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Reacting MoAlB with ZnCl2 at 550 °C produces metastable Mo2AlB2 through a one-step topochemical transformation. This reaction showcases differences in reactivity between boride-based MAB phases and carbide-based MAX phases, which are solid-state precursors to an important family of 2-D materials. [ABSTRACT FROM AUTHOR]

Data‐intensive discovery of water‐splitting catalysts can accelerate the development of sustainable energy technologies, such as the photocatalytic and/or electrocatalytic production of renewable hydrogen fuel. Through computational screening, 13 materials were recently predicted as potential water‐splitting photocatalysts: Cu3NbS4, CuYS2, SrCu2O2, CuGaO2, Na3BiO4, Sr2PbO4, LaCuOS, LaCuOSe, Na2TeO4, La4O4Se3, Cu2WS4, BaCu2O2, and CuAlO2. Herein, these materials are synthesized, their bandgaps and band alignments are experimentally determined, and their photoelectrocatalytic hydrogen evolution properties are assessed. Using cyclic voltammetry and chopped illumination experiments, 9 of the 13 materials are experimentally found to have bandgaps and band alignments that straddle the potentials required for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), as computationally predicted. During photocatalytic testing, 12 of the materials yield a measurable photocurrent. However, only three are found to be active for the HER, with Cu3NbS4, CuYS2, and Cu2WS4 producing H2 in amounts comparable to bare TiO2; a benchmark photocatalyst. This study provides experimental validation of computational bandgap and band alignment predictions while also successfully identifying active photocatalysts. [ABSTRACT FROM AUTHOR]

We report predictive guidelines for the substoichiometric cation exchange of model two-component metal sulfide nanorods containing divalent cations of similar hardness. Unit cell volume changes, cation radii, solubility constants, and solid state interfaces influence selectivity during substoichiometric exchange of Cu+ when multiple products are possible. [ABSTRACT FROM AUTHOR]

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 a priori become 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 nanomoles per hour, as these can become highly efficient with further co-catalyst loading and biasing. Here, we report a sensitive hydrogen detection system suitable for screening new photocatalysts. The hydrogen evolution rate of the prototypical rutile TiO2 loaded with 0.3 wt. % Pt is detected to be 78.0 ± 0.8 µmol/h/0.04 g, comparable with the rates reported in the literature. In contrast, sensitivity to an ultralow evolution rate of 11.4 ± 0.3 nmol/h/0.04 g is demonstrated for bare polycrystalline TiO2 without electrical bias. Two candidate photocatalysts, ZnFe2O4 (18.1 ± 0.2 nmol/h/0.04 g) and Ca2PbO4 (35.6 ± 0.5 nmol/h/0.04 g) without electrical bias or co-catalyst loading, are demonstrated to be potentially superior to bare TiO2. This work expands the techniques available for sensitive detection of photocatalytic processes toward much faster screening of new candidate photocatalytic materials in their bare state. [ABSTRACT FROM AUTHOR]

Topological materials have high carrier mobilities that can be maintained in the presence of crystal structure defects, which is useful for catalysis. Topological materials have been shown to be active catalysts, but it remains unclear if topology persists during catalysis. We studied the physical and chemical evolution of MoTe2 during photo‐ and electrocatalytic hydrogen production. This material offers a unique opportunity to directly compare a trivial semiconductor, 2H‐MoTe2, with a topological insulator, 1T'‐MoTe2, with comparable compositions, crystal structures, and surface roughnesses. We observed no major bulk changes in the materials after catalysis. The surfaces of the catalysts were significantly roughened and oxidized, but the carrier mobility of the topological phase remained high. These results suggest that topology persists during, and may be advantageous for, catalysis, and provide rationale for considering topology in the search for water‐splitting catalysts. [ABSTRACT FROM AUTHOR]

