Ultrahigh-current-density niobium disulfide catalysts for hydrogen evolution

Metallic transition metal dichalcogenides (TMDs)1???8 are good catalysts for the hydrogen evolution reaction (HER). The overpotential and Tafel slope values of metallic phases and edges9 of two-dimensional (2D) TMDs approach those of Pt. However, the overall current density of 2D TMD catalysts remains orders of magnitude lower (~10???100 mA cm???2) than industrial Pt and Ir electrolysers (>1,000 mA cm???2)10,11. Here, we report the synthesis of the metallic 2H phase of niobium disulfide with additional niobium (2H Nb1+xS2, where x is ~0.35)12 as a HER catalyst with current densities of >5,000 mA cm???2 at ~420 mV versus a reversible hydrogen electrode. We find the exchange current density at 0 V for 2H Nb1.35S2 to be ~0.8 mA cm???2, corresponding to a turnover frequency of ~0.2 s???1. We demonstrate an electrolyser based on a 2H Nb1+ xS2 cathode that can generate current densities of 1,000 mA cm???2. Our theoretical results reveal that 2H Nb1+ xS2 with Nb-terminated surface has free energy for hydrogen adsorption that is close to thermoneutral, facilitating HER. Therefore, 2H Nb1+ xS2 could be a viable catalyst for practical electrolysers

Hydrogen evolution enhancement of ultra-low loading, size-selected molybdenum sulfide nanoclusters by sulfur enrichment

Size-selected molybdenum sulfide (MoSx) nanoclusters obtained by magnetron sputtering and gas condensation on glassy carbon substrates are typically sulfur-deficient (x = 1.6 ± 0.1), which limits their crystallinity and electrocatalytic properties. Here we demonstrate that a sulfur-enriching method, comprising sulfur evaporation and cluster annealing under vacuum conditions, significantly enhances their activity towards the hydrogen evolution reaction (HER). The S-richness (x = 4.9 ± 0.1) and extended crystalline order obtained in the sulfur-treated MoSx nanoclusters lead to consistent 200 mV shifts to lower HER onset potentials, along with two-fold and more-than 30-fold increases in turnover frequency and exchange current density values respectively. The high mass activities (~111 mA mg-1 @ 400 mV) obtained at ultra-low loadings (~100 ng cm-2, 5 % surface coverage) are comparable to the best reported MoS2 catalysts in the literature

Improved electrochemical conversion of CO2 to multicarbon products by using molecular doping

The conversion of CO2 into desirable multicarbon products via the electrochemical reduction reaction holds promise to achieve a circular carbon economy. Here, we report a strategy in which we modify the surface of bimetallic silver-copper catalyst with aromatic heterocycles such as thiadiazole and triazole derivatives to increase the conversion of CO2 into hydrocarbon molecules. By combining operando Raman and X-ray absorption spectroscopy with electrocatalytic measurements and analysis of the reaction products, we identified that the electron withdrawing nature of functional groups orients the reaction pathway towards the production of C2+ species (ethanol and ethylene) and enhances the reaction rate on the surface of the catalyst by adjusting the electronic state of surface copper atoms. As a result, we achieve a high Faradaic efficiency for the C2+ formation of approximate to 80% and full-cell energy efficiency of 20.3% with a specific current density of 261.4 mA cm(-2) for C2+ products. Strategies to systematically tune CO2 electroreduction to multicarbon products are of high interests. Here the authors report electron withdrawing functional group alters the reaction pathway towards C2+ products by adjusting the oxidation state of surface copper.D.V., K.Q., and H.L.W. acknowledge funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement no. 804320). L.L., D.V., and H.L.W acknowledge the use of TEM instrumentation provided by the Nation Facility ELECMI ICTS (`Division de Microscopia Electronica', Universidad de Cadiz, DME-UCA). L.L. acknowledges funding from the Andalusian regional government (FEDER-UCA-18-106613), the European Union's Horizon 2020 research and innovation program (grant agreement 823717-ESTEEM3), and the Spanish Ministerio de Economia y Competitividad (PID2019-107578GA-I00). K.Q. and Y.Z. acknowledge financial support from the China Postdoctoral Science Foundation (2018M633127) and the Natural Science Foundation of Guangdong Province (2018A030310602). J.L. acknowledge financial support from the National Natural Science Foundation of China (21808134). We thank Soleil Synchrotron and Andrea Zitolo for allocating beamtime at beamline Samba within the proposal 20200732

MoS 2 and WS 2 nanocone arrays: Impact of surface topography on the hydrogen evolution electrocatalytic activity and mass transport

We report the fabrication and electrochemical study of edge-abundant transition metal dichalcogenide (TMD) nanocone arrays. Time-dependent etching by sequential use of isotropic O2 and anisotropic SF6/C4F8 plasmas on nanosphere monolayer-modified TMD crystals results in very high coverage nanocone array structures with tunable aspect ratios and interspacings. Electrochemical characterization of these arrays via the hydrogen evolution reaction (HER), using a low proton concentration electrolyte (2 mM HClO4, 0.1 M NaClO4) to reveal morphology-dependent mass transport features at the proton diffusion-controlled region, show significant changes in electrocatalytic behaviour at both WS2 and MoS2: notably onset potential shifts of 100 and 200 mV, and Tafel slope decreases of 50 and 120 mV dec−1 respectively. These improvements vary according to the geometry of the arrays and the availability of catalytic edge sites, and thus the observed electrochemical behaviour can be rationalized via kinetic and mass transport effects

