Tandem laser ablation synthesis in solution-galvanic replacement reaction (LASiS-GRR) for the production of PtCo nanoalloys as oxygen reduction electrocatalysts

• Tandem LASiS-GRR is used to synthesize PtCo nanoalloys (NAs) as electrocatalysts.
• Size and degrees of alloying are tuned by Pt salt concentrations and pH conditions.
• EELS mapping reveals Pt-rich shell on PtCo alloyed core.
• NAs with Co molar ratio∼22.1% indicate superior ORR activities in acid electrolytes.
• A mechanistic picture for LASiS-GRR controlling PtCo alloying process is proposed.

We have developed tandem laser ablation synthesis in solution-galvanic replacement reaction (LASiS-GRR) technique as a facile, green yet, efficient route to synthesize spherical PtCo NAs with varied sizes, compositions and degrees of alloying. The transformative concept here is the ability to design these nanostructured alloys by tuning the high-energy physico-chemical conditions emerging from liquid-confined, laser-induced plasma, and the solution-phase reaction pathways dictated by pH conditions and precursor salt concentrations. The resultant NAs exhibit uniformly alloyed cores with a Pt-rich shell of a few nanometers, as demonstrated by the electron energy loss spectroscopy (EELS) mapping. Such core–shell structure along with high degrees of alloying in these PtCo NAs promote their outstanding electrocatalytic ORR activities in acid electrolytes. Specifically, compared to commercial Pt/C catalysts, the PtCo NAs with Co molar ratio of 22.1% indicate a c.a. 3 and 6-fold increase in mass and specific activities respectively. Such enhanced ORR activities are attributed to the efficacy of tandem LASiS-GRR route to rationally tune size distributions/compositional ratios and alloying degrees of the NAs without the use of any surfactants or reducing agents that are otherwise indispensable in chemical synthesis methods, but harmful for catalytic performances.

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