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.

Brake pads in automobiles are crucial, since their effectiveness determines the safety of vehicles in operation. Alternatives for brake pad liners are continuously being researched as a way of replacing detrimental materials such as asbestos and graphite. This research was aimed at developing some eco-friendly brake pad liners with agro-residue materials. The brake pad liners were produced using compression moulding employing particle sizes of three different sieve ranges of 400-300, 300-250 and 400-00 µm. The composite materials for brake pad liners production included seashell, sawdust, palm kernel shell (PKS) and charcoal, serving the functions of structural, filler, abrasive and lubricant, respectively, while the binder used to hold the composite together was epoxy resin (polyepoxide) mixed with hardener (diethylenediamine) in 2:1 ratio. Microstructural analysis conducted on three samples, formulated based on selected sieve ranges, displayed the composite arrangement in the formulation, and the effect of particle sizes. Sample C (400-00 µm) displayed an evenly distributed and closely packed particle sample. Results revealed that hardness of the composite material decreased with smaller sieve ranges. Sample C, with the compressive strength of 4.0839 MPa, had lowest hardness value and highest thermal stability of 394 ºC, with corrosion rate of 0.0056 mm/yr. Keywords: automobile; brake pad; hardness; microstructure; structural material.

This study investigated theoretical methane potential (TMP)and biochemical methane potential (BMP) of Longkong (Lk) waste (peel and seed) and fruit pulp, and Napier grass (NG). TMP values were calculated using modified Buswell stoichiometric equation, while BMP assays were conducted to determine methane (CH4) production. TMP results showed that Lk waste had higher theoretical CH4 yield (0.5 L/g) of volatile solids (VS) than that from Lk pulp (0.39 L/g VS) and NG (0.46 L/g VS). BMP results showed that measured CH4 yield was 0.21, 0.3 and 0.33 L/g VS for Lk waste, Lk pulp and NG, respectively. Lk peel is a more suitable substrate for biogas production compared to its pulp, due to high moisture content, low alkalinity and high volatile fatty acid of the latter. CH4 potential of the three substrates compared favorably with those of others such as grapes and banana peels. The study recommends Lk peels and its leftover pulp for biogas production in regions with high cultivation. Keywords: biochemical methane potential; biogas; Duolong’s energy equation; modified Buswell stoichiometric equation; modified Gompertz equation; theoretical methane potentials.

Carbon paste electrode modified with zinc oxide (ZnO) nanoparticles was developed for Eugenol’s (Eg) electrochemical detection. Eg’s electrochemical behavior was investigated using Cyclic Voltammetry, Electrochemical Impedance Spectroscopy and Square Wave Voltammetry. ZnO-modified electrode exhibited enhanced sensitivity and low limit of detection, enabling Eg’s precise quantification. Eg’s concentration in the extract was found to be 12.84 µM. Keywords: chemically modified electrodes; Cyclic Voltammetry; Eugenol; Electrochemical Impedance Spectroscopy; Square Wave Voltammetry.

Density functional theory (DFT) has been used to calculate electrical and photovoltaic properties of diaminonaphthalene and its derivatives, and optimize them. Findings demonstrated that time-dependent DFT investigations employing Coulomb-attenuated hybrid method with polarized split-valence 6-311G (d,p) basis sets and polarizable continuum model were able to predict excitation energies and spectra of the compounds in a reasonable manner. Levels of Energy of Highest Occupied and Lowest Unoccupied Molecular Orbitals from these compounds can have a positive effect on electron injection and dye renewal processes. Energy gap, short-circuit current density, light-harvesting efficiency, thermodynamic injection driving force and open-circuit photovoltage allowed for qualitative predictions about the reactivity of the different dyes. Keywords: density functional theory; diaminonaphthalene; dye-sensitized solar cells; electronic and optical properties.

This article investigates the influence of inorganic electrolyte solutions on the efficiency of cleaning steel surfaces from oil contamination. Using an electrochemical method, it was demonstrated that electrolyte solutions, compared with pure water, significantly reduce free surface energy at the metal–solution interface due to the formation of a double electric layer and oxidation of the metal surface. However, complete cleaning is hindered by the presence of an oil barrier, the overcoming of which requires combined use of electrolytes and organic surfactants. Future research will be devoted to studying this combined effect on the cleaning process. Keywords: degreasing; double electric layer; electrochemical method; electrolytes; interphase boundary; metal cleaning; surfactants.