Tunable Fe/N co-doped 3D porous graphene with high density Fe-Nx sites as the efficient bifunctional oxygen electrocatalyst for Zn-air batteries

Nitrogen-doped transition metal materials display promising potential as bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, Fe/N co-doped three-dimensional (3D) porous graphene (FeN-3D-PG) is prepared via a template method using sodium alginate as the carbon source and low polymerization degree melamine resin as the nitrogen source. The low polymerization degree melamine resin can form complexes with Fe³⁺ in the aqueous solution and further forms high density Fe-N_x active sites during pyrolysis. Meanwhile, the formed 3D porous structure efficiently promotes the uniform distribution of Fe-N_x active sites. The FeN-3D-PG catalyst exhibits pH-independent ORR activity. For OER, the catalyst possesses a low over potential (370 mV at 10 mA cm⁻²) in alkaline electrolyte. The Zn-air batteries (ZABs) using FeN-3D-PG as cathode exhibits a power density up to 212 mW cm⁻², a high specific capacity of 651 mAh g⁻¹, and the charge-discharge stability of 80 h. This work provides new sight to transition metal materials based ZABs with excellent performance.     

Fe─N─C Electrocatalyst for Enhancing Fe(II)/Fe(III) Redox Kinetics in Thermo-Electrochemical Cells

Harvesting low-grade waste heat, which constitutes 60% of the overall waste heat, is key to halting climate change. Electrochemical waste-heat harvesting has recently drawn attention to practical low-grade waste-heat harvesting. In this study, a power density maximization strategy is presented in scalable and cost-effective aqueous redox couple-based thermo-electrochemical cells (TECs). The n-type feature of the water-soluble Fe^2+/3+ redox couple is essential for constructing the TEC p–n leg device; however, it has not been investigated much so far. The modulation of the chaotropicity of counteranions enhances the absolute value of the Seebeck coefficient for the Fe^2+/3+ redox couple with an inner-sphere reaction mechanism because of the greater structural disorder in the solvation shell. Moreover, the use of a cost-effective Fe─N─C electrocatalyst shows redox kinetics and a power density comparable to those of state-of-the-art Pt electrodes, economically compensating for the sluggish charge-transfer kinetics of the inner-sphere redox mechanism. The Fe─N─C -based TEC device exhibits 1.73 W m⁻² of power density at 0.1 $ W⁻¹ of cost per power, which is 1.24% with respect to the Carnot efficiency, exceeding 0.23–0.53% compared to those reported for previous Pt-based TEC devices with the same redox chemistry.     

Effects of yogurt containing probiotics on respiratory virus infections: Influenza H1N1 and SARS-CoV-2

Respiratory virus infections are an escalating issue and have become common worldwide. Influenza and COVID-19 are typical infectious respiratory diseases, and they sometimes lead to various complications. In a situation in which no established drug or treatment exists, consumption of proper food might be beneficial in maintaining health against external infections. We studied the potential effects of mixtures of probiotic strains on various viral infections. The purpose of this study was to assess the ability of yogurt containing probiotics to reduce the risk of respiratory viruses such as influenza H1N1 and SARS-CoV-2 infection. First, we performed in vitro tests using infected Madin-Darby canine kidney (MDCK) and Vero E6 cells, to evaluate the potential effects of yogurt containing high-dose probiotics against influenza H1N1 and SARS-CoV-2 infection. The yogurt significantly reduced plaque formation in the virus-infected cells. We also performed in vivo tests using influenza H1N1-infected C57BL/6 mice and SARS-CoV-2-infected Syrian golden hamsters, to evaluate the potential effects of yogurt. Yogurt was administered orally once daily during the experimental period. Yogurt was also administered orally as pretreatment once daily for 3 wk before viral infection. Regarding influenza H1N1, it was found that yogurt caused an increase in the survival rate, body weight, and IFN-γ, IgG1, and IL-10 levels against viral infection and a decrease in the inflammatory cytokines TNF-α and IL-6. Although the SARS-CoV-2 copy number was not significantly reduced in the lungs of yogurt-treated SARS-CoV-2-infected hamsters, the body weights and histopathological findings of the lungs were improved in the yogurt-treated group. In conclusion, we suggest that consumption of yogurt containing probiotics can lead to beneficial effects to prevent respiratory viral infections.     

