Specific Current Density Research Articles

Facile synthesis of MCo2O4(M= Ni, Cu, and Zn) materials for high-performing electrochemical capacitors with robust cyclic stability using redox additive electrolyte

Developing efficient electrochemical capacitors relies heavily on the quality of electrode materials and electrolytes used. This report presents the successful solvothermal synthesis of three cobaltites, NiCo2O4, CuCo2O4, and ZnCo2O4, and their electrochemical performance in a 2 M KOH electrolyte. Among the three cobaltites, NiCo2O4 showed the best electrochemical performance, delivering a specific capacity of 178 C/g when using FTO (fluorine-doped tin oxide) as the current collector. In addition, the performance of NiCo2O4 was tested in different aqueous electrolytes, including KOH, NaOH, NaCl, and Na2SO4, and the specific capacity was found to vary in the order of 2 M KOH > 2 M NaOH > 2 M NaCl > 2 M Na2SO4. The performance of NiCo2O4 was also assessed in various concentrations of KOH electrolyte (2 M KOH, 3 M KOH, and 4 M KOH), and the best performance was observed in 3 M KOH with a specific capacity of 928.3 C/g with Ni foam as the current collector. Finally, using redox additive electrolytes, the electrochemical performance of NiCo2O4 was evaluated in both 3-electrode and 2-electrode systems. No studies have been conducted on the electrochemical performance of NiCo2O4using KFCN redox additive in a 3 M KOH electrolyte. In the three-electrode system, NiCo2O4 showed a high specific capacity of 1005.5 C/g at 1 A/g, with 167 % capacity retention after 1000 charge-discharge cycles at a high current density of 30 A/g. The NiCo2O4//Activated Carbon asymmetric hybrid supercapacitors(AHSC) exhibited a maximum specific capacity of 115.6 C/g and a specific energy density of 85 Wh/kg at current density of 1 A/g. The AHSC also showed a capacitive retention of 120 % after 5000 charge-discharge cycles. The maximum power density was 13225 W/kg at a current density of 5 A/g while maintaining an energy density of 22 Wh/kg.

Electro-activation for efficient lactulose production: The impact of operational parameters, electrolyte types, and environmental conditions

The electro-activation (EA) process has been employed to convert lactose into lactulose, a potent prebiotic with numerous health benefits. The study identified optimal conditions for lactulose production, including a specific current density, the use of calcium chloride as an efficient electrolyte, and the superiority of a steel cathode over a graphite cathode. The formation of intermediates other than lactulose increased as the temperature increased. The changes in pH and oxidation-reduction potential during the isomerization process were observed, highlighting their vital role in the formation of an ideal alkaline environment for lactulose production. The resultant solution produced by the EA process has significant antioxidant characteristics, likely due to the formation of Maillard Reaction Products during lactulose production. In conclusion, the EA system, with optimal operating conditions, is an energy-efficient, reagent-free, and environmentally friendly alternative for lactulose production.

Balancing current density and electrolyte flow for improved zinc-air battery cyclability

Zinc-air batteries (ZABs), known for their high energy density and environmental friendliness, are emerging as promising solutions for sustainable energy storage. However, the irregular deposition of zinc on electrodes hinders the widespread utilization of rechargeable ZABs due to limited durability and stability. This study investigates the role of electrolyte flow in enhancing zinc electrodeposition and overall performance in zinc-air flow batteries (ZAFBs) at high current densities. We explore the interplay between current density, flow rate, and their influence on electrode surface morphology and the removal of the passivating zinc oxide layer to improve battery efficiency and lifespan. Using advanced in-situ synchrotron radiation x-ray tomography, we found that incorporating flowing electrolyte at specific current densities results in rounded dendrite tips, thinner and more uniform deposition layers, and improved zinc adhesion. Imaging and electrochemical analyses further reveal that flowing electrolyte enhances zinc morphology, reduces charge transfer resistance, diminishes passivation, and lowers galvanostatic charge/discharge polarization across various current densities, thereby improving battery cycling performance. Notably, the impact of flowing electrolyte is more pronounced at a moderate current density of 50 mA/cm2 compared to lower or higher currents. Our findings underscore the importance of electrolyte flow and current density management in developing high-performance ZAFBs, providing valuable insights for their future commercialization.

