Diffusion-controlled Process Research Articles

Alkaline pretreatment of a polymetallic sulfide (Fe-Pb-Mn) ore containing silver increases the efficiency of cyanidation by decreasing elemental sulfur content and by exposing sulfide surfaces

Polymetallic sulfide ores are often not amenable to cyanide leaching due to the presence of several elements and minerals capable of interfering with this process. Thus, various strategies, such as chemical pretreatments, are often studied to improve the efficiency of cyanidation. Beyond the results of such strategies, it is important to understand the changes occurring on the mineral samples during these pretreatments. Herein, an alkaline pretreatment was applied to a silver concentrate (∼8 kg Ag/t) composed of polymetallic sulfides (Fe-Pb-Mn), which increased the silver extraction during subsequent cyanidation from 40% to 80% and decreased the cyanide consumption in half (from approximately 60 to 30 kg NaCN/t). X-ray diffraction (XRD) and ICP-MS indicated that the pretreatment could remove significant amounts of elemental sulfur, which is a known cyanicidal agent. The dissolution of significant amounts of sulfur was confirmed by chemical analysis, which also demonstrated that the dissolution of iron, lead, manganese, and silver were negligible during pretreatment. At surface level, X-ray photoelectron spectroscopy (XPS) demonstrated that the pretreatment exposes fresh sulfide surfaces (e. g. pyrite). In addition, the XPS spectra indicated that the pretreatment facilitated the exposure of clean mineral surfaces. The presence of cleaner surfaces suggested a more uniform and less hindered diffusion of leaching agents through the mineral. Indeed, fitting the extraction data to the shrinking core model showed that pretreated samples featured a nearly ideal diffusion-controlled process, while in the case of untreated samples this fitting was less adequate. During cyanidation of both untreated and pretreated samples, lead build-up was detected on the surface (readsorption), which suggested that this phenomenon does not affect the efficiency of a leaching process. This study highlights the importance of combining bulk analytical methods with surface-sensitive techniques to obtain a more complete understanding of leaching processes.

Effective extraction of nickel and cobalt from sintered nickel alloy via reduction roasting and leaching

In this work, a carbothermic reduction technique is developed to improve the extraction of valuable metals from sintered nickel alloys by atmospheric acid leaching. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS) analyses indicate that NiO in the sintered nickel alloy and the NiO coated by Ni2O3 hinders further dissolution of nickel. Nickel oxides can be transformed into easily leached metallic nickel by carbothermic reduction. The reduction roasting was investigated and optimized by thermodynamic analysis, thermogravimetry-mass spectrometry, XRD, and response surface methodology (RSM). The results show that the leaching efficiencies of nickel and cobalt are respectively increased from 80.34% and 69.92% to 98.65% and 96.71% after the reduction roasting under the optimized conditions: 935 °C of temperature, 50 min of time, and 29.9% of carbon dosage. The leaching of nickel was optimized by single-factor test method and the optimum conditions have been established as: 150 g/L of H2SO4 concentration, 25% of H2O2 dosage, 10 mL/g of liquid–solid ratio, 400 rpm of stirring speed, 80 °C of temperature, and 80 min of time. The kinetic analysis of leaching process shows that the activation energies of nickel and cobalt leaching are 20.71 kJ/mol and 16.33 kJ/mol, respectively, indicating that the leaching process is an internal diffusion control process. This study provides a feasible and effective approach to extract nickel from sintered alloys.

Kinetics and Mechanism of Hydrogen Reduction of Lead-Silicate Slag

A systematic study on the microstructure evolution and kinetics analysis of PbO–SiO2 slag reduction using hydrogen was conducted. The reduction was carried out on PbO–SiO2 pellets (70 wt pct PbO–30 wt pct SiO2; or 38.6 mol pct PbO and 61.4 mol pct SiO2) using 15 pctH2/85 pctN2 gas, with a flowrate of 500mL/min for various reaction time (30 minutes to 3 hours) isothermally at 300 °C to 700 °C. The kinetics and reaction mechanism were assessed by measuring the weight loss over reaction time and applying kinetics models on the data; supported by detailed samples characterizations. The results from microstructure observation show a viscous and blackish glass structure formed on the pellets when the reduction was carried out above softening point (glass transition temperature). This viscous structure appeared to reduce the overall reduction rate. The kinetics analysis shows that the reduction appeared to be a diffusion-controlled process. The activation energy, Ea, was calculated to be 70.7 kJ/mol at temperature range of 300 °C to 500 °C; while between 500 °C and 700 °C the kinetics were found to decrease with increasing temperature due to the formation of the viscous glass. These results suggest that for a complete reduction in industrial process, the formation of the viscous glassy state should be avoided.

