Defect Induced in 3D-Rhombohedral MnCO3 Microcrystals by Substitution of Transition Metals for Aqueous and Solid-State Hybrid Supercapacitors

In this context, we synthesize pristine and transition metal (Fe, Co, Ni, and Cu) (TM)-doped uniform, 3D-rhombohedral manganese carbonate (MnCO3) microcrystals using a simple hydrothermal method. The substitution of different TMs notably induces structural defects in the 3D-rhombohedral microcrystals as evidenced by X-ray diffraction data and micro-Raman spectra. From the detailed investigation, the optimum Fe-MnCO3 sample exhibits a higher specific capacity of 55.83 mAh g(-1) at 1 Ag-1 with a remarkable rate capability of 64.39%. This is attributed to uniform morphology, abundant electroactive sites, homogeneous particle size, a higher amount of structural defects, and lower electronic/ionic resistance. Further, aqueous and solid-state hybrid supercapacitors (HSCs) were fabricated using 3D- rhombohedral Fe-MnCO3 as a positive electrode and activated carbon (AC) as a negative electrode in aqueous KOH and PVA/ KOH polymer gel electrolytes, respectively. The aqueous HSC (AHSC) and solid-state HSC (SHSC) devices deliver maximum energy densities of 22.38 and 19.74 Wh kg(-1) at power densities of 374 and 380 W kg(-1) along with good initial capacitance retentions of 88.85% and 82.63% after 10,000 cycles, respectively. The practical applicability of fabricated devices is proved by successfully powering a pair of light-emitting diodes (LEDs) of different colors (red, green, and blue) using two SHSCs connected in series.

Automated summary

By using a simple hydrothermal method, pristine and transition metal-doped 3D rhombohedral manganese carbonate microcrystals with enhanced specific capacity and improved cyclic stability were successfully synthesized. The fabricated aqueous and solid-state hybrid supercapacitors showed excellent performances in terms of energy density and cycling stability.