NaBH4 is a very cheap and hydrogen rich material and a potential hydrogen store. However, high temperature of its thermal decomposition (above 530°C) renders it inapplicable in practical use. Here, we have studied the effect of addition of diverse V containing catalysts on thermal hydrogen desorption. It turns out that mechanochemical doping of NaBH4 with vanadium metal, its oxides or nanoparticles lowers the temperature of pyrolysis significantly. Notably, NaBH4 milled for 3 hrs with 25 wt.% of V2O5 or VO2 releases ca. 70 % of stored hydrogen in the temperature range from ca. 370°C to 450°C. On the other hand, precursors and solvents used to prepare rather uniform vanadium nanoparticles (ca. 4nm) suspended in THF or less uniform and larger ones (ca. 28nm) in ortho difluorobenzene, have adverse effect on purity of hydrogen evolved.
Among transition metal dichalcogenides (TMdCs) as alternatives for Pt-based catalysts, metallic-TMdCs catalysts have highly reactive basal-plane but are unstable. Meanwhile, chemically stable semiconducting-TMdCs show limiting catalytic activity due to their inactive basal-plane. Here, we propose metallic vanadium sulfide (VSn) nanodispersed in a semiconducting MoS2 film (V-MoS2) as an efficient catalyst. During synthesis, vanadium atoms are substituted into hexagonal monolayer MoS2 to form randomly distributed VSn units. The V-MoS2 film on a Cu electrode exhibits Pt-scalable catalytic perform…
We investigate the influence of uniaxial strain on site occupancy of hydrogen vanadium, using density functional theory. The site occupancy is found to be strongly influenced by the strain state of the lattice. The results provide the conceptual framework of the atomistic description of the observed hysteresis in the alpha to beta phase transition in bulk, as well as the preferred octahedral occupancy of hydrogen in strained V layers.
We report modulation of a reversible phase transition in VO2 films by hydrogen doping. A metallic phase and a new insulating phase are successively observed at room temperature as the doping concentration increases. It is suggested that the polarized charges from doped hydrogens play an important role. These charges gradually occupy V3d-O2p hybridized orbitals and consequently modulate the filling of the VO2 crystal conduction band-edge states, which eventually evolve into new valence band-edge states. This demonstrates the exceptional sensitivity of VO2 electronic properties to electron conce…
An effective method for increasing the electrocatalytic activity of metallic glasses (MGs) in hydrogen evolution reaction (HER) is reported. This method applies a noble metal hybridization strategy to design a highly reactive catalyst for alkaline HER based on MGs with a nano-porous structure. The porous structure provides an abundance of active sites and exposes a large specific surface area to the electrolyte, thus effectively improving the activity of the HER catalysts. The doping of Au element can create electronic defects, adjust the electronic structure, change the electronic interaction…
Electrical and optical properties of amorphous vanadium oxide thin films obtained by electrochemical anodic oxidation are studied. It is shown that under cathodic polarization the hydrogen insertion into vanadium oxide from an electrolyte occurs. Metal-insulator transition in amorphous HxVO2 is found to be preserved up to high concentration (x ~ 1.5) of hydrogen. Memory switching with the N-type negative differential resistance, associated with the H+ ionic transfer, is observed in "V/hydrated amorphous vanadium oxide/Au" sandwich structures.
