Crystal Phase Transition Creates a Highly Active and Stable RuC_X Nanosurface for Hydrogen Evolution Reaction in Alkaline Media

Abstract

Although metastable crystal structures have received much attention owing to their utilization in various fields, their phase‐transition to a thermodynamic structure has attracted comparably little interest. In the case of nanoscale crystals, such an exothermic phase‐transition releases high energy within a confined surface area and reconstructs surface atomic arrangement in a short time. Thus, this high‐energy nanosurface may create novel crystal structures when some elements are supplied. In this work, the creation of a ruthenium carbide (RuCX, X < 1) phase on the surface of the Ru nanocrystal is discovered during phase‐transition from cubic‐close‐packed to hexagonal‐close‐packed structure. When the electrocatalytic hydrogen evolution reaction (HER) is tested in alkaline media, the RuCX exhibits a much lower overpotential and good stability relative to the counterpart Ru‐based catalysts and the state‐of‐the‐art Pt/C catalyst. Density functional theory calculations predict that the local heterogeneity of the outermost RuCX surface promotes the bifunctional HER mechanism by providing catalytic sites for both H adsorption and facile water dissociation.

Cerium-Doped Nickel Phosphide Nanosheet Arrays as Highly Efficient Electrocatalysts for the Hydrogen Evolution Reaction in Acidic and Alkaline Conditions

“…The corresponding Tafel plots constructed with the steady-state polarization curves also show slightly higher slopes of 88.3 mV dec –1 for Ce 0.10 -Ni 2 P@NF and 117.1 mV dec –1 for Ni 2 P@NF (Figure S6c). Moreover, EIS was also performed to estimate the HER kinetics on the surfaces of the catalysts. , The lower charge-transfer resistance ( R ct ) implies faster electron transfer and the enhanced HER kinetics toward the catalytic reaction. ,− As shown in the Nyquist plot and equivalent circuit in Figure c, the smaller semicircular radius for the Nyquist plot indicates a lower R ct . The R ct of the catalysts follows the order Pt/C (1.19 Ω) < Ce 0.10 -Ni 2 P@NF (2.10 Ω) < Ce 0.06 -Ni 2 P@NF (3.16 Ω mV dec –1 ) < Ce 0.03 -Ni 2 P@NF (4.14Ω) < Ni 2 P@NF (7.79 Ω), which is consistent with the order of geometric activity and Tafel slopes.…”

“…Moreover, EIS was also performed to estimate the HER kinetics on the surfaces of the catalysts. 71,72 The lower charge-transfer resistance (R ct ) implies faster electron transfer and the enhanced HER kinetics toward the catalytic reaction. 44,72−74 As shown in the Nyquist plot and equivalent circuit in Figure 3c, the smaller semicircular radius for the Nyquist plot indicates a lower R ct .…”

Tuning the electronic communication of the Ru–O bond in ultrafine Ru nanoparticles to boost the alkaline electrocatalytic hydrogen production activity at large current density

“…Ru nano-particles have promoted catalytic performance via suitable hetero-atom doping, adjusting the morphology and reconstituting the nanostructure. 20 According to a previous study, Youn and Choi successfully synthesized Ru/C nanoparticles and probed HER activity during the phase-transition process (Ru Δccp /C⋯Ru Δc→h /C⋯Ru Δhcp /C), 21 suggesting that atomic interactions on nanoparticle surfaces were activated by phasetransitions, which could optimize the HER performance in alkaline media. Moreover, the introduction of nonmetallic elements (N, 22,23 P, 24 S, 25 O, 26 etc.)…”

Phase-transition engineering induced lattice contraction of the molybdenum carbide surface for highly efficient hydrogen evolution reaction

“…31 Choi and co-workers discovered that the ruthenium carbide phase generated on the surface of the Ru nanocrystal during the phase transition from the cubic-close-packed to hexagonal-close-packed structure exhibited low overpotential and good stability, which benefited from the local heterogeneity of the outermost RuC x surface, providing catalytic sites for H adsorption and facile water dissociation. 32 Similarly, various approaches have been reported to modulate the surface properties of molybdenum carbide by introducing phase engineering for optimizing hydrogen evolution. Wang's group prepared the Mo/C, MoC–Mo 2 C, and Mo 2 C catalytic electrodes by controlling the synthesis temperature and illustrated the superior HER performance of MoC–Mo 2 C, which is attributed to the lower energy barrier for water dissociation and optimized Δ G H* .…”