Evolution of nanoscale amorphous, crystalline and phase-segregated PtNiP nanoparticles and their electrocatalytic effect on methanol oxidation reaction

Rich-grain-boundary Ni-Co-Se nanowire arrays for fast charge storage in alkaline electrolyte

In this work, the one-dimensional (1D) Ni-Co-Se nanowire arrays with rich grain-boundaries were prepared through the solvothermal method and gas-phase selenizaiton. The results showed that the structure and crystallization of the Ni-Co-Se nanowire arrays could be modulated through the optimization of selenizaiton time. The optimal Ni-Co-Se electrode sample displayed an area specific capacitance of 242.6μAh cm-2at 30 mA cm-2with a current retention rate of 68.34%. The assembled Ni-Co-Se/Active carbon (AC) electrode-based asymmetric supercapacitor (ASC) showed the area specific capacitances of 329.2μAh cm-2and 225.8μAh cm-2at 3 mA cm-2and 30 mA cm-2, respectively. A 73.33% retention rate of capacitance was observed after 8000 charge/discharge cycles. Besides, the further fabricated all-solid ASC delivered the power densities of 342.94 W kg-1and 3441.33 W kg-1at the energy densities of 37.62 Wh kg-1and 25.81 Wh kg-1, respectively. Those results suggested the potentials of the obtained Ni-Co-Se nanowire arrays as electrode material for the high-performance pseudocapacitors.

Understanding the Copper-Iridium Nanocrystals as Highly Effective Bifunctional pH-universal Electrocatalysts for Water Splitting

It is pivotal to develop an economical, effective, and stable catalyst to promote the oxygen/hydrogen evolution reaction (OER/HER) throughout pH electrolytes, as the demand for hydrogen energy will increase greatly with the future development. Herein, a series of Ir-Cu nanoparticle composite carbon (Ir_xCu_y/C) catalysts are successfully synthesized using ethylene glycol reduction. In addition, the structure, morphology and composition of the electrocatalysts were systematically characterized, and the OER/HER performance of the catalysts was also tested under different pH conditions. According to experimental findings, amorphous Ir₃Cu/C has superior competent performance to catalyze oxygen (O₂) production in alkaline and acidic environments. The comparatively low overpotentials required are 222 mV and 304 mV, respectively, while generating a current density of 10 mA cm^-2. The reduced amount of precious metal and the further improvement in activity and durability make Ir₃Cu/C an excellent noble metal-based electrocatalyst. Meanwhile, IrCu/C has significant electrocatalytic performance for the HER in acidic media.

Amorphous RuCoP Ultrafine Nanoparticles Supported on Carbon as Efficient Catalysts for Hydrogenation of Adipic Acid to 1,6-Hexanediol

As an important raw material for organic synthesis, the 1,6-hexanediol (HDOL) is synthesized by the complicated two-step process traditionally. The hydrogenation of adipic acid (AA) is a potential way to prepare 1,6-hexanediol. At present, amorphous RuMP (M: Co, Ni, Fe, etc.)-based alloys with low Ru content were developed by co-precipitation as the efficient catalysts for converting AA to HDOL via hydrogenation. Among these RuMP catalysts, RuCoP alloys exhibited the highest selectivity and yield to HDOL owing to the electronic effect. The selectivity and yield of HDOL for the optimized RuCoP/C sample was achieved to 80% and 64%, respectively, at 65 bar and 220 °C. A series of RuCoP alloys with different degrees of crystallinity and particle sizes were prepared to investigate the effect of morphology and structure on its catalytic performance. The results indicated that the high catalytic activity of RuCoP/C resulted from its rich active sites due to its amorphous phase and small particle size.

Adjusting grain boundary within NiCo2O4rod arrays by phosphating reaction for efficient hydrogen production

In this work, the density and electronic structures of the metal active sites in NiCo₂O₄nanorod arrays were concurrently tuned by controlling the sample's exposure time in a phosphorization process. The results showed that both the density and electronic structure of the active adsorption sites played a key role towards the catalytic activity for water splitting to produce hydrogen. The optimal catalyst exhibited 81 mV overpotential for hydrogen evolution reaction (HER) at 10 mA cm^-2and 313 mV overpotential towards oxygen evolution reaction at 50 mA cm^-2. The assembled electrode delivered a current density of 50 mA cm^-2at 1.694 V in a fully functional water electrolyzer. The further results of theoretical density functional theory calculations revealed the doping of P elements lowered down the H adsorption energies involved in the water splitting process on the various active sites of P-NiCo₂O₄-10 catalyst, and thus enhanced its HER catalytic activities.

