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Abstract Pt-Ni octahedral nanocrystals with exposed {111} facets are highly active oxygen reduction reaction (ORR) catalysts, yet achieving precise control over their particle size remains challenging. In this work, three Pt-Ni octahedral nanocatalysts with tunable sizes were synthesized using a one-pot colloidal method by adjusting the amount of NiCl₂·6H₂O precursor. Interestingly, both decreasing and increasing the Ni precursor amount relative to the standard value of 0.05 mmol resulted in smaller octahedra. At low precursor concentrations, limited Ni precursor supply restricts crystal growth, whereas at high concentrations, accelerated nucleation and Cl⁻-induced stabilization of the (111) facets inhibit further growth. Electrochemical measurements show that the catalyst exhibiting the smallest particle size delivers the highest ORR mass activity (1.98 A/mg_Pt), likely due to its large specific surface area. This work highlights the crucial role of precursor concentration in tailoring nanoparticle dimensions and enhancing the electrochemical activity of Pt-Ni catalysts for the ORR. Graphical abstract 

Abstract NiO_xnanocatalysts with two distinct morphologies, nano-spindles and nano-plates, were synthesized and evaluated for oxygen evolution reaction (OER) performance. Spindle-like NiO_xwas preparedviaa hydrothermal reaction of nickel nitrate and urea with cetyltrimethylammonium bromide as a surfactant at 120 °C for 24 h, forming Ni(OH)₂-based intermediates that were subsequently calcined at 300 °C for 3 h. In contrast, platelet-like Ni(OH)₂nanocrystals were obtained using nickel(II) acetate and KOH at 180 °C for 24 h, followed by calcination at 400 °C or 500 °C for 4 h to yield NiO_xnano-plates. The NiO_xnano-spindles exhibited an OER overpotential of 395 mV at 10 mA/cm², whereas the NiO_xnano-plates annealed at 400 °C and 500 °C showed overpotentials of 565 mV and 474 mV at 10 mA/cm², respectively. Structural characterization and X-ray photoemission spectroscopy indicate these differences arise from morphology-dependent surface structures that govern catalytic activity. Graphical abstract 

Hydrogen peroxide (H2O2) detection in both liquid and gas phases has garnered significant attention due to its importance in various biological and industrial processes. Monitoring H2O2 levels is essential for understanding its effects on biology, industry, and the environment. Significant advancements in the physical dimensions and performance of biosensors for H2O2 detection have been made, mainly through the integration of fluorescence techniques and nanotechnology. These advancements have resulted in more sensitive, selective, and versatile detection systems, enhancing our ability to monitor H2O2 in both liquid and gas phases effectively. However, limited comprehensive reviews exist on the detection of vaporized H2O2, which is used in disinfection and the production of explosive agents, making its detection vital. This review provides an overview of recent progress in nanostructured fluorescence sensors for H2O2 detection, covering both liquid and gas phases. It examines various fluorescence-based detection methods and focuses on emerging nanomaterials for sensor development. Additionally, it discusses the dual applications of H2O2 detection in biomedical and non-biomedical fields, offering insights into the current state of the field and future directions. Finally, the challenges and perspectives for developing novel nanostructured fluorescence sensors are presented to guide future research in this rapidly evolving area. 

Tin(IV) oxide nanocrystals (SnO2 NCs) have significant potential in various applications, with their performance closely related to their band gap. The band gap is influenced by the size and shape of the NCs, which can be precisely controlled by adjusting reaction conditions. In this study, we present deliberately designed synthesis protocols to produce high-quality SnO2 NCs with tunable band gaps using different methods. Key factors affecting the synthesis include control of the oxidizing agent, reaction temperature, solvent selection, and reaction time optimization. The resulting NCs were characterized by using TEM, XRD, XPS, and optical spectroscopy. Notably, SnO2 NCs synthesized by controlling the oxidizing agent (air injection) in a hot organic solution were smaller in size and exhibited abundant oxygen vacancies. In contrast, extending the reaction time or using ethanol as a solvent in hydrothermal systems facilitated larger spherical or rod-like SnO2 NCs with fewer oxygen vacancies. Further analysis of the band gap and valence band maximum energy revealed that the abundant vacancies in SnO2 NCs synthesized with the air-controlled hot organic solution method resulted in a narrower band gap and an upshifted valence band. These synthetic strategies illustrate the potential for deliberately designing SnO2 NCs with optimized electronic structures for various applications. 