Alloying metals can achieve enhanced kinetics for the hydrogen evolution reaction (HER), but most known HER alloy catalysts combine metals that are miscible in the bulk. Theoretical studies suggest that bulk‐immiscible AgRh alloys will exhibit near‐zero hydrogen binding energies, which is important for high‐performing HER catalysts. Current routes to AgRh nanoparticles yield only small quantities or require specialized setups. Here, we establish a ligand‐free, scalable synthesis of AgRh nanoparticles and demonstrate their catalytic viability for the HER under acidic conditions. AgRh nanoparticle electrodes exhibited low operating potentials with current densities of −10 and −100 mA/cm2 at overpotentials of −17 and −32 mV, respectively. The electrodes were highly durable with very little change in overpotentials required to maintain hydrogen production for 24 h and after 400 successive cycles. These results establish bulk‐immiscible AgRh alloys as promising non‐Pt HER catalysts. [ABSTRACT FROM AUTHOR]

Nanoscale transition metal tellurides are important materials for a variety of applications. However, solution‐phase methods to synthesize nanoscale transition metal tellurides are not as well‐developed as for related sulfide and selenide systems. Here, we show that pre‐formed colloidal metal nanoparticles react with bis(trimethylsilyl)telluride to form their corresponding tellurides. Nanoparticles of Pd, Pt, and Ni convert to nanoscale particles of the layered transition metal dichalcogenides PdTe2, PtTe2, and NiTe2 upon reaction with bis(trimethylsilyl)telluride. When Pd nanoparticles instead react with a TOP‐Te complex (TOP = trioctylphosphine), PdTe forms. This result demonstrates that the metal telluride phase that forms can be controlled by the reactivity of the tellurium reagent. Other nanoparticles, including Co, Ag, and Rh, also form crystalline metal tellurides upon reaction with bis(trimethylsilyl)telluride, which indicates that this approach to synthesizing nanoscale transition metal tellurides is general. [ABSTRACT FROM AUTHOR]

The M1 form of vanadium dioxide, which exhibits a reversible insulator-metal transition above room temperature, has been incorporated into nanoscale heterostructures through solution-phase epitaxial growth on the tips of rutile TiO2 nanorods. Four distinct classes of VO2-TiO2-VO2 nanorod heterostructures are accessible by modulating the growth conditions. Each type of VO2-TiO2-VO2 nanostructure has a different insulator-metal transition temperature that depends on the VO2 domain sizes and the TiO2-VO2 interfacial strain characteristics. [ABSTRACT FROM AUTHOR]

The M1 form of vanadium dioxide, which exhibits a reversible insulator-metal transition above room temperature, has been incorporated into nanoscale heterostructures through solution-phase epitaxial growth on the tips of rutile TiO2 nanorods. Four distinct classes of VO2-TiO2-VO2 nanorod heterostructures are accessible by modulating the growth conditions. Each type of VO2-TiO2-VO2 nanostructure has a different insulator-metal transition temperature that depends on the VO2 domain sizes and the TiO2-VO2 interfacial strain characteristics. [ABSTRACT FROM AUTHOR]

Transition metal ditellurides are gaining widespread attention due to their rich polymorphism and distinct electronic properties when compared to transition metal disulfides and diselenides. Here, we report the direct synthesis of Td-WTe2 nanostructures via a low-temperature solution-based method. A comprehensive structural characterization reveals the anisotropic pathway by which the few-layer WTe2 nanostructures grow, as well as the co-existence of multiple stacking motifs. The versatility of this synthetic approach is further expanded to access nanostructured MoxW1−xTe2 alloys across the entire solid solution that spans the 1T′-MoTe2 and Td-WTe2 end members, where the elemental composition and crystal structure can be systematically tuned by modulating the metal reagent ratios. The ability to access transition metal ditellurides using solution synthesis methods complements traditional gas-phase fabrication techniques and provides an alternative strategy for manufacturing an expanded library of composition-tunable TMD nanostructures. [ABSTRACT FROM AUTHOR]

