Solid-solution Alloy Nanoparticles Research Articles

Ruthenium-Cobalt Solid-Solution Alloy Nanoparticles for Enhanced Photopromoted Thermocatalytic CO2 Hydrogenation to Methane.

Bimetallic alloy nanoparticles have garnered substantial attention for diverse catalytic applications owing to their abundant active sites and tunable electronic structures, whereas the synthesis of ultrafine alloy nanoparticles with atomic-level homogeneity for bulk-state immiscible couples remains a formidable challenge. Herein, we present the synthesis of RuxCo1-x solid-solution alloy nanoparticles (ca. 2 nm) across the entire composition range, for highly efficient, durable, and selective CO2 hydrogenation to CH4 under mild conditions. Notably, Ru0.88Co0.12/TiO2 and Ru0.74Co0.26/TiO2 catalysts, with 12 and 26 atom % of Ru being substituted by Co, exhibit enhanced catalytic activity compared with the monometallic Ru/TiO2 counterparts both in dark and under light irradiation. The comprehensive experimental investigations and density functional theory calculations unveil that the electronic state of Ru is subtly modulated owing to the intimate interaction between Ru and Co in the alloy nanoparticles, and this effect results in the decline in the CO2 conversion energy barrier, thus ultimately culminating in an elevated catalytic performance relative to monometallic Ru and Co catalysts. In the photopromoted thermocatalytic process, the photoinduced charge carriers and localized photothermal effect play a pivotal role in facilitating the chemical reaction process, which accounts for the further boosted CO2 methanation performance.

First synthesis of RuSn solid-solution alloy nanoparticles and their enhanced hydrogen evolution reaction activity.

Solid-solution alloys based on platinum group metals and p-block metals have attracted much attention due to their promising potential as materials with a continuously fine-tunable electronic structure. Here, we report on the first synthesis of novel solid-solution RuSn alloy nanoparticles (NPs) by electrochemical cyclic voltammetry sweeping of RuSn@SnOx NPs. High-angle annular dark-field scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy maps confirmed the random and homogeneous distribution of Ru and Sn elements in the alloy NPs. Compared with monometallic Ru NPs, the RuSn alloy NPs showed improved hydrogen evolution reaction (HER) performance. The overpotentials of Ru0.94Sn0.06 NPs/C and Ru0.87Sn0.13 NPs/C to achieve a current density of 10 mA cm-2 were 43.41 and 33.19 mV, respectively, which are lower than those of monometallic Ru NPs/C (53.53 mV) and commercial Pt NPs/C (55.77 mV). The valence-band structures of the NPs investigated by hard X-ray photoelectron spectroscopy demonstrated that the d-band centre of RuSn NPs shifted downward compared with that of Ru NPs. X-ray photoelectron spectroscopy and X-ray absorption near-edge structure analyses indicated that in the RuSn alloy NPs, charge transfer occurs from Sn to Ru, which was considered to result in a downward shift of the d-band centre in RuSn NPs and to regulate the adsorption energy of intermediate Hads effectively, and thus enable the RuSn solid-solution alloy NPs to exhibit excellent HER catalytic properties.

RuIn Solid-Solution Alloy Nanoparticles with Enhanced Hydrogen Evolution Reaction Activity

RuIn Solid-Solution Alloy Nanoparticles with Enhanced Hydrogen Evolution Reaction Activity

Specific Hydrogen Spillover Pathways Generated on Graphene Oxide Enabling the Formation of Non-Equilibrium Alloy Nanoparticles.

