Three-dimensional Pt-on-Pd bimetallic nanodendrites supported on graphene nanosheet: facile synthesis and used as an advanced nanoelectrocatalyst for methanol oxidation

Nitrogen and Sulfur Co-Doped Graphene Composite Aerogel Microspheres Supporting Pt Electrode-Catalyzed Methanol Electro-Oxidation Reaction

Nitrogen and sulfur co-doped graphene composite aerogel microspheres containing pyrolyzed carbon (NS-GAMs@C) are prepared by pressure-spraying the graphene oxide (GO) dispersion with water-soluble phenolic resin and thiourea, followed by freeze shaping, freeze-drying, and high-temperature carbonization. The resulting NS-GAMs@C possesses interconnected porous structures with large surface areas and high doping levels of N/S elements. Furthermore, the platinum nanoparticles (Pt NPs) are grown onto the NS-GAMs@C via a solvothermal reduction reaction to obtain the Pt/NS-GAMs@C microspheres with an average particle size of ∼32.25 μm. The residual carbon species in situ formed by the high-temperature carbonization of phenolic resin can act as intercalation compounds to reduce the self-stacking of graphene sheets, which contributes to an enhanced specific surface area and doping level. The N/S co-doping in NS-GAMs@C improves the interaction between the Pt and carriers, reduces the size of Pt NPs, ensures their even distribution, and increases the proportion of highly active Pt (111) crystal planes. Consequently, the methanol oxidation activity of Pt/NS-GAMs@C is significantly improved compared to undoped materials. Specifically, the optimized Pt/NS-GAMs@C composites demonstrate a remarkable mass activity of 840.11 mA·mg-1 Pt for methanol electrooxidation, which is approximately 2.39, 3.94, 3.41, and 1.75 times higher than that of commercial Pt/C, Pt/rGO (reduced GO), Pt/GAMs without doping, and Pt/NS-GAB@C (bulk aerogel), respectively. Additionally, the Pt/NS-GAMs@C exhibits long-term electrocatalytic stability. This research provides a novel catalyst system based on aerogel microspheres for methanol electrooxidation fuel cells.

Enhanced Catalytic Activity of Pt Nanostructured Electrodes Deposited by Spark Ablation for Proton Exchange Membrane Fuel Cells

Catalyst layers play a crucial role in determining the performance of proton exchange membrane fuel cells (PEMFCs). However, the deposition of catalyst layers poses challenges in PEMFC stack production due to the complexity of the fabrication steps. Herein, we present a simplified approach to synthesize Pt nanostructures via spark ablation and simultaneously deposit them onto gas diffusion layers (GDL). The in situ deposited catalyst layers on GDL serve as electrodes for membrane electrode assembly (MEA) fabrication. Moreover, the carrier gas in the spark ablation process significantly influences the nucleation and growth of the Pt nanostructures. Pt nanostructures produced in forming gas (Pt_FG, 95% nitrogen, and 5% hydrogen) exhibit dendritic morphology distinct from those obtained in pure N2 (Pt_N2). Investigating the catalytic activity of Pt synthesized in different carrier gases reveals that the Pt_FG catalyst demonstrates enhanced half-wave potential, mass activity, and durability compared to those of Pt_N2 and commercial Pt-black catalysts. Single-cell measurements evaluate the electrocatalytic activity of the ionomer-free, in situ deposited catalyst layers. The Pt_FG MEA (0.2 mgPt cm-2) achieves a power density of 1285 mW cm-2 at 70 °C, 200 kPa, approximately 1.8 and 2 times higher than Pt_N2 and Pt-black MEAs, respectively. Further reduction of the catalyst loading to 0.1 mgPt cm-2 results in the Pt_FG MEA delivering 961 mW cm-2, indicating enhanced catalytic activity and Pt utilization efficiency. This study provides insights into fabricating catalytic layers using a facile strategy, circumventing the need for catalyst synthesis, ink formation, and electrode coating techniques.

Approaching Splendid Catalysts for Li-CO2 Battery from the Theory to Practical Designing: A Review

Lithium carbon dioxide (Li-CO2) batteries, noted for their high discharge voltage of approximately 2.8 V and substantial theoretical specific energy of 1876 Wh kg-1, represent a promising avenue for new energy sources and CO2 emission reduction. However, the practical application of these batteries faces significant hurdles, particularly at high current densities and over extended cycle lives, due to their complex reaction mechanisms and slow kinetics. This paper delves into the recent advancements in cathode catalysts for Li-CO2 batteries, with a specific focus on the designing philosophy from composition, geometry, and homogeneity of the catalysts to the proper test conditions and real-world application. It surveys the possible catalytic mechanisms, giving readers a brief introduction of how the energy is stored and released as well as the critical exploration of the relationship between material properties and performances. Specifically, optimization and standardization of test conditions for Li-CO2 battery research is highlighted to enhance data comparability, which is also critical to facilitate the practical application of Li-CO2 batteries. This review aims to bring up inspiration from previous work to advance the design of more effective and sustainable cathode catalysts, tailored to meet the practical demands of Li-CO2 batteries.

