Accelerating water oxidation kinetics via synergistic in-layer modification and interlayer reconstruction over hetero-epitaxial Fe-Mn-O nanosheets

Developing high-performance and low-cost oxygen evolution reaction (OER) electrocatalysts is critical for implementing industrial H2 production. Herein, ultrathin Fe-Mn-O hetero-nanosheets consisting of crystalline ε-Fe2O3 intercalated in amorphous Fe-doped δ-MnO2 have been fabricated through facile alkali hydrolysis of FeMn-based coordination polymer. Abundant Mn3+ active sites and oxygen vacancies are generated in Fe-doped δ-MnO2 layer due to in-layer/interlayer reformations, where interstitial ε-Fe2O3 is engineered to reinforce stability and conductivity. The optimal 0.5Fe-Mn-O nanosheets exhibit superb activity with low overpotentials of 258 (322) mV at 10 (300) mA cm−2 for OER together with strong stability under large current density over 100 h, ranking it among the best MnO2-based electrocatalysts. Importantly, in situ interlayer reconstruction from ε-Fe2O3 to β-FeOOH during OER has been unveiled, the evolved β-FeOOH triggers strong interfacial electronic coupling, which synergizes with oxygen vacancies and Fe3+ dopants to modulate surface electronic structure of δ-MnO2 for intermediates adsorption.