In situ generated 3D hierarchical Co3O4@MnO2 core–shell hybrid materials: self-assembled fabrication, morphological control and energy applications

Abstract

A simple in situ self-assembly strategy for a novel series of highly ordered 3D hierarchical Co₃O₄@MnO₂ core–shell hybrid materials with peculiar morphologies, uniform size and high quality has been successfully developed. The mechanisms of the morphology control, reaction process, product generation, calcining process, as well as the morphology evolution of Co₃O₄, the intermediates of Co₃O₄@C and Co₃O₄@MnO₂ hybrid materials, have been investigated and clarified in detail. The core–shell Co₃O₄@MnO₂ hybrid architectures have the advantages of morphological features, synergistic effects between core and shell, alternative products of Co₃O₄@C@MnO₂ or Co₃O₄@MnO₂, and facilitate electrolyte reactions. The 3D hierarchical Co₃O₄@MnO₂ core–shell hybrid materials are used, for the first time, for two typical Co-based energy applications in photoelectric conversion devices of dye-sensitized solar cells (DSSCs) and the decomposition of an important solid rocket propellant, ammonium perchlorate (AP). With the 3D hierarchical Co₃O₄ core and ultrathin MnO₂ shell, the developed hybrid materials exhibit superior performances and remarkable catalytic properties. As the alternative counter electrode of DSSCs, the developed Co₃O₄@MnO₂ core–shell hybrid system exhibited an impressive performance with the conversion efficiency of 7.08%, which was improved by 26.4% and 13.3% as compared with the Co₃O₄ and Co₃O₄@C counterparts, respectively. As the catalyzer of AP decomposition, the Co₃O₄ material obviously decreased the decomposition temperatures by about 118–143 °C and increased the exothermic heat to 933–1228 J g⁻¹. For the Co₃O₄@C counterpart, the decomposition temperatures were decreased by 120–131 °C with the increased exothermic heat of 1254–1306 J g⁻¹. The addition of Co₃O₄@MnO₂ core–shell hybrid materials decreased the decomposition temperatures by about 107–112 °C and remarkably increased the exothermic heat to 1311–1452 J g⁻¹. To the best of our knowledge, this is the first 3D hierarchical Co₃O₄@MnO₂ core–shell hybrid material series developed in situ and used for the energy applications of DSSCs and AP decomposition. These results provide a simple and effective strategy for designing new types of 3D hierarchical hybrid materials towards high catalytic activity in energy applications.