Zhenming Cao

Excavated Cubic Platinum-Tin Alloy Nanocrystals Constructed from Ultrathin Nanosheets with Enhanced Electrocatalytic Activity.

Excavated polyhedral noble-metal materials that were built by the orderly assembly of ultrathin nanosheets have both large surface areas and well-defined facets, and therefore could be promising candidates for diverse important applications. In this work, excavated cubic Pt-Sn alloy nanocrystals (NCs) with {110} facets were constructed from twelve nanosheets by a simple co-reduction method with the assistance of the surface regulator polyvinylpyrrolidone. The specific surface area of the excavated cubic Pt-Sn NCs is comparable to that of commercial Pt black despite their larger particle size. The excavated cubic Pt-Sn NCs exhibited superior electrocatalytic activity in terms of both the specific area current density and the mass current density towards methanol oxidation.

Platinum-nickel alloy excavated nano-multipods with hexagonal close-packed structure and superior activity towards hydrogen evolution reaction

Crystal phase regulations may endow materials with enhanced or new functionalities. However, syntheses of noble metal-based allomorphic nanomaterials are extremely difficult, and only a few successful examples have been found. Herein, we report the discovery of hexagonal close-packed Pt–Ni alloy, despite the fact that Pt–Ni alloys are typically crystallized in face-centred cubic structures. The hexagonal close-packed Pt–Ni alloy nano-multipods are synthesized via a facile one-pot solvothermal route, where the branches of nano-multipods take the shape of excavated hexagonal prisms assembled by six nanosheets of 2.5 nm thickness. The hexagonal close-packed Pt–Ni excavated nano-multipods exhibit superior catalytic property towards the hydrogen evolution reaction in alkaline electrolyte. The overpotential is only 65 mV versus reversible hydrogen electrode at a current density of 10 mA cm−2, and the mass current density reaches 3.03 mA μgPt−1 at −70 mV versus reversible hydrogen electrode, which outperforms currently reported catalysts to the best of our knowledge.

Composition-tunable synthesis of Pt–Cu octahedral alloy nanocrystals from PtCu to PtCu3 via underpotential-deposition-like process and their electro-catalytic properties

Bimetallic alloy nanocrystals (NCs) have received great attention because their physical and chemical properties greatly depend on their composition and structure. However, simultaneous control of the composition and surface structure (or morphology) of metal alloy NCs is challenging due to differences in standard redox potential (SRP). According to our previous research, well-shaped and composition-tunable Pt–Cu alloy NCs can be controlled in mild reduction conditions. However, the content of Cu in the as-prepared Pt–Cu alloy NCs cannot exceed 50% using N,N-dimethylformamide (DMF) as the weak reductant. In this paper, we reported a successful synthesis of the octahedral Pt–Cu bimetallic alloy NCs with a molar ratio of Cu ranging from 50% to 75% via introducing a slightly stronger reductant (n-butylalcohol) to improve the reducing ability and tune the sequential reaction kinetics. It is found that n-butylalcohol can solely reduce the Cu precursor to metallic copper. The UPD-like process ensures the formation of the Pt–Cu alloy due to the strong binding energy between Cu atoms and the Pt crystal surface. Owing to the successful control of Cu, the content in Pt–Cu alloy increased from 50% to 75%, and the relationship between the composition and the properties of the electro-catalytic oxidation of formic acid were further investigated. The results reveal that the electro-catalytic performance of the Pt–Cu alloy is enhanced along with Cu content, and that PtCu3 exhibits excellent catalytic activity and anti-poisoning ability.

Solvent-dependent evolution of cyclic penta-twinned rhodium icosahedral nanocrystals and their enhanced catalytic properties

Cyclic penta-twinned noble metal nanocrystals exhibit promising properties due to their unique geometric and electronic structures. However, the controlled synthesis of cyclic penta-twinned nanostructures, especially of noble metals with a high cohesive energy (e.g., Rh), is very difficult, and the corresponding growth mechanism is not fully understood. Herein, we report a facile one-pot hydrothermal approach for the synthesis of cyclic penta-twinned Rh icosahedral nanocrystals. It was found that apart from regulating the surface free energy by changing the concentration or category of the capping agents, the solvent might influence the adsorption ability of the surfactant on the Rh crystal surface, which results in a change in the surface free energy and thus allows the formation of Rh cyclic penta-twinned nanostructures. In addition, due to their unique electronic and geometric structures, the Rh icosahedral nanocrystals exhibit superior catalytic activity and stability for the electrooxidation of ethanol as compared to single-crystal Rh tetrahedral nanocrystals and commercial Rh black.

