Exploration and Size Engineering from Natural Chalcopyrite to High-Performance Electrode Materials for Lithium-Ion Batteries

Electrocatalytically active and charged natural chalcopyrite for nitrate-contaminated wastewater purification extended to energy storage Zn-NO3- battery

Charged natural chalcopyrite (CuFeS2, Ncpy) was developed for a three-dimensional electrochemical nitrate reduction (3D ENO3-RR) system with carbon fiber cloth cathode and Ti/IrO2 anode and Zn-NO3- battery. The 3D ENO3-RR system with Ncpy particle electrodes (PEs) possessed superior nitrate removal of 95.6 % and N2 selectivity of 76 % with excellent reusability under a broad pH range of 2-13 involving heterogeneous and homogeneous radical mechanisms. The Zn-NO3- battery with Ncpy cathode delivered an open-circuit voltage of 1.03 V and a cycling stability over 210 h. It was found that Ncpy PEs functioned through self-oxidation, surface dynamic reconstruction (Cu1.02Fe1.0S1.72O1.66 to Cu0.61Fe1.0S0.27O2.98), intrinsic micro-electric field (CuI, S2- anodic and FeIII cathodic poles), and reactive species (•OH, SO4•-, 1O2, •O2- and •H) generation. Computational analyses reveal that CuFeS2(112) surface with the lowest surface energy preferentially exposes Fe and Cu atoms. Cu site is beneficial for reducing NO3- to NO2-, Fe and Fe-Cu dual sites are conducive to N2 selectivity, lowering the overall reaction barriers. It paves the way for selective NO3- reduction in wastewater treatment and can be further extended to energy storage devices by utilizing low-cost Ncpy.

Enhanced persulfate activation by ethylene glycol-mediated bimetallic sulfide for imidacloprid degradation

CuFeS2 is regarded as a promising catalyst for heterogeneous activation to remove organic contaminants in wastewater. However, effects of solvents in regulating material synthesis and catalytic activity are still not clear. Herein, we reported the role of water, ethanol, ethylene glycol (EG), glycerol, and polyethylene glycol 200 on the synthesis of CuFeS2 micro-flowers and their performance in activating persulfate (PS) to remove imidacloprid (IMI) pesticide. The results showed that the solvent had an effect on the morphology, crystallinity, yields, specific surface areas and unpaired electrons of CuFeS2 micro-flowers. The degradation experiments revealed the efficient catalytic activity of EG-mediated CuFeS2 for heterogeneous PS activation. SO4•- and •OH were identified in EG-CuFeS2/PS system and •OH (90.4%) was the dominant reactive species. Meanwhile, stable 20% of η[PMSO2] (the molar ratio of PMSO2 generation to PMSO consumption) was achieved and demonstrated that Fe(IV) was also involved in the degradation process. Moreover, S2- promoted the cycling of Fe3+/Fe2+ and Cu2+/Cu+, enhancing the synergistic activation and reusability of the catalyst. Density functional theory (DFT) calculations verified that PS was adsorbed by Fe atom and electron transfer occurred on the catalyst surface. Three possible degradation pathways of IMI were proposed by analysis of the degradation intermediates and their toxicities were evaluated by ECOSAR. This study not only provides a theoretical foundation for catalyst design, but also promotes the industrial application of bimetallic sulfide Fenton-like catalysts for water management.

Interfacial Mo-S-C Bond with High Reversibility for Advanced Alkali-Ion Capacitors: Strategies for High-Throughput Production

The high-throughput scalable production of low-cost and high-performance electrode materials that work well under high power densities required in industrial application is full of challenges for the large-scale implementation of electrochemical technologies. Here, motivated by theoretical calculation that Mo-S-C heterojunction and sulfur vacancies can reduce the energy band gap, decrease the migration energy barrier, and improve the mechanical stability of MoS2 , the scalable preparation of inexpensive MoS2-x @CN is contrived by employing natural molybdenite as precursor, which is characteristic of high efficiency in synthesis process and energy conservation and the calculated costs are four orders of magnitude lower than MoS2 /C in previous work. More importantly, MoS2- x @CN electrode is endowed with impressive rate capability even at 5 A g-1 , and ultrastable cycling stability during almost 5000 cycles, which far outperform chemosynthesis MoS2 materials. Obtaining the full SIC cell assembled by MoS2- x @CN anode and carbon cathode, the energy/power output is high up to 265.3 W h kg-1 at 250 W kg-1 . These advantages indicate the huge potentials of the designed MoS2- x @CN and of mineral-based cost-effective and abundant resources as anode materials in high-performance AICs.

