Ultrafine Ni–Pt Alloy Nanoparticles Grown on Graphene as Highly Efficient Catalyst for Complete Hydrogen Generation from Hydrazine Borane

Ultrafine Ni–Pt alloy NPs grown on graphene (NiPt/graphene) have been facilely prepared via a simple one-step coreduction synthetic route and characterized by transmission electron microscopy, energy-dispresive X-ray spectroscopy, X-ray diffraction, inductively coupled plasma atomic emission spectroscopy, X-ray photoelectron spectroscopy, Raman and Fourier transform infrared methods. The characterized results showed that ultrafine Ni–Pt NPs with a small size of around 2.3 nm were monodispersed on the graphene nanosheet. Compared to the pure Ni_0.9Pt_0.1 alloy NPs, graphene supported Ni_0.9Pt_0.1 alloy NPs exhibited much higher activity and hydrogen selectivity (100%) toward conversion of hydrazine borane (HB) to hydrogen. It is first found that the durability of the catalyst can be greatly enhanced by the addition of an excess amount of NaOH in this reaction, because of the neutralization of NaOH by the byproduct H₃BO₃ produced from the hydrolysis of HB. After six cycles of the catalytic reaction, no appreciable decrease in activity was observed, indicating that the Ni_0.9Pt_0.1/graphene catalysts have good durability/stability

Controlled Synthesis of MOF-Encapsulated NiPt Nanoparticles toward Efficient and Complete Hydrogen Evolution from Hydrazine Borane and Hydrazine

The catalytic dehydrogenation of hydrazine borane (N₂H₄BH₃) and hydrous hydrazine (N₂H₄·H₂O) for H₂ evolution is considered as two of the pivotal reactions for the implementation of the hydrogen-based economy. A reduction rate controlled strategy is successfully applied for the encapsulating of uniform tiny NiPt alloy nanoclusters within the opening porous channels of MOFs in this work. The resultant Ni_0.9Pt_0.1/MOF core–shell composite with a low Pt content exerted exceedingly high activity and durability for complete H₂ evolution (100% hydrogen selectivity) from alkaline N₂H₄BH₃ and N₂H₄·H₂O solution. The features of small NiPt alloy NPs, strong synergistic effect between NiPt alloy NPs and the MOF, and open pore structure for freely mass transfer made NiPt/MIL-101 an excellent catalyst for highly efficient H₂ evolution from N₂H₄BH₃ or N₂H₄·H₂O

Synergetic Catalysis of Non-noble Bimetallic Cu–Co Nanoparticles Embedded in SiO₂ Nanospheres in Hydrolytic Dehydrogenation of Ammonia Borane

Ultrafine non-noble bimetallic Cu–Co nanoparticles (∼2 nm) encapsulated within SiO₂ nanospheres (Cu–Co@SiO₂) have been successfully synthesized via a one-pot synthetic route in a reverse micelle system and characterized by SEM, TEM, EDS, XPS, PXRD, ICP, and N₂ adsorption–desorption methods. In each core–shell Cu–Co@SiO₂ nanosphere, several Cu–Co NPs are separately embedded in SiO₂. Compared with their monometallic counterparts, the bimetallic core–shell nanospheres Cu_<i>x</i>Co_1–<i>x</i>@SiO₂ with different metal compositions show a higher catalytic performance for hydrogen generation from the hydrolysis of ammonia borane (NH₃BH₃, AB) at room temperature, due to the strain and ligand effects on the modification of the surface electronic structure and chemical properties of Cu–Co NPs in the SiO₂ nanospheres. Especially, the Cu_0.5Co_0.5@SiO₂ nanospheres show the best catalytic performance among all the synthesized Cu_<i>x</i>Co_1–<i>x</i>@SiO₂ catalysts in the hydrolytic dehydrogenation of AB. In addition, the activation energy (<i>E</i>_a) of Cu_0.5Co_0.5@SiO₂ core–shell structured nanospheres for the hydrolysis of AB is estimated to be 24 ± 2 kJ mol^–1, relatively low values among the bimetallic catalysts reported for the same reaction. Furthermore, the multi-recycle test shows that the bimetallic Cu_0.5Co_0.5@SiO₂ core–shell nanospheres are still highly active for hydrolytic dehydrogenation of AB even after 10 runs, implying a good recycling stability in the catalytic reaction

Interface Electronic Modulation of Monodispersed Co Metal-Co₇Fe₃ Alloy Heterostructures for Rechargeable Zn–Air Battery

Engineering heterointerfaces between metal and alloy to facilitate charge transfer would be an attractive strategy for superefficient electrocatalysis. Herein, a simple xerogel-pyrolysis strategy has been designed to prepare an advanced bifunctional electrocatalyst, Co/Co7Fe3 confined by a porous N-doped carbon nanosheets/CNTs composite (Co/Co7Fe3@PNCC). The formative Co/Co7Fe3 heterostructure promoted the charge transfers from metal Co to active alloy Co7Fe3, thus reducing the energy barrier of the oxygen reduction reaction and improving the catalytic kinetics and active surface area for the oxygen evolution reaction. The PNCC provided monodispersed confined space for Co/Co7Fe3 particles, which also owned a high specific surface area for ions/gases diffusion. Therefore, Co/Co7Fe3@PNCC exhibited excellent bifunctional oxygen catalysis activities and durability with an ultralow polarization gap (ΔE) of only 0.64 V. When practically adopted as an air electrode in ZAB, a large open-circuit voltage of 1.534 V, a maximum power density of 211.82 mW cm–2, an ultrahigh specific capacity of 807.33 mAh g–1, and superior durability over 800 h were obtained. This catalyst design concept offers a facile strategy toward modulating electronic structure to achieve efficient bifunctional electrocatalysts for ZAB

