Nickel-iron nanoparticles encapsulated in carbon nanotubes prepared from waste plastics for low-temperature solid oxide fuel cells

Electronic Configuration-Modulated Dual-Active Nanocomposite NiAlOx for Promoting Plastic-To-Green Hydrogen

Chemical upcycling of plastic waste to produce green H2 has emerged as a promising avenue. Highly efficient and robust NiAlOx catalysts with dual active nanocomposite (NiO-NiAl2O4) through a facile electronic configuration modulation strategy are synthesized for the decomposition-catalytic steam reforming (DCSR) of plastic wastes for enhancing H2 production while alleviating carbon deposition. Of these dual-active nanocomposite catalysts, NiAlOx-800 presents the highest proportions of Ni2+ cations and oxygen vacancies, contributing to the enhance structural stability and catalytic activity. NiAlOx-800 subjected to the DCSR process achieves the highest gas yield (244.42 mmol gplastic -1) with an extremely high H2 proportion of 70.14 vol%, due to its superior catalytic cracking and reforming ability. Furthermore, a high carbon conversion efficiency (≈100%) is achieved, suggesting that the C content in plastic is completely transformed into gases. More importantly, the catalyst's robustness and stability are evaluated in the time course study, where it maintains an exceptionally high gas yield (252.23 mmol gplastic -1) with 71.52 vol% of H2 after 200 min. In situ DRIFTS characterization is also performed to unravel the reaction mechanisms. Thus, this work innovatively explores a new strategy for developing an electronic configuration-modulated nanocomposite catalyst for upcycling waste plastics into highly pure green H2.

Catalytic pyrolysis of oxygen-containing waste polycarbonate for the preparation of carbon nanotubes and H2-rich syngas

In this study, ex-situ catalytic pyrolysis of oxygen-containing polycarbonate (PC) was conducted to prepare carbon nanotubes (CNTs) and H2-rich syngas. This study examined the influence of the active metal components (Ni and Fe), catalyst pre-reduction, and pre-deoxygenation of pyrolysis volatiles on the catalytic performance and mechanism. Results show that the reductive constituents in pyrolysis volatiles make it difficult to reduce the Fe oxides, thus hindering the CNTs growth on Fe catalysts, compared to Ni catalysts. H2 pre-reduction of Ni and Fe catalysts enhances the generation of CNTs and syngas. The pre-reduced Fe catalyst exhibits better carbon deposit performance, reaching 263 mg/gplastics. The pre-reduced Ni catalyst better facilitates the reforming reaction of CO2 and H2O, resulting in higher syngas yields of 32.75 mmol/gplastics, with a volume proportion of 94.4 vol%. The addition of the deoxygenation catalyst Ni/HZSM-5 promotes the growth of CNTs with fewer defects and higher graphitization on Ni catalysts. The excess CO2 and H2O generated by the introduction of Ni/HZSM-5 may oxidize the Fe0 on pre-reduced Fe catalysts, inhibiting the growth of CNTs. The mechanism of the growth of CNTs and syngas from PC is also explored. The findings can provide theoretical guidance for the disposal of waste plastics.

Preparation of high quality carbon nanotubes by catalytic pyrolysis of waste plastics using FeNi-based catalyst

Plastic waste pollution is the serious environmental problem, and catalytic pyrolysis of waste plastics is an effective way to solve this problem. Carbon nanotubes (CNTs) are prepared by catalytic pyrolysis of low-density polyethylene (LDPE) waste plastics by one-stage method using iron nitrate and nickel nitrate as catalyst. The growth mechanism of CNTs is analyzed in detail. TPO, XRD, SEM and Raman analyses show that increasing Ni content contributes to the production of CNTs with good morphology and high graphitization degree. While the increasing Fe content contributes to improving the yield of CNTs. The outer and inner diameters of the FeNi12-CNTs-800 are about 21 nm and 8 nm with the length of 18.9 μm, respectively. LDPE pyrolysis gases are analyzed to determine that the primary carbon source required for CNTs growth is C2H4. The C2H4 adsorption and decomposition processes on FeNi alloys are performed to reveal the growth mechanism of CNTs, based on density functional theory calculation. Three kinds of the growth models are proposed to explain the difference of the CNTs tubular shape. FeNi12-CNTs-800 are used to remove microplastics from wastewater due to existence of magnetic. PVC can be quickly removed from wastewater with removal of 100 % at 20 min. This study provides an effective way for recycling and treatment of waste plastic.

