Hydrazine borane (N(2)H(4)BH(3)) is the novel boron- and nitrogen-based material appearing to be a promising candidate in chemical hydrogen storage. It stores 15.4 wt% of hydrogen in hydridic and protic forms, and the challenge is to release H(2) with maximum efficiency, if possible all hydrogen stored in the material. An important step to realize this ambitious goal is to synthesize HB with high yields and high purity, and to characterize it fully. In this work, we report a 2-step synthesis (salt metathesis and solvent extraction-drying) through which N(2)H(4)BH(3) is successfully obtained in 3 days, with a yield of about 80% and a purity of 99.6%. N(2)H(4)BH(3) was characterized by NMR, IR, XRD, TGA and DSC, its stability in dioxane and water was determined, and its thermolysis by-products were characterized. We thus present a complete data sheet that should be very useful for future studies. Furthermore, we propose a discussion on the potential of HB (with H(2) released by either thermolysis or hydrolysis) in chemical hydrogen storage.

Today there is a consensus regarding the potential of NaBH4 as a good candidate for hydrogen storage and release via hydrolysis reaction, especially for mobile, portable and niche applications. However as gone through in the present paper two main issues, which are the most investigated throughout the open literature, still avoid NaBH4 to be competitive. The first one is water handling. The second one is the catalytic material used to accelerate the hydrolysis reaction. Both issues are objects of great attentions as it can be noticed throughout the open literature. This review presents and discusses the various strategies which were considered until now by many studies to manage water and to improve catalysts performances (reactivity and durability). Published studies show real improvements and much more efforts might lead to significant overhangs. Nevertheless, the results show that we are still far from envisaging short‐term commercialisation.

No abstract

The effect of the nature of the transition metal on the structure and activity for hydrogen evolution of Metal-N-C catalysts synthesized via the pyrolysis of metal salts and a Zn-based metal organic framework was investigated. It is found that W, Mo, Cu and Zn lead to amorphous carbons with high specific area while Cr, Mn, Fe, Co and Ni lead to more graphitic carbons with a lower specific area. Metal salts with a high redox potential are fully reduced during pyrolysis while others are only partially reduced. Electrochemical activity toward hydrogen evolution was investigated at pH 1 and pH 13. Hydrogen evolution on these Metal-N-C catalysts is generally more facile at pH 1 than at pH 13, paralleling the trends observed for noble metal surfaces. The Co-, Ni-and Fe-N-C catalysts are the most active at pH 13 while Co-N-C and Cr-N-C are the most active at pH 1. The activity of the latter catalysts stems from metallic cobalt particles encapsulated in carbon and from a chromium carbo-nitride phase, respectively.

Confocal Raman spectra of a lithium-sulfur battery electrolyte are recorded operando in a depth-of-discharge resolved manner for an electrochemical cell with a realistic electrolyte/sulfur loading ratio. The evolution of various possible polysulfides is unambiguously identified by combining Raman spectroscopy data with DFT simulations.

No abstract

Methanolysis of sodium borohydride (NaBH 4 ) is a way of recovering the hydrogen stored in the hydride. Though the reaction is spontaneous, it can be accelerated by virtue of Co-TiO 2 or Ru-TiO 2 catalysts. Under our experimental conditions, Co-TiO 2 shows high catalytic performances, higher than those of Ru-TiO 2 . Hydrogen generation rates of 144 to 644 L(H 2 ) min À1 g À1 (Co) were measured as the Co content was decreased. The kinetic parameters of the catalyzed reaction were determined. The Co-TiO 2 -catalyzed methanolysis follows a power law, i.e. r 20 ¼ k$[NaBH 4 ] 1.3 $[CH 3 OH] 0.9 with k ¼ 1.8 Â 10 À2 s À1 . The Langmuir-Hinshelwood bimolecular mechanism accounts for the kinetics. The apparent activation energy was found to be 20.4 kJ mol À1 whereas that of the catalyzed hydrolysis was 49.4 kJ mol À1 . Indeed, the catalyzed methanolysis was compared to the catalyzed hydrolysis as well as the catalyzed ethanolysis. For instance, it was remarked that water in methanol has a detrimental effect on the H 2 release kinetics. In parallel, the gravimetric hydrogen density of the system NaBH 4 -CH 3 OH has been optimized. Under our experimental conditions, it was found that the highest capacity that can be achieved is 3.4 wt%.

Abstract:The effect of ZIF-8 crystal size on the morphology and performance of Fe-N-C catalysts synthesized via the pyrolysis of a ferrous salt, phenanthroline and the metal-organic framework ZIF-8 is investigated in detail. Various ZIF-8 samples with average crystal size ranging from 100 to 1600 nm were prepared. The process parameters allowing a templating effect after argon pyrolysis were investigated. It is shown that the milling speed, used to prepare catalyst precursors, and the heating mode, used for pyrolysis, are critical factors for templating nano-ZIFs into nano-sized Fe-N-C particles with open porosity. Templating could be achieved when combining a reduced milling speed with a ramped heating mode. For templated Fe-N-C materials, the performance and activity improved with decreased ZIF-8 crystal size. With the Fe-N-C catalyst templated from the smallest ZIF-8 crystals, the current densities in H2/O2 polymer electrolyte fuel cell at 0.5 V reached ca. 900 mA cm −2 , compared to only ca. 450 mA cm −2 with our previous approach. This templating process opens the path to a morphological control of Fe-N-C catalysts derived from metal-organic frameworks which, when combined with the versatility of the coordination chemistry of such materials, offers a platform for the rational design of optimized Metal-N-C catalysts.