Micro-controlling of the grain boundaries in NiCo2O4/NiCo2S4 nanowires for enhanced charge storage

In this work, the micro-controlling of the grain boundaries in NiCo₂O₄/NiCo₂S₄ nanowire arrays was achieved by exposing them to a sulfur containing atmosphere at 300 °C with different exposure times. The results showed that the capacitance of the optimal NiCo₂S₄ sample reached 400 μA h cm^-2 at 30 mA cm^-2 with a current retention rate of 58.6%. The assembled NiCo₂O₄/NiCo₂S₄//activate carbon electrode delivered a capacitance of 299.2 μA h cm^-2 and 241.7 μA h cm^-2 at a current density of 3 mA cm^-2 and 30 mA cm^-2, respectively. The cycling tests showed a good current retention rate of 88.1% after 8000 cycles. Besides, the NiCo₂O₄/NiCo₂S₄ composite exhibited a power density of 480.1 W kg^-1 at an energy density of 47.87 W h kg^-1, and 4773.66 W kg^-1 at 38.67 W h kg^-1, which indicated its potential for practical applications.

Surfactant-Free Synthesis of Three-Dimensional Perovskite Titania-Based Micron-Scale Motifs Used as Catalytic Supports for the Methanol Oxidation Reaction

We synthesized and subsequently rationalized the formation of a series of 3D hierarchical metal oxide spherical motifs. Specifically, we varied the chemical composition within a family of ATiO3 (wherein "A" = Ca, Sr, and Ba) perovskites, using a two-step, surfactant-free synthesis procedure to generate structures with average diameters of ~3 microns. In terms of demonstrating the practicality of these perovskite materials, we have explored their use as supports for the methanol oxidation reaction (MOR) as a function of their size, morphology, and chemical composition. The MOR activity of our target systems was found to increase with decreasing ionic radius of the "A" site cation, in order of Pt/CaTiO3 (CTO) > Pt/SrTiO3 (STO) > Pt/BaTiO3 (BTO). With respect to morphology, we observed an MOR enhancement of our 3D spherical motifs, as compared with either ultra-small or cubic control samples. Moreover, the Pt/CTO sample yielded not only improved mass and specific activity values but also a greater stability and durability, as compared with both commercial TiO2 nanoparticle standards and precursor TiO2 templates.

Mechanochemically Synthetized PAN-Based Co-N-Doped Carbon Materials as Electrocatalyst for Oxygen Evolution Reaction

We report a new class of polyacrylonitrile (PAN)-based Co-N-doped carbon materials that can act as suitable catalyst for oxygen evolution reactions (OER). Different Co loadings were mechanochemically added into post-consumed PAN fibers. Subsequently, the samples were treated at 300 °C under air (PAN-A) or nitrogen (PAN-N) atmosphere to promote simultaneously the Co₃O₄ species and PAN cyclization. The resulting electrocatalysts were fully characterized and analyzed by X-ray diffraction (XRD) and photoelectron spectroscopy (XPS), transmission (TEM) and scanning electron (SEM) microscopies, as well as nitrogen porosimetry. The catalytic performance of the Co-N-doped carbon nanomaterials were tested for OER in alkaline environments. Cobalt-doped PAN-A samples showed worse OER electrocatalytic performance than their homologous PAN-N ones. The PAN-N/3% Co catalyst exhibited the lowest OER overpotential (460 mV) among all the Co-N-doped carbon nanocomposites, reaching 10 mA/cm². This work provides in-depth insights on the electrocatalytic performance of metal-doped carbon nanomaterials for OER.

Phase engineering of nanomaterials

Phase has emerged as an important structural parameter - in addition to composition, morphology, architecture, facet, size and dimensionality - that determines the properties and functionalities of nanomaterials. In particular, unconventional phases in nanomaterials that are unattainable in the bulk state can potentially endow nanomaterials with intriguing properties and innovative applications. Great progress has been made in the phase engineering of nanomaterials (PEN), including synthesis of nanomaterials with unconventional phases and phase transformation of nanomaterials. This Review provides an overview on the recent progress in PEN. We discuss various strategies used to synthesize nanomaterials with unconventional phases and induce phase transformation of nanomaterials, by taking noble metals and layered transition metal dichalcogenides as typical examples. Moreover, we also highlight recent advances in the preparation of amorphous nanomaterials, amorphous-crystalline and crystal phase-based hetero-nanostructures. We also provide personal perspectives on challenges and opportunities in this emerging field, including exploration of phase-dependent properties and applications, rational design of phase-based heterostructures and extension of the concept of phase engineering to a wider range of materials.

