Passive electrode blanketing in a fuel cell

Abstract

When a conventional fuel cell module is shutdown the conditions within the fuel cell stack change. The conditions change because elements that support and regulate the operation of the fuel cell stack switch to their respective shutdown states. For example, the input and output valves are closed, which cuts off the supply inflows and exhaust outflows. Moreover, when an element such as a flow control device switches to a shutdown state internal conditions, such as for example, the pressure within the anode electrodes change. When the internal conditions of the fuel cell stack change the reactants (e.g. hydrogen and oxygen) remaining in the fuel cell stack and the feed lines (between the fuel cell stack and the closed valves) are substantially consumed in combustion reactions as opposed to being consumed in electrochemical reactions yielding a useful form of energy.

1 . A fuel cell module, comprising: 
 a fuel cell stack including at least one fuel cell, each fuel cell including an anode electrode, a cathode electrode and an electrolyte medium arranged between the anode electrode and the cathode electrode, wherein during normal operation the anode electrode is provided with a first reactant and the cathode electrode is provided with a first mixture containing a second reactant and a non-reactive agent;    a parasitic load that is connectable across the anode and the cathode electrodes;    a first reactant supply port, fluidly connectable to the anode electrode, for supplying the first reactant to the anode electrode;    a side stream fluidly connectable to the first reactant supply and the anode electrode;    a reactant reservoir, fluidly connectable to the side stream, for storing an amount of the first reactant suitable for a shutdown process of the fuel cell module, whereby, in use when the fuel cell module is shutdown, the stored amount of the first reactant is drawn from the reactant reservoir and electrochemically reacts with the second reactant in the fuel cell module, to electrochemically consume the first and second reactants, thereby leaving a second mixture that substantially comprises the non-reactive agent; and    a pressure generating device, fluidly connectable to the side stream and positioned upstream of the reactant reservoir, for pressurizing and delivering the first reactant from the first reactant supply to the reactant reservoir.    
   
   
       2 . A fuel cell module according to  claim 1 , further comprising a flow control device which is fluidly connectable to the side stream and positioned downstream of the reactant reservoir, the flow control device regulating a flow of the first reactant from the reactant reservoir to the anode electrode when the fuel cell module is shutdown.  
   
   
       3 . A fuel cell module according to  claim 2 , further comprising a pressure sensor which is fluidly connectable with one of the reactant reservoir and the side stream, downstream of the reactant reservoir, and electrically connectable to the pressure generating device for sensing the pressure in the reactant reservoir and controlling the pressure generating device during regular operation of the fuel cell module.  
   
   
       4 . A fuel cell module according to  claim 3 , further comprising a solenoid valve which is fluidly connectable to the side stream and positioned intermediate the pressure generating device and the flow control device for preventing backflow of the first reactant from the flow control device.  
   
   
       5 . A fuel cell module as claimed in  claim 2 ,  3  or  4 , wherein a supply line is fluidly connectable between the first reactant supply port and the anode electrode, and wherein the side stream is connected in parallel to the supply line.  
   
   
       6 . A fuel cell module as claimed in  claim 2 , wherein a supply line is fluidly connectable between the first reactant supply port and the anode electrode, and wherein the side stream comprises a branch line connected at one end to the supply line, with both the pressure generating device and the flow control device located between said one end and the reactant reservoir, whereby in use, the pressure generating device and the flow control device are upstream of the reactant reservoir during pressurization thereof and downstream thereof when the first reactant is drawn from the reactant reservoir.  
   
   
       7 . A fuel cell module as claimed in  claim 6 , further including a pressure sensor connected to one of the reactant reservoir and the branch line between the reactant reservoir and the pressure generating device, and electrically connectable to the pressure generating device for sensing pressure in the reactant reservoir and controlling the pressure generating device during regular operation of the fuel cell module.  
   
   
       8 . A fuel cell module according to  claim 1 , wherein the reactant reservoir is a pressurized vessel.  
   
   
       9 . A fuel cell module according to  claim 1 , wherein the pressure generating device is a positive displacement pump.  
   
   
       10 . A fuel cell module according to  claim 1 , wherein the fuel cell stack comprises: 
 a cathode inlet port for supplying the first mixture to the cathode electrodes;    a cathode outlet port for evacuating un-reacted amounts of the second reactant, amounts of the non-reactive agent and exhaust products from the cathode electrodes;    an anode inlet port, fluidly connectable to the reactant reservoir, and for supplying the first reactant to the anode electrodes; and,    an anode outlet port for evacuating un-reacted amounts of the first reactant and exhaust products from the anode electrodes.    
   
   
       11 . A fuel cell module according to  claim 10 , wherein the electrolyte medium is a Proton Exchange Membrane (PEM).  
   
   
       12 . A fuel cell module according to  claim 11 , including at least one Proton Exchange Membrane that permits the non-reactant agent to cross over from the cathode to the anode and a valve permitting gas to flow from the cathode to the anode during the shutdown process.  
   
