Long-term evaluation of soil-based bioelectrochemical green roof systems for greywater treatment.

Water scarcity has generated the need to identify new sources. Due to its low organic contaminant load, greywater reuse has emerged as a potential alternative. Moreover, the search for decentralized treatment systems in urban areas has prompted research on using green roofs for greywater treatment. However, the performance of organic matter removal is limited by the type of substrate and height of the growing media. Bioelectrochemical systems (BESs) improve treatment performance by providing an additional electron acceptor (the electrode). In this study, nine reactors under three different conditions, i.e., open circuit (OC), microbial fuel cell (MFC), and microbial electrolysis cell (MEC), were built to evaluate the treatment of synthetic greywater in a substrate-growing medium composed of perlite and coconut fiber and operated in batch-cycle mode for 397 days. The results suggested that using BESs enables greywater treatment and the removal of pollutants to levels that allow their reuse for irrigation. Furthermore, electrical conductivity was reduced from 732.4 ± 41.2 µS/cm2 in OC to 637.32 ± 22.73 µS/cm2 and 543.15 ± 19.69 µS/cm2 in MEC and MFC, respectively. The soluble chemical oxygen demand in the latter treatments reached 76% removal, compared to levels above the OC, which only reached approximately 67%. Microbial community analysis revealed differences, mainly in the cathodes, showing a higher development of Flavobacterium, Azospirillum, and Zoogloea in MFCs, which could explain the higher levels of organic matter removal in the other conditions, suggesting that the BES could produce an enrichment of beneficial bacterial groups for treatment. Therefore, implementing BESs in green roofs enables sustainable long-term greywater treatment.

Reduction of Toxic Metal Ions and Production of Bioelectricity through Microbial Fuel Cells Using Bacillus marisflavi as a Biocatalyst.

Industrialization has brought many environmental problems since its expansion, including heavy metal contamination in water used for agricultural irrigation. This research uses microbial fuel cell technology to generate bioelectricity and remove arsenic, copper, and iron, using contaminated agricultural water as a substrate and Bacillus marisflavi as a biocatalyst. The results obtained for electrical potential and current were 0.798 V and 3.519 mA, respectively, on the sixth day of operation and the pH value was 6.54 with an EC equal to 198.72 mS/cm, with a removal of 99.08, 56.08, and 91.39% of the concentrations of As, Cu, and Fe, respectively, obtained in 72 h. Likewise, total nitrogen concentrations, organic carbon, loss on ignition, dissolved organic carbon, and chemical oxygen demand were reduced by 69.047, 86.922, 85.378, 88.458, and 90.771%, respectively. At the same time, the PDMAX shown was 376.20 ± 15.478 mW/cm2, with a calculated internal resistance of 42.550 ± 12.353 Ω. This technique presents an essential advance in overcoming existing technical barriers because the engineered microbial fuel cells are accessible and scalable. It will generate important value by naturally reducing toxic metals and electrical energy, producing electric currents in a sustainable and affordable way.

Insights in Pt-based electrocatalysts on carbon supports for electro-oxidation of carbohydrates: an EIS-DEMS analysis.

In this work, the electrochemical oxidation of carbohydrates (glucose, fructose, and sucrose) was induced at the interface of Pt-nanoparticles supported on different carbon-based materials as carbon vulcan (C) and carbon black (CB). It was found that the support plays an important role during carbohydrates electro-oxidation as demonstrated by electrochemical techniques. In this context, current-concentration profiles of the redox peaks show the behavior of the pathways at carbohydrates-based solutions. Herein, the trend of current measured was glucose > sucrose > fructose, attributed to differences in the organic functional groups and chain-structure. Raman, XRD, SEM-EDS and XPS put in clear important structural, morphological, and electronic differences linked with the intrinsic nature of the obtained material. Differential Electrochemical Mass Spectroscopy (DEMS) indicated that the selectivity and the conversion of the formed reaction products during oxidation is linked with the catalyst nature (distribution, particle size) and the interaction with the carbon-based support.

Methanol Oxidation Reaction in Alkaline Media Using Gold Nanoparticles Recovered from Electronic Waste.

