Raman Spectroscopy as Molybdenum and Tungsten Content Analysis Tool for Mesoporous Silica and Beta Zeolite Catalysts

Highly Active and Durable Nanostructured Nickel-Molybdenum Coatings as Hydrogen Electrocatalysts via Solution Precursor Plasma Spraying

The increasing demand for green hydrogen is driving the development of efficient and durable electrocatalysts for the hydrogen evolution reaction (HER). Nickel-molybdenum (NiMo) alloys are among the best HER electrocatalysts in alkaline electrolytes, and here we report a scalable solution precursor plasma spraying (SPPS) process to produce the highly active Ni4Mo electrocatalysts directly onto metallic substrates. The NiMo coating coated onto inexpensive Ni mesh revealed an excellent HER performance with an overpotential of only 26 mV at -10 mA cm-2 with a Tafel slope of 55 mV dec-1. Excellent operational stability with minimum changes in overpotential were also observed even after extensive 60 hour high-current stability test. In addition, we investigate the influence of different substrates over the catalytic performance and operational stability. We also proposed that a slow, but consistent, dissolution of Mo is the primary degradation mechanism of NiMo-based coatings. This unique SPPS approach enables the scalable production of exceptional NiMo electrocatalysts with remarkable activity and durability, positioning them as ideal cathode materials for practical applications in alkaline water electrolysers.

Quaternary Mixed Oxides of Non-Noble Metals with Enhanced Stability during the Oxygen Evolution Reaction

Robust electrocatalysts required to drive the oxygen evolution reaction (OER) during water electrolysis are still a missing component toward the path for sustainable hydrogen production. Here a new family of OER active quaternary mixed-oxides based on X-Sn-Mo-Sb (X = Mn, Fe, Co, or Ni) is reported. These nonstoichiometric mixed oxides form a rutile-type crystal structure with a random atomic motif and diverse oxidation states, leading to the formation of cation vacancies and local disorder. The successful incorporation of all cations into a rutile structure was achieved using oxidizing agents that facilitates the formation of Sb5+ required to form the characteristic octahedral coordination in rutile. The mixed oxides exhibit enhanced stability in both acidic and alkaline environments under anodic potentials with no changes in their crystal structure after extensive electrochemical stress. The improved stability of these mixed oxides highlights their potential application as scaffolds to host and stabilize OER active metals.

A Two-Step Femtosecond Laser-Based Deposition of Robust Corrosion-Resistant Molybdenum Oxide Coating

A two-step femtosecond-pulsed laser deposition (fs-PLD) process is reported for the rapid development of uniform, poreless, crack-free, and well-adhering amorphous coatings of source materials with a high melting point. The first step comprises a high-rate raw deposition of the source material via fs-PLD, followed by a second step of scanning the raw sample with fs laser pulses of optimized fluence and scan parameters. The technique is applied to develop substoichiometric molybdenum oxide (MoO_x, x < 3) coatings on mild steel. The thickness of the layer was ~4.25 μm with roughness around 0.27 μm. Comprehensive surface characterization reveals highly uniform and relatively moderate roughness coatings, implying the potential of these films as robust corrosion-resistant coats. Corrosion measurements in an aqueous NaCl environment revealed that the coated mild steel samples possess an average corrosion inhibition efficiency of around 95% relative to polished mild steel.

Insights into the effect of oxygen vacancies on the epoxidation of 1-hexene with hydrogen peroxide over WO3−x/SBA-15

The introduction of oxygen vacancies improved 1-hexene epoxidation performance over WO3−x/SBA-15 catalysts, which is attributed to the enhanced Lewis acidity of the active centers and the reduced energy barrier of the rate-determining step.