Constructing Patch-Ni-Shelled Pt@Ni Nanoparticles within Confined Nanoreactors for Catalytic Oxidation of Insoluble Polysulfides in Li-S Batteries

Reducing the deposit of discharge products and suppressing the polysulfide shuttle are critical to enhancing reaction kinetics in Li-S batteries. Herein, a Pt@Ni core-shell bimetallic catalyst with a patch-like or complete Ni shell based on a confined catalysis reaction in porous carbon spheres is reported. The Pt nanodots can effectively direct and catalyze in situ reduction of Ni²⁺ ions to form core-shell catalysts with a seamless interface that facilitates the charge transfer between the two metals. Thus, the bimetallic catalysts offer a synergic effect on catalyzing reactions, which shows dual functions for catalytic oxidation of insoluble polysulfides to soluble polysulfides by effectively reducing the energy barrier with simultaneous strong adsorption, ensuring a high reversible capacity and cycling stability. A novel process based on the Pt@Ni core-shell bimetallic catalyst with a patch-like Ni shell is proposed: electronic migration from Ni to Pt forces Ni to activate Li₂ S₂ /Li₂ S molecules by promoting the transformation of Li-S-Li to Ni-S-Li, consequently releasing Li⁺ and free electrons, simultaneously enhancing protonic/electronic conductivity. The presence of the intermediate state Ni-S-Li is more active to oxidize Li₂ S to polysulfides. The Li₂ S bound to adjacent Pt sites reacts with abundant -S-Li species and then releases the Pt sites for the next round of reactions.

Unique Ni Crystalline Core/Ni Phosphide Amorphous Shell Heterostructured Electrocatalyst for Hydrazine Oxidation Reaction of Fuel Cells

It is highly attractive but challenging to develop transition-metal electrocatalysts for direct hydrazine fuel cells (DHzFCs). In this work, a nickel crystalline core@nickel phosphide amorphous shell heterostructured electrocatalyst supported by active carbon (Ni@NiP/C) is developed. Ni@NiP/C with a P/Ni molar ratio of 3:100, Ni@NiP_3.0/C, exhibits outstanding catalytic activity for the hydrazine oxidation reaction (HzOR) in alkaline solution, achieving a much better catalytic activity (2675.1 A g_Ni^-1@0.25 V vs RHE) and high stability, as compared to Ni nanoparticles supported on carbon (Ni/C) and Pt/C catalysts. The results indicate that formation of the NiP amorphous shell effectively inhibits the passivation of the Ni core active sites and enhances the adsorption of hydrazine on Ni by improving the adsorption energy, leading to high electrochemical activity and stability of the Ni@NiP_3.0/C catalysts for HzOR. The density functional theory calculation confirms the structural and electrocatalytic effect of the core-shell heterostructure on the stability and activity of Ni active sites for HzOR. The unique crystalline core/amorphous shell-structured Ni@NiP/C demonstrates promising potential as an effective electrocatalyst for DHzFCs.

Coupling Ultrafine Pt Nanocrystals over the Fe2P Surface as a Robust Catalyst for Alcohol Fuel Electro-Oxidation

Ultrafine Pt nanocrystals with an average particle size of 2.2 ± 1 nm coupled over the petaloid Fe₂P surface are proposed as a novel, efficient, and robust catalyst for alcohol fuel electro-oxidation. The strong coupling effect of metal-support imparts a strong electronic interaction between the Fe₂P and Pt interface that can weaken the adsorption of poisoning CO species according to the d-band theory. Defects and increased surface area of the petaloid Fe₂P are beneficial to the Pt nanoparticle anchoring and dispersion as well as the charge transfer and reactant transportation during the electrochemical reaction. These features make the Pt-Fe₂P catalyst system exhibit excellent catalytic activity, antipoisoning ability, and catalytic stability for alcohol fuel of methanol and ethanol electro-oxidation compared with a controlled Pt/C catalyst. The high catalytic efficiency is proposed to come from the strong coupling effect of Pt and petaloid Fe₂P interface that can maintain the mechanical and chemical stability of the catalyst system. This kind of phosphide-supported ultrafine Pt nanocrystals will be a promising catalyst in fuel cells.

Shaping well-defined noble-metal-based nanostructures for fabricating high-performance electrocatalysts: advances and perspectives

This review highlights recent advances in shaping protocols and structure-activity relationships of noble-metal-based catalysts with well-defined nanostructures in electrochemical reactions.

Binary Transition-Metal Oxide Hollow Nanoparticles for Oxygen Evolution Reaction

Low-cost transition metal oxides are actively explored as alternative materials to precious metal-based electrocatalysts for the challenging multistep oxygen evolution reaction (OER). We utilized the Kirkendall effect allowing the formation of hollow polycrystalline, highly disordered nanoparticles (NPs) to synthesize highly active binary metal oxide OER electrocatalysts in alkali media. Two synthetic strategies were applied to achieve compositional control in binary transition metal oxide hollow NPs. The first strategy is capitalized on the oxidation of transition-metal NP seeds in the presence of other transition-metal cations. Oxidation of Fe NPs treated with Ni (+2) cations allowed the synthesis of hollow oxide NPs with a 1-4.7 Ni-to-Fe ratio via an oxidation-induced doping mechanism. Hollow Fe-Ni oxide NPs also reached a current density of 10 mA/cm² at 0.30 V overpotential. The second strategy is based on the direct oxidation of iron-cobalt alloy NPs which allows the synthesis of hollow Fe _xCo_{100- x}-oxide NPs where x can be tuned in the range between 36 and 100. Hollow Fe₃₆Co₆₄-oxide NPs also revealed the current density of 10 mA/cm² at 0.30 V overpotential in 0.1 M KOH.

