Tuning alloy nanoparticle catalysis for electrochemical redox reactions

Electrochemical reduction and oxidation reactions are crucial for energy storage and conversion. Nanoparticles, especially metallic alloy nanoparticles, have been extensively studied as catalysts to enhance the efficiency of these reactions. However, these processes often occur under conditions that are corrosive to nanoparticles, making it challenging to optimize the alloy composition for catalysis.

A common strategy to stabilize alloy nanoparticles is through the controlled formation of an intermetallic structure, where metal atoms are bonded via strong d-orbital interactions between alternating atomic layers. These intermetallic nanoparticles are more stable against chemical oxidation and acid etching, providing an excellent platform for studying alloy nanoparticle catalysis in various electrochemical reactions. We have demonstrated that the intermetallic L10-MPt/Pt (M = Fe or Co) structure is robust for studying the oxygen reduction reaction (ORR), while L10-MPt/AuPt is efficient for catalyzing alcohol oxidation reactions (AOR). The drawbacks of using intermetallic nanoparticles as catalysts lie in that they are typically obtained by high-temperature annealing, and small (<4 nm) intermetallic nanoparticles have been difficult to obtain.

Recently, we discovered that sub-4 nm solid solution AuCuPt nanoparticles can efficiently catalyze both AOR and ORR by simply controlling the Au/Pt ratios. The AOR catalyst was created by controlled etching of Au-rich AuCuPt nanoparticles, such as 3 nm Au53Cu36Pt11 nanoparticles, resulting in core/shell AuCuPt/AuPt with a defective AuPt shell. The ethanol oxidation reaction (EOR) catalysis in 1 M KOH reached 35 A/mgAuPt, and the catalyst was equally effective for methanol, propanol, and ethylene glycol oxidation reactions. When the nanoparticle composition was adjusted to Au9Cu41Pt50 from which AuCuPt/AuPt nanoparticles were obtained with a smooth AuPt shell, the catalyst became efficient for ORR not only in 0.1 M HClO4 but also in H3PO4. We are extending our studies to solid solution AuMPt nanoparticles (M = Ni, Co, Fe, Mn, etc) and demonstrate their potential as more practical catalysts for fuel cells and other energy conversion reactions.