Amorphous Cobalt Tin Oxide/Reduced Graphene Oxide Decorated on Graphite Felt as Positive Electrode for Vanadium Redox Flow Battery

The Vanadium Redox Flow Battery (VRFB) stands out as one of the most promising large-scale energy storage systems. Nevertheless, the graphite electrode materials commonly used in VRFBs often exhibit drawbacks such as limited electrochemical activity and insufficient conductivity, ultimately resulting in suboptimal performance for the VRFB. In this study, we utilized highly conductive reduced graphene oxide (rGO) as a carrier for cobalt tin oxide (CoSnO3), aiming to enhance their catalytic capability towards vanadium ions. CoSnO3/rGO composite was confirmed using XRD and TEM, revealing nanoboxes morphology and amorphous structure. XPS and EPR analysis showed an increase in oxygen vacancies after composite formation. In order to further prove the effect of CoSnO3/rGO composite catalyst modified graphite felt, the modified graphite felt electrode was applied to the positive electrodes of VRFB, and the charge and discharge tests at different current densities were carried out. At a current density of 160 mA/cm², the composite demonstrated a voltage efficiency of 74.22%, surpassing the heat treated graphite felt by 2.69%. Noteworthy enhancements in capacitance were also evident at this specific current density. Furthermore, stability testing over 50 cycles revealed no significant degradation, underscoring the superior performance and outstanding durability of the CoSnO3-rGO modified graphite felt throughout charge and discharge cycling. The result of this study highlight the promising potential of CoSnO3-rGO composites as efficient catalysts for vanadium redox flow batteries, providing improvements in electrochemical performance and long-term stability.

Grain-Boundary Engineering Boosted Undercoordinated Active Sites for Scalable Conversion of CO2 to Ethylene.

The development of highly selective and energy efficient technologies for electrochemical CO2 reduction combined with renewable energy sources holds great promise for advancing the field of sustainable chemistry. The engineering of copper-based electrodes facilitates the conversion of CO2 into high-value multicarbon products (C2+). However, the ambiguous determination of the intrinsic CO2 activity and the maximization of the density of exposed active sites have severely limited the use of Cu for the realization of practical electrocatalytic devices. Here, we report a scalable strategy to obtain a high density of undercoordinated sites by maximizing the exposure of grain-boundary active sites using a direct chronoamperometric pulse method. Our numerical investigations predicted that grain boundaries modulate the adsorption behavior of *CO on the Cu surface, which acts as a key intermediate species associated with the production of multicarbon species. We investigated the consequence of grain-boundary density on dendric Cu catalysts (GB-Cu) by combining transmission electron microscopy, in situ Raman spectroscopy, and X-ray photoelectron spectroscopy with electrochemical measurements. A linear relationship between the Faradaic efficiency of the C2+ product and the presence of undercoordinated sites was observed, which allowed to directly quantify the contribution of the grain boundary in Cu-based catalysts on the CO2RR properties and the formation of multicarbon products. Using a membrane electrode assembly electrolyzer, the high grain-boundary density Cu electrodes achieved a maximum Faradaic efficiency of 73.2% for C2+ product formation and a full-cell energy efficiency of 20.2% at a specific current density of 303.6 mA cm-2. The GB-Cu was implemented in a 25 cm2 MEA electrolyzer and demonstrated selectivity of over 62% for 70 h together with current retention of 88.4% at the applied potential of -3.80 V. The catalysts and electrolyzer were further coupled to an InGaP/GaAs/Ge triple-junction solar cell to demonstrate a solar-to-fuel (STF) conversion efficiency of 8.33%. This work designed an undercoordinated Cu-based catalyst for the realization of solar-driven fuel production.

