High-temperature-stable Au@SnO 2 core/shell supported catalyst was prepared by a simple intermetallicsbased dry-oxidation approach in which the size of the core can be controlled easily by varying the size of the pre-made Au seeds. The change of their structure was investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). In the as-prepared supported catalysts, Au particles with a mean size of ca. 15 nm were highly encapsulated by the SnO 2 shell. Moreover, the Au@SnO 2 core/shell supported catalysts showed superior catalytic activity compared to non-encapsulated Au-SnO 2 . XPS spectra showed that the interactions between the Au catalyst and oxide support in the wellencapsulated Au@SnO 2 core/shell nanoparticles are much stronger than those in the non-encapsulated Au-SnO 2 nanoparticles, further indicating the synergetic confinement effect in such nanoscaled catalyst/ support core/shell systems.

Novel R-Fe 2 O 3 hollow spheres with uniformly distributed mesoporosity on the shell were successfully synthesized on a large scale by a smart complex precursor method, in which the composite mesoporous hollow structures were generated by utilizing different removing modes of oxalate ligands in ferric potassium oxalate. The shell of the hollow spheres exhibited honeycomb-like mesoporous nanostructures composed of single-crystal iron oxide nanoparticles and the as-obtained R-Fe 2 O 3 composite hollow structures exhibited high gas sensitivity toward formaldehyde and ethanol at room temperature as well as favorable lithium ion battery performance.

Constructing catalysts with new and optimizational chemical components and structures, which can operate well for both the anodic oxygen evolution reaction (OER) and the cathodic hydrogen evolution reaction (HER) at large current densities, is of primary importance in practical water splitting technology. Herein, the NiFeO nanoparticles/NiFe layered double hydroxide (LDH) nanosheet heterostructure array on Ni foam was prepared via a simple one-step solvothermal approach. The as-prepared heterostructure array displays high catalytic activity toward the OER with a small overpotential of 213 mV at 100 mA cm and can afford a current density of 500 mA cm at an overpotential of 242 mV and 1000 mA cm at 265 mV. Moreover, it also presents outstanding HER activity, only needing a small overpotential of 101 mV at 10 mA cm, and can drive large current densities of 500 and 750 mA cm at individual overpotentials of 297 and 314 mV. A two-electrode electrolyzer using NiFeO nanoparticles/NiFe LDH nanosheets as both the anode and the cathode implements active overall water splitting, demanding a low voltage of 1.535 V to drive 10 mA cm, and can deliver 500 mA cm at 1.932 V. The NiFeO nanoparticles/NiFe LDH nanosheet array electrodes also show excellent stability against OER, HER, and overall water splitting at large current densities. Significantly, the overall water splitting with NiFeO nanoparticles/NiFe LDH nanosheets as both the anode and the cathode can be continuously driven by a battery of only 1.5 V. The intrinsic advantages and strong coupling effects of NiFeO nanoparticles and NiFe LDH nanosheets make NiFeO nanoparticles/NiFe LDH nanosheet heterostructure array abundant catalytically active sites, high electronic conductivity, and high catalytic reactivity, which remarkably contributed to the catalytic activities for OER, HER, and overall water splitting. Our work can inspire the optimal design of the NiFe bimetallic heterostructure electrocatalyst for application in practical water electrolysis.

An Fe-doped NiSe nanorod/nanosheet hierarchical array on Ni foam is constructed for efficient overall water splitting.