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.