Heat charge and discharge performance, mechanisms, and reversibility of coupled LaNi₅-La_0.6Ce_0.4Ni₅

A coupled LaNi₅-La_0.6Ce_0.4Ni₅ thermochemical heat storage system is proposed for storing waste heat at moderate charging temperatures (≤150 °C) and operating pressure of <30 bar H₂. LaNi₅ with lower equilibrium pressure (P _eq) and higher reaction enthalpy is used as a high-temperature hydride (HTH) for heat storage, while La_0.6Ce_0.4Ni₅ acts as a low-temperature hydride (LTH) for hydrogen storage. To improve the thermal conductivity and hydrogen diffusion of the hydride beds, the HTH and LTH were doped with 2 wt% multi-walled carbon nanotubes (MWCNTs). Subsequently, HTH and LTH powder samples were packed into two connected cylindrical containers (0.6 kg per container) assembled with a spiral tube heat exchanger. Upon heat charge and discharge cycles, gravimetric and volumetric energy densities reached 122.40 ± 1.37 kJ kg^-1 and 60.00 ± 0.65 kW h m^-3, respectively. During heat discharge, heating and cooling effects were transferred from the hydride beds using a heat transfer fluid. The compatible thermodynamics and kinetics of the HTH and LTH resulted in a comparable heat charge and discharge time (∼2 h). This is beneficial for the simple design of thermal storage systems since an extra unit of HTHs or LTHs is not required to optimize the heat exchange reaction rate.