Patent ID: 8237312

Claim:
A method comprising: operating a converter to convert a first voltage produced by an electrochemical cell stack in a power producing mode into a second voltage; and operating the converter to convert a third voltage into a fourth voltage to drive the electrochemical cell stack in a pumping mode in which the electrochemical cell stack functions as an electrochemical pump to purify an incoming flow to produce a purified fuel flow, wherein a polarity switch is disposed between the electrochemical cell stack and the converter to reverse a polarity of stack terminals between the power producing mode and the electrochemical cell pumping mode, wherein the polarity switch and the converter are disposed between the electrochemical cell stack and a bus so that when the power producing mode changes to the electrochemical cell pumping mode or vice versa, the polarity switch first reverses the polarity of the stack terminals and then the converter operates in a reverse direction.