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Oxides containing metals or metalloids from the p block of the periodic table (e.g., In, Sn, Sb, Pb, and Bi) are of technological interest as transparent conductors and light absorbers for solar-energy conversion due to the tunability of their electronic conductivity and optical absorption. Comparatively, these oxides have found limited applications in hydrogen photoelectrolysis, primarily due to their high electronegativity, which impedes electron transfer for reducing protons into hydrogen. We have shown recently that inserting s-block cations into p-block metal oxides is effective at lowering electronegativities while affording further control of band gaps. Here, we explain the origins of this dual tunability by demonstrating the mediator role of s-block cations in modulating orbital hybridization while not contributing to frontier electronic states. From this result, we carry out a comprehensive computational study of 109 ternary oxides of s- and p-block metal elements as candidate photocatalysts for solar hydrogen generation. We down-select the most desirable materials using band gaps and band edges obtained from Hubbard-corrected density-functional theory, with Hubbard parameters computed entirely from first principles, evaluate the stability of these oxides in aqueous conditions, and characterize experimentally four of the remaining materials, synthesized with high phase uniformity, to validate and further develop the computational models. We thus propose nine oxide semiconductors, including CsIn_{3}O_{5}, Sr_{2}In_{2}O_{5}, and KSbO_{2}, which, to the extent of our literature review, have not been previously considered as water-splitting photocatalysts.

Many binary late transition metal systems have large bulk miscibility gaps, and a variety of synthetic strategies have been developed to generate these non-equilibrium alloys as nanoparticles. While many of these methods strive to co-nucleate both elements by exploiting fast reduction kinetics or co-sequestration within a confined space, we show here that simple room-temperature borohydride co-reduction of appropriate aqueous metal salt solutions yields alloy nanoparticles in the bulk-immiscible Au–Rh, Au–Pt, Pt–Rh, and Pd–Rh systems. The compositions can be tuned across the entire Au1−xRhx, Au1−xPtx, Pt1−xRhx, and Pd1−xRhxsolid solutions by varying the ratio of metal salt reagents, and they form in the presence of a variety of molecular and polymeric surface stabilizers. Reaction pathway studies on the model Au–Rh system suggest that the alloy nanoparticles form viaa “conversion chemistry” mechanism: Au nanoparticle templates nucleate first, followed by diffusion of Rh to form homogeneous Au–Rh alloy nanoparticles. The alloy nanoparticles tend to be agglomerated, but this can be minimized by forming the nanoparticles directly on catalytically relevant high surface area carbon and biological supports, e.g.Vulcan carbon and wild-type M13 bacteriophage. [ABSTRACT FROM AUTHOR]

Binary intermetallic compounds have been synthesized in edible plant and seed oils through the reaction of molten metal dispersions of low-melting p-block metals with late transition metal powders. Specifically, apricot kernel, almond, safflower, and canola oils have been used to synthesize FeSn2, Ni3Sn4, CoSn3, CoGa3, Cu6Sn5, and Bi3Ni. This low-temperature strategy yields bulk-scale products that are highly crystalline, and the solvents used to synthesize them can be re-used several times. [ABSTRACT FROM AUTHOR]

A variety of binary intermetallic compounds of late transition metals with low-melting post-transition metals have been synthesized in bulk quantities by reacting molten metal dispersions with fine metal powders in hot polyalcohol solvents. Fourteen distinct intermetallics were formed using this technique: SbSn, FeSn 2, Cu 6Sn 5, CoSn 3, Ni 3Sn 4, FeGa 3, NiGa 4, Cu 9Ga 4, CoGa 3, Ni 2In 3, InSb, In 5Bi 3, InBi, and Bi 3Ni. Notable among these are a low-temperature phase (α-CoSn 3), textured intermetallic powders with anisotropic morphologies (α-CoSn 3and FeSn 2), and superconductors (Bi 3Ni and In 5Bi 3). Reaction pathway studies suggest that the molten low-melting metals diffuse into the larger higher melting powders, forming intermetallic compounds directly in a liquid-phase medium from bulk-scale powders of the constituent elements. [ABSTRACT FROM AUTHOR]

