Spinel oxides are important photothermal conversion material. ZnCo2O4, Co3O4, and CoAl2O4 were used as model spinel systems to investigate the influence of cation geometric configuration on photothermal conversion. In these systems, all of the octahedral sites (Oh) are occupied by Co3+ while all of the tetrahedral sites (Td) are occupied by Co2+. Experimental results indicate that Co3+-Oh (ZnCo2O4) exhibits a higher photothermal conversion efficiency (85.7%) than Co2+-Td (74.0%) under a light intensity of 94 W/m2. The superior performance of Co3+-Oh over Co2+-Td is attributed to the reduced bandgap, which enhances nonradiative transitions and electron–phonon coupling, thereby improving photothermal conversion efficiency. Furthermore, subsequent Ni doping into the Co3O4 framework promotes the migration of Co ions into octahedral sites, further improving the photothermal conversion efficiency to 86.5%, which surpasses the commercial material Pyromark 2500. This work elucidates the structure–property relationship of spinel-based photothermal materials and identifies the optimal geometric configuration.
Ma et al. (Fri,) studied this question.