carry different magnetic properties that can contribute to interesting magnetic-field patterns. For example, a diamagnetic electrode (e.g., carbon) would only alter the electrical field, but it does not interfere with the externally applied magnetic field; a paramagnetic electrode (e.g., platinum) or a ferromagnetic (e.g., iron) would alter both the electric field and the applied magnetic field.

Lorentz forces can also influence the performance of galvanic cells and rechargeable battery- related systems. Using a Zn-Cu system in either a single-cell or a double-cell configuration, shown in FIG. 7C, as an example, it was experimentally observed that an applied magnetic field leads to an increase in the electrochemical current. This increase can be explained by i) Lorentz forces enhance mass transport of molecules near electrode surfaces, and ii) magneto-hydrodynamics in the bulk drive electrode-passivating species (bubbles or oxidation products that are non-conductive) off from electrode surfaces, increasing the active surface area of the electrodes. Example 8:

The chlor-alkali reaction is the top electrochemical process used in industry, for the production of chlorine, hydrogen, and sodium hydroxide. Current process uses brine (26% NaCI) and water as two separate reagents in each half cell (FIG. 8A). At the anode, chloride is oxidized into chlorine; at the cathode, water is reduced into hydrogen, and hydroxide is produced at the same time. An ion-exchange membrane is necessary in the current industrial process, as chlorine reacts with water to form acids (e.g., HCIOx and HCI), which would react with the base near the cathode if it was not separated. With an applied magnetic field, magneto-hydrodynamics can lead to chemical separation without needing a separation membrane. This method will reduce the membrane cost, which currently contributes to the annual maintenance cost. Furthermore, the ion-exchange membrane is susceptible to contaminant ions present in the brine (Mg ²⁺ , Ca ²⁺ ) and the high-pressured gases produced, which shorten its lifetime. Last, the membrane-based cells must be powered by constant energy sources, as its gas pressures must remain balanced. The use of a membrane-free cell allows intermittent sustainable energy sources (solar, wind) to be applied.

Achieving homogenous current distribution (i.e. , mixing) is another challenge in the current chlor-alkali industrial process. As our experimental results have shown that fluidic rotations increase mixing and can reduce the voltage required to sustain a specific current (i.e., production rate), our method applied to this system can improve its energy efficiency (e.g., 10mV decrease in operating voltage leads to $2M/yr cost savings per industrial-scale setup).

Example 9:

The invention also provides ionic motors (e.g., use magneto-hydrodynamics to generate a mechanical output, as shown in FIG. 8B). Existing electric motors convert electrical energy into mechanical energy through the interaction between an applied magnetic field and an electric current in a wire winding to generate force (in the form of torque) applied on the motor’s shaft. In an ionic motor, electrochemical reactions with an applied magnetic field can lead to parallel electrical (if needed) and mechanical outputs, with improved energy efficiency. This can be useful for driving electrochemically-powered propellers in air or in ocean. An AC system (e.g., over rapid charging and discharging cycles) with an applied magnetic field will lead to alternating fluidic motions (FIG. 8C).

OTHER EMBODIMENTS

While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifications and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the invention that come within known or customary practice within the art to which the invention pertains and may be applied to the essential features hereinbefore set forth, and follows in the scope of the claims. Other embodiments are within the claims.