For the first time, Manganese ferrite (MnFe2O4) with two different catalytic and morphological properties were synthesized through the conventional and template-synthetic approaches. The typical conventionally prepared MnFe2O4 particles attained nanoscaled spherical structure, and the unique structured novel MnFe2O4 nano-agglomerates were conquered by the template synthesis. The templates of MnCO3 made MnFe2O4 to attain the nano-agglomeric structure with the abundant electroactive surface area and copious catalytic sites, which were confirmed through the structural, morphological, elemental, and electrochemical investigations. By the recent reports, the supercapacitor and heavy metal detection properties of MnFe2O4 were recognized. Therefore, both the MnFe2O4 nanospheres (NSs), and MnFe2O4 nano-agglomerates (NAs) were applied for the detection of Hg(II) ions in real samples, and also for the supercapacitor applications. Both the materials exhibited moral parameters in electrochemical sensing and supercapacitor applications, but the results obtained for the MnFe2O4 NAs is quite high (LOD: 0.14 nM and Specific capacitance: 1283 F/g at 5 mV/s) when compared to the NSs. Finally, the MnFe2O4 NAs was employed to be an active participant in supercapacitor and also to detect Hg(II) ions in seafood and industrial wastewater samples. (C) 2018 Elsevier Ltd. All rights reserved.