Facile Synthesis of Porous Dendritic Bimetallic Platinum-Nickel Nanocrystals as Efficient Catalysts for the Oxygen Reduction Reaction

Catalysis Sans Catalyst Loss: The Origins of Prolonged Stability of Graphene-Metal-Graphene Sandwich Architecture for Oxygen Reduction Reactions

Over the past decades, the design of active catalysts has been the subject of intense research efforts. However, there has been significantly less deliberate emphasis on rationally designing a catalyst system with a prolonged stability. A major obstacle comes from the ambiguity behind how catalyst degrades. Several degradation mechanisms are proposed in literature,   but with a lack of systematic studies, the causal relations between degradation and those proposed mechanisms remain ambiguous. Here, a systematic study of a catalyst system comprising of small particles and single atoms of Pt sandwiched between graphene layers, GR/Pt/GR, is studied to  unravel the degradation mechanism of the studied electrocatalyst for oxygen reduction reaction(ORR). Catalyst suffers from atomic dissolution under ORR harsh acidic and oxidizing operation voltages. Single atoms trapped in point defects within the top graphene layer on their way hopping through toward the surface of GR/Pt/GR architecture. Trapping mechanism renders individual Pt atoms as single atom catalyst sites catalyzing ORR for thousands of cycles before washed away in the electrolyte. The GR/Pt/GR catalysts also compare favorably to state-of-the-art commercial Pt/C catalysts and demonstrates a rational design of a hybrid nanoarchitecture with a prolonged stability for thousands of operation cycles.

Unraveling ultrasonic assisted aqueous-phase one-step synthesis of porous PtPdCu nanodendrites for methanol oxidation with a CO-poisoning tolerance

The tailored design of tri-metallic Pt-based porous nanodendrites (PNDs) is crucial for green energy production technologies, ascribed to their fancy features, great surface areas, accessible active sites, and stability against aggregation. However, their aqueous-phase one-step synthesis at room temperature remains a daunting challenge. Herein, we present a facile, green, and template-free approach for the one-step synthesis of PtPdCu PNDs by ultrasonication of an aqueous solution of metal salts and Pluronic F127 at 25 ℃, based on natural isolation among nucleation and growth step driven by the disparate reduction kinetics of the metals and acoustic cavitation mechanism of ultrasonic waves. The resultant PtPdCu PNDs formed in a spatial nanodendritic shape with a dense array of branches, open corners, interconnected pores, high surface area (46.9 m²/g), and high Cu content (21 %). The methanol oxidation reaction (MOR) mass activity of PtPdCu PNDs (3.66 mA/µg_Pt) is 1.45, 2.73, and 2.83 times higher than those of PtPd PNDs, PtCu PNDs, and commercial Pt/C, respectively based on equivalent Pt mass, which is superior to previous PtPdCu catalysts reported elsewhere, besides a superior durability and CO-poisoning tolerance. This study may pave the way for the controlled fabrication of ternary Pt-based PNDs for various electrocatalytic applications.

One-pot production of a sea urchin-like alloy electrocatalyst for the oxygen electro-reduction reaction

Designing a cost-effective catalyst with high performance towards the oxygen electro-oxidation reaction (ORR) is of great interest for the development of green energy storage and conversion technologies. We report herein a facile self-assembly strategy in a mild reducing environment to realize an urchin-like NiPt bimetallic alloy with the domination of the (111) facets as an efficient ORR electrocatalyst. In the rotating-disk electrode test, the as-obtained NiPt nanourchins (NUCs)/C catalyst demonstrates an increase in both onset potential (0.96 V_RHE) and half-wave potential (0.92 V_RHE) and a direct four-electron ORR pathway with enhanced reaction kinetics. Additionally, the as-made NiPt NUCs/C electrocatalyst also shows impressive ORR catalytic stability compared to a commercial Pt NPs/C catalyst after an accelerated durability test with 15.29% degradation in mass activity, which is 3.04-times lower than 46.48% of the Pt NPs/C catalyst. The great ORR performance of the as-made catalyst is due to its unique urchin-like morphology with the dominant (111) facets and the synergistic and electronic effects of alloying Ni and Pt. This study not only provides a robust ORR electrocatalyst, but also opens a facile but effective route for fabricating 3D Pt-based binary and ternary alloy catalysts.

