Nitrogen‐Doped Porous Molybdenum Carbide and Phosphide Hybrids on a Carbon Matrix as Highly Effective Electrocatalysts for the Hydrogen Evolution Reaction

Abstract

Platinum (Pt) is the most active and stable HER catalyst, but its high cost and low abundance hinder its widespread applications. [3][4][5][6] Recently, tremendous efforts have been devoted to the search for noble-metal-free catalysts to replace Pt-based catalysts in the generation of H 2 with a high current density at a low overpotential. [7][8][9][10] In particularly, molybdenum carbides and molybdenum phosphides have been demonstrated as active and robust HER catalysts due to their high conductivities, high catalytic activities, and excellent stabilities. [11][12][13][14][15] The high-performance catalytic activities of these materials may be related to the function of their heteroatoms, such as phosphorus, which possesses lone-pair electrons in 3p orbitals and vacant 3d orbitals and can thus accommodate the surface charge as well as induce local charge density. [16] Nitrides of transition metals have also been shown to have excellent catalytic activities in the HER. [17][18][19][20][21] Taking all the above works together, we predicted that nitrogen (N)-doped molybdenum carbide and phosphide hybrids, N@MoPCx, might be promising electrocatalysts for efficient hydrogen evolution. However, it remains a challenge to obtain a targeted N-doped molybdenum carbide and phosphide hybrid with a uniform distribution and desirable porosity that also exhibits high electrocatalytic activity, which requires (i) preventing the aggregation of nanoparticles; (ii) obtaining a desirable porosity; and (iii) achieving uniform carburization, phosphorization, and heteroatoms doping. To avoid the aggregation of nanoparticles and increase their electrical conductivities, substrates such as carbon cloth, carbon nanotubes, and graphene have been introduced into metal-based catalysts for use in multiple catalytic reactions. [22][23][24] However, the introduction of substrates creates additional cost and still cannot completely prevent aggregation.Polyoxometalates (POMs) are a special class of well-defined molecular metal oxide clusters with a wide range of applications in medicine, catalysis, materials sciences, etc. [25][26][27][28][29][30] It is well known that organoimido derivatives of POMs can be prepared by introducing exogenous N-containing ligands to replace the oxo groups in the POM clusters. [31][32][33][34][35] The controllable preparation of multifunctionalized derivatives of hexamolybdate has been achieved by the powerful N,N′-dicyclohexylcarbodiimide (DCC)-dehydrating protocol by Ruhlmann and our group. [36,37] P-containing organoimido derivatives of POMs could be The efficient evolution of hydrogen through electrocatalysis is considered a promising approach to the production of clean hydrogen fuel. Platinum (Pt)-based materials are regarded as the most active hydrogen evolution reaction (HER) catalysts. However, the low abundance and high cost of Pt hinders the large-scale application of these catalysts. Active, inexpensive, and earth-abundant electrocatalysts to replace Pt-based materials would be highly beneficial to the ...

In Situ Grown Bimetallic MOF‐Based Composite as Highly Efficient Bifunctional Electrocatalyst for Overall Water Splitting with Ultrastability at High Current Densities

“…In the equivalent circuit model, R s , R p , and R ct denote the solution, electrode porosity, and charge transfer resistances, respectively, whereas the CPE and C dl represent the constant phase element and double-layer capacitance, respectively. [45] The stability of the electrocatalysts at high current densities is one of the major concerns for large-scale practical applications. [46] In fact, the trend of R ct is in accord with those of η 10 , η 250 , η 500 , and Tafel slope.…”

“…The HER kinetic characteristics of the NFN-MOF/NF and comparison electrodes were next studied with Tafel plots (Figure 3c). [45] The high current stability of the NFN-MOF/NF electrode toward the HER was next evaluated with chronoamperometric and chronopotentiometric measurements for 30 h at −250 and −500 mA cm −2 . To further investigate the kinetic characteristics of the four sample electrodes, EIS was conducted at −0.20 V over a frequency range of 100 kHz to 100 mHz in 1 m KOH (Figure 3d).…”

Fine Tuning Electronic Structure of Catalysts through Atomic Engineering for Enhanced Hydrogen Evolution

“…[50][51][52][53] Covalently incorporating functional organic moieties in a controllable manner onto the POMs surfaces make the precursor structure versatility more accessible. [57] Herein, we propose that the amount of nitrogen incorporations into Mo 2 C structure could be well controlled by using various organoimido-derivatized POMs with inherent MoN bonds as precursors (Scheme 1). [54][55][56] Recent work by our group has demonstrated that organoimido-derivatized POM clusters with arylamine ligands and phenylphosphonic acid ligands can function as the molybdenum, carbon, nitrogen, and phosphorus sources, and in situ carbonization will result in the formation of Mo 2 C and MoP hybrids.…”

Devisable POM/Ni Foam Composite: Precisely Control Synthesis toward Enhanced Hydrogen Evolution Reaction at High pH

“…As revealed by the charge transfer resistance ( R ct ) in Table , the NiCo‐POM/Ni electrode displayed the R ct of 11.9 Ω, which was lower than those of NiMn‐POM/Ni (12.6 Ω), NiZn‐POM/Ni (15.1 Ω) and Ni‐POM/Ni (13.6 Ω). This result indicated that the NiCo‐POM/Ni possessed the lowest charge‐transfer resistance and superior conductivity, which enabled efficient interfacial electron transport without a binder or conductive additive for HER . To rationalize whether this finding was correlated to the electrochemically active surface areas (ECSA) of the electrodes, the ECSA values was determined based on the double‐layer capacitance ( C dl ) calculated from voltammetric data in the non‐faradaic region.…”