   
       13 . A fuel cell module according to  claim 11 , wherein the first reactant is hydrogen, the second reactant is oxygen carried in the air and the non-reactive agent is nitrogen carried in the air.  
   
   
       14 . A fuel cell module according to  claim 13 , further comprising: 
 a hydrogen supply port; and,    an anode input valve, connectable between the hydrogen supply port and the reactant reservoir, for cutting-off a flow of hydrogen from the hydrogen supply port to the anode inlet port during the shutdown process.    
   
   
       15 . A fuel cell module as claimed in  claim 1 , wherein the cathode electrode include a cathode inlet port and a cathode outlet port, and wherein at least one of a valve for the cathode inlet port and a valve for the cathode outlet port is provided to reduce disturbance of the second mixture present at the cathode after the shutdown process.  
   
   
       16 . A fuel cell module, comprising: 
 a fuel cell including a first electrode, a second electrode and an electrolyte medium arranged between the first and second electrodes, wherein during normal operation the first electrode is provided with a first reactant and the second electrode is provided with a first mixture containing a second reactant and a non-reactive agent;    a parasitic load that is connectable across the first and second electrodes;    a first reactant supply, fluidly connectable to the anode electrode, for supplying first reactant to the anode electrode;    a side stream fluidly connectable to the first reactant supply and the anode electrode;    a reactant reservoir, fluidly connectable to the side stream, for storing an amount of the first reactant suitable for a shutdown process of the fuel cell module, whereby, in use when the fuel cell module is shutdown, the stored amount of the first reactant is drawn from the reactant reservoir and electrochemically reacts with an amount of the second reactant remaining in the fuel cell module, to electrochemically consume the first and second reactants, thereby leaving a second mixture that substantially comprises the non-reactive agent; and    a pressure generating device, fluidly connectable to the side stream and positioned upstream of the reactant reservoir, for pressurizing and delivering the first reactant from the first reactant supply to the reactant reservoir.    
   
   
       17 . A reactant supply system for a fuel cell stack, having an anode inlet, an anode outlet, a cathode inlet and a cathode outlet, the reactant supply system comprising: 
 a first reactant supply port connectable in use to the anode inlet of the fuel cell stack;    a second reactant supply port connectable in use to the cathode inlet, for supply of a mixture comprising the second reactant and a non-reactant agent;    a parasitic load that is connectable across the anode and cathode electrodes of the fuel cell stack;    a side stream fluidly connectable to the first reactant supply line;    a reactant reservoir, fluidly connectable to the side stream, for storing an amount to the first reactant suitable for a shutdown process of the fuel cell stack, whereby, in use, when the fuel cell stack is shutdown, the stored amount of the first reactant is drawn from the reactant reservoir and electrochemically reacts with the secondary reactant in the fuel cell module, to electrochemically consume the first and second reactants, thereby leaving a second mixture that substantially comprises the non-reactive agent; and    a pressure generating device, fluidly connectable to the side stream for pressurizing delivering the first reactant to the reactant reservoir.    
   
   
       18 . A process for shutting down a fuel cell, the fuel cell including a first electrode, a second electrode and an electrolyte membrane arranged between the first and second electrodes, the process comprising during normal operation: 
 providing the first electrode with a first reactant and the second electrode with a first mixture containing a second reactant and a non-reactive agent, and;    pressurizing a portion of the first reactant and storing the first reactant in a reactant reservoir; and    the process further comprising at shutdown:    stopping an inflow of the first reactant into the first electrode;    cutting-off power to supporting balance of plant elements;    drawing current through a parasitic load connectable across the first and second electrodes;    permitting the stored first reactant to flow to the first electrode for the electrochemical consumption of a remaining amount of a second reactant;    wherein the first reactant electrochemically reacts with the remaining amount of the second reactant, thereby leaving a second mixture that substantially comprises the non-reactive agent.    
   
   
       19 . A process as claimed in  claim 18 , the process including storing a near stoichiometric amount of the first reactant for consumption of the remaining amount of the second reactant.  
   
   
       20 . A process as claimed in  claim 19 , including controlling the flow of the first reactant from the reactant reservoir with a flow control device.  
   
   
       21 . A process as claimed in  claim 20 , including, in normal operation, controlling the supply of the reactant to the first reservoir in dependence of the pressure in the first reservoir.  
   
   
       22 . A process as claimed in  claim 21 , including preventing backflow of the first reactant out of the first reservoir with a valve.  
   
   
       23 . A process as claimed in  claim 18 , including permitting the non- reactive agent to cross over from the second electrode to the first electrode at shutdown, whereby both the first and second electrodes are blanketed with the non-reactive gas at shutdown.  
   
   
       24 . A process as claimed in  claim 23 , including providing one of an electrolyte membrane that permits cross over of the non-reactive gas at shutdown and a valve permitting flow of gas from the second electrode to the first electrode at shutdown.