Shape-control and electrocatalytic activity-enhancement of Pt-based bimetallic nanocrystals

Thermodynamic Analysis of Size-Dependent Surface Energy in Pd Nanoparticles for Enhanced Alkaline Ethanol Electro-Oxidation

This work investigates the relationship between the mean diameter of palladium (Pd) nanoparticles and their surface energy, specifically in the context of alkaline ethanol electro-oxidation for fuel cell applications. Employing a recent generalization of the classical Laviron equation, we derive crucial parameters such as surface energy (σ), adsorption-desorption equilibrium constant (Keq), and electron transfer coefficient (α) from linear voltammograms obtained from Pd-based nanoparticles supported on Vulcan carbon. Synthesized using two distinct methods, these nanocatalysts exhibit mean diameters ranging from 10 to 41 nm. Our results indicate that the surface energy of the Pd/C nanocatalysts spans σ ~ 0.5-2.5 J/m2, showing a linear correlation with particle size while remaining independent of ethanol bulk concentration. The adsorption-desorption equilibrium constant varies with nanoparticle size (~0.1-6 × 10-6 mol-1) but is unaffected by ethanol concentration. Significantly, we identify an optimal mean diameter of approximately 28 nm for enhanced electrocatalytic activity, revealing critical size-dependent effects on catalytic efficiency. This research contributes to the ongoing development of cost-effective and durable fuel cell components by optimizing nanoparticle characteristics, thus advancing the performance of Pd-based catalysts in practical applications. Our findings are essential for the continued evolution of nanomaterials in fuel cell technologies, particularly in improving efficiency and reducing reliance on critical raw materials.

Surface Self-Diffusion Induced Sintering of Nanoparticles

Despite the critical role of sintering phenomena in constraining the long-term durability of nanosized 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.

The role of surface substitution in the atomic disorder-to-order phase transition in multi-component core-shell structures

Intermetallic phases with atomic ordering are highly active and stable in catalysts. However, understanding the atomistic mechanisms of disorder-to-order phase transition, particularly in multi-component systems, remains challenging. Here, we investigate the atom diffusion and phase transition within Pd@Pt-Co cubic nanoparticles during annealing, using in-situ electron microscopy and ex-situ atomic resolution element analysis. We reveal that initial outward diffusing Pd partially substitutes Pt, forming a (Pt, Pd)-Co ternary system in the surface region, enabling the phase transition at a low temperature of 400 °C, followed by shape-preserved inward propagation of the ordered phase. At higher temperatures, excessive interdiffusion across the interface changes the stoichiometric ratio, diminishing the atomic ordering, leading to obvious change in morphology. Calculations indicate that the Pd-substitute in (Pt, Pd)-Co system leads to a significantly lower phase transition temperature compared to that of Pt-Co alloy and thus a lower activation energy for atomic diffusion. These insights into atomistic behavior are crucial for future design of multi-component systems.

Mechanistic Insights into the Stabilization of In Situ Formed γ-NiOOH Species on Ni60Nb40 Nanoglass for Effective Urea Electro-Oxidation

The formation of NiOOH on the catalyst surface is widely considered to be the active species in electrochemical urea oxidation reactions (UOR). Though in situ-formed NiOOH species are reported to be more active than the synthesized ones, the mechanistic study of the actual active species remains a daunting task due to the possibility of different phases and instability of surface-formed NiOOH. Herein, mechanistic UOR aspects of electrochemically activated metallic Ni60Nb40 Nanoglass showing stability toward the γ-NiOOH phase are reported, probed via in situ Raman spectroscopy, supported by electron microscopy analysis and X-ray photoelectron spectroscopy in contrast with the β-NiOOH formation favored on Ni foil. Detailed mechanistic study further reveals that γ-NiOOH predominantly follows a direct UOR mechanism while β-NiOOH favors indirect UOR from time-dependent Raman study, and electrochemical impedance spectroscopy (EIS) analysis. The Nanoglass has shown outstanding UOR performance with a low Tafel slope of 16 mV dec-1 and stability for prolonged electrolysis (≈38 mA cm-2 for 70 h) that can be attributed to the nanostructured glassy interfaces facilitating more γ-NiOOH species formation and stabilization on the surface. The present study opens up a new direction for the development of inexpensive Ni-based UOR catalysts and sheds light on the UOR mechanism.

