Coupling PtNi Ultrathin Nanowires with MXenes for Boosting Electrocatalytic Hydrogen Evolution in Both Acidic and Alkaline Solutions.

Developing an efficient electrocatalyst for the hydrogen evolution reaction (HER) working in both acidic and alkaline solutions is highly desirable, but still remains challenging. Here, Ptx Ni ultrathin nanowires (NWs) with tunable compositions (x = 1.42, 3.21, 5.67) are in situ grown on MXenes (Ti3 C2 nanosheets), serving as electrocatalysts toward HER. Such Ptx Ni@Ti3 C2 electrocatalysts exhibit excellent HER performance in both acidic and alkaline solutions, with the Pt3.21 Ni@Ti3 C2 being the best one. Specifically, Pt3.21 Ni@Ti3 C2 achieves record-breaking performance in terms of lowest overpotential (18.55 mV) and smallest Tafel slope (13.37 mV dec-1 ) for HER in acidic media to date. Theory calculations and X-ray photoelectron spectroscopy analyses demonstrate that the coupling of MXenes with the NWs not only approaches the Gibbs free energy for hydrogen adsorption close to zero through the electron transfer between them in acidic media, but also provides additional active sites for water dissociation in alkaline solution, both of them being beneficial to the HER performance.

Tuning Surface Structure and Strain in Pd-Pt Core-Shell Nanocrystals for Enhanced Electrocatalytic Oxygen Reduction.

Icosahedral, octahedral, and cubic Pd@Pt core-shell nanocrystals with two atomic Pt layers are epitaxially generated under thermodynamic control. Such icosahedra exhibit remarkably enhanced catalytic properties for oxygen reduction reaction compared to the octahedra and cubes as well as commercial Pt/C, which can be attributed to ligand and geometry effects, especially twin-induced strain effect that is revealed by geometrical phase analysis.

Epitaxial Growth of Multimetallic Pd@PtM (M = Ni, Rh, Ru) Core-Shell Nanoplates Realized by in Situ-Produced CO from Interfacial Catalytic Reactions.

Pt-based multimetallic core-shell nanoplates have received great attention as advanced catalysts, but the synthesis is still challenging. Here we report the synthesis of multimetallic Pd@PtM (M = Ni, Rh, Ru) nanoplates including Pd@Pt nanoplates, in which Pt or Pt alloy shells with controlled thickness epitaxially grow on plate-like Pd seeds. The key to achieve high-quality Pt-based multimetallic nanoplates is in situ generation of CO through interfacial catalytic reactions associated with Pd nanoplates and benzyl alcohol. In addition, the accurate control in a trace amount of CO is also of great importance for conformal growth of multimetallic core-shell nanoplates. The Pd@PtNi nanoplates exhibit substantially improved activity and stability for methanol oxidation reaction (MOR) compared to the Pd@Pt nanoplates and commercial Pt catalysts due to the advantages arising from plate-like, core-shell, and alloy structures.

Can enterprise green transformation inhibit accrual earnings management? Evidence from China.

This study theoretically and empirically analyzes the impact and mechanism of corporate green transformation on accrual earnings management using a sample of China's A-share listed companies from 2015 to 2021. The results indicate that the green transformation of enterprises helps restrain accrual-based earnings management, especially accrual-based earnings management, which increases profits, and that the inhibition effect of enterprise green transformation on earnings management is more significant in high-tech and growth-stage enterprises. The mechanism test shows that corporate green transformation can inhibit accrual-based earnings management by increasing analyst follow-up and easing financing constraints. Using China's environmental tax law, promulgated in 2018, as an exogenous shock to construct the PSM-DID, the conclusion still holds after alleviating endogeneity. Further research has found that green transformations can also help inhibit real earnings management. This study provides new empirical evidence for a comprehensive understanding and evaluation of the governance role of corporate green transformation and provides a reference value for further comprehensively promoting the green transformation of Chinese enterprises and improving the quality of accounting information.

