Chemically modified gas diffusion electrodes probing electrochemical activity in proton exchange membrane fuel cells

Two examples of chemically modified gas diffusion electrodes are presented to demonstrate the value of electrode functionalization methods in the study of fuel cells. In one example, Os(2,2'-bipyridine)(3)(2+) has been added to the ionomer binder in the active layer of the electrode to measure the fraction of this ionomer that participates in ion transport within the layer. A lower fraction of the Os complex was electrochemically active in the cathode of an operating fuel cell, compared to a similar electrode that was in contact with an aqueous sulfuric acid solution. The difference is attributed to poor hydration of the fuel cell electrode. In a second example, a Ru complex has been covalently attached to a carbon-black fuel cell catalyst support to allow measurement of the fraction of the carbon surface that is in both electronic and ionic contact with the current collector and membrane, respectively. (C) 2000 The Electrochemical Society. S1099-0062(00)03-136-9. All rights reserved.