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.

1 . A hydrogen generator which includes a cascade of at least two electrolytic cells, each comprising a membrane electrode assembly incorporating a solid polymer electrolyte polarized so as to generate hydrogen from water at a cathode and oxygen at an anode, in which the membrane electrode of a first cell is at least partially exposed on one or both sides to a supply of liquid water and the hydrogen produced in this cell contacts the cathode surfaces of the or each successive electrolytic cell, wherein any water entrained in or carried over with the hydrogen produced in the first cell is the only significant feedstock for the or each successive electrolytic cell. 
     
     
         2 . A hydrogen generator as claimed in  claim 1  wherein the first and second cells share a common chamber enclosing the respective electrodes and electrode surfaces of the same polarity face each other. 
     
     
         3 . A hydrogen generator as claimed in  claim 2  wherein the common chamber incorporates a semi-porous membrane between the respective cathodes. 
     
     
         4 . A hydrogen generator as claimed in  claim 3  wherein the semi-porous membrane is hydrophobic. 
     
     
         5 . A hydrogen generator as claimed in  claim 4  wherein the semi-porous membrane is expanded polytetrafluoroethylene. 
     
     
         6 . A hydrogen generator which includes a cascade of at least two electrolytic cells, each comprising a membrane electrode assembly incorporating a solid polymer electrolyte polarized so as to generate hydrogen from water at a cathode and oxygen at an anode, in which the membrane electrode of a first cell is at least partially exposed on one or both sides to a supply of liquid water and the hydrogen produced in this cell contacts the cathode surfaces of the or each successive electrolytic cell, wherein any water entrained in or carried over with the hydrogen produced in the first cell is the only significant feedstock for the or each successive electrolytic cell; and wherein a space abutting the cathode of the first cell incorporates a semi-porous inner enclosure adjacent to said cathode and communicating with a space abutting the cathode of the second cell. 
     
     
         7 . A hydrogen generator as claimed in  claim 6  wherein the inner enclosure is essentially tubular. 
     
     
         8 . A hydrogen generator as claimed in  claim 6  wherein the semi-porous inner enclosure is expanded polytetrafluoroethylene. 
     
     
         9 . A hydrogen generator as claimed in  claim 1  wherein a space adjacent to the cathode of the first cell contains loose, porous, hydrophobic material. 
     
     
         10 . A hydrogen generator as claimed in  claim 1  wherein the solid electrolyte is a proton conducting polymer. 
     
     
         11 . A hydrogen generator as claimed in  claim 10  wherein the electrolyte is a perfluorinated sulfonic acid polymer. 
     
     
         12 . A hydrogen generator as claimed in  claim 1  wherein oxygen produced in the first cell contacts the anode surfaces of the or each successive electrolytic cell. 
     
     
         13 . A hydrogen generator as claimed in  claim 1  in which all the cells are operated at substantially the same cell potential, which generator includes a comparator for measuring the ratio of respective currents passing through the first and second cells. 
     
     
         14 . A method of generating dry hydrogen by electrolysis of water in a cascade of at least two electrolytic cells, each cell comprising a membrane electrode assembly incorporating a solid polymer electrolyte polarized so as to generate hydrogen from water at a cathode and oxygen at an anode, in which the membrane electrode of a first cell is at least partially exposed on one or both sides to a supply of liquid water and the hydrogen produced in this cell contacts the cathode surfaces of the or each successive electrolytic cell, wherein any water entrained in or carried over with the hydrogen produced in the first cell is the only significant feedstock for the or each successive electrolytic cell. 
     
     
         15 . A method of operating a hydrogen generator as claimed in  claim 14  wherein the first and second cells share a common chamber enclosing the respective electrodes and electrode surfaces of the same polarity face each other. 
     
     
         16 . A method of operating a hydrogen generator as claimed in  claim 14  wherein a space abutting the cathode of the first cell incorporates a semi-porous inner enclosure adjacent to said cathode and communicating with a space abutting the cathode of the second cell. 
     
     
         17 . A method of operating a hydrogen generator as claimed in  claim 16  wherein the inner enclosure is essentially tubular. 
     
     
         18 . A method of operating a hydrogen generator as claimed in  claim 14  wherein a space adjacent to the cathode of the first cell contains loose, porous, hydrophobic material. 
     
     
         19 . A method of operating a hydrogen generator as claimed in  claim 14  wherein the ratio of the respective currents passing through the first and second cells indicates the humidity of the hydrogen produced in the second cell. 
     
     
         20 . A method of operating a hydrogen generator as claimed in  claim 14  wherein the ratio of the respective currents passing through the first and second cells is a diagnostic of operation of the hydrogen generator.