Two-step pyrolysis-hydrothermal synthesis of hierarchical nickel‑cobalt phosphate nanoflakes decorated on g-C3N4 nanosheets for high-performance hybrid supercapacitors

Ni-Co phosphate (NCP) nanoflakes and graphitic carbon nitride (g-CN) nanosheets are combined to fabricate a composite electrochemical electrode via a two-step pyrolysis-hydrothermal process. Physicochemical characterizations reveal the proper formation of the target material with highly porous morphology and crumpled nanostructures with highly active surface sites. The electrochemical properties of the NCP/g-CN composite in a three-electrode system depict excellent pseudocapacitive performance due to the faradaic behavior and redox activities of both NCP and g-CN with a very high capacitive value of 2000 F/g (242 mAh/g) @ 1 A/g current density. The charge storage behavior is mainly dominated by the surface-controlled (capacitive) process at higher scan rates, which is mostly dominated by surface pseudocapacitance, whereas, at low scan rates both surface-controlled and diffusion-controlled processes are equally active to provide a combined battery-capacitor behavior. Due to this, a hybrid supercapacitor device, fabricated with NCP/g-CN as positive and activated carbon (AC) as a negative electrode, showed excellent energy density (50 Wh/kg) along with exceptional cyclability (∼90 % capacity retention over 5000 cycles). Additionally, the redox-rich g-CN matrix within the composite dominates the sluggish diffusion-controlled process at higher scan rates to enhance the capacitive process without compromising the charge storage kinetics, thus enhancing the power density to ∼7.0 kW/kg. This excellent energy-power performance of the NCP/g-CN//AC hybrid supercapacitor cell (HSC) is better than some of the commercial devices like lead-acid, Ni-Cd, and Ni-MH batteries, indicating potential applications in next-generation charge storage devices.

Surface-modified graphene oxide-based composites for advanced sequestration of basic blue 41 from aqueous solution

Advanced materials for the efficient treatment of textile wastewater need to be developed for the sustainable growth of the textile industry. In this study, graphene oxide (GO) was modified by the incorporation of natural clay (bentonite) and mixed metal oxide (copper-cobalt oxide) to produce GO-based binary and ternary composites. Two binary composites, GO/bentonite and GO/Cu–Co Ox (oxide), and one ternary composite, GO/bentonite/Cu–Co Ox, were characterized by Fourier transform-infrared spectroscopy (FTIR), scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and Brunauer-Emmett-Teller (BET) analysis. The adsorption efficiency of these composites was evaluated against a cationic dye, Basic Blue 41 (BB41). The composites had several surface functional groups, and the ternary composite had tubular porous structures formed by the cross-linking of the bentonite and GO planes. The BET surface area of the ternary composite was 50% higher than that of the GO. The BB41 removals were 92, 89, 80, and 69% for GO/bentonite/Cu–Co oxide, GO/bentonite, GO and GO/Cu–Co oxide, respectively. The pseudo-2nd-order and intraparticle diffusion models best describe the kinetics results, indicating chemisorption and slow pore diffusion-controlled adsorption processes. The Langmuir isotherm-derived adsorption capacity of GO/bentonite/Cu–Co oxide was 351.1 mg/g, which was very close to the measured value. After five consecutive cycles, the ternary composite retained 90% BB41 removal efficiency compared to its 1st cycle. Electrostatic interaction and pore diffusion were predicted to be the controlling mechanisms for the adsorption of the BB41. The GO-based ternary composite can be a feasible and scalable adsorbent for BB41 in wastewater treatment.

