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Oxygen generation apparatus and method

Oxygen generation apparatus and method description/claims

The invention relates to an oxygen generation apparatus and a method of generating oxygen. In particular, it is concerned with the generation of oxygen for use in the treatment of wounds and sores. However, it will be clear to those skilled in the art that the invention also has many other applications requiring oxygen or hydrogen generation. However, it will be clear to those skilled in the art that the invention also has many other applications requiring oxygen or hydrogen generation.

There is evidence in the literature that the supply of oxygen to a wound site can promote the healing of the wound. This applies to both humans and animals. Topical oxygen therapy, as it is known, encourages the growth of fresh skin tissue to close and heal wounds. It is believed that oxygen dissolves in tissue fluids and improves the oxygen content of the intercellular fluids.

Various methods have been described for the supply of oxygen to wounds. In some instances, the affected limb is placed in a chamber (U.S. Pat. No. 4,003,371 and U.S. Pat. No. 3,744,491) or a bag (U.S. Pat. No. 5,154,697 and U.S. Pat. No. 5,478,310) of oxygen that is fed from an oxygen cylinder. This approach is impractical for many patients as it restricts the mobility of the patient and necessitates the use of control valves to control the flow of oxygen. Furthermore, when healthy skin is exposed to gasses containing high concentrations of oxygen, it is possible that vasoconstriction and tissue destruction may occur.

In an alternative approach, U.S. Pat. No. 5,578,022, U.S. Pat. No. 5,788,682 and U.S. Pat. No. 5,855,570 describe devices that are incorporated into or above bandages that are placed over the wound. The oxygen is produced electrochemically by ionisation of the oxygen in the air at a cathode to form hydrogen peroxide that dissolves in a proton-conducting membrane adjacent the cathode. The hydrogen peroxide diffuses through the membrane to an anode where the hydrogen peroxide is decomposed to form water and pure oxygen that is transmitted to the wound.

The presence of hydrogen peroxide is not welcomed by physicians as it can kill healthy cells. It is desirable to be able to produce pure oxygen for healing of wounds without the use of a hydrogen peroxide intermediate; Unfortunately, all known proton-conducting membranes are highly acidic and under these conditions hydrogen peroxide is formed when oxygen is ionised at a cathode.

The invention provides an oxygen generation apparatus, a catalytic apparatus, a method of reducing hydrogen venting, a method of generating oxygen, and a method of supplying water as defined in the appended independent claims, to which reference should now be made. Preferred or advantageous features of the invention are defined in dependent sub-claims.

An oxygen generator for an oxygen-generation apparatus according to the invention comprises a proton-conducting membrane, a cathode contacting a first side, or cathodic side, of the membrane, an anode contacting a second as side, or anodic side, of the membrane, and a source of water for supply to the membrane. In use, an electrolysis voltage applied between the cathode and the anode causes electrolysis of the water to generate oxygen gas at the anode. Atmospheric oxygen, i.e. oxygen in the air, is substantially prevented from coming into contact with the cathode. For an acidic proton-conducting membrane this may substantially prevent the formation of hydrogen peroxide at the cathode.

The use of a proton-conducting membrane as an electrolyte is known from fuel-cell technology. One example of a suitable proton-conducting membrane is Dupont Nafion®, a perfluorosulfonate polymer that is highly permeable to water.

Water may be supplied to the proton-conducting membrane at its anodic side, i.e. the side of the membrane contacting the anode. If this is the case, dissociation of water takes place at the anode and protons migrate to the cathode, where they are discharged as hydrogen, and oxygen is discharged at the anode. In such a case the evolved oxygen may contain a larger proportion of water than in the alternative embodiments described below and oxygen may need to be separated from this water before use. The hydrogen discharged at the cathode may contain liquid water, due to hydration of the migrating proton, and this may need to be separated from it if the hydrogen is to be used.

Water may be supplied to the proton-conducting membrane at its cathodic side, i.e. the side of the membrane contacting the cathode. In this case water diffuses through the membrane, for example controlled by a concentration gradient. Hydrated hydrogen ions may migrate through the membrane due to the electro-osmotic flux proportional with the cell current. Oxygen produced by electrolysis of the water at the anode may advantageously be substantially free of water or contain a lower level of water vapour, unless water is also simultaneously being supplied on the anodic side of the membrane.

In a preferred embodiment water may, advantageously, be supplied to the proton-conducting membrane from an edge or edges of the membrane. Water supplied in such a way may, preferentially, saturate the entire membrane by diffusion.

Water may alternatively be supplied to the proton-conducting membrane by a combination of the possibilities described above, for instance from an edge and from the cathodic side simultaneously.

Hydrogen generated at the cathode may be vented directly to the atmosphere. Preferably a vent or vent means of a pre-determined shape and dimensions is provided such that the rate of hydrogen generation at the cathode produces a hydrogen flow through the vent, which is sufficient to prevent the substantial inflow of atmospheric oxygen through the vent. As described above, if oxygen contacts the cathode during electrolysis it may be ionised and disadvantageously form hydrogen peroxide. The required shape and dimensions of the vent to prevent substantial in-flow of air or atmospheric oxygen will depend upon the volume and rate of hydrogen produced by the generator. The volume of hydrogen produced in a given time may depend on a number of factors such as applied voltage, area of membrane and volume of membrane.

The vent or vent means may comprise one or more vents, or may comprise a gas-permeable membrane through which the hydrogen flows or diffuses. The vent or vent means may also, or alternatively, comprise one or more one-way valves.

Optionally, the hydrogen may flow into a cathode chamber before being vented to the atmosphere from the cathode chamber.

Hydrogen generated at the cathode may advantageously flow or diffuse away from the cathode through a gas-permeable membrane. Such a membrane may act as, or form part of, the vent or vent means and may advantageously prevent ingress of contaminants such as dust and/or liquid to the cathode and the proton-conducting membrane. Advantageously, such a gas-permeable membrane may be arranged either in contact with the cathode or spaced from the cathode.

Advantageously, hydrogen generated at the cathode may be used, for example as a standard gas supply for calibration.

In a further aspect of the invention, the oxygen-generation apparatus may comprise an oxidation catalyst at which hydrogen generated at the cathode reacts with atmospheric oxygen.

Advantageously, oxygen in the atmosphere may be prevented from reaching the cathode by the chemical reaction at the oxidation catalyst with the cathodically-generated hydrogen. The presence of the oxidation catalyst may also advantageously reduce or eliminate the volume of hydrogen vented to the atmosphere.

In certain circumstances, particularly where volumes of hydrogen generated are high, if the hydrogen is vented to the atmosphere it may concentrate in the region of the oxygen generator and form a potential explosion risk. A generator in which the volume of hydrogen vented to the atmosphere is reduced or is eliminated may therefore pose less of a safety risk than one that does vent hydrogen to the atmosphere (that is one in which provision is not made to reduce or eliminate hydrogen venting).

The oxidation catalyst may comprise any material that catalyses the reaction between hydrogen and oxygen. A particularly efficacious catalyst is platinum. Platinum may be present for example in the form of a foil or as a sputtered coating or as platinum particles loaded into a matrix, such as a carbon matrix.

Preferably the product of the reaction between hydrogen and atmospheric oxygen at the oxidation catalyst is water. Advantageously, such water may be returned to a source of water for supplying water to the proton-conducting membrane or returned directly to the proton-conducting membrane itself. Water consumed during electrolysis may thereby be replenished by water formed by the reaction of electrolytically-produced hydrogen and atmospheric oxygen at the oxidation catalyst.

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