Iron Triad-Based Bimetallic M-N-C Nanomaterials as Highly Active Bifunctional Oxygen Electrocatalysts.

The use of precious metal electrocatalysts in clean electrochemical energy conversion and storage applications is widespread, but the sustainability of these materials, in terms of their availability and cost, is constrained. In this research, iron triad-based bimetallic nitrogen-doped carbon (M-N-C) materials were investigated as potential bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The synthesis of bimetallic FeCo-N-C, CoNi-N-C, and FeNi-N-C catalysts involved a precisely optimized carbonization process of their respective metal-organic precursors. Comprehensive structural analysis was undertaken to elucidate the morphology of the prepared M-N-C materials, while their electrocatalytic performance was assessed through cyclic voltammetry and rotating disk electrode measurements in a 0.1 M KOH solution. All bimetallic catalyst materials demonstrated impressive bifunctional electrocatalytic performance in both the ORR and the OER. However, the FeNi-N-C catalyst proved notably more stable, particularly in the OER conditions. Employed as a bifunctional catalyst for ORR/OER within a customized zinc-air battery, FeNi-N-C exhibited a remarkable discharge-charge voltage gap of only 0.86 V, alongside a peak power density of 60 mW cm-2. The outstanding stability of FeNi-N-C, operational for about 55 h at 2 mA cm-2, highlights its robustness for prolonged application.

Cu2ZnSnS4 monograin layer solar cells for flexible photovoltaic applications.

Monograin powder technology is one possible path to developing sustainable, lightweight, flexible, and semi-transparent solar cells, which might be ideal for integration with various building and product elements. In recent years, the main research focus of monograin technology has centered around understanding the synthesis and optoelectronic properties of kesterite-type absorber materials. Among these, Cu2ZnSnS4 (CZTS) stands out as a promising solar cell absorber due to its favorable optical and electrical characteristics. CZTS is particularly appealing as its constituent elements are abundant and non-toxic, and it currently holds the record for highest power conversion efficiency (PCE) among emerging inorganic thin-film PV candidates. Despite its advantages, kesterite solar cells' PCE still falls significantly behind the theoretical maximum efficiency due to the large VOC deficit. This review explores various strategies aimed at improving VOC losses to enhance the overall performance of CZTS monograin layer solar cells. It was found that low-temperature post-annealing of CZTS powders reduced Cu-Zn disordering, increasing Eg by ∼100 meV and VOC values; however, achieving the optimal balance between ordered and disordered regions in kesterite materials is crucial for enhancing photovoltaic device performance due to the coexistence of ordered and disordered phases. CZTS alloying with Ag and Cd suppressed non-radiative recombination and increased short-circuit current density. Optimizing Ag content at 1% reduced CuZn antisite defects, but higher Ag levels compensated for acceptor defects, leading to reduced carrier density and decreased solar cell performance. Co-doping with Li and K resulted in an increased bandgap (1.57 eV) and improved VOC, but further optimization is required due to a relatively large difference between measured and theoretical VOC. Heterojunction modifications led to the most effective PCE improvement in CZTS-based solar cells, achieving an overall efficiency of 12.06%.

Cost-effective screen printing approach for Ce/Nd-doped ZnAl2O4 films: tuning crystallinity induced by the substrate.

Near-infrared (NIR) emitting phosphors are currently receiving considerable attention owing to their high demand in various applications, such as light detection and ranging (LiDAR), short-range communications, security, biosensing and night vision lighting applications. The miniaturization of photonic components demands the integration of thin films into exploitable devices. In this context, NIR emitting ZnAl2O4:Ce/Nd films of hundreds of nanometer thickness are synthesized using a scalable and cost-efficient approach to screen printing. Cerium co-doping is responsible for the Nd emission in the NIR through energy transfer by exciting the films under UV excitation at around 360 nm. Through the proper design of ink, dense Nd/Ce doped ZnAl2O4 ceramic films were produced using polycrystalline alumina. The use of polycrystalline alumina substrates opens up new opportunities because this ceramic is a cheap and well-known substrate for optoelectronic packaging. During manufacturing, as a direct effect of predominant crystal growth over the polycrystalline alumina substrate, an increase in emission intensity is achieved. The results obtained by X-ray photoelectron (XPS) and X-ray absorption near edge spectroscopy (XANES) serve to determine the oxidation state of Ce. The findings of this study indicate that a higher concentration of Ce4+ promotes NIR emission. This study may contribute to a better understanding of film production processes of films based on the ZnAl2O4 matrix and guide future studies on films for NIR emitters.