The development of active catalysts for hydrogen evolution reaction (HER) made from low-cost materials constitutes a crucial challenge in the utilization of hydrogen energy. Earth-abundant molybdenum disulfide (MoS$_2$) has been discovered recently with good activity and stability for HER. In this report, we employed the hydrothermal technique for MoS$_2$ synthesis which is a cost-effective and environmentally friendly approach and has the potential for future mass production. To investigate the structure-property relationship, scanning electron microscope (SEM), transmission electron microsco…
Advanced materials for electrocatalytic and photoelectrochemical water splitting are central to the area of renewable energy. Here, we developed a solvothermal synthesis of MoS2 nanoparticles selectively on reduced graphene oxide (RGO) sheets suspended in solution. The resulting MoS2/RGO hybrid material possessed nanoscopic few-layer MoS2 structures with abundant exposed edges stacked onto graphene, in strong contrast to large aggregated MoS2 particles grown freely in solution without GO. The MoS2/RGO hybrid exhibited superior electrocatalytic activity in the hydrogen evolution reaction (HER) …
Hydrogen spillover and storage for single-site metal catalysts, including single-atom catalysts (SACs) and single nanocluster catalysts, have been elucidated for various supports but remain poorly understood for inert carbon supports. Here, we use synchrotron radiation-based methods to investigate the role of single-site Ti catalysts on graphene for hydrogen spillover and storage. Our in-situ angle-resolved photoemission spectra results demonstrate a bandgap opening and the X-ray absorption spectra reveal the formation of C-H bonds, both indicating the partial graphene hydrogenation. With incr…
We reveal a correlation between the M-X bond energy descriptor EMX for the optimal catalyst in a family of stoichiometry MiXj, and an intensive quantity defined as the standard enthalpy of the catalyzed reaction normalized to one mole of element X transferred by this reaction from reactants to products. M is a transition element, and the stoichiometry MiXj is fixed at the solid/fluid interface by the reaction conditions. We illustrate this for a relevant set of reactions involved in solar energy and industrial applications such as oxygen evolution, oxygen reduction and hydrogen evolution in el…
MoS2 are facile, stable, non-toxic, affordable materials with reasonable price, and have exhibit its superior potential in catalysis, sensing, opt electrochemical, environmental relate application1, etc. Modification of MoS2 materials has been widely applied for adjusting and formulate the relative performance in certain application field. Making vacancy, doping with other atoms, expending of the layer space, heterojunction engineering, phase engineering etc. have been applied to facilitate the catalytic hydrogen evolution performance. We make a detailed summary on MoS2 characterization method…
The role of catalyst stability on the adverse effects of hydrogen peroxide (H2O2) formation rates in a proton exchange membrane fuel cell (PEMFC) is investigated for Pt, Pt binary (PtX, X = Co, Ru, Rh, V, Ni) and ternary (PtCoX, X = Ir, Rh) catalysts. The selectivity of these catalysts towards H2O2 formation in the oxygen reduction reaction (ORR) was measured on a rotating ring disc electrode. These measured values were used in conjunction with local oxygen and proton concentrations to estimate local H2O2 formation rates in a PEMFC anode and cathode. The effect of H2O2 formation rates on the m…
The d-band center descriptor based on the adsorption strength of adsorbate has been widely used in understanding and predicting the catalytic activity in various metal catalysts. However, its applicability is unsure for the single-atom-anchored two-dimensional (2D) catalysts. Here, taking the hydrogen (H) adsorption on the single-atom-anchored 2D basal plane as example, we examine the influence of orbitals interaction on the bond strength of hydrogen adsorption. We find that the adsorption of H is formed mainly via the hybridization between the 1s orbital of H and the vertical dz2 orbital of a…
Metal heteroatoms dispersed in nitrogen-doped graphene display promising catalytic activity for fuel cell reactions such as the hydrogen evolution reaction (HER). Here we explore the effects of dopant concentration on the synergistic catalytic behaviour of a paired metal atom active site comprised of Co and Pt atoms. The metals are coordinated to six atoms in a vacancy of N-doped graphene. We find that HER activity is enhanced with increasing N concentration, where the free energy of hydrogen atom adsorption ranges from 0.23 to -0.42 eV as the doping changes from a single N atom doped in the p…
Hydrogen is a promising energy carrier and key agent for many industrial chemical processes1. One method for generating hydrogen sustainably is via the hydrogen evolution reaction (HER), in which electrochemical reduction of protons is mediated by an appropriate catalyst-traditionally, an expensive platinum-group metal. Scalable production requires catalyst alternatives that can lower materials or processing costs while retaining the highest possible activity. Strategies have included dilute alloying of Pt2 or employing less expensive transition metal alloys, compounds or heterostructures (e.g…