The phenomenon of hydrogen spillover is investigated as a means of realizing a hydrogen-based society for over half a century. Herein, a graphene oxide having a precisely tuned architecture via calcination in air to introduce ether groups onto basal planes along with carbon defects is reported. This material provides specific pathways for the spillover of atomic hydrogen and has practical applications with regard to the synthesis of non-equilibrium solid-solution alloy nanoparticles. A combination of experimental work and simulations confirmed that the presence of ether groups associated with carbon defects facilitated hydrogen spillover within the basal planes of this graphene oxide. This enhanced hydrogen spillover ability, in turn, enables the simultaneous reduction of Ru3+ and Ni2+ ions to form RuNi alloy nanoparticles under hydrogen reduction conditions. Energy dispersive X-ray and X-ray absorption near edge structure simulations establish that this strategy forms unique alloy nanoparticles each comprising a Ru core with a RuNi solid-solution shell having a hexagonal close-packed structure. These non-equilibrium RuNi alloy nanoparticles exhibit greater catalytic activity than monometallic Ru nanoparticles during the hydrolysis of ammonia borane.

Molybdenum-Ruthenium-Carbon Solid-Solution Alloy Nanoparticles: Can They Be Pseudo-Technetium Carbide?

Technetium (Tc), atomic number 43, is an element that humans cannot freely use even in the 21st century because Tc is radioactive and has no stable isotope. In this report, we present molybdenum-ruthenium-carbon solid-solution alloy (MoxRu1-xCy) nanoparticles (NPs) that are expected to have an electronic structure similar to that of technetium carbide (TcCy). MoxRu1-xCy NPs were synthesized by annealing under a helium/hydrogen atmosphere following thermal decomposition of metal precursors. The obtained NPs had a solid-solution structure in the whole composition range. MoxRu1-xCy with a cubic structure (down to 30 atom % Mo in the metal ratio) showed a superconducting state, and the transition temperature (Tc) increased with increasing Mo composition. The continuous change in Tc across that of TcCy indicates the continuous control of the electronic structure by solid-solution alloying, leading to pseudo-TcCy. Density functional theory calculations indicated that the synthesized Mo0.53Ru0.47C0.41 has a similar electronic structure to TcC0.41.

Persistent Homology and Bond Orientational Order in Ir–Cu Solid-Solution Alloy Nanoparticles: Implications for Electrocatalysts

Persistent Homology and Bond Orientational Order in Ir–Cu Solid-Solution Alloy Nanoparticles: Implications for Electrocatalysts

Composition sensitive selectivity and activity of electrochemical carbon dioxide reduction on Pd–Cu solid-solution alloy nanoparticles

The alloy-composition-sensitive selectivity and activity of CO2RR have been demonstrated for Pd-Cu solid solution nanopaticles.

Gas-Phase Synthesis of PtMo Alloy Electrocatalysts with Enhanced Activity and Durability for Oxygen Reduction Reaction

The proton-exchange membrane fuel cell is a promising technology to effectively utilize hydrogen energy, which is the ideal alternative to fossil fuels. However, the high dependency on scarce Pt as an oxygen reduction reaction (ORR) electrocatalyst is still a severe barrier that hinders widespread commercialization. Herein, we propose a facile synthetic strategy facilitating mass production of Pt–Mo solid-solution alloy nanoparticles on a carbon support (PtMo/C) as a highly active ORR electrocatalyst. Without using organic surfactants or reducing agents, our synthesis process based on the gas-phase method in an inert atmosphere is cost-effective and does not require any post-treatment, unlike most reported solution-based reduction processes. Both molybdenum metal and carbon monoxide decomposed from molybdenum hexacarbonyl contribute to the reduction of the PtMo alloy during the annealing process. By elucidating the growth and synthesis mechanisms, we optimized the particle size of PtMo/C to approximately 3.1 nm, annealed at 800 °C (PtMo/C-800). Consequently, PtMo/C-800 shows high mass activity (146 mA mgPt–1), which is superior to that of commercial Pt/C, and excellent durability after accelerated degradation tests.

Crystal Structure Control of Binary and Ternary Solid-Solution Alloy Nanoparticles with a Face-Centered Cubic or Hexagonal Close-Packed Phase.

