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.

Synergistic interface between metal Cu nanoparticles and CoO for highly efficient hydrogen production from ammonia borane

The development of efficient non-noble metal catalysts for the dehydrogenation of hydrogen (H2) storage materials is highly desirable to enable the global production and storage of H2 energy. In this study, Cu x -(CoO)1-x /TiO2 catalysts with a Cu-CoO interface supported on TiO2 are shown to exhibit high catalytic efficiency for ammonia borane (NH3BH3) hydrolysis to generate H2. The best catalytic activity was observed for a catalyst with a Cu : Co molar ratio of 1 : 1. The highest dehydrogenation turnover frequency (TOF) of 104.0 molH2 molmetal -1 min-1 was observed in 0.2 M NaOH at room temperature, surpassing most of the TOFs reported for non-noble catalysts for NH3BH3 hydrolysis. Detailed characterisation of the catalysts revealed electronic interactions at the Cu-CoO heterostructured interface of the catalysts. This interface provides bifunctional synergetic sites for H2 generation, where activation and adsorption of NH3BH3 and H2O are accelerated on the surface of Cu and CoO, respectively. This study details an effective method of rationally designing non-noble metal catalysts for H2 generation via a metal and transition-metal oxide interface.

The Hydrogen-Storage Challenge: Nanoparticles for Metal-Catalyzed Ammonia Borane Dehydrogenation

Dihydrogen is one of the sustainable energy vectors envisioned for the future. However, the rapidly reversible and secure storage of large quantities of hydrogen is still a technological and scientific challenge. In this context, this review proposes a recent state-of-the-art on H₂ production capacities from the dehydrogenation reaction of ammonia borane (and selected related amine-boranes) as a safer solid source of H₂ by hydrolysis (or solvolysis), catalyzed by nanoparticle-based systems. The review groups the results according to the transition metals constituting the catalyst with a mention to their current cost and availability. This includes the noble metals Rh, Pd, Pt, Ru, Ag, as well as cheaper Co, Ni, Cu, and Fe. For each element, the monometallic and polymetallic structures are presented and the performances are described in terms of turnover frequency and recyclability. The structure-property links are highlighted whenever possible. It appears from all these works that the mastery of the preparation of catalysts remains a crucial point both in terms of process, and control and understanding of the electronic structures of the elaborated nanomaterials. A particular effort of the scientific community remains to be made in this multidisciplinary field with major societal stakes.

Gas-propelled biosensors for quantitative analysis

Gas-propelled biosensors display a simple gas-based signal amplification with quantitative detection features based on the target recognition event in combination with gas propulsion. Due to the liquid-gas conversion, the gas not only pushes the ink bar forward in the microchannel, but also serves as the power to propel the micromotors in the liquid. Thus, this continuous motion leads to a shift in distances which is associated with the target amount. Therefore, gas-propelled biosensors provide a visual quantification based on distance or speed signals without the need for expensive instruments. In this review, we focus on current developments in gas-propelled biosensors for quantitative analysis. First, we list the types of gas utilized as actuators in biosensors. Second, we review the representative gas-propelled biosensors, including the propulsion mechanisms and fabrication methods. Moreover, gas-propelled quantification based on distance and speed is summarized. Finally, we cover applications and provide a future perspective of gas-propelled biosensors.

Activating Co nanoparticles on graphitic carbon nitride by tuning the Schottky barrier via P doping for the efficient dehydrogenation of ammonia-borane

A highly active Mott–Schottky nanocatalyst for the efficient dehydrogenation of ammonia-borane was constructed by rationally tuning the Schottky barrier of Co/P_xCN (P-doped g-C₃N₄) via simply varying the doping amount of P atoms.

Co3O4–CuCoO2 hybrid nanoplates as a low-cost and highly active catalyst for producing hydrogen from ammonia borane

Co₃O₄–CuCoO₂ hybrid nanoplates are low-cost and highly active catalysts for producing hydrogen from ammonia borane with a turnover frequency (TOF) of 65.0 mol_hydrogen mol_cat.⁻¹ min⁻¹.