Tuning Pd-to-Ag Ratio to Enhance the Synergistic Activity of Fly Ash-Supported PdxAgy Bimetallic Nanoparticles

Fly ash (FA)-supported bimetallic nanoparticles (PdxAgy/FA) with varying Pd:Ag ratios were prepared by coprecipitation of Pd and Ag involving in situ reduction of Pd(II) and Ag(I) salts in aqueous medium. All the supported nanoparticles were thoroughly characterized with the aid of powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), electron microscopy (field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM)), and elemental analyses, which include inductively coupled plasma-optical emission spectroscopy (ICP-OES) and energy-dispersive X-ray spectroscopy (EDS). A gradual broadening and shifting of PXRD peaks, ascribable to Ag, to higher angles with an increase in the Pd:Ag ratio affirms the alloying of interface between Pd and Ag nanoparticles. The coexistence of Pd and Ag was further confirmed by EDS elemental mapping as well as by the presence of bimetallic lattices on the FA surface, as evident from the high-resolution TEM analysis. The dependency of crystallite size and average size of bimetallic nanoparticles on Ag loading (mol %) was elucidated with the help of a combination of PXRD and TEM studies. Based on XPS analysis, the charge transfer phenomenon between contacting Pd-Ag sites could be evident from the shifting of 3d core electron binding energy for both Pd and Ag compared with monometallic Pd and Ag nanoparticles. Following a pseudo-first-order reaction kinetics, all the nanocatalysts were able to efficiently reduce 4-nitrophenol into 4-aminophenol in aqueous NaBH4. The superior catalytic performance of the bimetallic nanocatalysts (PdxAgy/FA) over their monometallic (Pd100/FA and Ag100/FA) analogues has been demonstrated. Moreover, the tunable synergistic effect of the bimetallic systems has been explored in detail by varying the Pd:Ag mol ratio in a systematic manner which in turn allowed us to achieve an optimum reaction rate (k = 1.050 min-1) for the nitrophenol reduction using a Pd25Ag75/FA system. Most importantly, all the bimetallic nanocatalysts explored here exhibited excellent normalized rate constants (K ≈ 6000-15,000 min-1 mmol-1) compared with other supported bimetallic Pd-Ag nanocatalysts reported in the literature.

Immobilizing ultrasmall Pt nanocrystals on 3D interweaving BCN nanosheet-graphene networks enables efficient methanol oxidation reaction

Currently, the state-of-the-art anode catalysts employed in direct methanol fuel cells (DMFCs) consist of nanosize Pt dispersed on a carbonaceous support; however, the relatively weak Pt-carbon interfacial interactions severely affect their overall electrocatalytic activity and service life. Herein, we demonstrate a convenient and robust stereo-assembly strategy for the efficient immobilization of ultrasmall Pt nanocrystals on 3D interweaving porous B-doped g-C3N4 nanosheet-graphene networks (Pt/BCN-G) by combining thermal annealing and solvothermal processes. This delicate configuration endowed the resulting hybrid nanoarchitecture with unusual textural merits, including 3D crosslinked porous skeletons, well-separated ultrathin nanosheets, rich B and N species, homogeneous Pt dispersion, stable heterointerface, and high electrical conductivity. Consequently, the 3D Pt/BCN-G nanoarchitecture with an optimized composition exhibited a large electrochemically active surface area of up to 121.2 m2 g-1, high mass activity of 1782.2 mA mg-1, superior poison tolerance, and excellent cycling stability towards the electrooxidation of methanol, all of which exceeded that of the reference Pt/graphene, Pt/BCN, Pt/carbon nanotube, Pt/carbon black, and Pt/g-C3N4 catalysts.

Noble metal nanodendrites: growth mechanisms, synthesis strategies and applications

Inorganic nanodendrites (NDs) have become a kind of advanced nanomaterials with broad application prospects because of their unique branched architecture. The structural characteristics of nanodendrites include highly branched morphology, abundant tips/edges and high-index crystal planes, and a high atomic utilization rate, which give them great potential for usage in the fields of electrocatalysis, sensing, and therapeutics. Therefore, the rational design and controlled synthesis of inorganic (especially noble metals) nanodendrites have attracted widespread attention nowadays. The development of synthesis strategies and characterization methodology provides unprecedented opportunities for the preparation of abundant nanodendrites with interesting crystallographic structures, morphologies, and application performances. In this review, we systematically summarize the formation mechanisms of noble metal nanodendrites reported in recent years, with a special focus on surfactant-mediated mechanisms. Some typical examples obtained by innovative synthetic methods are then highlighted and recent advances in the application of noble metal nanodendrites are carefully discussed. Finally, we conclude and present the prospects for the future development of nanodendrites. This review helps to deeply understand the synthesis and application of noble metal nanodendrites and may provide some inspiration to develop novel functional nanomaterials (especially electrocatalysts) with enhanced performance.

Au-modified PtCu nanodendrites as a highly stable and active electrocatalyst

Direct galvanic replacement of surface Cu with Au³⁺ in PtCu₃ nanodendrites is applied to synthesize an Au-modified PtCu₃ nanodendrite catalyst (PtCu₃-Au), which shows both superior stability and excellent activity for the methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR). The PtCu₃-Au catalyst only lost 7% of its MOR activity and its ORR half-wave potential decreased 8 mV after 10 000 potential cycles.