The crystal structure significantly affects the physical and chemical properties of solids. However, the crystal structure-dependent properties of alloys are rarely studied because controlling the crystal structure of an alloy at the same composition is extremely difficult. Here, for the first time, we successfully demonstrate the synthesis of binary Ru-Pt (Ru/Pt = 7:3) and Ru-Ir (Ru/Ir = 7:3) and ternary Ru-Ir-Pt (Ru/Ir/Pt = 7:1.5:1.5) solid-solution alloy nanoparticles (NPs) with well-controlled hexagonal close-packed (hcp) and face-centered cubic (fcc) phases, through the chemical reduction method. The crystal structure control is realized by precisely tunning the reduction speeds of the metal precursors. The effect of the crystal structure on the catalytic performance of solid-solution alloy NPs is systematically investigated. Impressively, all the hcp alloy NPs show superior electrocatalytic activities for the hydrogen evolution reaction in alkaline solution compared with the fcc alloy NPs. In particular, hcp-RuIrPt exhibits extremely high intrinsic (mass) activity, which is 3.1 (3.2) and 6.7 (6.9) times enhanced compared to that of fcc-RuIrPt and commercial Pt/C.

Maximize mixing in highly polyelemental solid solution alloy nanoparticles

In this issue of <i>Matter</i>, Yao et al. report on advanced non-equilibrium high-temperature entropy-controlled synthesis of polyelemental nanoparticles. They achieve extreme mixing of 15 metals, some of them previously immiscible, in the form of a single phase solid solution. The compositionally tunable properties of such atomic scale mixtures within a simple crystal structure makes them highly interesting for the design of new materials, e.g., electrocatalysts.

Pt/Ag Solid Solution Alloy Nanoparticles in Miscibility Gaps Synthesized by Cosputtering onto Liquid Polymers.

Pt/Ag solid solution alloy nanoparticles (NPs) with mean size below 3 nm were obtained with composition in miscibility gaps by cosputtering onto liquid polyethylene glycol (PEG, MW = 600). Adjusting the sputtering currents from 10 to 50 mA did not influence the particle sizes obviously but caused a substantial difference in the composition and distributions of Pt/Ag NPs. This is different from sputtered Pt/Au NPs where particle size is correlated with composition. For a pair of sputtering currents, the formed Pt/Ag alloy NPs have a range of compositions. The normal distribution with Pt of 60.2 ± 16.2 at % is observed for the Pt/Ag sample with a nominal Pt content of 55.9 at %, whereas Pt-rich (85.1 ± 14.0 at % Pt) and Ag-rich (19.8 ± 12.2 at % Pt) Pt/Ag samples with nominal Pt contents of 90.9 and 11.9 at % contain more pure Pt and pure Ag NPs, respectively. Different from NPs obtained in PEG, the sputtered NPs on TEM grids had more uniform composition for a longer sputtering time along with a significant increase of particle sizes. This reveals that PEG hindered the combination of NPs and clusters, resulting in small particle sizes even for long time sputtering and broader composition distributions. Thus, the samples obtained in PEG have the compositions mainly determined by the random atom combination in the vacuum chamber and possibly in initial landing of atom/clusters on the PEG surface.

Improvement of Ni/Al2O3 Catalysts for Low-Temperature CO2 Methanation by Vanadium and Calcium Oxide Addition

CO2 methanation is a very promising technology for the production of alternative fuels with the simultaneous use of greenhouse gases. Therefore, intensive research is carried out on the optimization of catalysts with excellent properties for operation in the area of low temperatures. Here, we present research on a catalyst composed of 19 wt % NiO supported on alumina/calcium aluminate. The catalyst was modified with V2O5 in order to be suited for extrusion and scale-up in the frame of power to gas technology. Samples with various vanadium contents (Ni–xV, where x represents the amount of vanadium) were prepared in the form of ground granules obtained from 0.5 mm diameter spherical grains. X-ray diffraction (XRD), transmission electron microscopy (TEM), skeletal infrared (IR), diffuse reflectance ultraviolet–visible-near-infrared (DR-UV–vis-NIR), and X-ray photoelectron (XPS) spectroscopies, as well as H2 temperature-programmed reduction (H2-TPR), were used to characterize the samples. Catalytic performances of the catalyst samples were tested in CO2 hydrogenation at 1 atm. Among the many supported Ni catalysts tested in our laboratories, the catalysts of 0.5 and 1 wt % V showed very high activity, with the highest CH4 yield of 97% at 623 K. These catalysts exhibited 100% CH4 selectivity up to 673 K. The excellent performances of the studied catalysts are attributed to the possible formation of Ni–V solid solution alloy nanoparticles.

