Modulating the Acidic Properties of Mesoporous Mox-Ni0.8Cu0.2O Nanowires for Enhanced Catalytic Performance toward the Methanolysis of Ammonia Borane for Hydrogen Production

Localized Electron Redistribution in Methanol Molecules over the Sea Urchin-like Tricobalt Tetroxide/Copper Oxide Nanostructures for Fast Hydrogen Release

Catalytic methanolysis of ammonia borane (NH3BH3) is a prospective technology in the field of hydrogen energy in which hydrogen production and hydrogen storage can be integrated together. The splitting of the O-H bond is identified as the rate-determining step (RDS) in this reaction. Thus, a deep understanding of the relationship between the electronic structure of the catalyst, especially the localized electron density of active sites, and the breaking behaviors of the O-H bond is of extreme importance for the rational design of robust catalysts for the reaction. In this work, sea urchin-like tricobalt tetroxide/copper oxide (Co3O4/CuO) nanostructures with rich oxygen vacancies (Ov) were fabricated by a simple synthetic route. In NH3BH3 methanolysis, the optimal Co3O4/CuO sample exhibited ultrahigh catalytic activity with a turnover frequency (TOF) of 87.5 min-1. Interestingly, when NH3BH3 methanolysis was carried out under visible-light illumination, the TOF further increased to 116.4 min-1, which is the highest TOF value among those of the noble-metal-free catalysts ever documented in the literature. Theoretical calculation results evidenced that the Cu site in the Co3O4/CuO sample was in charge of the adsorption and activation of methanol molecules. Both the Ov and visible-light illumination can help electrons on the Cu site flow to the adsorbed methanol molecule, thus leading to localized electron redistribution of the methanol molecule and the extension of the O-H bond. The cooperation of Ov and visible light makes splitting of the O-H bond easier, which is favorable for fast hydrogen release from NH3BH3 methanolysis. This study helps us to gain an insight into the influence of localized electron redistribution of methanol molecules on the RDS, which conduces to the rational design of highly effective nanocatalysts. Moreover, the coinduction strategy for localized electron redistribution with oxygen vacancy engineering and visible-light illumination opens up a route to boost catalytic activity in NH3BH3 methanolysis.

Visible light-assisted hydrogen generation from ammonia borane over Z-Scheme NiO-CuO heterostructures

The design and fabrication of cheap and high-efficiency catalysts for ammonia borane (AB) hydrolysis for hydrogen production is crucial for its commercial applications. Improvement of the catalytic performance of the catalysts with the assistance of sunlight, a costless resource, is extremely attractive. Herein, we have constructed Z-scheme heterostructured VO-NiO-CuO catalysts with strong interfacial electronic interactions and abundant oxygen vacancies to enhance hydrogen production from NH3BH3 solution under visible light illumination. The as-prepared VO-NiO-CuO catalysts exhibit excellent catalytic activity with a high turnover frequency (TOF) of 35.3 molH2 molcat.-1 min-1 toward AB hydrolysis under visible light. It is demonstrated that excellent catalytic performance is highly related to the effective separation and migration of charge on the catalyst surface. As a result, dual active sites were created, making it easier for various reactants to be adsorbed and activated on the catalyst surface. Furthermore, the density functional theory (DFT) calculations indicate that the adsorption and activation of H2O occurred mainly at the Ni site of VO-NiO-CuO. When the VO-NiO-CuO is irradiated with visible light, the photogenerated electrons assembled on the conduction band were transferred to the O atom through the Ni-O bond, which made the bond length of H2O molecules longer and OH bonds more prone to breaking, thus facilitating AB hydrolysis under illumination. The findings in this work pave the way to design novel and efficient heterostructured catalysts for fast hydrogen release from NH3BH3 under visible light irradiation.

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.

Theoretical Study of Hydrogen Production from Ammonia Borane Catalyzed by Metal and Non-Metal Diatom-Doped Cobalt Phosphide

The decomposition of ammonia borane (NH3BH3) to produce hydrogen has developed a promising technology to alleviate the energy crisis. In this paper, metal and non-metal diatom-doped CoP as catalyst was applied to study hydrogen evolution from NH3BH3 by density functional theory (DFT) calculations. Herein, five catalysts were investigated in detail: pristine CoP, Ni- and N-doped CoP (CoPNi-N), Ga- and N-doped CoP (CoPGa-N), Ni- and S-doped CoP (CoPNi-S), and Zn- and S-doped CoP (CoPZn-S). Firstly, the stable adsorption structure and adsorption energy of NH3BH3 on each catalytic slab were obtained. Additionally, the charge density differences (CDD) between NH3BH3 and the five different catalysts were calculated, which revealed the interaction between the NH3BH3 and the catalytic slab. Then, four different reaction pathways were designed for the five catalysts to discuss the catalytic mechanism of hydrogen evolution. By calculating the activation energies of the control steps of the four reaction pathways, the optimal reaction pathways of each catalyst were found. For the five catalysts, the optimal reaction pathways and activation energies are different from each other. Compared with undoped CoP, it can be seen that CoPGa-N, CoPNi-S, and CoPZn-S can better contribute hydrogen evolution from NH3BH3. Finally, the band structures and density of states of the five catalysts were obtained, which manifests that CoPGa-N, CoPNi-S, and CoPZn-S have high-achieving catalytic activity and further verifies our conclusions. These results can provide theoretical references for the future study of highly active CoP catalytic materials.

Catalytic Hydrogen Evolution from H2S Cracking over CrxZnS Catalyst in a Cylindrical Single-Layered Dielectric Barrier Discharge Plasma Reactor

The use of non-thermal plasma technology in producing green fuels is a much-appreciated environmentally friendly approach. In this study, an Al₂O₃-supported Cr_xZnS semiconductor catalyst was tested for hydrogen evolution from hydrogen sulfide (H₂S) gas by using a single-layered dielectric barrier discharge (DBD) system. The Al₂O₃-supported Cr_xZnS catalyst (x = 0.20, 0.25, and 0.30) was produced by using a co-impregnation method and characterized for its structural and photocatalytic characteristics. The discharge column of the DBD system was filled with this catalyst and fed with hydrogen sulfide and argon gas. The DBD plasma was sustained with a fixed AC source of 10 kV where plasma produced species and UV radiations activated the catalyst to break H₂S molecules under ambient conditions. The catalyst (hexagonal-cubic-sphalerite structure) showed an inverse relationship between the band gap and the dopant concentration. The hydrogen evolution decreased with an increase in dopant concentration in the nanocomposite. The Cr_0.20ZnS catalyst showed excellent photocatalytic activity under the DBD exposure by delivering 100% conversion efficiency of H₂S into hydrogen. The conversion decreased to 96% and 90% in case of Cr_0.25ZnS and Cr_0.30ZnS, respectively.