Precursor Ratio Research Articles

Optimized heterostructure of FeS/Ni3S2 enabling robust oxygen evolution reaction for Zn-Air batteries

Construction heterointerfaces of transition metal sulfides is an effective strategy to enhance the catalytic activity of oxygen evolution reaction (OER) by modulating their electronic structures. Further, incorporating these sulfides with a carbon-based support can improve their catalytic stability by preventing metal active site demetallization and dissolution. Herein, we utilized a combined hard template-pyrolysis method to construct heterostructure of FeS and Ni3S2 encapsulated in N-doped carbon (FeS/Ni3S2-x/NC) and optimized the heterostructure by adjusting the Fe and Ni precursor ratio. Largely exposed FeS/Ni3S2 heterointerfaces enabled a high OER catalytic activity. Especially, the optimized heterostructure of FeS/Ni3S2-2/NC with a larger electrochemical active area and more activity sites (Ni3+) afforded a small OER overpotential of 270 mV at 10 mA cm−2, and exhibited a negligible voltage loss for 35-hour operation at 10 mA cm−2. Furthermore, FeS/Ni3S2-2/NC was employed in rechargeable zinc-air batteries as the air cathode, displaying a superior charge performance and operational stability over 300 h at 5 mA cm−2. This work provides a promising design and engineering strategy for transition metal sulfides as effective OER catalysts.

Engineering the Surface Chemistry and Morphology of Polymeric Carbon Nitrides Towards Greener Heterogeneous Catalysts for Biodiesel Synthesis.

Biodiesel remains one of the most promising alternatives to replace fossil fuel-derived petrodiesel. Nonetheless, conventional biodiesel synthesis relies on homogeneous alkali-based catalysts that involve long and tedious purification steps , increasing biodiesel production costs. Heterogeneous catalysts have emerged as promising alternatives to circumvent these drawbacks, as they can easily be recovered and reused. Herein, polymeric carbon nitride dots and nanosheets are synthesized through a solid-phase reaction between urea and sodium citrate. Their morphology and surface chemistry are tuned by varying the precursor's ratio, and the materials are investigated as catalysts in the transesterification reaction of canola oil to biodiesel. A conversion of > 98% is achieved using a 5 wt% catalyst loading, oil to methanol ratio of 1:36 at 90 °C for 4 h, with the performance maintained over at least five reuse cycles. In addition, the effect of the transesterification reaction parameters on the reaction kinetics is evaluated, which follows a pseudo-first-order (PFO) regime. Combined with a deep understanding of the catalyst's surface, these results have allowed us to propose a reaction mechanism similar to the one observed for homogenous alkali catalysts. These carbon nitride-based nanoparticles offer a metal-free and cost-effective alternative to conventional homogeneous and metal-based heterogeneous catalysts.

Lead-Free, Luminescent Perovskite Nanocrystals Obtained through Ambient Condition Synthesis.

Heterovalently substituting toxic lead is an increasingly popular design strategy to obtain environmentally sustainable variants of the exciting material class of halide perovskites. Perovskite nanocrystals (NCs) obtained through solution-based methods exhibit exceedingly high optical quality. Unfortunately, most of these synthesis routes still require reaction under inert gas and at very high temperatures. Herein a novel synthesis routine for lead-free double perovskite (LFDP) NCs is presented. An approach based upon the hot injection and ligand-assisted reprecipitation (LARP) methods to achieve a low-temperature and ambient atmosphere-based synthesis for manganese-doped Cs2 NaBiCl6 NCs is presented. Mn incorporation is critical for the otherwise non-emissive material, with a 9:1 Bi:Mn precursor ratio maximizing the bright orange photoluminescence (PL) and quantum yield (QY). Higher synthesis temperatures slightly increase the material's performance, yet NCs synthesized at room temperature are still emissive, highlighting the versatility of the synthetic approach. While the material's indirect bandgap limits its appeal for optoelectronics, this feature could benefit photocatalysis due to longer carrier lifetimes. Moreover, the developed synthesis is facile and can rapidly be adapted to other more viable material compositions and up-scaled to realize applications directly.

