Petal-like NiCoP sheets on 3D nitrogen-doped carbon nanofiber network as a robust bifunctional electrocatalyst for water splitting

Searching high-active, stable and abundant bifunctional catalysts to replace noble metals for hydrogen and oxygen evolution reactions (HER and OER) is desired. Herein, petal-like NiCoP sheets were synthesized on carbon paper covered with a 3D nitrogen-doped carbon nanofiber network (NiCoP/CNNCP) by a simple hydrothermal process followed by phosphorization. The HER overpotential in 0.5 M H₂SO₄ and OER overpotential in 1 M KOH of the NiCoP/CNNCP electrode only required 55 mV and 260 mV to drive a current density of 10 mA cm^?2, respectively, which was comparable or even better than most nickel-and cobalt-based phosphide catalysts. The overall water-splitting electrolyzer with an asymmetric electrolyte system assembled using NiCoP/CNNCP as bifunctional electrodes required an extremely low cell voltage of 1.04 V to achieve a current density of 10 mA cm^?2, which was much lower than almost all alkaline electrolysis systems.     

Qualitative analysis of PZT (52/48) MPB using different synthesis methods

The current work reports a comparison between the structural and optical attributes of PZT (52/48) powder and thin film prepared via solid-state reaction and sol-gel spin-coating technique, respectively. The two obtained PZT samples, PZT-I corresponding to powder which was calcined at 875°C for 2 h, and PZT-II corresponding to a thin film which was annealed at 650°C for 2 h, were investigated via X-Ray Diffraction, Raman Spectroscopy, UV–Vis Spectroscopy, and SEM analysis. The diffraction spectra suggested the creation of a polycrystalline perovskite structure in both the samples. The optical band gap was evaluated using Tauc's relation. The bandgap values were found to be 3.2 eV for PZT-I and 3.87 eV for PZT-II. The bandgap values are significantly different for the PZT materials prepared by the two different methods.     

Diluted chemical bath deposition of CdZnS as prospective buffer layer in CIGS solar cell

In this study, dilute chemical bath deposition technique has been used to deposit CdZnS thin films on soda-lime glass substrates. The structural, morphological, optoelectronic properties of as-grown films have been investigated as a function of different Zn²⁺ precursor concentrations. The X-ray diffractogram of CdS thin-film reveals a peak corresponding to (002) plane with wurtzite structure, and the peak shift has been observed with the increase of the Zn²⁺ concentration upon formation of CdZnS thin film. From morphological studies, it has been revealed that the diluted chemical bath deposition technique provides homogeneous distribution of film on the substrate even at a lower concentration of Zn²⁺. Optical characterization has shown that the transparency of the film is influenced by Zn²⁺ concentration and when the Zn²⁺ concentration is varied from 0 M to 0.0256 M, bandgap values of resulting films range from 2.42 eV to 3.90 eV while. Furthermore, electrical properties have shown that with increasing zinc concentration the resistivity of the film increases. Finally, numerical simulation validates and suggests that CdZnS buffer layer with composition of 0.0032 M Zn²⁺ concentration would be a promising candidate in CIGS solar cell.     

Modulation of electrical transport in calcium cobaltite ceramics and thick films through microstructure control and doping

Ca₃Co₄O₉ is a promising p-type thermoelectric oxide material having intrinsically low thermal conductivity. With low cost and opportunities for automatic large scale production, thick film technologies offer considerable potential for a new generation of micro-sized thermoelectric coolers or generators. Here, based on the chemical composition optimized by traditional solid state reaction for bulk samples, we present a viable approach to modulating the electrical transport properties of screen-printed calcium cobaltite thick films through control of the microstructural evolution by optimized heat-treatment. XRD and TEM analysis confirmed the formation of high-quality calcium cobaltite grains. By creating 2.0 at% cobalt deficiency in Ca_2.7Bi_0.3Co₄O_9+δ, the pressureless sintered ceramics reached the highest power factor of 98.0 μWm^?1 K^-2 at 823 K, through enhancement of electrical conductivity by reduction of poorly conducting secondary phases. Subsequently, textured thick films of Ca_2.7Bi_0.3Co_3.92O_9+δ were efficiently tailored by controlling the sintering temperature and holding time. Optimized Ca_2.7Bi_0.3Co_3.92O_9+δ thick films sintered at 1203 K for 8 h exhibited the maximum power factor of 55.5 μWm^?1 K^-2 at 673 K through microstructure control.     

Effect of Y concentration and film thickness on microstructure and electrical properties of HfO2 based thin films

In this work, we introduced a simple solution processing method to prepare yttrium (Y) doped hafnium oxide (HfO₂) based dielectric films. The films had high densities, low surface roughness, maximum permittivity of about 32, leakage current < 1.0 × 10^?7 A/cm² at 2 MV/cm, and breakdown field >5.0 MV/cm. In addition to dielectric performance, we investigated the influence of YO_1.5 fraction on the electronic structure between Y doped HfO₂ thin films and silicon (Si) substrates. The valence band electronic structure, energy gap and conduction band structure changed linearly with YO_1.5 fraction. Given this cost-effective deposition technique and excellent dielectric performance, solution-processed Y doped HfO₂ based thin films have the potential for insulator applications.     