Design and regulation of defective electrocatalysts

Electrocatalysts are the key components of electrochemical energy storage and conversion devices. High performance electrocatalysts can effectively reduce the energy barrier of the chemical reactions, thereby improving the conversion efficiency of energy devices. The electrocatalytic reaction mainly experiences adsorption and desorption of molecules (reactants, intermediates and products) on a catalyst surface, accompanied by charge transfer processes. Therefore, surface control of electrocatalysts plays a pivotal role in catalyst design and optimization. In recent years, many studies have revealed that the rational design and regulation of a defect structure can result in rearrangement of the atomic structure on the catalyst surface, thereby efficaciously promoting the electrocatalytic performance. However, the relationship between defects and catalytic properties still remains to be understood. In this review, the types of defects, synthesis methods and characterization techniques are comprehensively summarized, and then the intrinsic relationship between defects and electrocatalytic performance is discussed. Moreover, the application and development of defects are reviewed in detail. Finally, the challenges existing in defective electrocatalysts are summarized and prospected, and the future research direction is also suggested. We hope that this review will provide some principal guidance and reference for researchers engaged in defect and catalysis research, better help researchers understand the research status and development trends in the field of defects and catalysis, and expand the application of high-performance defective electrocatalysts to the field of electrocatalytic engineering.

Development of Electrochemical Cells and Their Application for Spatially Resolved Analysis Using a Multitechnique Approach: From Conventional Experiments to X-Ray Nanoprobe Beamlines

Real (electro)catalysts are often heterogeneous, and their activity and selectivity depend on the properties of specific active sites. Therefore, unveiling the so-called structure-activity relationship is essential for a rational search for better materials and, consequently, for the development of the field of (electro-)catalysis. Thus, spatially resolved techniques are powerful tools as they allow us to characterize and/or measure the activity and selectivity of different regions of heterogeneous catalysts. To take full advantage of that, we have developed spectroelectrochemical cells to perform spatially resolved analysis using X-ray nanoprobe synchrotron beamlines and conventional pieces of equipment. Here, we describe the techniques available at the Carnaúba beamline at the Sirius-LNLS storage ring, and then we show how our cells enable obtaining X-ray (XRF, XRD, XAS, etc.) and vibrational spectroscopy (FTIR and Raman) contrast images. Through some proof-of-concept experiments, we demonstrate how using a multi-technique approach could render a complete and detailed analysis of an (electro)catalyst overall performance.

Recent Advances in Bimetallic Nanoporous Gold Electrodes for Electrochemical Sensing

Bimetallic nanocomposites and nanoparticles have received tremendous interest recently because they often exhibit better properties than single-component materials. Improved electron transfer rates and the synergistic interactions between individual metals are two of the most beneficial attributes of these materials. In this review, we focus on bimetallic nanoporous gold (NPG) because of its importance in the field of electrochemical sensing coupled with the ease with which it can be made. NPG is a particularly important scaffold because of its unique properties, including biofouling resistance and ease of modification. In this review, several different methods to synthesize NPG, along with varying modification approaches are described. These include the use of ternary alloys, immersion-reduction (chemical, electrochemical, hybrid), co-electrodeposition-annealing, and under-potential deposition coupled with surface-limited redox replacement of NPG with different metal nanoparticles (e.g., Pt, Cu, Pd, Ni, Co, Fe, etc.). The review also describes the importance of fully characterizing these bimetallic nanocomposites and critically analyzing their structure, surface morphology, surface composition, and application in electrochemical sensing of chemical and biochemical species. The authors attempt to highlight the most recent and advanced techniques for designing non-enzymatic bimetallic electrochemical nanosensors. The review opens up a window for readers to obtain detailed knowledge about the formation and structure of bimetallic electrodes and their applications in electrochemical sensing.