Electrochemical impedance spectroscopy of AB3 active electrode in nickel metal hydride accumulators: The effect of temperatures and immersion times

The electrochemical impedance spectroscopy (EIS) method was employed systematically to investigate the kinetic properties of the LaY2Ni9 electrode, which serves as negative electrode in Ni-MH accumulators. Through this analysis, a comprehensive understanding of the electrode’s behaviour was achieved.EIS measurements were performed on the LaY2Ni9 electrode at different temperatures (ranging from 15 °C to 75 °C) and at different immersion times using a potentiostat and frequency response analyser.The EIS spectra were fitted using an equivalent circuit model to extract the electrode impedance parameters, such as the charge transfer resistance, Rtc, the absorption/double layer capacities, Cad and Cdl, the specific current density, I0,EIS, and the hydrogen penetration depth, δ. The results show that temperatures have significant effects on the EIS impedance of the LaY2Ni9 electrode. The Rtc and the Cdl parameters increase with temperature, indicating a decrease in electrode kinetics due to the higher activation energy and an increase in electrode area due to thermal expansion. The penetration depth, δ, is directly proportional to the temperature increase.According to the EIS results, it is generally considered advantageous to maintain an operating temperature of around 30 °C for the LaY2Ni9 electrode. Moreover, a correlation can be observed between the variations in the kinetic parameter (DH) and the corresponding changes in other electrochemical parameters.Inconsistencies arise when comparing the exchange current density values obtained through cyclic voltammetry (I0,CV) and impedance spectroscopy (I0,EIS), highlighting contradictory findings. These disparities can be ascribed to multiple factors, including temperature variations, electrode geometry, and concentration gradients near the electrode interface. Overall, this study provides valuable information on the performance and degradation mechanisms of the LaY2Ni9 electrode under temperature and immersion time conditions and highlights the importance of EIS impedance measurements for battery research and development.

Spontaneous-Spin-Polarized 2D π-d Conjugated Frameworks Towards Enhanced Oxygen Evolution Kinetics.

Alternative strategies to design sustainable-element-based electrocatalysts enhancing oxygen evolution reaction (OER) kinetics are demanded to develop affordable yet high-performance water-electrolyzers for green hydrogen production. Here, it is demonstrated that the spontaneous-spin-polarized 2D π-d conjugated framework comprising abundant elements of nickel and iron with a ratio of Ni:Fe = 1:4 with benzenehexathiol linker (BHT) can improve OER kinetics by its unique electronic property. Among the bimetallic NiFex:y-BHTs with various ratios with Ni:Fe = x:y, the NiFe1:4-BHT exhibits the highest OER activity. The NiFe1:4-BHT shows a specific current density of 140Ag-1 at the overpotential of 350mV. This performance is one of the best activities among state-of-the-art non-precious OER electrocatalysts and even comparable to that of the platinum-group-metals of RuO2 and IrO2. The density functional theory calculations uncover that introducing Ni into the homometallic Fe-BHT (e.g., Ni:Fe = 0:1) can emerge a spontaneous-spin-polarized state. Thus, this material can achieve improved OER kinetics with spin-polarization which previously required external magnetic fields. This work shows that a rational design of 2D π-d conjugated frameworks can be a powerful strategy to synthesize promising electrocatalysts with abundant elements for a wide spectrum of next-generation energy devices.

Atomically dispersed Iridium on Mo2C as an efficient and stable alkaline hydrogen oxidation reaction catalyst

Hydroxide exchange membrane fuel cells (HEMFCs) have the advantages of using cost-effective materials, but hindered by the sluggish anodic hydrogen oxidation reaction (HOR) kinetics. Here, we report an atomically dispersed Ir on Mo2C nanoparticles supported on carbon (IrSA-Mo2C/C) as highly active and stable HOR catalysts. The specific exchange current density of IrSA-Mo2C/C is 4.1 mA cm−2ECSA, which is 10 times that of Ir/C. Negligible decay is observed after 30,000-cycle accelerated stability test. Theoretical calculations suggest the high HOR activity is attributed to the unique Mo2C substrate, which makes the Ir sites with optimized H binding and also provides enhanced OH binding sites. By using a low loading (0.05 mgIr cm−2) of IrSA-Mo2C/C as anode, the fabricated HEMFC can deliver a high peak power density of 1.64 W cm−2. This work illustrates that atomically dispersed precious metal on carbides may be a promising strategy for high performance HEMFCs.

