A Flexible Vertical-Section Wood/MXene Electrode with Excellent Performance Fabricated by Building a Highly Accessible Bonding Interface.

Cross-section wood (CW) is generally used as a host for free-standing electrodes, as the abundant opened pores can provide large space for loading guest materials with high electrical conductivity and electrochemical activity. However, there is still a challenge for CW to be used in flexible supercapacitors (SCs) because of its low mechanical strength. Herein, as an alternative to CW, vertical-section wood (VW) with excellent mechanical strength and good flexibility is developed and used as a free-standing and flexible electrode by using Ti3C2Tx (MXene) with ultrahigh conductivity and good electrochemical activity as a guest material. In particular, the highly accessible bonding interface for Ti3C2Tx is first built by delignification on VW to generate abundant pores for continuously absorbing Ti3C2Tx and to expose cellulose with abundant oxygen-containing groups for stable combination with Ti3C2Tx. Then, cyclic pressing is used to form negative pressure to pump the Ti3C2Tx suspension into VW, combining with a preheating process to trigger layer-by-layer self-assembly of Ti3C2Tx nanosheets onto a wood cell wall by evaporating water in the suspension. As a result, the free-standing electrode has a large Ti3C2Tx loading mass proportion of 33 wt %, a high conductivity of 3.14 S cm-1, and good flexibility with much higher mechanical strength of 15.1 MPa than 0.4 MPa of CW. The symmetric SC delivers a good specific capacitance of 805 mF cm-2 at 0.5 mA cm-2, a remarkably high rate capability of 84% to 10 mA cm-2, and an energy density of 13.85 µW h cm-2 at 87.5 µW cm-2. Additionally, this SC shows a long lifespan of 90.5% after 10,000th charge and discharge cycles even at a constant bending angle of 90°, suggesting promising potential in flexible devices.

Effect of support type and crystal form of support in the catalytic gasification of old corrugated containers using Fe-based catalysts.

Catalytic gasification of old corrugated containers with Fe-based catalysts is a promising way to produce renewable H2 along with the utilization of solid waste. In this study, the effect of support type and crystal form of support in Fe-based catalysts on the catalytic gasification of old corrugated containers was systematically investigated. The results show that, the introduction of Fe/γ-Al2O3, Fe/TiO2, Fe/SiO2, and Fe/ZSM5-30 promote H2 production. Among them, Fe/TiO2 has the highest catalytic activity on H2 yield (25.10 mmol/g) related to the formation of Fe2TiO5 solid-melt material. Fe/γ-Al2O3 shows the best H2 selectivity (46.34 %) and good H2 yield (24.19 mmol/g) due to good dispersity of Fe. Further, the order of catalytic effect on H2 selectivity is Fe/amorphous Al2O3 (51.46 %) > Fe/α-Al2O3 (46.98 %) > Fe/γ-Al2O3 (46.34 %). With the increase in cycle index, Fe/amorphous Al2O3 shows the best catalytic effect on H2 yield (25.56 mmol/g) after 11 indexes due to the formation of Al2FeO4. Fe/γ-Al2O3 shows the best stability on H2 selectivity (∼43 %) after 11 indexes.

High-value products from ex-situ catalytic pyrolysis of polypropylene waste using iron-based catalysts: the influence of support materials.

Catalytic pyrolysis is considered a promising strategy for the utilisation of plastic waste from the economic and environmental perspectives. As such, the supporting materials play a critical role in the properties of the catalyst. This study clarified this influence on the dispersion of the iron (Fe) within an experimental context. Four different types of typical supports with different physical structures were introduced and explored in a two-stage fixed-bed reactor; these included metallic oxides (Al2O3, TiO2), a non-metallic oxide (SiO2), and molecular sieves (ZSM-5). The results show that the liquid products were converted into carbon deposits and lighter gaseous products, such as hydrogen. The Al2O3-supported catalyst with a relatively moderate specific surface areas and average pore diameter exhibited improved metal distribution with higher catalytic activity. In comparison, the relatively low specific surface areas of TiO2 and small average pore diameters of ZSM-5 had a negative impact on metal distribution and the subsequent catalytic reformation process; this was because of the inadequate reaction during the catalytic process. The Fe/Al2O3 catalyst produced a higher yield of carbon deposits (30.2 wt%), including over 65% high-value carbon nanotubes (CNTs) and hydrogen content (58.7 vol%). Additionally, more dispersive and uniform CNTs were obtained from the Fe/SiO2 catalyst. The Fe/TiO2 catalyst promoted the formation of carbon fibre twisted like fried dough twist. Notably, there was interesting correspondence between the size of the reduced Fe nanoparticles and the product distribution. Within certain limits, the smaller Fe particle size facilitates the catalytic activity. The smaller and better dispersed Fe particles over the support materials were observed to be essential for hydrocarbon cracking and the subsequent formation of carbon deposits. The findings from this study may provide specific guidance for the preparation of different forms of carbon materials.

Bimetallic carbon nanotube encapsulated Fe-Ni catalysts from fast pyrolysis of waste plastics and their oxygen reduction properties.

