Gongbiao Xin

MOF derived catalysts for electrochemical oxygen reduction

Developing noble metal free catalysts for the oxygen reduction reaction (ORR) is of critical importance for the production of low cost polymer electrolyte membrane fuel cells. In this paper, metal organic frameworks (MOFs) are used as precursors to synthesize ORR catalysts via pyrolysis in an inert atmosphere. The ORR performance is found to be closely associated with the metal/ligand combination in MOFs. The Co-imidazole based MOF (ZIF-67) derived catalyst exhibits the best ORR activity in both alkaline and acidic electrolytes. The Co cations coordinated by the aromatic nitrogen ligands in ZIF-67 may assist the formation of ORR active sites in the derived catalyst. The best ORR performance is obtained when the porosity of the derived catalyst is maximized, by optimizing the pyrolysis temperature and the acid leaching process. The performance of the best MOF derived catalyst is comparable to that of Pt/C in both alkaline and acidic electrolytes.

In situ hybridization of LiNH2–LiH–Mg(BH4)2 nano-composites: intermediate and optimized hydrogenation properties

Nano-composites of LiNH(2)-LiH-xMg(BH(4))(2) (0 ≤ x ≤ 2) were prepared by plasma metal reaction followed by a nucleation growth method. Highly reactive LiNH(2)-LiH hollow nanoparticles offered a favorable nucleus during a precipitation process of liquid Mg(BH(4))(2)·OEt(2). The electron microscopy results suggested that more than 90% of the obtained nano-composites were in the range 200-400 nm. Because of the short diffusion distance and ternary mixture self-catalyzing effect, this material possesses enhanced hydrogen (de)sorption attributes, including facile low-temperature kinetics, impure gases attenuation and partial reversibility. The optimal hydrogen storage properties were found at the composition of LiNH(2)-LiH-0.5Mg(BH(4))(2), which was tentatively attributed to a Li(4)(NH(2))(2)(BH(4))(2) intermediate. 5.3 wt% hydrogen desorption could be recorded at 150 °C, with the first 2.2 wt% release being reversible. This work suggests that controlled in situ hybridization combined with formula optimization can improve hydrogen storage properties.

Excellent hydrogen sorption kinetics of thick Mg–Pd films under mild conditions by tailoring their structures

500 nm thick Mg–Pd films with different structures were prepared and their hydrogen storage properties were investigated. Results indicated that thin Ti interlayers in the Mg bulk film could significantly improve the hydrogen sorption kinetics and reversibility, offering an effective way to improve the hydrogen storage properties of thick Mg-based films.

Thermodynamic Property Study of Nanostructured Mg-H, Mg-Ni-H, and Mg-Cu-H Systems by High Pressure DSC Method

Mg, Ni, and Cu nanoparticles were synthesized by hydrogen plasma metal reaction method. Preparation of Mg2Ni and Mg2Cu alloys from these Mg, Ni, and Cu nanoparticles has been successfully achieved in convenient conditions. High pressure differential scanning calorimetry (DSC) technique in hydrogen atmosphere was applied to study the synthesis and thermodynamic properties of the hydrogen absorption/desorption processes of nanostructured Mg-H, Mg-Ni-H, and Mg-Cu-H systems. Van’t Hoff equation of Mg-Ni-H system as well as formation enthalpy and entropy of Mg2NiH4 was obtained by high pressure DSC method. The results agree with the ones by pressure-composition isotherm (PCT) methods in our previous work and the ones in literature.

Porous Mg thin films for Mg–air batteries

An alkaline primary Mg-air battery made from a porous Mg thin film displayed superior discharge performances, including a flat discharge plateau, a high open-circuit voltage of 1.41 V and a large discharge capacity of 821 mAh g(-1), suggesting that the electrochemical performances of Mg-air batteries can be improved by controlling the Mg anode morphology.

Preparation and Dehydrogenation Properties of Lithium Hydrazidobis(borane) (LiNH(BH3)NH2BH3)

LiNH(BH3)NH2BH3, the first example of metal-substituted hydrazine bisborane (HBB), is synthesized via the reaction between HBB and n-butyllithium in ether solution. (11)B NMR and Fourier transform infrared spectroscopy indicate a new structure, in which one of the N-H bonds is replaced by a N-Li bond. The X-ray diffraction pattern of the product also indicates the formation of a new crystal structure. This compound releases hydrogen at 126 and 170 °C with satisfactory purity and exhibits superior hydrogen storage properties compared with HBB. Differential scanning calorimetry measurement suggests the dehydrogenation reaction of this compound is less exothermic than that of HBB.

Promising hydrogen storage properties of cost-competitive La(Y)–Mg–Ca–Ni AB3-type alloys for stationary applications

In this paper, La(0.65−x)YxMg1.32Ca1.03Ni9 (x = 0, 0.05, 0.20, 0.40, 0.60) alloys were prepared by an induction melting method, and the effects of Y substitution on the hydrogen storage properties were systematically investigated. The results showed that the hydrogen sorption plateau pressures could be easily tailored by altering the Y amount, and the effective hydrogen desorption capacities at 0.1 MPa H2 below 80 °C could be greatly promoted with the optimal amount of Y substitution. In addition, the cost of the prepared alloys is quite low due to the absence of high price rare earth metals. Therefore, the cost-competitive La(Y)–Mg–Ca–Ni AB3-type alloys prepared in this study successfully meet the demands of proton-exchange membrane fuel cells and other stationary apparatus, showing broad application potential.

Improved electrochemical hydrogen storage properties of Mg-Y thin films as a function of substrate temperature

Abstract Pd-capped Mg78Y22 thin films have been prepared by direct current magnetron co-sputtering system at different substrate temperatures and their electrochemical hydrogen storage properties have been investigated. It is found that rising substrate temperature to 60 °C can coarsen the surface of thin film, thus facilitating the diffusion of hydrogen atoms and then enhancing its discharge capacity to ~1725 mAh·g−1. Simultaneously, the cyclic stability is effectively improved due to the increased adhesion force between film and substrate as a function of temperature. In addition, the specimen exhibits a very long and flat discharge plateau at about −0.67 V, at which nearly 60% of capacity is maintained. The property is favorable for the application in metal hydride/nickel secondary batteries. The results indicate that rising optimal substrate temperature has a beneficial effect on the electrochemical hydrogen storage of Mg-Y thin films.