We describe a unified and general template-based strategy for synthesizing a library of morphology-controllable M−Sn ( M= Co, Ni, Cu, Ag, Au, Pt, Ru) intermetallic nanorods. The reaction of β-Sn nanorod templates with appropriate metal salt solutions under reducing conditions yields single-crystal intermetallic nanorods of CoSn 3, Ni 3Sn 4, Cu 6Sn 5, Ag 4Sn, AuSn, PtSn, and RuSn 2. Temperature plays a key role in maintaining the morphology of the β-Sn nanorod templates in the final M−Sn products and also selectively generating spherical nanocrystals vs dense nanorods vs hollow nanorods, in some cases (e.g., CoSn 3) within the same system. These observations are linked to the diffusion process, and accordingly, the melting points of the transition elements used in this study can help us understand and predict the morphologies that can be formed, as well as the lowest temperature at which a particular intermetallic compound can form using low-temperature solution routes. [ABSTRACT FROM AUTHOR]

Multi-metal nanoparticles, particularly alloys and intermetallic compounds, are useful catalysts for a variety of chemical transformations. Supported intermetallic nanoparticle catalysts are usually prepared by depositing precursors onto a support followed by high-temperature annealing, which is necessary to generate the intermetallic compound but causes sintering and minimizes surface area. Here we show that solution chemistry methods for converting metal nanoparticles into intermetallic compounds are applicable to supported nanoparticle catalyst systems. Unsupported nanocrystalline Pt can be converted to nanocrystalline PtSn, PtPb, PtBi, and FePt3 by reaction with appropriate metal salt solutions under reducing conditions. Similar reactions convert Al2O3, CeO2, and carbon-supported Pt nanoparticles into PtSn, PtPb, PtSb, Pt3Sn, and Cu3Pt. These reactions generate supported alloy and intermetallic nanoparticles directly in solution without the need for high temperature annealing or additional surface stabilizers. These supported intermetallic nanoparticles are catalytically active for chemical transformations such as formic acid oxidation (PtPb/Vulcan) and CO oxidation (Pt3Sn/graphite). Notably, PtPb/Vulcan XC-72 was found to electrocatalytically oxidize formic acid at a lower onset potential (0.1 V) than commercial PtRu/Vulcan XC-72 (0.4 V). [ABSTRACT FROM AUTHOR]

Metal phosphides can have important properties such as superconductivity, magnetoresistance, magnetocaloric behavior, catalytic activity, and lithium intercalation capacity, which make them useful for a variety of technological applications. Bulk metal phosphides usually require high temperatures and harsh reaction conditions to form, and metal phosphide nanocrystals can also be challenging to synthesize. Here we elaborate on a recently developed alternative approach for synthesizing metal phosphides, which involves the solution-mediated reaction of pre-formed metals with trioctylphosphine (TOP) at temperatures below 370 °C. This chemical conversion strategy is shown to be general and highly versatile, successfully forming a wide range of transition-metal and post-transition-metal phosphides using a range of both bulk and nanoscale metals as precursors. Metal nanocrystals, bulk powders, foils, wires, thin films, lithographically patterned substrates, and supported nanocrystals can all be converted to metal phosphides by reaction with TOP. Collectively, this represents a general, unified, and robust strategy for forming metal phosphides using readily available reagents and metal precursors. [ABSTRACT FROM AUTHOR]

Alloys and intermetallic compounds offer a wide range of desirable physical and chemical properties. However, accessing these compounds as nanocrystals is not always straightforward, and the continued development of appropriate synthetic pathways is required. Developing processes that are general toward many systems can be particularly challenging, especially when trying to incorporate highly electropositive metals or metals whose precursors are difficult to reduce into alloy or intermetallic compounds using solution chemistry strategies. Here we report a generalized strategy to access nanocrystalline M−Zn intermetallics (M Au, Cu, Pd) via the chemical conversion of metal nanoparticles using zerovalent organometallic zinc precursors. Using commercially available reagents, transition-metal nanocrystals are made in hot organoamine solvents, which can be further reacted with diethylzinc or diphenylzinc to form intermetallic AuZn, Au3Zn, Cu5Zn8, and PdZn. The reaction pathway from the single-metal precursor to the intermetallic product is confirmed, and the overall particle morphology of the metal nanoparticle precursors is generally conserved in the intermetallic nanoparticle products throughout the conversion reaction. This method offers a general and robust route to zinc-based intermetallics with known catalytic, shape-memory, and corrosion-resistant properties. [ABSTRACT FROM AUTHOR]