Electrochemical detection of heavy metals and chloramphenicol using a Nafion/graphene quantum dot modified electrode

<span>Graphene quantum dots (GQDs) with a uniform particle size were successfully synthesized using a simple in-situ electrolytic graphite rod method at a specific current density. Nafion/GQD-modified glassy carbon electrodes (nafion/GQDS/GCE) were then fabricated. Anodic stripping voltammetry and differential pulse voltammetry were utilized for the detection of heavy metals, specifically Pb(II) and Cd(II), as well as chloramphenicol. The results indicated that the dissolution currents for Pb(II) and Cd(II) increased with their concentrations, showing a strong linear relationship. The linear range for Pb(II) was 4.82 × 10</span><sup>−8</sup><span> to 9.65 × 10</span><sup>−7</sup><span> mol/L (</span><em>R</em><span>² = 0.9923), and for Cd(II), it was 1.07 × 10</span><sup>−7</sup><span> to 1.96 × 10</span><sup>−6</sup><span> mol/L (</span><em>R</em><span>² = 0.9912), with detection limits of 1.61 × 10</span><sup>−8</sup><span> mol/L for Pb(II) and 3.57 × 10</span><sup>−8</sup><span> mol/L for Cd(II). The nafion/GQDS/GCE exhibited significant electrocatalytic activity towards chloramphenicol, with an irreversible reaction involving 6 electrons and an electron transfer rate constant (KS) of 105.4 s</span><sup>−1</sup><span>. The catalytic reduction current for chloramphenicol at the modified electrode ranged from 5.00 × 10</span><sup>−7</sup><span> to 2.50 × 10</span><sup>−3</sup><span> mol/L, showing a good linear relationship, and the detection limit (S/N = 3) was 1.67 × 10</span><sup>−7</sup><span> mol/L. The nafion/GQDS/GCE also demonstrated excellent anti-interference, stability, and reproducibility, yielding satisfactory results for the detection of actual samples.</span>

Rational design of cobalt-infused styrofoam nickel manganese oxide: Unlocking unprecedented capacitance for supercapacitor applications

Advancement in low to high-power device technology requires smart solutions for the energy-storing property of the devices. The Pseudo-capacitor with battery-type charge storing discharging mechanism can possess a high energy density. In this study, we present the synthesis of combustion-derived AxNi1-xMn2O4 (A = Co, Cu, Zn, & X = 0.01, 0.02, 0.03) nanoparticles for supercapacitor application. Among all the electrode materials studied, the Styrofoam structure of Co0.03Ni0.97Mn2O4 (3CoNMO) exhibited an utmost specific capacitance of 747.42 F/g at 50 mV/s, and galvanostatic charge/discharge (GCD) studies confirmed that the 3CoNMO has an outstanding specific capacitance of 746.76 F/g at 1 A/g. Moreover, the 3CoNMO exhibits remarkable cyclic stability retention (89.26%) after 10,000 continuous cycles at 10 A/g. Similarly, the asymmetric supercapacitor device was fabricated for the optimized working electrode, and the (3CoNMO||AC) delivers an outstanding specific capacitance of 31.85 F/g at a specific current density of 1A/g, it provides energy and power density of 11.25 WhKg−1 and 847.45WKg-1. The results highlighted that Co0.03Ni0.97Mn2O4 nanoparticle as an auspicious nominee for supercapacitor applications and exhibit good long-term stability.

Exploring the Potential of Nitrogen-Doped Graphene in ZnSe-TiO2 Composite Materials for Supercapacitor Electrode.

The current study explores the prospective of a nitrogen-doped graphene (NG) incorporated into ZnSe-TiO2 composites via hydrothermal method for supercapacitor electrodes. Structural, morphological, and electronic characterizations are conducted using XRD, SEM, Raman, and UV analyses. The electrochemical study is performed and galvanostatic charge-discharge (GCD) and cyclic voltammetry (CV) are evaluated for the supercapacitor electrode material. Results demonstrate improved performance in the ZnSe-NG-TiO2 composite, indicating its potential for advanced supercapacitors with enhanced efficiency, stability, and power density. Specific capacity calculations and galvanic charge-discharge experiments confirmed the promising electrochemical activity of ZnSe-NG-TiO2, which has a specific capacity of 222 C/g. The negative link among specific capacity and current density demonstrated the composite's potential for high energy density and high-power density electrochemical devices. Overall, the study shows that composite materials derived from multiple families can synergistically improve electrode characteristics for advanced energy storage applications.

