Portugaliae
Electrochimica Acta

Numerous developed nations have adopted a bio-based economy, with thermochemical conversion of municipal solid waste biomass (Bm) being the most effective method to accomplish this objective. Hydrothermal carbonization (HTC) presents a viable method for conversion of waste Bm through an environmentally sustainable process that utilizes water as reaction medium and operates at moderate temperatures (180-280 °C). HTC has effectively generated targeted carbonaceous products from diverse waste sources, including lignocellulosic Bm, sewage effluent, algae and municipal solid waste. This study examines critical HTC process parameters and chemical and physical properties of resultant hydrochar, while exploring potential conversion of modified and functionalized materials into sustainable solutions for the future.

High ash yield (AY) from the co-combustion of palm kernel shells (PKS) and cashew nut shells (CNS) presents significant challenges for efficient biomass combustion in a grate furnace. This study aimed to optimize AY from co-combustion of PKS, CNS and kaolin additive (KA) in a tubular furnace. Optimization of the components' mixture, and of factors such as temperature, particle size (PS) and residence time (RT), was conducted utilizing an optimal combined design within Design Expert software (version 13). AY of PKS-CNS fuel mixture, with and without KA, was then analysed using X-ray Diffraction (X-RD), to identify mineral phase compounds within the ash. Optimized composition consisted of PKS (69.6%), CNS (23.3%) and KA (7.1%), at 900 °C, with PS of 1.00 mm and RT of 120 min. This composition resulted in the lowest AY of 10.10% and higher heating value of 21.34 MJ/kg. X-RD analysis revealed a decrease in K-Na-Ca-Mg-Fe-Al compounds, and a significant increase in SiO2, along with disappearance of potassium chloride peaks. This suggests that optimizing PKS-CNS mixture with KA and adjusting combustion parameters significantly reduced AY and improved fuel's energy content. Keywords: Ash yield; cashew nut shells; kaolin additive; optimization; palm kernel shells.

The transition towards sustainable energy sources requires the development of cost-effective and highly efficient electrocatalysts for water electrolysis. This study reports the fabrication and optimization of a non-precious bifunctional quaternary electrocatalyst from Co-Fe-Mn-Ni (CFMN) via electrodeposition for water-splitting reactions of both hydrogen (HER) and oxygen evolution (OER) reactions. Physicochemical characterizations showed that optimized quaternary CFMN electrocatalyst, deposited from an acetate electrolyte, had a composition of Co1.54-Fe0.11-Mn0.01-Ni0.043, with polycrystalline nanosheet morphology. Electrochemical activity assessment revealed remarkable electrocatalytic performance for both HER and OER, surpassing that of single-metal catalysts. CFMN electrocatalyst displayed an overpotential () of 110 and 310 mV, with current density values of 8.3 x 10-4 and 4.5 x 10-2 A/cm-2, for HER and OER, respectively. Moreover, the catalyst exhibited excellent stability, retaining over 86.3% of its initial current density during 4000 s of chronoamperometric testing and showing negligible performance degradation after 1000 continuous linear sweep voltammetry cycles. This study aims to contribute to the advancement of multi-element, efficient and cost-effective electrocatalysts for water-splitting reactions and hydrogen fuel production. Keywords: Acetate bath; bifunctional catalysts; Co-Ni-Mn-Fe electrocatalyst; fabrication; Hydrogen evolution reaction; Oxygen evolution reaction; renewable energy.

Natural waters are exposed to significant risks of contamination by antibiotic-resistant bacteria, which pose significant environmental and health risks. Heterogeneous Fenton-type photocatalytic processes can ensure efficient pathogen removal, with advantages in terms of recycling, solid-liquid separation and by-product avoidance. In this study, an iron-modified carbon paste electrode (CPE) was proposed as catalyst. Iron atoms are deposited by electrodeposition of Fe2+ ions on the CPE surface. This ensures a more efficient synergistic Fenton-type photocatalytic reaction, generating additional hydroxyl radicals and enabling effective water disinfection. Electrochemical methods including Cyclic Voltammetry, Electrochemical Impedance Spectroscopy, Square Wave Voltammetry and Tafel lines were invested in this work. Keywords: electrochemical methods; Escherichia coli; Fenton reaction; wastewater.