Ethanol Electro-Oxidation on Catalysts with S-ZrO2-Decorated Graphene as Support in Fuel Cell Applications

Direct ethanol fuel cells (DEFCs) are considered the most suitable direct alcohol fuel cell (DAFC) in terms of safety and current density. The obstacle to DEFC commercialization is the low reaction kinetics of ethanol (C₂H₅OH) oxidation because of the poor performance of the electrocatalyst. In this study, for the first time, graphene nanoplates (GNPs) were coated with sulfated zirconium dioxide (ZrO₂) as adequate support for platinum (Pt) catalysts in DEFCs. A Pt/S-ZrO₂-GNP electrocatalyst was prepared by a new process, polyol synthesis, using microwave heating. Field emission scanning electron microscope (FESEM) imaging revealed well-dispersed platinum nanoparticles supported on the S-ZrO₂-GNP powder. Analysis of the Fourier transform infrared (FTIR) spectrometry confirmed that sulfate modified the surfaces of the sample. In X-ray diffraction (XRD), no effect of S-ZrO₂ on the crystallinity net in Pt was found. Pt/S-ZrO₂-GNP electrode outperformed those with unsulfated counterparts, primarily for the higher access with electron and proton, confirming sulfonating as a practical approach for increasing the performance, electrocatalytic activity, and carbon monoxide (CO) tolerance in an electrocatalyst. A considerable decrease in the voltage of the CO electrooxidation peak from 0.93 V for Pt/C to 0.76 V for the Pt/S-ZrO₂-GNP electrode demonstrates that the new material increases activity for CO electrooxidation. Moreover, the as-prepared Pt/S-ZrO₂-GNPs electrocatalyst exhibits high catalytic activity for the EOR in terms of electrochemical surface area with respect to Pt/ZrO₂-GNPs and Pt/C (199.1 vs. 95 and 67.2 cm².mg^-1 Pt), which may be attributed to structural changes caused by the high specific surface area of graphene nanoplates catalyst support and sulfonating effect as mentioned above. Moreover, EIS results showed that the Pt/S-ZrO₂-GNPs electrocatalyst has a lower charge transfer resistance than Pt/ ZrO₂-GNPs and Pt/C in the presence of ethanol demonstrating an increased ethanol oxidation activity and reaction kinetics by Pt/S-ZrO₂-GNPs.

Platinum Nanocrystals Embedded in Three-Dimensional Graphene for High-Performance Li-O2 Batteries

Graphene is considered as a promising cathode candidate for Li-O₂ batteries because of its excellent electronic conductivity and oxygen adsorption capacity. However, for Li-O₂ batteries, the self-stacking effect caused by two-dimensional (2D) structural properties of graphene is not conducive to the rapid oxygen transport and mass transfer process, thereby affecting the electrode kinetics. Here, we successfully prepared three-dimensional (3D) graphene with different scales by plasma-enhanced chemical vapor deposition and physical pulverization strategies, in which CH₄ is the carbon source and H₂/Ar mixed gas is the etching gas. Meanwhile, we fabricated 3D graphene-based Pt nanocatalysts by an ultraviolet-assisted construction strategy and then applied them in Li-O₂ batteries. Systematic studies reveal a special relevance between electrochemical performance and graphene particle size, and the smaller-sized 3D graphene can better maintain the microstructure distribution in both the Pt embedding process and electrochemical applications, which is beneficial to the transport of oxygen and Li ions, lowering the decomposition energy barrier of Li₂O₂, and further obtaining reduced charge overpotential (0.22 V) and prolonged cycle life for Li-O₂ batteries. Finally, we anticipate that this work could promote the practical application of 2D materials and larger-sized 3D materials in Li-O₂ batteries.

Superimposed Effect of La Doping and Structural Engineering to Achieve Oxygen-Deficient TiNb2O7 for Ultrafast Li-Ion Storage

TiNb₂O₇ (TNO) is a competitive candidate of a fast-charging anode due to its high specific capacity. However, the insulator nature seriously hinders its rate performance. Herein, the La³⁺-doped mesoporous TiNb₂O₇ materials (La-M-TNO) were first synthesized via a facile one-step solvothermal method with the assistance of polyvinyl pyrrolidone (PVP). The synergic effect of La³⁺ doping and the mesoporous structure enables a dual improvement on the electronic conductivity and ionic diffusion coefficient, which delivers an impressive specific capacity of 213 mAh g^-1 at 30 C. The capacity retention (@30C/@1C) increases from 33 to 53 and 74% for TNO, M-TNO, and La-M-TNO (0.03), respectively, demonstrating a step-by-step improvement of rate performance by making porous structures and intrinsic conductivity enhancement. DFT calculations verify that the enhancement in electronic conductivity due to La³⁺ doping and oxygen vacancy, which induce localized energy levels via slight hybridization of O 2p, Ti 3d, and Nb 4d orbits. Meanwhile, the GITT result indicates that PVP-induced self-assembly of TNO accelerates the lithium ion diffusion rate by shortening the Li⁺ diffusion path. This work verifies the effectiveness of the porous structure and highlights the significance of electronic conductivity to rate performance, especially at >30C. It provides a general approach to low-conductivity electrode materials for fast Li-ion storage.