A fundamental understanding of the behavior of non-noble based materials toward the hydrogen evolution reaction is crucial for the successful implementation into practical devices. Through the implementation of a highly sensitive inductively coupled plasma mass spectrometer coupled to a scanning flow cell, the activity and stability of non-noble electrocatalysts is presented. The studied catalysts comprise a range of compositions, including metal carbides (WC), sulfides (MoS2), phosphides (Ni5P4, Co2P), and their base metals (W, Ni, Mo, Co); their activity, stability, and degradation behavior was elaborated and compared to the state-of-the-art catalyst platinum. The non-noble materials are stable at HER potentials but dissolve substantially when no current is flowing. Through pre- and post-characterization of the catalysts, explanations of their stability (thermodynamics and kinetics) are discussed, challenges for the application in real devices are analyzed, and strategies for circumventing dissolution are suggested. The precise correlation of metal dissolution with applied potential/current density allows for narrowing down suitable material choices as replacement for precious group metals as for example, platinum and opens up new ways in finding cost-efficient, active, and stable new-generation electrocatalysts. [ABSTRACT FROM AUTHOR]

A fundamental understanding of the behavior of non-noble based materials toward the hydrogen evolution reaction is crucial for the successful implementation into practical devices. Through the implementation of a highly sensitive inductively coupled plasma mass spectrometer coupled to a scanning flow cell, the activity and stability of non-noble electrocatalysts is presented. The studied catalysts comprise a range of compositions, including metal carbides (WC), sulfides (MoS2), phosphides (Ni5P4, Co2P), and their base metals (W, Ni, Mo, Co); their activity, stability, and degradation behavior was elaborated and compared to the state-of-the-art catalyst platinum. The non-noble materials are stable at HER potentials but dissolve substantially when no current is flowing. Through pre- and post-characterization of the catalysts, explanations of their stability (thermodynamics and kinetics) are discussed, challenges for the application in real devices are analyzed, and strategies for circumventing dissolution are suggested. The precise correlation of metal dissolution with applied potential/current density allows for narrowing down suitable material choices as replacement for precious group metals as for example, platinum and opens up new ways in finding cost-efficient, active, and stable new-generation electrocatalysts. [ABSTRACT FROM AUTHOR]

The ability to selectively form one crystal structure among several options in a polymorphic system is an important goal in solid-state synthesis. Nanocrystal cation exchange, which proceeds rapidly under mild conditions, can retain key structural features and yield otherwise inaccessible phases, but the extent to which crystal structure can be retained and therefore selectively targeted during such reactions has been limited. Here, we show that nanocrystals of digenite Cu2−xS transform to zincblende MnS and CoS upon cation exchange. Zincblende MnS and CoS, which are metastable in bulk, retain both the tetrahedral cation coordination and cubic close packed anion sublattice of digenite Cu2−xS. Comparison with wurtzite MnS and CoS, which have been accessed previously through analogous cation exchange of roxbyite Cu2−xS, demonstrates the selective formation of the related zincblende vs. wurtzite polymorphs by cation exchange of structurally distinct templates. [ABSTRACT FROM AUTHOR]

The ability to selectively form one crystal structure among several options in a polymorphic system is an important goal in solid-state synthesis. Nanocrystal cation exchange, which proceeds rapidly under mild conditions, can retain key structural features and yield otherwise inaccessible phases, but the extent to which crystal structure can be retained and therefore selectively targeted during such reactions has been limited. Here, we show that nanocrystals of digenite Cu2−xS transform to zincblende MnS and CoS upon cation exchange. Zincblende MnS and CoS, which are metastable in bulk, retain both the tetrahedral cation coordination and cubic close packed anion sublattice of digenite Cu2−xS. Comparison with wurtzite MnS and CoS, which have been accessed previously through analogous cation exchange of roxbyite Cu2−xS, demonstrates the selective formation of the related zincblende vs. wurtzite polymorphs by cation exchange of structurally distinct templates. [ABSTRACT FROM AUTHOR]

Bulk iron pyrite (FeS2) functions as an inexpensive, Earth-abundant, off-the-shelf catalyst capable of selectively hydrogenating a broad scope of substituted nitroarenes to their corresponding aniline derivatives using molecular hydrogen. [ABSTRACT FROM AUTHOR]

