Ultrafine RhNi Nanocatalysts Confined in Hollow Mesoporous Carbons for a Highly Efficient Hydrogen Production from Ammonia Borane

Ultrafast joule-heating-assisted O, N dual-doping of unfunctionalized carbon enhances Ru nanoparticle-catalyzed hydrogen production

The development of a rapid and convenient strategy to regulate the surface microenvironment of inert carbon supports, along with the physicochemical properties of their supported metal nanoparticles, is essential for enhancing catalytic performance. In this study, we describe a straightforward and efficient solid-state microwave method that utilizes a household microwave oven to achieve the co-doping of oxygen and nitrogen in unfunctionalized carbon black (ONCB) using urea as a nitrogen source. The microwave solid-state treatment of commercial carbon black (CB) with urea not only introduces a significant number of heteroatomic functional groups but also substantially increases the pore size and pore volume of the matrix. These enhancements facilitate the uniform growth and dispersion of ultrafine Ru nanoparticles on the surface of ONCB. Consequently, the Ru/ONCB catalyst provides abundant catalytic active sites and mass transfer channels, thereby improving catalytic performance for hydrogen evolution from ammonia borane hydrolysis (ABH). The turnover frequency of Ru/ONCB for ABH reaches 4529 ± 238 min-1 (determined based on Ru dispersion), surpassing a range of analogues and many previously reported carbon-supported Ru catalysts. This study presents a simple and rapid strategy to regulate the surface microenvironment of unfunctionalized carbon support, thereby enhancing the catalytic performance of its supported metal nanoparticles for catalytic hydrogen generation.

Boron/nitrogen-trapping and regulative electronic states around Ru nanoparticles towards bifunctional hydrogen production

Developing a straightforward and general strategy to regulate the surface microenvironment of a carbon matrix enriched with N/B motifs for efficient atomic utilization and electronic state of metal sites in bifunctional hydrogen production via ammonia-borane hydrolysis (ABH) and water electrolysis is a persistent challenge. Herein, we present a simple, green, and universal approach to fabricate B/N co-doped porous carbons using ammonia-borane (AB) as a triple functional agent, eliminating the need for hazardous and explosive functional agents and complicated procedures. The pyrolysis of AB induces the regulation of the surface microenvironment of the carbon matrix, leading to the formation of abundant surface functional groups, defects, and pore structures. This regulation enhances the efficiency of atom utilization and the electronic state of the active component, resulting in improved bifunctional hydrogen evolution. Among the catalysts, B/N co-doped vulcan carbon (Ru/BNC) with 2.1 wt% Ru loading demonstrates the highest performance in catalytic hydrogen production from ABH, achieving an ultrahigh turnover frequency of 1854 min-1 (depending on the dispersion of Ru). Furthermore, this catalyst shows remarkable electrochemical activity for hydrogen evolution in alkaline water electrolysis with a low overpotential of 31 mV at 10 mA cm-2. The present study provides a simple, green, and universal method to regulate the surface microenvironment of various carbons with B/N modulators, thereby adjusting the atomic utilization and electronic state of active metals for enhanced bifunctional hydrogen evolution.

Recent Advances and Perspectives on Supported Catalysts for Heterogeneous Hydrogen Production from Ammonia Borane

Ammonia borane (AB), a liquid hydrogen storage material, has attracted increasing attention for hydrogen utilization because of its high hydrogen content. However, the slow kinetics of AB hydrolysis and the indefinite catalytic mechanism remain significant problems for its large-scale practical application. Thus, the development of efficient AB hydrolysis catalysts and the determination of their catalytic mechanisms are significant and urgent. A summary of the preparation process and structural characteristics of various supported catalysts is presented in this paper, including graphite, metal-organic frameworks (MOFs), metal oxides, carbon nitride (CN), molybdenum carbide (MoC), carbon nanotubes (CNTs), boron nitride (h-BN), zeolites, carbon dots (CDs), and metal carbide and nitride (MXene). In addition, the relationship between the electronic structure and catalytic performance is discussed to ascertain the actual active sites in the catalytic process. The mechanism of AB hydrolysis catalysis is systematically discussed, and possible catalytic paths are summarized to provide theoretical considerations for the designing of efficient AB hydrolysis catalysts. Furthermore, three methods for stimulating AB from dehydrogenation by-products and the design of possible hydrogen product-regeneration systems are summarized. Finally, the remaining challenges and future research directions for the effective development of AB catalysts are discussed.