Shape-Controlled Synthesis of Platinum-Based Nanocrystals and Their Electrocatalytic Applications in Fuel Cells

To achieve environmentally benign energy conversion with the carbon neutrality target via electrochemical reactions, the innovation of electrocatalysts plays a vital role in the enablement of renewable resources. Nowadays, Pt-based nanocrystals (NCs) have been identified as one class of the most promising candidates to efficiently catalyze both the half-reactions in hydrogen- and hydrocarbon-based fuel cells. Here, we thoroughly discuss the key achievement in developing shape-controlled Pt and Pt-based NCs, and their electrochemical applications in fuel cells. We begin with a mechanistic discussion on how the morphology can be precisely controlled in a colloidal system, followed by highlighting the advanced development of shape-controlled Pt, Pt-alloy, Pt-based core@shell NCs, Pt-based nanocages, and Pt-based intermetallic compounds. We then select some case studies on models of typical reactions (oxygen reduction reaction at the cathode and small molecular oxidation reaction at the anode) that are enhanced by the shape-controlled Pt-based nanocatalysts. Finally, we provide an outlook on the potential challenges of shape-controlled nanocatalysts and envision their perspective with suggestions.

Construction of Millimeter-Wide Monolayers of Ordered Nanocubes as a Stain of "Wineglass Tears" Driven by the Marangoni Flow

We constructed millimeter-wide monolayers consisting of tetragonally ordered BaTiO₃ (BT) nanocubes through the liquid film formation caused by the Marangoni flow in a toluene-hexane binary liquid containing oleic acid. A thin liquid film containing BT nanocubes was overspread on a standing silicon substrate through the condensation of toluene at the advancing front after the preferential evaporation of hexane. Then, the oscillatory droplet formation like "wineglass tears" occurred on the substrate. Finally, two-dimensionally ordered BT nanocubes were observed as a stain of "wineglass tears" on the substrate after the liquid film receded through evaporation. The presence of a thin liquid film in the binary system is essential for the production of millimeter-wide monolayers on the substrate because multilayer deposition occurs without the formation of a thin liquid film in monocomponent systems. We improved the regularity of the ordered arrays of nanocubes by adjusting the liquid component and evaporation conditions.

Colloidal synthesis of monodisperse trimetallic Pt-Fe-Ni nanocrystals and their enhanced electrochemical performances

Among the multi-metallic nanocatalysts, Pt-based alloy nanocrystals (NCs) have demonstrated promising performance in fuel cells and water electrolyzers. Herein, we demonstrate a facile colloidal synthesis of monodisperse trimetallic Pt-Fe-Ni alloy NCs through a co-reduction of metal precursors. The as-synthesized ternary NCs exhibit superior mass and specific activities toward oxygen reduction reaction (ORR), which are ∼2.8 and 5.6 times as high as those of the benchmark Pt/C catalyst, respectively. The ORR activity of the carbon-supported Pt-Fe-Ni nanocatalyst is persistently retained after the durability test. Owing to the incorporation of Fe and Ni atoms into the Pt lattice, the as-prepared trimetallic Pt-alloy electrocatalyst also manifestly enhances the electrochemical activity and durability toward the oxygen evolution reaction with a reduced overpotential when compared with that of the benchmark Pt/C (△η= 0.20 V, at 10 mA cm^-2). This synthetic strategy paves the way for improving the reactivity for a broad range of electrocatalytic applications.

Tungsten-Based Nanocatalysts: Research Progress and Future Prospects

The high price of noble metal resources limits its commercial application and stimulates the potential for developing new catalysts that can replace noble metal catalysts. Tungsten-based catalysts have become the most important substitutes for noble metal catalysts because of their rich resources, friendly environment, rich valence and better adsorption enthalpy. However, some challenges still hinder the development of tungsten-based catalysts, such as limited catalytic activity, instability, difficult recovery, and so on. At present, the focus of tungsten-based catalyst research is to develop a satisfactory material with high catalytic performance, excellent stability and green environmental protection, mainly including tungsten atomic catalysts, tungsten metal nanocatalysts, tungsten-based compound nanocatalysts, and so on. In this work, we first present the research status of these tungsten-based catalysts with different sizes, existing forms, and chemical compositions, and further provide a basis for future perspectives on tungsten-based catalysts.

