Microstructural evolution and performance of hydrogen storage andelectrochemistry of Co-added La0.75Mg0.25Ni3.5−xCox (x = 0, 0.2, 0.5 at%)alloys

Microstructural evolution and performance of hydrogen storage and electrochemistry of Co-added La_(0.75)Mg_(0.25)Ni_(3.5-x)Co_x(x=0,0.2,0.5 at%) alloys

Microstructure, hydrogen storage and electrochemical performances of Co-added La_(0.75)Mg_(0.25)Ni_(3.5_x)Co_x(x = 0,0.2, 0.5 at%) alloys are studied. XRD and rietveld refinement results suggest that the samples are mainly composed of(LaMg)Ni_3,(LaMg)_2Ni_7 and LaNi_5 phases, Co substitution for Ni changes the phase abundance,but not the phase composition. With the rising of Co content, the amount of(LaMg)_2 Ni_7 phase decreases, but the amount of LaNi_5 phase increases, while the amount of(LaMg)Ni_3 phase firstly increases and then decreases.The alloys reversibly absorb and desorb hydrogen at 298 K smoothly. When Co content is 0.2 at%, the hydrogen absorption capacity reaches the maximum value of 1.14 H/M, and the absorption capacities reach 1.09 H/M and 1.03 H/M in the first minute at 298 K and 323 K, respectively. Electrochemical performance measurement results show that La_(0.75)Mg_(0.25)Ni_(3.5-x)Co_x alloys are completely activated within 2 cycles, and the cyclic stability of La_(0.75)Mg_(0.25)Ni_(3.3)Co_(0.2) alloy approaches 63.7% after 100 charge/discharge cycles, which is higher than that(S_(100) = 60%) of La_(0.75)Mg_(0.25)Ni_(3.0)Co_(0.5) alloy. Thus, the La_(0.75)Mg_(0.25)Ni_(3.3)Co_(0.2) alloy exhibits optimum comprehensive properties of hydrogen storage and electrochemistry.