This study investigates the potential of using gold nanoparticles (Au NPs) synthesized from e-waste as electrocatalysts for the methanol oxidation reaction (MOR), with the aim of applying them as an anode in alkaline direct methanol fuel cells (ADMFCs). The research addresses the pressing environmental challenge of e-waste disposal and explores the recycling of e-waste to obtain valuable materials for sustainable applications. Vulcan-supported gold nanoparticles (Aue-w/C NPs) are synthesized from gold coatings recovered from Intel Pentium 4 processor pins, demonstrating the feasibility of e-waste as electrocatalyst precursors. Comprehensive characterization techniques such as UV-Vis spectroscopy, high-resolution transmission and transmission electron microscopy (HR-TEM, TEM), selected area electron diffraction (SAED), scanning electron microscopy (SEM), and X-ray diffraction (XRD) are employed to evaluate the structural properties of the electrocatalyst. Electrochemical evaluation in 0.5 M KOH electrolyte by cyclic voltammetry reveals that the synthesized Aue-w/C NPs exhibit electrocatalytic activity (25.5 mA·mg-1Au) comparable to their commercially synthesized counterparts (30.1 mA·mg-1Au). This study highlights the potential for sustainable approaches in the production of electrocatalysts by utilizing e-waste as a source of valuable catalyst materials. It represents a pioneering effort in harnessing e-waste as a sustainable resource, offering new avenues for sustainable energy technologies while addressing environmental concerns and technological challenges in the field of ADMFCs.

Obtaining Electrospun Membranes of Chitosan/PVA and TiO2 as a Solid Polymer Electrolyte with Potential Application in Ion Exchange Membranes.

A binary polymeric blend was prepared using chitosan (CS) and polyvinyl alcohol (PVA) at a ratio of 80:20, respectively, to obtain a solid polymeric electrolyte with possible application for the generation of an electric current in proton or anion exchange electrochemical cells. With a 6% m/m solution, a membrane was formed using the electrospinning technique, and the influence of the incorporation of titanium oxide (TiO2) nanoparticles, at a concentration between 1000 and 50,000 ppm, on the physicochemical properties of the material was evaluated. The micrographs obtained by SEM revealed that the diameter of the nanofibers was close to 100 nm. Likewise, it was found that the incorporation of the nanoparticles affected the moisture absorption of the material, reaching a predominantly hydrophobic behavior in the composite with the highest concentrations of these (2% absorption), while for the lowest content of the filler, the absorption reached values close to 13%. On the other hand, Thermogravimetric Analysis (TGA) showed lower dehydration in the fibrous composite with a 1000 ppm TiO2 content, while Differential Scanning Calorimetry (DSC) showed that these nanoparticles did not significantly affect the thermal transition (Tm) of the composite. Additionally, with the incorporation of nanoparticles, a shift in the Tg from 44 to 37 °C was found concerning the unfilled binary membrane, which increased the possibility of achieving higher ionic conductivities with the nanocomposites at room temperature. Complex Impedance Spectroscopy determined the material's activation energy, decreasing this by adding the TiO2 filler at a concentration of 1000 ppm. On the other hand, when the membranes were doped with a 1 M KOH solution, the fibrous structure of the membrane changed to a porous cork-like configuration. In future research, the electrospun membrane could be used in the development of a composite to validate the energy efficiency of the new solid polymer electrolyte.

Synthetic Biology Toolkit for a New Species of Pseudomonas Promissory for Electricity Generation in Microbial Fuel Cells.

