Remarkably boosted water oxidation activity and dynamic stability at large-current-density of Ni(OH)₂ nanosheet arrays by Fe ion association and underlying mechanism

There have been reports about the promoted oxygen evolution reaction (OER) activity by adding of Fe ions into alkaline electrolytes for Ni-based catalysts. However, the origin and reason for the OER activity improvement remains vague. In this work, we endeavor to recognize the activity enhancement by a series of control and in/ex situ experiments. After introducing of 500 mu M of Fe(III) to 1.0 M KOH, the current density of Ni(OH)(2) nanosheet arrays at 1.6 V increases substantially from 36 to 1052 mA cm(-2), and the overpotentials required to reach 100 mA cm(-2) reduces obviously from 422 to 269 mV and 1,000 mA cm(-2) from 616 to 367 mV. The electrochemical water splitting electrolyzer with Ni(OH)(2) as anode and Pt/Ni-Mo as cathode exhibits robust activity and stability for 1,000 h at 1,000 mA cm(-2) @ 1.7 V. In/ex situ electrochemical analysis, morphology and structure characterizations reveal that Fe(III) serves as the active sites and promotes the OER kinetics by two ways: (1) mainly cyclical formation of intermediates (Fe(III) -> (Ni)Fex+ -> (Ni)Fe-OH -> (Ni)Fe-O -> (Ni)Fe-OOH -> Fe(III) (+O-2)) on the electrode/electrolyte interface and (2) growth of the Ni-FeOOH/Fe-NiOOH interface on the surface of Ni (OH)(2). The results provide insights into the Fe(III)-catalysis effect and guidance for the development of high-performance commercial water-splitting systems.