Magneli phases of titanium dioxide (such as Ti4O7, Ti5O9, etc.) provide electronic properties, namely a stable metallic behavior at room temperature. In this manuscript, we demonstrate that nanoscopic Magneli phases, formed intrinsically in anatase during a thermal aerosol synthesis, can enable significant photocatalytic H2 generation. This without the use of any extrinsic co-catalyst in anatase. Under optimized conditions, mixed phase particles of 30 percent anatase, 25 percent Ti4O7 and 20 percent Ti5O9 are obtained that can provide, under solar light, direct photocatalytic H2 evolution at a…
High throughput theoretical methods are increasingly used to identify promising photocatalytic materials for hydrogen generation from water as a clean source of energy. While most promising water splitting candidates require co-catalyst loading and electrical biasing, computational costs to predict them apriori becomes large. It is therefore important to identify bare, bias-free semiconductor photocatalysts with small initial hydrogen production rates, often in the range of tens of nano-mols per hour, as these can become highly efficient with further co-catalyst loading and biasing. Here we re…
Topological quantum catalysts (TQCs), where metallic surface states from nontrivial band topology serve as the mechanism to favor heterogeneous catalysis processes, have been well demonstrated in three dimensional (3D) examples but have been rarely discussed in 2D scale. Here, we develop a design scheme to realize 2D TQCs with showing traversing nodal line at the Brillouin zone boundary, large Fermi arc on the edge, and nearly zero Gibbs free energy (ΔGH*) for hydrogen evolution reaction (HER). We demonstrate the 2D Cu2C2N4 sheet is a such example. The material manifests an open nodal line tra…
The use of highly active and robust catalysts is crucial for producing green hydrogen by water electrolysis as we strive to achieve global carbon neutrality. Noble metals like platinum are currently used in industry for the hydrogen evolution reaction (HER), but suffer from scarcity, high price and unsatisfied performance and stability at large current density, restricting their large scale implementations. Here we report the synthesis of a new type of monolithic catalyst (MC) consisting of a metal disulfide (e.g., TaS2) catalyst vertically bonded to a conductive substrate of the same metal by…
Clean hydrogen production through efficient and cost-effective electrochemical water splitting is highly promising to meeting future global energy demands. The design of Earth-abundant materials with both high activity for hydrogen evolution reaction (HER) and electrochemical stability in both acidic and alkaline environments summarize the outcomes needed for practical applications. Here, we report a non-noble 3d metal Cl-chemical doping of liquid phase exfoliated single/few-layer flakes of MoSe2 for creating MoSe2 nanoflakes/3d metal oxide-hydr(oxy)oxide hybrid HER-catalysts. We propose that …
Topological nodal line (DNL) semimetals, formed by a closed loop of the inverted bands in the bulk, result in the nearly flat drumhead-like surface states with a high electronic density near the Fermi level. The high catalytic active sites associated with the high electronic densities, the good carrier mobility, and the proper thermodynamic stabilities with $ΔG_{H^*}$$\approx$0 are currently the prerequisites to seek the alternative candidates to precious platinum for catalyzing electrochemical hydrogen (HER) production from water. Within this context, it is natural to consider whether or not …
We report the performance of a hydrogen-chlorine electrochemical cell with a chlorine electrode employing a low precious metal content alloy oxide electrocatalyst for the chlorine electrode: (Ru_0.09Co_0.91)_3O_4. The cell employs a commercial hydrogen fuel cell electrode and transports protons through a Nafion membrane in both galvanic and electrolytic mode. The peak galvanic power density exceeds 1 W cm^-2, which is twice previous literature values. The precious metal loading of the chlorine electrode is below 0.15 mg Ru cm^-2. Virtually no activation losses are observed, allowing the cell t…
The high-throughput scalable production of cheap, efficient and durable electrocatalysts that work well at high current densities demanded by industry is a great challenge for the large-scale implementation of electrochemical technologies. Here we report the production of a 2D MoS2-based ink-type electrocatalyst by a scalable top-down exfoliation technique followed by a simple heat treatment. The catalyst shows a high current density of 1000 mA cm^-2 at an overpotential of 454 mV for the hydrogen evolution reaction (HER) without the need of iR correction, as well as good stability over 24 hour…
Complex light metal hydrides possess many properties which make them attractive as a storage medium for hydrogen, but typically, catalysts are required to lower the hydrogen desorption temperature and to facilitate hydrogen uptake in the form of a reversible reaction. The overwhelming focus in the search for catalysing agents has been on compounds containing titanium, but the precise mechanism of their actions remains somewhat obscure. A recent experiment has now shown that fullerenes (C$_{60}$) can also act as catalyst for both hydrogen uptake and release in lithium borohydride (LiBH$_4$). In…
The hydrogen evolution reaction (HER) is a key process in electrochemical water splitting. To lower the cost and environmental impact of this process, it is highly motivated to develop electrocatalysts with low or no content of noble metals. Here we report on a novel and ingenious synthesis of hybrid PtxNi1-x electrocatalysts in the form of a nanoparticle-necklace structure named nanotrusses, with very low noble metal content. The nanotruss structure possesses important features, such as good conductivity, high surface area, strong interlinking and substrate adhesion, which renders for an exce…
