Yagya N. Regmi

Multiple Phases of Molybdenum Carbide as Electrocatalysts for the Hydrogen Evolution Reaction

Molybdenum carbide has been proposed as a possible alternative to platinum for catalyzing the hydrogen evolution reaction (HER). Previous studies were limited to only one phase, β-Mo2C with an Fe2N structure. Here, four phases of Mo-C were synthesized and investigated for their electrocatalytic activity and stability for HER in acidic solution. All four phases were synthesized from a unique amine-metal oxide composite material including γ-MoC with a WC type structure which was stabilized for the first time as a phase pure nanomaterial. X-ray photoelectron spectroscopy (XPS) and valence band studies were also used for the first time on γ-MoC. γ-MoC exhibits the second highest HER activity among all four phases of molybdenum carbide, and is exceedingly stable in acidic solution.

Carbides of group IVA, VA and VIA transition metals as alternative HER and ORR catalysts and support materials

High surface area nano dimensional carbides of nine transition metals in group IV–VI have been synthesized using a salt flux method. Uniformity was maintained throughout the investigation, from synthesis method to electrochemical tests, so that a comparison can be made for the various carbides for their catalytic activities towards hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). Catalytic activities are dependent on synthesis method which determines the properties of the catalyst, and electrochemical conditions. Maintaining uniformity throughout the investigation allows for a more balanced comparison of a family of materials. Activity of all nine carbides show increased HER activity compared to bare glassy carbon working electrode. Mo2C, WC, and V8C7 show particularly enhanced HER activity. Similarly, Mo2C, Cr3C2, and V8C7 have significant ORR activities. Using a wet impregnation method, dispersed platinum nanoparticles ranging between 3 and 5 nm were successfully deposited on the carbides. The Pt deposited carbides have as much as three times higher HER activity and four times higher ORR activity compared to commercially available Pt/C catalyst, and show enhanced stability under fuel cell conditions.

Nanocrystalline Mo2C as a Bifunctional Water Splitting Electrocatalyst

Mo2C is a well‐known low cost catalyst for the hydrogen evolution reaction (HER), but the other water splitting half reaction, the oxygen evolution reaction (OER), has not been previously reported. To investigate both reactions and the origin of the catalytic sites, four synthesis methods were employed to prepare hexagonal Fe2N type Mo2C. A comparison of the HER activities in acidic and alkaline electrolyte and OER activities in alkaline electrolyte revealed that changes in synthesis route leads to morphological and surface composition variations resulting in different catalytic activities. In general, the trend in HER and OER activities show remarkably similar trends across the carbides synthesized via different routes irrespective of either electrolyte employed or reaction probed for electrocatalytic activities. Mo2C templated on multiwalled carbon nanotubes demonstrated the highest bifunctional catalytic activities, as well as superior electrochemical stability for both HER and OER.

Electrocatalytic Activity and Stability Enhancement through Preferential Deposition of Phosphide on Carbide

Phosphides and carbides are among the most promising families of materials based on earth‐abundant elements for renewable energy conversion and storage technologies such as electrochemical water splitting, batteries, and capacitors. Nickel phosphide and molybdenum carbide in particular have been extensively investigated for electrochemical water splitting. However, a composite of the two compounds has not been explored. Here, we demonstrate preferential deposition of nickel phosphide on molybdenum carbide in the presence of carbon by using a hydrothermal synthesis method. We employ the hydrogen evolution reaction in acid and base to analyze the catalytic activity of phosphide‐deposited carbide. The composite material also shows superior electrochemical stability in comparison to unsupported phosphide. We anticipate that the enhanced electrochemical activity and stability of carbide deposited with phosphide will stimulate investigations into the preparation of other carbide–phosphide composite materials.