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The control of morphology in the synthesis of Rh nanocrystals can be used to precisely tailor the electronic surface structure; this in turn directly influences their performance in catalysis applications. Many works have brought attention to the development of Rh nanostructures with low-index surfaces, but limited effort has been devoted to the study of high-index and surface defect-enriched nanocrystals as they are not favored by thermodynamics because of the involvement of high-energy surfaces and increased surface-to-volume ratios. In this work, we demonstrate an aqueous synthesis of concave Rh nanotetrahedra (CTDs) serving as efficient catalysts for energy conversion reactions. CTDs are surface defect-rich structures that form through a slow growth rate and follow the four-step model of metallic nanoparticle growth. Via the tuning of the surfactant concentration, the morphology of Rh CTDs evolved into highly excavated nanotetrahedra (HETDs) and twinned nanoparticles (TWs). Unlike the CTD surfaces with abundant adatoms and vacancies, HETDs and TWs have more regular surfaces with layered terraces. Each nanocrystal type was evaluated for methanol electrooxidation and hydrogen evolution from hydrolysis of ammonia borane, and the CTDs significantly showed the best catalytic performance because of defect enrichment, which benefits the surface reactivity of adsorbates. In addition, both CTDs and HETDs have strong absorption near the visible light region (382 and 396 nm), for which they show plasmon-enhanced performance in photocatalytic hydrogen evolution under visible light illumination. CTDs are more photoactive than HETDs, likely because of more pronounced localized surface plasmon resonance hot spots. This facile aqueous synthesis of large-surface-area, defect-rich Rh nanotetrahedra is exciting for the fields of nanosynthesis and catalysis.

Copper is an earth-abundant element that can be used to reduce the high cost and unsatisfactory durability of pure Pt catalysts by the formation of bimetallic Pt–M nanocrystals. Among CuPt nanostructures, nanocages attract great interest for catalysis as they allow passage of reactant species to their porous interiors, which provide a high fraction of surface sites. They may also enhance reactivity through an increase in collision frequency by enclosing reagents within nanoscale cavities and by lattice strain effects of the alloy. Recent reports apply solvothermal chemistry to obtain CuPt nanocages in one step. However, there is still a lack of understanding in the formation mechanism and its impact on catalytic activity for such hollow CuPt nanostructures. In this work, we adopt a two-step method in which we synthesize rhombic dodecahedral (RD) Cu–CuPt core–shell nanocrystals by the deposition of Pt on Cu nanocubes to form CuPt shells less than 2 nm in thickness, followed by removing Cu cores to obtain ultrathin octahedral (OCT) nanocages for catalytic applications. By adjustment to shorter and longer reaction time frames, the core–shell nanocrystals were also made into quasi-RD (QRD) and spiny-RD (SRD) morphologies, which lead to porous (POCT) and spiny (SOCT) OCT nanocages, respectively, upon etching. These three types of CuPt nanocages (POCT, OCT, and SOCT) were then examined in the electrocatalytic oxygen reduction reaction (ORR) and the hydrogen evolution reaction (HER) by the hydrolysis of NH3BH3 to study their performance. As a result, the SOCT CuPt nanocages exhibit the highest Pt mass activity (0.3 A/mgPt) in the ORR, a 3-fold improvement over commercial Pt/C. They also show the lowest activation energy (24.3 kJ/mol) in the HER that is better than the commercial catalyst by a factor of 4. HER photocatalysis results show that the POCT and OCT nanocages have localized surface plasmon resonance (LSPR)-enhancement while the SOCT nanocages do not, which is attributed to inhomogeneity in Cu–Pt distributions at shorter reaction times.

This study investigated the selective leaching, chemical compositions, and electrochemical properties of CuXAl4Ni (X = 12.5, 13.0, and 13.5) shape memory alloys (SMAs). The selective leaching results showed that the CuXAl4Ni SMAs released approximately 200 ppb of Cu ions, 200 ppb of Al ions, and 600 ppb of Ni ions after immersion in Ringer's solution for 90 days. The low concentrations of Cu and Al ions stem from the oxidation of Cu and Al atoms near the surface of the CuXAl4Ni SMAs to form Cu 2 O and Al 2 O 3 films. The selective leaching properties of the CuXAl4Ni SMAs were inferior to that of the TiNi SMA, which possessed a highly passive TiO 2 film on the surface, but were much better than those of the TiNiCu and TiNiFe SMAs, whose TiO 2 films were deteriorated by the formation of NiO, Cu 2 O, and Fe 2 O 3 oxides. CuXAl4Ni SMAs are potential candidates to serve as biomaterials, owing to their acceptable surface and selective leaching properties, high martensitic transformation temperatures, low cost, good machinability, and excellent electric and thermal conductivities.

All enterprises, regardless of industry, are exposed to fraud risk. In the retail industry, the perpetrators of fraud manipulate the sales price of products instead of the quantity sold to avoid inventory discrepancies. Fraud examiners attempt to identify anomalous transactions using data analysis. This study analyzes the causes of fraudulent behavior, conceptualized based on the aspect of rational choice, and proposes an anomalous transaction detection model using variables identified as indicating fraud. A two-phase experiment analyzing a real-world data set from a retailer in Taiwan was designed to evaluate the performance of fraud variables. The findings demonstrate that these variables could slightly improve the results of the analysis and demonstrate that machine learning is applicable to fraud detection. In addition, this study contributes to rational choice theory to validate the applicability in fraud detection. Fraud examiners in the retail industry could reduce fraud losses by adopting the proposed approach, implemented using Weka software, to identify anomalies.