Femtosecond laser synthesis of metastable PtRu/graphene electrocatalysts for efficient hydrogen evolution reaction in acidic and alkaline solutions

Facile synthesis of nanoalloys with atomic dispersity is an effective means to engineer highly efficient electrocatalysts by maximizing the exposure of catalytically active sites. However, such effort faces challenges in practice. One key issue is the thermodynamic-driven phase separation because of differences in redox potentials across different elements. Conventional wet chemistry methods often lack the rapid high-energy input required to non-selectively reduce precursors and mix elements with differing crystallographic parameters or phases, processes hindered by kinetic barriers. Here, we employ a femtosecond (fs) laser liquid ablation technique to synthesize defect-rich PtRu alloys on carbon supports without the application of external reducing agents or capping ligands. The extreme light field generated by fs lasers facilitates the rapid synthesis and stabilization of nanoalloy particles. The synthesized PtRu nanoparticles exhibited remarkable hydrogen evolution reaction (HER) activity in 1 M KOH and 0.5 M H₂SO₄, with overpotentials of 15.5 mV and 13.6 mV at 10 mA cm⁻², respectively. In alkaline and acidic solutions, the mass activity of PtRu/graphene catalyst was 4.7 and 4.3 times that of commercial Pt/C catalysts, respectively. The electrolyte/electrode interfacial properties were investigated using in-situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS). It was found that alloying Pt with Ru activates water molecules and optimizes the interfacial water structure and hydrogen adsorption energy. Populated free water molecules at the electrolyte/electrode (PtRu/graphene) interface facilitate the transport of reaction intermediates. In-situ Raman spectroscopy reveals that Ru directly participates in the Volmer step, serving as the active site for water dissociation. Our study demonstrates the potential of using fs lasers for materials engineering and designing ligand-free metastable nanoalloys for various applications.