Highly Reproducible Epitaxial Growth of Wafer-Scale Single-Crystal Monolayer MoS2 on Sapphire.

2D semiconducting transition-metal dichalcogenides (TMDs) have attracted considerable attention as channel materials for next-generation transistors. To meet the industry needs, large-scale production of single-crystal monolayer TMDs in highly reproducible and energy-efficient manner is critically significant. Herein, it is reported that the high-reproducible, high-efficient epitaxial growth of wafer-scale monolayer MoS2 single crystals on the industry-compatible sapphire substrates, by virtue of a deliberately designed "face-to-face" metal-foil-based precursor supply route, carbon-cloth-filter based precursor concentration decay strategy, and the precise optimization of the chalcogenides and metal precursor ratio (i.e., S/Mo ratio). This unique growth design can concurrently guarantee the uniform release, short-distance transport, and moderate deposition of metal precursor on a wafer-scale substrate, affording high-efficient and high-reproducible growth of wafer-scale single crystals (over twoinches, six times faster than usual). Moreover, the S/Mo precursor ratio is found as a key factor for the epitaxial growth of MoS2 single crystals with rather high crystal quality, as convinced by the relatively high electronic performances of related devices. This work demonstrates a reliable route for the batch production of wafer-scale single-crystal 2D materials, thus propelling their practical applications in highly integrated high-performance nanoelectronics and optoelectronics.

Facile fabrication of carbon aerogel by cellulose extracted from tea grounds and carboxymethyl cellulose for adsorption and energy storage applications

Carbon aerogel (CA) was synthesized from cellulose-extracted tea grounds with carboxymethyl cellulose as the crosslinking agent and facilitated by pyrolysis. The analytical results indicated a high porosity of more than 75% and ultra-low density of the CA. Besides, the material also possessed a corrugated surface with the presence of numerous pores due to the random distribution of carbon sheets. Additionally, the CA2 material corresponding to the precursor ratio of 1:10 was selected as the most appropriate sample with the highest ciprofloxacin adsorption capacity and energy storage performance of 60.47 mg/g and 155.20F/g, respectively.

Bonding effect of a Zr/Si coating prepared on zirconia using a sol-gel method

Statement of problemZirconia has been widely used as a dental prosthetic material. However, bonding to zirconia is challenging, and whether a Zr/Si coating would improve bonding is unclear. PurposeThe purpose of this in vitro study was to prepare a Zr/Si coating on zirconia ceramics using a sol-gel method and to determine whether the bonding to resin is improved. Material and methodsPresintered zirconia specimens were prepared and divided into 5 groups: 4 experimental groups with ratios of the binary sol-gel precursor (zirconium oxychloride/tetraethoxysilane) set as 2:1 (Z2), 1:1 (Z1), 0.5:1 (Z0.5), and 0.25:1 (Z0.25) and Group C as the control group. In addition to surface roughness measurements, scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), and X-ray diffraction (XRD) were carried out to characterize the surface. Each group was divided into 2 subgroups according to whether a silane coupling agent was applied. Half of the bond specimens were stored in deionized water for 24 hours; the remaining half were aged using 5000 thermocycles. The shear bond strength (SBS) of resin bonded to specimens was tested for the initial and durable bond strength, and the bonding interface was also observed by SEM after debonding. Data were subjected to 1-way ANOVA and the post hoc Tukey honestly significant difference test (α=.05). ResultsThe Zr/Si coating formed on zirconia ceramics. Z0.5 had the greatest mean ±standard deviation roughness (2.13 ±0.15 μm) and had the highest silicon content (21.7 ±0.21%). t-ZrO2, m-ZrO2, c-SiO2, and ZrSiO4 were detected by XRD in Z1. The SBS values were decreased by aging but were significantly increased by Zr/Si coating, especially for Z0.5, with the application of silane (initial: 22.92 ±2.79 MPa; aged: 9.91 ±0.92 MPa). ConclusionsThe Zr/Si coating significantly improved the initial and aged bond strength, and the optimal Zr/Si ratio of the sol-gel appeared to be 0.5:1.

