Search

Constructing a heterogeneous interface using different components is one of the effective measures to achieve the bifunctionality of nanocatalysts, while synergistic interactions between multiple interfaces can further optimize the performance of single-interface nanocatalysts. The non-precious metal nanocatalysts MoS2/NiSe2/reduced graphene oxide (rGO) bilayer sandwich-like nanostructure with multiple well-defined interfaces is prepared by a simple hydrothermal method. MoS2 and rGO are layered nanostructures with clear boundaries, and the NiSe2 nanoparticles with uniform size are sandwiched between both layered nanostructures. This multiple-interfaced sandwich-like nanostructure is prominent in catalytic water splitting with low overpotential for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) and almost no degradation in performance after a 20 h long-term reaction. In order to simulate the actual overall water splitting process, the prepared nanostructures are assembled into MoS2/NiSe2/rGO||MoS2/NiSe2/rGO modified two-electrode system, whose overpotential is only 1.52 mV, even exceeded that of noble metal nanocatalyst (Pt/C||RuO2~1.63 mV). This work provides a feasible idea for constructing multi-interface bifunctional electrocatalysts using nanoparticle-doped bilayer-like nanostructures. [ABSTRACT FROM AUTHOR]

Designing low-cost, highly efficient, and stable electrocatalysts for oxygen evolution reactions is of great significance for water splitting, which is a green and sustainable method of producing hydrogen. Herein, a series of transition metal sulphide-based nanostructures, including Au–CoNi2S4 core–shell, Au–NiS core–shell, Au–Co3S4 core–shell, and bare CoNi2S4 nanoparticles (NPs), have been rationally designed. Among them, the Au–CoNi2S4 core–shell NPs exhibit superior electrocatalytic properties for oxygen evolution. It requires an overpotential of only 264 mV to reach a current density of 10 mA cm−2, while the Tafel slope (35.6 mV dec−1) is also the lowest among the as-prepared nanostructures. X-ray photoelectron spectra and electrochemical impedance spectra demonstrate that the electronic structure and chemical state of Au–CoNi2S4 core–shell heterostructure are regulated by the delicate structural design. The enhanced electrocatalytic performance of the Au–CoNi2S4 core–shell heterostructure can be attributed to the combined effects of constructing bimetallic sulphide instead of its monometallic counterparts and forming metal–sulphide core–shell interface. It provides a way to develop a superior electrocatalyst by constructing a metal–bimetallic sulphide core–shell heterostructure. [ABSTRACT FROM AUTHOR]

Single-crystalline hollow CoO nanooctahedra were successfully synthesized by the combination of self-gas-leaching and Ostwald ripening processes through a template-free route. Elaborate microscopy evidence discloses that hollow CoO nanocrystals (NCs) evolve from the channeled CoO NCs, which is an essential intermediate state to construct the hollow structure. Electrochemical measurements indicate that hollow CoO NCs exhibit three times higher specific capacitance than the solid CoO and show excellent cycling stability with the specific capacitance retaining more than 97% after 4500 cycles at a current density of 2 A g−1. Meanwhile, as a catalyst for oxygen evolution reaction and hydrogen production from hydrolysis of sodium borohydride, the hollow and channeled CoO NCs exhibit much better performances than their solid counterparts. The hollow CoO NCs afford a current density of 10 mA cm−2 at a small overpotential of merely 0.375 V and a small Tafel slope of 55 mV decade−1, and they also possess more steady catalytic activity than the channeled CoO. [ABSTRACT FROM AUTHOR]

Transition metal sulfides have attracted a lot of attention as potential oxygen evolution reaction (OER) catalysts. Bimetallic sulfide possesses superior physicochemical properties due to the synergistic effect between bimetallic cations. By introducing a metal-semiconductor interface, the physicochemical properties of transition metal sulfide can be further improved. Using the solvothermal method, Au@NiCo2S4 core-shell heterostructure nanoparticles (NPs) and bare NiCo2S4 NPs were prepared. The measurement of the OER catalytic performance showed that the catalytic activity of Au@NiCo2S4 core-shell heterostructure was enhanced compared to bare NiCo2S4 NPs. At the current density of 10 mA cm−2, the overpotential of Au@NiCo2S4 (299 mV) is lower than that of bare NiCo2S4 (312 mV). The Tafel slope of Au@NiCo2S4 (44.5 mV dec−1) was reduced compared to that of bare NiCo2S4 (49.1 mV dec−1), indicating its faster reaction kinetics. Detailed analysis of its electronic structure, chemical state, and electrochemical impedance indicates that the enhanced OER catalytic performances of bare Au@NiCo2S4 core-shell NPs were a result of its increased proportion of high-valance Ni/Co cations, and its increased electronic conductivity. This work provides a feasible method to improve OER catalytic performance by constructing a metal-semiconductor core-shell heterostructure. [ABSTRACT FROM AUTHOR]