Exploring the influence of KOH electrolyte concentration on the electrochemical properties of Co3O4-GO nanocomposite

In this study, we investigate the electrochemical performance of Co3O4-GO nanocomposite, synthesized via a hydrothermal method, as a function of electrolyte concentration. XRD, Raman, SEM, TEM, XPS, and BET techniques have been employed to examine the structural, microstructural, chemical states, and specific surface area characteristics of the composite material. According to SEM micrographs, the aggregated particles have a sheet-like morphology, and these sheets have been assembled into clusters. Using N2-adsorption/desorption isotherms, the pore volume, diameter, and specific surface area of composite were determined to be 0.24 cm3/g, 15 nm, and 63 m2/g, respectively. Based on cyclic voltammograms (CVs) recorded at different scan rates and electrolyte concentrations, the working electrode demonstrated pseudocapacitance behavior. The specific capacitance (Cs) of the fabricated electrode was estimated from GCD curves recorded at different current densities and electrolyte concentrations. For 1 M KOH solution, Cs of the composite electrode is found to be 258 F/g at 1 A/g, and this value drops to 222 F/g at 5 A/g. Furthermore the composite electrode's Cs decreases with increasing electrolyte concentration at a specific current density. The study indicates that 1 M of KOH electrolyte is the optimal electrolyte concentration for optimal energy storage.

Synergistic interactions of electronic modulation and low crystallization in Ru-RuO2/C heterostructure for highly efficient multifunctional electrocatalysis

Developing electrocatalysts with multifunctional performance is crucial for hydrogen energy storage and conversion, but still a great challenge. Herein, an efficient trifunctional electrocatalyst with heterostructure is fabricated by a sequential reduction and annealing approach. With different annealing atmospheres, Ru-RuO2/C electrocatalysts having different Ru/RuO2 atomic ratios or different crystallinities were achieved. Among these electrocatalysts, Ru-RuO2/C annealed from N2-air mixed atmosphere (Ru-RuO2/C 250NA) displays the most excellent performance, affording overpotential values of 30.63 mV for alkaline hydrogen evolution reaction (HER) and 273.42 mV for alkaline oxygen evolution reaction (OER) at 10 mA cm−2, much lower than those of state-of-the-art Pt/C (η10, HER = 46.57 mV) and RuO2 (η10, OER = 288.99 mV). Not only that, it also delivers favorable activity for alkaline hydrogen oxidation reaction (HOR), with 2.1 times of mass specific exchange current density than that of Pt/C. The experimental and theoretical investigations prove the electron rearrangement at Ru and RuO2 interface with abundant defects and amorphous/crystalline structures. The synergistic effect of dual active sites simultaneously optimizes H and OH as well as H2O adsorption energies, endowing the Ru-RuO2/C 250NA as the preferential electrocatalysts.

Efficiency improvement strategy of fuel cell system based on oxygen excess ratio and cathode pressure two-dimensional optimization

Improving the commercial fuel cell system efficiency is critical to reducing hydrogen consumption and improving the operational economy. This paper studies the power consumption pattern of the air supply subsystem, the most power-consuming auxiliary components, aiming to improve the system’s efficiency. A method was proposed to get the extremum of the system net power by optimizing the oxygen excess ratio and cathode pressure. Mathematical models describing the fuel cell stack and air supply subsystem power characteristics were developed based on the mechanism analysis and estimation of unknown parameters. Then, a system net power model for energy efficiency optimization was developed. The operating conditions for optimal efficiency at a specific current density can be obtained by numerical calculation. To verify the method’s effectiveness, a series of experiments were conducted, and the results show that the proposed method can maximize system net power output at various current density conditions. Compared with the conventional oxygen excess rate based one-dimensional optimization, the two-dimensional method can improve system efficiency by 2.06%, offering a good application prospect.

