Morphological modulation of iron carbide embedded nitrogen-doped hierarchically porous carbon by manganese doping as highly efficient bifunctional electrocatalysts for overall water splitting

•Designing MnO functionalized Fe3C@nitrogen doped mesoporous FexMny@NC materials.•Mn boosts the formation of mesoporous structures along surfaces of FexMny@NC.•The HER Eonset and E10 values of Fe3Mn1@NC just 84.8 and 156 mV more negative than Pt/C.•The OER Eonset and E10 values of Fe3Mn1@NC just 8 and 18.7 mV more positive than RuO2.•A low voltage of 1.6287 V at 10 mA cm−2 for Fe3Mn1@NC||Fe3Mn1@NC just 24.9 mV larger than 1.6038 V of Pt/C||RuO2.