Iron doping and interface engineering on amorphous/crystalline Fe-NixSy heterostructures toward high-stability and kinetically accelerated water splitting.

It is very important to develop transition metal-based electrocatalysts with excellent activity, high stability and low-cost for overall water splitting. In this work, the Fe-doped NixSy/NF amorphous/crystalline heterostructure nanoarrays (Fe-NixSy/NF) was synthesized by a simple one-step method. The resulting hierarchically structured nanoarrays offer the advantages of large surface area, high structural void fraction and accessible internal surfaces. These advantages not only furnish additional catalytically active sites, but also enhance the stability of the structure and effectively accelerate mass diffusion and charge transport. Experimental and characterization results indicate that Fe doping increases the electrical conductivity of amorphous/crystalline NixSy/NF, and the NiS-Ni3S2 heterojunctions evoke interfacial charge rearrangement and optimize the adsorption free energy of the intermediates, which allows the catalyst to exhibit low overpotential and superior electrocatalytic activity. Especially, the overpotentials of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) of Fe-NixSy/NF at 10 mA cm-2 in an alkaline environment are 102.4 and 230.5 mV, respectively. When applied as a bifunctional catalyst for overall water splitting, it requires only 1.45 V cell voltage to deliver a current density of 10 mA cm-2, which is preferable to the all-noble metal Pt/C || IrO2 electrocatalyst (1.62 mV @ 10 mA cm-2). In addition, Fe-NixSy/NF has excellent stability, and there is no obvious degradation after 96 h continuous operation at a current density of 100 mA cm-2. This work affords insights into the application of doping strategies and crystalline/amorphous synergistic modulation of the electrocatalytic activity of transition metal-based catalysts in energy conversion systems.

Emergence of Insulating Ferrimagnetism and Perpendicular Magnetic Anisotropy in 3d-5d Perovskite Oxide Composite Films for Insulator Spintronics.

Magnetic insulators with strong perpendicular magnetic anisotropy (PMA) play a key role in exploring pure spin current phenomena and developing ultralow-dissipation spintronic devices, rendering them highly desirable to develop new material platforms. Here, we report the epitaxial growth of La2/3Sr1/3MnO3 (LSMO)-SrIrO3 (SIO) composite oxide films (LSMIO) with different crystalline orientations fabricated by a sequential two-target ablation process by pulsed laser deposition. The LSMIO films exhibit high crystalline quality with a homogeneous mixture of LSMO and SIO at an atomic level. Ferrimagnetic and insulating transport characteristics are observed, with the temperature-dependent electric resistivity well fitted by the Mott variable-range-hopping model. Moreover, the LSMIO films show strong PMA. By further constructing all-perovskite-oxide heterostructures of the ferrimagnetic insulator LSMIO and a strong spin-orbital-coupled SIO layer, pronounced spin Hall magnetoresistance (SMR) and spin Hall-like anomalous Hall effect (SH-AHE) were observed. These results illustrate the potential application of the ferrimagnetic insulator LSMIO in developing all-oxide ultralow-dissipation spintronic devices.