A highly conductive and robust micrometre-sized SiO anode enabled by an in situ grown CNT network with a safe petroleum ether carbon source

SiO-based materials as lithium-ion anodes have attracted huge attention owing to their ultrahigh capacity. However, they usually undergo severe volume expansion over the repeated lithiation/delithiation processes and have low electronic conductivity, leading to an inferior cycling stability and poor rate capability. In this study, carbon nanotubes in situ grown on the surface of commercially available micro-sized SiO (D50 = 5 μm) were prepared. The conductive network composed of one-dimensional carbon nanotubes could enhance its conductivity and enhance the structural stability during the cycling. The synthesized 3D-SiO@C material demonstrates good long-term cycling stability, with a reversible capacity of up to 687.7 mA h g-1 after 1000 cycles, and it maintains a high reversible capacity of 736.8 mA h g-1, even at a high current density of 1 A g-1.

Simultaneous production of high-valued carbon nanotubes and hydrogen from catalytic pyrolysis of waste plastics: The role of cellulose impurity

Upcycling waste plastics into valuable carbon nanotubes (CNTs) and hydrogen via catalytic pyrolysis is a sustainable strategy to mitigate white pollution. However, real-world plastics are complex and generally contain organic impurities, such as cellulose, which have a non-negligible impact on the catalytic pyrolysis process and product distribution. In this study, cellulose was chosen as a model compound to distinguish the effects of oxygen-containing components on the CNTs and hydrogen production during the catalytic pyrolysis of waste polypropylene. Different amounts of cellulose were mixed with polypropylene to regulate the O/C mass ratio of the feedstock, and the relationship between the O/C mass ratio and the yield of products has been built quantificationally. The results revealed that the relative content of CNTs increased to over 95%, and the stability and purity of carbon deposition increased accordingly when the O/C mass ratio is 0.05. This could be ascribed to the etching effects caused by small amounts of H2O and CO2 on amorphous carbon. However, further increasing the amount of cellulose caused the deactivation of the Fe-Ni catalyst. This not only decreased the carbon yield but had an adverse impact on its morphology and graphitization, leading to the increase of amorphous carbon. This study can provide fundamental guidance for the efficient utilization of waste plastics that take advantage of organic impurities in waste plastic to promote the formation of high-purity CNTs.

Magnetic Heating Amorphous NiFe Hydroxide Nanosheets Encapsulated Ni Nanoparticles@Wood Carbon to Boost Oxygen Evolution Reaction Activity

The oxygen evolution reaction (OER) has significant effects on the water-splitting process and rechargeable metal-air batteries; however, the sluggish reaction kinetics caused by the four-electron transfer process for transition metal catalysts hinder large-scale commercialization in highly efficient electrochemical energy conversion devices. Herein, a magnetic heating-assisted enhancement design for low-cost carbonized wood with high OER activity is proposed, in which Ni nanoparticles are encapsulated in amorphous NiFe hydroxide nanosheets (a-NiFe@Ni-CW) via direct calcination and electroplating. The introduction of amorphous NiFe hydroxide nanosheets optimizes the electronic structure of a-NiFe@Ni-CW, accelerating electron transfer and reducing the energy barrier in the OER. More importantly, the Ni nanoparticles located on carbonized wood can function as magnetic heating centers under the effect of an alternating current (AC) magnetic field, further promoting the adsorption of reaction intermediates. Consequently, a-NiFe@Ni-CW demonstrated an overpotential of 268 mV at 100 mA cm^-2 for the OER under an AC magnetic field, which is superior to that of most reported transition metal catalysts. Starting with sustainable and abundant wood, this work provides a reference for highly effective and low-cost electrocatalyst design with the assistance of a magnetic field.