Patent ID: 7887963

Claim:
A method of operating an electrochemical conversion assembly comprising a membrane electrode assembly, an anode flow field, and a cathode flow field, wherein: said membrane electrode assembly comprises a proton exchange membrane separating an anode and cathode of said assembly; said membrane electrode assembly comprises a catalyst supported by a relatively high surface area support material; said proton exchange membrane comprises a material characterized by enhanced proton conductivity under wet conditions; and said method comprises initiating a start up sequence, operating said electrochemical conversion assembly under wet conditions by driving a hydrogenous gas through said anode flow field and an oxygen-containing gas through said cathode flow field, and initiating a shut down sequence comprising driving a substantially dry oxygen-containing reactant gas through said cathode flow field for an amount of time sufficient to reduce the water content of said proton exchange membrane to a level sufficient to suppress catalyst dissolution and corrosion in said membrane electrode assembly, wherein said substantially dry oxygen-containing reactant gas is initially introduced at a first temperature characterized by a relatively high vapor capacity and is subsequently introduced at a second, cooler temperature sufficient to reduce the temperature of said membrane electrode assembly; interrupting a flow of said substantially dry oxygen-containing reactant gas when the water content of said proton exchange membrane is reduced; supplying said hydrogenous gas through said anode flow field after interrupting said flow of said substantially dry oxygen-containing reactant gas for a time sufficient to dilute an oxygen content of said cathode flow field; and introducing a substantially dry air purge into said anode flow field following dilution of said oxygen content.