Engineering Electronic and Morphological Structure of Metal–Organic-Framework-Derived Iron-Doped Ni₂P/NC Hollow Polyhedrons for Enhanced Oxygen Evolution

The rational design of an oxygen electrocatalyst with low cost and high activity is greatly desired for realization of the practical water-splitting industry. Herein, we put forward a rational method to construct nonprecious-metal catalysts with high activity by designing the microstructure and modulating the electronic state. Iron (Fe)-doped Ni2P hollow polyhedrons decorated with nitrogen-doped carbon (Fe-Ni2P/NC HPs) are prepared by a sequential metal–organic-framework-templated strategy. Benefiting from the strong electronic coupling, rapid charge-transfer capability, and abundant catalytic active sites, the obtained Fe-Ni2P/NC HPs exhibit an impressive electrocatalytic performance toward the oxygen evolution reaction (OER) with an ultralow overpotential of 228 mV at a current density of 10 mA cm–2 and a small Tafel slope of 33.4 mV dec–1, superior to the commercial RuO2 and most reported electrocatalysts. Notably, this catalyst also shows long durability with an almost negligible activity decay over 210 h for the OER. Combining density functional theory calculations with experiments demonstrates that the doped Fe and the incorporated carbon effectively modulate the electronic structure, enhance the conductivity, and greatly reduce the energy barrier of the rate-determining step in the process of OER. Thus, fast OER kinetics is realized. Moreover, this synthetic strategy can be extended to the synthesis of Fe-NiS2/NC HPs and Fe-NiSe2/NC HPs with excellent OER performance and long-term durability. This work furnishes an instructive idea in pursuit of nonprecious-metal materials with robust electrocatalytic activity and long durability

Engineering Electronic and Morphological Structure of Metal–Organic-Framework-Derived Iron-Doped Ni₂P/NC Hollow Polyhedrons for Enhanced Oxygen Evolution

The rational design of an oxygen electrocatalyst with low cost and high activity is greatly desired for realization of the practical water-splitting industry. Herein, we put forward a rational method to construct nonprecious-metal catalysts with high activity by designing the microstructure and modulating the electronic state. Iron (Fe)-doped Ni2P hollow polyhedrons decorated with nitrogen-doped carbon (Fe-Ni2P/NC HPs) are prepared by a sequential metal–organic-framework-templated strategy. Benefiting from the strong electronic coupling, rapid charge-transfer capability, and abundant catalytic active sites, the obtained Fe-Ni2P/NC HPs exhibit an impressive electrocatalytic performance toward the oxygen evolution reaction (OER) with an ultralow overpotential of 228 mV at a current density of 10 mA cm–2 and a small Tafel slope of 33.4 mV dec–1, superior to the commercial RuO2 and most reported electrocatalysts. Notably, this catalyst also shows long durability with an almost negligible activity decay over 210 h for the OER. Combining density functional theory calculations with experiments demonstrates that the doped Fe and the incorporated carbon effectively modulate the electronic structure, enhance the conductivity, and greatly reduce the energy barrier of the rate-determining step in the process of OER. Thus, fast OER kinetics is realized. Moreover, this synthetic strategy can be extended to the synthesis of Fe-NiS2/NC HPs and Fe-NiSe2/NC HPs with excellent OER performance and long-term durability. This work furnishes an instructive idea in pursuit of nonprecious-metal materials with robust electrocatalytic activity and long durability

Effects of Organic Compounds on Ni/AlLaCe Catalysts for Ammonia Decomposition to Hydrogen

Ammonia has attracted extensive attention from scholars due to its high energy density and hydrogen content. In this work, we synthesized a series of Ni-based catalysts by an impregnation method to investigate the influence of organic compounds on Ni/AlLaCe catalysts for NH3 decomposition. The effects of different organic compounds like β-cyclodextrin (β-CD), citric acid (CA), and poly(vinylpyrrolidone) (PVP) on the catalyst structure and performance have been examined through a series of characterizations. Experimental results indicated that citric acid significantly affects the size of the active metal particles and promotes metal–support interaction compared to other organic compounds. At the same time, the introduction of citric acid increased the number of strongly basic sites and oxygen vacancies of the catalyst. Among the catalysts tested, the NALC-60CA sample demonstrated a high conversion of 99.7% for ammonia decomposition at a gas hourly space velocity of 30,000 mL·h–1·g–1 and a temperature of 600 °C. Additionally, NALC-60CA exhibited good stability during a 55 h activity test at a temperature of 525 °C