Nanostructured Metallic Glass in a Highly Upgraded Energy State Contributing to Efficient Catalytic Performance

Metallic glasses (MGs), with high density of low coordination sites and high Gibbs free energy state, are novel promising and competitive candidates in the family of electrochemical catalysts. However, it remains a grand challenge to modify the properties of MGs by control of the disordered atomic structure. Recently, nanostructured metallic glasses (NGs), consisting of amorphous nanometer-sized grains connected by amorphous interfaces, have been reported to exhibit tunable properties compared to the MGs with identical chemical composition. Here, it is demonstrated that electrodeposited Ni-P NG is characterized by an extremely high energy state due to its heterogeneous structure, which significantly promotes the catalytic performance. Moreover, the Ni-P NG with a heterogeneous structure is a perfect precursor for the fabrication of unique honey-like nanoporous structure, which displays superior catalytic performance in the urea oxidation reaction (UOR). Specifically, modified Ni-P NG requires a potential of mere 1.36 V at 10 mA cm^-2 , with a Tafel slope of 13 mV dec^-1 , which is the best UOR performance in Ni-based alloys. The present work demonstrates that the nanostructurization of MGs provides a universal and effective pathway to upgrade the energy state of MGs for the design of high-performance catalysts in energy conversion.

Seeded Growth of Gold-Copper Janus Nanostructures as a Tandem Catalyst for Efficient Electroreduction of CO2 to C2+ Products

Gold-copper (Au-Cu) Janus nanostructures (Au-Cu Janus NSs) are successfully prepared using N-oleyl-1,3-propanediamine as capping agent and Cu(acac)₂ as the precursor in a typical seeded growth strategy. By preferably depositing Cu atoms on one side of concave cubic Au seeds, the Cu part gradually grows larger as more Cu precursors are added, making the size tuning feasible in the range of 74-156 nm. When employed as an electrocatalyst for electrochemical CO₂ reduction (CO₂ RR), the Au-Cu Janus NSs display superior performance to Au@Cu core-shell NSs and Cu NPs in terms of C₂₊ products selectivity (67%) and C₂₊ partial current density (-0.29 A cm^-2 ). Combined experimental verification and theoretical simulations reveal that CO spillover from Au sites to the nearby Cu counterparts would enhance CO coverage and thus promote C-C coupling, highlighting the unique structural advantages of the Au-Cu Janus NSs toward deep reduction of CO₂ . The current work provides a facile strategy to fabricate tandem catalyst with a Janus structure and validates its structural advantages toward CO₂ RR, which are of critical importance for the rational design of efficient CO₂ RR catalyst.

Nanostructural synergism as MnNC channels in manganese (IV) oxide and fluffy g-C3N4 layered composite with exceptional catalytic capabilities

The avenues of catalysis and material science are always accepted and it is hoped that a state-of-the-art catalyst with exceptional intrinsic redox characteristics would be produced. This study focused on developing a multi-featured catalyst of high economical and commercial standards to meet the multi-directional applications of environmental and energy demands. Manganese (IV) oxide nanosheets made of fluffy-sheet-like g-C₃N₄ material were successfully synthesized by pyrolysis method. The electron-rich g-C₃N₄ network and semiconducting metallic oxides of MnO₂ nanosheets generated high electron density interfaces within the intra-composite structure. The input of active interfaces along with strong metal-to-support interactions achieved between two parallel nanosheets in MnO₂/g-C₃N₄ catalyst intrinsically boosted up its electrochemical and optical characteristics for it to be used in multi-catalytic fields. Successful trails of catalysts' performance have been made in three major catalytic fields with enhanced activities such as heterogeneous catalysis (reduction of nitrobenzene with rate constant of "K = 0.734 min^-1" and hydrogenation of styrene with "100% conversion" efficiency, including negligible change in five consecutive cycles), photocatalysis (degradation of methylene blue dye model within 20 min with negligible change in five consecutive cycles) and electrocatalysis (oxygen reduction reactions having comparable "diffusion-limited-current density" behaviour with that of the commercial Pt/C catalyst). The enhanced performance of catalysts in transforming chemicals, degrading organic pollutant species and producing sustainable energy resources from air oxygen can mitigate the challenges faced in environmental and energy crises, respectively.