Coupling Interface Constructions of MoS2/Fe5Ni4S8 Heterostructures for Efficient Electrochemical Water Splitting

Water splitting is considered as a pollution‐free and efficient solution to produce hydrogen energy. Low‐cost and efficient electrocatalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) are needed. Recently, chemical vapor deposition is used as an effective approach to gain high‐quality MoS2 nanosheets (NSs), which possess excellent performance for water splitting comparable to platinum. Herein, MoS2 NSs grown vertically on FeNi substrates are obtained with in situ growth of Fe5Ni4S8 (FNS) at the interface during the synthesis of MoS2. The synthesized MoS2/FNS/FeNi foam exhibits only 120 mV at 10 mA cm−2 for HER and exceptionally low overpotential of 204 mV to attain the same current density for OER. Density functional theory calculations further reveal that the constructed coupling interface between MoS2 and FNS facilitates the absorption of H atoms and OH groups, consequently enhancing the performances of HER and OER. Such impressive performances herald that the unique structure provides an approach for designing advanced electrocatalysts.Strong coupling interfaces of a vertical MoS2 array and in situ grown Fe5Ni4S8 are formed by chemical vapor deposition. The interfacial coupling of the MoS2 array on FeNi foam shows outstanding activity of both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER): 120 mV @ 10 mA cm–2 for HER and 204 mV @ 10 mA cm–2 for OER.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/146422/1/adma201803151_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146422/2/adma201803151-sup-0001-S1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146422/3/adma201803151.pd

Molybdenum Disulfide-Coated Lithium Vanadium Fluorophosphate Anode: Experiments and First-Principles Calculations

To develop a new anode material to meet the increasing demands of lithium-ion battery, MoS2 is used for the first time to modify the C/LiVPO4F anode to improve its lithium-storage performance between 3 and 0.01 V. Morphological observations reveal that the MoS2-modified C/LiVPO4F particles (M-LVPF) are wrapped by an amorphous carbon as interlayer and layered MoS2 as external surface. Charge–discharge tests show that M-LVPF delivers a high reversible capacity of 308 mAh g−1 at 50 mA g−1. After 300 cycles at 1.0 A g−1, a capacity retention of 98.7 % is observed. Moreover, it exhibits high rate capability with a specific capacity of 199 mAh g−1 at 1.6 A g−1. Electrochemical impedance spectroscopy tests indicate that the lithium-ion diffusion and charge-exchange reaction at the surface of M-LVPF are greatly enhanced. First-principles calculations for the MoS2 (001)/C/LiVPO4F (010) system demonstrate that the absorption of MoS2 on C/LiVPO4F is exothermic and spontaneous and that the electron transfer at the MoS2-absorbed C/LiVPO4F surface is enhanced.postprin

Self-optimizing, highly surface-active layered metal dichalcogenide catalysts for hydrogen evolution

Low-cost, layered transition-metal dichalcogenides (MX_2) based on molybdenum and tungsten have attracted substantial interest as alternative catalysts for the hydrogen evolution reaction (HER). These materials have high intrinsic per-site HER activity; however, a significant challenge is the limited density of active sites, which are concentrated at the layer edges. Here we unravel electronic factors underlying catalytic activity on MX_2 surfaces, and leverage the understanding to report group-5 MX_2 (H-TaS_2 and H-NbS_2) electrocatalysts whose performance instead mainly derives from highly active basal-plane sites, as suggested by our first-principles calculations and performance comparisons with edge-active counterparts. Beyond high catalytic activity, they are found to exhibit an unusual ability to optimize their morphology for enhanced charge transfer and accessibility of active sites as the HER proceeds, offering a practical advantage for scalable processing. The catalysts reach 10 mA cm^(−2) current density at an overpotential of ∼50–60 mV with a loading of 10–55 μg cm^(−2), surpassing other reported MX2 candidates without any performance-enhancing additives

Engineering grain boundaries at the 2D limit for the hydrogen evolution reaction

Atom-thin transition metal dichalcogenides (TMDs) have emerged as fascinating materials and key structures for electrocatalysis. So far, their edges, dopant heteroatoms and defects have been intensively explored as active sites for the hydrogen evolution reaction (HER) to split water. However, grain boundaries (GBs), a key type of defects in TMDs, have been overlooked due to their low density and large structural variations. Here, we demonstrate the synthesis of wafer-size atom-thin TMD films with an ultra-high-density of GBs, up to ~1012 cm−2. We propose a climb and drive 0D/2D interaction to explain the underlying growth mechanism. The electrocatalytic activity of the nanograin film is comprehensively examined by micro-electrochemical measurements, showing an excellent hydrogen-evolution performance (onset potential: −25 mV and Tafel slope: 54 mV dec−1), thus indicating an intrinsically high activation of the TMD GBs

Boosting cross-border regions through better cross-border transport services. The European case

Cross-border regions are the laboratories of European integration. Daily interactions across European borders let citizens experience the benefits of the European Union (EU) internal market. Still, many border barriers continue to prevent individuals and organisations from exploiting the full-potential of European border regions and the benefits of a more integrated European territory. Amongst these barriers are the absence or inappropriate supply of cross-border public transport services. In this context, this paper presents potential policy tools to increase border permeability related to cross-border public transport as well as practical results from a few case-studies implemented across Europe.info:eu-repo/semantics/publishedVersio