De-alloyed PtCu/C catalysts with enhanced electrocatalytic performance for the oxygen reduction reaction

In electrochemical reactions, interactions between reaction intermediates and catalytic surfaces control the catalytic activity, and thereby require to be optimized. Electrochemical de-alloying of mixed-metal nanoparticles is a promising strategy to modify catalysts' surface chemistry and/or induce lattice strain to alter their electronic structure. Perfect design of the electrochemical de-alloying strategy to modify the catalyst's d-band center position can yield significant improvement on the catalytic performance of the oxygen reduction reaction (ORR). Herein, carbon supported PtCu catalysts are prepared by a simple polyol method followed by an electrochemical de-alloying treatment to form PtCu/C catalysts with a Pt-enriched porous shell with improved catalytic activity. Although the pristine PtCu/C catalyst exhibits a mass activity of 0.64 A mg^-1_Pt, the dissolution of Cu atoms from the catalyst surface after electrochemical de-alloying cycling leads to a significant enhancement in mass activity (1.19 A mg^-1_Pt), which is 400% better than that of state-of-the-art commercial Pt/C (0.24 A mg^-1_Pt). Furthermore, the de-alloyed PtCu/C-10 catalyst with a Pt-enriched shell delivers prolonged stability (loss of only 28.6% after 30 000 cycles), which is much better than that of Pt/C with a loss of 45.8%. By virtue of scanning transmission electron microscopy and elemental mapping experiments, the morphology and composition evolution of the catalysts could clearly be elucidated. This work helps in drawing a roadmap to design highly active and stable catalyst platforms for the ORR and relevant proton exchange membrane fuel cell applications.

Catalytic Methane Decomposition to Carbon Nanostructures and COx-Free Hydrogen: A Mini-Review

Catalytic methane decomposition (CMD) is a highly promising approach for the rational production of relatively CO_x-free hydrogen and carbon nanostructures, which are both important in multidisciplinary catalytic applications, electronics, fuel cells, etc. Research on CMD has been expanding in recent years with more than 2000 studies in the last five years alone. It is therefore a daunting task to provide a timely update on recent advances in the CMD process, related catalysis, kinetics, and reaction products. This mini-review emphasizes recent studies on the CMD process investigating self-standing/supported metal-based catalysts (e.g., Fe, Ni, Co, and Cu), metal oxide supports (e.g., SiO₂, Al₂O₃, and TiO₂), and carbon-based catalysts (e.g., carbon blacks, carbon nanotubes, and activated carbons) alongside their parameters supported with various examples, schematics, and comparison tables. In addition, the review examines the effect of a catalyst’s shape and composition on CMD activity, stability, and products. It also attempts to bridge the gap between research and practical utilization of the CMD process and its future prospects.

Unveiling One-Pot Template-Free Fabrication of Exquisite Multidimensional PtNi Multicube Nanoarchitectonics for the Efficient Electrochemical Oxidation of Ethanol and Methanol with a Great Tolerance for CO

Multidimensional bimetallic Pt-based nanoarchitectonics are highly promising in electrochemical energy conversion technologies because of their fancy structural merits and accessible active sites; however, hitherto their precise template-free fabrication remains a great challenge. We report a template-free solvothermal one-pot approach for the rational design of cocentric PtNi multicube nanoarchitectonics via adjusting the oleylamine/oleic acid ratio with curcumin. The obtained multidimensional PtNi multicubes comprise multiple small interlace-stacked nanocube subunits assembled in spatially porous branched nanoarchitectonics and bound by high-index facets. The synthetic mechanism is driven by spontaneous isolation among prompt nucleation and oriented attachment epitaxial growth. These inimitable architectural and compositional merits of PtNi multicubes endowed the ethanol oxidation mass and specific activity by 5.6 and 9.03 times than the Pt/C catalyst, respectively, along with the enhancement of methanol oxidation mass activity by 2.3 times. Moreover, PtNi multicubes showed superior durability and a higher tolerance for CO poisoning than the Pt/C catalyst. This work may pave the way for tailored preparation of Pt-based nanoarchitectonics for myriad catalytic reactions.

