Synthesis of Nanostructured (Ni0.7-W0.3)1-XRux Electrocatalysts for Hydrogen Evolution Reaction in PEM Water Electrolysis
Authors: Choi Kanghoon , Omanovic Sasha 
Published: December 2024

The development of cost-effective and efficient electrocatalysts for the hydrogen evolution reaction (HER) is crucial for advancing renewable energy applications. Recently, the authors identified the Ni0.7-W0.3 sample as a promising alternative electrocatalyst candidate for HER in acidic media. However, further enhancement of the electrocatalytic activity of this material is needed. Therefore, to improve the activity towards hydrogen evolution in acidic media, the influence of adding small amounts (≤10 mol.%) of Ru to the Ni0.7-W0.3 sample was studied. Ruthenium is known for its highly efficient performance in the HER and is considered a promising alternative to Pt due to its relatively low price and similar hydrogen bonding strength. Low-Ru-loading hybrid electrocatalysts have great potential as efficient materials for HER, achieving a balance of low cost and high activity.
Herein, ternary (Ni0.7-W0.3)1-xRux (x = 0, 2, 4, 6, 8, 10) nanocomposite electrocatalysts with different proportions of Ru were synthesized using the solution combustion synthesis (SCS) method, followed by annealing under a reductive atmosphere (10 vol.% H2/Ar flow) for application as HER electrocatalysts in acidic electrolysis. Morphological characteristics of the nanocomposite materials were examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), along with energy-dispersive X-ray spectroscopy (EDX). Microscopy techniques revealed a porous, coral-like morphology, a distinctive feature commonly observed in combustion products synthesized using the SCS methodology. EDX elemental mapping analyses confirmed the uniform dispersion of Ru, Ni, and W elements throughout the sample, suggesting a close interconnection of the ternary species within the nanostructure. N2 adsorption/desorption measurements showed a high specific surface area and mesoporous structures in the as-prepared products. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses revealed that the (Ni0.7-W0.3)1-xRux nanocomposites consist of Ru and Ni0.85W0.15 metallic phases, along with oxygen-deficient WO2, with their composition varying depending on the Ru:Ni:W molar ratio in the precursor solution.
Electrochemical assessments in an acidic medium (0.5 M H2SO4) using linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) unveiled that the incorporation of Ru into the Ni0.7-W0.3 matrix yielded a synergetic effect, resulting in a significant improvement of the catalyst’s intrinsic electrocatalytic activity relative to both Ni0.7-W0.3 and the commercial 5 wt.% Ru/C. This improvement was attributed to the synergistic effects arising from the change in the electronic structure of the catalyst induced by the interaction between different electrocatalyst components (Ru, Ni, and W), which effectively accelerated the kinetics of the HER, enhancing the catalytic activity. The change in the electronic structure was evident in the spectroscopy techniques, which revealed the shift in the oxidation state of Ru, inducing a downshift of the d-band center of Ru nanoparticles, resulting in reduced binding strength to reactive intermediates and improved HER kinetics on the Ru surface. Furthermore, its three-dimensional structure, stemming from the nanoparticle morphology and mesoporous structure, contributes to the high exposure of active sites throughout the nanocomposite material. This work has demonstrated that engineering the electronic interactions between ternary composite systems is a promising route for constructing high-performance electrocatalysts. Although inferior to the state-of-the-art 20 wt.% Pt/C, the ternary Ru-Ni-W nanocomposite emerges as a promising and cost-effective alternative cathode material for HER in acidic media. This research contributes to the ongoing efforts to develop efficient and economically viable electrocatalysts for renewable energy technologies.