Interface Engineering of Hierarchical Branched Mo‐Doped Ni3S2/NixPy Hollow Heterostructure Nanorods for Efficient Overall Water Splitting

Engineering single-atom electrocatalysts with high-loading amount holds great promise in energy conversion and storage application. Herein, we report a facile and economical approach to achieve an unprecedented high loading of single Ir atoms, up to ∼18wt%, on the nickel oxide (NiO) matrix as the electrocatalyst for oxygen evolution reaction (OER). It exhibits an overpotential of 215 mV at 10 mA cm-2 and a remarkable OER current density in alkaline electrolyte, surpassing NiO and IrO2 by 57 times and 46 times at 1.49 V vs RHE, respectively. Systematic characterizations, including X-ray absorption spectroscopy and aberration-corrected Z-contrast imaging, demonstrate that the Ir atoms are atomically dispersed at the outermost surface of NiO and are stabilized by covalent Ir-O bonding, which induces the isolated Ir atoms to form a favorable ∼4+ oxidation state. Density functional theory calculations reveal that the substituted single Ir atom not only serves as the active site for OER but also activates the surface reactivity of NiO, which thus leads to the dramatically improved OER performance. This synthesis method of developing high-loading single-atom catalysts can be extended to other single-atom catalysts and paves the way for industrial applications of single-atom catalysts.

Ultrahigh-Loading of Ir Single Atoms on NiO Matrix to Dramatically Enhance Oxygen Evolution Reaction.

Rational design of the catalysts is impressive for sustainable energy conversion. However, there is a grand challenge to engineer active sites at the interface. Herein, hierarchical transition bimetal oxides/sulfides heterostructure arrays interacting two-dimensional MoOx/MoS2 nanosheets attached to one-dimensional NiOx/Ni3S2 nanorods were fabricated by oxidation/hydrogenation-induced surface reconfiguration strategy. The NiMoOx/NiMoS heterostructure array exhibits the overpotentials of 38 mV for hydrogen evolution and 186 mV for oxygen evolution at 10 mA cm−2, even surviving at a large current density of 500 mA cm−2 with long-term stability. Due to optimized adsorption energies and accelerated water splitting kinetics by theory calculations, the assembled two-electrode cell delivers the industrially relevant current densities of 500 and 1000 mA cm−2 at record low cell voltages of 1.60 and 1.66 V with excellent durability. This research provides a promising avenue to enhance the electrocatalytic performance of the catalysts by engineering interfacial active sites toward large-scale water splitting. While water splitting is an appealing carbon-neutral strategy for renewable energy generation, there is a need to develop new active, cost-effective catalysts. Here, authors prepare a nickel-molybdenum oxide/sulfide heterojunctions as bifunctional H2 and O2 evolution electrocatalysts.

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Engineering active sites on hierarchical transition bimetal oxides/sulfides heterostructure array enabling robust overall water splitting

Hydrogen has been deemed as an ideal substitute fuel to fossil energy because of its renewability and the highest energy density among all chemical fuels One of the most economical, ecofriendly, and high-performance ways of hydrogen production is electrochemical water splitting Recently, 2D transition metal dichalcogenides (also known as 2D TMDs) showed their utilization potentiality as cost-effective hydrogen evolution reaction (HER) catalysts in water electrolysis Herein, recent representative research efforts and systematic progress made in 2D TMDs are reviewed, and future opportunities and challenges are discussed Furthermore, general methods of synthesizing 2D TMDs materials are introduced in detail and the advantages and disadvantages for some specific methods are provided This explanation includes several important regulation strategies of creating more active sites, heteroatoms doping, phase engineering, construction of heterostructures, and synergistic modulation which are capable of optimizing the electrical conductivity, exposure to the catalytic active sites, and reaction energy barrier of the electrode material to boost the HER kinetics In the last section, the current obstacles and future chances for the development of 2D TMDs electrocatalysts are proposed to provide insight into and valuable guidelines for fabricating effective HER electrocatalysts

2D Transition Metal Dichalcogenides: Design, Modulation, and Challenges in Electrocatalysis.

Hydrogen produced via water electrolysis can act as an ideal clean chemical fuel with superb gravimetric energy density and high energy conversion efficiency, solving the problems of conventional fossil fuel exhaustion and environmental contamination. Transition metal sulfides (TMS) have been extensively explored as effective, widely available alternatives to precious metals in overall water splitting. Herein, recent advances, covering preparation methods, intrinsic electrocatalytic performance, and optimization strategies, relating to TMS-based bifunctional electrocatalysts have been summarized systematically and comprehensively. Firstly, a general introduction to the reaction mechanisms and key parameters of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is provided. Next, the physicochemical properties of TMS and typical synthesis methods are introduced to give guidance for fabricating TMS materials with well-defined structures, controllable compositions, and excellent performance. Importantly, the intrinsic activities of TMS-based electrocatalysts and several strategies for improving their bifunctional electrocatalytic performance during water electrolysis are discussed in detail. Finally, perspectives covering the challenges and opportunities related to the further development of TMS-based materials with high activity and long-term durability for overall water splitting are given. The aim herein is to provide guidelines for the design and fabrication of TMS-based bifunctional electrocatalysts with excellent performance and to accelerate their large-scale practical application in water electrolysis.

