Effect of cobalt substitution for nickel on microstructural evolution and hydrogen storage properties of La_(0.66)Mg_(0.34)Ni_(3.5-x)Co_(x) alloys

Superlattice hydrogen storage alloys offer a compelling advantage with rapid hydriding rate and high storage capacity.However,its practical applications face challenges including complex structure,low dehydriding capacity,and cyclic instability.In this work,we successfully prepared La_(0.66)Mg_(0.34)Ni_(3.5-x)Co_(x) superlattice hydrogen storage alloys with enhanced dehydriding capacity and stability by partially substituting Co for Ni.X-ray diffraction(XRD)refinements analysis reveals the presence of(La,Mg)_(3)Ni_(9),(La,Mg)_5Ni_(19),and LaNi_(5) phases within the alloy.Following Co substitution in the La_(0.06)Mg_(0.34)Ni_(3.4)Co_(0.1)alloy,there is a significant increase in content of the(La,Mg)_(3)Ni_(9) phase and a reduction in the hysteresis factor,resulting in an improved reversible hydrogen storage capacity from 1.45 wt%to 1.60 wt%.The dehydriding kinetics of the alloy is controlled by diffusion model with an activation energy of 8.40 kJ/mol.Furthermore,the dehydriding enthalpy value of the Co-substituted alloy decreases from 30.84 to 29.85 kJ/mol.Impressively,the cycling performance of the alloy after Co substitution exhibits excellent stability,with a capacity retention rate of 92.3%after 100 cycles.These findings provide valuable insights for the development of cost-effective hydrogen storage materials.

Polyaniline-derived carbon nanofibers with a high graphitization degree loading ordered PtNi intermetallic nanoparticles for oxygen reduction reaction

At present,the catalysts commercially used for the oxygen reduction reaction of the cathode of proton exchange membrane fuel cells(PEMFCs)are carbon-supported platinum-based catalysts.However,the carbon supports are susceptible to corrosion under harsh working conditions,which greatly shortens the life of the catalysts.Highly stable carbon supports are urgently required for high-performance PEMFCs.In this work,we developed structure-stable and highly graphitized three-dimensional network carbon nanofibers(CNF)derived from polyaniline by heat treatment at 1200℃.The CNF-1200-based catalyst(PtNi/CNF-1200)loaded with PtNi nanoparticles showed excellent stability.After 5000 cycles from 1.0 to 1.5 V in oxygen saturated 0.1 M HClO_(4) electrolyte,the losses in the half-wave potential and mass activity were only 5 mV and 15%,respectively,far lower than those of commercial Pt/C.The high graphitization degree of CNF-1200 promotes the corrosion resistance of the catalyst.In addition,nitrogen doping effectively facilitates the catalyst–support interaction,stabilizes the highly dispersed PtNi nanoparticles,and improves the stability and activity of PtNi/CNF-1200.