Mn-Zr co-doped CaO composite particles for thermochemical energy storage: cycling stability enhancement mechanism and solar-driven conversion characteristics

Solar-driven calcium-looping offers a promising pathway for efficient storage and utilization of concentrated solar energy. However, the large-scale application of calcium-based heat carriers is hindered by low solar absorptance, poor sintering resistance, and slow reaction kinetics. Moreover, the energy conversion characteristics and particle behavior under direct irradiation remain poorly understood. In this study, Mn-Zr co-doped CaO composite particles were synthesized via an extrusion-spheronization method, achieving high absorptance, strong sintering resistance, and rapid reaction kinetics. Specifically, the co-doping of Mn and Zr significantly enhances absorptance to 67.7% while effectively reduces cracking. The stable framework of CaMnO 3 and CaZrO 3 maintains abundant mesoporous channels and suppresses sintering. The composite particles exhibit outstanding cycling stability, maintaining an energy storage density of 1148 kJ/kg after 40 cycles with only 22.9% degradation, far outperforming pure CaO materials (64.9% degradation after 20 cycles). Direct irradiation experiments confirm their high solar-thermal conversion efficiency, with particle temperature within the light spot reaching 1600 °C in 3 s. The irradiation-induced particle inhomogeneous sintering mechanism was preliminary proposed. Meanwhile, the effect of non-uniform irradiation on energy storage characteristics and particle behavior is revealed. Non-uniform irradiation led to localized hotspots and increased thermal stress, which aggravated particle breakage and sintering within the light spot.