"On-Off" Control for On-Demand H2 Release upon Dimethylamineborane Hydrolysis over Ru0.8Ni0.2/MoS2 Nanohybrids

In spite of the fact that remarkable developments are achieved in the design and development of novel nanocatalysts for H₂ release upon dimethylamineborane hydrolysis, the development of an "on-off" switch for demand-based H₂ evolution upon dimethylamineborane hydrolysis is still a matter of supreme importance, however. Herein, we synthesized a string of MoS₂ nanosheet-supported RuNi bimetallic nanohybrids (Ru_xNi_1-x/MoS₂), by fixation of RuNi nanoparticles at the MoS₂ surface, for the H₂ evolution upon the hydrolysis of dimethylamineborane at 30 °C. For safely and effectively generating, transporting, and storing H₂ gas, the selective "on-off" switch for on-demand H₂ evolution upon dimethylamineborane hydrolysis over the Ru_0.8Ni_0.2/MoS₂ nanohybrid has been successfully realized by the Zn²⁺/EDTA-2Na system. In particular, the H₂ evolution is totally switched off by adding Zn(NO₃)₂. It seems that Zn²⁺ ions are attached and anchored at the Ru_0.8Ni_0.2/MoS₂ surface, inhibiting their surface-active sites, leading to the termination of H₂ evolution. Then, the H₂ generation is subsequently reactivated by adding the EDTA-2Na solution because of its excellent coordination ability with Zn²⁺ ions. This study not only offers a new and efficient RuNi nanocatalyst for dimethylamineborane hydrolysis but also proposes a new method for the demand-based H₂ production.

Cobalt-Promoted Noble-Metal Catalysts for Efficient Hydrogen Generation from Ammonia Borane Hydrolysis

Ammonia borane (AB) has been regarded as a promising material for chemical hydrogen storage. However, the development of efficient, cost-effective, and stable catalysts for H₂ generation from AB hydrolysis remains a bottleneck for realizing its practical application. Herein, a step-by-step reduction strategy has been developed to synthesize a series of bimetallic species with small sizes and high dispersions onto various metal oxide supports. Superior to other non-noble metal species, the introduction of Co species can remarkably and universally promote the catalytic activity of various noble metals (e.g., Pt, Rh, Ru, and Pd) in AB hydrolysis reactions. The optimized Pt_0.1%Co_3%/TiO₂ catalyst exhibits a superhigh H₂ generation rate from AB hydrolysis, showing a turnover frequency (TOF) value of 2250 mol_H2 mol_Pt^-1 min^-1 at 298 K. Such a TOF value is about 10 and 15 times higher than that of the monometal Pt/TiO₂ and commercial Pt/C catalysts, respectively. The density functional theory (DFT) calculation reveals that the synergy between Pt and CoO species can remarkably promote the chemisorption and dissociation of water molecules, accelerating the H₂ evolution from AB hydrolysis. Significantly, the representative Pt_0.25%Co_3%/TiO₂ catalyst exhibits excellent stability, achieving a record-high turnover number of up to 215,236 at room temperature. The excellent catalytic performance, superior stability, and low cost of the designed catalysts create new prospects for their practical application in chemical hydrogen storage.

Alkaline ultrasonic irradiation-mediated boosted H2 production over O/N-rich porous carbon anchored Ru nanoclusters

Developing efficient catalytic systems to boost hydrogen evolution from hydrolytic dehydrogenation of ammonia borane (AB) is of broad interest but remains a formidable challenge since the widespread usages of hydrogen have been considered as sustainable solutions to ensure future energy security. Herein, we developed an alkaline ultrasonic irradiation-mediated catalytic system with O/N-rich porous carbon supported Ru nanoclusters (NCs) (Ru/ONPC) to considerably boost the catalytic activity for hydrogen production from the hydrolytic dehydrogenation of AB. The uniformly distributed sub-2.0 nm Ru NCs on the ONPC were demonstrated to be efficient catalysts to boost hydrogen generation from the hydrolytic dehydrogenation of AB with the synergistic effect between ultrasonic irradiation and alkaline additive without any additional heating. An ultrahigh turnover frequency (TOF) of 4004 min^-1 was achieved in the developed catalytic system, which was significantly higher than that of ultrasound-mediated AB hydrolysis without alkali (TOF: 485 min^-1) and alkaline AB hydrolysis (TOF: 1747 min^-1) without ultrasound mixing. The alkaline ultrasonic irradiation was beneficial for the cleavage of the OH bonds in the attacked H₂O molecules catalyzed by the Ru/ONPC and thus considerably boost the catalytic hydrogen generation from AB. This study provides a tractable and ecofriendly pathway to promote the activity toward AB hydrolysis to release hydrogen.

Synergistic catalytic hydrolysis of ammonia borane to release hydrogen over AgCo@CN

Synergistic catalytic AB hydrolysis to generate hydrogen was achieved over AgCo@CN synthesized by auto-reduction between Co@CN and a Ag precursor.