Enhanced electrocatalytic reduction of CO2 to formate via doping Ce in Bi2O3 nanosheets.

Formate is considered as the most economically viable product of the prevalent electrochemical CO2 reduction (ECR) products. However, most of the catalysts for ECR to formate in aqueous solution often suffer from low activity and limited selectivity. Herein, we report a novel Ce-doped Bi2O3 nanosheet (NS) electrocatalyst by a facile solvothermal method for highly efficient ECR to formate. The 5.04% Ce-doped Bi2O3 NSs exhibited a current density of 37.4 mA cm-2 for the production of formate with a high formate faradaic efficiency (FE) of 95.8% at -1.12 V. The formate FE was stably maintained at about 90% in a wide potential range from -0.82 to -1.22 V. More importantly, density functional theory (DFT) calculations revealed that Ce doping can lead to a significant synergistic effect, which promotes the formation and the adsorption of the OCHO* intermediate for ECR, while significantly inhibiting the hydrogen evolution reaction via depressing the formation of *H, thus helping achieve high current density and FE. This work provides an effective and promising strategy to develop efficient electrocatalysts with heteroatom doping and new insights for boosting ECR into formate.

Strain effect in Pd@PdAg twinned nanocrystals towards ethanol oxidation electrocatalysis.

The strain effect is a critical knob to tune the catalytic performance and has received unprecedented research interest recently. However, it is difficult to distinguish the strain effect from the synergistic effect, especially in alloyed catalysts. Here we have synthesized Pd@PdAg icosahedra and {111} truncated bi-pyramids with only different surface strains between them as electrocatalysts for the ethanol oxidation reaction (EOR). Due to the same exposed facets and compositions of the two electrocatalysts, their EOR performances are mainly determined by the surface strains of PdAg alloys. These two electrocatalysts provide a perfect model to investigate the role of the strain effect in tuning the EOR performance. It is indicated that Pd@PdAg {111} truncated bi-pyramids with a surface strain of 0.3% show better catalytic activity and durability than Pd@PdAg icosahedra with a surface strain of 2.1% including commercial Pd/C. Density functional theory (DFT) calculations reveal that the lowered d-band center of 0.3% strained PdAg alloys relative to 2.1% strained ones reduced the adsorption energy of the acetate-evolution key intermediate *CH3CO, thereby promoting the enhancement in the catalytic performance of Pd@PdAg nanocrystals for the EOR. Electrochemical analysis further verifies this demonstration on the key role of the strain effect in PdAg alloys for tuning catalytic performance.

Facile Synthesis of Pd@PtM (M = Rh, Ni, Pd, Cu) Multimetallic Nanorings as Efficient Catalysts for Ethanol Oxidation Reaction.

Pt-based multimetallic nanorings with a hollow structure are attractive as advanced catalysts due to their fantastic structure feature. However, the general method for the synthesis of such unique nanostructures is still lack. Here we report the synthesis of Pd@PtM (M = Rh, Ni, Pd, Cu) multimetallic nanorings by selective epitaxial growth of Pt alloyed shells on the periphery of Pd nanoplates in combination with oxidative etching of partial Pd in the interior. In situ generation of CO and benzoic acid arising from interfacial catalytic reactions between Pd nanoplates and benzaldehyde are critical to achieve high-quality Pt-based multimetallic nanorings. Specifically, the in-situ generated CO promotes the formation of Pt alloyed shells and their epitaxial growth on Pd nanoplates. In addition, the as-formed benzoic acid and residual oxygen are responsible for selective oxidative etching of partial Pd in the interior. When evaluated as electrocatalysts, the Pd@PtRh nanorings exhibit remarkably enhanced activity and stability for ethanol oxidation reaction (EOR) compared to the Pd@PtRh nanoplates and commercial Pt/C due to their hollow nanostructures.

Tuning Surface Structure of Pd3Pb/Pt n Pb Nanocrystals for Boosting the Methanol Oxidation Reaction.