Facile Synthesis of Platinum Right Bipyramids by Separating and Controlling the Nucleation Step in a Continuous Flow System

Colloidal synthesis of metal nanocrystals with controlled shapes and internal structures calls for a tight control over both the nucleation and growth processes. Here we report a method for the facile synthesis of Pt right bipyramids (RBPs) by separating nucleation from growth and controlling the nucleation step in a continuous flow reactor. Specifically, homogeneous nucleation was thermally triggered by introducing the reaction solution into a tubular flow reactor held at an elevated temperature to generate singly-twinned seeds. At a lower temperature, the singly-twinned seeds were protected from oxidative etching to allow their slow growth and evolution into RBPs while additional nucleation of undesired seeds could be largely suppressed to ensure RBPs as the main product. Further investigation indicated that the internal structure and growth pattern of the seeds were determined by the temperatures used for the nucleation and growth steps, respectively. The Br^- ions involved in the synthesis also played a critical role in the generation of RBPs by serving as a capping agent for the Pt{100} facets while regulating the reduction kinetics through coordination with the Pt(IV) ions.

In-situ loading synthesis of graphene supported PtCu nanocube and its high activity and stability for methanol oxidation reaction

A perfect PtCu nanocube with partial hollow structure was prepared by hydrothermal reaction and its electrocatalytic methanol oxidation reaction (MOR) was studied. The appropriate concentration of shape-control additives KI and triblock pluronic copolymers, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO₁₉-PPO₆₉-PEO₁₉) (P123) play crucial roles in the final product morphology. The PtCu nanocubes can be perfectly in situ immobilizedonto graphene under the action of P123 while the structure and cubic morphologyremain unchanged. The electrochemical tests suggest that the obtained PtCu nanocube (PtCu-NCb) exhibits better MOR activity and stability than PtCu hexagon nanosheet (PtCu-NSt), PtCu nanoellipsoid (PtCu-NEs) and commercial Pt/C in alkaline medium. When in situ immobilized onto graphene, the MOR catalytic activity and stability of PtCu cubes are further improved. The markedly enhanced electrocatalytic activity and durability maybe attributed to the special cubic morphology with partial hollow structure enclosed by highly efficient facet and the probably the synergistic effect of PtCu and intermediate state CuI decorated on the surface and graphene.

Platinum-Based Electrocatalysts for Direct Alcohol Fuel Cells: Enhanced Performances toward Alcohol Oxidation Reactions

In the past few decades, Pt-based electrocatalysts have attracted great interests due to their high catalytic performances toward the direct alcohol fuel cell (DAFC). However, the high cost, poor stability, and the scarcity of Pt have markedly hindered their large-scale utilization in commerce. Therefore, enhancing the activity and durability of Pt-based electrocatalysts, reducing the Pt amount and thus the cost of DAFC have become the keys for their practical applications. In this minireview, we summarized some basic concepts to evaluate the catalytic performances in electrocatalytic alcohol oxidation reaction (AOR) including electrochemical active surface area, activity and stability, the effective approaches for boosting the catalytic AOR performance involving size decrease, structure and morphology modulation, composition effect, catalyst supports, and assistance under other external energies. Furthermore, we also presented the remaining challenges of the Pt-based electrocatalysts to achieve the fabrication of a real DAFC.

Atomistic Imaging of Competition between Surface Diffusion and Phase Transition during the Intermetallic Formation of Faceted Particles

To explore the ordering mechanism of facet alloy nanocrystals with randomly distributed atoms, we investigate kinetic and thermodynamic behaviors of the ordering phase transition from face-centered cubic Pt₃Co nanocrystals to L1₂-Pt₃Co intermetallic nanocrystals. It is observed that the ordering occurs from the surface and then gradually into the interior in a layer-by-layer mode, involving the competition between two kinds of phase transition modes: long-range surface diffusion-induced phase transition (SDIPT) and short-range reconstruction-induced body phase transition (RIBPT). The density functional theory calculations demonstrate that the surface status acts as a pivotal part in the thermodynamics and kinetics of the nanoscale ordering transition. With the development of the controllable heating process, both SDIPT and RIBPT modes can be manipulated as well as the morphology of the final product. This in situ work lays the foundations for potentially realizing shape-controlled intermetallic nanostructures by utilizing the thermal annealing method and makes preparations for the rational design of the surface and near-surface atomic configurations at the atomic scale.