Carbon-based bimetallic electrocatalysts were obtained by catalytic pyrolysis of waste plastics with Fe-Ni-based catalysts and were used as efficient oxygen reduction reaction (ORR) catalysts in this study. The prepared iron-nickel alloy nanoparticles encapsulated in oxidized carbon nanotubes (FeNi-OCNTs) are solid products with a unique structure. Moreover, the chemical composition and structural features of FeNi-OCNTs were determined. The iron-nickel alloy nanoparticles were wrapped in carbon layers, and the carbon nanotubes had an outer diameter of 20-50 nm and micron-scale lengths. FeNi-OCNT with a Fe/Ni ratio of 1:2 (FeNi-OCNT12) exhibited remarkable electrochemical performance as an ORR catalyst with a positive onset potential of 1.01 V (vs. RHE) and a half-wave potential of 0.87 V (vs. RHE), which were comparable to those of a commercial 20% Pt/C catalyst. Furthermore, FeNi-OCNT12 exhibited promising long-term stability and higher tolerance to methanol than the commercial 20% Pt/C catalyst in an alkaline medium. These properties were attributable to the protective OCNT coating of the iron-nickel alloy nanoparticles.

Preparation of Iron- and Nitrogen-Codoped Carbon Nanotubes from Waste Plastics Pyrolysis for the Oxygen Reduction Reaction.

A novel method for the preparation of iron- and nitrogen-codoped carbon nanotubes (Fe-N-CNTs) is proposed, based on the catalytic pyrolysis of waste plastics. First, carbon nanotubes are produced from pyrolysis of plastic waste over Fe-Al2 O3 ; then, Fe-CNTs and melamine are heated together in an inert atmosphere. Different co-pyrolysis temperatures are tested to optimize the electrocatalyst production. A high doping temperature improves the degree of graphite formation and promotes the conversion of nitrogen into a more stable form. Compared with commercial Pt/C, the electrocatalyst obtained from pyrolysis at 850 °C shows remarkable properties, with an onset potential of 0.943 V versus RHE and a half-wave potential of 0.811 V versus RHE, and even better stability and anti-poisoning properties. In addition, zinc-air battery tests are performed, and the optimized catalyst exhibits a high maximum power density.

Pyrolysis of Chinese chestnut shells: Effects of temperature and Fe presence on product composition.

To understand the role of Fe on biomass pyrolysis, Fe-catalyzed biomass pyrolysis in a fixed-bed reactor was investigated. It was found that the introduction of Fe increased the yields of gases and solid char while decreasing the yield of liquid oil. With increasing temperature, Hydrogen content in gaseous products obtained in the presence of Fe increased, while that of CH4 decreased. In the case of liquid oil, the introduction of Fe promoted the formation of ketones and acids at 400-600 °C, and these species became dominant (67.51%) at 700-800 °C. Finally, solid char obtained in the presence of Fe at 700-800 °C featured a larger pore volume, specific surface area, and graphitization degree, and was characterized by a mesoporous structure with narrow pores size distribution (∼5.3 nm).

Mechanism of biomass activation and ammonia modification for nitrogen-doped porous carbon materials.

The effect of chemical activation and NH3 modification on activated carbons (ACs) was explored via two contrasting bamboo pyrolysis strategies involving either two steps (activation followed by nitrogen doping in NH3 atmosphere) or one step (activation in NH3 atmosphere) with several chemical activating reagents (KOH, K2CO3, and KOH + K2CO3). The ACs produced by the two-step method showed relatively smaller specific surface areas (∼90% micropores) and lower nitrogen contents. From the one-step method, the ACs had larger pore diameters with about 90% small mesopores (2-3.5 nm). Due to a promotion effect with the KOH + K2CO3 combination, the AC attained the greatest surface area (2417 m2 g-1) and highest nitrogen content (3.89 wt%), endowing the highest capacitance (175 F g-1). The balance between surface area and nitrogen content recommends KOH + K2CO3 activation via the one-step method as the best choice for achieving both greener production process and better pore structure.

Pyrolysis behavior and economics analysis of the biomass pyrolytic polygeneration of forest farming waste.

The pyrolysis behavior of Chinese chestnut and Jatropha curcas shells (CNS and JCS, respectively) were investigated to determine the optimum operating temperature for biomass pyrolytic polygeneration systems. At low temperatures (250-450 °C), CO2 was the main component of the pyrolytic gas, and high acidity oil was obtained. When the temperature increased to 550-650 °C, phenol-enriched oil and high LHV biochar (∼26 MJ/kg) were obtained; H2 and CO yields increased. At high temperatures (750-950 °C), heavy-oil and high LHV pyrolytic gas (∼15 MJ/m3) were obtained. Meanwhile, the biochar showed a highly condensed aromatic ring system and low H/C (∼0.1) and O/C (∼0.05) ratios. CNS and JCS biochars showed different tendencies with regard to their structure evolution. An economic analysis was performed, which suggested that the optimum operating temperatures were 450 °C for CNS and 350 °C for JCS.