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

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 Ru 2 P structure were replaced with M = Co, Ni, or Mo to produce M 2− x Ru x P 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 Ru 2 P‐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 Ru 2 P 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 Ru 2 P with Pt‐like activity in 0.5 M H 2 SO 4 ( η 10 = 12.3 mV; η 100 = 52 mV; turnover frequency (TOF) = 4.7 s −1 ). It remains extraordinarily active in alkaline conditions ( η 10 = 12.9 mV; η 100 = 43.5 mV) with a TOF of 4.5 s −1 , which is 4x higher than that of Ru 2 P 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 Co 1.9 Ru 0.1 P remains comparable to that of Ru 2 P and higher than that of Pt/C, highlighting the viability of the adopted approach to prepare cost‐efficient catalysts.