Water electrolyzer

Abstract

A direct impure water electrolysis (DIWE) approach generates green hydrogen in a modified proton-exchange membrane pure water electrolyzer (PEM-PWE), that avoids fouling, corrosion, deactivation, and side reactions normally caused by the ions in impure or saline waters. Conventional electrolyzers require ultrapure deionized (DI) water as feed because: 1) the proton-exchange membrane (PEM) and electrocatalysts are readily poisoned by the anions, e.g., chloride, and cations, e.g., sodium, calcium, and magnesium that are present in seawater or brackish water; and 2) the chloride anions readily form chlorine at the PEM-electrolyzer anode, which is toxic and corrosive. This adds substantially to the cost and complexity of the electrolyzer plant due to the water treatment plant needed for producing ultrapure DI water. The tolerance of impure water as described herein avoids reverse osmosis and deionization requirements steps which is beneficial for use in semi-arid regions with a paucity of fresh water.

What is claimed is: 
     
         1 . An electrolysis device, comprising:
 an anode in an anode flow field in fluid communication with an aqueous input;   a cathode in a cathode flow field configured for passing a gaseous product;   a proton-exchange membrane disposed between the anode flow field and the cathode flow field;   a voltage source connected between the anode and the cathode for imparting a voltage differential across the proton-exchange membrane; and   a selective membrane between the anode and the aqueous input for preventing passage of contaminants in the aqueous input.   
     
     
         2 . The device of  claim 1  wherein the selective membrane is a porous hydrophobic layer permeable to water vapor. 
     
     
         3 . The device of  claim 2  wherein the selective membrane is a hydrophobic membrane resistive to the passage of liquid water and ions and contaminants therein. 
     
     
         4 . The device of  claim 1  wherein the selective membrane is hydrophobic and permeable to water vapor and gaseous products. 
     
     
         5 . The device of  claim 1  wherein the anode flow field includes an anode layer and an anode catalyst layer, the anode layer electrically coupled to the aqueous flow and the anode catalyst layer in communication with the proton-exchange membrane. 
     
     
         6 . The device of  claim 5  wherein the anode layer includes titanium and the anode catalyst layer includes iridium, the iridium contributing to an oxygen evolution reaction separating protons and electrons from oxygen. 
     
     
         7 . The device of  claim 1  wherein the cathode flow field includes a cathode layer and a cathode catalyst layer, the cathode layer electrically coupled with the gaseous product in the cathode flow field. 
     
     
         8 . The device of  claim 7  wherein the cathode layer includes graphite and the cathode catalyst layer includes platinum, the platinum contributing to a hydrogen evolution reaction forming hydrogen gas (H 2 ). 
     
     
         9 . The device of  claim 2  wherein the porous hydrophobic layer includes at least one of polymeric, ceramic, or carbon materials based on a hydrophobicity and pore size for passing water vapor and hydrogen and oxygen gas while retaining liquid water and contaminants therein. 
     
     
         10 . The device of  claim 7  wherein a heat of vaporization at the selective membrane is generated by heat resulting from an oxygen evolution reaction (OER) occurring at the anode. 
     
     
         11 . The device of  claim 10  wherein the heat of vaporization at the selective membrane is received from a heat of vapor condensation within an ionomer layer in the cathode catalyst layer in communication with the cathode flow field. 
     
     
         12 . A proton-exchange membrane water electrolyzer flow cell device for impure water comprising:
 a cathode configured to be in fluid communication with a hydrogen recovery system configured for gas dehydration and water recycling;   an anode configured to be in fluid communication with a direct impure water source and an oxygen recovery system;   a hydrogen evolution catalyst layer in contact with the cathode;   a proton-exchange membrane (PEM) in contact with the hydrogen evolution catalyst layer;   an oxygen evolution catalyst layer in contact with an opposed side of the PEM and an anode; and   a porous hydrophobic layer (PHL) in contact with the anode and the direct impure water feed.   
     
     
         13 . The flow electrolyzer cell device of  claim 12 , wherein the porous hydrophobic layer (PHL) provides only pure water vapor to pass to the anode, an anode flow field allowing oxygen to egress, the porous hydrophobic layer configured to retain dissolved ions, nonvolatile and particulate water impurities on an impure water feed side of the PHL; the impure water feed side configured to expel the impure water feed and the egressed oxygen. 
     
     
         14 . The flow electrolyzer cell device of  claim 12 , further comprising a PHL-water interface defined by contact of the impure water feed with the PHL, a water vaporization process at the PHL-water interface utilizes the heat produced within the electrolyzer flow cell device. 
     
     
         15 . The flow electrolyzer cell device of  claim 12 , wherein the cathode is in fluid communication with the water recovered from the hydrogen recovery system. 
     
     
         16 . The flow electrolyzer cell device of  claim 12 , wherein a second porous hydrophobic layer is disposed between the cathode and a hydrogen flow channel. 
     
     
         17 . The flow electrolyzer cell device of  claim 16 , further comprising a second direct impure water feed to the cathode. 
     
     
         18 . The flow electrolyzer cell device of  claim 12 , wherein the porous hydrophobic layer includes at least one of polymeric, ceramic and carbon materials for providing a predetermined hydrophobicity. 
     
     
         19 . The flow electrolyzer cell device of  claim 12 , wherein the PEM further comprises a liquid electrolyte supported on a polymeric or a ceramic support and encapsulated by the PHL. 
     
     
         20 . A system comprising:
 a source of water that has been pretreated to remove particulate and microbial impurities but without the reverse osmosis (RO) or the deionization (DI) steps and thus retains salts and soluble minerals normally present in impure water sources such as city water, saline water, and sea water;   a source of electrical power that has been conditioned appropriately to provide DC power to the electrolyzer cells; and   a balance of plant to recover oxygen from the anode exhaust stream and discard or reuse the remaining impure water;   a balance of plant to recover hydrogen from the cathode exhaust stream and recycle the recovered water to the electrolyzer cells or for other use as pure desalinated water;   a plurality of flow electrolyzer cells in fluid communication with the sources of impure water, the flow electrochemical cells comprising:   
       an anode comprising of an oxygen evolution catalyst,
 a cathode comprising of a hydrogen evolution catalyst, 
 a proton-exchange membrane in contact with the anode and the cathode, respectively, 
 a first porous hydrophobic layer between the anode and the flow plate, and/or 
 a second porous hydrophobic layer between the cathode and the flow plate, wherein the flow electrolyzer cells are configured for hydrogen and oxygen generation and electrical energy storage.