Developing an efficient Pt-based electrocatalyst with well-defined structures for the methanol oxidation reaction (MOR) is critical, however, still remains a challenge. Here, a one-pot approach is reported for the synthesis of Pd3Pb/Pt n Pb nanocubes with tunable Pt composition varying from 3.50 to 2.37 and 2.07, serving as electrocatalysts toward MOR. Their MOR activities increase in a sequence of Pd3Pb/Pt3.50Pb << Pd3Pb/Pt2.07Pb < Pd3Pb/Pt2.37Pb, which are substantially higher than that of commercial Pt/C. Specifically, Pd3Pb/Pt2.37Pb electrocatalysts achieve the highest specific (13.68 mA cm-2) and mass (8.40 A mgPt -1) activities, which are ≈8.8 and 6.8 times higher than those of commercial Pt/C, respectively. Structure characterizations show that Pd3Pb/Pt2.37Pb and Pd3Pb/Pt2.07Pb are dominated by hexagonal-structured PtPb intermetallic phase on the surface, while the surface of Pd3Pb/Pt3.50Pb is mainly composed of face-centered cubic (fcc)-structured Pt x Pb phase. As such, hexagonal-structured PtPb phase is much more active than the fcc-structured Pt x Pb one toward MOR. This demonstration is supported by density functional theory calculations, where the hexagonal-structured PtPb phase shows the lowest adsorption energy of CO. The decrease in CO adsorption energy and structural stability also endows Pd3Pb/Pt n Pb electrocatalysts with superior durability relative to commercial Pt/C.

Ultra-small Rh nanoparticles supported on WO3-x nanowires as efficient catalysts for visible-light-enhanced hydrogen evolution from ammonia borane.

Hydrolysis of ammonia borane (AB) is a safe and convenient means of H2 production when efficient catalysts are used. Here we report a facile one-pot solvothermal method to synthesize Rh/WO3-x hybrid nanowires. Ultra-small Rh nanoparticles with an average size of ∼1.7 nm were tightly anchored on WO3-x nanowires. Rh/WO3-x catalysts exhibited substantially enhanced activity for hydrolytic dehydrogenation of AB under both dark and visible light irradiation conditions relative to mixed Rh nanoparticles and WO3-x nanowires (Rh + WO3-x ), and Rh/C and WO3-x nanowires. X-ray photoelectron spectroscopy (XPS) analysis indicated that the synergistic effect between Rh nanoparticles and WO3-x nanowires was responsible for such an enhancement in activity. Specifically, Rh/WO3-x achieved the highest turnover frequency (TOF) with a value of 805.0 molH2 molRh -1 min-1 at room temperature under visible light irradiation. The H2 release rate as a function of reaction time exhibited a volcano plot under visible light irradiation, indicating that a self-activation process occurred in the hydrolytic dehydrogenation of AB due to additional oxygen vacancies arising from in situ reduction of WO3-x nanowires by AB, and thus an enhanced localized surface plasmon resonance (LSPR). Such a self-activation process was responsible for the enhanced catalytic activity under visible light irradiation relative to that under dark conditions, which was supported by the lower activation energy (45.2 vs. 50.5 kJ mol-1). In addition, Rh/WO3-x catalysts were relatively stable with only little loss in activity after five cycles due to the tight attachment between two components.

Enhanced oxygen reduction activity of Pt shells on PdCu truncated octahedra with different compositions.