Microbial fuel cells (MFCs) offer sustainable solutions for various biotechnological applications and are a crucial area of research in biotechnology. MFCs can effectively treat various refuse, such as wastewater and biodiesel waste by decomposing organic matter and generating electricity. Certain Pseudomonas species possess extracellular electron transfer (EET) pathways, enabling them to transfer electrons from organic compounds to the MFC's anode. Moreover, Pseudomonas species can grow under low-oxygen conditions, which is advantageous considering that the electron transfer process in an MFC typically leads to reduced oxygen levels at the anode. This study focuses on evaluating MFCs inoculated with a new Pseudomonas species grown with 1 g.L-1 glycerol, a common byproduct of biodiesel production. Pseudomonas sp. BJa5 exhibited a maximum power density of 39 mW.m-2. Also, the observed voltammograms and genome analysis indicate the potential production of novel redox mediators by BJa5. Additionally, we investigated the bacterium's potential as a synthetic biology non-model chassis. Through testing various genetic parts, including constitutive promoters, replication origins and cargos using pSEVA vectors as a scaffold, we assessed the bacterium's suitability. Overall, our findings offer valuable insights into utilizing Pseudomonas spp. BJa5 as a novel chassis for MFCs. Synthetic biology approaches can further enhance the performance of this bacterium in MFCs, providing avenues for improvement.

Design, Development and Testing of a Monitoring System for the Study of Proton Exchange Fuel Cells and Stacks.

This article is about the design, development and validation of a new monitoring architecture for individual cells and stacks to facilitate the study of proton exchange fuel cells. The system consists of four main elements: input signals, signal processing boards, analogue-to-digital converters (ADCs) and a master terminal unit (MTU). The latter integrates a high-level graphic user interface (GUI) software developed by National Instruments LABVIEW, while the ADCs are based on three digital acquisition units (DAQs). Graphs showing the temperature, currents and voltages in individual cells as well as stacks are integrated for ease of reference. The system validation was carried out both in static and dynamic modes of operation using a Ballard Nexa 1.2 kW fuel cell fed by a hydrogen cylinder, with a Prodigit 32612 electronic load at the output. The system was able to measure the voltage distributions of individual cells, and temperatures at different equidistant points of the stack both with and without an external load, validating its use as an indispensable tool for the study and characterization of these systems.

The Role of a Sn Promoter on an Anodic Pt Electrocatalyst Prepared over H2 O2 -Functionalized Carbon Supports for Direct Ethanol Fuel Cell (DEFC) Applications.

Multiwalled carbon nanotubes and Vulcan carbon were functionalized with a 30 %v/v hydrogen peroxide solution and employed as supports for Pt and PtSn catalysts prepared by the polyol method. PtSn catalysts with a Pt loading of 20 wt.% and a Pt : Sn atomic ratio equal to 3 : 1 were evaluated in the ethanol electrooxidation reaction. The effects of the oxidizing treatment on the surface area and the surface chemical nature were analyzed through N2 adsorption, isoelectric point, and temperature-programmed desorption measurements. Results showed that the H2 O2 treatment affects the surface area of the carbons to a great extent. Characterization results indicated that the performance of the electrocatalysts strongly depends both on the presence of Sn and on the support functionalization. PtSn/CNT-H2 O2 electrocatalyst displays a high electrochemical surface area and enhanced catalytic activity for ethanol oxidation in comparison to other catalysts in the present study.

Transition metal chalcogenides carbon-based as bifunctional cathode electrocatalysts for rechargeable zinc-air battery: An updated review.

The rechargeable alkaline aqueous zinc-air batteries (ZABs) are prospective candidates to supply the energy demand for their high theoretical energy density, inherent safety, and environmental friendliness. However, their practical application is mainly restricted by the unsatisfactory efficiency of the air electrode, leading to an intense search for high-efficient oxygen electrocatalysts. In recent years, the composites of carbon materials and transition metal chalcogenides (TMC/C) have emerged as promising alternatives because of the unique properties of these single compounds and the synergistic effect between them. In this sense, this review presented the electrochemical properties of these composites and their effects on the ZAB performance. The operational fundamentals of the ZABs were described. After elucidating the role of the carbon matrix in the hybrid material, the latest developments in the ZAB performance of the monometallic structure and spinel of TMC/C were detailed. In addition, we report topics on doping and heterostructure due to the large number of studies involving these specific defects. Finally, a critical conclusion and a brief overview sought to contribute to the advancement of TMC/C in the ZABs.

Passivity-Based Control for Output Voltage Regulation in a Fuel Cell/Boost Converter System.