Mathematical modelling of the biofiltration treating mixtures of toluene and N-propanol in the biofilm and gas phase

This paper presents a mathematical model in the biofilm phase and in the gas phase that has been successfully applied to investigate various aspects of the biofiltration process. The mixtures of volatile organic compounds (VOCs) are emitted from a wide range of industries, such as chemical, petrochemical, pharmaceutical, pulp paper mills, printing and paint workshops, etc. The objective of the present study is, presence of high n-propanol loading negatively affected the toluene removal; however, n-propanol removal was not affected by the presence of toluene and was effectively removed in the biofilter despite high toluene loadings. A model for toluene and n-propanol biofiltration could predict the cross-inhibition effect of n-propanol on toluene removal. Further, we studied the effects of many physical and biological parameters on model prediction. The mathematical equations (2.12)-(2.16) which are non-linear partial differential equations are solved by using the homotopy perturbation technique. Also, we derived the semi-analytical results for toluene and n -propanol concentrations for saturated and unsaturated kinetics. It is verified that the proposed solution is validated by comparing it with numerical solutions.     

Spherical mesoporous Fe–N–C catalyst for the air cathode of membrane-less direct formate fuel cells

Fe–N–C catalysts with excellent performance regarding the oxygen reduction reaction (ORR) have aroused enormous interest in direct-formate fuel cells (DFFCs). However, their limited mass transfer ability, insufficient ORR active sites, and complex fabrication processes remain significant obstacles to the widespread application of Fe–N–C catalysts. Herein, we propose a simple hydrothermal-annealing method with agarose powders to synthesize a uniform spherical Fe–N–C catalyst (∼3 μm) with well-developed mesopores (Fe/rG@C/H-Agar-900). The resultant Fe/rG@C/H-Agar-900 catalyst possesses rich oxygen-containing functional groups and enhanced interconnected pores, which can significantly boost the content of catalytic sites and facilitate mass transport, resulting in a high content of active sites. In the meantime, the mesopore content of Fe/rG@C/H-Agar-900, which can facilitate the formation of the three-phase gas/electrolyte/catalyst interfaces, was optimized by varying the annealing temperature. As a result, the Fe/rG@C/H-Agar-900 demonstrates a half-wave potential of 0.91 V vs. RHE, nearly four-electron pathway selectivity, excellent durability, and excellent formate tolerance for ORR. Furthermore, when used as the air cathode in membrane-less DFFCs, the Fe/rG@C/H-Agar-900-based device exhibits a remarkable peak power density of 24.5 mW cm⁻², significantly outperforming the 20 wt% commercial Pt/C. This research facilitates the synthesis of an advanced Fe–N–C catalyst and promotes the practical development of membrane-less DFFCs.     

Novel up-conversion N,S co-doped carbon dots/g-C3N4 photocatalyst for enhanced photocatalytic hydrogen evolution under visible and near-infrared light

In photocatalytic splitting water for hydrogen evolution, narrow light response range and fast electron-hole recombination of g-C₃N₄ (CN) limit its photocatalytic activity. In this article, the N, S co-doped carbon dots (NSCDs) with up-converted property were loaded on CN nanosheets by thermal polymerization to obtain NSCDs/CN composite catalyst. Characterization, electrochemical researches and hydrogen evolution tests suggest that the photocatalytic activity of CN is greatly promoted by the introduction of NSCDs. Under visible and near-infrared irradiation, the hydrogen evolution rate is 5033.1 μmol g^?1 h^?1 of NSCDs-5/CN, which is 8.3 times higher than that of CN. The performance improvement is mainly attributed to the increased specific surface area, elevated hydrophilic surface, increased light absorption and suppressed carrier recombination of CN after the introduction of NSCDs. This work unveils the mechanism of the hydrogen evolution activity improvement in NSCDs-5/CN, and also offers a new prospect in the design of high-performance CN-based photocatalysts.     

Nitrogen doped FeCoNiS nanoparticles on N,S-co-doped vertical graphene as bifunctional electrocatalyst for water splitting

It's important to develop an economical and efficient electrocatalyst for water splitting. Nitrogen-doped FeCoNiS nanoparticles are supported on N, S-co-doped vertical graphene (N–FeCoNiS/SVG) by one-step electrodeposition. The SEM and TEM results show that 30–115 nm nanoparticles grow uniformly on SVG. The XRD results show that N–FeCoNiS/SVG is a polycrystalline material. N–FeCoNiS/SVG exhibits excellent hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) potentials of 44 mV and 138 mV (10 mA cm^?2), respectively, in 1 M KOH. The Faraday efficiency of N–FeCoNiS/SVG for overall water splitting is about 97%. The electrocatalyst also shows excellent stability over 24 h. The XPS results illustrate that N-doping promotes the electron transfer between metal and heteroatom and effectively modulates the electronic structure of FeCoNiS. N–FeCoNiS/SVG has excellent electrocatalytic performance for water splitting. This work provides theoretical and technical support for the study of water splitting bifunctional electrocatalysts.     