Highly Active Wood-Derived Nitrogen-Doped Carbon Catalyst for the Oxygen Reduction Reaction.

In this recent decade, great interest has risen to develop metal-free and cheap, biomass-derived electrocatalysts for oxygen reduction reaction (ORR). Herein, we report a facile strategy to synthesize an electrochemically active nanocarbon material from the renewable and biological resource, wood biomass. The ORR activity of the catalyst material was investigated in 0.1 M KOH solution by employing the rotating disc electrode method. Scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy were employed to obtain more information about the catalyst material's morphology and composition. The material exhibits outstanding electrocatalytic activity with low onset potential and high current density, similar to that of a commercial Pt/C catalyst in an alkaline medium. The results clearly ascertain that wooden biomass can be easily transformed into novel carbon nanostructures with superior ORR activity and possibility to be used in fuel cells and metal-air batteries.

Ferrocene Introduced into 5-Methylresorcinol-Based Organic Aerogels.

The polycondensation sol-gel reaction of 5-methylresocinol and formaldehyde with additional compounds in reaction media is a relatively simple way to produce modified aerogels. In order to obtain aerogels with a large surface area and high porosity, the conditions for gel formation, the solvent exchange process before drying, and the supercritical drying process were optimized. A successful attempt was made to introduce ferrocene units into 5-methylresocinol-formaldehyde-based aerogels. The resulting aerogels are amorphous substrates, and no aggregated ferrocene units were found in their structures. All of the aerogel samples that were obtained are structurally similar despite differences in the original ferrocene units and their initial concentration. It was found that the inclusion limit of ferrocene structural blocks into an aerogel is ~6% wt. The structures of the inclusions in which all of the Fe atoms in the aerogel substrates were present in ferrocene/ferrocenium at an approximate ratio of 60/40 to 55/45 were confirmed by X-ray photoelectron spectroscopy and Mössbauer spectroscopy. Aerogels with ferrocene/ferrocenium inclusions are likely to exhibit reversible redox activity in reactions with gaseous reagents.

Growth and Characterization of Cu2Zn1-xFexSnS4 Thin Films for Photovoltaic Applications.

Photovoltaics is a promising technology to produce sustainable energy, thanks to the high amount of energy emitted by the sun. One way of having solar cells with low production costs is to apply thin-film technology and with earth-abundant raw materials. A keen interest is arising in kesterite compounds, which are chalcogenides composed of abundant and non-toxic elements. They have already achieved excellent performance at the laboratory level. Here, we report the synthesis and characterization of mixed chalcogenides based on copper, zinc, iron, and tin. Solutions have been studied with different zinc and iron ratios. The distortion of the elementary cell of kesterite increases with the addition of iron until a phase transition to stannite occurs. The process of synthesis and deposition proposed herein is cheap and straightforward, based on the sol-gel technique. These thin films are particularly attractive for use in cheap and easily processable solar cells. The synthesized layers have been characterized by X-ray diffraction, UV-Vis absorption, and Raman, X-ray photoelectron, and energy-dispersive X-ray spectroscopy measurements.

Adhesion of Single-Walled Carbon Nanotube Thin Films with Different Materials.

Single-walled carbon nanotubes (SWCNTs) possess extraordinary physical and chemical properties. Thin films of randomly oriented SWCNTs have great potential in many opto-electro-mechanical applications. However, good adhesion of SWCNT films with a substrate material is pivotal for their practical use. Here, for the first time, we systematically investigate the adhesion properties of SWCNT thin films with commonly used substrates such as glass (SiO2), indium tin oxide (ITO), crystalline silicon (C-Si), amorphous silicon (a-Si:H), zirconium oxide (ZrO2), platinum (Pt), polydimethylsiloxane (PDMS), and SWCNTs for self-adhesion using atomic force microscopy. By comparing the results obtained in air and inert Ar atmospheres, we observed that the surface state of the materials greatly contributes to their adhesion properties. We found that the SWCNT thin films have stronger adhesion in an inert atmosphere. The adhesion in the air can be greatly improved by a fluorination process. Experimental and theoretical analyses suggest that adhesion depends on the atmospheric conditions and surface functionalization.