Pore-scale modeling of thermal-hydro-mechanical-chemical coupled rock dissolution and fracturing process

Acid fracturing can effectively improve the connectivity inside underground reservoirs, which is of significance for geothermal exploitation and geological carbon sequestration. It involves a complex thermal-hydro-mechanical-chemical (THMC) coupled process. This work first develops a pore-scale THMC coupled model combining the lattice Boltzmann method (LBM) and the discrete element method (DEM) to describe the acid fracturing process, particularly covering chemical damage, rock dissolution, and solute transport. A chemical damage variable based on the cohesive bond is proposed to characterize the alteration of mechanical parameters caused by local rock dissolution. The change of fluid pathway due to rock dissolution is handled by the lattice Boltzmann solute transport model combined with the volume of pixel method. Based on the proposed model, the influence of injection pressure and Damkohler number (Da) on the THMC coupled rock dissolution and fracturing process is analyzed. Results indicate three types according to dissolution morphologies, i.e., permeation, cavity, and permeation-cavity. The first and second types are related to the reaction-controlled and diffusion-controlled processes, respectively. Particularly, the permeation-cavity type occurs at conditions with high injection pressure and high Da and is the combination of the first two types, where the dissolution around the main fracture presents the cavity type but converts into the permeation type around secondary fractures. Additionally, the evolution patterns of reactive surface area and dissolution rate with time differ significantly with rock dissolution types. In particular, for the permeation type, the aperture of fracture far away from the injection hole could be larger than that near the injection hole under the THMC coupling, which is quite different from HM and THM coupling.

Simulation of reaction initiation in powder compacting from the surface with composite formation in equivalent reaction cell

In the present work, we propose a new variant of the model of the composite synthesis under surface heating. We believe that the formation of the composition occurs at the level of reaction cell. The diffusion-controlled process of reduction of one material by another from an oxide is described in the framework of the problem with moving boundaries. It is assumed that the formation of the matrix composition is carried out by the diffusion mechanism. From the position of interfaces, we find the relative volume fractions of oxide phases and the fraction of volume occupied by the matrix. The averaging method of the analysis results at the reaction cell level makes it possible to use these data at the macroscopic level. Volume fractions of phases and average matrix composition (obtained by averaging over the area occupied by the matrix) provide values reflecting the composition of the composite at the macro level. The problem is solved numerically in dimensionless formulation. Dimensionless complexes of physical quantities are distinguished. The estimation of these parameters is performed. The conditions of correctness of the proposed approach are established from comparison of temporal and spatial scales of thermal and diffusion phenomena. A numerical algorithm for the joint solution of macro- and mesolevel problems has been developed. The proposed algorithm makes possible the investigation of the dynamics of composition changes at all points. The model is supplemented by the calculation of stresses and strains from the data on composition and temperature changes in reaction cells. Averaged values of stresses are transferred to macro level.

Electrochemical Determination of Paraquat Using Ordered Mesoporous Carbon (CMK-3) Modified Glassy Carbon Electrode

Ordered mesoporous carbon namely, CMK-3 was synthesized by nano casting method, and characterized using various physicochemical and electroanalytical tools like HESEM, HRTEM, BET, etc. Using Cyclic voltammetric (CV) measurements on CMK-3 modified glassy carbon electrode (CMK-3/GCE) in the standard redox couple, [Fe(CN)6]3−/4−, the electrochemical surface area was deduced as 0.081 cm2. The modified electrode was used as an electrocatalyst for the determination of one of the herbicides, paraquat (PQ). The modified electrode shows enhanced sensitivity for the determination of PQ in phosphate buffer solution at pH 9.2 as compared to bare GCE. The concentration dependant CV studies showed a linear variation in sensitivity in the concentration range of 60 μM to 450 μM. The effect of the scan rate shows a linear variation in sensitivity as a function of the square root of scan rate suggesting a diffusion-controlled process during the detection of PQ. Anodic stripping square wave voltammetry (ASSWV) reveals the sensitivity and limit of detection as 9.51 μA μM−1 and 64 nM, respectively. The interfering ability of the other foreign molecules like metal ions, environmental samples, biomolecules, and pesticides was analyzed using CMK-3/GCE. The results revealed that the electrode is able to sense paraquat, with the retention in sensitivity ranges between 91% and 102%. The real-time applicability of the electrode was examined using vegetable and fruit extracts. The analysis revealed that the recovery values were between 102 % – 105 %.