Mixed Cu-Fe Sulfides Derived from Polydopamine-Coated Prussian Blue Analogue as a Lithium-Ion Battery Electrode

Batteries employing transition-metal sulfides enable high-charge storage capacities, but polysulfide shuttling and volume expansion cause structural disintegration and early capacity fading. The design of heterostructures combining metal sulfides and carbon with an optimized morphology can effectively address these issues. Our work introduces dopamine-coated copper Prussian blue (CuPB) analogue as a template to prepare nanostructured mixed copper-iron sulfide electrodes. The material was prepared by coprecipitation of CuPB with in situ dopamine polymerization, followed by thermal sulfidation. Dopamine controls the particle size and favors K-rich CuPB due to its polymerization mechanism. While the presence of the coating prevents particle agglomeration during thermal sulfidation, its thickness demonstrates a key effect on the electrochemical performance of the derived sulfides. After a two-step activation process during cycling, the C-coated KCuFeS₂ electrodes showed capacities up to 800 mAh/g at 10 mA/g with nearly 100% capacity recovery after rate handling and a capacity of 380 mAh/g at 250 mA/g after 500 cycles.

Enhanced Cr(VI) reduction on natural chalcopyrite mineral modulated by degradation intermediates of RhB

Wastewater with complex compositions of both heavy metals and organic pollutants is of critical environmental and socioeconomic threat worldwide, which urgently requires feasible remediation technologies to target this challenge. In this study, natural chalcopyrite (CuFeS₂, NCP), the most abundant copper-based mineral in the Earth's crust, has been discovered to be a heterogeneous catalyst that can activate peroxydisulfate (PDS) for the simultaneous degradation of organic pollutant Rhodamine B (RhB) and reduction of hexavalent chromium (Cr(VI)). Batch experimental results indicate that both RhB and Cr(VI) could be simultaneously removed under a near-neutral condition in NCP/PDS combined system. The radicals SO₄^•- and ^•OH generated from PDS activation are the main oxidative species detected by electron paramagnetic resonance (EPR) spectroscopy. SO₄^•- acted as a predominant role in RhB degradation, while Cr(VI) reduction is mainly attributed to the oxidization of S^2- and S₂^2- species on NCP surface, as well as the photoreduction performance of NCP, which could be enhanced by the intermediates generated from RhB degradation. Density functional theory (DFT) calculation results disclose that Fe is the critical catalytic site for PDS activation. This work demonstrates a user-friendly strategy for remediation of complex wastewater containing both heavy metal and organic pollutants by combining photoreduction and advanced oxidation processes (AOPs) with natural minerals. It paves a way for wastewater treatment by utilizing low-cost natural abundant minerals as catalysts.

CuFeS2 as a Very Stable High-Capacity Anode Material for Sodium-Ion Batteries: A Multimethod Approach for Elucidation of the Complex Reaction Mechanisms during Discharge and Charge Processes

Highly crystalline CuFeS₂ containing earth-abundant and environmentally friendly elements prepared via a high-temperature synthesis exhibits an excellent electrochemical performance as an anode material in sodium-ion batteries. The initial specific capacity of 460 mAh g^-1 increases to 512 mAh g^-1 in the 150th cycle and then decreases to a still very high value of 444 mAh g^-1 at 0.5 A g^-1 in the remaining 550 cycles. Even for a large current density, a pronounced cycling stability is observed. Here, we demonstrate that combining the results of X-ray powder diffraction experiments, pair distribution function analysis, and ²³Na NMR and Mössbauer spectroscopy investigations performed at different stages of discharging and charging processes allows elucidation of very complex reaction mechanisms. In the first step after uptake of 1 Na/CuFeS₂, nanocrystalline NaCuFeS₂ is formed as an intermediate phase, which surprisingly could be recovered during charging. On increasing the Na content, Cu⁺ is reduced to nanocrystalline Cu, while nanocrystalline Na₂S and nanosized elemental Fe are formed in the discharged state. After charging, the main crystalline phase is NaCuFeS₂. At the 150th cycle, the mechanisms clearly changed, and in the charged state, nanocrystalline Cu_xS phases are observed. At later stages of cycling, the mechanisms are altered again: NaF, Cu₂S, and Cu_7.2S₄ appeared in the discharged state, while NaF and Cu₅FeS₄ are observed in the charged state. In contrast to a typical conversion reaction, nanocrystalline phases play the dominant role, which are responsible for the high reversible capacity and long-term stability.