Recent advances in transition-metal-sulfide-based bifunctional electrocatalysts for overall water splitting

Designing and constructing bifunctional electrocatalysts is vital for water splitting. Particularly, the rational interface engineering can effectively modify the active sites and promote the electronic transfer, leading to the improved splitting efficiency. Herein, free-standing and defect-rich heterogeneous MoS2/NiS2 nanosheets for overall water splitting are designed. The abundant heterogeneous interfaces in MoS2/NiS2 can not only provide rich electroactive sites but also facilitate the electron transfer, which further cooperate synergistically toward electrocatalytic reactions. Consequently, the optimal MoS2/NiS2 nanosheets show the enhanced electrocatalytic performances as bifunctional electrocatalysts for overall water splitting. This study may open up a new route for rationally constructing heterogeneous interfaces to maximize their electrochemical performances, which may help to accelerate the development of nonprecious electrocatalysts for overall water splitting.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/advs.201900246

Defect-Rich Heterogeneous MoS2/NiS2 Nanosheets Electrocatalysts for Efficient Overall Water Splitting.

Rational design of efficient bifunctional electrocatalysts is highly imperative but still a challenge for overall water splitting Herein, we construct novel freestanding Mo-doped NiCoP nanosheet arrays by the hydrothermal and phosphation processes, serving as bifunctional electrocatalysts for overall water splitting Notably, Mo doping could effectively modulate the electronic structure of NiCoP, leading to the increased electroactive site and improved intrinsic activity of each site Furthermore, an electrochemical activation strategy is proposed to form Mo-doped (Ni,Co)OOH to fully boost the electrocatalytic activities for oxygen evolution reaction Benefiting from the unique freestanding structure and Mo doping, Mo-doped NiCoP and (Ni,Co)OOH show the remarkable electrochemical performances, which are competitive among current researches In addition, an overall water splitting device assembled by both electrodes only requires a cell voltage of 161 V to reach a current density of 10 mA cm−2 Therefore, this work opens up new avenues for designing nonprecious bifunctional electrocatalysts by Mo doping and in situ electrochemical activation

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Bifunctional Electrocatalysts Based on Mo-Doped NiCoP Nanosheet Arrays for Overall Water Splitting

Strong chemical bonds between transition metal oxides and carbon materials which enable fast electron transfer kinetics are highly required in supercapacitor electrodes. Meanwhile, hollow transition metal oxide nanostructures have promising potential for advanced energy storage applications. Herein, an oxygen vacancy assisted hydroxyl modification method is proposed to encapsulate Mn3O4 hollow spheres with controlled shell numbers in reduced graphene oxide (Mn3O4–rGO). The strong bonds between Mn3O4 and graphene result in fast charge transport, uniform distribution, increased active sites and enhanced structural stability. Originating from the structural features, when these materials were evaluated as electrodes for supercapacitors, Mn3O4–rGO shows a high specific capacitance of 561.5 C g−1 with good rate performance and excellent stability with 98% retention after 10 000 cycles. In order to widen the potential application of supercapacitors, asymmetric supercapacitors (ASCs) are assembled using Mn3O4–rGO as positive electrodes and active carbon as negative electrodes. The ASCs exhibit a high specific capacitance of 180.2 F g−1, delivering a high energy density of 72.3 W h kg−1 at a power density of 864 W kg−1. This surface-confined strategy may pave a way for realizing strong chemical bonds between hollow oxides and carbon-based materials for high performance supercapacitors.

Xiaoqing Si

Papers

Defect-Rich Heterogeneous MoS2/NiS2 Nanosheets Electrocatalysts for Efficient Overall Water Splitting.

Bifunctional Electrocatalysts Based on Mo-Doped NiCoP Nanosheet Arrays for Overall Water Splitting

Designing oxygen bonding between reduced graphene oxide and multishelled Mn3O4 hollow spheres for enhanced performance of supercapacitors

Reactive air brazing of YSZ ceramic with novel Al2O3 nanoparticles reinforced Ag-CuO-Al2O3 composite filler: Microstructure and joint properties

Brazing ZTA ceramic to TC4 alloy using the Cu foam as interlayer