Hexagonal CuCo₂O₄ Nanoplatelets, a Highly Active Catalyst for the Hydrolysis of Ammonia Borane for Hydrogen Production

Boosted Catalytic Activity toward the Hydrolysis of Ammonia Borane by Mixing Co- and Cu-Based Catalysts

Promoting the activity of heterogeneous catalysts in the hydrolysis of ammonia borane for hydrogen production is still a challenging topic for researchers in the hydrogen energy and catalysis fields. Herein, we present a universal, simple and efficient strategy to boost the catalytic performance toward AB hydrolysis by mixing Co- and Cu-based catalysts for the first time. Synergistic catalysts with remarkably enhanced activity can be obtained by mixing a Co-based catalyst and a Cu-based catalyst together, such as Co3O4 and Cu3(MoO4)2(OH)2, Co3O4 and Cu3(PO4)2, Co3(PO4)2 and Cu3(MoO4)2(OH)2, Co3(PO4)2 and Cu3(PO4)2, and CuO and Co3O4. For example, the turnover frequency (TOF) for the mixture catalyst of Co3O4 and Cu3(MoO4)2(OH)2 with a mass ratio of 4:1 is up to 77.3 min−1, which is approximately 11.5 times higher than that of the sum of Co3O4 and Cu3(MoO4)2(OH)2. The reasons for these findings are discussed in detail. The observations and conclusions in this work may provide a guideline for promoting the hydrolysis of ammonia borane through a simple and effective approach.

Catalytic Behavior of Iron-Containing Cubic Spinel in the Hydrolysis and Hydrothermolysis of Ammonia Borane

The paper presents a comparative study of the activity of magnetite (Fe₃O₄) and copper and cobalt ferrites with the structure of a cubic spinel synthesized by combustion of glycine-nitrate precursors in the reactions of ammonia borane (NH₃BH₃) hydrolysis and hydrothermolysis. It was shown that the use of copper ferrite in the studied reactions of NH₃BH₃ dehydrogenation has the advantages of a high catalytic activity and the absence of an induction period in the H₂ generation curve due to the activating action of copper on the reduction of iron. Two methods have been proposed to improve catalytic activity of Fe₃O₄-based systems: (1) replacement of a portion of Fe²⁺ cations in the spinel by active cations including Cu²⁺ and (2) preparation of highly dispersed multiphase oxide systems, involving oxide of copper.

Fabrication of Bimetallic Oxides (MCo2O4: M=Cu, Mn) on Ordered Microchannel Electro-Conductive Plate for High-Performance Hybrid Supercapacitors

AB2O4-type binary-transition metal oxides (BTMOs) of CuCo2O4 and MnCo2O4 were successfully prepared on ordered macroporous electrode plates (OMEP) for supercapacitors. Under the current density of 5 mA cm−2, the CuCo2O4/OMEP electrode achieved a specific capacitance of 1199 F g−1. The asymmetric supercapacitor device prepared using CuCo2O4/OMEP as the positive electrode and carbon-based materials as the negative electrode (CuCo2O4/OMEP//AC) achieved the power density of 14.58 kW kg−1 under the energy density of 11.7 Wh kg−1. After 10,000 GCD cycles, the loss capacitance of CuCo2O4/OMEP//AC is only 7.5% (the retention is 92.5%). The MnCo2O4/OMEP electrode shows the specific and area capacitance of 843 F g−1 and 5.39 F cm−2 at 5 mA cm−2. The MnCo2O4/OMEP-based supercapacitor device (MnCo2O4/OMEP//AC) has a power density of 8.33 kW kg−1 under the energy density of 11.6 Wh kg−1 and the cycle stability was 90.2% after 10,000 cycles. The excellent power density and cycle stability prove that the prepared hybrid supercapacitor fabricated under silicon process has a good prospect as the power buffer device for solar cells.

A Novel Au@Cu2O-Ag Ternary Nanocomposite with Highly Efficient Catalytic Performance: Towards Rapid Reduction of Methyl Orange Under Dark Condition

Au@Cu2O core-shell nanocomposites (NCs) were synthesized by reducing copper nitrate on Au colloids with hydrazine. The thickness of the Cu2O shells could be varied by adjusting the molar ratios of Au: Cu. The results showed that the thickness of Cu2O shells played a crucial role in the catalytic activity of Au@Cu2O NCs under dark condition. The Au@Cu2O-Ag ternary NCs were further prepared by a simple galvanic replacement reaction method. Moreover, the surface features were revealed by TEM, XRD, XPS, and UV-Vis techniques. Compared with Au@Cu2O NCs, the ternary Au@Cu2O-Ag NCs had an excellent catalytic performance. The degradation of methyl orange (MO) catalyzed by Au@Cu2O-Ag NCs was achieved within 4 min. The mechanism study proved that the synergistic effects of Au@Cu2O-Ag NCs and sodium borohydride facilitated the degradation of MO. Hence, the designed Au@Cu2O-Ag NCs with high catalytic efficiency and good stability are expected to be the ideal environmental nanocatalysts for the degradation of dye pollutants in wastewater.

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.