Large domain-wall currents in epitaxial Au/BiFeO3/SrRuO3 thin-film capacitors with modulated oxygen vacancy and wall densities

Large domain wall (DW) conductivity in an insulating ferroelectric plays an important role in the future nanosensors and nonvolatile memories. However, the wall current was usually too small to drive high-speed memory circuits and other agile nanodevices requiring high output-powers. Here, a large domain-wall current of 67.8 μA in a high on/off ratio of ~4460 was observed in an epitaxial Au/BiFeO₃/SrRuO₃ thin-film capacitor with the minimized oxygen vacancy concentration. The studies from read current-write voltage hysteresis loops and piezo-response force microscope images consistently showed remaining of partially unswitched domains after application of an opposite poling voltage that increased domain wall density and wall current greatly. A theoretical model was proposed to explain the large wall current. According to this model, the domain reversal occurs with the appearance of head-to-head and tail-to-tail 180° domain walls (DWs), resulting in the formation of highly conductive wall paths. As the applied voltage increased, the domain-wall number increased to enhance the on-state current, in agreement with the measurements of current-voltage curves. This work paves a way to modulate DW currents within epitaxial Au/BiFeO₃/SrRuO₃ thin-film capacitors through the optimization of both oxygen vacancy and domain wall densities to achieve large output powers of modern domain-wall nanodevices.     

Development of cellulose nanofibrils reinforced polyvinyl alcohol films incorporated with alizarin for intelligent food packaging

Visual pH-sensing films were fabricated using cellulose nanofibrils (CNF) reinforced polyvinyl alcohol (PVA) and alizarin. The relationships between the ratio of PVA: CNF hydrogel (2:1, 1:1, 1:2) and the physical properties and colour response efficiency of indicator films were investigated. Fourier transform infrared spectroscopy of films evidenced alizarin and CNF was properly incorporated by physical interaction. A new weak X-ray diffraction peak appeared at 2θ = 22.4°, which was affected by the incorporation of CNF. The increase in the CNF content induced enhancements of thermal stability, tensile strength, water contact angle and colour sensitivity of the indicator films. The colourimetric films had a higher sensitivity to discolouration when exposed to acidic vapours than alkaline vapours. The films presented a remarkable colour change varied from purple in alkaline condition to yellow in acidic condition. Therefore, this colourimetric film can be used as a volatile acid sensor for intelligent packaging.     

Preparation and Characterization of Hydrophobic Bagasse Hemicellulose-based Films

To improve the hydrophobicity of bagasse hemicellulose-based films, glutaraldehyde was applied when preparing films of original and cationic bagasse hemicellulose with the addition of polyvinyl alcohol and sorbitol. The results showed that the cationic modification could increase the hydrophobicity of the hemicellulose-based film, and the hydrophobicity of hemicellulose-based films crosslinked with glutaraldehyde also increased. However, cationic modification of hemicellulose decreased the stress of the hemicellulose-based film. While crosslinking with glutaraldehyde increased the stress of both the original and cationic hemicellulose-based films. Macrophotography indicated that the film formability of the original hemicellulose was better than that of cationic hemicellulose. Through SEM observation, the degree of bonding of different components of the films was found to be increased due to crosslinking with glutaraldehyde. The crosslinking reaction between glutaraldehyde and hemicellulose was further confirmed by FT-IR spectroscopy.     

Tunable microwave absorption properties of nickel-carbon nanofibers prepared by electrospinning

The nickel-carbon nanofibers (Ni-C NFs) were fabricated by the electrospinning of poly(vinyl alcohol) (PVA) and nickel acetate tetrahydrate (NiAc) solution precursor with succedent PVA pyrolyzation and calcination process. The microwave absorption performance and electromagnetic (EM) parameters of the NFs were researched over the frequency range of 2.0–18.0?GHz. Both the impedance matching and EM wave absorption properties of the Ni-C NFs were improved by changing the carbonization temperature. The effect of graphitization degree on reflection loss (RL) and the possible loss mechanisms were directly displayed in the comparative study of each sample. The optimal RL value of ??44.9?dB and an effective frequency bandwidth of 3.0?GHz under a thickness of 3.0?mm can be reached by a sample calcined at 650?°C. These lightweight Ni-C NFs composites can be promising candidates for EM wave absorbers due to the combination of multiple loss mechanisms, nano-size effect and good impedance matching between Ni nanoparticles and CNFs.     

Performance of surface ionic conduction single chamber fuel cell prepared by the sol gel method

The performance of surface ionic conduction single chamber fuel cell (SIC‐SCFC) prepared by the sol gel method was studied on electric characteristics due to the differences of the operating temperature and humidity, the electrode distance and electrolyte film depth, and multiple cells with the series and parallel connections. The SIC–SCFC was arranged the both anode of Pt and cathode of Au on the boehmite electrolyte. The open circuit voltage (OCV) of single cell achieved a maximum of 530mV in the dry gas mixtures of O₂/H₂=50% in room temperature operation, and but it became decrease as over 60%. The OCV was maintained the constant value between operating temperatures of 30°C to 80°C, and but it was decreased sharply at over 90°C because a humidity on the cell became lower as increasing operating temperature. Then, the cell property was improved to 120°C by adding to the humidity of 70% using a humidifier. The electrode distance and the electrolyte film depth of SIC‐SCFC found to be contributed to the reductions of the cell resistance and the surface roughness on the electrode, respectively. Moreover, the power property of SIC‐SCFC was significantly improved by cell stacks comprised of the series or parallel connection of a cell.