A durable and robust Fe–N–C electrocatalyst for oxygen reduction reactions by introducing Ti3C2–TiO2 as radical scavengers

Modern Fe–N–C electrocatalysts are promising as alternatives to expensive Pt-based catalysts for oxygen reduction reactions (ORR). Although the activity of this type of electrocatalyst have been improved over the years, their durability and longevity need critical enhancements for practical applications in fuel cells. Typically, the incomplete oxygen reduction inevitably generates reactive oxygen species, including ·OH and HO₂· radicals, which will fiercely attack the carbon support and directly damage active sites in Fe–N–C electrocatalysts. Herein, a durable and robust Fe–N–C@Ti₃C₂–TiO₂ electrocatalyst for high-efficiency ORR is synthesized, in which Ti₃C₂–TiO₂ could effectively scavenge ·OH radicals or decompose H₂O₂ molecules, and synergistically work with Fe–N–C catalysts to improve the durability. Consequently, the Fe–N–C@Ti₃C₂–TiO₂ electrocatalyst shows prominent ORR performance in both alkaline and acidic electrolytes, low H₂O₂ yield, and long-term stability. This work provides great prospects for the design of highly stable ORR electrocatalysts by introducing radical scavengers as an active defense to proactively eliminate H₂O₂ and its radicals.     

Constructing Ru@C3N4/Cu Tandem Electrocatalyst with Dual-Active Sites for Enhanced Nitrate Electroreduction to Ammonia

Electroreduction of nitrate to ammonia reaction (NO₃⁻RR) is considered as a promising carbon-free energy technique, which can eliminate nitrate from waste-water also produce value-added ammonia. However, it remains a challenge for achieving satisfied ammonia selectivity and Faraday efficiency (FE) due to the complex multiple-electron reduction process. Herein, a novel Tandem electrocatalyst that Ru dispersed on the porous graphitized C₃N₄ (g-C₃N₄) encapsulated with self-supported Cu nanowires (denoted as Ru@C₃N₄/Cu) for NO₃⁻RR is presented. As expected, a high ammonia yield of 0.249 mmol h⁻¹ cm⁻² at −0.9 V and high FE_NH3 of 91.3% at −0.8 V versus RHE can be obtained, while achieving excellent nitrate conversion (96.1%) and ammonia selectivity (91.4%) in neutral solution. In addition, density functional theory (DFT) calculations further demonstrate that the superior NO₃⁻RR performance is mainly resulted from the synergistic effect between the Ru and Cu dual-active sites, which can significantly enhance the adsorption of NO₃⁻ and facilitate hydrogenation, as well as suppress the hydrogen evolution reaction, thus lead to highly improved NO₃⁻RR performances. This novel design strategy would pave a feasible avenue for the development of advanced NO₃⁻RR electrocatalysts.     

An Innovative Design for the Fabrication of Flexible Composite Films from Si3N4 Fiber Paper

A high-temperature-resistant flexible substrate is a critical component of high-performance flexible electronic components. Herein, a method that does not require flowing gas and which is suitable for volume production is presented for the preparation of several-millimeter-long silicon nitride (Si₃N₄) fibers with a cross-sectional dimension of 0.1–1.0 μm. Further, a square sheet of paper with a weight of 0.050 g, side lengths of 105 mm each, and thickness of 15 μm is fabricated using the Si₃N₄ fibers via a conventional laboratory paper-making method. Subsequently, the Si₃N₄ paper is coated with an LaNiO₃ sol using a blade-coating machine, dried at 80 °C for 10 min, and then annealed at 650 °C for 60 min to prepare Si₃N₄ fiber paper/LaNiO₃ composite films to evaluate the feasibility of applying the paper as a substrate for fabricating flexible functional films. The experimental results confirm that the Si₃N₄ fiber paper has excellent high-temperature resistance during annealing in air, and the Si₃N₄ paper/LaNiO₃ composite film presents excellent flexibility and conductivity. Thus, membranous flexible electronic components can be fabricated from Si₃N₄ fiber paper/LaNiO₃ paper by a regular high-temperature annealing process.