Preparation of superhydrophobic surface from raspberry like particles of bifunctional polyssesquioxane

AbstractIn this article, we selected MTMS and ETMS as mixed precursors to generate polysiloxane particles on the surface of styrene copolymer microspheres, forming raspberry‐like particles. The best experimental formula was obtained by orthogonal test. When the ratio of MTMS and ETMS was 3:1, the hydrophobic properties of composite particles reached the best, with a water contact angle (WCA) of 163° and a WSA of 3°. The hydrophobic models of raspberry particles were established. And the influence of gas–liquid contact components, surface roughness and precursor ratio on hydrophobic properties was clarified by theoretical calculation, Fourier transform infrared and X‐ray diffraction analysis. The prepared superhydrophobic surface shows great application potential in self‐cleaning, antifouling and other fields.

Chitosan reduced in-situ synthesis of gold nanoparticles on paper towards fabricating highly sensitive, stable uniform SERS substrates for sensing applications

Surface-Enhanced Raman Spectroscopy (SERS) is a powerful surface-sensitive technique for molecular analysis. Its use is limited due to high cost, non-flexible rigid substrates such as silicon, alumina or glass and less reproducibility due to non-uniform surface. Recently, paper-based SERS substrates, a low-cost and highly flexible alternative, received significant attention. We report here a rapid, inexpensive method for chitosan-reduced, in-situ synthesis of gold nanoparticles (GNPs) on paper devices towards direct utilization as SERS substrates. GNPs have been prepared by reducing chloroauric acid with chitosan as a reducing and capping reagent on the cellulose-based paper surface at 100 °C, under the saturated humidity condition (100 % humidity). GNPs thus obtained were uniformly distributed on the surface and had fairly uniform particle size with a diameter of 10 ± 2 nm. Substrate coverage of resulting GNPs directly depended on the precursor's ratio, temperature and reaction time. Techniques such as TEM, SEM, and FE-SEM were utilized to determine the shape, size, and distribution of GNPs on paper substrate. SERS substrate produced by this simple, rapid, reproducible and robust method of chitosan-reduced, in situ synthesis of GNPs, showed exceptional performance and long-term stability, with a detection limit of up to 1 pM concentration of test analyte, R6G. Present paper-based SERS substrates are cost-effective, reproducible, flexible, and suitable for field applications.

3D lamellar skeletal network of porous carbon derived from hull of water chestnut with excellent microwave absorption properties

Biomass derived carbon has attracted extensive attention in the field of microwave absorption because of its sustainability and porous structure beneficial to microwave attenuation. In this study, 3D lamellar skeletal network porous carbon was successfully obtained from hull of water chestnut using biomass waste as raw material by controlling the ratio of KOH and precursors in a one-step carbonization process. The optimization of biomass carbon morphology was achieved and its microwave absorption properties were investigated. At the temperature of 600 °C, when the ratio of hull of water chestnut to KOH is 1:1, the porous carbon material with filling ratio of 35% can reach the effective absorption bandwidth (RL < −10 dB) of 6.0 GHz (12–18 GHz) at the matching thickness of 1.90 mm, covering the whole Ku band. When the thickness is 2.97 mm, the optimal reflection loss reaches −60.76 dB. The surface defects, interface polarization and dipole polarization of 3D porous skeleton network structure derived from hull of water chestnut contribute to the excellent reflection loss and bandwidth of porous carbon materials. The porous carbon with low density, low cost and simple preparation method has broad application prospects in the preparation of biomass-derived microwave absorbers.

Rapid Data-Efficient Optimization of Perovskite Nanocrystal Syntheses through Machine Learning Algorithm Fusion.

