Efficient and durable FeCoNi-(Oxy)hydroxide anode: Stoichiometric ration regulated morphology-, defect- and valence-dependent water oxidation performance

Morphological design to expose more active sites and surface defect engineering to regulate the electronic structure are the two main methods to improve material properties. It is also well documented that metal sites in high valence states are beneficial to the OER process. Herein, we combine the advantages of the above three methods to fabricate extraordinary catalysts just by facile adjusting the Fe content. The catalysts with different Fe contents exhibit excellent activity and outstanding stability beyond the yardstick material (RuO 2 ) in alkaline condition. The resultant FeCoNi (oxy)hydroxide nanosheets is one of the most active trimetal-based oxygen evolution catalysts to date. Specifically, the resultant Fe 1.25 (Co 2 Ni 1 ) 2.5 (oxy)hydroxide can deliver a minimum overpotential of 212 mV to reach the current density of 10 mA cm −2 with a small Tafel slope of 52 mV dec −1 and a negligible activity attenuation after excess 72 h long-term test at 100 mA cm −2 . Most importantly, when use Fe 1.25 (Co 2 Ni 1 ) 2.5 (oxy)hydroxide as a water splitting anode, an electrolyzer delivers a current density of 10 mA cm −2 at a very low cell voltage of 1.51 V. This excellent performance is attributed to the large number of active sites exposed by the nanosheets, the active center of the catalyst to the higher valence state and the large number of oxygen defects produced. This work can provide more valuable insights to promote the development of the highly efficient oxygen evolution for applications.