In this paper, a passivity-based control (PBC) scheme for output voltage regulation in a fuel-cell/boost converter system is designed and validated through real-time numerical results. The proposed control scheme is designed as a current-mode control (CMC) scheme with an outer loop (voltage) for voltage regulation and an inner loop (current) for current reference tracking. The inner loop's design considers the Euler-Lagrange (E-L) formulation to implement a standard PBC and the outer loop is implemented through a standard PI controller. Furthermore, an adaptive law based on immersion and invariance (I&I) theory is designed to enhance the closed-loop system behavior through asymptotic approximation of uncertain parameters such as load and inductor parasitic resistance. The closed-loop system is tested under two scenarios using real-time simulations, where precision and robustness are shown with respect to variations in the fuel cell voltage, load, and output voltage reference.

Electric Current Generation by Increasing Sucrose in Papaya Waste in Microbial Fuel Cells.

The accelerated increase in energy consumption by human activity has generated an increase in the search for new energies that do not pollute the environment, due to this, microbial fuel cells are shown as a promising technology. The objective of this research was to observe the influence on the generation of bioelectricity of sucrose, with different percentages (0%, 5%, 10% and 20%), in papaya waste using microbial fuel cells (MFCs). It was possible to generate voltage and current peaks of 0.955 V and 5.079 mA for the cell with 20% sucrose, which operated at an optimal pH of 4.98 on day fifteen. In the same way, the internal resistance values of all the cells were influenced by the increase in sucrose, showing that the cell without sucrose was 0.1952 ± 0.00214 KΩ and with 20% it was 0.044306 ± 0.0014 KΩ. The maximum power density was 583.09 mW/cm2 at a current density of 407.13 A/cm2 and with a peak voltage of 910.94 mV, while phenolic compounds are the ones with the greatest presence in the FTIR (Fourier transform infrared spectroscopy) absorbance spectrum. We were able to molecularly identify the species Achromobacter xylosoxidans (99.32%), Acinetobacter bereziniae (99.93%) and Stenotrophomonas maltophilia (100%) present in the anode electrode of the MFCs. This research gives a novel use for sucrose to increase the energy values in a microbial fuel cell, improving the existing ones and generating a novel way of generating electricity that is friendly to the environment.

Use of Onion Waste as Fuel for the Generation of Bioelectricity.

The enormous environmental problems that arise from organic waste have increased due to the significant population increase worldwide. Microbial fuel cells provide a novel solution for the use of waste as fuel for electricity generation. In this investigation, onion waste was used, and managed to generate maximum peaks of 4.459 ± 0.0608 mA and 0.991 ± 0.02 V of current and voltage, respectively. The conductivity values increased rapidly to 179,987 ± 2859 mS/cm, while the optimal pH in which the most significant current was generated was 6968 ± 0.286, and the ° Brix values decreased rapidly due to the degradation of organic matter. The microbial fuel cells showed a low internal resistance (154,389 ± 5228 Ω), with a power density of 595.69 ± 15.05 mW/cm2 at a current density of 6.02 A/cm2; these values are higher than those reported by other authors in the literature. The diffractogram spectra of the onion debris from FTIR show a decrease in the most intense peaks, compared to the initial ones with the final ones. It was possible to identify the species Pseudomona eruginosa, Acinetobacter bereziniae, Stenotrophomonas maltophilia, and Yarrowia lipolytica adhered to the anode electrode at the end of the monitoring using the molecular technique.

Rumen Inoculum Enhances Cathode Performance in Single-Chamber Air-Cathode Microbial Fuel Cells.

During the last decade, bioprospecting for electrochemically active bacteria has included the search for new sources of inoculum for microbial fuel cells (MFCs). However, concerning power and current production, a Geobacter-dominated mixed microbial community derived from a wastewater inoculum remains the standard. On the other hand, cathode performance is still one of the main limitations for MFCs, and the enrichment of a beneficial cathodic biofilm emerges as an alternative to increase its performance. Glucose-fed air-cathode reactors inoculated with a rumen-fluid enrichment and wastewater showed higher power densities and soluble chemical oxygen demand (sCOD) removal (Pmax = 824.5 mWm-2; ΔsCOD = 96.1%) than reactors inoculated only with wastewater (Pmax = 634.1 mWm-2; ΔsCOD = 91.7%). Identical anode but different cathode potentials suggest that differences in performance were due to the cathode. Pyrosequencing analysis showed no significant differences between the anodic community structures derived from both inocula but increased relative abundances of Azoarcus and Victivallis species in the cathodic rumen enrichment. Results suggest that this rarely used inoculum for single-chamber MFCs contributed to cathodic biofilm improvements with no anodic biofilm effects.