Molecular cluster route for the facile synthesis of a stable and active Pt nanoparticle catalyst

Molecular platinum clusters can be used for the synthesis of very small (ca. 1.5 nm) Pt nanoparticles with enhanced catalytic activity and stability towards the oxygen reduction reaction. The Pt–C interactions were characterized by TEM and EXAFS.

Fe-Doping induced divergent growth of Ni–Fe alloy nanoparticles for enhancing the electrocatalytic oxygen reduction

Separate (111)- and (200)-faceted Ni–Fe nanoparticles were synthesized and their oxygen reduction reaction activity studied via density functional theory calculations and experiments.

Anion-Modulated Platinum for High-Performance Multifunctional Electrocatalysis toward HER, HOR, and ORR

Efficient electrocatalyst toward hydrogen evolution/oxidation reactions (HER/HOR) and oxygen reduction reaction (ORR) is desirable for water splitting, fuel cells, etc. Herein, we report an advanced platinum phosphide (PtP2) material with only 3.5 wt % Pt loading embedded in phosphorus and nitrogen dual-doped carbon (PNC) layer (PtP2@PNC). The obtained catalyst exhibits robust HER, HOR, and ORR performance. For the HER, a much low overpotential of 8 mV is required to achieve the current density of 10 mA cm-2 compared with Pt/C (22 mV). For the HOR, its mass activity (MA) at an overpotential of 40 mV is 2.3-fold over that of the Pt/C catalyst. Interestingly, PtP2@PNC also shows exceptional ORR MA which is 2.6 times higher than that of Pt/C and has robust stability in alkaline solutions. Undoubtedly, this work reveals that PtP2@PNC can be employed as nanocatalysts with an impressive catalytic activity and stability for broad applications in electrocatalysis.

Carbon-supported Pd-Ir nanoalloys as cathodic catalyst for oxygen reduction reaction

Pd as cathodic catalyst exhibits relatively low current density in mixing kinetic/diffusion controlled region. To improve catalytic activity of Pd, alloying Pd with another transition metal is an effective approach. Here, we prepared carbon-supported Pd-Ir nanoalloys (Pd-Ir/C) through impregnation method. Four types of Pd-Ir/C were designed and referred as Pd19Ir/C, Pd9Ir/C, Pd3Ir/C, and PdIr/C using nominal Pd/Ir atomic ratios of 19:1, 9:1, 3:1, and 1:1, respectively. The results showed that Pd and Ir formed the nanoalloy structures and Pd-Ir/C exhibited significantly improved catalytic activity for oxygen reduction reaction than Pd/C, indicating that Ir had important effect on Pd-Ir nanoalloys.

Random alloy and intermetallic nanocatalysts in fuel cell reactions

Fuel cells that use small organic molecules or hydrogen as the anode fuel can power clean electric vehicles. From an experimental perspective, the possible fuel cells' electrocatalytic reaction mechanisms are obtained through in situ electrochemical spectroscopy techniques and density functional theory calculations, providing theoretical guidance for further development of novel nanocatalysts. As advanced nanocatalysts for fuel cells' electrochemical reactions, alloy nanomaterials have greatly improved electrocatalytic activity and stability and have attracted widespread attention. Enhanced electrocatalytic performance of alloy nanocatalysts could be closely related to the synergistic effects, such as electronic and strain effects. Depending on the arrangement of atoms, alloys can be classified into random alloy and intermetallic compounds (ordered structure). Intermetallic compounds generally have lower heats of formation and stronger heteroatomic bonding strength relative to the random alloy, resulting in high chemical and structural stability in either full pH solutions or electrochemical tests. Here, we summarize the latest advances and the structure-function relationship of noble metal alloy nanocatalysts, among which Pt-based catalysts are the main ones, as well as comprehensively understand why they significantly affect the electrocatalytic performance of fuel cells. Novel alloy nanocatalysts with a robust three-phase interface to achieve efficient charge and mass transfer can obtain desirable activity and stability in the electrochemical workstation tests, and is expected to acquire a higher power density on fuel cell test systems with harsh test conditions.