The oxygen evolution reaction (OER) is regarded as the efficiency-limiting step because it suffers from a kinetically sluggish four-electron process in water splitting. The intrinsic catalytic activity could be improved by adjusting the electronic structure of the catalyst through interface modification engineering. In this work, Fe ion-chelated tannic acid was coated on Ni-WO x nanowires to form TA-Fe@Ni-WO x hierarchical structure by the interfacial coordination assembly process. The hierarchical structure has abundant active sites and good electrical conductivity, which exhibits extraordinary OER performance in alkaline electrolytes. Specifically, the TA-Fe@Ni-WO x catalyst requires low over-potentials of 240 and 260 mV at 20 mA cm−2 and 50 mA cm−2, respectively. X-ray photoelectron spectroscopy results confirm that the electronic structure of TA-Fe@Ni-WO x is more beneficial to OER than Ni-WO x due to the introduction of the TA-Fe nano-sheets overlayer on the surface of Ni-WO x nanowires. Furthermore, the ultraviolet photoelectron spectroscopy results confirm that the TA-Fe@Ni-WO x hierarchical structure has an upward-moving Fermi energy and a smaller ionization potential, providing a more electron-rich environment. It is demonstrated that this simple interfacial coordination assembly coating strategy is an effective way to reasonably adjust the surface properties of metal oxides for promising applications. • TA-Fe@Ni-WO x hybrids were constructed via an interfacial coordination assembly strategy. • The electronic structure and the electron transfer efficiency of Ni-WO x are effectively regulated by TA-Fe nanosheets. • TA-Fe@Ni-WO x exhibited excellent OER catalytic activities with low over-potential of 240 mV at 20 mA cm−2. [ABSTRACT FROM AUTHOR]

• The self-supported serrated Ni-WO 3 on Ni foam was obtained by one step in-situ etching method. • The NH 4 + and SO 4 2- had synergistic effect on the unique structure. • The serrated Ni-WO 3 exhibits excellent OER activities with low over-potentials of 265 mV at 10 mA cm−2. The effect of etching agent type and reaction time on the morphology and properties of materials was studied in this paper and the reconstruction phenomenon in OER pre-catalyst was confirmed. The serrated Ni-WO 3 -3 has excellent OER performance with an over-potential of only 265 mV at 10 mA cm−2. The serrated Ni-WO 3 electrode undergoes a self-reconstruction of structure and material during OER to form nickel oxy(hydroxide) nanoparticles. [Display omitted] The slow kinetics of oxygen evolution reaction (OER) severely restricts the application of water splitting. In this paper, a free-standing serrated Ni-WO 3 electrode for OER was synthesized by a simple in-situ etching method using (NH 4) 2 SO 4 as etchant. The effect of etchant on structures of Ni-WO 3 were studied carefully, indicating that the NH 4 + and SO 4 2- have a synergistic effect on the unique structure. The serrated Ni-WO 3 -3 (where 3 is the mass of (NH 4) 2 SO 4) dramatically enhance OER performance, an over-potential of only 265 mV at 10 mA cm−2 as compared with that 365 mV of serrated-free Ni-WO 3. Interestingly, the structure and composition of the serrated Ni-WO 3 electrode undergoes a self-reconstruction process during OER, the finally catalyst is interconnected by low crystallinity nickel oxy-hydroxide nanoparticles. This work mainly explores the influence of etching agent type, usage and reaction time on the morphology and properties of materials, and the reconstruction phenomenon in OER pre-catalyst was confirmed. [ABSTRACT FROM AUTHOR]

[Display omitted] • An exquisite externally layered and internally hollow CoP@MoS 2 electrocatalyst was successfully prepared. • CoP can effectively enhance the catalytic ability of MoS 2 on hydrogen evolution reaction. • The externally layered and internally hollow nanostructure can accelerate the transfer of charge and mass. As the star material among nonprecious electrocatalysts, molybdenum disulfide (MoS 2) has received much attention. However, the catalytic inertness of the basal plane, low conductivity of its steady state (2H phase), and the agglomeration of lamellar structures have seriously hindered its catalytic performance. It is very essential to design and modulate the morphology and phase of MoS 2 to improve the above issues by synergistic regulation of electrical structure and defect engineering. Herein, MoS 2 was delicately composited on CoP nanoframe derived from a typical metal–organic frame nanostructure (ZIF-67), forming the hollow CoP@MoS 2 hetero-nanoframe. This exquisite externally layered and internally hollow CoP@MoS 2 electrocatalyst demonstrated excellent catalytic performance for the hydrogen evolution reaction, with a low overpotential of 119 mV at 10 mA cm−2, a small Tafel slope of 49 mV dec−1, a large electric double-layer capacitance of 10.28 mF cm−2, and prominent long-term stability. The remarkable catalytic performance of hollow CoP@MoS 2 hetero-nanoframe can be attributed to the unique architecture of the hetero-nanostructures, appropriate component ratios, strong interaction between CoP and MoS 2 , and large-scale defects and disorder. First-principles density-functional theory calculations can prove the above arguments adequately, the hydrogen adsorption free energy of CoP@MoS 2 is close to zero. [ABSTRACT FROM AUTHOR]