Abstract Cobalt ferrites (CoFe2O4) for oxygen reduction reaction (ORR) electrocatalytic activity were synthesized by solution combustion synthesis, with varied amounts of borax as additive (10 to 50 at% B). Synthesized catalysts were characterized by X-Ray diffraction, X-Ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscopy (SEM) techniques. XPS showed the presence of Fe3+ and Co2+ in prepared samples. Brunauer-Emmet-Teller (BET) isotherms indicated the positive effect of borax as an additive on the surface area. Rotating Disk Electrode (RDE) voltammetry studies indicated that, with increasing amount of borax (10 to 50 at% B), for synthesis of CoFe2O4, ORR current density increased from 0.15 to 3.56 mA/cm2. Highest onset potential value of 0.77 V vs. reference hydrogen electrode was observed with lower Tafel slope value for FeCo, 10FeCo and 20FeCo, at 66.4, 80.9 and 75 mV/dec, respectively. Koutecky-Levich plot revealed a ~4e ORR process for 20FeCo, which was found to be the best catalyst. Keywords: borax; cobalt ferrites; electrocatalysis; oxygen reduction reaction; sustainable energy; Tafel plot.

There has been a surge in demand of electronic devices that serve better durability under adverse environmental conditions. This study investigated electrical conductivity (σDC) of samarium (BFS) and niobium (BFN) doped Biochar/ferrite-based nanocomposites (NC). NC were synthesized using sol-gel method and characterized through Fourier Transform Infrared and UV-diffuse Reflectance Spectroscopy. Structural properties and thermal stability of developed NC were analyzed through Scanning Electron Microscopy and Thermo Gravimetric Analysis. BFS and BFN-based working electrodes (WE) were fabricated by coating them over stainless-steel current collectors, and their surface morphology and electrical properties were investigated. To compare effects of Sm and Nb doping on σDC of NC, measurements of BFS and BFN were performed at variable voltages, temperatures, baking and humid environments. Results showed that BFN had better σDC (0.83 mS/cm) than from BFS counterparts, maybe due to effective incorporation of Nb ions into NC lattice, which improved charge carrier mobility. Arrhenius curve of BFS and BFN was plotted with activation energy value of 27.64 and 26.36 J/mol-1, respectively. Additionally, BFS-derived WE showed higher stability and durability in humid and baking environments. Results demonstrated that BFN can be used as potential candidates for preparing electrode materials. Keywords: biochar; DC conductivity; electrode materials; ferrite; Nb2O5; Sm2O3; working electrodes.

This paper focused on enhancing Pitzer equation and its application for calculating activity and osmotic coefficients. Proposed modification specifically addresses long-range term, as expressed by Debye-Hückel equation, which accounts for size of ions in aqueous solutions. Additionally, experimental data for osmotic and activity coefficients of 103 strong electrolyte systems, including 1-1, 1-2, 2-1, 2-2 and 3-1 electrolytes, as well as 27 ternary systems, were herein correlated. Results obtained from the modified model were compared with those from original Pitzer parameters and other existing models. Improved thermodynamic model demonstrated significant utility in efficiently computing activity and osmotic coefficients, offering an accurate representation of deviations from ideality in electrolyte solutions. Furthermore, the modified model enabled precise predictions of salt solubility in aqueous solutions containing multiple electrolytes. Keywords: osmotic and activity coefficients; Pitzer model; strong electrolytes; thermodynamic modeling.

The development of aluminum–air batteries provide a promising solution for stabilizing intermittent renewable energy sources, such as solar and wind. A significant challenge to their large-scale deployment is the stability on aluminum electrodes in the electrolyte, which presents both economic and corrosion-related challenges. Issues related to corrosion, cost and electrode thinning compromises the performance of aluminum electrodes. Nonetheless, aluminum alloys are emerging as a compelling alternative for aluminium electrodes due to their high electrochemical activity and ease of processing. Herein, an integrated framework that combines Pourbaix diagrams (PD) with finite element modeling (FEM) is proposed to systematically investigate the stability of aluminum-based electrode materials. Within this framework, PD predict the stability regions of key electro active species of aluminum and its alloys, such as Al (OH)₃, AlO₂⁻ and Al (OH)₄⁻, under various pH, concentration and temperature. PD offer a comprehensive assessment of material behavior in corrosive environments. A FEM model incorporated in the framework illustrates thinning of the electrode–electrolyte interface due to electrode corrosion. The model predictions are validated against experimental data in an inbuilt cell, showing good agreement in electrode thickness reduction and corrosion rate predictions under acidic conditions. The model shows that pure Al obtained a pit with a depth of 1.31 mm at overpotential of 1.93 V, while Al 7075 eroded into a 1.9 mm pit at 1.87 V, thus having a larger corroded area. These findings provide a foundation for screening aluminum-based electrodes based on corrosion rates and thermodynamics parameters for batteries used in energy storage systems. Keywords: Pourbaix diagram; passivation; Finite element model; Tafel polarization curve.

