Fe-induced crystalline-amorphous interface engineering of a NiMo-based heterostructure for enhanced water oxidation.

Engineering heterostructures with a unique surface/interface structure is one of the effective strategies to develop highly active noble-metal-free catalysts for the oxygen evolution reaction (OER), because the surface/interface of catalysts is the main site for the OER. Herein, we design a coralloid NiMo(Fe)-20 catalyst with a crystalline-amorphous interface through combining a hydrothermal method and an Fe-induced surface reconfiguration strategy. That is, after Fe3+ impregnation treatment, the Ni(OH)2-NiMoO4 pre-catalyst with a complete crystalline surface is restructured into a trimetallic heterostructure with a crystalline-amorphous interface, which facilitates mass diffusion and charge transfer during the OER. As expected, self-supported NiMo(Fe)-20 exhibits excellent electrocatalytic water oxidation performance (overpotential: η-10 = 220 mV, η-100 = 239 mV) in the alkaline electrolyte, and its electrocatalytic performance hardly changes after maintaining the current density of 50 mA cm-2 for 10 hours. Furthermore, nickel foam (NF) supported commercial Pt/C and self-supported NiMo(Fe)-20 served as the cathode and anode of the Pt/C‖NiMo(Fe)-20 electrolyzer, respectively, which exhibits a lower cell voltage (E-100 = 1.53 V) than that of the Pt/C‖RuO2 electrolyzer (E-100 = 1.58 V) assembled with noble metal-based catalysts. The enhanced electrocatalytic performance of the NiMo(Fe)-20 catalyst is mainly attributed to the synergistic effect between the crystalline-amorphous interface and the coralloid trimetallic heterostructure.

Surface defect-engineered Fe doping in layered Co-based complex as highly efficient bifunctional electrocatalysts for overall water splitting.

The electrocatalytic splitting of water to produce hydrogen is regarded as an efficient and promising strategy but is limited by its large overpotential; thus, a highly efficient electrocatalyst is urgently needed. Mixed metal doping is an important strategy in defect engineering because the heteroatoms can change the intrinsic structure to form defects by affecting the atomic coordination mode and adjusting the electronic structure, which is often accompanied by morphological changes. Herein, two-dimensional layered bimetallic Co-pydc containing axially coordinated water molecules was selected by producing surface defects through Fe doping in Co centers as bifunctional electrocatalysts for OER and HER. The optimized Co0.59Fe0.41-pydc possesses outstanding OER performance with the lowest overpotential of 262 mV to reach j = 10 mA cm-2, and Co0.75Fe0.25-pydc possesses superior HER performance with the lowest overpotential of 96 mV at j = 10 mA cm-2. Furthermore, the overall water splitting device assembled with Co0.59Fe0.41-pydc@NF//Co0.59Fe0.41-pydc@NF affords a current density of 10 mA cm-2 at only 1.687 V. This work emphasizes the surface defects formed by tuning the electronic structure of metal centres accompanied with morphological changes of bimetallic dopants for efficient overall water splitting.