POOL BOILING HEAT TRANSFER CHARACTERISTICS OF POROUS NICKEL MICROSTRUCTURE SURFACES

Pool boiling is an effective heat dissipation approach in electronic cooling, battery thermal management, etc. This study used the electrochemical deposition method to fabricate one smooth nickel specimen (named Ni-smooth) and three specimens with a porous nickel-stacked structure. The three porous specimens were created with deposition current densities of 0.5 A·cm<sup>-2</sup> (named Ni-0.5), 2.0 A·cm<sup>-2</sup> (names Ni-2.0), and 5.0 A·cm<sup>-2</sup> (named Ni-5.0), respectively. The four samples underwent microstructural characterization via scanning electron microscopy. The increasing current density led to the porous nickel surface exhibiting a more distinct pore structure, and the nickel sphere grains became more refined, developing a loose "mound-like" structure. A marked increase in the nickel film thickness was also observed. Through visual experiments, we evaluated their wettability, and through pool-boiling experiments, we tested their boiling heat-transfer properties. Our findings suggest that samples incorporating a porous nickel structure consistently outperform unmodified samples regarding heat-transfer efficiency. Specifically, sample Ni-0.5A demonstrated the most optimal boiling heat-transfer performance, evidenced by a 32.2% reduction in temperature at the onset of boiling, a 19.9% increase in critical heat flux density, and a 78.6% larger maximum heat-transfer coefficient compared to the smooth nickel sample. These marked improvements are intrinsically linked to the specific characteristics of the porous nickel structure. The higher performance of samples Ni-0.5 can be attributed to the presence of additional nucleation sites within the porous structure and the formation of smaller micro-crystalline dendritic constructs due to the specific current density applied during electrodeposition. Understanding this relationship between surface characteristics and electrodeposition is essential in maximizing heat-transfer efficiency.

Nanosized Chevrel phases for dendrite-free zinc-ion based energy storage: unraveling the phase transformations.

The nanoscale form of the Chevrel phase, Mo6S8, is demonstrated to be a highly efficient zinc-free anode in aqueous zinc ion hybrid supercapacitors (ZIHSCs). The unique morphological characteristics of the material when its dimensions approach the nanoscale result in fast zinc intercalation kinetics that surpass the ion transport rate reported for some of the most promising materials, such as TiS2 and TiSe2. In situ Raman spectroscopy, post-mortem X-ray diffraction, Hard X-ray photoelectron spectroscopy, and density functional theory (DFT) calculations were combined to understand the overall mechanism of the zinc ion (de)intercalation process. The previously unknown formation of the sulfur-deficient Zn2.9Mo15S19 (Zn1.6Mo6S7.6) phase is identified, leading to a re-evaluation of the mechanism of the (de)intercalation process. A full cell comprised of an activated carbon (YEC-8A) positive electrode delivers a cell capacity of 38 mA h g-1 and an energy density of 43.8 W h kg-1 at a specific current density of 0.2 A g-1. The excellent cycling stability of the device is demonstrated for up to 8000 cycles at 3 A g-1 with a coulombic efficiency close to 100%. Post-mortem microscopic studies reveal the absence of dendrite formation at the nanosized Mo6S8 anode, in stark contrast to the state-of-the-art zinc electrode.

The feasibility study of cascade waste heat recovery in a molten carbonate fuel cell-driven system

The use of solid-state converters in power production, particularly in combination with molten carbonate fuel cells, holds promise for improving overall power generation efficiency. These systems are designed to capture and utilize the considerable waste heat generated during power production, leading to enhanced performance and energy recovery. The specific approach discussed in this investigation involves a solid-state system consisting of an alkali metal thermal electric converter and a thermally regenerative electrochemical cycle for waste heat recovery and additional power generation. The study conducts a comprehensive analysis of this combined system, focusing on various aspects, including energy, exergy, and economic considerations. One key variable investigated is the current density, which plays a significant role in determining system performance. The investigation considers sensitivity analysis by varying six design parameters, offering insights into how different factors affect the system's performance. One of the notable findings is the identification of the overall maximum power density, which reaches 2642 W/m2 at a specific current density of 4686 A/m2. Evaluating the overall performance of the system, the study reports energetic efficiency, exergetic efficiency, and exergy destruction rate density. The energetic efficiency stands at approximately 44.04 %, while the exergetic efficiency is notably higher at 47.09 %. Additionally, the exergy destruction rate density is reported at 2968 W/m2. The research highlights the significance of the operating temperature of the molten carbonate fuel cell, as it has a substantial impact on the overall performance of the system. Increasing the operating temperature of the fuel cell leads to improvements in system efficiency and performance. In summary, the investigation demonstrates the potential of a solid-state system with waste heat recovery components in combination with a molten carbonate fuel cell. This approach enhances power production efficiency, making it a promising solution for sustainable and efficient energy generation.