With the demand for renewable energy and efficient devices rapidly increasing, a need arises to find and optimize novel (nano)materials. With sheer limitless possibilities for material combinations and synthetic procedures, obtaining novel, highly functional materials has been a tedious trial and error process. Recently, machine learning has emerged as a powerful tool to help optimize syntheses; however, most approaches require a substantial amount of input data, limiting their pertinence. Here, three well-known machine-learning models are merged with Bayesian optimization into one to optimize the synthesis of CsPbBr3 nanoplatelets with limited data demand. The algorithm can accurately predict the photoluminescence emission maxima of nanoplatelet dispersions using only the three precursor ratios as input parameters. This allows us to fabricate previously unobtainable seven and eight monolayer-thick nanoplatelets. Moreover, the algorithm dramatically improves the homogeneity of 2-6-monolayer-thick nanoplatelet dispersions, as evidenced by narrower and more symmetric photoluminescence spectra. Decisively, only 200 total syntheses are required to achieve this vast improvement, highlighting how rapidly material properties can be optimized. The algorithm is highly versatile and can incorporate additional synthetic parameters. Accordingly, it is readily applicable to other less-explored nanocrystal syntheses and can help rapidly identify and improve exciting compositions' quality.

Optimization of alkali-activated binders using natural minerals and industrial waste materials as precursor materials

This paper presents the results of a study on developing optimized alkali-activated binders (AABs) utilizing selected natural minerals and industrial byproducts as precursor materials in addition to sodium hydroxide and sodium silicate as activators. Four selected precursor materials (natural pozzolana, limestone powder, red mud, and silicomanganese fume) were characterized in terms of their physical and chemical properties. The proportioning of the four precursor materials was optimized based on the results of flow, setting time, and compressive strength tests conducted on trial mortars. After reaching an optimal proportioning of the four precursor materials, the natural pozzolan was partially replaced by ordinary Portland cement (maximum 30% by wt.) to significantly enhance the properties of the AABs. The activator to precursor (A/P) ratio, sodium silicate to sodium hydroxide (NS/NH) ratio, sodium hydroxide (NH) molarity, and water to precursor (W/P) ratio, were varied from 0.3 to 0.6, 1 to 2.5, 8 to14 M, and 0.35 to 0.55, respectively. The influence of these activation parameters (at the optimally selected proportioning of precursor materials) on the physical and mechanical properties of AABs besides their mineral composition and morphology was investigated leading towards selecting the optimum AABs. The compressive strength at 28 days ranged from 28.5 to 32 MPa, 24.15 to 31.8 MPa, 24.2 to 33.1 MPa, 15.33 to 31.16 MPa, and 19.7 to 34.1 MPa, as A/P ratio, NS/NH ratio, NH molarity, W/P ratio, and curing method and duration were varied, respectively. XRD, FTIR, and SEM analyses of the AABs were conducted to validate the trends observed in the compressive strength results with variation in the activation parameters. The main phases detected by XRD included CSH, CASH, Mn-SH, KASH, and NASH. FTIR analysis showed bands that coincide with reported vibration and stretching of Si–O-M (M → Al, Si, or Mn) that are associated with geopolymerization, while SEM imaging showed dense microstructure with a homogenous distribution of polymerization gels that filled the microcracks and voids. Additionally, the effect of curing regimes (oven, steam and ambient-air curing) on the performance of AABs was also examined. The results of the present work enabled to identify the optimum proportioning of the selected precursor materials, optimum combination of A/P ratio, NS/NH ratio, NH molarity, and W/P ratio for producing the AABs with enhanced performance.