Modern Chemical Routes for the Controlled Synthesis of Anisotropic Bimetallic Nanostructures and Their Application in Catalysis

Bimetallic nanoparticles (BNPs) have attracted greater attention compared to its monometallic counterpart because of their chemical/physical properties. The BNPs have a wide range of applications in the fields of health, energy, water, and environment. These properties could be tuned with a number of parameters such as compositions of the bimetallic systems, their preparation method, and morphology. Monodisperse and anisotropic BNPs have gained considerable interest and numerous efforts have been made for the controlled synthesis of bimetallic nanostructures (BNS) of different sizes and shapes. This review offers a brief summary of the various synthetic routes adopted for the synthesis of Palladium(Pd), Platinum(Pt), Nickel(Ni), Gold(Au), Silver(Ag), Iron(Fe), Cobalt(Co), Rhodium(Rh), and Copper(Cu) based transition metal bimetallic anisotropic nanostructures, growth mechanisms e.g., seed mediated co-reduction, hydrothermal, galvanic replacement reactions, and antigalvanic reaction, and their application in the field of catalysis. The effect of surfactant, reducing agent, metal precursors ratio, pH, and reaction temperature for the synthesis of anisotropic nanostructures has been explained with examples. This review further discusses how slight modifications in one of the parameters could alter the growth mechanism, resulting in different anisotropic nanostructures which highly influence the catalytic activity. The progress or modification implied in the synthesis techniques within recent years is focused on in this article. Furthermore, this article discussed the improved activity, stability, and catalytic performance of BNS compared to the monometallic performance. The synthetic strategies reported here established a deeper understanding of the mechanisms and development of sophisticated and controlled BNS for widespread application.

Unraveling template-free fabrication of carbon nitride nanorods codoped with Pt and Pd for efficient electrochemical and photoelectrochemical carbon monoxide oxidation at room temperature

The tailored synthesis of carbon nitrides (CNs) is of particular interest in multidisciplinary catalytic applications. However, their fabrication in the form of one-dimensional (1D) nanorods for electrocatalytic carbon monoxide (CO) oxidation is not hitherto reported. Herein, a facile roadmap is presented for the rational design of Pt- and Pd-codoped CN (PtPd/CNs) nanorods via protonation of melamine in an ethylene glycol solution containing Pt and Pd precursors using NaNO3 and HCl and subsequent annealing. The protonation induces the polymerization of melamine to melon nanosheets that consequently roll up to CN nanorods. This tailored the prompt high mass production of uniform 1D CN nanorods (94 ± 2 nm) with a high surface area (155.2 m2 g-1) and they were atomically codoped with Pt and Pd (1.5 wt%) without a template and/or multiple complicated steps. The electrocatalytic CO oxidation activity of PtPd/CNs is 2.01 and 23.41 times greater than that of the commercial Pt/C catalyst and metal-free CNs, respectively, at room temperature. Meanwhile, the UV-vis light irradiation enhanced the CO oxidation activity of PtPd/CNs nanorods by 1.48 fold compared to that in the dark, emanated from the coupling between the drastic inbuilt catalytic merits of PtPd and the inimitable physicochemical properties of CNs. The presented study may pave the way for using CN-based materials in gas conversion reactions.

Trimetallic PtPdNi-Truncated Octahedral Nanocages with a Well-Defined Mesoporous Surface for Enhanced Oxygen Reduction Electrocatalysis

Engineering the architectures and compositions of noble metal-based nanocrystals is an effective strategy to optimize their catalytic performance. Herein, we report the synthesis of unique trimetallic PtPdNi mesoporous-truncated octahedral nanocages (PtPdNi MTONs), which is simply performed by first constructing Pd@PtPdNi core-shell mesoporous truncated octahedra (Pd@PtPdNi MTOs) and further selective etching of the Pd cores using concentrated nitric acid. The rational combinations of polyhedral shape, mesoporous surface, and hollow structure provide sufficiently exposed active sites and efficient reactant permeability. With these unique properties, the PtPdNi MTONs show improved catalytic activity and stability toward the oxygen reduction reaction.

Facile solvothermal synthesis of Pt71Co29 lamellar nanoflowers as an efficient catalyst for oxygen reduction and methanol oxidation reactions

The research for highly efficient and stable electrocatalysts in fuel cells has attracted substantial interest. Herein, bimetallic alloyed Pt₇₁Co₂₉ lamellar nanoflowers (LNFs) with abundant active sites were obtained by a one-pot solvothermal method, where cetyltrimethylammonium chloride (CTAC) and 1-nitroso-2-naphthol (1-N-2-N) served as co-structure-directors, while oleylamine (OAm) as the solvent and reducing agent. The fabricated Pt₇₁Co₂₉ LNFs exhibited the higher mass activity (MA, 128.29 mA mg^-1) for oxygen reduction reaction (ORR) than those of home-made Pt₄₈Co₅₂ nanodendrites (NDs), Pt₇₉Co₂₁ NDs and commercial Pt black with the values of 39.46, 49.42 and 22.91 mA mg^-1, respectively. Meanwhile, the MA (666.23 mA mg^-1) and specific activity (SA, 2.51 mA cm^-2) of the constructed Pt₇₁Co₂₉ LNFs for methanol oxidation reaction (MOR) are superior than those of Pt₄₈Co₅₂ NDs (213.91 mA mg^-1, 1.99 mA cm^-2), Pt₇₉Co₂₁ NDs (210.09 mA mg^-1, 1.12 mA cm^-2) and Pt black (57.03 mA mg^-1, 0.25 mA cm^-2). Also, the Pt₇₁Co₂₉ LNFs catalyst exhibited the best durable ability relative to the references. This work demonstrates that the developed strategy provides a facile platform for synthesis of high-performance, low-cost and robust catalysts in practical catalysis, energy storage and conversion.

