A simple facile synthesis for phase transforming of δ-MnO2 into α-MnO2 and thereby enhancing Na-ion supercapacitive performance

This study presents a phase transformation of MnO2 from δ to α-phase through a simple facile and efficient method without any surfactant. Different hierarchical architectures of MnO2 were achieved with the successful conversion of the crystal structure. Growth of 3D dandelion flowers is realized when MnO2 is in the δ-phase whereas, with varying reaction time, it gets converted to α-MnO2 with hollow 3D urchin-like architecture composed of 1D nanorods tightly arranged in a dense alignment. Initially, this phase transformation was realized from structural and morphological characterizations. The electrodes of δ and α-phase MnO2 architectures were fabricated on Ni foam. These electrodes were then systematically tested for supercapacitive features in sodium ions, revealing that α-MnO2 has superior Na-ion supercapacitive behavior compared to the δ-phase counterpart. Electrochemical performance reflects that the 3D urchin-like structure has the highest capacitive features with 173.6 F g−1 at 3 mA cm−2 with ultralong capacitive retention performance of 134.8