Microstructures and electrochemical properties of Co-free AB5-type hydrogen storage alloys through substitution of Ni by Fe

Improvement in the low-temperature performance of AB5 metal hydride alloys by Fe-addition

“…Previous works of partially replacing Ni with Fe in AB 5 MH alloy showed both lower [25][26][27] and higher [28,29] gaseous hydrogen storages, either lower [25][26][27]30,31] or higher equilibrium plateau pressures [32], a low electrochemical capacity [24,33,34], a higher HRD due to higher surface area [24,34] or a lower HRD due to low exchange current and diffusion coefficient [35], and a harder activation [31,34]. In the case of Fe substitution for both Ni and Co, both the electrochemical capacity and plateau pressure decrease, and both lattice constants increase [36].…”

Improvement in high-temperature performance of Co-free high-Fe AB5-type hydrogen storage alloys

“…More apparently, S 125 i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 1 2 3 7 5 e1 2 3 8 3 increases from 7.1% for high-Co alloy to 44.1% for high-Fe alloy at the elevated temperature (60 C). The difference of S 150 at 20 C may be related to the lower cell volume change and lattice strain during hydriding/dehydriding cycling of Fecontaining alloy [11,15,18]. However, corrosion may become the most critical influences at high temperature, which will be discussed in the following section.…”

“…This is because that the atomic radius of Fe (1.72 Å ) is slightly larger than that of Co (1.67 Å ), and correspondingly results in a bigger cell volume, suggesting that Fe-containing MH has stronger metalehydrogen (MeH) bond strength. The anisotropy (ratios of c/a) for all the Fe-containing alloy samples is larger than that of the iron-free sample, which may relieve the stress concentration and reduce the volume swelling during hydriding/dehydriding cycles [11,19]. The fullwidth at half-maximum (FWHM) of the diffraction peak (101) of the Fe-free alloy is larger than that of Fe-containing alloys, and the crystallite sizes, derived from the FWHMs, increase as the increase of Fe content (summarized in Table 1).…”

Investigations on rate constants of the charging/discharging processes for metal hydride electrodes

“…The electrochemical method is a powerful instrument to research the kinetics performance and a series of them has been utilized to measure the kinetics parameters of hydrogen storage alloys [5][6][7][8]. Among these methods, constant potential and constant current discharge can only be used to measure an average diffusion coefficient from the given depth of discharge (DOD) to fully discharge state (100% DOD), because these methods disregard the dependence of the hydrogen diffusion coefficient on hydrogen concentration in the electrode [9].…”