Novel Bi-Doped Amorphous SnOx Nanoshells for Efficient Electrochemical CO2 Reduction into Formate at Low Overpotentials

Engineering novel Sn-based bimetallic materials could provide intriguing catalytic properties to boost the electrochemical CO₂ reduction. Herein, the first synthesis of homogeneous Sn_{1- x} Bi_x alloy nanoparticles (x up to 0.20) with native Bi-doped amorphous SnO_x shells for efficient CO₂ reduction is reported. The Bi-SnO_x nanoshells boost the production of formate with high Faradaic efficiencies (>90%) over a wide potential window (-0.67 to -0.92 V vs RHE) with low overpotentials, outperforming current tin oxide catalysts. The state-of-the-art Bi-SnO_x nanoshells derived from Sn_0.80 Bi_0.20 alloy nanoparticles exhibit a great partial current density of 74.6 mA cm^-2 and high Faradaic efficiency of 95.8%. The detailed electrocatalytic analyses and corresponding density functional theory calculations simultaneously reveal that the incorporation of Bi atoms into Sn species facilitates formate production by suppressing the formation of H₂ and CO.

Nanocomposites of NiO/CuO Based MOF with rGO: An Efficient and Robust Electrocatalyst for Methanol Oxidation Reaction in DMFC

In this work a novel bimetallic nickel oxide/copper oxide metal–organic framework (NiO/CuO MOF) has been developed by using two linkers: Benzene Dicarboxylic acid (BDC) and Pyrazine. The composites of NiO/CuO MOF with different amounts of reduced graphene oxide (rGO) were synthesized through a hydrothermal method and subsequently characterized by multiple significant techniques like XRD, SEM, EDX, FTIR and Raman IR for an investigation of their structural and morphological properties. The prepared series of material was later employed for electrochemical oxidation of methanol, tested by cyclic voltammetry (CV) in basic medium on a modified glassy carbon electrode (GCE). The electrochemical response depicts that increasing concentration of rGO enhances the electrocatalytic activity of the catalyst for methanol oxidation reaction (MOR). The catalyzed oxidation reaction of methanol by NiO/CuO MOF and rGO-NiO/CuO MOF composites give a superlative current density of 437. 28 mA/cm² at 0.9 V potential at 50 mV/s scan rate. This activity makes it a promising catalytic material for electrolysis of methanol in direct methanol fuel cell (DMFC).

Co-doped Pt Nanowire Networks with Clean Surfaces for Enhanced Oxygen Reduction Reactions

Surfactants or capping agents are usually employed to control the shapes and sizes of metal nanowires (NWs). Polyvinylpyrrolidone (PVP) and oleylamine (OAm) are the most common capping agents used in the synthesis of metal nanowires. However, these capping agents bind strongly onto the surface of the nanowires and severely prevent the reactant molecules from entering the active sites. In the present research, a facile acetic acid/NaBH₄ treatment technology is reported to effectively remove PVP and OAm from the surface of the co-doped Pt NWs. Interestingly, the morphology of poor crystalline platinum nanowires treated with NaBH₄ solution is transformed into nanowire networks (NWNs) with higher crystallinity. Furthermore, in comparison with the commercial Pt/C catalyst, the catalytic activity of co-doped Pt NWNs with clean surfaces shows improvements of up to 4.1 times for mass activity and 5.1 times for specific activity, respectively.

High quality electrocatalyst by Pd-Pt alloys nanoparticles uniformly distributed on polyaniline/carbon nanotubes for effective methanol oxidation

In the present work, Pd-Pt nanoparticle/polyaniline/carbon nanotube (NP/PANI/CNT) composites, synthesized through the uniform distribution of Pd-Pt NPs, whose single size was controlled to 2-4 nm by citric acid, on a PANI/CNT compound, served as the electrode catalysts for effective methanol oxidation. The structural characteristics were identified by x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy, and revealed that the Pt₆₅Pd₃₅ NP/PANI/CNT composite displayed superior electrocatalytic oxidation performance and vitality in various Pd-Pt NPs. The results indicated that as an excellent anode catalyst the complex would have application prospects for effective methanol oxidation.

