High-Temperature Thermochemical Heat Storage Via the CuO/Cu2O Redox Cycle: from Material Synthesis to Packed-Bed Reactor Engineering and Cyclic Operation

A thermochemical redox cycle based on the CuO/Cu2O pair is considered for high-temperature heat storage in concentrated solar energy applications. A synthesis method is developed for the manufacture of porous CuO-based granules with yttria-stabilized zirconia (YSZ) as the sintering inhibitor. The synthesized granules exhibit high and reversible redox conversion over 100 consecutive cycles in air between 950 and 1050 degrees C and yield a gravimetric energy storage density associated with the endothermic/exothermic redox reactions in the range of 470 to 615 kJ/kg for 50 to 65 wt % CuO-YSZ granules. A lab-scale packed-bed reactor is designed for direct heat transfer between the granules and an air/N-2 flow serving simultaneously as the gaseous reactant and heat transfer fluid. The reactor is applied to perform two sets of 30 consecutive redox cycles subjected to either temperature-swing (isobaric) or pressure-swing (isothermal) operational mode. Stable charging-discharging cycling performances are achieved in both modes, with narrow thermal hysteresis between reduction/oxidation onset temperatures (<= 10 degrees C) and self-stabilization of the discharging temperature in the range of 1020-1025 degrees C when operating under an air flow.