Highly efficient hydrogen production from hydrolysis of ammonia borane over nanostructured Cu@CuCoOx supported on graphene oxide

Designing highly efficient and cheap nanocatalysts for room-temperature hydrolysis of ammonia borane (AB) is of great significance for their real application in hydrogen (H₂)-based fuel cells. Here, we report a kind of noble metal (NM)-free hybrid nanocatalysts composed of heterostructured Cu@CuCoO_x nanoparticles and a graphene oxide support (denoted as Cu@CuCoO_x@GO) and demonstrate their high catalytic performance toward the hydrolysis of AB. By rationally controlling synthetic parameters, we find that optimum Cu_0.3@Cu_0.7CoO_x@GO achieves a superior catalytic activity with a turnover frequency of 44.6 mol_H2 mol_M^-1 min^-1 in H₂O and 98.2 mol_H2 mol_M^-1 min^-1 in 0.2 M NaOH, better than most of previously reported NM-free nanocatalysts. This catalyst also discloses a very low activation energy (E_a) of 35.4 kJ mol^-1. The studies on catalytic kinetics and isotopic experiments attribute the high activity to synergistically structural and compositional advantages of Cu_0.3@Cu_0.7CoO_x@GO, which kinetically accelerates the oxidative cleavage of OH bond in attacked H₂O (the rate-determining step of the hydrolysis of AB). This study thus provides an opportunity for rational design of cheap NM-free nanocatalysts for H₂ production from chemical H₂-storage materials.

Printed gas sensors

This review presents the recent development of printed gas sensors based on functional inks.

Ni0.5Cu0.5Co2O4 Nanocomposites, Morphology, Controlled Synthesis, and Catalytic Performance in the Hydrolysis of Ammonia Borane for Hydrogen Production

The catalytic hydrolysis of ammonia borane (AB) is a promising route to produce hydrogen for mobile hydrogen‒oxygen fuel cells. In this study, we have successfully synthesized a variety of Ni_0.5Cu_0.5Co₂O₄ nanocomposites with different morphology, including nanoplatelets, nanoparticles, and urchin-like microspheres. The catalytic performance of those Ni_0.5Cu_0.5Co₂O₄ composites in AB hydrolysis is investigated. The Ni_0.5Cu_0.5Co₂O₄ nanoplatelets show the best catalytic performance despite having the smallest specific surface area, with a turnover frequency (TOF) of 80.2 mol_hydrogen·min^-1·mol^-1_cat. The results reveal that, in contrast to the Ni_0.5Cu_0.5Co₂O₄ nanoparticles and microspheres, the Ni_0.5Cu_0.5Co₂O₄ nanoplatelets are more readily reduced, leading to the fast formation of active species for AB hydrolysis. These findings provide some insight into the design of high-performance oxide-based catalysts for AB hydrolysis. Considering their low cost and high catalytic activity, Ni_0.5Cu_0.5Co₂O₄ nanoplatelets are a strong candidate catalyst for the production of hydrogen through AB hydrolysis in practical applications.

Cu0.4Co0.6MoO4 Nanorods Supported on Graphitic Carbon Nitride as a Highly Active Catalyst for the Hydrolytic Dehydrogenation of Ammonia Borane

As a typical chemical hydride, ammonia borane (AB) has received extensive attention because of its safety and high hydrogen storage capacity. The aim of this work was to develop a cost-efficient and highly reactive catalyst for hydrolyzing AB. Herein, we synthesized a series of CuxCo1–xMoO4 dispersed on graphitic carbon nitride (g-C3N4) to dehydrogenate AB. Among those CuxCo1–xMoO4/g-C3N4 catalysts, Cu0.4Co0.6MoO4/g-C3N4 exhibited the highest site time yield (STY) value of 75.7 m o l H 2 m o l c a t − 1   m i n − 1 with a low activation energy of 14.46 kJ mol−1. The STY value for Cu0.4Co0.6MoO4/g-C3N4 was about 4.3 times as high as that for the unsupported Cu0.4Co0.6MoO4, indicating that the g-C3N4 support plays a crucial role in improving the catalytic activity. Considering its low cost and high catalytic activity, our Cu0.4Co0.6MoO4/g-C3N4 catalyst is a strong candidate for AB hydrolysis for hydrogen production in practical applications.