Effect of the Titanium Isopropoxide:Acetylacetone Molar Ratio on the Photocatalytic Activity of TiO2 Thin Films.

TiO2 thin films with different titanium isopropoxide (TTIP):acetylacetone (AcacH) molar ratios in solution were prepared by the chemical spray pyrolysis method. The TTIP:AcacH molar ratio in spray solution varied from 1:3 to 1:20. TiO2 films were deposited onto the glass substrates at 350 °C and heat-treated at 500 °C. The morphology, structure, surface chemical composition, and photocatalytic activity of the obtained TiO2 films were investigated. TiO2 films showed a transparency of ca 80% in the visible spectral region and a band gap of ca 3.4 eV irrespective of the TTIP:AcacH molar ratio in the spray solution. TiO2 films consist of the anatase crystalline phase with a mean crystallite size in the range of 30-40 nm. Self-cleaning properties of the films were estimated using the stearic acid (SA) test. A thin layer of 8.8-mM SA solution was spin-coated onto the TiO2 film. The degradation rate of SA as a function of irradiation time was monitored by Fourier-transform infrared spectroscopy (FTIR). An increase in the TTIP:AcacH molar ratio from 1:4 to 1:8 resulted in a ten-fold increase in the photodegradation reaction rate constant (from 0.02 to the 0.2 min-1) under ultraviolet light and in a four-fold increase under visible light.

Pulsed laser deposition of Zn(O,Se) layers in nitrogen background Pressure.

Zinc oxy-selenide Zn(O,Se) is a novel material, that can replace the toxic CdS buffer layer in thin film solar cells and other optoelectronic devices. In this paper a systematic study of the structural, optical and electrical properties of Zn(O,Se) layers, grown by pulsed laser deposition under 50 mTorr of nitrogen background pressure, over a wide range of the substrate temperature, from RT to 600 °C, is reported. XRD, Raman, HR-SEM, XPS, UV-Vis techniques and Hall effect measurements have been used to investigate the structural, and optoelectronic properties of Zn(O,Se) layers. XRD analysis revealed that the polycrystalline ternary Zn(O,Se) phase formed at 500 °C. Raman analysis confirmed the formation of the polycrystalline Zn(O,Se) phase at 500 °C and an amorphous phase at substrate temperatures below 500 °C. Similarly, XPS analysis accompanied with the modified Auger parameters confirmed formation of ternary Zn(O,Se) layer at 500 °C as well. HR-SEM investigation showed the growth of homogenous, dense and adherent films onto a glass substrate. Furthermore, optical studies revealed that all prepared films are practically transparent in the visible region of the spectrum, with a band gap around 3 eV. Hall effect measurements revealed that conductivity, and electron concentration, increased by four orders of magnitude at 600 °C. It was found, that nitrogen background pressure maintained stable ratios of elemental contents in the whole range of the substrate temperature for Zn(O,Se) layers.

Aerosol-Assisted Fine-Tuning of Optoelectrical Properties of SWCNT Films.

We propose a novel, scalable, and simple method for aerosol doping of single-walled carbon nanotube (SWCNT) films. This method is based on aerosolization of a dopant solution (HAuCl4 in ethanol) and time-controlled deposition of uniform aerosol particles on the nanotube film surface. The approach developed allows fine-tuning of the SWCNT work function in the range of 4.45 (for pristine nanotubes) to 5.46 eV, controllably varying the sheet resistance of the films from 79 to 3.2 Ω/□ for the SWCNT films with 50% transmittance (at 550 nm). This opens a new avenue for traditional and flexible optoelectronics, both to replace existing indium-tin oxide electrodes and to develop novel applications of the highly conductive transparent films.