Rationally Dispersed Molybdenum Phosphide on Carbon Nanotubes for the Hydrogen Evolution Reaction

Abstract

Molybdenum phosphide (MoP) is viewed as a potential electrocatalyst for the electrochemical hydrogen evolution reaction (HER). However, crystallization of MoP occurs at rather high temperature (>600 °C). At this temperature, coalescence and agglomeration, which affect the performance severely, become inevitable. Herein, an oxalate-guided nonhydrolytic method is demonstrated for the preparation of MoP with smaller particle size and better dispersion qualities onto the surface of carbon nanotubes (CNTs). Molybdenum is coordinated with the oxalate group using oxalic acid, which modifies the self-assembling of molybdenum at the molecular level and renders discrete nucleation and growth of MoP on CNTs. Phosphoric acid (crystalline) was used as a source of phosphorus. The method is simple with the potential to scale-up. A probable mechanism for the growth of MoP on CNTs is proposed. The as-derived MoP/CNT electrode exhibits excellent performance, outperforming most of the MoP-based electrocatalysts, for hydrogen evolution in both acidic and basic media. In addition, the electrode possesses excellent stability. The higher performance of the electrode is rationalized in terms of small particle size with uniform dispersion, high specific and electrochemically active surface area, electrical conductivity, interfacial charge transfer kinetics, and turnover frequency. Estimation of Tafel slope is consistent with electrochemical desorption of hydrogen gas following the Volmer−Heyrovsky mechanism as the rate-determining step.

Multi‐Elemental Electronic Coupling for Enhanced Hydrogen Generation

“…The hydrogen turnover frequency (TOF) for each active site of NPSCL@S-MoP NSs/CC and S-MoP NSs/CC were estimated based on a common method reported in previous studies to reveal the intrinsic catalytic activity of these electrocatalysts in acidic medium as well as illustrate the synergistic effect of S-MoP NSs and NPSCL. [29] As it can be seen in the polarization curves shown in Figure S8 (Supporting Information), after being normalized by the active sites and expressed in terms of TOF, an overpotential of ≈106 mV is needed to achieve a TOF of 1.0 s −1 for NPSCL@S-MoP NSs/CC, which is much smaller than that required for S-MoP NSs/CC (161 mV) and superior to the reported MoP/CC (0.93 s −1 at η = 114 mV) [30] and MoP@NC-MF (0.6 s −1 at η = 150 mV). [31] This result suggests that the NPSCL@S-MoP NSs/CC obtained by hybridizing S-MoP NSs with NPSCL can enhance the intrinsic HER activity via their synergistic effects.…”

Facile fabrication of MoP nanodots embedded in porous carbon as excellent anode material for potassium-ion batteries

“…The peak located at 134.4 eV is assigned to PAO bond caused by slight oxidation [63]. Meanwhile, the peak at 130.2 eV can be attributed to the PAMo bond in MoP@PC [64]. The XPS spectrum of N 1 s shows two peaks: pyridinic nitrogen (397.8 eV) and graphitic nitrogen (400.2 eV) ( Fig.…”

Synthesis of Co-Doped Tungsten Phosphide Nanoparticles Supported on Carbon Supports as High-Efficiency HER Catalysts

“…These two peaks are caused by oxidation during passivation and exposure to air. 45,47 In the P 2p spectrum (Figure 2b), doublet peaks near 130.1 eV, together with the ones near 129.2 eV, are assigned to P bonded to W in the form of metal phosphide (P δ− ), 11 and the superficial oxidation in air or the passivation procedure results in the oxidized P species, whose peaks are among 133.4−134.0 eV, coinciding with previous reports. 22,31,48 Of particular note are the peaks near 132.9 eV, which can be ascribed to P−C species.…”

“…Both the results of the lattice spacing in HRTEM pictures and diffraction spots in SAED strengthen our initial assumption that the complexation of tungsten and cobalt with citric acid contributes to a good combination of Co and a discrete complex distance and thus control the growth of WP nanoparticles. 47,62 This leads to the formation of the well and uniformly dispersed WP on KB and the successful intrusion of Co into the crystalline structure of WP. Moreover, energy-dispersive X-ray spectroscopy (EDS) mapping is used to probe the elemental distribution further (Figures S5−S7).…”