Crystal Structure and Composition-Dependent Electrocatalytic Activity of Ni–Mo Nanoalloys for Water Splitting To Produce Hydrogen

Abstract

Electrocatalytic water splitting presents an exciting opportunity to produce environmentally benign fuel to power human activities and reduce reliance on fossil fuels. Transition metal nanoparticles (NPs) and their alloys are emerging as promising candidates to replace expensive platinum group metal (PGM) catalysts. Herein, we report the synthesis of distinct crystal phases and compositions of Ni1–x Mo x alloy NPs as low-cost, earth-abundant electrocatalysts for the hydrogen evolution reaction (HER) in alkaline medium. Phase-pure cubic and hexagonal Ni and Ni1–x Mo x alloy NPs, with sizes ranging from 18 to 43 nm and varying Mo composition (∼0–11.4%), were produced by a low-temperature colloidal chemistry method. As-synthesized NPs show spherical to polygonal morphologies and a systematic shifting of Bragg reflections to lower 2θ angles with increasing Mo, suggesting the growth of homogeneous alloys. XPS analysis indicates the dominance of metallic Ni(0) and Mo(0) species in the core of the alloy NPs as well as the presence of higher valent Ni n+ and Mo n+ surface species, stabilized by surfactant ligands. The cubic alloys exhibit significantly higher HER activity in comparison to the hexagonal alloys. For a current density of −10 mA/cm2, the cubic alloys demonstrate overpotentials of −62 to −177 mV compared to −162 to −242 mV for the hexagonal alloys. The overpotentials of cubic alloys are comparable to the commercial Pt-based electrocatalysts for which the overpotentials range from −68 to −129 mV at −10 mA/cm2. In general, a decrease in overpotential and an increase in HER activity were observed with increasing concentration of Mo (up to 6.6%) for the cubic alloys. The cubic Ni0.934Mo0.066 alloy NPs exhibit the highest activity as alkaline HER electrocatalysts.

Molybdenum and Phosphorous Dual Doping in Cobalt Monolayer Interfacial Assembled Cobalt Nanowires for Efficient Overall Water Splitting

“…Although the Co-Mo-P/CoNWs showed a small gap of 55 mV compared with that of a commercial Pt/C product, its activity was one of the best nonprecious-metalbased catalysts stated in 1.0 m KOH (alkaline medium) so far (Figure 4c). [35][36][37][38][39][40][41][42][43][44] Impressively, a superior behavior of Co-Mo-P/CoNWs to Pt/C material was observed at a current density higher than 170 mA cm −2 . LSV curves of the Co-Mo-P/CoNWs in Figure S4a (Supporting Information) revealed that the current density response only slightly increased with the scan rate, implying that hydrogen could be mostly adsorbed or desorbed under even low scan rates.…”

Self‐Supporting Ni‐M (M = Mo, Ge, Sn) Alloy Nanosheets via Topotactic Transformation of Oxometallate Intercalated Layered Nickel Hydroxide Salts: Synthesis and Application for Electrocatalytic Hydrogen Evolution Reaction

“…Despite the exciting progresses made thus far, most of the reported Ni‐alloy electrocatalysts are either synthesized in the form of powders or prepared directly by electrodeposition of micrometer‐sized films . Typically, they would expose limited active sites, and require additional binder material such as Nafion to coat onto glassy carbon electrode, which will introduce extra interfacial resistance and deteriorate the electrocatalytic activity.…”

Intra-Lattice Inverse Charge Transfer in Bimetallic Electrocatalysts

“…The HER activity of Ni73Mo in 1M KOH is better or comparable with previously reported Ni-Mo catalysts with lower Ni:Mo ratio (Figure S15a). [19][20][21][22][23]34,[54][55][56][57][58][59] Also, since Mo is less abundant in the Earth's crust (28%) with respect to Ni (68%), the incorporation of nominal Mo in our case is commercially lucrative.…”