This is a bibliometric study of Portugaliae Electrochimica Acta (PEA) from 2008 to 2024, encompassing 558 published documents within the scope of electrochemistry. The purpose was to systematically chart the scientific output and thematic development of the journal, marking the research focus, essential contributors and collaboration networks. Relevant data were retrieved from Scopus to ensure high-quality metadata and comprehensive coverage. The study’s assessment included performance indicators such as publication and citation counts, as well as author activity measured through science mapping methods, including co-authorship, co-citation and keyword co-occurrence analysis. The results are anticipated to illustrate emergent contributing authors, institutions and countries, together with evolving research themes. Collaborative and intellectual structures are depicted through bibliometric mapping. This research helps to understand the role of the journal in the growth of electrochemical research. It provides information that can be relevant for editorial strategies, outlining prospective collaborations, or informing newcomers to the discipline. Keywords: bibliometric analysis; citation analysis; Portugaliae Electrochimica Acta; publication patterns; science mapping.

Electrooxidation behavior of 1,2-dihydroxybenzene (catechol) in the presence of isoleucine was systematically investigated in aqueous buffer solutions, over a pH range from 5 to 11, using cyclic voltammetry, differential pulse voltammetry, controlled-potential coulometry and Fourier transform infra-red spectroscopy. At higher concentrations of isoleucine, a secondary electrochemical response was observed during reverse scan, attributed to the formation of a product resulting from the reaction between o-benzoquinone and isoleucine. This product is (2S,3S)-2-((3,4-dihydroxyphenyl)amino)-3-methylpentanoic acid, which undergoes oxidation at more negative potentials than catechol. Electrochemical response was strongly influenced by both pH and isoleucine concentration, with optimal conditions identified at 70 mM isoleucine and 2 mM catechol in a buffer solution of pH 7. Overall mechanism was found to follow an electron transfer–chemical reaction–electron transfer pathway, governed by a diffusion-controlled process. These findings provide insight into amino acid–quinone interactions, and have potential implications for understanding redox processes in biological and electrochemical systems. Keywords: catechol-isoleucine adduct; controlled potential coulometry; electrosynthesis; oxidation reaction pathway; voltammetry techniques.

Abstract This experimental study investigated electrocatalytic properties of a novel device consisting of a graphite/Tuff composite electrode combined with an aqueous bioelectrolyte (0.1 M NaCl) enriched with electroactive bacteria (EcB). Systematic electrochemical analyses using cyclic voltammetry (CV) and chronoamperometry revealed that this hybrid system has promising energy storage capacities under the applied potential. The involved mechanisms combined electrochemical double-layer phenomena at the porous surface of the carbonaceous material with redox processes catalyzed by the microbial biofilm. The results demonstrate significant catalytic efficiency, resulting in high charge densities and good system stability, opening up interesting prospects for the development of energy storage solutions incorporating biological components. This original approach combines advantages of nanostructured carbon materials with catalytic properties of electroactive microorganisms. Keywords: chronoamperometry; CV; EcB.

Abstract Interaction between Human Serum Albumin (HSA) and Natamycin (NA), a widely used antifungal agent, was herein investigated using a combination of electrochemical, spectroscopic and molecular docking (MD) techniques. UV-Vis spectroscopy revealed that interaction between HSA and NA leads to structural changes in HSA, evidenced by increased absorption peaks. Electrochemical studies demonstrated that NA exhibits irreversible oxidation on a glassy carbon electrode, and its electrochemical activity decreases in presence of HSA, indicating complex formation. Thermodynamic analysis suggested that binding process is spontaneous, driven primarily by Van der Waals forces and hydrogen bonds, with a binding constant (Kb) of 6.86 × 10³, at 298 K. MD further confirmed the interaction, identifying Sudlow site I as primary binding site, with a binding energy of -8.78 kcal/mol. Keywords: human serum albumin; molecular docking; Natamycin; spectroscopy; voltammetry.

