Huaiyu Shao

Hydrogen generation via hydrolysis of magnesium with seawater using Mo, MoO2, MoO3 and MoS2 as catalysts

Hydrogen generation is one of the enabling technologies for realization of hydrogen economy. In this study, we developed a high-performance hydrogen generation system using the transition metal Mo and its compounds (MoS2, MoO2, and MoO3) for catalyzing the hydrolysis of Mg composites in seawater. These Mg-based composites for the hydrolysis process were synthesized through a simple planetary ball mill technique. The results demonstrate that small amounts of added MoS2 could significantly accelerate and enhance the hydrolysis reaction of Mg in seawater. In particular, the Mg–10 wt% MoS2 composite releases 838 mL g−1 hydrogen in 10 min (about 89.8% of the theoretical hydrogen generation yield), and the recycled catalysts exhibit high cycle stability, which is the most significant achievement in this study. In addition, Mo, MoO2, and MoO3 also showed similar enhancement in the hydrolysis reaction of Mg. The activation energies for the hydrolysis of Mg decreased from 63.9 kJ mol−1 to 27.6 kJ mol−1, 20.4 kJ mol−1, 14.3 kJ mol−1, and 12.1 kJ mol−1 on introducing Mo, MoS2, MoO2, and MoO3, respectively. The attractive hydrolysis performance of the composites of Mg milled with Mo and its compounds in seawater may shed light on future developments of hydrogen generation technologies.

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.

Variation in the ratio of Mg2Co and MgCo2 in amorphous-like mechanically alloyed MgxCo100–x using atomic pair distribution function analysis

Abstract Mg2Co- and MgCo2-like local atomic arrangements in mechanically alloyed MgxCo100–x were investigated using atomic pair distribution function (PDF) analysis derived from synchrotron X-ray total scattering data. We show that changes in MgxCo100–x PDFs with x are well explained by the structural features of Mg2Co and MgCo2. This strongly supports our two-phase model picture where Mg2Co-like phase continuously increases while MgCo2 decreases with increasing Mg content in MgxCo100–x.

Synthesis and hydrolysis of NaZn(BH4)3 and its ammoniates

The synthesis and hydrolysis performance of NaZn(BH4)3 and its ammoniates were investigated in this paper. The successful synthesis of NaZn(BH4)3 and its ammoniates was confirmed by X-ray diffractometry and Fourier transform infrared spectroscopy measurements. The hydrolysis results show that NaZn(BH4)3 is able to generate 1740 mL g−1 hydrogen in 5 min and 1956 mL g−1 hydrogen in 30 min without concomitant release of undesirable gases such as ammonia or boranes. This rate can be too fast to be controllable in some hydrogen generation cases. In addition, it is found that NaZn(BH4)3·2NH3 generates 118 mL g−1 hydrogen in 5 min and 992 mL g−1 hydrogen in 2 h, accompanied by an emission of a small amount of ammonia. Furthermore, an enhanced hydrolysis performance can be achieved by formation of NaZn(BH4)3/NaZn(BH4)3·2NH3 composites. These composites synthesized via a planetary ball milling technique may generate hydrogen with a very reasonable and controllable speed of 717 mL g−1 hydrogen in 5 min and 1643 mL g−1 hydrogen in 2 h. The activation energies for the hydrolysis in deionized water of NaZn(BH4)3, NaZn(BH4)3·2NH3 and the NaZn(BH4)3/NaZn(BH4)3·2NH3 composite milled for 30 min were calculated to be 11.9 kJ mol−1, 56.9 kJ mol−1 and 32.5 kJ mol−1, respectively. These results demonstrate that the catalyst-free NaZn(BH4)3 and its ammoniates show better hydrolysis kinetics than other NaBH4 based materials and have the potential to be used as solid hydrogen generation materials.

Hydrogen generation properties and the hydrolysis mechanism of Zr(BH4)4·8NH3

Zr(BH4)4·8NH3 is considered to be a promising solid-state hydrogen-storage material, due to its high hydrogen density and low dehydrogenation temperature. However, the release of ammonia hinders its practical applications. To further reduce the dehydrogenation temperature and suppress ammonia release, here we investigated its hydrolysis process to evaluate its hydrogen generation performance. The results showed that the hydrolysis of Zr(BH4)4·8NH3 in water can generate about 1067 mL g−1 pure hydrogen in 240 min at 298 K without the release of diborane or ammonia impurity gases. With heat-assistance, the hydrogen generation rate can be significantly enhanced, and its activation energy was calculated to be 29.38 kJ mol−1. The hydrolysis mechanism was clarified. The results demonstrate that Zr(BH4)4·8NH3 may work as one promising hydrogen generation material.

Advanced SEM and TEM Techniques Applied in Mg-Based Hydrogen Storage Research

Mg-based materials are regarded as one of the most promising candidates for hydrogen storage. In order to clarify the relationship between the structures and properties as well as to understand the reaction and formation mechanisms, it is beneficial to obtain useful information about the size, morphology, and microstructure of the studied materials. Herein, the use of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques for the representation of Mg-based hydrogen storage materials is described. The basic principles of SEM and TEM are presented and the characterizations of the size, morphology observation, phase and composition determination, and formation and reaction mechanisms clarification of Mg-based hydrogen storage materials are discussed. The applications of advanced SEM and TEM play significant roles in the research and development of the next-generation hydrogen storage materials.

Solid Hydrogen Storage Materials: High Surface Area Adsorbents

This chapter describes main hydrogen adsorption characteristics and key parameters closely related to the sorption mechanism of high surface area sorbent materials by highlighting two promising materials of nanostructured carbon and metal-organic-frameworks (MOFs).

Synthesis, Morphology, and Hydrogen Absorption Properties of TiVMn and TiCrMn Nanoalloys with a FCC Structure

TiVMn and TiCrMn alloys are promising hydrogen storage materials for onboard application due to their high hydrogen absorption content. However, the traditional synthesis method of melting and continuous necessary heat treatment and activation process are energy- and time-consuming. There is rarely any report on kinetics improvement and nanoprocessing in TiVMn- and TiCrMn-based alloys. Here, through ball milling with carbon black as additive, we synthesized face-centered cubic (FCC) structure TiVMn- and TiCrMn-based nanoalloys with mean particle sizes of around a few to tens of μm and with the crystallite size just 10 to 13 nm. Differential scanning calorimetry (DSC) measurements under hydrogen atmosphere of the two obtained TiVMn and TiCrMn nanoalloys show much enhancement on the hydrogen absorption performance. The mechanism of the property improvement and the difference in the two samples were discussed from microstructure and morphology aspects. The study here demonstrates a new potential methodology for development of next-generation hydrogen absorption materials.