Battery-Type Behavior of Al-Doped CuO Nanoflakes to Fabricate a High-Performance Hybrid Supercapacitor Device for Superior Energy Storage Applications

The ever-increasing energy demands have prompted researchers to develop innovative charge-storage devices. Here, aluminum-doped copper-oxide nanoflakes were fabricated via a simple co-precipitation method to investigate the electrochemical properties, which depicted a novel dominant battery-type charge-storage mechanism, manifested by the porous morphology of the electrodes to enhance the diffusion-controlled process. Copper oxide was chosen as the electroactive material due to its low cost, easy processability, environmental friendliness, and multiple oxidation states, all of which are very important for practical applicability in charge-storage devices. Additionally, aluminum was chosen as a dopant due to its elemental abundance, non-toxicity, and energetically favorable ionic radius for substitutional doping. A maximum 272 C/g (@1 A/g current-density) specific capacity was observed for 5 wt% Al-doped CuO. Evidently, higher Al-doping provided increased defects and doping sites to enhance the redox activity in order to improve the supercapacitive performance. A combinatorial battery−capacitor charge-storage mechanism was proposed in terms of the accumulation and intercalation of charges at the inner electroactive sites of the nanoflakes through a large number of voids and cavities in order to contribute towards dominant battery-type diffusion capacitance, while optimum Al-doping created considerable redox-active sites to promote surface-controlled pseudocapacitance. The optimized Al-CuO electrode revealed extraordinary long-term cycling stability with 99% capacity retention over 5000 charge/discharge cycles. A hybrid two-electrode device, made up of a battery type Al-CuO positrode and capacitor-type activated-carbon negatrode, demonstrated a remarkable energy-power performance with a maximum energy density of 30 Wh/kg and a maximum power density of 7.25 kW/kg, with an excellent cycle life (98% capacity retention over 5000 cycles). This work demonstrates a novel strategy to fabricate high-performance hybrid supercapacitors for the next generation charge-storage devices.

Kinetic study of hybrid supercapacitor using transition metal quantum dots @ graphenes composite as a model electrode

In this study, a series of materials with electric double-layer capacitance (EDLC) and pseudocapacitance (PC) have been prepared by adjusting the functional groups and anchoring transition metal quantum dots (TMQDs) on the surface of reduced graphene oxide (rGO) by chemical bonds. The nano-sized TMQDs interlayered in rGOs can contribute a large portion of PC, meanwhile rGOs supply the EDLC to the hybrid supercapacitor. Electrochemical testing results demonstrated that the Fe/Co/Ni TMQDs anchored the rGO (Fe/Co/Ni-TMQD@rGO) exhibited the improved capacitive and rate performances. To elucidate the reaction kinetics of the electrodes, the capacitance contributions of diffusion-controlled processes (DCPs) and surface-controlled processes (SCPs) were separated by the theoretical calculation. It was found that the capacitance contributed by the DCPs is closely related with the number of the valence electrons of the iron group transition metal elements (ITMEs). The ITMEs with more valence electrons exhibited the higher DCPs contribution to the capacitance of the composite. Further, the quantum chemical calculation results suggested that OH– adsorption energy is deeply related to the contribution proportion of SCP to the total capacitance. The discovered mechanism supplies a guidance to the design and development of novel composite electrode materials for hybrid supercapacitors.

Interface dissolution kinetics and porosity formation of calcite and dolomite (1 1 0) and (1 0 4) planes: An implication to the stability of geologic carbon sequestration

