Improved Non-Pt Alloys for the Oxygen Reduction Reaction at Fuel Cell Cathodes Predicted from Quantum Mechanics

Based on studies on Pt3Co and Pt3Ni, we developed the hypothesis that improved alloy catalysts for the oxygen reduction reaction (ORR) at fuel cell cathodes should have a surface layer that is noble (e.g., Pt, Pd, or Rh) while the second layer should have similar to 50% electropositive metal to decrease the critical barriers for ORR, and we used quantum mechanics (QM) to examine 80 binary alloys of composition Y3X, where Y = Pt, Pd, Rh, and Xis any of the three rows of transition metals (columns 3-11). This study identified that for Pd3X, good segregating alloys include X = Re (best), W, Os, Mo, Ru, Ir, Tc, Rh, Co, Ta, Nb, and Ni. Of these we selected Pd3W as particularly promising since it is known experimentally to form an ordered alloy and was found to have a desirable d-band center. We then examined the critical barriers for various steps of the ORR with Pd3W and compared them to the analogous barriers for Pt, Pt3Co, and Pd. These results suggest that Pd3W will exhibit ORR properties dramatically improved over pure Pd and close to that of pure Pt. The cost of Pd3W is similar to 6 times less than pure Pt, suggesting that Pd3W catalysts might lead to significant decreases in catalyst cost, while maintaining performance.