Abstract
The long-standing challenges facing Pt-based alloy catalysts in oxygen reduction reactions (ORRs) are rapid oxidation and loss of transition metal/Pt in proton exchange membrane fuel cells (PEMFCs). In this work, we report a concept of "covalentization" in intermetallic L1(0)-PtMM' (M = Fe, Co, Ni and M' = one of the 4(th)-period elements (from Ti to Ge)) alloys to enhance their electrochemical stability. Specifically, the formation of a quasi-covalent bond network in L1(0)-PtMM' due to the less occupied antibonding states induced by high d-band positions of M' elements (e.g., Ti, V, Cr) enhances atomic bond order and strength, diminishing Co anodic dissolution via strengthened Pt/Co-M' bonds and reducing Co cathodic corrosion by inhibiting Pt oxidation through an electron buffering effect. The developed L1(0)-PtCoCr/C catalysts show a high mass activity (MA = 1.27 A mg(Pt)(-1)) and rated power (16.5 W mg(Pt)(-1)) in PEMFCs at a low total Pt loading of 0.075 mg(Pt) cm(-2). The catalysts also exhibit high electrochemical stability with ~3% and 5% loss of MA and rated power after 30,000 accelerated durability testing cycles and projects a lifetime of about 42,000 hours.