Geologic carbon sequestration (GCS) via injecting CO2 into deep carbonate reservoirs (mainly calcite and dolomite) is a promising strategy to reduce CO2 level. However, the dissolution or precipitation of calcite/dolomite planes on minerals/solution interface during long-term GCS process develops intergranular porosity and thus affects the permeability and stability of reservoirs. To investigate this process, both calcite and dolomite were dissolved in acetic and carbonic acids. A diffusion-controlled process was identified, with greater diffusion rates in acetic acid than that in carbonic acid. Quantified planes activity of both minerals follows (110) > (116) > (101) > (113) > (018) > (104) through density functional theory. Accomplished with preferential dissolution of calcite (110) planes in carbonic acid, calcite crystals precipitated with (104) planes at 423.15 K, under which, more calcite crystals were observed on dolomite surface, producing Ca-deplete surface. Molecular dynamic calculations showed higher dissolution rates of calcite/dolomite (110) planes than (104). In addition, the dissolution coefficients of Ca2+ were approximately triple of that Mg2+. Therefore, this study reveals the interface dissolution mechanisms of calcite and dolomite, especially on (110) and (104) planes at an atomic level, for the first time, providing better understanding for the stability of long-term GCS process.

Decoration of Bi2O3NPs-AgNPs-ErGO as a first electrochemical nanosensor for sensitive determination of nelarabine in pharmaceutical dosage form and human serum samples

In view of the unquestionable necessity for rapid and accurate analysis of drug molecules to monitor patient overdose, numerous nanosensor-based technologies have been developed in addition to quality control of pharmaceutical manufacture and drug administration. In this regard, sensitive detection of a potent anticancer agent, nelarabine (NEL) was examined at the bare and modified glassy carbon electrode (GCE) with the help of differential pulse (DP) and cyclic voltammetry (CV) techniques. A unique and highly effective nanosensor was developed using a combination of bismuth (III) oxide nanoparticles (Bi2O3NPs), silver nanoparticles (AgNPs), and electrochemically reduced graphene oxide (ErGO) onto the GCE surface. The modified Bi2O3NPs-AgNPs-ErGO/GCE was characterized by scanning electron microscopy (SEM), CV, and electrochemical impedance spectroscopy (EIS) investigations. Influences of various parameters viz., loading of Bi2O3NPs, AgNPs, and GO on the modified GCE, electrolyte pH (PBS 7.0), accumulation potential (–0.2 V), and time (60 s), and scan rate (50 mV s−1) were optimized for NEL response. An enhancement in the current responses toward the oxidation of NEL was observed with the Bi2O3NPs-AgNPs-ErGO/GCE compared to that noticed with bare GCE. The modified GCE affirmed high sensitivity, low limit of detection (LOD), excellent reproducibility, repeatability, and storage stability that clearly indicated the effective accuracy of the developed nanosensor. The linear behavior in the concentration range was found to be 0.02–1.0 µM, with LOD values of 0.003 nM in PBS 7.0 and 0.065 nM in serum samples. The electrochemical mechanism of NEL at the bare and modified GCEs were revealed as diffusion-controlled and adsorption-controlled mechanism processes, respectively. The linear calibration curves at both the bare and modified GCEs were noticed for increasing NEL concentrations, as constructed from the DPV measurements. Applications of the Bi2O3NPs-AgNPs-ErGO/GCE for NEL detection in pharmaceutical dosage form and human serum sample showed well-accepted recovery results of 98–99 %. The effect of interfering agents was checked on the selectivity of the developed method, and the modified electrode was found to be selective toward NEL in the presence of these interfering agents.

Cu-MOF/Pd derived oxide nanoparticles based carbon composite - An innovative electrochemical sensing platform for Bisphenol A

Bisphenol A (BPA), an endocrine disrupting chemical, had been used worldwide as a raw material in water bottles and food packages. It leaches into food products and water sources and hence, it should be monitored effectively. Herein, an electrochemical sensing platform based on Cu-MOF@Pd-500 modified glassy carbon (GC) electrode was fabricated for the sensing of BPA. The material was synthesized by a simple solvothermal method, carbonized at 500 ⁰C, and characterized by various surface analytical techniques. Cyclic voltammetric (CV) analysis reveals that the Cu-MOF@Pd-500 modified GCE exhibits 1.5 folds hike in peak current and a considerable shift in peak potential towards the anodic side when compared to Cu-MOF@ 500, suggesting the higher electrocatalytic activity of the former than that of the later. The electrochemical oxidation of BPA provides an irreversible diffusion-controlled process involving two electrons and two protons. Differential pulse voltammetric (DPV) analysis reveals that the constructed sensor material provides a linear response over BPA concentration of 1 − 150 µM with a low detection limit (LOD) of 0.06 µM, (S/N = 3) and amperometric studies deliver a linear range of 1–22 µM with a LOD of 0.025 µM in 0.1 M PBS at a pH 7.0. Additionally, the Cu-MOF@Pd-500 delivers good repeatability, stability, and anti-interference capabilities. The results obtained also support the effectiveness of Cu-MOF@Pd-500 for quantifying and identifying BPA in real sample analysis (plastic water bottles) with an average recovery of the ratio of 101.93 having a relative standard deviation (RSD) of 0.42%.

