Activating Ru in the pyramidal sites of Ru2P‐type structures with earth‐abundant transition metals for achieving extremely high HER activity while minimizing noble metal content

• Published in: Carbon energy 2024-09, Vol.6 (9), p.n/a
• Main Authors: El‐Refaei, Sayed M., Russo, Patrícia A., Schultz, Thorsten, Chen, Zhe‐Ning, Amsalem, Patrick, Koch, Norbert, Pinna, Nicola
• Format: Article
• Language: English
• Subjects: Atomic structure; Carbon; Catalysts; Crystal structure; Density functional theory; Diffraction; electrocatalysis; Electrochemistry; Electrons; Heavy metals; Hydrogen evolution reactions; Hydrogen production; Ligands; Metals; Molybdenum; Nanocrystals; Nickel; Noble metals; Quantum dots; Ruthenium; ruthenium phosphide; Solid solutions; Sulfuric acid; transition metal phosphonates; Transition metals; Water splitting
• ISSN: 2637-9368; 2637-9368
• DOI: 10.1002/cey2.556

Rational design of efficient pH‐universal hydrogen evolution reaction catalysts to enable large‐scale hydrogen production via electrochemical water splitting is of great significance, yet a challenging task. Herein, Ru atoms in the Ru2P structure were replaced with M = Co, Ni, or Mo to produce M2−xRuxP nanocrystals. The metals show strong site preference, with Co and Ni occupying the tetrahedral sites and Ru the square pyramidal sites of the CoRuP and NiRuP Ru2P‐type structures. The presence of Co or Ni in the tetrahedral sites leads to charge redistribution for Ru and, according to density functional theory calculations, a significant increase in the Ru d‐band centers. As a result, the intrinsic activity of CoRuP and NiRuP increases considerably compared to Ru2P in both acidic and alkaline media. The effect is not observed for MoRuP, in which Mo prefers to occupy the pyramidal sites. In particular, CoRuP shows state‐of‐the‐art activity, outperforming Ru2P with Pt‐like activity in 0.5 M H2SO4 (η10 = 12.3 mV; η100 = 52 mV; turnover frequency (TOF) = 4.7 s−1). It remains extraordinarily active in alkaline conditions (η10 = 12.9 mV; η100 = 43.5 mV) with a TOF of 4.5 s−1, which is 4x higher than that of Ru2P and 10x that of Pt/C. Further increase in the Co content does not lead to drastic loss of activity, especially in alkaline medium, where, for example, the TOF of Co1.9Ru0.1P remains comparable to that of Ru2P and higher than that of Pt/C, highlighting the viability of the adopted approach to prepare cost‐efficient catalysts. A facile synthesis approach to drive Ru‐based bimetallic phosphides MRuP (M = Co, Ni, and Mo) that adapt the same crystal structure has been developed, allowing to understand the possible synergism between metals toward hydrogen evolution reaction. Among them, CoRuP exhibits outstanding performance, outperforming Pt/C in alkaline medium and comparable to it in acidic medium, thanks to the induced charge redistribution according to X‐ray photoelectron spectroscopy and density functional theory analysis.