Electrocatalytic performance of ultrasmall Mo₂C affected by different transition metal dopants in hydrogen evolution reaction

Abstract

Molybdenum carbides are considered as one type of privileged noble-metal-free electrocatalysts for hydrogen evolution reactions (HER) due to their d-band electron structure, which is similar to Pt. Especially, the electronic structure of such materials can be further adjusted by elemental doping to improve their electrocatalytic activity. Herein, we selected the Anderson-type polyoxometalates (POMs) (NH4)n[TMMo6O24H6]·5H2O (TM = Ni2+, Co2+, n = 4; TM = Fe3+, Cr3+, n = 3) as precursors to prepare new transition-metal-doped Mo2C materials. When these POMs were mixed with dicyandiamide (DCA) by solid grinding, and carbonized at a high temperature, a series of Ni-, Co-, Fe-, and Cr-doped Mo2C composite nanoparticles covered by few-layer graphitic carbon shells (abbr. TM-Mo2C@C) were obtained. All these nanoparticles possess a similar size, morphology, and TM/Mo component ratio, and thus it is feasible to systematically investigate the influence of different TM dopants on the electrocatalytic activity of Mo2C for HER. Both electrocatalytic experiments and DFT calculations reveal that TM dopants have a significant effect on the hydrogen binding energy (ΔGH*) and the catalytic activity of Mo2C. The sequence of HER electrocatalytic activity is as follows: Ni-Mo2C > Co-Mo2C > Fe-Mo2C > Cr-Mo2C. As a result, Ni-Mo2C@C possesses the best HER performance, which required an overpotential of 72 mV at a current density of 10 mA cm-2 and the Tafel slope is 65.8 mV dec-1. This work suggests a shortcut to reasonably investigate the effects of elemental doping on molybdenum carbides and explore new high-efficient and low-cost electrocatalysts for HER.

Ni Strongly Coupled with Mo2C Encapsulated in Nitrogen‐Doped Carbon Nanofibers as Robust Bifunctional Catalyst for Overall Water Splitting

“…In‐depth test of N 1s spectra at 398.8, 399.8, and 401.5 eV can be ascribed to pyridinic N, pyrrolic N, and graphitic N, respectively (Figure d) . The N 1s XPS profile illustrates that most N atoms are doped into the carbon framework and the C atoms adjacent to the N atoms in the N‐doped carbon provides better catalytic performance …”

“…In recent years, transition metal carbides have attracted ample attention as promising HER electrocatalysts because of their favorable corrosion resistance, high mechanical strength, and excellent stability . Among them, molybdenum carbide (Mo 2 C) is interesting due to its innocuous preparation process, large pH stability, and equivalent d‐band electronic structure to Pt‐group metals, demonstrating a great potential as an electrocatalyst candidate for the hydrogen generation. In spite of the aforementioned advantages, in view of its poor conductivity and slow interfacial reaction kinetics, the catalytic activity of Mo 2 C alone are far from that of Pt‐based materials.…”

Structural Design and Electronic Modulation of Transition‐Metal‐Carbide Electrocatalysts toward Efficient Hydrogen Evolution

“…And the accordingly lower Tafel slope on Fe‐Ni 3 C suggested the promoted H ads desorption due to doping. To systematically investigate the influence of different transition‐metal (TM) doping in HER, Li and co‐workers recently selected the Anderson‐type polyoxometalates (POMs) (NH 4 ) n [TMMo 6 O 24 H 6 ]·5H 2 O (TM = Ni 2+ , Co 2+ , n = 4; TM = Fe 3+ , Cr 3+ , n = 3) as precursors to prepare a series of Ni‐, Co‐, Fe‐, and Cr‐doped Mo 2 C nanoparticles covered by a few‐layer graphitic carbon shells . Both electrocatalytic experiments and DFT calculations revealed that TM dopants have a significant effect on the ΔG H* and the catalytic activity of Mo 2 C. The sequence of activity is as follows: Ni–Mo 2 C > Co–Mo 2 C > Fe–Mo 2 C > Cr–Mo 2 C, consistent with their gradually weakened H‐binding.…”

Synergistic Effect of Molybdenum and Tungsten in Highly Mixed Carbide Nanoparticles as Effective Catalysts in the Hydrogen Evolution Reaction under Alkaline and Acidic Conditions

“…[11] Thus, to intrinsically improve the performance of Mo carbide in catalyzing the HER, the most straight-forward solution is to weaken the strong MoÀ H ads bond, so that the H ads À H ads recombination step (the Tafel reaction) or the H ads À H + electrochemical desorption step (the Heyrovsky reaction) are facilitated for faster H 2 generation. Various efforts have been made to achieve this goal such as doping with non-metallic elements, e. g. N, P, S [12][13][14] and electron-rich metals, e. g. Fe, Co, [15][16][17] and the fabrication of heterogeneous structures consisting of Mo carbides and other materials. [18][19][20] These attempts improved the electrocatalytic performance to some degree, but led to slow mass transport of both reactants and products, low carbide crystallinity and decreased stability.…”