Clean Electrochemical Synthesis of Pd–Pt Bimetallic Dendrites with High Electrocatalytic Performance for the Oxidation of Formic Acid

Pd–Pt bimetallic catalysts with a dendritic morphology were in situ synthesized on the surface of a carbon paper via the facile and surfactant-free two step electrochemical method. The effects of the frequency and modification time of the periodic square-wave potential (PSWP) on the morphology of the Pd–Pt bimetallic catalysts were investigated. The obtained Pd–Pt bimetallic catalysts with a dendritic morphology displayed an enhanced catalytic activity of 0.77 A mg⁻¹, almost 2.5 times that of the commercial Pd/C catalyst reported in the literature (0.31 A mg⁻¹) in acidic media. The enhanced catalytic activity of the Pd–Pt bimetallic catalysts with a dendritic morphology towards formic acid oxidation reaction (FAOR) was not only attributed to the large number of atomic defects at the edges of dendrites, but also ascribed to the high utilization of active sites resulting from the “clean” electrochemical preparation method. Besides, during chronoamperometric testing, the current density of the dendritic Pd–Pt bimetallic catalysts for a period of 3000 s was 0.08 A mg⁻¹, even four times that of the commercial Pd/C catalyst reported in the literature (about 0.02 A mg⁻¹).

Improving Nonenzymatic Biosensing Performance of Electrospun Carbon Nanofibers decorated with Ni/Co Particles via Oxidation

Nonenzymatic biosensors do not require enzyme immobilization nor face degradation problem. Hence, nonenzymatic biosensors have recently attracted growing attention due to the stability and reproducibility. Here, a comparative study was conducted to quantitatively evaluate the glucose sensing of pure/oxidized Ni, Co, and their bimetal nanostructures grown on electrospun carbon nanofibers (ECNFs) to provide a low-cost free-standing electrode. The prepared nanostructures exhibited sensitivity (from 66.28 to 610.6 μA mM^-1 cm^-2), linear range of 2-10 mM, limit of detection in the range of 1 mM, and the response time (< 5 s), besides outstanding selectivity and applicability for glucose detection in the human serum. Moreover, the oxidizable interfering species, such as ascorbic acid (AA), uric acid (UA), and dopamine (DA), did not cause interference. Co-C and Ni-C phase diagrams, solid-state diffusion phenomena, and rearrangement of dissolved C atoms after migration from metal particles were discussed. This study undoubtedly provides new prospects on the nonenzymatic biosensing performance of mono-metal, bimetal, and oxide compounds of Ni and Co elements, which could be quite helpful for the fabrication of biomolecules detecting devices.

Core-shell Pd-P@Pt-Ni nanoparticles with enhanced activity and durability as anode electrocatalyst for methanol oxidation reaction

Pd-P@Pt-Ni core-shell nanoparticles, which consisted of a Pd-P alloy as a core and Pt-Ni thin layer as a shell, were explored as electrocatalysts for methanol oxidation reaction. The crystallographic information and the electronic properties were fully investigated by X-ray diffraction and X-ray photoelectron spectroscopy. In the methanol electrooxidation reaction, the particles showed high catalytic activity and strong resistance to the poisoning carbonaceous species in comparison with those of commercial Pt/C and the as-prepared Pt/C catalysts. The excellent durability was demonstrated by electrochemically active surface area loss and chronoamperometric measurements. These results would be due to the enhanced catalytic properties of Pt by the double synergistic effects from the core part and the nickel species in the shell part.

Origins of Electron-Transfer Regime in Persulfate-Based Nonradical Oxidation Processes

Persulfate-based nonradical oxidation processes (PS-NOPs) are appealing in wastewater purification due to their high efficiency and selectivity for removing trace organic contaminants in complicated water matrices. In this review, we showcased the recent progresses of state-of-the-art strategies in the nonradical electron-transfer regimes in PS-NOPs, including design of metal and metal-free heterogeneous catalysts, in situ/operando characterization/analytical techniques, and insights into the origins of electron-transfer mechanisms. In a typical electron-transfer process (ETP), persulfate is activated by a catalyst to form surface activated complexes, which directly or indirectly interact with target pollutants to finalize the oxidation. We discussed different analytical techniques on the fundamentals and tactics for accurate analysis of ETP. Moreover, we demonstrated the challenges and proposed future research strategies for ETP-based systems, such as computation-enabled molecular-level investigations, rational design of catalysts, and real-scenario applications in the complicated water environment. Overall, this review dedicates to sharpening the understanding of ETP in PS-NOPs and presenting promising applications in remediation technology and green chemistry.

In situ lattice tuning of quasi-single-crystal surfaces for continuous electrochemical modulation

The ability to control the atomic-level structure of a solid represents a straightforward strategy for fabricating high-performance catalysts and semiconductor materials. Herein we explore the capability of the mechanically controllable surface strain method in adjusting the surface structure of a gold film. Underpotential deposition measurements provide a quantitative and ultrasensitive approach for monitoring the evolution of surface structures. The electrochemical activities of the quasi-single-crystalline gold films are enhanced productively by controlling the surface tension, resulting in a more positive potential for copper deposition. Our method provides an effective way to tune the atom arrangement of solid surfaces with sub-angstrom precision and to achieve a reduction in power consumption, which has vast applications in electrocatalysis, molecular electronics, and materials science.

We reported a new method capable of adjusting the lattice structure of solid surfaces with sub-angstrom precision and achieved in situ and continuous control over electrochemical activity.

