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

Abstract

Based on studies on Pt_3Co and Pt_3Ni, 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 ~50% electropositive metal to decrease the critical barriers for ORR, and we used quantum mechanics (QM) to examine 80 binary alloys of composition Y_3X, where Y = Pt, Pd, Rh, and X is any of the three rows of transition metals (columns 3−11). This study identified that for Pd_3X, good segregating alloys include X = Re (best), W, Os, Mo, Ru, Ir, Tc, Rh, Co, Ta, Nb, and Ni. Of these we selected Pd_3W 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 Pd_3W and compared them to the analogous barriers for Pt, Pt_3Co, and Pd. These results suggest that Pd_3W will exhibit ORR properties dramatically improved over pure Pd and close to that of pure Pt. The cost of Pd_3W is ~6 times less than pure Pt, suggesting that Pd_3W catalysts might lead to significant decreases in catalyst cost, while maintaining performance.