Electrochemical production of hydrogen from water has been directed to the search for non-noble metal based and earth-abundant catalysts. In this work, we propose a novel cost-effective catalyst, molybdenum phosphide that exhibits high activity towards the hydrogen evolution reaction (HER) in both acid and alkaline media even in bulk form. Comparative analysis of Mo, Mo3P and MoP as catalysts for HER clearly indicates that phosphorization can potentially modify the properties of the metal and different degrees of phosphorization lead to distinct activities and stabilities. Theoretical calculations by density functional theory also show that a simple phosphorization of molybdenum to form MoP introduces a good ‘H delivery’ system which attains nearly zero binding to H at a certain H coverage. With the combination of experimental results and theoretical calculations, this work has enlightened a new way of exploring cost-effective catalysts for HER.

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Molybdenum phosphide as an efficient electrocatalyst for the hydrogen evolution reaction

Development of nonnoble metal catalysts for hydrogen evolution reaction (HER) is critical to enable an efficient production of hydrogen at low cost and large scale. In this work, a novel bimetallic carbide nanostructure consisting of Mo2C and WC is synthesized. Based on a highly conductive WC backbone, nanosized Mo2C particles are integrated onto WC, forming a well-defined and highly robust nanowire structure. More importantly, it is found that electrochemical activation can partially remove surface carbon and activate the catalyst by changing its surface hydrophilicity. As a result, the residual carbon contributes positively to the activity, besides its role of protecting carbide from oxidation. Benefiting from the structure, the catalyst achieves high activity, stable electrolysis towards HER.

Novel molybdenum carbide-tungsten carbide composite nanowires and their electrochemical activation for efficient and stable hydrogen evolution

Searching for non-noble-metal hydrogen evolution reaction (HER) electrocatalysts with high efficiency and excellent durability is a great challenge for the hydrogen-based energy industry. In this paper, a three-dimensional self-supported hydrogen evolution cathode is present, where the MoP nanosheet array was grown on flexible carbon cloth (MoP NA/CC) via a two-step strategy: hydrothermally growing MoS 2 nanosheet array on CC (MoS 2 NA/CC) in advance, and then phosphidation to chemically convert the MoS 2 NA/CC precusor into MoP NA/CC. When used as an integrated three-dimensional electrode for HER, MoP NA/CC shows a quiet low onset overpotential (50 mV vs reversible hydrogen electrode), high current density (j > 10 mA cm −2 at η = 124 mV), and a small Tafel slope (58 mV dec −1 ), as well as remarkable stability (

Flexible molybdenum phosphide nanosheet array electrodes for hydrogen evolution reaction in a wide pH range

A composite of ultrafine MoO2 nanoparticles homogeneously distributed in a carbon matrix has been fabricated on a large scale by an easy impregnation–reduction–carbonization route. Firstly, a cotton/PMA composite was formed by incorporating phosphomolybdate clusters into a cotton framework. Then it was treated in a H2/Ar atmosphere at 500 °C for 5 h and in situ reduced/carbonized into a black monolith comprising ultrafine MoO2 nanoparticles (<2 nm) embedded in the carbon matrix. The electrochemical tests demonstrate that the as-formed MoO2/C hybrid exhibits high capacity and excellent capacity retention as an anode material for lithium-ion batteries. The specific discharge capacity is as high as 1207 mA h g−1 in the first cycle and 734 mA h g−1 over 350 cycles at a current density of 50 mA g−1.

Ultrafine MoO2 nanoparticles embedded in a carbon matrix as a high-capacity and long-life anode for lithium-ion batteries

This paper presents a novel strategy to synthesize MoO2/carbon nanowires based on organic–inorganic hybrid nanocomposites with nanometre periodic structures. The organic–inorganic hybrid precursors provide uniform reactions throughout the composites for achieving novel carbon-hybrid structures and nano-morphology via easy calcination. Through the systematic physical characterization including scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, etc., the one-dimensional and carbon-hybrid structure of MoO2/C nanowires was confirmed. This synthetic strategy is also proved universal for other novel MoO2/C nanostructures based on various organic-inorganic hybrid precursors. Furthermore, the MoO2/C hybrid nanowires show good rate capability even at the high current density of 1000 mA g−1 as anode material for lithium ion battery.

Synthesis, characterization and lithium-storage performance of MoO2/carbon hybrid nanowires

The present investigation is focused on the performance of molybdenum dioxide (MoO 2 ) as a catalyst for the partial oxidation of isooctane. Metallic character and high oxygen mobility exhibited by this oxide appear to enhance its catalytic activity, which can be explained in terms of the Mars–van Krevelen mechanism. An oxygen-to-carbon ratio (O/C) of 0.72 seems to stabilize the catalytic performance, which could reach H 2 yields of 78% and carbon conversions of 100%, at 700 °C and 1 atm, after 20 h on stream. In addition, the catalyst was tested for sulfur tolerance using thiophene as model sulfur compound. Our findings indicate that the catalytic activity is barely affected even at sulfur concentrations as large as 500 ppm, after 7 h on stream. Finally, the catalyst performance was compared to that of a nickel catalyst using premium gasoline as fuel. MoO 2 displayed a stable performance whereas the Ni catalyst deactivated due to coke formation.

Oscar G. Marin Flores

Papers

Activity and stability studies of MoO2 catalyst for the partial oxidation of gasoline

Study of the performance of Mo2C for iso-octane steam reforming