Zinc, sulfur and nitrogen co-doped carbon from sodium chloride/zinc chloride-assisted pyrolysis of thiourea/sucrose for highly efficient oxygen reduction reaction in both acidic and alkaline media

Engineering Mn-Nx sites on porous carbon via molecular assembly strategy for long-life zinc-air batteries

Nitrogen-coordinated manganese atoms on carbon materials denoted as MnNC, serve as the highly active non-precious metal electrocatalysts for oxygen reduction reaction (ORR) in zinc-air batteries (ZABs). Nonetheless, a significant challenge arises from the tendency of Mn atoms to aggregate during heat treatment, thereby compromising ORR performance in ZABs. In this work, the molecular assembly strategy based on the hydrogen bond interaction was employed to fabricate the MnNC electrocatalyst. This approach promotes the dispersion of Mn atoms, creating abundant Mn-Nx active sites. Furthermore, the resulting three-dimensional porous nanostructure, formed by molecular assembly, significantly enhances accessibility to the Mn-Nx active sites. The porous nanostructure not only shortens the diffusion path of reactants and charges but also improves mass transfer. The MnNC exhibits impressive ORR catalytic performance with a half-wave potential of 0.90 V (vs. RHE). The liquid-type ZAB based on MnNC displays a high specific capacity of 816.6 mAh/g and an extended charge-discharge cycle life of 1000 h. Quasi-solid-state ZAB based on MnNC can operate stably for 24 h. This work presents an effective strategy to synthesize transition metal-nitrogen-carbon (MNC) electrocatalysts tailored for long-life zinc-air battery.

Activation of peroxymonosulfate by biochar-supported Fe3O4 derived from oily sludge to enhance the oxidative degradation of tetracycline hydrochloride

Carbon materials used for catalysis in advanced oxidation processes tend to be obtained from cheap and readily available raw materials. We constructed a carbon material, OSC@Fe3O4, by loading Fe3O4 onto the pyrolyzed hazardous waste oily sludge. OSC@Fe3O4 was then used to activate peroxymonosulfate (PMS) for the removal of tetracycline hydrochloride (TTCH) from water. At 298 K, 0.2 g⋅L-1 of catalyst and 0.3 g⋅L-1 of PMS, the reaction rate constant of the OSC@I-2/PMS system reached 0.079 min-1, with a TTCH removal efficiency of 92.6%. The degradation efficiency of TTCH remained at 81% after five cycles. The specific surface area and pore volume of OSC@I-2 were 263.9 m2⋅g-1 and 0.42 cm3⋅g-1, respectively, which improved the porous structure of the carbon material and provided more active points, thus improving the catalytic performance. N and S were doped into the oily sludge carbon due to the presence of N- and S-containing compounds in the raw oily sludge. N and S doping led to more electron-rich sites with higher negative charges in OSC@I-2 and gave the oily sludge carbon a higher affinity to PMS, thereby promoting its ability to activate PMS. Sulfate radicals (SO4•‾) played a dominant role in the degradation of TTCH, with demethylation and the breaking of double bonds being a possible degradation pathway. A biotoxicity test showed that the microbial toxicity of the degradation intermediates was significantly reduced. This work provides a strategy for the application of PMS-based catalysts derived from waste carbon resources.

Constructing FeS and ZnS Heterojunction on N,S-Codoped Carbon as Robust Electrocatalyst toward Oxygen Reduction Reaction

