and electrons together with the oxygen molecule and the formation of one water molecule. The potentials in each case are given with respect to the standard hydrogen electrode. Polymer electrolyte membrane To function, the membrane must conduct hydrogen ions (protons) but not electrons as this would in effect "short circuit" the fuel cell. The membrane must also not allow either gas to pass to the other side of the cell, a problem known as gas crossover. Finally, the membrane must be resistant to the reducing environment at the cathode as well as the harsh oxidative environment at the anode. Splitting of the hydrogen molecule is relatively easy by using a platinum catalyst. Unfortunately however, splitting the oxygen molecule is more difficult, and this causes significant electric losses. An appropriate catalyst material for this process has not been discovered, and platinum is the best option. Strengths 1. Easy sealing PEMFCs have a thin, polymeric membrane as the electrolyte. This membrane is located in between the anode and cathode catalysts and allows the passage of protons to pass to the cathode while restricting the passage of electrons. Compared to liquid electrolytes, a polymeric membrane has a much lower chance of leakage [2]. The proton-exchange membrane is commonly made of materials such as perfluorosulfonic acid (PSFA) or Nafion, which minimize gas crossover and short circuiting of the fuel cell. 2. Low Operating Temperature Under extreme sub-freezing conditions, the water produced by fuel cells can freeze in porous layers and flow channels. This freezing water can block gas and fuel transport as well as cover catalyst reaction sites, resulting in a loss of output power and a start-up failure of the fuel cell. However, the low operating temperature of a PEM fuel cell allows it to reach a suitable temperature with less heating compared to other types of fuel cells. With this approach, PEM fuel cells have been shown to be capable of cold start processes from −20°C. 3. Light mass and high power density (transport applications) PEM fuel cells have been shown to be capable of high energy densities up to 39.7 kW/kg, compared to 2.5 kW/kg for solid oxide fuel cells. Due to this high power density, much research is being done on potential applications in transportation as well as wearable technology. Weaknesses Fuel Cells based on PEM still have many issues: 1. Water management Water management is crucial to performance: if