Photocatalytic H2 Evolution from Ammonia Borane: Improvement of Charge Separation and Directional Charge Transmission

Co/M^II Fe layered double hydroxide (LDH) LDH photocatalysts have been designed from the aspect of employing stable half-filled Fe³⁺ to trap photogenerated electrons, adjusting the M^II -O-Fe oxo-bridged structure to optimize the short-range directional charge transmission and intercalating oxometallate anions into the LDH to further improve light absorption along with electron-hole separation and non-noble metal Co NP loading and reduction to form a heterojunction. These LDH-based photocatalysts are employed for photocatalytic H₂ evolution from ammonia borane in aqueous solution under visible light at 298 K. The photocatalytic H₂ evolution activity is greatly improved through adjustment of the M^II -O-Fe oxo-bridged structure and molybdate intercalation into the LDH. Turnover frequencies of up to 113.2 min^-1 are achieved with Co/CoFe-Mo. Alongside the experimental results and materials characterization, capture experiments and in situ DRIFTS analysis are carried out to study the photocatalytic hydrogen production mechanism.

Defect-Rich Co-CoOx -Graphene Nanocatalysts for Efficient Hydrogen Production from Ammonia Borane

Chemical hydrogen storage ammonia borane has attracted extensive attention as a method of efficient utilization of hydrogen energy. The high-efficiency catalysts are the main factor restricting the hydrogen production of ammonia borane. In this paper, the synergistic effect of Co and CoO_x supported on graphene (named Co-CoO_x @GO-II) promotes the efficient hydrogen production of ammonia borane, and its catalytic hydrogen production rate can reach 5813 mL min^-1  g_Co ^-1 at 298 K, the corresponding TOF is 15.33 min^-1 . After five stability tests, Co-CoO_x @GO-II maintained 65% of its original catalytic performance. The synergy of metal and metal oxide and the defects in the atomic arrangement ensure the catalytic activity, the large specific surface area of graphene ensures the dispersion and fixation. This strategy may provide a possibility to design high-performance transition metal catalysts.

Boron: Its Role in Energy-Related Processes and Applications

Boron's unique position in the Periodic Table, that is, at the apex of the line separating metals and nonmetals, makes it highly versatile in chemical reactions and applications. Contemporary demand for renewable and clean energy as well as energy-efficient products has seen boron playing key roles in energy-related research, such as 1) activating and synthesizing energy-rich small molecules, 2) storing chemical and electrical energy, and 3) converting electrical energy into light. These applications are fundamentally associated with boron's unique characteristics, such as its electron-deficiency and the availability of an unoccupied p orbital, which allow the formation of a myriad of compounds with a wide range of chemical and physical properties. For example, boron's ability to achieve a full octet of electrons with four covalent bonds and a negative charge has led to the synthesis of a wide variety of borate anions of high chemical and electrochemical stability-in particular, weakly coordinating anions. This Review summarizes recent advances in the study of boron compounds for energy-related processes and applications.

Ultra-fine platinum species supported on niobium pentoxide for CO oxidation

Platinum oxide supported on a Lewis acid niobium oxide (Nb₂O₅) support has been used for various heterogeneous and homogeneous catalysts. In this work, we used urea as a precipitating agent to obtain crystallized Nb₂O₅ with high surface area via a hydrothermal route. Nb₂O₅-supported Pt catalysts were subsequently synthesized via an incipient wetness impregnation approach. Multiple characterizations including X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and nitrogen adsorption/desorption confirmed the identical structural and textural properties of the Nb₂O₅ support before and after the impregnation process. Furthermore, the X-ray absorption fine structure technique (XAFS) results with related data analysis indicate that the platinum species in the fresh and H₂-pretreated samples were in the form of single atoms or ultrafine clusters. In addition, the decrease in coordination number (CN) of the first-shell Pt–O bond, as well as the formation of Pt–Pt contribution with very low CN, after H₂-pretreatment was verified, which corresponds to the decrease of oxidation state for Pt species on the surface of supports. Thus, the ultrafine-clustered metallic Pt species are considered to be more active than the oxidized Pt single ions. The current results will be of great significance in controllable synthesis of active Pt-based catalysts for other catalytic oxidation reactions.