Pd@Pt core-shell nanocrystals with ultrathin Pt layers have received great attention as active and low Pt loading catalysts for oxygen reduction reaction (ORR). However, the reduction of Pd loading without compromising the catalytic performance is also highly desired since Pd is an expensive and scarce noble-metal. Here we report the epitaxial growth of ultrathin Pt shells on Pd x Cu truncated octahedra by a seed-mediated approach. The Pd/Cu atomic ratio (x) of the truncated octahedral seeds was tuned from 2, 1 to 0.5 by varying the feeding molar ratio of Pd to Cu precursors. When used as catalysts for ORR, these three Pd x Cu@Pt core-shell truncated octahedra exhibited substantially enhanced catalytic activities compared to commercial Pt/C. Specifically, Pd2Cu@Pt catalysts achieved the highest area-specific activity (0.46 mA cm-2) and mass activity (0.59 mA µgPt -1) at 0.9 V, which were 2.7 and 4.5 times higher than those of the commercial Pt/C. In addition, these Pd x Cu@Pt core-shell catalysts showed a similar durability with the commercial Pt/C after 10 000 cycles due to the dissolution of active Cu and Pd in the cores.

Nanoscale kinetics of asymmetrical corrosion in core-shell nanoparticles.

Designing new materials and structure to sustain the corrosion during operation requires better understanding on the corrosion dynamics. Observation on how the corrosion proceeds in atomic scale is thus critical. Here, using a liquid cell, we studied the real-time corrosion process of palladium@platinum (Pd@Pt) core-shell nanocubes via transmission electron microscopy (TEM). The results revealed that multiple etching pathways operatively contribute to the morphology evolution during corrosion, including galvanic etching on non-defected sites with slow kinetics and halogen-induced etching at defected sites at faster rates. Corners are the preferential corrosion sites; both etching pathways are mutually restricted during corrosion. Those insights on the interaction of nanostructures with reactive liquid environments can help better engineer the surface structure to improve the stability of electrocatalysts as well as design a new porous structure that may provide more active sites for catalysis.

Tailoring the Edge Sites of 2D Pd Nanostructures with Different Fractal Dimensions for Enhanced Electrocatalytic Performance.

The important role of edge sites in atomically thin 2D materials serving as catalysts is already of concerned in plenty of material systems and catalytic reactions, whereas comprehensive study of the edge sites in 2D noble-metal nanocatalysts is still lacking. Herein, for the first time, a controllable etching approach to tailor the fractal dimensions and edge sites of Pd nanosheets is developed and the edge sites in these 2D nanostructures from both structural and chemical aspects are investigated. The as-tailored 2D Pd nanostructures with extra edge sites exhibit substantially enhanced electrocatalytic performance for the formic acid oxidation reaction (FAOR). Moreover, careful analysis of the results from electrocatalytic measurements reveals that the specific activities for the edge sites in the 2D nanostructures far exceed the activities for the low-index planes of Pd and even dominate the overall activity exhibited by the 2D noble-metal catalysts.

Multimetallic AuPd@Pd@Pt core-interlayer-shell icosahedral electrocatalysts for highly efficient oxygen reduction reaction.

Incorporating Pt with core metals into Pt-based core-shell catalysts is regarded as a promising strategy to substantially enhance the catalytic properties towards oxygen reduction reaction (ORR) in fuel cells due to the synergetic effect between distinct metals. In this wok, ultrathin Pt skins with two atomic layers were epitaxially coated on as-prepared icosahedral Au50Pd50, Au60Pd40 and Au66Pd34 nanocrystal seeds, which are constructed with alloyed cores and Pd shells with different thickness. Through electron microscopic characterizations, Pd interlayers with tunable thickness of 3, 6, and 12 atomic layers can be found in the Au66Pd34@Pt, Au60Pd40@Pt and Au50Pd50@Pt icosahedra, respectively. These icosahedral AuPd@Pd@Pt nanocrystals show substantially enhanced activities and durabilities in electrocatalytic measurements towards ORR compared to Au75Pd25@Pt icosahedra without Pd interlayer and commercial Pt/C catalysts. Specifically, Au60Pd40@Pt icosahedra with 6 atomically thick Pd interlayer display the best electrocatalytic performances, whose mass activities before and after durability tests of 50,000 cycles are 11.6 and 30.2 times, respectively, as high as that of the commercial Pt/C.

Intermetallic Nanocrystals: Syntheses and Catalytic Applications.