The efficient catalysis of water electrolysis using Earth-abundant materials is considered to underpin the large-scale implementation of several clean energy technologies. Here, we report the synthesis of molybdenum rich Co–Mo nanoparticles, which function as highly active and stable electrocatalysts for the hydrogen evolution reaction (HER) in alkaline aqueous solutions. The Co–Mo nanoparticles have an average diameter of approx. 3 nm, a Co : Mo ratio of approx. 1 : 9, and are poorly crystalline. The Co–Mo nanoparticles deposited onto Ti foil substrates at a loading of approx. 1 mg cm−2 required an overpotential of only −75 mV to produce an operationally relevant current density of −10 mA cm−2, placing them among the most highly active Earth-abundant HER catalysts in alkaline media. [ABSTRACT FROM AUTHOR]

Molybdenum ditelluride, MoTe2, is emerging as an important transition-metal dichalcogenide (TMD) material because of its favorable properties relative to other TMDs. The 1T ′ polymorph of MoTe2 is particularly interesting because it is semimetallic with bands that overlap near the Fermi level, but semiconducting 2H-MoTe2 is more stable and therefore more accessible synthetically. Metastable 1T ′-MoTe2 forms directly in solution at 300 °C as uniform colloidal nanostructures that consist of few-layer nanosheets, which appear to exhibit an approx. 1 % lateral lattice compression relative to the bulk analogue. Density functional theory calculations suggest that small grain sizes and polycrystallinity stabilize the 1T ′ phase in the MoTe2 nanostructures and suppress its transformation back to the more stable 2H polymorph through grain boundary pinning. Raman spectra of the 1T ′-MoTe2 nanostructures exhibit a laser energy dependence, which could be caused by electronic transitions. [ABSTRACT FROM AUTHOR]

Molybdenum ditelluride, MoTe2, is emerging as an important transition-metal dichalcogenide (TMD) material because of its favorable properties relative to other TMDs. The 1T ′ polymorph of MoTe2 is particularly interesting because it is semimetallic with bands that overlap near the Fermi level, but semiconducting 2H-MoTe2 is more stable and therefore more accessible synthetically. Metastable 1T ′-MoTe2 forms directly in solution at 300 °C as uniform colloidal nanostructures that consist of few-layer nanosheets, which appear to exhibit an approx. 1 % lateral lattice compression relative to the bulk analogue. Density functional theory calculations suggest that small grain sizes and polycrystallinity stabilize the 1T ′ phase in the MoTe2 nanostructures and suppress its transformation back to the more stable 2H polymorph through grain boundary pinning. Raman spectra of the 1T ′-MoTe2 nanostructures exhibit a laser energy dependence, which could be caused by electronic transitions. [ABSTRACT FROM AUTHOR]

Ion exchange reactions of colloidal nanocrystals provide access to complex products that are synthetically challenging using traditional hot-injection methods. However, such reactions typically achieve only partial material transformations by employing either cation or anion exchange processes. It is now shown that anion and cation exchange reactions can be coupled together and applied sequentially in one integrated pathway that leads to complete material transformations of nanocrystal templates. Although the product nanocrystals do not contain any of the original constituent elements, the original morphology is retained, thereby fully decoupling morphology and composition control. The sequential anion/cation exchange process was applied to pseudo-spherical CdO nanocrystals and ZnO tetrapods, producing fully transformed and shape-controlled nanocrystals of copper and silver sulfides and selenides. Furthermore, hollow core-shell tetrapod ZnS@CdS heterostructures were readily accessible. [ABSTRACT FROM AUTHOR]

Ion exchange reactions of colloidal nanocrystals provide access to complex products that are synthetically challenging using traditional hot-injection methods. However, such reactions typically achieve only partial material transformations by employing either cation or anion exchange processes. It is now shown that anion and cation exchange reactions can be coupled together and applied sequentially in one integrated pathway that leads to complete material transformations of nanocrystal templates. Although the product nanocrystals do not contain any of the original constituent elements, the original morphology is retained, thereby fully decoupling morphology and composition control. The sequential anion/cation exchange process was applied to pseudo-spherical CdO nanocrystals and ZnO tetrapods, producing fully transformed and shape-controlled nanocrystals of copper and silver sulfides and selenides. Furthermore, hollow core-shell tetrapod ZnS@CdS heterostructures were readily accessible. [ABSTRACT FROM AUTHOR]