Highly active and cost-efficient electrocatalysts for oxygen reduction reaction (ORR) are significant for developing renewable energy conversion devices. Herein, a nanocomposite Fe/ZnS-SNC electrocatalyst with an FeS and ZnS heterojunction on N,S-codoped carbon has been fabricated via a facile one-step sulfonating of the pre-designed Zn- and Fe-organic frameworks. Benefitting from the electron transfer from FeS to adjacent ZnS at the heterointerfaces, the optimized Fe/ZnS-SNC900 catalyst exhibits excellent ORR performances, featuring the half-wave potentials of 0.94 V and 0.81 V in alkaline and acidic media, respectively, which is competitive with the commercial 20 wt.% Pt/C (0.87 and 0.76 V). The flexible Zn-air battery equipping Fe/ZnS-SNC900 affords a higher open-circuit voltage (1.45 V) and power density of 30.2 mW cm-2. Fuel cells assembled with Fe/ZnS-SNC900 as cathodic catalysts deliver a higher power output of 388.3 and 242.8 mW cm-2 in H2-O2 and -air conditions. This work proposes advanced heterostructured ORR electrocatalysts that effectively promote renewable energy conversions.

ZnS modified N, S dual-doped interconnected porous carbon derived from dye sludge waste as high-efficient ORR/OER catalyst for rechargeable zinc-air battery

Facile and rational design of high-efficient oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) bifunctional electrocatalysts is significant for rechargeable Zinc-air batteries. In this study, ZnS modified N, S dual-doped interconnected porous carbon (ZnS/NSC) derived from the dye sludge waste is successfully fabricated via a facile ZnCl₂-assisted pyrolysis process. The effect of ZnCl₂ and carbonization temperature on the microstructure and electrocatalytic performance is systematically investigated. By virtue of the synergistic effect between ZnS nanoparticles and N, S dual-doped porous carbon network, the obtained catalyst ZnS/NSC calcined at 1000 °C exhibits a decent bifunctional electrocatalytic performance with potential gap (ΔE=E_OER,10-E_ORR,1/2) of 0.76 V comparable with commercial electrocatalysts (Pt/C and RuO₂). In addition, a rechargeable zinc-air battery employed ZnS/NSC-1000 as the air cathode also displays the favorable electrochemical performance, in which the power density is 125 mW cm^-2, the specific capacity is 763.27 mAh g^-1 and the cycling stability at 10 mA cm^-2 is more than 85 h, indicating a promising application prospect in rechargeable Zinc-air batteries.

Synergistic melamine intercalation and Zn(NO3)2 activation of N-doped porous carbon supported Fe/Fe3O4 for efficient electrocatalytic oxygen reduction

Developing inexpensive, efficient and good stability transition metal-based oxygen reduction reaction (ORR) electrocatalysts is a research topic of great concern in the commercial application of fuel cells. Herein, with zinc nitrate as activator, iron nitrate as active component and melamine as intercalating agent and nitrogen source, an N-doped porous carbon supported Fe/Fe₃O₄ (Fe/Fe₃O₄@NC) catalyst is successfully synthesized by an impregnation–calcination method combined with freeze-drying technique. The positive onset potential (E_onset), half-wave potential (E_1/2) and limiting current density (J_L) of the optimal Fe/Fe₃O₄@NC catalyst are 1.012, 0.90 V vs. RHE and 5.87 mA cm⁻², respectively. Furthermore, Fe/Fe₃O₄@NC catalyzes ORR mainly through a 4e⁻ pathway, and the yield of H₂O₂ is less than 5%. It also manifests a robust stability after 5000 CV cycles of ADT testing, and the half-wave potential is only negatively shifted 17 mV. The structural characterization and experimental results further suggest that the outstanding ORR electrocatalytic performance of the Fe/Fe₃O₄@NC catalyst benefits from the synergetic effect of zinc nitrate activation and nitrogen doping, which can greatly improve the specific surface area, thus better dispersing more metal active sites. This work puts forward a simple and practicable way for preparing high-performance non-noble metal-based biomass ORR electrocatalysts.

N-doped 2D porous carbon supported Fe/Fe₃O₄ composite is fabricated by melamine intercalation and zinc nitrate as activator. The synergistic effect makes the catalyst shows excellent ORR activity and decent durability compared with commercial Pt/C.

