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

Abstract

It is urgently required to develop highly efficient and stable bifunctional non‐noble metal electrocatalysts for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) for water splitting. In this study, a facile electrospinning followed by a post‐carbonization treatment to synthesize nitrogen‐doped carbon nanofibers (NCNFs) integrated with Ni and Mo2C nanoparticles (Ni/Mo2C‐NCNFs) as water splitting electrocatalysts is developed. Owing to the strong hydrogen binding energy on Mo2C and high electrical conductivity of Ni, synergetic effect between Ni and Mo2C nanoparticles significantly promote both HER and OER activities. The optimized hybrid (Ni/Mo2C(1:2)‐NCNFs) delivers low overpotentials of 143 mV for HER and 288 mV for OER at a current density of 10 mA cm−2. An alkaline electrolyzer with Ni/Mo2C(1:2)‐NCNFs as catalysts for both anode and cathode exhibits a current density of 10 mA cm−2 at a voltage of 1.64 V, which is only 0.07 V larger than the benchmark of Pt/C‐RuO2 electrodes. In addition, an outstanding long‐term durability during 100 h testing without obvious degradation is achieved, which is superior to most of the noble‐metal‐free electrocatalysts reported to date. This work provides a simple and effective approach for the preparation of low‐cost and high‐performance bifunctional electrocatalysts for efficient overall water splitting.

Sandwiched NiO/β‐Mo2C/RGO as Improved Electrocatalyst for Hydrogen Evolution Reaction: Solvothermal‐Assisted Self‐Assembly and Catalytic Mechanism

“…The binding energies of Ni 2p of Ni 2+ in the NiO/β‐Mo 2 C/RGO are distinctly higher than those (855.1 eV for 2p 3/2 and 873.6 eV for 2p 1/2 ) of Ni anchored on graphene, indicating higher valence state of Ni species in NiO/β‐Mo 2 C/RGO. The opposite shifts of binding energies of Mo 3d, C 1s, and Ni 2p can be explained by electron transfer from Ni to Mo 2 C, this was also observed in previous work and showed an important effect on the surface electronic state of Mo 2 C and thus the electrocatalytic HER activity. No peak related to Ni 0 was observed in the Ni 2p XPS spectrum, confirming that Ni species exists in the form of nickel oxide, this is in good agreement with the observation of the characteristic lattice fringes of nickel oxide in the high‐resolution TEM (HRTEM) image.…”

“…As shown in it, an increased electron density presents on the Mo and C atoms, which located near the loading NiO. This indicates the distinct charge transfers from NiO to Mo 2 C, which has also been confirmed by XPS analysis . The loading NiO modified the electronic structure of β‐Mo 2 C and changed the electron density on the surface of β‐Mo 2 C (101) to electron‐rich state, the number of unoccupied d orbitals of Mo was effectively reduced to enhance the HER activity .…”

“…This indicates the distinct charge transfers from NiO to Mo 2 C, which has also been confirmed by XPS analysis. [31] The loading NiO modified the electronic structure of β-Mo 2 C and changed the electron density on the surface of β-Mo 2 C (101) to electron-rich state, the number of unoccupied d orbitals of Mo was effectively reduced to enhance the HER activity. [32] The hydrogen absorption Gibbs free energies (ΔG H* ) on β-Mo 2 C (101) and NiO/β-Mo 2 C (101), an indicator for the HER electrocatalytic activity, have been calculated and shown in Figure 6d.…”

“…[29] A Ni-Mo 2 C/C composite electrocatalyst with higher HER activity than Mo 2 C/C composite catalyst was also reported by Wang et al [30] Ni strongly coupled with Mo 2 C encapsulated in nitrogen-doped carbon nanofibers was prepared via facile electrospinning followed by a postcarbonization treatment and had a low overpotential of 143 mV at a current density of 10 mA cm À 2 for HER in alkaline solution. [31] Heterostructures composed of N-Doped carbon nanotubes encapsulating cobalt and β-Mo 2 C nanoparticle exhibited excellent HER activity with η 10 values of 170 mV in alkaline electrolyte. [32] However, these catalysts involve complicated in-situ carbonization and transition metal doping process, this limits their extensive industrial application.…”

Pore Surface Engineering of Covalent Triazine Frameworks@MoS2 Electrocatalyst for the Hydrogen Evolution Reaction

“…By thermogravimetry [differential scanningc alorimetry (DSC)/thermal gravimetric analysis (TGA)]m easurements ( Figure S13), we established that the intercalation compound was NH 4 + . [36,37] More importantly,t he MoS 2 nanoparticles are tightly grown on the surfaceo fc rystal CTFs and the synergistic effect of the coordi-nation of triazine units with Mo atoms will sharplyi ncrease the catalytic active sites, accelerating the mass and charget ransfer in HER. In reported 2D CTFs, highly orderedA A( fully eclipsed) stacking leads to large electrostatic coupling and charged elocalization, thus the electron can be not only delocalized effectively in the 2D plane, but also transmitted in the vertical 2D plane direction.…”