A facile fabrication of zinc oxide‐doped carbon aerogel by cellulose extracted from coconut peat and sodium alginate for energy storage application

AbstractIn this study, ZnO‐doped carbon aerogel is synthesized from cellulose in coconut peat with sodium alginate as a binder via both freeze‐drying and pyrolysis processes. Of those, zinc nitrate is used as not only a crosslinking agent to form gel but also a precursor source to dope ZnO in the carbon aerogel matrix. The effect of precursor ratios on the characterization and energy storage capacity of composite aerogel is investigated. As a result, it is indicated that the formed ZnO‐doped carbon aerogel possesses a highly porous structure which is typical for aerogel structure shown by SEM images, density, and porosity. Besides, via the XRD patterns, the confirmation of the ZnO crystal structure is found within the carbon aerogel lattice. In terms of energy storage, based on the specific capacitance results, the ZCA‐4 sample with a sodium alginate and cellulose weight ratio of 1:20 shows the best energy storage with a specific capacitance of 105 F/g in the voltage range of 0–0.5 V and scan‐rate speed of 0.005 V. Therewithal, the ZCA‐4 also performs high durability, high scanning speed tolerance, and stable storage performance with efficiency reaching more than 99% after 500 consecutive scan cycles. These results demonstrate that the ZnO‐doped carbon aerogel has potential applications as electrode materials in supercapacitors.

Controllable synthesis of sea urchin-like Cu–Au bimetallic nanospheres and their utility as efficient catalyst for hydrogenation of 4-nitrophenol

4-nitrophenol (4-NP) is a harmful aromatic compound to environment. The catalytic hydrogenation of 4-NP was considered as a profitable approach due to the valuable organic intermediate product. High efficiency catalysts are crucial. Herein, Cu–Au bimetallic nanospheres (BNSs) with sea urchin structure were fabricated by tuning the reaction condition and ratio of precursors. The Cu–Au BNSs exhibited effective catalytic activity in the reduction of 4-NP and K3[Fe(CN)6]. The optimum catalyst can be determined as the Cu–Au BNSs prepared by 15 ​mL AA, 4-NP can be reduced to 4-AP in 150 ​s ​(k ​= ​3.02 ​× ​10−2 s−1) with TOF value of 0.149 (s−1). The reusability of Cu–Au BNSs was evaluated with high effectiveness, the catalytic activity remained negligible loss over 18 cycles with efficiency over 95%, indicated their good reusability, which can be attributed to the synergistic effect of Cu–Au BNSs. The fabrication of bimetallic nanostructures provided an efficient approach to design efficient catalyst.

An in-situ strategy to construct uracil-conjugated covalent organic frameworks with tunable fluorescence/recognition characteristics for sensitive and selective Mercury(II) detection

Previous researches of covalent organic frameworks (COFs) have shown their potential as fluorescent probes, but the regulation of their optical properties and recognition characteristics still remains a challenge, and most of reports required complicated post-decoration to improve the sensing performance. In this context, we propose a novel in-situ strategy to construct uracil-conjugated COFs and modulate their fluorescence properties for sensitive and selective mercury(II) detection. By using 1,3,6,8-tetrakis(4-formylphenyl)pyrene (TFPPy) and 1,3,6,8-tetrakis(4-aminophenyl)pyrene (TAPPy) as fundamental blocks and 5-aminouraci (5-AU) as the functional monomer, a series of COFs (Py-COFs and Py-U-COFs-1 to Py-U-COFs-5) with tunable fluorescence were solvothermally synthesized through an in-situ Schiff base reaction. The π-conjugated framework serves as a signal reporter, the evenly and densely distributed uracil acts as a mercury(II) receptor, and the regular pores (channels) make the rapid and sensitive detection of the mercury(II) possible. In this research, we manage to regulate the crystalline structure, the fluorescence properties, and the sensing performance of COFs by simply changing the molar ratio of precursors. We expect this research to open up a new strategy for effective and controllable construction of functionalized COFs for environmental analysis.