Zn (II) AND Pb (II) ADSORPTION ON TO AGRICULTURAL SOILS FROM EAST OF ALGERIA

Soil properties have an important role in the movement of minerals in the environment. Therefore, the study of mineral adsorption and soil properties can help solve environmental pollution problems. In the present work, batch adsorption of zinc and lead was studied on some Algerian soils (clay soil, sandy loam soil, and sandy soil), as a function of contact time, pH, metal concentration and physicochemical properties. The results showed the metal adsorption amount depends on soil pH and initial ion concentration, soil type, temperature, exchange capacity, and metal hydrolysis. Ionic strength and organic matter content investigation indicate that, clay soil presents greater adsorption of both metals than the two other soils. The metal ions’ adsorption decreases with decreasing pH and increasing ionic strength. The results showed that the adsorption amount of lead is better than that of zinc in all studied samples. The equilibrium data good fit well with Langmuir and Freundlich’s models. The tested kinetic models showed that soil adsorption of these metals are biphasic and diffusion-controlled process. For all pH values, the adsorption was relatively fast at the beginning followed by a slower phase at reaching the equilibrium time.

Fe-N/C anode with pseudocapacitive behavior derived from Fe-modified ZIF-8/C composites for phosphorus capture

Capacitive deionization (CDI) is a promising phosphorus (P) electrosorption technology with no secondary pollution, cost-effectiveness, energy efficiency, and easy regeneration. In this study, Fe-N/C composites have been successfully synthesized for phosphorus capture. The optimal Fe-N/C-1000 electrode presented higher electrosorption performance and low energy consumption (3.823 kWh/kg (1.447 ×10−2 kWh/m3)) for 5 mg P/L solution than Fe-N/C-900 and Fe-N/C-800 at 1.2 V, which was owed to its superior conductive network, high specific surface area, and abundant Fe-Nx sites. The diffusion-controlled process (pseudocapacitive) contributed more significantly to the electrosorption of Fe-N/C-1000 than the capacitance-controlled process. The effects of key operational factors on phosphorus uptake in the CDI process, and the corresponding kinetics and Ragone plot were also discussed in detail. The phosphorus capture mechanism was fully explicated by discussing the characterization data and experimental results. This study may provide new insight for further applications of low-cost Fe-N/C in CDI processes.

Core-Shell Structured Carbon Nanofiber-Based Electrodes for High-Performance Supercapacitors.

The combination of multiple electrode materials and their reasonable structural design are conducive to the preparation of composite electrodes with excellent performance. In this study, based on carbon nanofibers grown with Ni(OH)2 and NiO (CHO) prepared by electrospinning, hydrothermal growth, and low-temperature carbonization, five transition metal sulfides (MnS, CoS, FeS, CuS, and NiS) were hydrothermally grown on their surfaces, exhibiting that CHO/NiS had the optimal electrochemical properties. Subsequently, the effect of hydrothermal growth time on CHO/NiS revealed that the electrochemical performance of CHO/NiS-3h was optimal, with a specific capacitance of up to 1717 F g-1 (1 A g-1), due to its multistage core-shell structure. Moreover, the diffusion-controlled process of CHO/NiS-3h dominated its charge energy storage mechanism. Finally, the asymmetric supercapacitor assembled with CHO/NiS-3h as the positive electrode demonstrated an energy density of 27.76 Wh kg-1 at a maximum power density of 4000 W kg-1, and it still maintained a power density of 800 W kg-1 at a maximum energy density of 37.97 Wh kg-1, exhibiting the potential application of multistage core-shell composite materials in high-performance supercapacitors.