Valleriite, a Natural Two-Dimensional Composite: X-ray Absorption, Photoelectron, and Mössbauer Spectroscopy, and Magnetic Characterization

Valleriite is of interest as a mineral source of basic and precious metals and as an unusual material composed of two-dimensional (2D) Fe-Cu sulfide and magnesium hydroxide layers, whose characteristics are still very poorly understood. Here, the mineral samples of two types with about 50% of valleriites from Noril'sk ore provenance, Russia, were examined using Cu K- and Fe K-edge X-ray absorption fine structure (XAFS) spectroscopy, X-ray photoelectron spectroscopy (XPS), ⁵⁷Fe Mössbauer spectroscopy, and magnetic measurements. The Cu K X-ray absorption near-edge structures (XANES) spectra resemble those of chalcopyrite, however, with a higher electron density at Cu⁺ centers and essentially differ from those of bornite Cu₅FeS₄; the Fe K-edge was less informative because of accompanying oxidized Fe-containing phases. The post-edge XANES and extended XAFS (EXAFS) analysis reveal differences in the bond lengths, e.g., additional metal-metal distances in valleriites as compared with chalcopyrite. The XPS spectra confirmed the Cu⁺ and Fe³⁺ state in the sulfide sheets and suggest that they are in electron equilibrium with (Mg, Al) hydroxide layers. Mössbauer spectra measured at room temperature comprise central doublets of paramagnetic Fe³⁺, which decreased at 78 K and almost disappeared at 4.2 K, producing a series of hyperfine Zeeman sextets due to internal magnetic fields arising in valleriites. Magnetic measurements do not reveal antiferromagnetic transitions known for bornite. The specific structure and properties of valleriite are discussed in particular as a platform for composites of the 2D transition metal sulfide and hydroxide (mono)layers stacked by the electrical charges, promising for a variety of applications.

Chalcopyrite-Derived NaxMO2 (M = Cu, Fe, Mn) Cathode: Tuning Impurities for Self-Doping

Discovering cathode materials composed of earth-abundant elements has become the current priority for developing sodium-ion batteries (SIBs) to meet the ever-increasing demand of large-scale energy storage. Herein, for the first time, layered Na_xMO₂ (M = Cu, Fe, Mn) cathodes are successfully prepared by directly using concentrated chalcopyrite ores as precursors. Greatly, impurity elements like Si and Ca are found to be crucial to tailoring the phase structure of as-obtained layered oxides as a P2 or O3 type, which removes the traditional concern that the impurities may restrict the utilization of natural ores. More interestingly, a certain amount of the Ca elements remaining in the Na sites through a self-doping process endows the P2-type products with enhanced structural stability. In half-cells, P2-type Na_xMO₂ with self-doped Ca elements shows superior rate capability and cycling stability (56 mAh g^-1 at 5 C and 90% capacity retention after 100 cycles at 1 C). In contrast, less impurity elements are favorable for O3-type oxides to achieve a high capacity of 107 mAh g^-1 at 0.1 C and 84% capacity retention after 200 cycles at 2 C. This new strategy would efficiently shorten the process for preparing electrode materials and open a feasible route to construct cheap and durable SIBs.