Synthesis of single-crystal hyperbranched rhodium nanoplates with remarkable catalytic properties

The catalytic properties of noble metal nanocrystals can be tuned via engineering their structures. Nanocrystals with fractal structures are fascinating catalysts regarding their large surface area-to-volume ratios, large numbers of edges and corners, which can be tuned simultaneously by their hierarchical ordering. However, it is still a great challenge to control the hierarchical ordering of noble metal fractal nanocrystals and their formation mechanism is not fully understood. Herein, we report a facile solvothermal method for the direct preparation of a unique single-crystal Rh-hyperbranched structure, which consists of hierarchically ultrathin nanoplates with threefold symmetry, large surface area and high density of low-coordinated edge/corner sites. Importantly, the hierarchical ordering can be readily tuned by changing the composition of solvent. In addition, we found the as-prepared single-crystal hyperbranched Rh nanoplates possessed great structure stability, and exhibited better catalytic performance towards both ethanol electrooxidation and hydrogenation of styrene than the commercial Rh black, which can be attributed to the large surface area and high-dentisty of edge/corner sites.摘要贵金属纳米晶的催化性质与其结构密切相关. 比表面积越大、配位不饱和的边角原子密度越高, 贵金属纳米晶在催化反应过程中表现出的性能往往越优异. 相比于常见的具有完整几何形貌的贵金属纳米晶, 具有多重分级结构特征的超支化贵金属纳米晶拥有更大的比表面积以及更丰富的配位不饱和的活性位点, 因此被认为是一种潜在的性能优异的催化剂. 但这种具有多重分级结构特征的超支化贵金属纳米晶无论是在生长机理研究还是可控制备上都还存在巨大的挑战. 本文通过简单的湿化学法成功制备出一种具有多重分级结构特征的超支化Rh纳米薄片. 该产物由三角形纳米片在扩散限制条件下分级生长形成, 整体呈现三次对称性的单晶特征. 研究表明, 该纳米结构不仅具有出色的结构稳定性, 而且其生长级数可通过反应溶剂比例的简单调节进行调控, 从而实现Rh纳米薄片比表面积和位于边/角活性位点的原子比例的调控. 由于拥有更大的比表面积以及更为丰富的配位不饱和的活性位点, 这种具有多重分级结构的超支化Rh纳米薄片在乙醇电催化氧化和苯乙烯催化加氢催化反应中展现出了比目前主流商业催化剂Rh黑更为优异的催化活性.

Ligand-Assisted, One-Pot Synthesis of Rh-on-Cu Nanoscale Sea Urchins with High-Density Interfaces for Boosting CO Oxidation

Predictable synthesis of bimetallic nanocrystals with spatially controlled metal distributions offers a versatile route to the development of highly efficient nanocatalysts. Here we report a one-pot synthesis of super branched Rh-on-Cu nanoscale sea urchins (Rh-Cu NSUrs) with a high density of Cu-Rh interfaces by manipulating the ligand coordination chemistry. Structural analysis and UV-vis spectra reveal that ascorbic acid can serve as a Rh-selective coordination ligand in the nonaqueous synthesis to reverse the reduction potentials of Rh3+ and Cu2+ cations. The sequential reduction of Cu2+ and then Rh3+ cations, as well as the island epitaxial growth of Rh atoms on Cu cores, leads to the formation of Rh-on-Cu nanostructures mimicking sea urchin. The size of the Cu cores and the density of Rh branches can both be facilely regulated by tuning the mole ratio of Cu to Rh. The Cu-Rh NSUrs show enhanced activity and stability in catalyzing CO oxidation, as the intrinsic Cu-Rh interfaces can act as catalytic hot spots through a bifunctional mechanism. The Cu-Rh two-component system can separate the adsorption and activation of CO and O2 on the Rh and Cu surfaces, respectively, accelerating the generation of CO2 at the interfaces.

Cyclic Penta-Twinned Rhodium Nanobranches as Superior Catalysts for Ethanol Electro-oxidation

Developing active and durable electro-catalysts toward ethanol oxidation reaction (EOR) with high selectivity toward the C-C bond cleavage is an important issue for the commercialization of direct ethanol fuel cell. Unfortunately, current ethanol oxidation electro-catalysts (e.g., Pt, Pd) still suffer from poor selectivity for direct oxidation of ethanol to CO2, and rapid activity degradation. Here we report a facile route to the synthesis of a new kind of cyclic penta-twinned (CPT) Rh nanostructures that are self-supported nanobranches (NBs) built with 1-dimension CPT nanorods as subunits. Structurally, the as-prepared Rh NBs possess high percentage of open {100} facets with significant CPT-induced lattice strains. With these unique structural characteristics, the as-prepared CPT Rh NBs exhibit outstanding electrocatalytic performance toward EOR in alkaline solution. Most strikingly, the selectivity of complete conversion ethanol to CO2 on the CPT Rh NBs is measured to be as high as 14.5 ± 1.1% at -0.15 V, far exceeding that for single-crystal tetrahedral nanocrystals, icosahedral nanocrystals, and commercial Rh black, as well as majority of reported values for Pt or Pd-based electro-catalysts. By combining with density functional theory calculation, the effects of different structural features of Rh on EOR are definitively elucidated. It was found that the large amount of open Rh (100) facets dominantly contribute to the outstanding activity and exceptionally high selectivity, while the additional tensile strain on (100) planes can further boost the catalytic activity by enhancing the adsorption strength and lowering the reaction barrier of dehydrogenation process of ethanol. As a proof of concept, the present work shows that rationally optimizing surface and electronic structure of electro-catalysts by simultaneously engineering their surface and bulk structures is a promising strategy to promote the performance of electro-catalysts.