Protein-Energy Malnutrition during Gestation and Lactation in Rats Affects Growth Rate, Brain Development and Essential Fatty Acid Metabolism

The influence of feeding a low protein diet to rat dams during gestation and lactation on lipid metabolism in pups was studied. Wistar rats were fed 5, 10, 15 and 25% dietary protein during gestation and lactation. Pup growth was monitored until weaning, and brain weight, protein concentration, proteolipid concentration and total lipid phosphorus concentration of brain were analyzed. The levels of fatty acids in dam milk as well as in pup liver phospholipids and brain prosphatidylcholine and phosphatidylethanolamine were determined. The progressive deprivation of maternal dietary protein produced a reduction in the total saturated fatty acid concentration of dam milk and an increment in the concentration of nonmetabolized linoleic acid. Pup body and brain weights as well as proteolipid, protein and total lipid phosphorus concentrations in brain were reduced in proportion to the degree of dietary protein deficiency. The products:precursor ratio of (n-6) fatty acids in liver phospholipids revealed an impairment in the elongation-desaturation pathway due to maternal protein deficiency. Both (n-6) and (n-3) polyunsaturated fatty acids within brain phosphatidylethanolamine were decreased by reduced maternal dietary protein intake, whereas only the linoleic acid-derived products were similarly affected in the corresponding phosphatidylcholine fraction. These results demonstrate the widespread and profound deleterious effects of low protein levels of maternal diet on the growth rate, brain development and fatty acid metabolism of rat pups.

Layer-by-Layer Hollow Mesoporous Silica Nanoparticles with Tunable Degradation Profile.

Silica nanoparticles (SNPs) have shown promise in biomedical applications such as drug delivery and imaging due to their versatile synthetic methods, tunable physicochemical properties, and ability to load both hydrophilic and hydrophobic cargo with high efficiency. To improve the utility of these nanostructures, there is a need to control the degradation profile relative to specific microenvironments. The design of such nanostructures for controlled combination drug delivery would benefit from minimizing degradation and cargo release in circulation while increasing intracellular biodegradation. Herein, we fabricated two types of layer-by-layer hollow mesoporous SNPs (HMSNPs) containing two and three layers with variations in disulfide precursor ratios. These disulfide bonds are redox-sensitive, resulting in a controllable degradation profile relative to the number of disulfide bonds present. Particles were characterized for morphology, size and size distribution, atomic composition, pore structure, and surface area. No difference was observed between in vitro cytotoxicity profiles of the fabricated nanoparticles at 24 h in the concentration range below 100 µg mL-1. The degradation profiles of particles were evaluated in simulated body fluid in the presence of glutathione. The results demonstrate that the composition and number of layers influence degradation rates, and particles containing a higher number of disulfide bridges were more responsive to enzymatic degradation. These results indicate the potential utility of layer-by-layer HMSNPs for delivery applications where tunable degradation is desired.

Boron-induced controlled synthesis of Co-nano particles over Bx(CN)y matrix for CO hydrogenation in aqueous media

Bx(CN)y supported cobalt nanoparticles have been synthesized by regulating the ratios of melamine and boric acid precursors. The carbonization step is adequate to generate the desired controlled-sized cobalt particles at an auto-reduced state that can eliminate the requirement of promotors (e.g., Pt) for the hydrogen-spillover effect. The presence of nitrogen in support enhances the dispersion of cobalt particles by providing sites for cobalt to nucleate and grow due to the interaction between cobalt and Π electrons from the sp2-N center. Boron in the catalyst system significantly stabilizes the catalyst, thus improving its lifetime. However, the excess of boron promotes the aggregation of cobalt particles; therefore, optimal boron loading is preferable. Moreover, the binding energy calculation of Co6 over the B-doped and undoped C3N4 surface computed through DFT studies shows a reduction in metal-support interaction with the addition of boron, which leads to the aggregation of the cobalt particles with high boron. Overall, the catalyst with the optimized boron and nitrogen-containing support-stabilized cobalt particles is highly efficient in the aqueous phase Fischer-Tropsch synthesis.

