NOVELTY - A component system for controlling concentration of gaseous redox byproduct(s) (710) in fuel cell fuel solution, comprises barrier(s) that is at least partially permeable to the byproduct. The barrier comprises first and second surface(s), with the first surface having effective amount of contact with the solution.    USE - The invention is used for controlling the concentration of gaseous redox byproduct in anode fuel solution and/or cathode oxidant solution of fuel cell.    ADVANTAGE - The invention allows user- or designer-controlled processing and/or partitioning of gases produced during operation of fuel cell. It has the ability to operate a fuel cell in any orientation to vent gaseous byproducts while retaining the fluid solution without leakage or fluid migration.    DETAILED DESCRIPTION - A component system for controlling concentration of gaseous redox byproduct(s) in anode fuel solution and/or cathode oxidant solution of fuel cell, comprises barrier(s) that is at least partially permeable to the byproduct. The barrier comprises first and second surface(s). The first surface has effective amount of contact with the solution. The barrier is disposed to at least effectively seal the system from migration of the solution and the gaseous compound(s) beyond the second surface of the barrier other than by permeative transport through the barrier.    INDEPENDENT CLAIMS are also included for:    (a) a method for controlling the concentration of gaseous by product(s) in anode fuel solution and/or cathode fuel solution of fuel cell, comprising flowing solution through a fluid flow field; and    (b) a fuel cell for generating electricity having component system for controlling exhaust transport of gaseous compound comprising anode(s) and cathode(s), fluid flow field, barrier, fluid flow inlet(s), and fluid flow outlet(s).    DESCRIPTION OF DRAWING(S) - The figure shows a side elevation view of integrated Direct Methanol Fuel Cell system having component sub-system for at least partially partitioning carbon dioxide.    Byproduct carbon dioxide (710)    Methanol sensor (750)    Supply fuel path (770)    Venting ports (785, 794)    Exhaust vent (790)