Ultra‐Small Molybdenum Carbide Nanoparticles in situ Entrapped in Mesoporous Carbon Spheres as Efficient Catalysts for Hydrogen Evolution

Unlocking Efficiency: Minimizing Energy Loss in Electrocatalysts for Water Splitting

Catalysts play a crucial role in water electrolysis by reducing the energy barriers for hydrogen and oxygen evolution reactions (HER and OER). Research aims to enhance the intrinsic activities of potential catalysts through material selection, microstructure design, and various engineering techniques. However, the energy consumption of catalysts has often been overlooked due to the intricate interplay among catalyst microstructure, dimensionality, catalyst-electrolyte-gas dynamics, surface chemistry, electron transport within electrodes, and electron transfer among electrode components. Efficient catalyst development for high-current-density applications is essential to meet the increasing demand for green hydrogen. This involves transforming catalysts with high intrinsic activities into electrodes capable of sustaining high current densities. This review focuses on current improvement strategies of mass exchange, charge transfer, and reducing electrode resistance to decrease energy consumption. It aims to bridge the gap between laboratory-developed, highly efficient catalysts and industrial applications regarding catalyst structural design, surface chemistry, and catalyst-electrode interplay, outlining the development roadmap of hierarchically structured electrode-based water electrolysis for minimizing energy loss in electrocatalysts for water splitting.

Design of a long-lived Mo2C-MoO2@GC-N electrocatalyst by the ambient DC arc plasma for the hydrogen evolution reaction

A crucial challenge in hydrogen production through electrolysis is developing inexpensive, earth-abundant, and highly efficient Pt-free electrocatalysts for the hydrogen evolution reaction (HER). Molybdenum carbide is ideal for this application because of its special electrical structure, low cost, and advantageous characteristics. Herein, the long-lived electrocatalysts for HER have been synthesized via the direct current (DC) arc discharge plasma method under ambient air conditions, and the relationship between the properties of materials and catalytic characteristics has been established. The samples differed in the ratio of molybdenum, graphite, and melamine. The sample with the highest proportion of melamine in the initial mixture has Mo2C-MoO2 heterointerfaces, which demonstrates the highest and most stable electrocatalytic activity with the overpotential of 148 mV at 10 mA·cm-2 and Tafel slope of 63 mV·dec-1 in alkaline electrolyte. Meanwhile, the electrodes demonstrated long-lived electrochemical durability for two weeks and investigated the features of forming a stable system for HER.

Core-shell Mo2C@NC/Mo2C hollow microspheres as highly efficient electrocatalysts for the hydrogen evolution reaction

Developing low-cost and highly efficient electrocatalysts for the hydrogen evolution reaction (HER) has stimulated extensive interest. Molybdenum carbide materials have been proposed as promising alternatives to noble platinum-based catalysts due to their earth abundance and tunable physicochemical characteristics. Here, we report Mo₂C@NC/Mo₂C hollow microspheres composed of a β-Mo₂C core and small β-Mo₂C particles embedded within a nitrogen-doped carbon shell and prepared using guanosine and hexaammonium molybdate as precursors via a hydrothermal self-assembly process, which results in outstanding catalytic activity and fast kinetics in hydrogen evolution in both acidic and alkaline solutions. The significant activity improvement of Mo₂C@NC/Mo₂C can be attributed to the large ratio of exposed active sites and abundant interfacial structures. This work provides a new template-free strategy for the design of a highly active Mo₂C@NC/Mo₂C hollow microsphere HER catalyst.

Anchoring ultra-small Mo2C nanocrystals on honeycomb-structured N-doped carbon spheres for efficient hydrogen evolution

Molybdenum carbide (Mo₂C) has attracted considerable research interest as one of the most efficient non-noble electrocatalysts for the hydrogen evolution reaction (HER). Supporting nanosized Mo₂C on a conductive carbon matrix with high porosity and large surface area represents an efficient strategy to enhance its HER performance. Herein, we constructed a Mo₂C based HER catalyst consisting of ultra-small Mo₂C nanocrystals anchored on honeycomb-structured N-doped carbon spheres (Mo₂C-HNCS). The as-prepared Mo₂C-HNCS manifests a high HER catalytic activity in alkaline media with an overpotential of 128 mV at 10 mA cm^-2, a Tafel slope of 60 mV decade^-1, and good stability.

Bifunctional Pt–Mo catalyst for in situ hydrogenation of methyl stearate into alkanes using formic acid as a hydrogen donor

In situ hydrogenation of methyl stearate on Pt–Mo/AC has a high hydrogen utilization rate due to the strong interaction between Pt and β-Mo2C.

Hierarchical Porous Molybdenum Carbide Based Nanomaterials for Electrocatalytic Hydrogen Production

The electrocatalytic hydrogen evolution reaction (HER) for the preparation of hydrogen fuel is a very promising technology to solve the shortage of hydrogen storage. However, in practical applications, HER catalysts with excellent performance and moderate price are very rare. Molybdenum carbide (Mo_xC) has attracted extensive attention due to its electronic structure and natural abundance. Here, a comprehensive review of the preparation and performance control of hierarchical porous molybdenum carbide (HP-Mo_xC) based catalysts is summarized. The methods for preparing hierarchical porous materials and the regulation of their HER performance are mainly described. Briefly, the HP-Mo_xC based catalysts were prepared by template method, morphology-conserved transformations method, and secondary conversion method of an organic-inorganic hybrid material. The intrinsic HER kinetics are enhanced by the introduction of a carbon-based support, heteroatom doping, and the construction of a heterostructure. Finally, the future development of HP-Mo_xC based catalysts is prospected in this review.

Agaric-derived N-doped carbon nanorod arrays@nanosheet networks coupled with molybdenum carbide nanoparticles as highly efficient pH-universal hydrogen evolution electrocatalysts

Non-precious, stable and efficient catalysts for the pH-universal hydrogen evolution reaction (HER) are highly desirable to meet the vast energy demands. Herein, we report a facile and scalable strategy using agaric as a precursor to construct a Mo2C-based HER electrocatalyst consisting of ultrafine Mo2C nanoparticles embedded within biomass-derived 3D N-doped carbon nanorod arrays@nanosheet networks (Mo2C@N-CANs). This electrocatalyst is highly active for the pH-universal hydrogen evolution reaction and requires overpotentials of only 82 mV, 100 mV and 350 mV to drive a current density of -10 mA cm-2 in acidic, alkaline and neutral media, exhibiting stable operation for 3000 cycles and 24 h long-term stability. Theoretical calculations indicate that coupling Mo2C, N and CANs into a hybrid results in producing wrinkles on carbon nanolayers, which changes the direction of sp2 hybrid orbitals to push the Gibbs free energy toward zero. This result reinforces the presence of a synergy effect between Mo2C and N-CANs in Mo2C@N-CAN catalysts, which leads to their impressive HER performances.