NOVELTY - An oxidizer catalyst assembly (118) for oxidizing gas, comprises first catalyst member (202) arranged along a gas flow path; and second catalyst member (204) arranged along the gas flow path following the first catalyst member. Each of the first and second catalyst members includes through channels (203, 205) for passing gas and oxidizing catalyst (205a) in each through channel. The channels of the second catalyst member have a channel density which is greater than that of the first catalyst member and a channel width which is less than that of the channels of the first catalyst member.    USE - The oxidizer catalyst assembly is in fuel cell system for oxidizing gas, e.g. anode exhaust gas (claimed).    ADVANTAGE - The assembly reduces electrolyte particulate build-up on the surface of the assembly, delays blocking of the gas flow through the oxidizer catalyst assembly by accumulated electrolyte particulates, and can be used together with the electrolyte removal practices described in the U.S. patent application Ser. No. 11/022,914.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) oxidizing a gas comprising passing the gas through channels having an oxidizing catalyst of a first catalyst member and through channels having an oxidizing catalyst of a second catalyst member; and    (2) fuel cell system comprising a fuel cell including an anode and a cathode, the anode having an inlet for receiving fuel and an outlet for discharging anode exhaust gas containing fuel gas, and the cathode having an inlet for receiving oxidant gas and an outlet for discharging exhaust oxidant gas; and an oxidizer catalyst assembly for oxidizing anode exhaust gas from the outlet of the anode to produce oxidizing gas for the cathode.    DESCRIPTION OF DRAWING(S) - The figure shows the oxidizer catalyst assembly of the fuel cell system.    Oxidizer catalyst assembly (118)    First catalyst member (202)    Through channels (203, 205)    Second catalyst member (204)