To engineer low-cost, high-efficiency, and stable oxygen evolution reaction (OER) catalysts, structure effects should be primarily understood. Focusing on this, we systematically investigated the relationship between structures of materials and their OER performances by taking four 2D α-Ni(OH) as model materials, including layer-stacked bud-like Ni(OH)-NB, flower-like Ni(OH)-NF, and petal-like Ni(OH)-NP as well as the ultralarge sheet-like Ni(OH)-NS. For the first three (layer-stacking) catalysts, with the decrease of stacked layers, their accessible surface areas, abilities to adsorb OH, diffusion properties, and the intrinsic activities of active sites increase, which accounts for their steadily enhanced activity. As expected, Ni(OH)-NP shows the lowest overpotential (260 mV at 10 mA cm) and Tafel slope (78.6 mV dec) with a robust stability over 10 h among the samples, which also outperforms the benchmark IrO (360 mV and 115.8 mV dec) catalyst. Interestingly, Ni(OH)-NS relative to Ni(OH)-NP exhibits even faster substance diffusion due to the sheet-like structure, but shows inferior OER activity, which is mainly because the Ni(OH)-NP with a smaller size possesses more active boundary sites (higher reactivity of active sites) than Ni(OH)-NS, considering the adsorption properties and accessible surface areas of the two samples are quite similar. By comparing the different structures and their OER behaviors of four α-Ni(OH) samples, our work may shed some light on the structure effect of 2D materials and accelerate the development of efficient OER catalysts.

Hydrogen produced from electrocatalytic water splitting is a promising route due to the sustainable powers derived from the solar and wind energy. However, the sluggish kinetics at the anode for water splitting makes the highly effective and inexpensive electrocatalysts desirable in oxygen evolution reaction (OER) by structure and composition modulations. Metal-organic frameworks (MOFs) have been intensively used as the templates/precursors to synthesize complex hollow structures for various energy-related applications. Herein, an effective and facile template-engaged strategy originated from bimetal MOFs is developed to construct hollow microcubes assembled by interconnected nanopolyhedron, consisting of intimately dominant FeNi alloys coupled with a small NiFeO oxide, which was confined within carbonitride outer shell (denoted as FeNi/NiFeO@NC) via one-step annealing treatment. The optimized FeNi/NiFeO@NC exhibits excellent electrocatalytic performances toward OER in alkaline media, showing 10 mA·cm at η = 316 mV, lower Tafel slope (60 mV·dec), and excellent durability without decay after 5000 CV cycles, which also surpasses the IrO catalyst and most of non-noble catalysts in the OER, demonstrating a great perspective. The superior OER performance is ascribed to the hollow interior for fast mass transport, in situ formed strong coupling between FeNi alloys and NiFeO for electron transfer, and the protection of carbonitride layers for long stability.

Shape-controlled synthesis of multicomponent metal nanocrystals (NCs) bounded by high-index facets (HIFs) is of significant importance in the design and synthesis of highly active catalysts. It is a highly challenging task to design and synthesize ternary alloy NCs with HIFs due to the formidable difficulties in controlling the nucleation/growth kinetics of NCs in the presence of three metal precursors with different reduction potentials. We report herein, for the first time, the preparation of Pt–Ni–Cu alloy NCs by tuning their shape from crossed, dendritic, concave nanocubic (CNC) to rough octahedral (ROH) NCs through a facile one-pot solvothermal synthesis method. Specifically, the crossed and CNC Pt–Ni–Cu alloy NCs are bounded by high-index {hk0} facets and ROH with rich lattice defects. The electrocatalytic activities of these Pt–Ni–Cu alloy NCs toward methanol and formic acid oxidation were tested. It was shown that these Pt–Ni–Cu alloy NCs exhibited enhanced activity and stability compared to commercial Pt black and Pt/C catalysts as well as previous Pt–Ni and Pt CNCs under the same reaction conditions, demonstrating the superior electrocatalytic activity of Pt–Ni–Cu ternary alloys compared to monometal and binary Pt–Ni NCs. Surprisingly, we have found that the Pt–Ni–Cu ROH NCs have exhibited a higher specific catalytic activity than the crossed and CNC Pt–Ni–Cu alloy NCs with HIFs. The electronic and structure effects have been extensively discussed to shed light on the excellent electrocatalytic performance of Pt–Ni–Cu ROH NCs.

The development of designing and searching inexpensive electrocatalysts with high activity for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is significant to enable water splitting as a future renewable energy source. Herein, we synthesize a new CoP­(MoP)-CoMoO3 heterostructure coated by a N-doped carbon shell [CoP­(MoP)-CoMoO3@CN] via thermal decomposition and phosphatizing of the CoMoO4·0.9H2O nanowires encapsulated in N-doped carbon. At 10 mA·cm–2, this CoP­(MoP)-CoMoO3@CN nanocomposite exhibits superior electrocatalytic activity at low overpotentials of 296 mV for OER and 198 mV for HER in alkaline media. More importantly, we achieve a current density of 10 mA·cm–2 at 1.55 V by using this CoP­(MoP)-CoMoO3@CN as both cathode and anode for overall water splitting. This promising performance could be due to the high activity of CoP­(MoP)-CoMoO3 and the good conductivity of the external mesoporous N-carbon shell, which makes the CoP­(MoP)-CoMoO3@CN nanowires a competitive alternative to noble-metal-based catalysts for water splitting.

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