Fuel assisted crystal structure tailoring of manganese oxides and their surface reactivity towards oxygen evolution reaction

A simple and robust method has been proposed to synthesize manganese oxide polymorphs wherein the phase transition among the manganese oxides crystal structures was evidenced under the assistance of fuels via solution combustion route. The cubic-Mn 2 O 3 dominated with glycine and urea, while spinel tetragonal-Mn 3 O 4 was favored with sucrose, citric acid and maleic acid fuels. The average particle size of 17 nm and 21 nm is observed for Mn 2 O 3 derived from urea and glycine respectively. The Mn 2 O 3 derived from urea (Mn 2 O 3 –U) exhibits high fraction of Mn 3+ content and oxygen defects on the surface compared to the Mn 2 O 3 derived from glycine (Mn 2 O 3 –G). In addition, Mn 2 O 3 –U exhibits ~ 5 times higher electrochemical active surface area (237 cm −2 ) compared to Mn 2 O 3 –G (47.5 cm −2 ). Owing to the enhanced surface properties, Mn 2 O 3 –U demonstrates superior OER performance where it exhibits a low overpotential of 270 mV at the current density of 10 mA cm −2 compared to Mn 2 O 3 –G (590 mV 10 mA cm −2 ). The Mn 3 O 4 derived from sucrose (Mn 3 O 4 –S), citric acid (Mn 3 O 4 –C) and maleic acid (Mn 3 O 4 –M) exhibits inferior OER performance compared to Mn 2 O 3 and followed the order: Mn 2 O 3 –U > Mn 2 O 3 –G > Mn 3 O 4 –S > Mn 3 O 4 –C > Mn 3 O 4 –M. The findings of the results collectively suggest that the fuel alters the surface structure and crystallization process, with further impacts the electrocatalytic performance. Graphical abstract Fuels used in the synthesis step altered the crystallization kinetic and surface structural features.