Within the ORR, O 2 from the surrounding environment will first diffuse into the fuel cell's cathode and bind to the surface of cathode catalysts. In ORR, this bound molecular oxygen electrochemically onto the catalyst surfaces, where it lowers the energy barrier of the oxygen bond and breaks the O-O bond in the oxygen molecule. These molecules will then react with four protons and electrons to create oxygen ions. The oxygen ions then travel through the electrolyte to react with hydrogen gas at the anode that releases electricity and water as by-products, completing the ORR cycle. The efficiency of this ORR dictates the electric potential generated by the fuel cell, where higher efficiency corresponds to higher potentials.