Spherical PDA@MnO2 cathode for rechargeable aqueous zinc ion batteries

The PDA@MnO2 with unique structure was prepared by reacting KMnO4 with spherical PDA, and used as the cathode material of aqueous zinc ion batteries. Electrochemical test results show that, the spherical PDA@MnO2 had an initial discharge capacity of 378.4 mAh g−1 at a current density of 0.2 A g−1, indicating the superior performance compared to that of irregular PDA@MnO2. The spherical structure is beneficial to improve the electrochemical performance of the diffusion control process and achieve the purpose of improving the utilization rate and mass specific capacity of irregular PDA@MnO2. This excellent performance and novel structure demonstrate that spherical PDA@MnO2 can find a wide range of applications in energy storage.

Insights into Perovskite Film Formation Using the Hybrid Evaporation/Spin-Coating Route: An In Situ XRD Study

The hybrid evaporation/spin-coating route has been widely used for fabrication of highly efficient fully textured perovskite silicon tandem solar cells and is a promising route for upscaling. Nevertheless, fundamental aspects of the fabrication process such as the kinetics of perovskite crystallization and the influence of the environmental conditions remain uncertain. In this work, we investigate the individual stages of tandem-relevant 1.66 eV bandgap perovskite formation and map the structural evolution from the precursor to the perovskite phase until the degradation phase. We find that the kinetics of these transitions can be tuned by varying the humidity or the temperature during the annealing treatment. Specifically, increasing the relative humidity up to 50% elevates the reaction rate and results in improved perovskite quality. This is directly reflected in the solar cell power conversion efficiency with a 3%abs increment on average. While high annealing temperatures are found to promote large grain size growth and enhanced crystallinity, we observe that above 150 °C the remnant PbI2 precursor compromises film quality. Furthermore, the perovskite formation kinetics is fitted using the Johnson–Mehl–Avrami–Kolmogorov model. The Avrami constant is found in the range 0.66–0.87, indicating a diffusion-controlled one-dimensional growth process with an associated activation energy of 54.49 kJ/mol. Using in situ XRD, this work gives insights on key process parameters to ensure reproducible synthesis of high-quality perovskite films.

Synthesis of Low-Crystalline MnO2/MXene Composites for Capacitive Deionization with Efficient Desalination Capacity

MXene has drawn widespread attention as a potential material for electrode use in capacitive deionization (CDI). However, the applications of MXene are limited by its property of low electrical capacity. Herein, a MnO2/MXene composite was firstly evaluated in a capacitive deionization system, in which the MnO2 acts as intercalation-type pseudocapacitive electrodes to enhance the electrical capacity, and MXene provides an electron conduction highway network that improves the charge transfer of the MnO2. The result showed that the low-crystallinity MnO2 with irregular particles was well-distributed on the surface of the MXene. The desalination capacity of 30.5 mg·g−1 is achieved at a voltage window of 1.2 V, which was higher than that of the reported pure MXene and MnO2. The electrical double-layer (EDL) capacitive and the diffusion-controlled processes are the main charge storage mechanisms, and the EDL contribution provides 50.3% to the total capacitance. This result suggests a promising direction for further applying a MnO2/MXene composite in CDI.

Electrochemical Behavior and Electrical Stability of a Needle-Shaped Zinc Metal-Organic Framework Modified Graphite Electrode

In this paper, a novel needle-shaped Zinc organic framework was formed on the surface of a functionalized graphite electrode (Zn-MOF/CE) to create a methodical alternative electrode. The characterization of the Zn-MOF modifier was investigated via XRD, FT-IR, FESEM-EDS mapping, and N2 sorption. The redox behavior of the modified electrode was examined, showing high stability and conductivity under a diffusion-controlled process as a desirable working electrode. Also, the redox process of hydroquinone, as an organic molecule model, at the surface of the modified electrode was investigated and its operation was optimized and modeled by the central composite design (CCD) method. Based on the obtained results and CCD model, the process exhibited the best performance in scan rate 560 mV/s, pH= 9.9. Moreover, the frequency domain using bode plots, and two identical electrical models were evaluated by CCD results that could be employed in stability and electrode material performance prediction.