Abstract In this study, hydrated iron oxide-modified silicates (Si-Fe(n)) with varying iron concentrations were synthesized via one-step loading. Comprehensive characterization using N₂ adsorption-desorption, Fourier Transform Infrared spectrophotometer, Scanning Electron Microscope, Transmission Electron Microscopy, Energy-dispersive X-ray and X-ray Diffraction revealed that Fe incorporation preserved silica's phase composition and crystal structure (evidenced by consistent XRD peak broadening), achieved uniform iron distribution within silica matrix (EDX/TEM), with 12.5 nm average particle size, and enhanced surface area and Fe-bonded OH groups (FT-IR). These modifications correlated with improved catalytic performance in benzaldehyde oxidation, for which the reaction mechanism was elucidated. Keywords; Benzaldehyde oxidation; catalysis; Density Functional Theory; Hydrated iron oxide modified silicates.

Abstract The development of aluminum metal matrix composites (AMMC) has been advanced in recent years. For advanced engineering materials, various scientists are seeking ways to improve matrix alloys through the utilization of reinforcements. Combining hybrid reinforcements over monolithic reinforcement in matrix alloy composite development has shown to be advantageous, since hybrid reinforcements complement each other in the matrix alloy. Production route of metal matrix composites (MMC) development is germane to improving their properties. This paper reviews the synergetic effects of hybrid reinforcements for AMMC on physical-mechanical properties and microstructure of the alloy. Various production routes were discussed, and the effects of utilizing hybrid reinforcement particulates were examined. Most studies employ stir casting route for MMC production, due to its ease of production and inexpensiveness. The study revealed that the utilization of hybrid reinforcements in MMC improves mechanical properties, with their even dispersion. Improvements in composites’ strength are linked to three mechanisms: Hall-Petch, coefficient of thermal expansion and Orowan’s strengthening mechanisms. Future research perspectives, such as novel processing techniques for MMC production, long-term performance and reliability examination on developed hybrid composites, were suggested to be further studied. Keywords: advanced engineering materials; composite materials; hybrid reinforcement; mechanical engineering; metal matrix composites.

Abstract Understanding how ionizing radiation affects insulating materials is essential for maintaining the reliability and safety of high-voltage systems operating in radiation-prone environments that use mineral insulating oil. In this research, mineral insulating oil was irradiated with gamma rays from a cobalt source of Co60, with a radioactivity of 70 kcl. The irradiation process was carried out at a dose rate of 8.9 kGy/h, and doses up to 250 kGy were used. This study focused on density factor. Other parameters such as moisture content, acidity and breakdown voltage were measured according to internationally recognized standards. Fourier transform infrared spectroscopy (FTIR) was also used to detect changes in oil’s chemical composition. Results indicated that gamma radiation caused a decrease in oil density, with the lowest value of 0.853 mg/cm3. These changes were effectively modeled using polynomial regression, with a high correlation coefficient (R²) of 0.982, demonstrating the model’s reliability in capturing the relationship between radiation dose and density change. Keywords: dielectric; density; gamma irradiation; mineral oil.

Concerns about environmental pollution and depletion of petroleum and coal supplies in the twenty-first century have prompted a shift towards more sustainable and environmentally friendly alternatives. Lignocellulosic biomass (LCB), which contains hemicellulose, lignin (Ln), and cellulose, is a widely available natural bioresource. Ln, a natural biopolymer, has become more recognized as a valuable material with economic uses. The current research provides in-depth information on the evolution of phenol, from an impediment to a bridge connecting many industries with diverse applications. Successful valorization of Ln for the production of bio-based platforms, fuels, and chemical products has been the subject of extensive investigation. Understanding Ln properties and factors that influence its conversion into useful products might help optimize biomass utilization. Improved bioprocessing processes can convert LCB components into value-added products, including Ln. This study summarises and compares current improvements in Ln extraction, along with depolymerization technologies that might improve bioprocessing cost-effectiveness. Commercial importance of Ln-derived goods, such as aromatics, biological polymers, and biofuels, including agrochemicals, is also addressed. Most recent trends in Ln conversion into value-added compounds, and current technical and commercial applications of Ln that have economic significance are herein discussed. Keywords: agricultural waste; Bf; Bm; LCB; Ln extraction.