One-step fabrication of bimetallic PtNi mesoporous nanospheres as an efficient catalyst for the oxygen reduction reaction

The controlled synthesis of Pt-based bimetallic porous nanostructures is highly important for the design of electrocatalysts with high performance. Herein, we report a one-step method for the direct synthesis of well-dispersed bimetallic PtNi mesoporous nanospheres (PtNi MNs) at high yield. Benefitting from the synergistic effect of composition (bimetallic PtNi) and structure (mesoporous and highly open structure), the as-obtained PtNi MNs exhibit superior catalytic activity and stability for the oxygen reduction reaction.

Bimetallic Platinum-Rhodium Alloy Nanodendrites as Highly Active Electrocatalyst for the Ethanol Oxidation Reaction

Rationally designing and manipulating composition and morphology of precious metal-based bimetallic nanostructures can markedly enhance their electrocatalytic performance, including selectivity, activity, and durability. We herein report the synthesis of bimetallic PtRh alloy nanodendrites (ANDs) with tunable composition by a facile complex-reduction synthetic method under hydrothermal conditions. The structural/morphologic features, formation mechanism, and electrocatalytic performance of PtRh ANDs are investigated thoroughly by various physical characterization and electrochemical methods. The preformed Rh crystal nuclei effectively catalyze the reduction of Pt²⁺ precursor, resulting in PtRh alloy generation due to the catalytic growth and atoms interdiffusion process. The Pt atoms deposition distinctly interferes in Rh atoms deposition on Rh crystal nuclei, resulting in dendritic morphology of PtRh ANDs. For the ethanol oxidation reaction (EOR), PtRh ANDs display the chemical composition and solution pH co-dependent electrocatalytic activity. Because of the alloy effect and particular morphologic feature, Pt₁Rh₁ ANDs with optimized composition exhibit better reactivity and stability for the EOR than commercial Pt nanocrystals electrocatalyst.

Rational one-step synthesis of porous PtPdRu nanodendrites for ethanol oxidation reaction with a superior tolerance for CO-poisoning

Precise fabrication of porous ternary Pt-based nanodendrites is very important for electrochemical energy conversion owing to high surface area and great molecular accessibility of these nanodendrites. Herein, PtPdRu porous nanodendrites (PNDs) were prepared via a facile one-step ultrasonic irradiation approach at room temperature. Intriguingly, the ultrasonic irradiation drove the formation of PtPdRu PNDs with spatially interconnected porous structures, whereas magnetic stirring produced PtPdRu nanoflowers (NFs) with less porosity. The formation mechanism was ascribed to the acoustic cavitation effect and fast-reduction kinetics under sonication. The as-made PtPdRu PNDs displayed a superior catalytic performance towards ethanol oxidation reaction with a high tolerance for CO-poisoning as compared to PtPdRu NFs, PtPd NDs, and commercial Pt/C catalyst.

One-pot synthesis of PtRu nanodendrites as efficient catalysts for methanol oxidation reaction

Bimetallic Pt-based nanodendrites are of particular interest in various catalytic applications due to their high surface areas and low densities. Herein, we provide a facile method for one-pot synthesis of PtRu nanodendrites via the co-reduction of Pt and Ru precursors in oleylamine by H₂. The as-fabricated PtRu nanodendrites exhibit superior catalytic activity and durability compared with PtRu nanocrystals (NCs), synthesized under the same reaction conditions, and the commercial Pt/C catalyst towards the methanol oxidation reaction (MOR).

Rational design of porous binary Pt-based nanodendrites as efficient catalysts for direct glucose fuel cells over a wide pH range

Porous binary PtPd, AuPt, PtCu, and PtNi nanodendrites prepared by a facile one-step reduction under ultrasonic irradiation at room temperature, exhibited a substantial catalytic activity towards glucose oxidation reaction at different pH values relative to a commercial Pt/C catalyst.