Electrochemical Eqs. 1 and 2 mainly take place in the heart of the fuel cell, called Membrane Electrode Assembly (MEA). MEA is composed of an ion conducting polymer, called the membrane, sandwiched between the catalyst layer (CL), a gas diffusion layer (GDL) and a microporous layer (MPL) on each side. The GDL is a porous material that has a good transport capability, allowing mass and heat transport within its microstructure, ultimately affecting the fuel cell performance. MPL is a thin, carbon-based coating applied on top of the GDL and serves as the interface between the GDL and CL. The GDL and MPL allow gas transport, maintaining water balance and supporting efficient electrochemical reactions within the fuel cell. Typically, GDL is a bi-layer carbon-based porous material made up of an MPL with a usual thickness of 10-100 μm and a macroporous substrate with a typical thickness of 150-400 μm, depending on the manufacturer, type and compression level. The GDL should allow the flow of reactant gases (H2 and oxygen) and product gases to pass through it. The water formed in a cell should not choke the pores, so they are precoated with polytetrafluoroethylene (PTFE) or so called Nafion, which makes the GDL surface hydrophobic. The MPL, commonly manufactured by intermixing a hydrophobic polymer (PTFE) with carbon black, enhances water removal rate, enhances electrical connectivity, relieves water accumulation by pushing the liquid water from cathode to anode, and improves evaporation in the electrodes. In the upcoming paragraph, we describe some of the key factors in determining the overall performance and efficiency of PEMFC.