Enhancement of the electron transfer and ion transport phenomena in microbial fuel cells containing humic acid-modified bioanodes.

Although microbial fuel cells (MFCs) are an attractive alternative to environmental remediation and power generation, there are still significant limitations related to power density and coulombic efficiency. Previous works have shown that the addition of humic acids (HA, a type of organic matter contained in soils and composting-by-products), improves the fuel to electricity conversion at the porous bioanodes (ba)|anolyte junction. In this work, MFCs having HA-modified bioanodes (MFC/baHA) were prepared and electrochemically analyzed utilizing discharge curves (cell potential vs current density plots) and electrochemical impedance spectroscopy (EIS). This investigation was motivated by looking for a deeper understanding of the functional effects of HA molecules on the operation of baHA-containing Microbial Fuel Cells (MFC/baHA). Our results revealed that the modification of bioanodes with HA molecules decreases the activation energy of the acetate ion oxidation, increasing by a factor of three the consumption rate of this fuel at the baHA|anolyte interface, and enhancing the diffusive transport of these ions through the pores of the baHA permeated by the anolyte.

Pt-Free Metal Nanocatalysts for the Oxygen Reduction Reaction Combining Experiment and Theory: An Overview.

The design and manufacture of highly efficient nanocatalysts for the oxygen reduction reaction (ORR) is key to achieve the massive use of proton exchange membrane fuel cells. Up to date, Pt nanocatalysts are widely used for the ORR, but they have various disadvantages such as high cost, limited activity and partial stability. Therefore, different strategies have been implemented to eliminate or reduce the use of Pt in the nanocatalysts for the ORR. Among these, Pt-free metal nanocatalysts have received considerable relevance due to their good catalytic activity and slightly lower cost with respect to Pt. Consequently, nowadays, there are outstanding advances in the design of novel Pt-free metal nanocatalysts for the ORR. In this direction, combining experimental findings and theoretical insights is a low-cost methodology-in terms of both computational cost and laboratory resources-for the design of Pt-free metal nanocatalysts for the ORR in acid media. Therefore, coupled experimental and theoretical investigations are revised and discussed in detail in this review article.

Life cycle inventory data for power production from sugarcane press-mud.

This data article is associated with the research article "Technical and environmental analysis on the power production from residual biomass using hydrogen as energy vector". This paper shows the procedure to calculate the Life Cycle Inventory (LCI) of the foreground system to perform the Life Cycle Assessment (LCA) of the power production from sugarcane press-mud. Said process encompasses four main stages: i) bioethanol production; ii) bioethanol purification; iii) syngas production and purification; and iv) power production. Additionally, other processes such as biomethane production and manufacturing of catalyst were included. Foreground data related to bioethanol production was gathered from experimental procedures at lab-scale. While foreground data, concerning the other processes such as bioethanol purification, syngas production and purification, power production, and biomethane production, was built by using material and energy flows obtained from Aspen Plus®. Lastly, LCI of the catalyst manufacturing was built based on literature review and the approach stated by Ecoinvent. All the inventories are meaningful to carry out future environmental assessments involving sustainable energy systems based on bioethanol, biomethane, or hydrogen.

A review of recent advances in electrode materials for emerging bioelectrochemical systems: From biofilm-bearing anodes to specialized cathodes.