Trimetallic PtAuNi alloy nanoparticles as an efficient electrocatalyst for the methanol electrooxidation reaction

Platinum is an excellent electrocatalyst. However, the disadvantages of Pt as an electrocatalyst lie in its poor earth abundance, high cost, and poor stability due to surface poisoning. Thus it remains a challenge to find suitable alternative electrocatalysts and/or reduce the use of Pt. Herein, we report the solvothermal synthesis of bimetallic (PtAu and PtNi) and trimetallic (PtAuNi) alloy nanoparticles (NPs) with controlled percentages of individual metals. With an optimized Ni content, the trimetallic (Pt₆₆Au₁₁Ni₂₃) alloy NPs show superior electrocatalytic activity (in terms of lower onset oxidation potential and higher mass activity) not only to bimetallic alloy NPs (PtAu and PtNi) but also to commercial Pt/C (20% Pt loading) for methanol electrooxidation (MEO). This enhanced electrocatalytic activity is due to the synergistic role of different metals in MEO catalysis. In particular, the catalytic activity is found to be controlled by the balance between the adsorption of methanol species on Pt and the removal of carbonaceous species from the catalyst surface by Au and Ni, as demonstrated here. The multimetallic alloy of optimal individual content thereby not only reduces the Pt content in the catalyst but also exhibits higher electrocatalytic activity than Pt/C for MEO that is desirable for fuel cell applications.

Tuning the performance of Pt–Ni alloy/reduced graphene oxide catalysts for 4-nitrophenol reduction

Pt–Ni alloy nanoparticles with different atomic ratios were supported on RGO. Pt–Ni/RGO (1 : 9) has the highest catalytic rate for 4-NP reduction. It is also proved as an efficient nanocatalyst with high activity and stability.

Ultrafine Pt nanoparticle decoration with CoP as highly active electrocatalyst for alcohol oxidation

Ultrafine Pt nanoparticles decorated with CoP provide a promising bifunctional electrocatalyst for alcohol oxidation.

The role of hydrogen during Pt–Ga nanocatalyst formation

The behavior and role of hydrogen is investigated by using Pt–Ga nano-alloy formation as a probe reaction.

Ruthenium and ruthenium oxide nanofiber supports for enhanced activity of platinum electrocatalysts in the methanol oxidation reaction

Ru and RuO₂ nanofiber composites arranged into nanosized grains as Pt catalyst supports are synthesized by electrospinning and post-calcination, which show excellent electrochemical activity.

Synthesis of dendritic Pt–Ni–P alloy nanoparticles with enhanced electrocatalytic properties

Dendritic Pt–Ni–P nanoparticles were synthesizedviaa wet-chemical route, exhibiting a higher electrocatalytic activity than dendritic Pt–Ni nanoparticles and commercial Pt/C.

Room-temperature synthesis with inert bubble templates to produce “clean” PdCoP alloy nanoparticle networks for enhanced hydrazine electro-oxidation

PdCoP alloy nanoparticle networks prepared using inert bubbles as template exhibited high activity for hydrazine oxidation.

Amorphous PtNiP particle networks of different particle sizes for the electro-oxidation of hydrazine

Amorphous PtNiP particle networks with different particle sizes prepared via the reaction temperature control method showed high catalytic activity for hydrazine oxidation compared to the Pt and PtNi catalysts due to its porous, amorphous structure.

Facile synthesis of reduced graphene oxide/Pt–Ni nanocatalysts: their magnetic and catalytic properties

The synthesis of RGO/Pt–Ni nanocatalysts and the catalytic reduction of p-nitrophenol using the as-synthesized nanocatalysts (magnetic separation and recycling).

Gas–liquid interface-mediated room-temperature synthesis of “clean” PdNiP alloy nanoparticle networks with high catalytic activity for ethanol oxidation

PdNiP alloy nanoparticle networks prepared via a gas–liquid interface reaction had markedly high activity and durability for ethanol oxidation.

Synthesis of ultrafine amorphous PtP nanoparticles and the effect of PtP crystallinity on methanol oxidation

Ultrafine amorphous PtP nanoparticles supported on carbon black were prepared. Comparison of electrocatalytic performance of the samples with different levels of crystallinity showed ultrafine amorphous PtP nanoparticles have high catalytic activity for methanol oxidation due to their small particle size and amorphous structure.