1,721,203 research outputs found
Hydrogen storage in thin film magnesium-scandium alloys
No full textThorough electrochemical materials research has been performed on thin films of novel magnesium–scandium hydrogen storage alloys. It was found that palladium-capped thin films of MgxSc(1-x) with different compositions (ranging from x=0.50 –0.90) show an increase in hydrogen storage capacity of more than 5–20% as compared to their bulk equivalents using even higher discharge rates. The maximum reversible hydrogen storage capacity at the optimal composition (Mg80Sc20) amounts to 1795 mAh/g corresponding to a hydrogen content of 2.05 H/M or 6.7 wt.%, which is close to five times that of the commonly used hydride-forming materials in commercial NiMH batteries. Galvanostatic intermittent titration technique (GITT) measurements show that the equilibrium pressure during discharge is lower than that of bulk powders by one order of magnitude (10-7 mbar versus 10-6 mbar, respectively)
Mechanical alloying and electrochemical hydrogen storage of Mg-based systems
No full textResults on mechanical alloying of binary and ternary Mg-Ti-based mixtures are reported. Using fine-powdered reactants and a process-control-agent, a mixture of two face-centered cubic compounds is obtained. Using a coarse Mg precursor without addition of a milling agent results in a hexagonal-solid solution of Ti in Mg due to a lower oxygen content in the Mg starting material. Upon introduction of Ni or A1 as a third element, the amount of dissolved Ti decreases to form a nanocrystalline secondary phase. The electrochemical charging capacity of the hexagonal compounds is far superior to that of the cubic ones, whereas the discharge capacity is significantly increased only upon addition of Ni. The secondary TiNi phase acts as a rapid diffusion path for hydrogen, greatly improving the rate capability of the alloys. The reversible hydrogen storage capacity reaches values of up to 3.2 wt% at room temperature for (Mg0.75 Ti0.25)0.90 Ni0.10. © 2008 Materials Research Societ
The influence of O2 on the electrochemistry of thin film, hydrogen storage, electrodes
No full textThe influence of oxygen on the electrochemical response of magnesium–scandium (Mg–Sc) thin film electrodes has been investigated. It was found that the impact of oxygen dissolved in the electrolyte is two-fold. Firstly, it gives rise to a mixed-potential under open-circuit conditions that is much more positive than the true equilibrium potential of the hydride material, thus yielding incorrect thermodynamic data. Secondly, it causes self-oxidation of the hydrogenated thin films, making calculations regarding hydrogen storage capacities (mAh/g) not straightforward. A novel oxygen-scrubbing device was developed to de-oxygenate the argon used as purging gas during the electrochemical measurements. This self-regenerative system is based on the high reactivity of the methylviologen single radical towards oxygen. A comparison between various electrochemical responses of identical Mg–Sc thin film electrodes, measured with and without the presence of oxygen, showed distinct deviations in equilibrium potential and hydrogen storage capacity
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