Pt Edge-Doped MoS2 : Activating the Active Sites for Maximized Hydrogen Evolution Reaction Performance

The demand of clean energy calls for efficient and low-cost hydrogen evolution reaction electrocatalysts. Fabricating hybrid catalysts from noble/non-noble catalysts is a practical route to reducing the consumption of noble metals and enhancing catalytic efficiency. Here, 2H-MoS₂ is etched and edge-doped with Pt nanoparticles using focused ion beam and photoreduction techniques. Precise comparison of as-prepared samples demonstrates that the enhancement of catalytic performance can be controlled through tuning the catalyst defect length. On this basis, remarkably high performance is obtained by designing a specific defect array that is superior to commercial Pt/C with less Pt loading and higher mass activity. It has been proved by experimentation and COMSOL Multiphysics simulations that the promotion of catalytic activity not only benefits from the synergistic effect of Pt and edge active sites, but also contributes to the increased potential at the edges of the designed defect. This study sheds light on the mechanism of understanding nanoscale edge-doped hybrid catalysts and provides a feasible strategy for the full utilization of noble metals.

Antibacterial and Antibiofouling Activities of Antimicrobial Peptide-Functionalized Graphene-Silver Nanocomposites for the Inhibition and Disruption of Staphylococcus aureus Biofilms

Owing to the emergence of antibiotic-resistant strains, bacterial infection and biofilm formation are growing concerns in healthcare management. Herein, we report an eco-benign strategy for the synthesis and functionalization of graphene-silver (rGOAg) nanocomposites with an antimicrobial peptide (AMP) for the treatment of Staphylococcus aureus infection. The synthesis of rGOAg nanocomposites was carried out by simple microwave reduction, and the as-synthesized rGOAg was covalently functionalized with an AMP. As a natural AMP, poly-l-lysine (PLL) functionalization of rGOAg enhanced the antibacterial efficacy and target specificity against the S. aureus biofilm. The robust bactericidal efficiency and biofilm disruption by AMP-functionalized rGOAg (designated as GAAP) occurred through the "contact-kill-release" mode of action, where the electrostatic interaction with bacterial cells together with intracellular ROS generation induced physical disruption to the cell membrane. The internalization of GAAP into the cytoplasm through the damaged cell membrane caused an outburst of intracellular proteins and DNA. Crystal violet staining along with fluorescence and confocal microscopic images showed an effective inhibition and disruption of the S. aureus biofilm upon treatment with GAAP. PLL functionalization also prevented the dissolution of Ag⁺ ions and thereby minimized the in vitro toxicity of GAAP to the 3 T6 fibroblast and human red blood cells. The ex vivo rat skin disinfection model further demonstrated the potency of GAAP in eliminating the biofilm formation and disruption of the S. aureus biofilm. The obtained results demonstrated a general approach for designing a functional nanocomposite material to disrupt the mature biofilm and provided a promising strategy for treating bacterial infection.

Sandwich electrochemical carcinoembryonic antigen aptasensor based on signal amplification of polydopamine functionalized graphene conjugate Pd-Pt nanodendrites

Carcinoembryonic antigen (CEA) is considered as a disease biomarker, which is related to various cancers and tumors in the human bodies. Sensitive detection of CEA is significant for clinical diagnosis and treatment. Herein, we proposed an electrochemical aptasensor for CEA detection based on the amplification driven by polydopamine functional graphene and Pd-Pt nanodendrites (PDA@Gr/Pd-PtNDs), conjugated hemin/G-quadruplex (hemin/G4), which possess mimicking peroxidases activity. Firstly, PDA@Gr was modified on the electrode surface for fixing CEA aptamer 1 (Apt1). Then, PDA@Gr/Pd-PtNDs with large surface area served as matrix for immobilization of hemin/G4 to obtain the secondary aptamer. In virtue of the sandwich-type specific reaction between CEA and the corresponding aptamers, the second aptamer was captured on the sensing interface, which can catalyze the oxidation of signal probe hydroquinone (HQ) with H₂O₂ and amplify current signal. Furthermore, the electrochemical signals of HQ were proportional with CEA concentrations. Under the optimal conditions, a dynamic response range from 50 pg/mL to 1.0 μg/mL and a detection limit of 6.3 pg/mL for CEA were obtained. Moreover, the proposed strategy represented satisfactory sensitivity and stability, and showed a good precision in real samples application.

Highly Porous Pt2Ir Alloy Nanocrystals as a Superior Catalyst with High-Efficiency C-C Bond Cleavage for Ethanol Electrooxidation

Achieving high catalytic performance with high CO₂ selectivity is critical for commercialization of direct ethanol fuel cells. Here, we report carbon-supported highly porous Pt₂Ir alloy nanocrystals (p-Pt₂Ir/C) for an ethanol oxidation reaction (EOR) that displays nearly 7.2-fold enhancement in mass activity and promotes antipoisoning ability and durability for the EOR as compared with the commercial Pt/C-JM. Moreover, the catalyst exhibits high CO₂ selectivity, 3.4-fold at 0.65 V (vs. SCE) and 4.1-fold at 0.75 V (vs. SCE) higher as compared with the carbon-supported porous Pt nanocrystals (p-Pt/C). The highly porous structure is composed of interconnected one-dimensional (1D) rough branches with an average diameter of only 1.9 nm, largely promoting Pt utilization efficiency and accelerating mass transfer. The 1D rough branch surface exposed many atomic steps/corners endowed with abundant high activity sites. Alloying with Ir can significantly improve the antipoisoning ability, durability, and C-C bond cleavage ability, thereby evidently enhancing its EOR performance.