High-Performance Pt-Co Nanoframes for Fuel-Cell Electrocatalysis

Pt-based alloy catalysts are promising candidates for fuel-cell applications, especially for cathodic oxygen reduction reaction (ORR) and anodic methanol oxidation reaction (MOR). The rational design of composition and morphology is crucial to promoting catalytic performances. Here, we report the synthesis of Pt-Co nanoframes via chemical etching of Co from solid rhombic dodecahedra. The obtained Pt-Co nanoframes exhibit excellent ORR mass activity in acidic electrolyte, which is as high as 0.40 A mg_Pt^-1 initially and 0.34 A mg_Pt^-1 after 10 000 potential cycles at 0.95 V_RHE. Furthermore, their MOR mass activity in alkaline media is up to 4.28 A mg_Pt^-1 and is 4-fold higher than that of commercial Pt/C catalyst. Experimental studies indicate that the weakened binding of intermediate carbonaceous poison contributes to the enhanced MOR behavior. More impressively, the Pt-Co nanoframes also demonstrate remarkable stability under long-term testing, which could be attributed to the negligible electrochemical Co dissolution.

Ultrathin Film PtxPd(1-x) Alloy Catalysts for Formic Acid Oxidation Synthesized by Surface Limited Redox Replacement of Underpotentially Deposited H Monolayer

This work emphasizes the development of a green synthetic approach for growing ultrathin film PtxPd(1-x) alloy catalysts for formic acid oxidation (FAO) by surface limited redox replacement of underpotentially deposited H sacrificial layer. Up to three-monolayers-thick PtxPd(1-x) films with different composition are generated on Au electrodes and characterized for composition and surface roughness using XPS and electrochemical methods, respectively. XPS results show close correlation between solution molar ratio and atomic composition, with slightly higher Pt fraction in the deposited films. The accordingly deposited Pt42Pd58 films demonstrated remarkable specific and mass activities of up to 35 mAcm−2 and 45 Amg−1 respectively, lasting for more than 1500 cycles in FAO tests. This performance, found to be better twice or more than that of pure Pt counterparts, renders the Pt42Pd58 films comparable with the frontrunner FAO catalysts. In addition, the best alloy catalyst establishes a nearly hysteresis-free FAO CV curve a lot earlier than its Pt counterpart and thus supports the direct FAO pathway for longer. Overall, the combination of high Pd activity and CO tolerance with the remarkable Pt stability results in highly active and durable FAO catalysts. Finally, this facile and cost-effective synthetic approach allows for scaling the catalyst production and is thus appropriate for foreseeable commercialization.

Preserving the Exposed Facets of Pt3Sn Intermetallic Nanocubes During an Order to Disorder Transition Allows the Elucidation of the Effect of the Degree of Alloy Ordering on Electrocatalysis

Controlling which facets are exposed in nanocrystals is crucial to understanding different activity between ordered and disordered alloy electrocatalysts. We modify the degree of ordering of Pt₃Sn nanocubes, while maintaining the shape and size, to enable a direct evaluation of the effect of the order on ORR catalytic activity. We demonstrate a 2.3-fold enhancement in specific activity by 60- and 30%-ordered Pt₃Sn nanocubes compared to 95%-ordered. This was shown to be likely due to surface vacancies in the less-ordered particles. The greater order, however, results in higher stability of the electrocatalyst, with the more disordered nanoparticles showing the dissolution of tin and platinum species during electrocatalysis.

Recent Advances in Noble Metal (Pt, Ru, and Ir)-Based Electrocatalysts for Efficient Hydrogen Evolution Reaction

Noble metal (Pt, Ru, and Ir)-based electrocatalysts are currently considered the most active materials for the hydrogen evolution reaction (HER). Although they have been associated with high cost, easy agglomeration, and poor stability during the HER reaction, recent efforts to intentionally tailor noble-metal-based catalysts have led to promising improvements, with lower cost and superior activity, which are critical to achieving large-scale production of pure hydrogen. In this mini-review, we focus on the recent advances in noble-metal-based HER electrocatalysts. In particular, the synthesis strategies to enhance cost-effectiveness and the catalytic activity for HER are highlighted.

Facile synthesis of clean PtAg dendritic nanostructures with enhanced electrochemical properties

PtAg dendritic nanocrystals were synthesized by a one-step and surfactant-free route and exhibited excellent activities in both MOR and ORR.

Degradation of the transition metal@Pt core–shell nanoparticle catalyst: a DFT study

Electrocatalysts in acidic media face the issues of inactivation and degradation with complex thermodynamic processes.