Gas Diffusion Electrode (GDE) is a type of electrode used in electrochemical systems, such as fuel cells and electrolyzers, where it is used as a catalyst for the electrochemical reaction between a gas and a liquid. The GDE is designed to allow gases, such as oxygen or hydrogen, to diffuse through it and come into contact with the catalyst layer on the electrode surface.

The GDE consists of a porous layer made of carbon fibers or other materials that provide a high surface area for the catalytic reaction to occur. The porous layer is typically coated with a catalyst material, such as platinum, to enhance the reaction rate. The catalyst layer is then sandwiched between two layers of gas-permeable material, such as Teflon, to allow gases to diffuse through the electrode.

GDEs are used in a variety of applications, including proton exchange membrane (PEM) fuel cells, direct methanol fuel cells, and electrochemical oxygen generators. They are important components in these devices as they provide a means of converting chemical energy into electrical energy.