Maximizing hydrogen production by AB hydrolysis with Pt@cobalt oxide/N, O-rich carbon and alkaline ultrasonic irradiation

Non-precious metal oxide/carbon hybrid has been identified as a promising platform to stabilized precious metals for ammonia borane (AB) hydrolysis to produce hydrogen, whereas their facile and environmental-friendly synthesis remains...

Efficient Near-Infrared-Activated Photocatalytic Hydrogen Evolution from Ammonia Borane with Core-Shell Upconversion-Semiconductor Hybrid Nanostructures

In this work, the photocatalytic hydrogen evolution from ammonia borane under near-infrared laser irradiation at ambient temperature was demonstrated by using the novel core-shell upconversion-semiconductor hybrid nanostructures (NaGdF4:Yb3+/Er3+@NaGdF4@Cu2O). The particles were successfully synthesized in a final concentration of 10 mg/mL. The particles were characterized via high resolution transmission electron microscopy (HRTEM), photoluminescence, energy dispersive X-ray analysis (EDAX), and powder X-ray diffraction. The near-infrared-driven photocatalytic activities of such hybrid nanoparticles are remarkably higher than that with bare upconversion nanoparticles (UCNPs) under the same irradiation. The upconverted photoluminescence of UCNPs efficiently reabsorbed by Cu2O promotes the charge separation in the semiconducting shell, and facilitates the formation of photoinduced electrons and hydroxyl radicals generated via the reaction between H2O and holes. Both serve as reactive species on the dissociation of the weak B-N bond in an aqueous medium, to produce hydrogen under near-infrared excitation, resulting in enhanced photocatalytic activities. The photocatalyst of NaGdF4:Yb3+/Er3+@NaGdF4@Cu2O (UCNPs@Cu2O) suffered no loss of efficacy after several cycles. This work sheds light on the rational design of near-infrared-activated photocatalysts, and can be used as a proof-of-concept for on-board hydrogen generation from ammonia borane under near-infrared illumination, with the aim of green energy suppliers.

Demonstration of Controlled Hydrogen Release Using Rh@GQDs during Hydrolysis of NH3BH3

Achieving the controlled release of H₂ through an effective approach still faces many challenges. Herein, high-quality graphene quantum dots (GQDs) are synthesized from a new precursor, 1,2,4-trihydroxy benzene, and a multifunctional platform of Rh@GQDs is further developed for the controlled H₂ evolution upon the hydrolysis of NH₃BH₃ (AB). More importantly, the designing concepts of multistep and stepless speed controls have been introduced in the domains of both H₂ evolution for the first time. Through a novel designing protocol, the rate of H₂ evolution can be freely regulated and constantly varied on demand by means of chelation between Zn²⁺ and ethylene diamine tetraacetic acid (EDTA). The density functional theory calculation indicates that Zn²⁺ has the priority to be adsorbed onto Rh(100) due to its larger adsorption energy (107.98 kcal·mol^-1) than that of AB (36.36 kcal·mol^-1). A controlling mechanism is presented such that Zn²⁺ will cover the active sites of the nanocatalyst to prevent the H₂ evolution, and EDTA can chelate Zn²⁺ to reactivate the nanocatalyst for the production of H₂, greatly facilitating use of this strategy in other catalytic reactions. Moreover, it is demonstrated that the protocol is equally valid for diverse hydrogen storage materials. Therefore, this work not only establishes whole new concepts for the controlled production of H₂ but also explains their mechanism, thus remarkably advancing the utilization of H₂ energy and significantly enlightening the controlled process of catalysis.

Bimetallic Nanocrystals: Structure, Controllable Synthesis and Applications in Catalysis, Energy and Sensing

In recent years, bimetallic nanocrystals have attracted great interest from many researchers. Bimetallic nanocrystals are expected to exhibit improved physical and chemical properties due to the synergistic effect between the two metals, not just a combination of two monometallic properties. More importantly, the properties of bimetallic nanocrystals are significantly affected by their morphology, structure, and atomic arrangement. Reasonable regulation of these parameters of nanocrystals can effectively control their properties and enhance their practicality in a given application. This review summarizes some recent research progress in the controlled synthesis of shape, composition and structure, as well as some important applications of bimetallic nanocrystals. We first give a brief introduction to the development of bimetals, followed by the architectural diversity of bimetallic nanocrystals. The most commonly used and typical synthesis methods are also summarized, and the possible morphologies under different conditions are also discussed. Finally, we discuss the composition-dependent and shape-dependent properties of bimetals in terms of highlighting applications such as catalysis, energy conversion, gas sensing and bio-detection applications.