The development of earth-abundant transition-metalbased electrocatalysts with bifunctional properties (oxygen evolution reaction (OER) and hydrogen evolution reaction (HER)) is crucial to commercial hydrogen production. In this work, layered double hydroxide (LDH)-zinc oxide (ZnO) heterostructures and oxygen vacancies are constructed synchronously by plasma magnetron sputtering of NiFe-LDH. Using the optimal conditions, ZnO nanoparticles are uniformly distributed on the NiFe-LDH nanoflowers, which are prepared uniformly on the three-dimensional porous Ni foam. In the LDH-ZnO heterostructures and oxygen vacancies, electrons are depleted at the Ni cations on the NiFe-LDH surface and the active sites change from Fe cations to Ni cations during OER. Our theoretical assessment confirms the change of active sites after the deposition of ZnO and reveals the chargetransfer mechanism. Owing to the significant improvement in the OER dynamics, overall water splitting can be achieved at only 1.603 V in 1 M KOH when the Ni/LDH-ZnO and Ni/LDH are used as the anode and cathode, respectively. The work reveals a novel design of self-supported catalytic electrodes for efficient water splitting and also provides insights into the surface modification of catalytic materials.

An atmospheric-pressure non-thermal plasma jet driven by high frequency alternating current and operating on N 2 and N 2 /O 2 gas mixture is investigated. The plasma jet can reach 55 mm in length at a gas flow rate of 2500 l/h. The gas temperature at a distance of 4 mm from the nozzle is close to room temperature. Optical emission spectroscopy is employed to investigate the important plasma parameters such as the excited species, rotational temperature, vibrational temperature, and excitation temperature under different discharge conditions. The results show that the plasma source operates under non-equilibrium conditions. The absolute irradiance intensity of the vibrational band N 2 (C-B) in the active region is measured. Taking into account the irradiance intensity of N 2 (C-B,0-0) and N 2 (B-X,0-0) as well as measured current, the electron density, which is determined by considering direct and step-wise electron impact excitation of nitrogen emission, reaches a maximum value of 5.6 Â 10 20 /m 3. V

Plasma functionalization can increase the efficiency of MoSe2 in the hydrogen evolution reaction (HER) by providing multiple species but the interactions between the plasma and catalyst are not well understood. In this work, the effects of the ion energy and plasma density on the catalytic properties of MoSe2 nanosheets are studied. The through‐holes resulting from plasma etching and multi‐vacancies induced by plasma‐induced damage enhance the HER efficiency as exemplified by a small overpotential of 148 mV at 10 mA cm–2 and Tafel slope of 51.6 mV dec–1 after the plasma treatment using a power of 20 W. The interactions between the plasma and catalyst during etching and vacancies generation are evaluated by plasma simulation. Finite element and first‐principles density functional theory calculations are also conducted and the results are consistent with the experimental results, indicating that the improved HER catalytic activity stems from the enhanced electric field and more active sites on the catalyst, and reduced bandgap and adsorption energy arising from the etched through‐holes and vacancies, respectively. The results convey new fundamental knowledge about the plasma effects and means to enhance the efficiency of catalysts in water splitting as well insights into the design of high‐performance HER catalysts.

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MoSe 2 is an efficient catalyst for the hydrogen evolution reaction (HER) and can potentially replace conventional catalysts composed of noble metals such as Pt. The HER activity of MoSe 2 originates mainly from the edge sites of Se atoms, but the low concentration of Se exposed to the electrolyte hampers the performance. Hence, activating a larger portion of the basal plane of Se atoms is an effective way to improve the HER properties. Herein, a 3D hierarchic nanoflower structure comprising MoSe 2 with atomic-scale interlayered graphene layers in the nanosheets is designed and prepared to improve the electron conductivity and decrease the proportions of inactive basal planes. Raman scattering, transmission electron microscopy, and energy-dispersive X-ray spectroscopy verify effective insertion of graphene layers in MoSe 2 , and the HER characteristics are improved as exemplified by a small overpotential of 175 mV at 10 mA cm −2 , small Tafel slope of 58 mV dec −1 , and excellent durability with only small deterioration of 10 mV after 10,000 cycles. First-principles density functional theory and finite element method calculations corroborate the experimental results, revealing better conductivity and hydrogen adsorption/desorption ability rendered by the graphene layers. Our results reveal a new and effective strategy to optimize the structure and composition and reduce the hydrogen adsorption energy barrier in the pursuit of high-efficiency non-noble metal catalysts.

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Estimation of electron temperature and density of the decay plasma in a laser-assisted discharge plasma extreme ultraviolet source by using a modified Stark broadening method An atmospheric-pressure non-thermal plasma jet excited by high frequency alternating current using nitrogen is developed and the electron density in the active region of this plasma jet is investigated by two different methods using optical emission spectroscopy, Stark broadening, and irradiance intensity method. The irradiance intensity method shows that the average electron density is about 10 20 /m 3 which is slightly smaller than that by the Stark broadening method. However, the trend of the change in the electron density with input power obtained by these two methods is consistent. V C 2014 AIP Publishing LLC. [http://dx.