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Abstract:
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Controlling catalyst morphology and composition are required to make meaningful structure -activity /stability relationships for the design of future catalysts . Herein , we have employed strategies of presynthesis and infusion or electroless deposition to achieve exquisite control over catalyst composite morphology . The oxygen reduction (ORR ) and the oxygen evolution reactions (OER ) were chosen as model systems , as their slow kinetics is a major limiting factor preventing the commercialization of fuel cells and rechargeable metal air batteries . In acid , bimetallic (Pt -Cu , Pd -Pt ) and monometallic (Pt ) catalysts were presynthesized in the presence of capping ligands . Well alloyed Pt -Cu nanoparticles (3 -5 nm ) adsorbed on graphitic mesoporous carbon (GMC ) displayed an ORR activity >4x that of commercial Pt . For both presynthesized Pt and Pt -Cu nanocrystals on GMC , no activity loss was also observed during degradation cycling due to strong metal -support interactions and the oxidation resistance of graphitic carbon . Similar strong metal -support interactions were achieved on non -graphitic carbon for Pd3Pt2 ( <4 nm ) nanoparticles due to disorder in the metal surface This led to enhanced mass activity 1 .8x versus pure Pt , as well as improved stability . For basic electrolytes , we developed an electroless co -deposition scheme to deposit Ag (3 nm ) next to MnOx nanodomains on carbon . We achieved a mass activity for Ag -MnOx /VC , 3x beyond the linear combination of pure component activities due to ensemble effects , where Ag and MnOx domains catalyze different ORR steps , and ligand effects from the unique electronic interaction at the Ag -MnOx interface . Activity synergy was also shown for Ag -Pd alloys ( ~5 nm ) , achieving up to 5x activity on a Pd basis , resulting from the unique alloy surface of single Pd atoms surrounded by Ag . Lastly , we combined arrested growth of amorphous nanoparticles with thin film freezing to create a high surface area , pure phase perovskite aggregate of nanoparticles after calcination . Sintering was mitigated during the high temperature calcination required to form the perovskite crystals . The high surface areas and phase purity led to OER mass activities ~2 .5x higher than the benchmark IrO2 catalyst . |