Microwave-Assisted Synthesis of Core-Shell Structured Pd@PdPtCuFe Recessed Truncated Octahedral Nanocrystals for Multifunctional Electrocatalysis

Developing cost-efficient and durable multifunctional electrocatalysts of hydrogen evolution reaction, oxygen reduction reaction and oxygen evolution reaction is crucial for improving energy conversion efficiency in electrolytic water splitting electrolyzer and advancing rechargeable zinc-air batteries. Polyhedral shaped nanocrystals with well-defined crystal facets represent a type of model catalysts that enables the exploration of structure-activity relationships. However, it is still very challenging to prepare alloy nanocrystals with multiple metal components due to their complicated redox potentials and mixing enthalpy. Herein, we report a rapid microwave-assisted polyol reduction method for syntheses of core-shell Pd@PdPtCu, Pd@PdPtCuNi, Pd@PdPtCuCo and Pd@PdPtCuZn octahedral nanocrystals, and recessed truncated-octahedral Pd@PdPtCuFe nanocrystals. Ascribing to the fast reduction and nucleation rate of Pd precursors, Pd core was firstly formed. Further concurrent reduction and efficient diffusion of the rest metal precursors resulted in the PdPtCu or PdPtCuM (M = Ni, Co, Fe and Zn) alloy shell. It was observed that Fe plays a decisive role in driving the morphological evolution from octahedral to recessed truncated-octahedral nanocrystals. The Fe³⁺-Br^– coordination modulates crystal growth kinetics by altering surface adsorption dynamics, resulting in a mixed exposure of {111} and {100} facets rich in edge and vertex sites. Structural analyses confirmed a well-defined Pd core and homogeneous PdPtCuFe alloy shell with a face-centered-cubic phase. Owing to the synergistic electronic coupling between Fe and noble-metal components and the strain-regulated surface configuration, the obtained Pd@PdPtCuFe/C exhibited superior multifunctional activity with a HER overpotential of 18 mV at 10 mA·cm^–2 and Tafel slope of 27 mV·dec^–1, the most active HER catalyst among the five prepared core@shell catalysts and superior to commercial Pt/C. In addition, it delivered an OER overpotential of 360 mV at 10 mA·cm^–2 and a Tafel slope of 75.9 mV·dec^–1 comparable to benchmark IrO₂ catalysts. All the prepared catalysts exhibited certain ORR activity in alkaline electrolytes, and the champion catalyst Pd@PdPtCuFe/C is manifested with an ORR half-wave potential of 0.792 V in alkaline electrolytes. When applied as a cathode catalyst in ZABs, the Pd@PdPtCuFe/C showed a peak power density of 81.2 mW·cm^–2 and maintained stable upon cycling for over 50 h. This work provides a generalizable route for ultrafast morphology-controlled synthesis of multimetallic nanocrystals, paving the way for the rational design of high-performance, low-PGM bifunctional catalysts for next-generation energy conversion and storage systems.