Preparation of ZnS@N-doped-carbon composites via a ZnS-amine precursor vacuum pyrolysis route

ZnS/carbon nanocomposites have potential electrochemical applications due to their improved conductivity and more active sites through modification of the carbon materials. Herein, we report a facile method to synthesize the nanocomposites comprising ZnS nanoparticles and nitrogen-doped carbon (ZnS@NC). The inorganic–organic hybrid ZnS-amine material ZnS(ba) (ba = n-butylamine) is synthesized on a large scale by a reflux method, which effectively shortens the reaction time while maintaining the high yield compared with the solvothermal method. Then ZnS(ba) is used as precursor for obtaining ZnS@NC nanocomposites via a vacuum pyrolysis route, in which the content of carbon and nitrogen can be controlled by adjusting the pyrolysis temperature. Further, a series of ZnS-amine hybrid materials ZnS(ha), ZnS(en)_0.5 and ZnS(pda)_0.5 (ha = n-hexylamine; en = ethylenediamine; pda = 1,3-propanediamine) are synthesized and used as precursors for the preparation of ZnS@NC materials, indicating the universality of this method. Moreover, the as-synthesized ZnS@NC materials exhibit remarkable lithium storage performance with outstanding cycling stability, high-rate capability and remarkable pseudo-capacitance characteristics.

ZnS/N-doped-carbon nanocomposites exhibiting remarkable Li storage performance are facilely prepared through the temperature-controllable vacuum pyrolysis of various ZnS-amine precursors.

Crystalline carbon modified hierarchical porous iron and nitrogen co-doped carbon for efficient electrocatalytic oxygen reduction

Hierarchical porous iron and nitrogen co-doped carbon (Fe-N/C) materials have been considered as an appealing non-noble metal-based catalyst in oxygen reduction reactions (ORR). However, the conductivity loss caused by the scattering of electrons on pores and defects markedly limits their catalytic activity, which attracted seldom attention in this area. Herein, a novel crystalline carbon modified hierarchical porous Fe-N/C electrocatalyst with enhanced electronic conductivity is designed and prepared via a two-step calcination-catalysis process. The resistivity of hierarchical porous Fe-N/C is decreased from 2.123 Ω cm to 0.479 Ω cm after crystalline carbon introduction. The electrocatalyst annealed at 800 °C (Fe-N/C-800) exhibits a superior activity with the half-wave potential (E_1/2) of 0.89 V, which outperforms the commercial carbon-supported platinum (Pt/C) catalyst (0.85 V). The strategy of crystalline carbon modification provides a fresh approach to improve the electronic conductivity of porous carbon-based materials.

Multi-role graphitic carbon nitride-derived highly porous iron/nitrogen co-doped carbon nanosheets for highly efficient oxygen reduction catalyst

Pyrolyzing precursors containing iron, nitrogen and carbon elements is a commonly used process for synthesizing FeNC catalysts for oxygen reduction reaction (ORR). Generally, aggregation of iron-based species is prone to occur because of a lack of chemical bonds between iron-based species and carbon matrix and synthesizing highly porous FeNC catalysts is difficult because carbon skeleton is prone to collapse during pyrolysis. Herein, highly porous FeNC catalysts with fine iron-based species are synthesized by selecting glucose as carbon source, FeCl₃ as iron source, and urea-derived g-C₃N₄ as nitrogen source, iron anchoring and stabilizing species, and pore-forming template. The multi-role g-C₃N₄-derived catalyst synthesized at 1100 °C (FeNC1100) has fine iron-based species, large specific surface area (737 m² g^-1), and extremely high pore volume (2.66 cm³ g^-1). Accordingly, FeNC1100 shows a larger half-wave potential (E_1/2 = 0.894 V), a higher stability (ΔE_1/2 = 6 mV) after 10,000 potential cycles in alkaline media, and a higher peak power density (P = 152 mW cm^-2) when employed as ORR catalyst of zinc-air battery, which are all superior to those of the commercial Pt/C catalyst (E_1/2 = 0.864 V, ΔE_1/2 = 30 mV, P = 134 mW cm^-2). The present work brings a new method for synthesizing highly porous FeNC catalysts decorated with fine active sites for ORR.