Highly Stable and Active Solid‐Solution‐Alloy Three‐Way Catalyst by Utilizing Configurational‐Entropy Effect

Since 1970, people have been making every endeavor to reduce toxic emissions from automobiles. After the development of a three-way catalyst (TWC) that concurrently converts three harmful gases, carbon monoxide (CO), hydrocarbons (HCs), and nitrogen oxides (NOx ), Rh became an essential element in automobile technology because only Rh works efficiently for catalytic NOx reduction. However, due to the sharp price spike in 2007, numerous efforts have been made to replace Rh in TWCs. Nevertheless, Rh remains irreplaceable, and now, the price of Rh is increasing significantly again. Here, it is demonstrated that PdRuM ternary solid-solution alloy nanoparticles (NPs) exhibit highly durable and active TWC performance, which will result in a significant reduction in catalyst cost compared to Rh. This work provides insights into the design of highly durable and efficient functional alloy NPs, guiding how to best take advantage of the configurational entropy in addition to the mixing enthalpy.

Boosting reverse water-gas shift reaction activity of Pt nanoparticles through light doping of W

We report PtW solid-solution alloy nanoparticles (NPs) as a reverse water-gas shift (RWGS) reaction catalyst for the first time. Atomic-level alloying of Pt and W significantly enhanced the RWGS reaction activity of Pt NPs.

Nonequilibrium Flow-Synthesis of Solid-Solution Alloy Nanoparticles: From Immiscible Binary to High-Entropy Alloys

Solid-solution alloy nanoparticles (NPs), where the constituents mix at the atomic level, show a variety of attractive properties due to their tunable electronic structures. However, it is still difficult to stably synthesize them, particularly nonequilibrium alloys that consist of combinations immiscible in the bulk. Here, we first report the successful syntheses of solid-solution alloy NPs including PdRu and PdRuIr, which are immiscible in the bulk, and of IrPdPtRhRu high-entropy alloy NPs through a continuous-flow reactor providing a high productivity with high reproducibility. The designed solvothermal flow reactor enabled us to use a lower alcohol as a reductant that cannot be applied in a batch synthesis for these NPs.

Solid-solution alloying of immiscible Pt and Au boosts catalytic performance for H2O2 direct synthesis

Here, we propose the solid-solution alloy nanoparticles (NPs) composed of Pt and Au supported on TiO2 as an efficient catalyst for direct H2O2 synthesis, although Pt and Au are entirely immiscible in the bulk phases. Pt and Au atoms were homogeneously distributed in a wide composition range of PtxAu100-x NPs (10 ≤ x ≤ 80) supported on TiO2. The most Au-rich Pt10Au90 NPs/TiO2 exhibits the best catalytic performances, H2O2 selectivity (94.5 ± 0.6%) and productivity (959 ± 12 mmolH2O2•gmetal−1•h−1), even under mild conditions (10 °C, 1 atm) and without halide-ion additives. Density functional theory calculations reveal that the introduction of inactive Au atoms strongly suppresses both O-O bond scission and OH hydrogenation, thereby enabling near unity selectivity. The Pt-Au catalyst is Pd-absent, which is noteworthy given previous efforts in direct H2O2 synthesis are mostly limited to prototypical Pd or Pd-based modifications. This work will stimulate active utilization of immiscible elemental combinations for the direct H2O2 synthesis catalyst development.