CoP nanostructures that exposed predominantly (111) crystal facets were synthesized and evaluated for performance as electrocatalysts for the hydrogen-evolution reaction (HER). The branched CoP nanostructures were synthesized by reacting cobalt(ii) acetylacetonate with trioctylphosphine in the presence of trioctylphosphine oxide. Electrodes comprised of the branched CoP nanostructures deposited at a loading density of ∼1 mg cm−2 on Ti electrodes required an overpotential of −117 mV to produce a current density of −20 mA cm−2 in 0.50 M H2SO4. Hence the branched CoP nanostructures belong to the growing family of highly active non-noble-metal HER electrocatalysts. Comparisons with related CoP systems have provided insights into the impact that shape-controlled nanoparticles and nanoparticle–electrode interactions have on the activity and stability of nanostructured HER electrocatalysts. [ABSTRACT FROM AUTHOR]

Nanoparticles of cobalt phosphide, CoP, have been prepared and evaluated as electrocatalysts for the hydrogen evolution reaction (HER) under strongly acidic conditions (0.50 M H2SO4, pH 0.3). Uniform, multi-faceted CoP nanoparticles were synthesized by reacting Co nanoparticles with trioctylphosphine. Electrodes comprised of CoP nanoparticles on a Ti support (2 mg cm−2 mass loading) produced a cathodic current density of 20 mA cm−2 at an overpotential of −85 mV. The CoP/Ti electrodes were stable over 24 h of sustained hydrogen production in 0.50 M H2SO4. The activity was essentially unchanged after 400 cyclic voltammetric sweeps, suggesting long-term viability under operating conditions. CoP is therefore amongst the most active, acid-stable, earth-abundant HER electrocatalysts reported to date. [ABSTRACT FROM AUTHOR]

Nanoparticles of cobalt phosphide, CoP, have been prepared and evaluated as electrocatalysts for the hydrogen evolution reaction (HER) under strongly acidic conditions (0.50 M H2SO4, pH 0.3). Uniform, multi-faceted CoP nanoparticles were synthesized by reacting Co nanoparticles with trioctylphosphine. Electrodes comprised of CoP nanoparticles on a Ti support (2 mg cm−2 mass loading) produced a cathodic current density of 20 mA cm−2 at an overpotential of −85 mV. The CoP/Ti electrodes were stable over 24 h of sustained hydrogen production in 0.50 M H2SO4. The activity was essentially unchanged after 400 cyclic voltammetric sweeps, suggesting long-term viability under operating conditions. CoP is therefore amongst the most active, acid-stable, earth-abundant HER electrocatalysts reported to date. [ABSTRACT FROM AUTHOR]

REFERENCE 1 H. Wang, R. Katz, J. Fanghanel, R. E. Schaak, and V. Gopalan, "Ultrasensitive electrode-free and co-catalyst-free detection of nanomoles per hour hydrogen evolution for the discovery of new photocatalysts", Rev. Sci. Instrum. Erratum: "Ultrasensitive electrode-free and co-catalyst-free detection of nanomoles per hour hydrogen evolution for the discovery of new photocatalysts" [Rev. Sci. Instrum. In the first paragraph of the original paper,[1] the sentence "Given that the Earth receives 3 × 10 SP -24 sp J of solar energy annually..." should be changed to "Given that the Earth receives 3 × 10 SP 24 sp J of solar energy annually...." In Eq. (2) of the paper, the format should be corrected to HT ht (2) The requested changes do not affect the main body of the work or compromise in anyway the conclusions of the article. [Extracted from the article]