At the forefront of nanochemistry, there exists a research endeavor centered around intermetallic nanocrystals, which are unique in terms of long-range atomic ordering, well-defined stoichiometry, and controlled crystal structure. In contrast to alloy nanocrystals with no elemental ordering, it is challenging to synthesize intermetallic nanocrystals with a tight control over their size and shape. Here, recent progress in the synthesis of intermetallic nanocrystals with controllable sizes and well-defined shapes is highlighted. A simple analysis and some insights key to the selection of experimental conditions for generating intermetallic nanocrystals are presented, followed by examples to highlight the viable use of intermetallic nanocrystals as electrocatalysts or catalysts for various reactions, with a focus on the enhanced performance relative to their alloy counterparts that lack elemental ordering. Within the conclusion, perspectives on future developments in the context of synthetic control, structure-property relationships, and applications are discussed.

Strain-induced Stranski-Krastanov growth of Pd@Pt core-shell hexapods and octapods as electrocatalysts for methanol oxidation.

Bimetallic nanocrystals with a branched shape have received great interest as catalysts due to their unique structures and fascinating properties. However, the conventional synthetic approaches based on the island growth mode often lead to the dendritic nanostructures with inhomogeneous and uncontrolled branches. Here precise control over the number of branches has been realized in the deposition of Pt on Pd seeds through the Stranski-Krastanov growth mechanism. Based on such a growth mode, Pd@Pt core-shell hexapods and octapods have been generated by a seeded growth with Pd octahedra and cubes as the seeds, respectively. We found that Pt atoms are initially deposited on the side faces of Pd seeds through a layer-by-layer epitaxial growth in the presence of oleylamine (OAm), leading to a local strain focused at their corners. These strain-concentrated sites promote the subsequent island growth of Pt atoms at the corners of the Pd seeds, resulting in the Pd@Pt core-shell hexapods or octapods. Both the Pd@Pt core-shell hexapods and octapods exhibit the substantially enhanced catalytic properties in terms of activity and stability towards a methanol oxidation reaction (MOR) relative to the commercial Pt/C. Specifically, the Pd@Pt core-shell hexapods show the highest specific (1.97 mA cm-2) activity and mass activity (0.52 mA µgPt-1) for the MOR, which are 5.8 and 2.6 times higher than those of the commercial Pt/C, respectively. This enhancement can probably be attributed to their unique structures and the synergistic effect between Pt and Pd.

Embedding Ultrafine and High-Content Pt Nanoparticles at Ceria Surface for Enhanced Thermal Stability.

Ultrafine Pt nanoparticles loaded on ceria (CeO2) are promising nanostructured catalysts for many important reactions. However, such catalysts often suffer from thermal instability due to coarsening of Pt nanoparticles at elevated temperatures, especially for those with high Pt loading, which leads to severe deterioration of catalytic performances. Here, a facile strategy is developed to improve the thermal stability of ultrafine (1-2 nm)-Pt/CeO2 catalysts with high Pt content (≈14 wt%) by partially embedding Pt nanoparticles at the surface of CeO2 through the redox reaction at the solid-solution interface. Ex situ heating studies demonstrate the significant increase in thermal stability of such embedded nanostructures compared to the conventional loaded catalysts. The microscopic pathways for interparticle coarsening of Pt embedded or loaded on CeO2 are further investigated by in situ electron microscopy at elevated temperatures. Their morphology and size evolution with heating temperature indicate that migration and coalescence of Pt nanoparticles are remarkably suppressed in the embedded structure up to about 450 °C, which may account for the improved thermal stability compared to the conventional loaded structure.

Seed-mediated growth of Au nanorings with size control on Pd ultrathin nanosheets and their tunable surface plasmonic properties.