Understanding of Strain-Induced Electronic Structure Changes in Metal-Based Electrocatalysts: Using Pd@Pt Core-Shell Nanocrystals as an Ideal Platform

While metal-based electrocatalysts have garnered extensive attention owing to the large variety of enzyme-mimic properties, the search for such highly-efficient catalysts still relies on empirical explorations, owing to the lack of predictive indicators as well as the ambiguity of structure-activity relationships. Notably, surface electronic structures play a crucial role in metal-based catalysts yet remain unexplored in enzyme-mimics. Herein, the authors investigate the electronic structure as a possible indicator of electrocatalytic activities of H₂ O₂ decomposition and glucose oxidation using Pd@Pt core-shell nanocrystals as a well-defined platform. The electron densities of the Pd@Pt are modulated with the correlation of strain through precise control of surface orientation and the number of atomic layers. The close relationships between the electrocatalytic activities and the surface charge accumulation are found, in which the increase of the electron accumulation can enhance both the enzyme-mimic activities. As a result, the Pd@Pt_3L icosahedra with compressive strain in Pt shells exhibit the highest electrocatalytic activities for H₂ O₂ decomposition and glucose oxidation. Such systematic and comprehensive study provides the structure-activity relationships and paves a new way for the rational design of metal-based electrocatalysts. Especially, the charge accumulation degrees may serve as a general performance indicator for metal-based catalysts.

Porous PdAg alloy nanostructures with a concave surface for efficient electrocatalytic methanol oxidation

Tuning the composition and surface structure of the metal nanocrystals offered viable avenues for enhancing catalytic performances. Herein, we report a facile one-pot strategy for the formation of PdAg porous alloy nanostructures (PANs) with a concave surface. Due to their highly open nanostructures and tunable d-band center features, PdAg PANs exhibit superior electrocatalytic activity and long-term durability than Pd nanoparticles (NPs) and Pd/C for methanol oxidation reaction (MOR) in alkaline media. Our results provide a feasible and efficient approach for the controlled synthesis of high-performance Pd-based nanomaterials for alkaline MOR.

Fischer–Tropsch Synthesis: Study of Different Carbon Materials as Cobalt Catalyst Support

In this work, cobalt Fischer–Tropsch synthesis (FTS) catalyst supported on various carbon materials, i.e., carbon nanotube (CNT), activated carbon (AC), graphene oxide (GO), reduced graphene oxide (rGO), and carbon nanofiber (CNF), were prepared via impregnation method. Based on TGA, nitrogen physisorption, XRD, Raman spectroscopy, H2-TPR, NH3-TPD, ICP, SEM, and TEM characterization, it is confirmed that Co3O4 particles are dispersed uniformly on the supports of carbon nanotube, activated carbon and carbon nanofiber. Furthermore, the FT catalyst performance for as-prepared catalysts was evaluated in a fixed-bed reactor under the condition of H2:CO = 2:1, 5 SL·h−1·g−1, 2.5 MPa, and 210 °C. Interestingly, the defined three types of carbon materials exhibit superior performance and dispersion compared with graphene oxide and reduced graphene oxide. The thermal stability and pore structure of the five carbon materials vary markedly, and H2-TPR result shows that the metal–support interaction is in the order of Co/GO > Co/CNT > Co/AC > Co/CNF > Co/rGO. In brief, the carbon nanofiber-supported cobalt catalyst showed the best dispersion, the highest CO conversion, and the lowest gas product but the highest heavy hydrocarbons (C5+) selectivity, which can be attributed to the intrinsic property of CNF material that can affect the catalytic performance in a complicated way. This work will open up a new gateway for cobalt support catalysts on various carbon-based materials for Fischer–Tropsch Synthesis.

Coupling of Silk Fibroin Nanofibrils Enzymatic Membrane with Ultra-Thin PtNPs/Graphene Film to Acquire Long and Stable On-Skin Sweat Glucose and Lactate Sensing

The applications of enzymatic biosensors are largely limited by their relatively poor stability and short lifespan. Herein, a bio-active porous enzymatic nanofiber (PEN) membrane composed of silk fibroin nanofibrils (SFNFs) and enzymes is developed to effectively retain the enzymes in the 3D space. The 3D functional scaffolds formed by SFNFs can immobilize enzymes and provide a large surface area for molecular/ion diffusion and biochemical reactions. The PEN membrane is subsequently attached to an ultra-thin PtNPs/graphene (Pt-G) nanocomposite film to facilitate the electron transport between the enzymes and electrodes, permitting highly effective glucose and lactate sensing with long and stable performance. The as-assembled glucose and lactate sensors demonstrate high sensitivity, good cyclic reproducibility, and in particular long-term stability of up to 25 and 23.6 h, respectively. These glucose sensors have a working life that is ≈1.25-times longer than that of the best available sensors reported so far. Moreover, a wearable platform based on the sensors is developed for real-time analysis of sweat during outdoor exercising to transmit signals to a mobile handset. The high sensitivity, comfort and long-term stability of the device can benefit for long-term in-line surveillance of physiological conditions.

Tunable metal–organic framework nanoarrays on carbon cloth constructed by a rational self-sacrificing template for efficient and robust oxygen evolution reactions

The morphology and electronic structure of MOF-74 nanoarrays on carbon cloth were modulated for oxygen evolution reactions with self-sacrificing templates of Co/Ni(OH)2 nanosheets.

