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Ultrafine α-Phase Molybdenum Carbide Decorated with Platinum Nanoparticles for Efficient Hydrogen Production in Acidic and Alkaline Media.

ABSTRACT: The development of efficient electrocatalysts is important to produce clean and sustainable hydrogen fuel on a large scale. With respect to cathodic reactions, Pt exhibits an overwhelming electrocatalytic capability in the hydrogen evolution reaction (HER) in comparison with other earth-abundant electrocatalysts, despite its rarity and high cost. So, a hybrid catalyst that combines a low-cost electrocatalyst with Pt would balance cost-effectiveness with catalytic activity. Herein, α-phase molybdenum carbide (MoC_1- _x ) nanoparticles (NPs) decorated with a small amount of Pt (MoC_1- _x /Pt-NPs) are designed to achieve high-performance hydrogen production in acidic and alkaline media. MoC_1- _x -NPs exhibit good electrocatalytic HER activity as well as stability and durability. They show favorable catalytic kinetics in an alkaline medium, suggesting an active water dissociation process. After Pt decoration, Pt-NPs that are 2-3 nm in diameter are well incorporated with MoC_1- _x -NPs. MoC_1- _x /Pt-NPs with a small amount of Pt (2.7-3 wt%) and are able to perform superior electrocatalytic HER activity, and possess stability and durability that is comparable to that of commercial Pt/C. Notably, they exhibit a higher intrinsic catalytic activity compared to that of Pt/C in an alkaline medium, indicating that they promote the sluggish catalytic kinetics of Pt in alkaline medium.

SUBMITTER: Song HJ

PROVIDER: S-EPMC6468960 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Molybdenum Carbide Nanoparticles Coated into the Graphene Wrapping N-Doped Porous Carbon Microspheres for Highly Efficient Electrocatalytic Hydrogen Evolution Both in Acidic and Alkaline Media.

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Nitrogen-Doped Oxygenated Molybdenum Phosphide as an Efficient Electrocatalyst for Hydrogen Evolution in Alkaline Media.

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Project description:In this work, we study how the cation identity and concentration alter the kinetics of the hydrogen evolution reaction (HER) on platinum and gold electrodes. A previous work suggested an inverted activity trend as a function of alkali metal cation when comparing the performance of platinum and gold catalysts in alkaline media. We show that weakly hydrated cations (K+) favor HER on gold only at low overpotentials (or lower alkalinity), whereas in more alkaline pH (or high overpotentials), a higher activity is observed using electrolytes containing strongly hydrated cations (Li+). We find a similar trend for platinum; however, the inhibition of HER by weakly hydrated cations on platinum is observed already at lower alkalinity and lower cation concentrations, suggesting that platinum interacts more strongly with metal cations than gold. We propose that weakly hydrated cations stabilize the transition state of the water dissociation step more favorably due to their higher near-surface concentration in comparison to a strongly hydrated cation such as Li+. However, at high pH and consequently higher near-surface cation concentrations, the accumulation of these species at the outer Helmholtz plane inhibits HER. This is especially pronounced on platinum, where a change in the rate-determining step is observed at pH 13 when using a Li+- or K+-containing electrolyte.

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Project description:Carbides/carbon composites are emerging as a new kind of binary dielectric systems with good microwave absorption performance. Herein, we obtain a series of tungsten carbide/carbon composites through a simple solvent-free strategy, where the solid mixture of dicyandiamide (DCA) and ammonium metatungstate (AM) is employed as the precursor. Ultrafine cubic WC1-x nanoparticles (3-4 nm) are in situ generated and uniformly dispersed on carbon nanosheets. This configuration overcomes some disadvantages of conventional carbides/carbon composites and is greatly helpful for electromagnetic dissipation. It is found that the weight ratio of DCA to AM can regulate chemical composition of these composites, while less impact on the average size of WC1-x nanoparticles. With the increase in carbon nanosheets, the relative complex permittivity and dielectric loss ability are constantly enhanced through conductive loss and polarization relaxation. The different dielectric properties endow these composites with distinguishable attenuation ability and impedance matching. When DCA/AM weight ratio is 6.0, the optimized composite can produce good microwave absorption performance, whose strongest reflection loss intensity reaches up to - 55.6 dB at 17.5 GHz and qualified absorption bandwidth covers 3.6-18.0 GHz by manipulating the thickness from 1.0 to 5.0 mm. Such a performance is superior to many conventional carbides/carbon composites.

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