Quantum materials such as Topological Insulators (TI) have been promising due to diverse applications of their robust surface/edge states in the bulk (3D) and two-dimensional (2D) regime. Such conducting surface states in 3D systems, host "\textit{electron bath}" which are known to facilitate catalysis. However, the analogous effects in 2D scenarios wherein, conducting helical edge states giving rise to Fermionic accumulation has been scarcely addressed. Using density functional theory based \textit{first-principles} calculations, we demonstrate that, the conducting edge states in 2D TI such a…
Synthesis of monolayer MoS2 is essential for fulfilling the potential of MoS2 in catalysis, optoelectronics and valleytronics, etc. Herein, we report for the first time the scalable growth of high quality, domain size tunable (edge length from ~ 200 nm to 50 μm), strictly monolayer MoS2 on commercially available Au foils, via a low pressure chemical vapor deposition method. The nanosized triangular MoS2 flakes on Au foils was proved to be an excellent electrocatalyst for hydrogen evolution reaction (HER), featured by a rather low Tafel slope (61 mV/decade) and a supreme exchange current densit…
Two-dimensional materials supported by single atom catalysis (SACs) are foreseen to replace platinum for large-scale industrial scalability of sustainable hydrogen generation. Here, a series of metal (Al, Sc, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn) and non-metal (B, C, N, O, F, Si, P, S, Cl) single atoms embedded on various active sites of g-C$_3$N$_4$ are screened by DFT calculations and six machine learning (ML) algorithms (support vector regression, gradient boosting regression, random forest regression, AdaBoost regression, multilayer perceptron regression, ridge regression). Our results based on f…
Designing electrocatalysts for HER in alkaline conditions to overcome the sluggish kinetics associated with the additional water dissociation step is a recognized challenge in promoting the hydrogen economy. To this end, delicately tuning the atomic-scale structure and surface composition of nanoparticles is a common strategy and, specifically, making use of hybrid structures, can produce synergistic effects that lead to highly active catalysts. Here, we present a core-shell catalyst of Ag@MoS$_2$ that shows promising results towards the hydrogen evolution reaction (HER) in both 0.5 M H2SO4 an…
Electrocatalytic hydrogen evolution reaction (HER) in alkaline media is a promising electrochemical energy conversion strategy. Ruthenium (Ru) is an efficient catalyst with a desirable cost for HER, however, the sluggish H2O dissociation process, due to the low H2O adsorption on its surface, currently hampers the performances of this catalyst in alkaline HER. Herein, we demonstrate that the H2O adsorption improves significantly by the construction of Ru-O-Mo sites. We prepared Ru/MoO2 catalysts with Ru-O-Mo sites through a facile thermal treatment process and assessed the creation of Ru-O-Mo i…
A simple physical conception explaining the experimentally observed temperature dependence of the local mode frequencies in the ordering metal hydrides is proposed. Calculations are performed for bcc vanadium deuterides. The model can be applied to other physical phenomena which are related to the hydrogen motion in metal lattices.
Compositionally tunable vanadium oxyhydrides Sr2VO4-xHx (x = 0 - 1) without considerable anion vacancy were synthesized by high-pressure solid state reaction. The crystal structures and their properties were characterized by powder neutron diffraction, synchrotron X-ray diffraction, thermal desorption spectroscopy, and first-principles density functional theory (DFT) calculations. The hydrogen anions selectively replaced equatorial oxygen sites in the VO6 layers via statistical substitution of hydrogen in the low x region (x < 0.2). A new orthorhombic phase (Immm) with an almost entirely hydro…
Topological states of matter and their corresponding properties are classical research topics in condensed matter physics. Quite recently, the application of materials that feature these states has been extended to the field of electrochemical catalysis and become an emerging research topic that is receiving increasing interest. In particular, several recent experimental studies performed on topological semimetals have already revealed high catalytic performance towards hydrogen evolution reaction (HER), strongly promoting acceptance of the fresh concept of the topological catalyst. This emerg…
2D semiconducting nanosheets of Transition Metal Dichalcogenides are attractive materials for solar energy conversion because of their unique absorption properties. Here, we propose Mo thio- and oxo-thio-complexes anchored on 2D p-WSe2 nanosheets for efficient water splitting under visible light irradiation with photocurrent density up to 2.0 mA cm-2 at -0.2 V/NHE. Besides developing high electro-catalytic activity, the Mo complexe films were shown to display ability to heal surface defects. We propose that the observed healing of surface defects arises from the strong adsorption on point defe…
Chemical transformation of MgH2/V2O5 composite to Mg-V-O rock salt and its influence on the electrochemical Li conversion and hydrogen storage characteristics of MgH2