PtPd nanoframes derived from Pd@PdPt core–shell rhombic dodecahedrals with excellent catalytic performance toward methanol oxidation

PtPd nanoframes with excellent catalytic properties were obtained by etching Pd@PdPt core–shell RDs with Fe³⁺ in an acid environment.

Operando Surface Characterization on Catalytic and Energy Materials from Single Crystals to Nanoparticles

Modern surface science faces two major challenges, a materials gap and a pressure gap. While studies on single crystal surface in ultrahigh vacuum have uncovered the atomic and electronic structures of the surface, the materials and environmental conditions of commercial catalysis are much more complicated, both in the structure of the materials and in the accessible pressure range of analysis instruments. Model systems and operando surface techniques have been developed to bridge these gaps. In this Review, we highlight the current trends in the development of the surface characterization techniques and methodologies in more realistic environments, with emphasis on recent research efforts at the Korea Advanced Institute of Science and Technology. We show principles and applications of the microscopic and spectroscopic surface techniques at ambient pressure that were used for the characterization of atomic structure, electronic structure, charge transport, and the mechanical properties of catalytic and energy materials. Ambient pressure scanning tunneling microscopy and X-ray photoelectron spectroscopy allow us to observe the surface restructuring that occurs during oxidation, reduction, and catalytic processes. In addition, we introduce the ambient pressure atomic force microscopy that revealed the morphological, mechanical, and charge transport properties that occur during the catalytic and energy conversion processes. Hot electron detection enables the monitoring of catalytic reactions and electronic excitations on the surface. Overall, the information on the nature of catalytic reactions obtained with operando spectroscopic and microscopic techniques may bring breakthroughs in some of the global energy and environmental problems the world is facing.

Engineering the morphology of palladium nanostructures to tune their electrocatalytic activity in formic acid oxidation reactions

Pd nanomaterials can be cheaper alternative catalysts for the electrocatalytic formic acid oxidation reaction (FAOR) in fuel cells. The size and shape of the nanoparticles and crystal engineering can play a crucial role in enhancing the catalytic activities of Pd nanostructures. A systematic study on the effect of varying the morphology of Pd nanostructures on their catalytic activities for FAOR is reported here. Palladium nanoparticles (Pd_0D), nanowires (Pd_1D) and nanosheets (Pd_2D) could be synthesized by using swollen liquid crystals as 'soft' templates. Swollen liquid crystals are lyotropic liquid crystals that are formed from a quaternary mixture of a surfactant, cosurfactant, brine and Pd salt dissolved in oil. Pd_1D nanostructures exhibited 2.7 and 19 fold higher current density than Pd_0D and Pd_2D nanostructures in the FAOR. The Pd_1D nanostructure possess higher electrochemically active surface area (ECSA), better catalytic activity, stability, and lower impedance to charge transfer when compared to the Pd_0D and Pd_2D nanostructures. The presence of relatively higher amounts of crystal defects and enriched (100) crystal facets in the Pd_1D nanostructure were found to be the reasons for their enhanced catalytic activities.

Plasmonic Metallic Heteromeric Nanostructures

Binary, ternary, and other high-order plasmonic heteromers possess remarkable physical and chemical properties, enabling them to be used in numerous applications. The seed-mediated approach is one of the most promising and versatile routes to produce plasmonic heteromers. Selective growth of one or multiple domains on desired sites of noble metal, semiconductor, or magnetic seeds would form desired heteromeric nanostructures with multiple functionalities and synergistic effects. In this work, the challenges for the synthetic approaches are discussed with respect to tuning the thermodynamics, as well as the kinetic properties (e.g., pH, temperature, injection rate, among others). Then, plasmonic heteromers with their structure advantages displaying unique activities compared to other hybrid nanostructures (e.g., core-shell, alloy) are highlighted. Some of the main most recent applications of plasmonic heteromers are also presented. Finally, perspectives for further exploitation of plasmonic heteromers are demonstrated. The goal of this work is to provide the current know-how on the synthesis routes of plasmonic heteromers in a summarized manner, so as to achieve a better understanding of the resulting properties and to gain an improved control of their performances and extend their breadth of applications.

Pt-on-Pd Dendritic Nanosheets with Enhanced Bifunctional Fuel Cell Catalytic Performance

Pd-Pt bimetallic nanocrystals have become appealing in the electrocatalytic field by virtue of their synergy effects derived from the electronic coupling between two metals. Herein, a facile seed-mediated growth approach is reported for synthesis of Pt-on-Pd dendritic nanosheets (DNSs) through the growth of Pt branches on ultrathin Pd nanosheets (NSs). The as-obtained Pt-on-Pd DNSs exhibit superior catalytic activity toward both oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR), with mass activities (MAs) 2.2 times higher for ORR and 3.4 times higher for MOR than commercial Pt/C catalysts. Moreover, these spatially separated Pt branches supported on 2D NSs also endow the Pt-on-Pd DNSs with impressive durability for ORR with only 18.9% loss in MA, whereas the Pt/C catalyst loses 50.0% after 10,000-cycle accelerated durability tests. This 2D DNS architecture can be extended to other 2D metallic NS substrates for constructing Pt-based electrocatalysts with excellent electrocatalytic performance.