A Simple and Scalable Route to Synthesize Cox Cu1- x Co2 O4 @Coy Cu1- y Co2 O4 Yolk-Shell Microspheres, A High-Performance Catalyst to Hydrolyze Ammonia Borane for Hydrogen Production

Yolk-shell structured micro/nano-sized materials have broad and important applications in different areas due to their unique spatial configurations. In this study, yolk-shell structured Co₃ O₄ @Co₃ O₄ is prepared using a simple and scalable hydrothermal reaction, followed by a calcination process. Then, Co_x Cu_{1- x} Co₂ O₄ @Co_y Cu_{1- y} Co₂ O₄ microspheres are synthesized via adsorption and calcination processes using the as-prepared Co₃ O₄ @Co₃ O₄ as the precursor. A possible formation mechanism of the yolk-shell structures is proposed based on the characterization results, which is different from those of yolk-shell structures in previous study. For the first time, the catalytic activity of yolk-shell structured catalysts in ammonia borane (AB) hydrolysis is studied. It is discovered that the yolk-shell structured Co_x Cu_{1- x} Co₂ O₄ @Co_y Cu_{1- y} Co₂ O₄ microspheres exhibit high performance with a turnover frequency (TOF) of 81.8 mol_hydrogen min^-1 mol_cat ^-1 . This is one of the highest TOF values reported for a noble-metal-free catalyst in the literature. Additionally, the yolk-shell structured Co_x Cu_{1- x} Co₂ O₄ @Co_y Cu_{1- y} Co₂ O₄ microspheres are highly stable and reusable. These yolk-shell structured Co_x Cu_{1- x} Co₂ O₄ @Co_y Cu_{1- y} Co₂ O₄ microsphere is a promising catalyst candidate in AB hydrolysis considering the excellent catalytic behavior and low cost.

Carbon nitride supported Ni0.5Co0.5O nanoparticles with strong interfacial interaction to enhance the hydrolysis of ammonia borane

Ammonia borane (AB) is an ideal hydrogen-storage material for fuel cells but its application has been strongly limited by using rare noble-metal-based catalysts. Here we have prepared a hybrid material of Ni_0.5Co_0.5O nanoparticles on nitric-acid treated carbon nitride (NCN) for the hydrolysis of AB. The Ni_0.5Co_0.5O-NCN catalyst achieves a high total turnover frequency (TOF) value of 76.1 (H₂) mol per (Cat-metal) mol min in pure water at room temperature, with a good stability by keeping 83.2% activity after 6 runs. The TOF is comparable to the best values ever reported for noble-metal-free catalysts without extra conditions such as light illumination or a strong alkaline environment. Synchrotron radiation based X-ray absorption spectroscopy reveals that the carbon nitride substrate has two reaction centers to form stable interfacial interaction with the NPs, in which carbon can act as the electron acceptor while nitrogen acts as the electron donor. Thus the NP-NCN system has a hybridized electronic structure which is favorable for the catalytic reaction to produce hydrogen. In-depth understanding of the interfacial interaction between NCN and NPs may also shed light on the mechanism study of various energy-related applications based on carbon nitride.

Ni_0.5Co_0.5O on carbon nitride shows a high TOF value for the hydrolysis of ammonia borane due to the interfacial interaction.

MoO₃-Doped MnCo₂O₄ Microspheres Consisting of Nanosheets: An Inexpensive Nanostructured Catalyst to Hydrolyze Ammonia Borane for Hydrogen Generation

Production of hydrogen by catalytically hydrolyzing ammonia borane (AB) has attracted extensive attention in the field of catalysis and energy. However, it is still a challenge to develop a both inexpensive and active catalyst for AB hydrolysis. In this work, we designed a series of MoO₃-doped MnCo₂O₄ (x) catalysts, which were fabricated by a hydrothermal process. The morphology, crystalline structure, and chemical components of the catalysts were systematically analyzed. The catalytic behavior of the catalyst in AB hydrolysis was investigated. Among these catalysts, MoO₃-doped MnCo₂O₄ (0.10) microspheres composed of nanosheets exhibited the highest catalytic activity. The apparent activation energy is 34.24 kJ mol⁻¹ and the corresponding turnover frequency is 26.4 mol_hydrogen min⁻¹ mol_cat⁻¹. Taking into consideration the low cost and high performance, the MoO₃-doped MnCo₂O₄ (0.10) microspheres composed of nanosheets represent a promising catalyst to hydrolyze AB for hydrogen production.