Sometimes it might be necessary to carry out types of electrochemical reactions, wherein one or more of the reactants are in gas phase.
In this case, using conventional electrodes the reaction would proceed at a slow rate, making the process inapplicable or at least uneconomical: the gas solubility is usually small, and its consequent low concentration would lead to a severe limitation of mass transport phenomena toward the electrode surfaces.
A different electrode, with engineered porous structure, capable of favoring the contact between catalyst (solid) and reactants in liquid and gas phase (three phase region), allowing fast removal of the reaction products and an effective electric current transport is then necessary for these reactions: a GAS DIFFUSION ELECTRODE.
The right GDE structure is designed for the specific application and obtained by optimization of the electrode porosity, hydrophobicity, hydrophilicity and thickness.
The catalyst employed also depends on the field of utilization of the electrode, usually being a noble metal compound in form of a finely dispersed metal or oxide, supported on a material having a large surface area, such as active carbon, and embedded in a polymer binder.