Abstract The electrochemical oxygen reduction reaction (ORR) is critical for fuel cell application, and modifying surface structures of electrocatalysts has proven effective in improving their catalytic performances. In this study, we investigated surface‐engineered Pt−Ni nano‐octahedra subjected to annealing in various atmospheres. All octahedral nanocrystals retained their Pt−Ni {111} facets at an elevated temperature following the annealing treatments. Air annealing led to the formation of nickel‐rich shells on the Pt−Ni surface. In contrast, hydrogen (H₂) as a reducing gas facilitated the reduction of surface Ni species, incorporating them into the Pt−Ni bulk alloy, which resulted in superior mass activity and specific activity for ORR‐approximately 2.4 and 2.3 times as high as those from the unmodified counterpart, respectively. After 20,000 potential cycles, the H₂/Ar‐annealed Pt−Ni nano‐octahedra maintained a mass activity of 3.92 A/, surpassing the initial mass activity of the unannealed counterparts (2.95 A/). These findings demonstrate a viable approach for tailoring catalyst surfaces to enhance performance in various energy storage and conversion applications. 

We have previously shown that Pt–Ni alloy nano-octahedra with {111} facets exhibit outstanding electrochemical performance in the oxygen reduction reaction (ORR) in acidic media when their surfaces are finely tailored at the atomic level. In this investigation, we further refine the surface structure of Pt2.2Ni octahedral nanocatalysts to improve ORR performance in a 0.1 M KOH solution using diverse surface manipulation techniques. Through systematic analysis using electrochemical CO stripping, cyclic voltammetry, and X-ray photoelectron spectroscopy, we examined the surfaces of Pt2.2Ni octahedral nanocatalysts pretreated with various methods, including etching in acetic acid or perchloric acid, and subsequent electrochemical activation in an alkaline solution or an acidic solution. Among these treatments, those involving acidic media, particularly electrochemical cycling in acidic electrolytes, demonstrated significantly enhanced ORR activity in 0.1 M KOH. The latter exhibited a mass activity of 2.95 A/mgpt and a specific activity of 8.71 mA/cm2 at 0.90 V, surpassing state-of-the-art Pt/C by 12-fold and 34-fold, respectively. Furthermore, this identified nanocatalyst displayed robust stability, with negligible activity decay observed after 10,000 cycles. This study suggests that the improved ORR activity can be attributed to the Pt-rich surfaces with well-preserved {111} lattices on the surface-modified Pt–Ni nano-octahedra. 

Despite the critical role of sintering phenomena in constraining the long-term durability of nano-sized particles, a clear understanding of nanoparticle sintering has remained elusive due to the challenges in atomically tracking the neck initiation and discerning different mechanisms. Through the integration of in-situ transmission electron microscopy and atomistic modeling, this study uncovers the atomic dynamics governing the neck initiation of Pt-Fe nanoparticles via a surface self-diffusion process, allowing for coalescence without significant particle movement. Real-time imaging reveals that thermally activated surface morphology changes in individual nanoparticles induce significant surface self-diffusion. The kinetic entrapment of self-diffusing atoms in the gaps between closely spaced nanoparticles leads to the nucleation and growth of atomic layers for neck formation. This surface self-diffusion-driven sintering process is activated at a relatively lower temperature compared to the classic Ostwald ripening and particle migration and coalescence processes. The fundamental insights have practical implications for manipulating the morphology, size distribution, and stability of nanostructures by leveraging surface self-diffusion processes. 

Abstract We present a one‐pot colloidal synthesis method for producing monodisperse multi‐metal (Co, Mn, and Fe) spinel nanocrystals (NCs), including nanocubes, nano‐octahedra, and concave nanocubes. This study explores the mechanism of morphology control, showcasing the pivotal roles of metal precursors and capping ligands in determining the exposed crystal planes on the NC surface. The cubic spinel NCs, terminated with exclusive {100}‐facets, demonstrate superior electrocatalytic activity for the oxygen reduction reaction (ORR) in alkaline media compared to their octahedral and concave cubic counterparts. Specifically, at 0.85 V, (CoMn)Fe₂O₄spinel oxide nanocubes achieve a high mass activity of 23.9 A/g and exhibit excellent stability, highlighting the promising ORR performance associated with {100}‐facets of multi‐metal spinel oxides over other low‐index and high‐index facets. Motivated by exploring the correlation between ORR performance and surface atom arrangement (active sites), surface element composition, as well as other factors, this study introduces a prospective approach for shape‐controlled synthesis of advanced spinel oxide NCs. It underscores the significance of catalyst shape control and suggests potential applications as nonprecious metal ORR electrocatalysts.