University of Aveiro（阿威罗大学）；LASI - Intelligent Systems Associate Laboratory（智能系统联合实验室）；International Iberian Nanotechnology Laboratory (INL)（伊比利亚纳米技术国际实验室）
Wide proliferation of low temperature hydrogen fuel cell systems, a key part of the hydrogen economy, is hindered by degradation of the platinum cathode catalyst. Here, we provide a device level assessment of the molecular scale catalyst degradation phenomena, using advanced operando X-ray scattering tomography tailored for device-scale imaging. Each cell component, including the catalyst, carbon support, polymer electrolyte, and liquid water can be simultaneously mapped, allowing for deep correlative analysis. Chemical and thermal gradients formed inside the operating fuel cell produce highly…
The ability to efficiently evolve hydrogen via electrocatalysis at low overpotentials holds tremendous promise for clean energy. Hydrogen evolution reaction (HER) can be easily achieved from water if a voltage above the thermodynamic potential of the HER is applied. Large overpotentials are energetically inefficient but can be lowered with expensive platinum based catalysts. Replacement of Pt with inexpensive, earth abundant electrocatalysts would be significantly beneficial for clean and efficient hydrogen evolution. Towards this end, promising HER characteristics have been reported using 2H …
Introduction of interstitial dopants has opened a new pathway to optimize nanoparticle catalytic activity for, e.g., hydrogen evolution/oxidation and other reactions. Here, we discuss the stability of a property-enhancing dopant, B, introduced through controlled synthesis of an electrocatalyst Pd aerogel. We observe significant removal of B after the hydrogen evolution/oxidation reaction. Ab-initio calculations show that the high stability of sub-surface B in Pd is substantially reduced when H is ad/absorbed on the surface, favoring its departure from the host nanostructure. The destabilizatio…
Effect of doping with H and W on the properties of V2O5 and VO2 derived from V2O5 gel has been studied. It is shown that the treatment of V2O5 in low-temperature RF hydrogen plasma for 1 to 10 min. leads to either hydration of vanadium pentoxide or its reduction (depending on the treatment conditions) to lower vanadium oxides. For some samples, which are subject to plasma treatment in the discharge active zone, a non-ordinary temperature dependence of resistance, with a maxi-mum at T ~ 100 K, is observed. For W-doped VO2 films, it is shown that substitution of V4+ with W6+ results in a decreas…
Large scale implementation of electrochemical water splitting for hydrogen evolution requires cheap and efficient catalysts to replace expensive platinum. Molybdenum disulfide is one of the most promising alternative catalysts but its intrinsic activity is still inferior to platinum. There is therefore a need to explore new active site origins in molybdenum disulfide with ultrafast reaction kinetics and to understand their mechanisms. Here, we report a universal cold hydrogen plasma reduction method for synthesizing different single atoms sitting on two-dimensional monolayers. In case of molyb…
The design of efficient and cost-effective catalysts for the hydrogen evolution reaction (HER) is the key for molecular hydrogen (H2) production from electrochemical water splitting. Transition metal dichalcogenides (MX2), most notably group-6 MX2 (e.g., MoS2 and WS2), are appealing catalysts for the HER alternative to the best, but highly expensive, Pt-group elements. However, their HER activity is typically restricted to their edge sites rather than their basal plane. Furthermore, their semiconducting properties hinder an efficient electron transfer to the catalytic sites, which impedes a hi…
Large scale production of hydrogen by electrochemical water splitting is considered as a promising technology to address critical energy challenges caused by the extensive use of fossil fuels. Although nonprecious nickel-based catalysts work well at low current densities, they need large overpotentials at high current densities that hinders their potential applications in practical industry. Here we report a hydroxide-mediated nickel based electrocatalyst for high current density hydrogen evolution, which delivers a current density of 1000 mA cm-2 at an overpotential of 98 mV. Combined X-ray a…
Increasing anthropogenic carbon dioxide (CO$_2$) emissions have led to rising global temperatures and climate change. Using earth-abundant metal-oxide catalysts such as Cu$_2$O for reducing CO$_2$ through RWGS reaction seems lucrative. In this work, we have used Cu$_2$O nanostructures and identified its activity, stability, and selectivity for reducing CO$_2$ to carbon monoxide (CO) which can be further hydrogenated to higher hydrocarbons using Fisher Tropsch synthesis. We have observed that the rate of CO$_2$ conversion increases by 4 times and significantly drops at 300 C where the catalyst …
Simultaneously probing the electronic structure and morphology of materials at the nanometer or atomic scale while a chemical reaction proceeds is significant for understanding the underlying reaction mechanisms and optimizing a materials design. This is especially important in the study of nanoparticle catalysts, yet such experiments have rarely been achieved. Utilizing an environmental transmission electron microscope (ETEM) equipped with a differentially pumped gas cell, we are able to conduct nanoscopic imaging and electron energy loss spectroscopy (EELS) in situ for cobalt catalysts under…
