Intrinsic poorly-crystallized Fe 5 O 7 (OH)·4H 2 O: a highly efficient oxygen evolution reaction electrocatalyst under alkaline conditions.

As the bottleneck of electrochemical overall water splitting, the oxygen evolution reaction (OER) needs efficient catalysts to lower the required overpotential. Electrocatalysts with an amorphous form are highly active but suffer with low structural stability. Poorly crystallized materials with activity like amorphous forms, while maintaining the mechanical robustness of crystalline forms, are expected to be ideal materials. Towards this direction, we, for the first time, developed low-crystalline Fe 5 O 7 (OH)·4H 2 O as an excellent OER electrocatalyst with an overpotential of 269 mV, in order to drive a current density of 100 mA cm -2 in a 1.0 M KOH environment, and this outperforms most of the reported Fe-based electrocatalysts. Notably, its activity can be maintained for at least 100 hours. A one-pot synthesis for the poorly-crystallized material using one of the most abundant metal elements to obtain effective OER catalysis will provide great convenience in practical applications.