In the current stage, platinum (Pt)-based catalysts are considered the most efficient catalyst for ORR in fuel cells for several reasons . First, highly active noble-metal catalysts such as Pt, Pd, Rh, and Au are capable of breaking the O-O bond. Because these catalysts have a d-band center that is well-aligned with the energy level associated with the oxygen bond, this alignment of energy levels facilitates the transfer of electrons that are active in ORR and weakens the oxygen bond of the oxygen molecules interacting with the catalyst surface. Also, this alignment helps reduce the activation energy required for breaking the O-O bond, which makes the overall reaction more efficient. Second, like ORR, these noble-metal catalysts also follow a 4-electron pathway, making them more suitable for ORR . Therefore, noble-metal catalysts are considered the most efficient catalysts to use within fuel cells. Because of the outstanding stability of the Pt-skin structure of the Pt-based catalysts, they stand out among these other metal catalysts.