Stable Sulfur‐Intercalated 1T′ MoS2 on Graphitic Nanoribbons as Hydrogen Evolution Electrocatalyst10/17/2018 The metastable 1T’ polymorph of MoS2 is an excellent catalyst towards the hydrogen evolution reaction. However, its production is limited by its lower energetic stability compared to the semiconductor 2H MoS2 phase. Stabilization of the 1T’ polymorph can be achieved through intercalation of sulfur-based compounds without adversely affecting its catalytic properties. In this occasion, the production of stable intercalated 1T′ MoS2 nanosheets attached on graphitic nanoribbons was published in the journal of Advanced Functional Materials. Joakim Ekspong, Robin Sandström, Lakshmy Pulickal Rajukumar, Mauricio Terrones, Thomas Wågberg, and Eduardo Gracia‐Espino. Advanced Functional Materials, 2018, 1802744 https://doi.org/10.1002/adfm.201802744 Abstract The metastable 1T′ polymorph of molybdenum disulfide (MoS2) has shown excellent catalytic activity toward the hydrogen evolution reaction (HER) in water‐splitting applications. Its basal plane exhibits high catalytic activity comparable to the edges in 2H MoS2 and noble metal platinum. However, the production and application of this polymorph are limited by its lower energetic stability compared to the semiconducting 2H MoS2 phase. Here, the production of stable intercalated 1T′ MoS2 nanosheets attached on graphitic nanoribbons is reported. The intercalated 1T′ MoS2 exhibits a stoichiometric S:Mo ratio of 2.3 (±0.1):1 with an expanded interlayer distance of 10 Å caused by a sulfur‐rich intercalation agent and is stable at room temperature for several months even after drying. The composition, structure, and catalytic activity toward HER are investigated both experimentally and theoretically. It is concluded that the 1T′ MoS2 phase is stabilized by the intercalated agents, which further improves the basal planes′ catalytic activity toward HER.
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We created Fe vacancies as an approach to modulate the electronic structure and catalytic activity of iron phosphide (FeP). The Fe-vacancy-rich FeP nanoparticulate films showed excellent HER activity achieving a current density of 10 mA cm-2 at overpotentials of 108 mV in 1 M KOH, and 65 mV in 0.5 M H2SO4. This work was carried out in collaboration with Prof. Messinger (Uppsala University). W. L. Kwong, E. Gracia-Espino, C. C. Lee, R. Sandström, T. Wågberg, and J. Messinger. ChemSusChem (2017) DOI: 10.1002/cssc.201701565 AbstractEngineering the electronic properties of transition metal phosphides has shown great effectiveness in improving their intrinsic catalytic activity for the hydrogen evolution reaction (HER) in water splitting applications. Herein, we report for the first time, the creation of Fe vacancies as an approach to modulate the electronic structure of iron phosphide (FeP). The Fe vacancies were produced via chemical leaching of Mg that was introduced into FeP as 'sacrificial dopant'. The obtained Fe-vacancy-rich FeP nanoparticulate films, which were deposited on Ti foil, shows excellent HER activity as compared to pristine FeP and Mg-doped FeP, achieving a current density of 10 mA cm-2 at overpotentials of 108 mV in 1 M KOH and 65 mV in 0.5 M H2SO4, with a near-100% Faradaic efficiency. Our theoretical and experimental analyses reveal that the improved HER activity originates from the presence of Fe vacancies, which lead to a synergistic modulation of the structural and electronic properties that result in a near optimal hydrogen adsorption free energy and enhanced proton trapping. The success in catalytic improvement via the introduction of cationic vacancy defects has not only demonstrated the potential of Fe-vacancy-rich FeP as highly efficient, earth abundant HER catalyst, but also opened up an exciting pathway for activating other promising catalysts for electrochemical water splitting.
We report the production of a hybrid catalyst electrode comprising semicrystalline molybdenum sulfide (MoS2+x) attached on nitrogen-doped carbon nanotubes. The nitrogen-doping of the carbon nanotubes stabilizes a semicrystalline structure of MoS2+x with a high exposure of active sites for HER resulting in enhanced catalytic activity. The results are published in the journal of Advanced Functional Materials. Joakim Ekspong, Tiva Sharifi, Andrey Shchukarev, Alexey Klechikov, Thomas Wågberg, and Eduardo Gracia-Espino. Adv. Funct. Mater, 2016. DOI: 10.1002/adfm.201601994 Abstract Finding an abundant and cost-effective electrocatalyst for the hydrogen evolution reaction (HER) is crucial for a global production of hydrogen from water electrolysis. This work reports an exceptionally large surface area hybrid catalyst electrode comprising semicrystalline molybdenum sulfide (MoS2+x) catalyst attached on a substrate based on nitrogen-doped carbon nanotubes (N-CNTs), which are directly grown on carbon fiber paper (CP). It is shown here that nitrogen-doping of the carbon nanotubes improves the anchoring of MoS2+x catalyst compared to undoped carbon nanotubes and concurrently stabilizes a semicrystalline structure of MoS2+x with a high exposure of active sites for HER. The well-connected constituents of the hybrid catalyst are shown to facilitate electron transport and as a result of the good attributes, the MoS2+x/N-CNT/CP electrode exhibits an onset potential of −135 mV for HER in 0.5 m H2SO4, a Tafel slope of 36 mV dec−1, and high stability at a current density of −10 mA cm−2.
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