Correlation between d Electrons and the Sweet Spot for the Hydrogen Evolution Reaction: Is Platinum Always the Best Electrocatalyst?

Herein, two Laves intermetallic series, ZrCo 1.75 M 0.25 and NbCo 1.75 M 0.25 ( M = Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, and Pt), were synthesized, and their hydrogen evolution reaction (HER) activities were examined to reveal the influence of d electrons to the corresponding HER activities. Owing to the different electronegativity between Zr and Nb (χ Zr = 1.33; χ Nb = 1.60), Co and/or M elements receive more electrons in ZrCo 1.75 M 0.25 than that of the Nb one. This leads to the overall weak H adsorption energy (Δ G Had ) of ZrCo 1.75 M 0.25 series compared to that of NbCo 1.75 M 0.25 and rationalizes well the superior HER activity of the Rh member compared to that of the Pt one in the ZrCo 1.75 M 0.25 series. Under industrial conditions (333 K, 6.0 M KOH), ZrCo 1.75 Rh 0.25 only requires an overpotential of 110 mV to reach the current density of 500 mA/cm 2 and can be operated at high current density over 400 h. This work demonstrates that with a proper combination between elements in intermetallic phases, one can manipulate d electrons of the active metal to be closer to the sweet spot (Δ G Had = 0). The Pt member may no longer exhibit the best HER activity in series, and all elements exhibit the potential to outperform the Pt member in the HER with careful control of the d electron population.