Bimetallic Catalysts for Volatile Organic Compound Oxidation

In recent years, the impending necessity to improve the quality of outdoor and indoor air has produced a constant increase of investigations in the methodologies to remove and/or to decrease the emission of volatile organic compounds (VOCs). Among the various strategies for VOC elimination, catalytic oxidation and recently photocatalytic oxidation are regarded as some of the most promising technologies for VOC total oxidation from urban and industrial waste streams. This work is focused on bimetallic supported catalysts, investigating systematically the progress and developments in the design of these materials. In particular, we highlight their advantages compared to those of their monometallic counterparts in terms of catalytic performance and physicochemical properties (catalytic stability and reusability). The formation of a synergistic effect between the two metals is the key feature of these particular catalysts. This review examines the state-of-the-art of a peculiar sector (the bimetallic systems) belonging to a wide area (i.e., the several catalysts used for VOC removal) with the aim to contribute to further increase the knowledge of the catalytic materials for VOC removal, stressing the promising potential applications of the bimetallic catalysts in the air purification.

Bimetallic and postsynthetically alloyed PtCu nanostructures with tunable reactivity for the methanol oxidation reaction

Designing effective catalysts by controlling morphology and structure is key to improving the energy efficiency of fuel cells. A good understanding of the effects of specific structures on electrocatalytic activity, selectivity, and stability is needed. Here, we propose a facile method to synthesize PtCu bimetallic nanostructures with controllable compositions by using Cu nanowires as a template and ascorbic acid as a reductant. A further annealing process provided the alloy PtCu with tunable crystal structures. The combination of distinct structures with tunable compositions in the form of PtCu nanowires provides plenty of information for better understanding the reaction mechanism during catalysis. HClO₄ cyclic voltammetry (CV) tests confirmed that various phase transformations occurred in bimetallic and alloy samples, affecting morphology and unit cell structures. Under a bifunctional synergistic effect and the influence of the insertion of a second metal, the two series of structures show superior performance toward methanol electrooxidation. Typically, the post-product alloy A-Pt₁₄Cu₈₆ with a cubic structure (a = 3.702 Å) has better methanol oxidation reaction (MOR) catalysis performance. Density functional theory (DFT) calculations were performed to determine an optimal pathway using the Gibbs free energy and to verify the dependence of the electrocatalytic performance on the lattice structure via overpotential changes. Bimetallic PtCu has high CO tolerance, maintaining high stability. This work provides an approach for the systematic design of novel catalysts and the exploration of electrocatalytic mechanisms for fuel cells and other related applications.

Bimetallic alloy and semiconductor support synergistic interaction effects for superior electrochemical catalysis

The design and fabrication of economically viable anode catalysts for the methanol oxidation reaction (MOR) have been challenging issues in direct methanol fuel cells (DMFCs) over the decades. In this work, a composite electrochemical catalyst of Pd-coupled Ag and ZnO for the possible replacement of expensive Pt catalysts in DMFCs is successfully prepared. The as-made Pd@Ag/ZnO exhibits specific activity, which is 1.8-fold, 2.8-fold, and 4.6-fold higher than that of a Pd/ZnO catalyst, 20% Pd/C catalyst and Pd black, respectively. The improvement of the catalytic mechanism is likely due to the synergistic interaction between Pd@Ag and ZnO. The density functional theory (DFT) calculation results confirm that Ag doped into Pd weakens the adsorption of CO, dramatically improving the capability to resist CO poisoning.

Effect of Hybrid mono/bimetallic Nanocomposites for an enhancement of Catalytic and Antimicrobial Activities

Exploring the new catalytic systems for the reduction of organic and inorganic pollutants from an indispensable process in chemical, petrochemical, pharmaceutical and food industries, etc. Hence, in the present work, authors motivated to synthesize bare reduced graphene oxide (rGO), polyaniline (PANI), three different ratios of rGO-PANI_{(80:20,50:50, 10:90)} composites and rGO-PANI_{(80:20,50:50, 10:90)} supported mono (Pd) & bimetallic [Pd: Au_{(1:1,1:2, 2:1)}] nanocomposite by a facile chemical reduction method. Also, it investigated their catalytic performances for the reduction of organic/inorganic pollutants and antimicrobial activities. All the freshly prepared bare rGO, PANI, three different ratios of rGO-PANI_{(80:20, 50:50,10:90)} composites and rGO-PANI_{(80:20, 50:50,10:90)}/Pd & Pd: Au_{(1:1, 1:2,2:1)} nanocomposite hybrid catalysts were characterized using UV-Vis, FT-IR, SEM, FE-SEM, EDAX, HR-TEM, XRD, XPS and Raman spectroscopy analysis. Among them, an optimized best composition of rGO-PANI_(80:20)/Pd: Au_(1:1) bimetallic nanocomposite hybrid catalyst exhibits better catalytic reduction and antimicrobial activities than other composites, as a result of strong electrostatic interactions between rGO, PANI and bimetal (Pd: Au) NPs through a synergistic effect. Hence, an optimized rGO-PANI_(80:20)/Pd:Au_(1:1) bimetallic nanocomposite catalyst would be considered as a suitable catalyst for the reduction of different nitroarenes, organic dyes, heavy metal ions and also significantly inhibit the growth of S. aureus, S. Typhi as well as Candida albicans and Candida kruesi in wastewater.