Bioelectrochemical systems (BES), mainly microbial fuel cells (MEC) and microbial electrolysis cells (MFC), are unique biosystems that use electroactive bacteria (EAB) to produce electrons in the form of electric energy for different applications. BES have attracted increasing attention as a sustainable, low-cost, and neutral-carbon option for energy production, wastewater treatment, and biosynthesis. Complex interactions between EAB and the electrode materials play a crucial role in system performance and scalability. The electron transfer processes from the EAB to the anode surface or from the cathode surface to the EAB have been the object of numerous investigations in BES, and the development of new materials to maximize energy production and overall performance has been a hot topic in the last years. The present review paper discusses the advances on innovative electrode materials for emerging BES, which include MEC coupled to anaerobic digestion (MEC-AD), Microbial Desalination Cells (MDC), plant-MFC (P-MFC), constructed wetlands-MFC (CW-MFC), and microbial electro-Fenton (BEF). Detailed insights on innovative electrode modification strategies to improve the electrode transfer kinetics on each emerging BES are provided. The effect of materials on microbial population is also discussed in this review. Furthermore, the challenges and opportunities for materials scientists and engineers working in BES are presented at the end of this work aiming at scaling up and industrialization of such versatile systems.

Data that support the structural, chemical and morphological characterization and its influence on the electrochemical performance of stabilized PdxPt1-x alloys as electrode materials for methanol oxidation in alkaline medium.

Structural, compositional, morphological and electrochemical characterization are important to determinate the influence of platinum in the methanol oxidation in alkaline media. These data and analysis support the research article catalytic performance of alloyed PtxPd1-x nanostructures supported on Vulcan XC-72R for the methanol oxidation in alkaline medium [1]. The data here presented included changes in the chemical composition, structure and microstructure. Also, complement data of cyclic voltammograms during activation in alkaline media as well as in presence of 1 M CH3OH to observe CO tolerance and Electrochemical Impedance Spectroscopy measurements at two different overpotentials (0.2 and 0.3 mV) on the onset potential for methanol electro-oxidation are published in this paper. The data can be used as a reference to determinate the effect of added different amounts of Pd to Pt/C catalysts, using an organometallic compounds method and octylamine as stabilizer. The data provided in this article have not been previously published and are available to enable critical or extended analyses.

Coupled Dynamics of Anode and Cathode in Proton-Exchange Membrane Fuel Cells.

An external reference electrode was used to monitor individually the evolution of the anodic and cathodic potentials during the stationary as well as oscillatory operation of a Direct Formic Acid Fuel Cell (DFAFC) and a Direct Methanol Fuel Cell (DMFC). Besides evidencing the large activation loss in both cells, we were able to observe how the oscillatory operation of such devices affects their cathodes. In fact, cathodic oscillations synchronized with the cell voltage dynamics were observed, hitherto never reported on fuel cells. We have addressed these phenomena taking into account two main coupling processes: through the proton concentration and a global coupling stemming from the control mode (potentiostatic or galvanostatic).

A Flexible Microsupercapacitor with Integral Photocatalytic Fuel Cell for Self-Charging.

With the rapid advancement in different kinds of portable electronics, self-powered systems with small volume and high-performance characteristics have attracted great attention in recent years. It would be rather exciting if one integrated system can not only convert recyclable energy or waste to electricity but also store energy at the same time. Here, flexible all-in-one energy chips composed of urea-based photocatalytic fuel cells (PFCs) and asymmetric microsupercapacitors (AMSCs) are designed on the same plane for powering small portable electronics. The planar PFC consisting of TiO2 photoanode and Ag counter electrode, utilizing urea as fuel, can produce a stable energy output (highest power density of 3.04 µW cm-2 in 1 M urea solution under a UV intensity of 30 mW cm-2) while purify this wasted water simultaneously. Besides, the AMSC comprised of NiCoP@NiOOH positive electrode and zeolite imidazolide framework derived carbon (ZIF-C) negative electrode achieves a high areal capacitance of 54.7 mF cm-2 at 0.5 mA cm-2 and an excellent energy density of 13.9 µWh cm-2 at the power density of 270.5 µW cm-2. Its stability can be confirmed by 86% capacitance retention after 8000 electrochemical cycles and almost no decay after 500 bending cycles. Four PFCs and two AMSCs can be easily constructed into an energy chip and power small electronics. This eco-friendly and self-sustainable system has great potential in future portable electronics.