Synthesis of BiRh Nanoplates with Superior Catalytic Performance in the Semihydrogenation of Acetylene

Highly uniform and well-crystallized nanoparticles of the intermetallic compound BiRh were obtained by low-temperature synthesis at 240 °C using the microwave-assisted polyol process. In this time- and energy-efficient reaction the polyol acts as solvent, reducing agent, and surfactant, while the microwave radiation leads to fast and homogeneous nucleation and crystal growth. Electron microscopy studies confirmed the presence of pseudohexagonal nanoplates with a primary particle diameter of 60 nm and high crystallinity. As indicated by high-resolution transmission electron microscopy, the plate normal is generally not parallel to [001] but coincides with [421]. Powder X-ray diffraction and energy dispersive X-ray spectroscopy revealed the single-phase nature and the equimolar composition. The specific surface area (0.54 m² g^–1) and the particle size distribution were measured by fractional sedimentation. According to the analysis of the chemical bonding by means of quantum chemical calculations, 0.62 electrons are transferred from Bi to Rh. Covalent homoatomic Rh–Rh as well as heteroatomic three-center Rh–Bi–Rh bonds define a three-dimensional bonding network. Unsupported BiRh nanoparticles exhibit an extraordinary high selectivity of 88 to 93% in the semihydrogenation of acetylene, which makes them an interesting model compound as well as a promising candidate for the application as an industrial catalyst

Important Impact of the Slurry Mixing Speed on Water-Processed Li₄Ti₅O₁₂ Lithium-Ion Anodes in the Presence of H₃PO₄ as the Processing Additive

The aqueous processing of lithium transition metal oxides into battery electrodes is attracting a lot of attention as it would allow for avoiding the use of harmful N-methyl-2-pyrrolidone (NMP) from the cell fabrication process and, thus, render it more sustainable. The addition of slurry additives, for instance phosphoric acid (PA), has been proven to be highly effective for overcoming the corresponding challenges such as aluminum current collector corrosion and stabilization of the active material particle. Herein, a comprehensive investigation of the effect of the ball-milling speed on the effectiveness of PA as a slurry additive is reported using Li4Ti5O12 (LTO) as an exemplary lithium transition metal oxide. Interestingly, at elevated ball-milling speeds, rod-shaped lithium phosphate particles are formed, which remain absent at lower ball-milling speeds. A detailed surface characterization by means of SEM, EDX, HRTEM, STEM-EDX, XPS, and EIS revealed that in the latter case, a thin protective phosphate layer is formed on the LTO particles, leading to an improved electrochemical performance. As a result, the corresponding lithium-ion cells comprising LTO anodes and LiNi0.5Mn0.3Co0.2O2 (NMC532) cathodes reveal greater long-term cycling stability and higher capacity retention after more than 800 cycles. This superior performance originates from the less resistive electrode–electrolyte interphase evolving upon cycling, owing to the interface-stabilizing effect of the lithium phosphate coating formed during electrode preparation. The results highlight the importance of commonly neglectedfrequently not even reportedelectrode preparation parameters

Cobalt Disulfide Nanoparticles Embedded in Porous Carbonaceous Micro-Polyhedrons Interlinked by Carbon Nanotubes for Superior Lithium and Sodium Storage

Transition metal sulfides are appealing electrode materials for lithium and sodium batteries owing to their high theoretical capacity. However, they are commonly characterized by rather poor cycling stability and low rate capability. Herein, we investigate CoS₂, serving as a model compound. We synthesized a porous CoS₂/C micro-polyhedron composite entangled in a carbon-nanotube-based network (CoS₂-C/CNT), starting from zeolitic imidazolate frameworks-67 as a single precursor. Following an efficient two-step synthesis strategy, the obtained CoS₂ nanoparticles are uniformly embedded in porous carbonaceous micro-polyhedrons, interwoven with CNTs to ensure high electronic conductivity. The CoS₂-C/CNT nanocomposite provides excellent bifunctional energy storage performance, delivering 1030 mAh g^–1 after 120 cycles and 403 mAh g^–1 after 200 cycles (at 100 mA g^–1) as electrode for lithium-ion (LIBs) and sodium-ion batteries (SIBs), respectively. In addition to these high capacities, the electrodes show outstanding rate capability and excellent long-term cycling stability with a capacity retention of 80% after 500 cycles for LIBs and 90% after 200 cycles for SIBs. <i>In situ</i> X-ray diffraction reveals a significant contribution of the partially graphitized carbon to the lithium and at least in part also for the sodium storage and the report of a two-step conversion reaction mechanism of CoS₂, eventually forming metallic Co and Li₂S/Na₂S. Particularly the lithium storage capability at elevated (dis-)­charge rates, however, appears to be substantially pseudocapacitive, thus benefiting from the highly porous nature of the nanocomposite

Ultrafast Ionic Liquid-Assisted Microwave Synthesis of SnO Microflowers and Their Superior Sodium-Ion Storage Performance

Tin oxide (SnO) is considered one of the most promising metal oxides for utilization as anode material in sodium ion batteries (SIBs), because of its ease of synthesis, high specific gravimetric capacity, and satisfactory cycling performance. However, to aim at practical applications, the Coulombic efficiency during cycling needs to be further improved, which requires a deeper knowledge of its working mechanism. Here, a microflower-shaped SnO material is synthesized by means of an ultrafast ionic liquid-assisted microwave method. The as-prepared SnO anode active material exhibits excellent cycling performance, good Coulombic efficiency as well as a large capacity delivered at low potential, which is fundamental to maximize the energy output of SIBs. These overall merits were never reported before for pure SnO anodes (i.e., not in a composite with, for example, graphene). Additionally, by combining ex situ XRD and XPS, it is clearly demonstrated for the first time that the Sn–Na alloy, which is formed during the initial sodium sodiation, desodiates in two successive but fully separated steps. Totally different from the previous report, the pristine SnO phase is not regenerated upon desodiation up to 3 V vs Na/Na⁺. The newly disclosed reaction route provides an alternative view of the complex reaction mechanism of these families of metal oxides for sodium ion batteries

Self-Supporting Hierarchical Porous PtAg Alloy Nanotubular Aerogels as Highly Active and Durable Electrocatalysts

Developing electrocatalysts with low cost, high activity, and good durability is urgently demanded for the wide commercialization of fuel cells. By taking advantage of nanostructure engineering, we fabricated PtAg nanotubular aerogels (NTAGs) with high electrocatalytic activity and good durability via a simple galvanic replacement reaction between the in situ spontaneously gelated Ag hydrogel and the Pt precursor. The PtAg NTAGs have hierarchical porous network features with primary networks and pores from the interconnected nanotubes of the aerogel and secondary networks and pores from the interconnected thin nanowires on the nanotube surface, and they show very high porosities and large specific surface areas. Due to the unique structure, the PtAg NTAGs exhibit greatly enhanced electrocatalytic activity toward formic acid oxidation, reaching 19 times higher metal-based mass current density as compared to the commercial Pt black. Furthermore, the PtAg NTAGs show outstanding structural stability and electrochemical durability during the electrocatalysis. Noble metal-based NTAGs are promising candidates for applications in electrocatalysis not only for fuel cells, but also for other energy-related systems