Increasing the Size-Selectivity in Laser-Based g/h Liquid Flow Synthesis of Pt and PtPd Nanoparticles for CO and NO Oxidation in Industrial Automotive Exhaust Gas Treatment Benchmarking.

PtPd catalysts are state-of-the-art for automotive diesel exhaust gas treatment. Although wet-chemical preparation of PtPd nanoparticles below 3 nm and kg-scale synthesis of supported PtPd/Al2O3 are already established, the partial segregation of the bimetallic nanoparticles remains an issue that adversely affects catalytic performance. As a promising alternative, laser-based catalyst preparation allows the continuous synthesis of surfactant-free, solid-solution alloy nanoparticles at the g/h-scale. However, the required productivity of the catalytically relevant size fraction <10 nm has yet to be met. In this work, by optimization of ablation and fragmentation conditions, the continuous flow synthesis of nanoparticles with a productivity of the catalytically relevant size fraction <10 nm of >1 g/h is presented via an in-process size tuning strategy. After the laser-based preparation of hectoliters of colloid and more than 2 kg of PtPd/Al2O3 wash coat, the laser-generated catalysts were benchmarked against an industry-relevant reference catalyst. The conversion of CO by laser-generated catalysts was found to be equivalent to the reference, while improved activity during NO oxidation was achieved. Finally, the present study validates that laser-generated catalysts meet the size and productivity requirements for industrial standard operating procedures. Hence, laser-based catalyst synthesis appears to be a promising alternative to chemical-based preparation of alloy nanoparticles for developing industrial catalysts, such as those needed in the treatment of exhaust gases.

Tuning the electronic structure of AuNi homogeneous solid-solution alloy with positively charged Ni center for highly selective electrochemical CO2 reduction

Designing bimetallic electrocatalysts with homogenous element distribution and tunable electronic structure is attractive strategy to enhance the CO selectivity in electrochemical carbon dioxide reduction reaction (CO2RR). Herein, we report a concept of atom-polymer hybridization to synthesize AuNi homogeneous solid-solution alloy nanoparticles (NPs) with positively charged Ni center supported on electrospun carbon nanofibers (CNFs). The nanofibers host can strong restrict the separated growth of Au and Ni nanoclusters during the directly graphitization process, leading to the formation of homogeneous AuNi alloy. In-situ characterizations reveal the formation process and phase evolution of the AuNi alloy during the carbonization. The positively charged Ni when alloying with Au lead to the enhanced local electronic structure on AuNi homogeneous solid-solution alloy due to the electron-withdrawal effect of nearby Au atoms. The AuNi homogeneous solid-solution alloy exhibits a high CO selectivity with an optimal CO Faradaic efficiency (FECO) of 92% at −0.98 V (vs. RHE). Theoretical calculations indicate that the incorporation of Ni into Au can make the d-band center more positive and reduce the free energy barrier for the CO2 activation into *COOH and *CO desorption. Operando Raman spectroscopy provides the evidences that AuNi homogeneous solid-solution alloy can facilitate the activation of CO2 into *COOH and enhance the interaction between *COOH and AuNi (111) due to the change of electronic structure.

Frontispiece: New Aspects of Platinum Group Metal‐Based Solid‐Solution Alloy Nanoparticles: Binary to High‐Entropy Alloys

Recent advances in platinum group metal (PGM)-based solid-solution alloy nanoparticles (NPs), with particular attention to immiscible alloy systems are summarized. The concepts, synthesis, and properties of the alloy NPs are introduced, and the existing challenges and future perspectives are discussed in the Review article by H. Kitagawa et al. on page 5105 ff.

Capturing the Equilibration Pathway of Nanomaterials Metastable in Both Crystal Structure and Morphology

In this issue of Matter, Li et al. used in situ electron microscopy to investigate the equilibration pathway of Au nanoribbons that are metastable in terms of both crystal structure and morphology when they are subjected to thermal stress.