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Enhanced hydrogen evolution reaction on hybrids of cobalt phosphide and molybdenum phosphide

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ABSTRACT

Production of hydrogen from water electrolysis has stimulated the search of sustainable electrocatalysts as possible alternatives. Recently, cobalt phosphide (CoP) and molybdenum phosphide (MoP) received great attention owing to their superior catalytic activity and stability towards the hydrogen evolution reaction (HER) which rivals platinum catalysts. In this study, we synthesize and study a series of catalysts based on hybrids of CoP and MoP with different Co/Mo ratio. The HER activity shows a volcano shape and reaches a maximum for Co/Mo = 1. Tafel analysis indicates a change in the dominating step of Volmer–Hyrovský mechanism. Interestingly, X-ray diffraction patterns confirmed a major ternary interstitial hexagonal CoMoP2 crystal phase is formed which enhances the electrochemical activity.

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SEM images of (a) CoP, (b) Co0.5Mo0.5P and (c) MoP crystals taken at a magnification of 100 000x.
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RSOS161016F3: SEM images of (a) CoP, (b) Co0.5Mo0.5P and (c) MoP crystals taken at a magnification of 100 000x.

Mentions: The reaction between the cobalt and/or molybdenum precursors with ammonium hydrogen phosphate under hydrogen environment at 800°C generated uniform phosphide microparticles. The SEM image in figure 3 shows that the CoP and the Co0.5Mo0.5P samples are composed of primary particles, but the MoP contains mostly secondary aggregated particles. These results indicate that the ratio of Co and Mo precursors affects the basic morphology of the catalysts. This can be ascribed to the complicated decomposition process regarding the reduction of MoOx in the high-temperature reduction reaction. The Co0.5Mo0.5P hybrid was characterized by transmission electron microscopy (TEM). The TEM image (see the electronic supplementary material, figure S3) showed interconnected structure composed of large particles (0.3–0.6 µm) which is in good agreement with the SEM result. The energy dispersive X-ray (EDX) spectra (as shown in electronic supplementary material, figure S4) collected on the TEM showed signals from Co, Mo and P elements. The Cu signals resulted from the Cu grid. The atomic percentages of Co, Mo and P elements obtained are 26.9, 24.2 and 48.9%, respectively, which answers to the composition of Co0.5Mo0.5P well.Figure 3.


Enhanced hydrogen evolution reaction on hybrids of cobalt phosphide and molybdenum phosphide
SEM images of (a) CoP, (b) Co0.5Mo0.5P and (c) MoP crystals taken at a magnification of 100 000x.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5383849&req=5

RSOS161016F3: SEM images of (a) CoP, (b) Co0.5Mo0.5P and (c) MoP crystals taken at a magnification of 100 000x.
Mentions: The reaction between the cobalt and/or molybdenum precursors with ammonium hydrogen phosphate under hydrogen environment at 800°C generated uniform phosphide microparticles. The SEM image in figure 3 shows that the CoP and the Co0.5Mo0.5P samples are composed of primary particles, but the MoP contains mostly secondary aggregated particles. These results indicate that the ratio of Co and Mo precursors affects the basic morphology of the catalysts. This can be ascribed to the complicated decomposition process regarding the reduction of MoOx in the high-temperature reduction reaction. The Co0.5Mo0.5P hybrid was characterized by transmission electron microscopy (TEM). The TEM image (see the electronic supplementary material, figure S3) showed interconnected structure composed of large particles (0.3–0.6 µm) which is in good agreement with the SEM result. The energy dispersive X-ray (EDX) spectra (as shown in electronic supplementary material, figure S4) collected on the TEM showed signals from Co, Mo and P elements. The Cu signals resulted from the Cu grid. The atomic percentages of Co, Mo and P elements obtained are 26.9, 24.2 and 48.9%, respectively, which answers to the composition of Co0.5Mo0.5P well.Figure 3.

View Article: PubMed Central - PubMed

ABSTRACT

Production of hydrogen from water electrolysis has stimulated the search of sustainable electrocatalysts as possible alternatives. Recently, cobalt phosphide (CoP) and molybdenum phosphide (MoP) received great attention owing to their superior catalytic activity and stability towards the hydrogen evolution reaction (HER) which rivals platinum catalysts. In this study, we synthesize and study a series of catalysts based on hybrids of CoP and MoP with different Co/Mo ratio. The HER activity shows a volcano shape and reaches a maximum for Co/Mo = 1. Tafel analysis indicates a change in the dominating step of Volmer–Hyrovský mechanism. Interestingly, X-ray diffraction patterns confirmed a major ternary interstitial hexagonal CoMoP2 crystal phase is formed which enhances the electrochemical activity.

No MeSH data available.