The following work presents a new method that aims to study the quality of toothpastes, in particular, excessive presence of fluoride, which is a corrosive agent for dental alloys. Results showed that the proposed method allowed analysis of electrochemical properties from compounds that exist in these oral hygiene products, generally based on the concentration effect of fluoride present in toothpastes. Excess doses of fluoride can cause serious effects, such as corrosion of dental alloys. Cyclic voltammetry (CV), linear voltammetry (LV) and electrochemical impedance spectroscopy (EIS) curves were herein recorded to identify characteristic electrochemical signals of different ingredients, in particular, fluoride concentration Keywords: CV; EIS, fluor; LV; toothpastes.

Agricultural residues are being explored as sustainable energy sources to mitigate global warming and reduce greenhouse gas emissions. This study investigates biofuel production from a free-fall reactor using sugarcane bagasse (SCB) and cassava rhizome (CR) as feedstocks, employing both experimental and modelling approaches. Pyrolysis was conducted with varying SCB-CR blend ratios, from 400 to 650 °C, with a 30 min residence time, to analyse yields of biochar, bio-oil and biogas. Ultimate and proximate analyses were performed on feedstocks and biofuels, to determine their properties. Mathematical models for biofuel yields were developed using multi-expression programming (MEP), and validated against multilinear regression (MLR). Optimal 50:50 SCB-CR composition produced the highest bio-oil yield of 36.2%, with a heating value of 23.6 MJ/kg, at 550 °C, alongside with 16.2% biochar and 47.6% biogas. MEP models demonstrated superior accuracy, with R² values of 0.974, 0.917 and 0.774, for biochar, bio-oil and biogas, respectively, outperforming MLR models. Results indicate that co-pyrolysis of SCB and CR enhanced biofuel yield and quality, due to synergistic effects. Integration of experimental data with modelling provides a pathway in optimizing process parameters for large-scale biofuel production. Keywords: biofuel; CR; modelling; MEP; pyrolysis; SCB.

Nanocomposites (NC) derived from electrically conductive polymers have emerged as promising materials for advanced applications in sensors, semiconductors and supercapacitors. The performance of these materials is critically influenced by environmental factors, with humidity exposure (HE) playing a pivotal role in determining their thermal and electrical behaviours. PIN, recognized for its high redox activity, tunable conductivity and thermal stability, has been integrated with WC, a material known for its exceptional hardness, wear resistance, high electrical conductivity (σDC) and thermal resilience. In this study, a novel series of NC electro polymers with WC were synthesized via FeCl₃-initiated chemical oxidative polymerization of indole in CTAB presence. WC was incorporated at varying wt% (5, 10 and 15), to assess its impact on the composites’ properties. Influence of relative humidity (40%) on thermal stability and σDC of NC was systematically evaluated. Structural and morphological analyses were performed to elucidate composites’ conductivity, stability and reliability under fluctuating humidity conditions. Results revealed that inclusion of WC significantly enhanced thermal and electrical properties of PIN, while providing superior resistance to humidity-induced degradation. Notably, NC with 15 wt% WC exhibited highest σDC, achieving 36.4mS/cm after 6h of HE. These findings highlight NC’s potential as robust materials for diverse applications in industrial, environmental, medical and agricultural domains, where stability under variable humidity conditions is paramount. Keywords:band gap; conductivity; HE; nanocomposite; PIN; WC.

This work focused on the electrochemical behaviour of a silver (Ag) deposit, from a mirror factory effluent, on the surface of an aluminium electrode. To carry out this study, two samples were taken from the same location of the mirror factory, before and after copper plating. Different applied potentials were selected based on results obtained from linear sweep voltammetry (LSV) analysis (potential window). Based on chronoamperometry (CA) measurements and electrochemical impedance spectroscopy (EIS) results, it can be seen that applied potentials affected the Ag deposit’s electrochemical behaviour, proving that it tended to be favoured by cathodic potential. Keywords: Ag recovery; CA; electrochemical behaviour; electrodeposition; EIS; LSV; SEM; EDS; XRD; XRF.