Self-Formed Channel Boosts Ultrafast Lithium Ion Storage in Fe3O4@Nitrogen-Doped Carbon Nanocapsule

Investigations into conversion-type materials such as transition-metal oxides have dominated in energy-storage systems, especially for lithium ion batteries in recent years. A common understanding of taking account of high energy density and high power density allows us to design reasonable electrodes. In this study, the unique Fe₃O₄@nitrogen-doped carbon (denoted as Fe₃O₄@NC) nanocapsule with self-formed channels was synthesized based on a facile hydrothermal-coating-annealing route. With respect to the effect of this rational architecture on lithium-storage performance, excellent behavior (a high reversible capacity of 480 mAh g^-1) could be maintained at 20 A g^-1 during 1000 cycles, with an average Coulombic efficiency of 99.97%. It also means that such a Fe₃O₄@NC electrode can meet a fast-charge challenge (end-of-charge within ∼2 min). By a series of investigations, we certainly considered that uniform carbon coating improved electrical conductivity and acted as a buffer layer to accommodate volume variations of Fe₃O₄ nanoparticles during cycling. It is more interesting that self-formed channels can effectively shorten the ion diffusion path and provide a necessary space to buffer volume expansion as well. Benefiting from these synergetic advantages, this Fe₃O₄@NC nanocapsule also delivered outstanding electrochemical performances in full cells.

The role of cupric ions in the oxidative dissolution process of marmatite: A dependence on Cu2+ concentration

Cupric ions (Cu²⁺) play an important role in the oxidative dissolution process of marmatite in an acidic environment. In this work, dissolution experiments and numerous analytical techniques were utilized to investigate the role of Cu²⁺ in the oxidative dissolution process of marmatite in sulfuric acid. The dissolution experiments showed that the role of Cu²⁺ is significantly dependent on its concentration. A low Cu²⁺ concentration (0.25-750 mg/L) can significantly accelerate marmatite dissolution, and a relatively high Cu²⁺ concentration (above 1000 mg/L) can hinder marmatite dissolution. Element analysis, synchrotron radiation-based X-ray diffraction (SR-XRD) and Raman spectra of the leaching residues proved that no copper containing mineralogical phase was produced by the reactions between Cu²⁺ and marmatite. The X-ray photoelectron spectroscopy (XPS) analysis indicated that Cu²⁺ was first adsorbed on the marmatite surface and then produced Cu-S surface species. An electrochemical measurement further indicated that the adsorption of Cu²⁺ can remarkably enhance the electrochemical reactivity of the marmatite surface, thus catalyzing the oxidative dissolution process. However, a high percentage of Cu²⁺ adsorption on the marmatite surface can produce a passivation layer when the Cu²⁺ concentration is high in the solution, which decreases the electrochemical reactivity, thus resulting in the hinderance of the oxidative dissolution process of marmatite.

Interactions between marmatite and bornite during the oxidative dissolution process in abiotic and biotic systems

Marmatite and bornite are commonly associated together in nature, and their interactions in an acidic environment are vital for both (bio)hydrometallurgy and acid mine drainage (AMD) production. In this work, dissolution experiments (marmatite : bornite = 2 : 0, 3 : 1, 1 : 1, 1 : 3 and 0 : 2) accompanied by analytic techniques such as electrochemical methods, Raman spectroscopy and synchrotron radiation-XRD (SR-XRD) were utilized to interpret the interactions between marmatite and bornite in acidic abiotic and biotic systems. The dissolution experiments showed that marmatite can significantly accelerate the oxidative dissolution of bornite, especially in the abiotic system. On the contrary, bornite inhibited the oxidative dissolution of marmatite when the percentage of bornite was high. Electrochemical measurements proved that the galvanic interactions between marmatite and bornite were slight and should not be the main cause for the interactions. Combined with the dissolution experiments, analytic techniques and previous references, it could be speculated that marmatite accelerated bornite dissolution mainly by providing an iron source, which acted as the energy source for microorganisms and oxidants. Bornite affected the dissolution of marmatite mainly by Cu²⁺ ions dissolving from bornite. Bornite inhibited the oxidative dissolution of marmatite mainly because a high Cu²⁺ concentration could significantly hinder marmatite dissolution. In addition, the formation of elemental sulfur or jarosite was also one important cause. Bornite intensified marmatite dissolution when the percentage of bornite or the Cu²⁺ concentration was extremely low and then, a synergic dissolution process occurred.

Interactions between marmatite and bornite during the oxidative dissolution process in abiotic and biotic systems.