Impact of synthesis temperature and precursor ratio on the crystal quality of MOCVD WSe2 monolayers

Structural defects in transition metal dichalcogenide (TMDC) monolayers (ML) play a significant role in determining their (opto)electronic properties, triggering numerous efforts to control defect densities during material growth or by post-growth treatments. Various types of TMDC have been successfully deposited by MOCVD (metal-organic chemical vapor deposition), which is a wafer-scale deposition technique with excellent uniformity and controllability. However, so far there are no findings on the extent to which the incorporation of defects can be controlled by growth parameters during MOCVD processes of TMDC. In this work, we investigate the effect of growth temperature and precursor ratio during MOCVD of tungsten diselenide (WSe2) on the growth of ML domains and their impact on the density of defects. The aim is to find parameter windows that enable the deposition of WSe2 ML with high crystal quality, i.e. a low density of defects. Our findings confirm that the growth temperature has a large influence on the crystal quality of TMDC, significantly stronger than found for the W to Se precursor ratio. Raising the growth temperatures in the range of 688 °C to 791 °C leads to an increase of the number of defects, dominating photoluminescence (PL) at low temperatures (5.6 K). In contrast, an increase of the molar precursor ratio (DiPSe/WCO) from 1000 up to 100 000 leads to less defect-related PL at low temperatures.

Compressive Test and Microstructure Analysis of the Coconut Fiber Ash-based Geopolymer Binder

This watchfulness goal is to define the compressive test value and microstructure of a geopolymer binder made from coconut fiber ash (CFA). CFA comes from the combustion of coconut fibers in the tile-making industry in Tabanan, Bali. This waste is processed into CFA, which consists of 8.24% silicon dioxide, 70.6% potassium oxide, 14.1% chlorine, 2.3% diphosphate pentoxide, and 2.25% iron dioxide. CFA is then used as a crude material for the manufacture of geopolymer binders. The mixture's proportion consisted of three groups of variations: the ratio of precursors and activators, P/A: 70%:30%; 75%:25%; and 80%:20%. In the experiment, Na₂SiO₃ and a 14 M molar concentration of NaOH were combined in weight ratios of 1:1, 1.5:1, and 2:1. These are both alkaline activators. The sample was shaped into 50-mm cubes, dried in an 80℃ heater for 24 hours, and then tested at 7 and 28 days. The ASTM-C39 standard was used for the compression test, while the microstructural analysis used X-RD and SEM-EDX. The results showed that coconut fiber ash precursors could be used to generate a geopolymer binder with a compressive value of 4.67 MPa and 6.24 MPa on the 7^th and 28^th days of testing, respectively. The microstructure of the solid sample, which was associated with the rise in compressive value, was characterized using scanning electron microscopy. Using 80% CFA gave the best results.

Optimization and Fabrication of Binder-Free Nickel-Copper Phosphate Battery-type Electrode Using Microwave-Assisted Hydrothermal Method

In this study, a binder-free nickel-copper phosphate battery-type electrode was fabricated using a microwave-assisted hydrothermal technique. The fabrication process was optimized with Design of Experiment (DoE) software and then validated experimentally. The electrode made at 90 °C for 12.5 min, with a Ni:Cu precursor ratio of 3:1, had the highest specific capacity. The experimental specific capacity of the optimized nickel-copper phosphate (Ni3-Cu-P) binder-free electrode was 96.2% of the theoretical value predicted by the software, which was within 10% error. Moreover, the growth of amorphous Ni3-Cu-P electrode material with irregular microspheres of small size was observed on the surface of nickel foam. These amorphous microspherical shapes of the Ni3-Cu-P electrode material provide more electroactive sites and a larger active surface area for faradaic reaction. In electrochemical energy storage applications, the Ni3-Cu-P electrode outperformed the bare Ni-P and Cu-P electrodes, with the highest areal capacity (0.77 C cm−2), the lowest charge transfer resistance (81.7 Ω), and the highest capacity retention (83.9%) at 2.0 mA cm−2. The study indicates that the Ni3-Cu-P electrode’s exceptional electrochemical properties result from the interaction between nickel and copper in the binary metal phosphate framework, making it an excellent choice for battery-type electrodes used in electrochemical energy storage applications.