Evaluation of Stability of Performance of Electrochemically Exfoliated Graphene for Electrochemical Double-Layer Capacitors

Energy storage devices are known as supercapacitors. One highlighted characteristic of them is high specific power and cycling long-life. These properties are associated with charging and discharging in short periods of time, especially useful for high demanding systems, such as regenerative technologies, strong acceleration in mobility and radical maneuvers in aeronautics. So, market demands for supercapacitors have been growing fastly. The performance improvement and cost reduction of supercapacitors are essential for the popularization of electromobility all over the world. For this aim, graphene and carbon nanotubes, among others, are materials widely used to such proposes due to their high specific surface area and excellent pseudocapacitive and electrochemical double layer properties. In this work, the use of graphene oxide obtained by electrochemical exfoliation and polyvinylpyrrolidone as active mass of supercapacitor electrodes was studied. The electrodes were prepared using the dip coating technique. To characterize the samples obtained, cyclic voltammetry (CV) and galvanostatic charge and discharge (GCD) were carried out in a 3-electrode cell with a 1 M sulfuric acid solution. CV was used to define the potential window, estimate capacitive profile and observe possible faradic phenomena. After that, GCD was used to study the material’s stability during 1000 operation cycles, at three specific current densities: 1.0; 1.5; and 2.0 A g-1. The voltammograms obtained are shown in Figure 1. It was possible to observe a symmetrical voltammogram with discrete quasi-reversible faradic phenomena (pseudocapacitive effects) defined by the cathodic peak at 0.48 V and anodic peak at 0.22 V. These peaks may be related to the redox reactions of graphene oxide. GCD was carried out to evaluate coulombic efficiency and charge retention such as shown in Figure 2. There was no great damage during the cycles; there was a slight positive change (increase) during 1000 cycles for all current densities. Furthermore, an increase in charge retention was observed for all current densities, this effect can be related to elongation of the polymeric chain due to electrostatic interaction of the binder in acidic media, leading to a higher effect of double-layer. For the 1 A g-1 current density, the increase of charge retention and coulombic efficiency were more relevant. These increases may be associated with gradual and discrete pseudocapacitive processes also observed in cyclic voltammetry measurements. The determined values of capacitance, energy and power densities are shown in Table 1. The values obtained at 1 A g-1 specific current density showed a higher coulombic efficiency and a significant increase in charge retention, despite having presented a lower power density. to this material, it is possible to assert to be a working condition better than others. At specific current densities of 1.5 A g-1 and 2 A g-1 higher values of energy and power density were determined, but lower coulombic efficiency. Figure 1

Quasi-in-Situ Analysis of Electropolished Additively Manufactured Stainless Steel Surfaces