New synthetic innovations are rapidly being developed to address the demand for complex, next-generation nanomaterials with rigorously controlled architectures and interfaces. This Review highlights key strategies for the chemical transformation and stepwise synthesis of multicomponent inorganic nanostructures, with the existing nanoscale transformations categorized into classes of reactions that are related to those used in the synthesis of organic molecules. The application of concepts used in molecular synthesis-including site-selectivity, regio- and chemoselectivity, orthogonal reactivity, coupling reactions, protection/deprotection strategies, and procedures for separation and purification-to nanoscale systems is emphasized. Collectively, the resulting synthetic concept represents an emerging model for the synthesis of complex inorganic nanostructures on the basis of the guiding principles that underpin the multistep total synthesis of complex organic molecules and natural products. [ABSTRACT FROM AUTHOR]

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Colloidal hybrid nanoparticles contain multiple nanoscale domains fused together by solid-state interfaces. They represent an emerging class of multifunctional lab-on-a-particle architectures that underpin future advances in solar energy conversion, fuel-cell catalysis, medical imaging and therapy, and electronics. The complexity of these 'artificial molecules' is limited ultimately by the lack of a mechanism-driven design framework. Here, we show that known chemical reactions can be applied in a predictable and stepwise manner to build complex hybrid nanoparticle architectures that include M-Pt-Fe3O4 (M = Au, Ag, Ni, Pd) heterotrimers, MxS-Au-Pt-Fe3O4 (M = Pb, Cu) heterotetramers and higher-order oligomers based on the heterotrimeric Au-Pt-Fe3O4 building block. This synthetic framework conceptually mimics the total-synthesis approach used by chemists to construct complex organic molecules. The reaction toolkit applies solid-state nanoparticle analogues of chemoselective reactions, regiospecificity, coupling reactions and molecular substituent effects to the construction of exceptionally complex hybrid nanoparticle oligomers. [ABSTRACT FROM AUTHOR]

In an effort to determine the active state of supported palladium for the direct formation of H2O2 from H2 and O2, the catalytic behavior of Pd0/SiO2, PdO/SiO2 and partially reduced PdO/SiO2 was determined. The results obtained in an ethanol slurry, with chloride ions and H2SO4 being present, showed that the PdO/SiO2 catalyst was almost completely inactive for the formation of H2O2 at 10 °C. The Pd0/SiO2 catalyst exhibited the highest activity for H2O2 formation, and the PdO/SiO2 material, reduced under very mild conditions, exhibited an intermediate activity. The state of Pd on the three catalysts was characterized by XRD, TEM and XPS methods. Only Pd0 (the metal phase) and PdO were observed on Pd0/SiO2 and PdO/SiO2, respectively. As expected, with the partially reduced PdO/SiO2 catalyst, both Pd0 and PdO phases were evident. The TEM results revealed that the Pd0 particles decorated the larger PdO particles. The results reported here support the role of metallic palladium, rather than the oxide, as the active phase for the direct formation of H2O2. [ABSTRACT FROM AUTHOR]

Amorphous tungsten phosphide (WP), which has been synthesized as colloidal nanoparticles with an average diameter of 3 nm, has been identified as a new electrocatalyst for the hydrogen-evolution reaction (HER) in acidic aqueous solutions. WP/Ti electrodes produced current densities of -10 mA cm-2 and -20 mA cm-2 at overpotentials of only -120 mV and -140 mV, respectively, in 0.50 M H2SO4(aq). [ABSTRACT FROM AUTHOR]

A material specific peptide bound to Fe2O3 facilitates the selective sequestration of Au from a colloidal mixture of Au and CdS nanoparticles; the Au–Fe2O3 precipitate can then be magnetically separated from the colloidal CdS, and the Au nanoparticles can be recovered upon release from the Fe2O3. [ABSTRACT FROM AUTHOR]

Palladium is converted into palladium hydride, β-PdHx, in polyol solution using NaBH4 as a hydrogen source; nanocrystalline Pd reacts to form PdHx faster and at lower temperatures than bulk Pd, and can be made to release hydrogen to regenerate Pd. [ABSTRACT FROM AUTHOR]

Palladium is converted into palladium hydride, β-PdHx, in polyol solution using NaBH4as a hydrogen source; nanocrystalline Pd reacts to form PdHxfaster and at lower temperatures than bulk Pd, and can be made to release hydrogen to regenerate Pd. [ABSTRACT FROM AUTHOR]