Nanorings made of noble metals such as Au and Ag have attracted particular interest in plasmonic properties since they allow remarkable tunability of plasmon resonance wavelengths associated with their unique structural features. Unfortunately, most of the syntheses for Au nanorings involve complex procedures and/or require highly specialized and expensive facilities. Here, we report a seed-mediated approach for selective deposition of Au nanorings on the periphery of Pd seeds with the structure of an ultrathin nanosheet through the island growth mode. In combination with selective etching of Pd nanosheets, Au nanorings are eventually produced. We can control the outer diameter and wall thickness of the nanorings by simply varying the size of the Pd nanosheets and reaction time. By taking the advantage of this size controllability, the nanorings show tunable surface plasmonic properties in the near infrared (NIR) region arising from both the in-plane dipole and face resonance modes. Owing to their good surface plasmonic properties, the nanorings show substantially enhanced surface-enhanced Raman spectroscopy (SERS) performance for rhodamine 6G, and are therefore confirmed as good SERS substrates to detect trace amounts of molecules.

Single-crystalline Pd square nanoplates enclosed by {100} facets on reduced graphene oxide for formic acid electro-oxidation.

Single-crystalline Pd square nanoplates enclosed by {100} facets were generated on reduced graphene oxide and exhibited the substantially enhanced properties for the formic acid oxidation reaction. The combination of carbonyl groups formed on the surface of annealed graphene oxide and Br- ions played important roles in this synthesis.

Controlled Growth of Li2O2 by Cocatalysis of Mobile Pd and Co3O4 Nanowire Arrays for High-Performance Li-O2 Batteries.

For Li-O2 batteries, a challenge still remains to achieve high discharge capacity and easy decomposition of the discharge product (Li2O2) simultaneously. In this work, conformal growth of thin-layered Li2O2 on Co3O4 nanowire arrays (Co3O4 NAs) during discharge is realized through the cocatalytic effect of solid/immobile Co3O4 NAs and mobile Pd nanocrystals (Pd NCs), rendering easy decomposition of Li2O2 during recharge. Meanwhile, high discharge capacity is also ensured with unique array-type design of the catalytic cathode despite the surface growth mode of Li2O2. The Li-O2 cells can deliver a high discharge capacity of 5337 mAh g-1 and keep a stable cycling of 258 cycles at a limited capacity of 500 mAh g-1. The achievement of excellent electrochemical performance is attributed to the highly efficient cocatalytic ability of Co3O4 NAs and Pd NCs as well as the desirable array-type architecture of the catalytic electrode free of carbon and binder. The cocatalytic mechanism of Co3O4 NAs and Pd NCs is clarified by systematic electrochemical tests, microstructural analyses, and ζ-potential measurements.

Kinetically-controlled growth of cubic and octahedral Rh-Pd alloy oxygen reduction electrocatalysts with high activity and durability.

Rh is a promising candidate as an indispensible component in bimetallic catalysts due to its unique capability to resist against the aggressive corrosion from the reaction medium. However, Rh has a very strong oxygen binding ability and is generally not suitable for the oxygen reduction reaction (ORR). Here, we have demonstrated shape-controlled synthesis of Rh-Pd alloy nanocrystals with high activity and durability for ORR by retarding the reaction kinetics at an ultra-slow injection rate of metal salts using a syringe pump. Under precise control of sluggish reaction kinetics, Pd followed a preferential overgrowth along the <100> direction, whereas the growth behavior of Rh was dominant along the <111> direction. These different kinetically-controlled growth behaviors associated with Rh and Pd were essential for achieving the shape transition between the cube and the octahedron of their alloys. The Rh8Pd92 alloy octahedra exhibited the highest mass activity with a value of 0.18 mA µg(-1) in terms of the equivalent Pt cost, and were two-fold higher than that of commercial Pt/C. Significantly, all Rh-Pd alloy nanocrystals were highly stable with only less than 25% loss in mass activity after 30,000 CV cycles in O2 saturated acid solution compared to ∼ 56% loss of the commercial Pt/C (E-TEK). Indeed, the mass activity of Rh8Pd92 was 3.3 times higher than that of commercial Pt/C after the accelerated stability test (ADT). This improvement in activity and durability may arise possibly from synergistic effects between the facet and the surface composition.