Pem fuel cell power systems with efficient hydrogen generation

Abstract

Methods and devices for generating power using PEM fuel cell power systems comprising a rotary bed reactor for hydrogen generation are disclosed. Hydrogen is generated by the hydrolysis of fuels such as lithium aluminum hydride and mixtures thereof Water required for hydrolysis may be captured from the fuel cell exhaust. Water is preferably fed to the reactor in the form of a mist generated by an atomizer. An exemplary 750 We-h, 400 We PEM fuel cell power system may be characterized by a specific energy of about 550 We-h/kg and a specific power of about 290 We/kg.

What is claimed: 
     
         1 . A method of producing power using a fuel cell power system, the method comprising:
 providing an open cathode PEM fuel cell stack comprising a plurality of fuel cells, each cell having an anode side and a cathode side that enables operation of the cathode side at substantially ambient pressure;   feeding water from a water storage to a rotary bed reactor to generate hydrogen by the hydrolysis of a fuel in the reactor;   routing hydrogen to the anode side of the fuel cell stack at a rate that is excess of that required by the fuel cell stack for producing power and a recirculation hydrogen stream;   enriching recirculation hydrogen exiting the anode with water; and,   routing the water-enriched recirculation hydrogen stream to the reactor.   
     
     
         2 . The method of  claim 1 , wherein the feeding water step comprises feeding water from the water storage during start-up and stopping water feed during operation. 
     
     
         3 . The method of  claim 1  wherein the feeding water step comprises feeding water from the water storage at a first flow rate during start-up and reducing the water feed rate to a rate that is below the first flow rate during operation. 
     
     
         4 . The method of  claim 1  further comprising converting liquid water from the water storage to a mist comprising a plurality of water droplets using an atomizer and feeding the water mist to the reactor. 
     
     
         5 . The method of  claim 1  wherein the enriching step comprises increasing the water content of the recirculation hydrogen stream by water exchange with the wet cathode exhaust stream using a humidifier. 
     
     
         6 . The method of  claim 1  wherein the enriching step comprises:
 condensing water from the cathode air exhaust; 
 converting the condensed water to a mist comprising a plurality of water droplets using an atomizer; and, 
 entraining the water mist in the recirculation hydrogen stream. 
 
     
     
         7 . The method of  claim 1  wherein the enriching step comprises splitting the recirculation hydrogen stream into a first recirculation stream and a second recirculation stream using a 3-way valve and routing the first recirculation stream, to a humidifier and the second recirculation stream directly to the reactor bypassing a humidifier. 
     
     
         8 . The method of  claim 1  wherein the fuel comprises lithium aluminum hydride. 
     
     
         9 . The method of  claim 1  wherein the fuel comprises an admixture of lithium aluminum hydride and an additive comprising at least one of AlCl 3 , MgCl 2 , BeCl 2 , CuCl 2 , LiCl, NaCl, and KCl. 
     
     
         10 . The method of  claim 9  wherein the amount of additive in the admixture is <65 wt.-%. 
     
     
         11 . The method of  claim 4  wherein the atomizer is an ultrasonic water mist generator. 
     
     
         12 . A method of producing power using a fuel cell power system, the method comprising:
 providing a closed cathode PEM fuel cell stack comprising a plurality of fuel cells, each cell having an anode side and a cathode side that enables operation of the cathode side at a pressure above ambient pressure;   feeding water from a first water storage to a rotary bed reactor during start-up to generate hydrogen by the hydrolysis of a fuel in the reactor;   stopping water feed from the first water storage during normal operation,   using condensed water during normal operation;   routing hydrogen to the anode side of the fuel cell stack at a hydrogen flow rate sufficient for producing power and a recirculation hydrogen stream;   enriching the recirculation hydrogen stream exiting the anode with water; and,   routing the water-enriched recirculation stream to the rotary bed reactor, wherein condensed water is removed from the cathode side of the fuel cell stack;   wherein enriching further comprises converting water to a mist having a plurality of water droplets; and,   wherein the atomizer is an ultrasonic water mist generator that is entrained by the recirculation hydrogen stream into the rotary bed reactor.   
     
     
         13 . The method of  claim 12  wherein the fuel comprises lithium aluminum hydride. 
     
     
         14 . The method of  claim 12  wherein the fuel comprises an admixture of lithium aluminum hydride and an additive comprising at least one of AlCl 3 , MgCl 2 , BeCl 2 , CuCl 2 , LiCl, NaCl, and KCl.