Ultrafine-clustered metallic Pt species are considered to be more active than oxidized Pt single ions for CO oxidation reaction.

A Simple and Efficient Device and Method for Measuring the Kinetics of Gas-Producing Reactions

We present a new device for quantifying gases or gas mixtures based on the simple principle of bubble counting. With this device, we can follow reaction kinetics down to volume step sizes of 8–12 μL. This enables the accurate determination of both time and size of these gas quanta, giving a very detailed kinetic analysis. We demonstrate this method and device using ammonia borane hydrolysis as a model reaction, obtaining Arrhenius plots with over 300 data points from a single experiment. Our device not only saves time and avoids frustration, but also offers more insight into reaction kinetics and mechanistic studies. Moreover, its simplicity and low cost open opportunities for many lab applications.

Sub-3 nm Rh nanoclusters confined within a metal–organic framework for enhanced hydrogen generation

Rh@UIO-66, prepared by using the double-solvent host–guest strategy and excess reduction methods, exhibited a higher catalytic activity in AB hydrolysis compared with Rh/UIO-66 because the ultrafine Rh nanoparticles were confined to UIO-66 channels. This confinement effect played a key role in enhancing the catalytic activity for AB hydrolysis.

Zirconium-Porphyrin-Based Metal-Organic Framework Hollow Nanotubes for Immobilization of Noble-Metal Single Atoms

Single atoms immobilized on metal-organic frameworks (MOFs) with unique nanostructures have drawn tremendous attention in the application of catalysis but remain a great challenge. Various single noble-metal atoms have now been successfully anchored on the well-defined anchoring sites of the zirconium porphyrin MOF hollow nanotubes, which are probed by aberration-corrected scanning transmission electron microscopy and synchrotron-radiation-based X-ray absorption fine-structure spectroscopy. Owing to the hollow structure and excellent photoelectrochemical performance, the HNTM-Ir/Pt exhibits outstanding catalytic activity in the visible-light photocatalytic H₂ evolution via water splitting. The single atom immobilized on MOFs with hollow structures are expected to pave the way to expand the potential applications of MOFs.

Novel photocatalyst gold nanoparticles with dumbbell-like structure and their superiorly photocatalytic performance for ammonia borane hydrolysis

Gold nanoparticles (Au NPs) have attracted remarkable research interests in heterogeneous catalysis due to their unique physical and chemical properties. However, only small-size Au NPs (<7 nm) exhibit promising catalytic activity. In this work, dumbbell-like Au NPs (D-Au NPs) with average size of 37 × 11 nm were prepared by a secondary seed-mediated growth method to serve as novel photocatalyst for ammonia borane (AB) hydrolysis in the solution with specific pH value. Our results demonstrate that ⅰ) the strengthened LSPR compensation effect could effectively remedy the loss of catalytic activity resulting from the size enlarging of D-Au NPs, proven by that the heating power of a single Au nanoparticle (Ps) and turnover frequency of AB molecules within 10 minutes of D-Au NPs are 52.5 and 3.89 times higher than that of spherical Au NPs; ⅱ) the extinction coefficient and Ps of D-Au NPs are almost 2.72 and 2.42 times as high as that of rod-like Au NPs, demonstrating the promoting structure-property relationship of dumbbell-like structure.; ⅲ) when the pH value of AB solution was lower than 6.0, the hydrolysis rate was highly promoted, indicating that H+ ions play an active role in the hydrolysis process. This work greatly extends the application of noble metals and provides a new insight into AB hydrolysis.

Cube-like CuCoO nanostructures on reduced graphene oxide for H2 generation from ammonia borane

Cu_0.5Co_0.5O cubes on rGO shows a high TOF of 81.7 (H₂) mol (Cat-metal)mol⁻¹ min⁻¹ in the hydrolysis of ammonia borane.