Hydrogen generation

Abstract

A hydrogen generator includes at least two electrolytic cells, each comprising a membrane electrode assembly incorporating a solid polymer electrolyte. The membrane electrode of a first cell is exposed to water and the hydrogen produced in this cell contacts the cathode surfaces of the successive electrolytic cells, wherein any water entrained in or carried over with the hydrogen produced in the first cell is the only significant feedstock for the successive electrolytic cells.In some embodiments, the first and second cells share a common chamber enclosing the respective electrodes. Hydrogen generated by the first cell diffuses into an expanded polytetrafluoroethylene tube adjacent to the cathode. The tube discharges into a space abutting the cathode of the second cell.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application draws priority from the following U.K. Patent Applications: (i) GB 1013368.4 filed on 9 Aug. 2010 and (ii) GB 1019831.5 filed on 23 Nov. 2010.FIELD OF THE INVENTION[0002]This invention concerns the electrolysis of water to form hydrogen.BACKGROUND AND RELATED ART[0003]Hydrogen is used in large quantities in oil refining, for example in the breaking down large hydrocarbon molecules into smaller ones in the process known as hydrocracking. It is also used in manufacture of ammonia by the Haber process. Such hydrogen is usually sourced from the reaction of a fossil fuel, typically coal or methane, with water.[0004]Hydrogen is also required as a chemical intermediate in various synthetic processes. In semiconductor manufacture it is occasionally required in an ultrapure state. It is used as a specialist fuel source, for example in the operation of flame ionisation detectors. Hydrogen is also widely recognised as a clean altern...

AI Technical Summary

Benefits of technology

[0017]Embodiments of the present invention enable electrochemically produced hydrogen to be dried not only more efficiently, but also so as to eliminate the need for condensate removal. Embodiments of the present invention confer an increased efficiency on a hydrogen electrolyser, and afford a diagnostic for monitoring the dryness of hydrogen produced by the water generator.

[0021]In some embodiments, the first and second cells share a common chamber enclosing the respective electrodes. Electrode surfaces of the same polarity face each other. In order to reduce the quantity of water being carried from the first to the second cell, the common chamber incorporates a semi-porous membrane between the respective cathodes.

[0028]In every embodiment of the invention, it is necessary for there to be some region of confinement of water in the primary cell in contact with its membrane electrode assembly. It is usually convenient for this contact to be made at the cathode. It is frequently an advantage to confine such water with a material such as porous PTFE which allows for the facile passage of gas, but prevents passage of water droplets from one location to another.

Problems solved by technology

Any inefficiency in hydrogen production is manifest as waste heat.

However, according to the present art, alkaline electrolytes are typically liquids, which afford a particular risk of gas migration between the anode and cathode, and often carry a hazard associated with their being highly caustic.

Any admixture of the two gases in the vicinity of the cathode or anode substantially reduces the cell efficiency, because hydrogen at an anode is more readily oxidised to protons than water to oxygen, and oxygen at a cathode is more readily reduced to water than protons to hydrogen.

Moreover, mixtures of pure hydrogen and oxygen, particularly in the ratio of 2:1 in which they are formed by electrolysis, can be explosive.

These restrictions are all liable to blockage by water condensate, particularly in view of hydrogen exiting the cell being warm and therefore prospectively being inclined to condensation.

Whilst very effective, a Peltier requires considerable electrical power and therefore is a distinct disadvantage in a portable and battery operated tool.

Further, the condensed water trapped by any means needs to be removed and is liable to migrate where it is not wanted when the Peltier cooler is turned off.

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