Progress in additive manufacturing is leading to the emergence of new areas of application. Laser Powder Bed Fusion (L-PBF) is increasingly used for the development of metallic medical implants, but for high-risk implants like vascular support structures (stents), surface quality is critical to ensure successful implantation without harming the surrounding tissue and ensure the patients’ health. Therefore, enhancing the surface quality is crucial. Electropolishing is a method for removing surface roughness by smoothing out micro-peaks and valleys. However, L-PBF structures have a high surface roughness due to metal particles adhering on the surface. To achieve a smooth surface for additively manufactured implants like stents using electropolishing, the removal of these particles needs to be studied in more detail.The objective of this study is to examine the electropolishing mechanism of 316L stainless steel samples additively manufactured through Laser Powder Bed Fusion (L-PBF). The main objective is to investigate the removal properties and surface characteristics during electropolishing. To achieve this, various surfaces were characterized for morphology and roughness during Hull cell experiments. Markings are utilized on the Hull cell sample surfaces to identify points of interest during quasi-in-situ measurements. The surfaces are then analyzed after multiple time steps, applying different currents to investigate particle dissolution. The surface characteristics are analyzed through scanning electron microscopy, and surface roughness is analyzed using laser scanning microscopy.The results show that the electropolishing process preferentially removes the adhering particles present on the surface of the samples. Increasing the current density results in faster particle dissolution and a smoother surface (see Figure 1a and b). The mechanism of material removal of various surface features, as shown in Figure 1 (red circle, yellow arrow and red square), was assessed based on the experimental results of the surface structures seen on the SEM images. It was found that different surface features were removed during the experiment at different polishing times and current densities. The amount of charge flowed was found to correlate with surface morphology.Based on the obtained results, various surface features (such as large adherent particles, agglomerates of smaller particles, and valleys) and their changes with increasing test duration and current density were observed by quasi-in situ analyses. A reduction in the diameter of round particles adhering to the surface was observed at both low and higher current densities (see Figure 1a red circle a). Increasing the polishing time resulted in leveling of both large particles and valleys (see Figure 1b red square). Also, dissolution of agglomerates of smaller particles occurred at different polishing times as a function of current density and polishing time (see Figure 1a yellow arrow) are observed.Smoothed surface structures can be observed in regions with equivalent surface charge density (see Figure 2). As a result, comparable surface morphologies may appear at the same area charge density, irrespective of a specific current density. So, it may be adequate to only consider the amount of charge flowed to describe the electropolishing of additive materials.In conclusion, comprehending the dissolution characteristics of particles on L-PBF surfaces is essential for attaining satisfactory surface finish in electropolishing. The results of this study offer valuable perspectives into the electropolishing mechanism of additively manufactured 316L stainless steel and can guide future investigations on surface finishing and polishing of additive manufactured implants like stents. Figure 1

(Invited) Delivering Electrons and Protons to the Substrate in Molecularly-Based Reductive Electrocatalysis

To steer away from fossil fuels the primary sourcing for goods and chemicals, combining renewable electricity with sustainable feedstocks in an electrochemical strategy is a formidable synthetic opportunity. In that frame, we investigate how molecular electrocatalysis can foster electrosynthetic conversions, in particular for organics reductions.[1] Here, we will disclose that alkyne semihydrogenation, an important synthetic manifold, can be selectively electrocatalyzed by a simple molecular catalyst [Ni(bpy)3]2+, based on the earth-abundant metal nickel.[ 2 ] Our combined electrochemical, synthetic and computational investigations support that the catalytic cycle proceeds via the protonation of a nickelacyclopropene species and bypasses the need to generate a competent hydride.[3] As a proof-of-concept for molecular electrocatalytic alkyne semihydrogenation, this work opens a platform to develop original electrochemical routes for the hydrogenation/-functionalization of organics and small molecules.We will also discuss the use of Pickering emulsion that separates organic substrates and aqueous electrolytes in different phases for electrocatalytic hydrogenation at the interface. We developed a hybrid design based on carbon nanotube-supported Pd nanoparticles that places at the interface and acts both as emulsion stabilizer and electrocatalyst. The system electrohydrogenates styrene into ethylbenzene with high faradaic efficiency (95.0%) and Pd specific current density (–148.1 mA·cm–2). Our system combines good solubility of the substrates, high conductivity, facile product isolation and applies to the transformation of various alkenes. This strategy may thus provide original solutions to the ECH of substrates having low water-solubility.[4] References [1] N. Kaeffer, W. Leitner, JACS Au, 2022, 2, 1266.[2] M.-Y. Lee, C. Kahl, N. Kaeffer, W. Leitner, JACS Au, 2022, 2, 573.[3] G. Durin, M.-Y. Lee, T. Weyhermüller, N. Kaeffer, W. Leitner, ChemRxiv, 10.26434/chemrxiv-2023-whtfd.[4] C. Han, J. Zenner, J. Johny, N. Kaeffer, A. Bordet, W. Leitner, Nat. Catal., 2022 , 5, 1110.