Carbon-based air-breathing cathodes for microbial fuel cells

© 2016 by the authors; licensee MDPI, Basel, Switzerland. A comparison between different carbon-based gas-diffusion air-breathing cathodes for microbial fuel cells (MFCs) is presented in this work. A micro-porous layer (MPL) based on carbon black (CB) and an activated carbon (AC) layer were used as catalysts and applied on different supporting materials, including carbon cloth (CC), carbon felt (CF), and stainless steel (SS) forming cathode electrodes for MFCs treating urine. Rotating ring disk electrode (RRDE) analyses were done on CB and AC to: (i) understand the kinetics of the carbonaceous catalysts; (ii) evaluate the hydrogen peroxide production; and (iii) estimate the electron transfer. CB and AC were then used to fabricate electrodes. Half-cell electrochemical analysis, as well as MFCs continuous power performance, have been monitored. Generally, the current generated was higher from the MFCs with AC electrodes compared to the MPL electrodes, showing an increase between 34% and 61% in power with the AC layer comparing to the MPL. When the MPL was used, the supporting material showed a slight effect in the power performance, being that the CF is more powerful than the CC and the SS. These differences also agree with the electrochemical analysis performed. However, the different supporting materials showed a bigger effect in the power density when the AC layer was used, being the SS the most efficient, with a power generation of 65.6 mW·m−2, followed by the CC (54 mW·m−2) and the CF (44 mW·m−2)

Transition metal-nitrogen-carbon catalysts for oxygen reduction reaction in neutral electrolyte

© 2016 The Authors Platinum group metal-free (PGM-free) catalysts based on M-N-C types of materials with M as Mn, Fe, Co and Ni and aminoantipyrine (AAPyr) as N-C precursors were synthesized using sacrificial support method. Catalysts kinetics of oxygen reduction reaction (ORR) was studied using rotating ring disk electrode (RRDE) in neutral pH. Results showed that performances were distributed among the catalysts as: Fe-AAPyr>Co-AAPyr>Mn-AAPyr>Ni-AAPyr. Fe-AAPyr had the highest onset potential and half-wave potential. All the materials showed similar limiting current. Fe-AAPyr had an electron transfer involving 4e− with peroxide formed lower than 5%. Considering H2O2 produced, it seems that Co-AAPyr, Mn-AAPyr and Ni-AAPyr follow a 2×2e− mechanism with peroxide formed during the intermediate step. Durability test was done on Fe-AAPyr for 10,000cycles. Decrease of activity was observed only after 10,000cycles

Influence of platinum group metal-free catalyst synthesis on microbial fuel cell performance

© 2017 The Authors Platinum group metal-free (PGM-free) ORR catalysts from the Fe-N-C family were synthesized using sacrificial support method (SSM) technique. Six experimental steps were used during the synthesis: 1) mixing the precursor, the metal salt, and the silica template; 2) first pyrolysis in hydrogen rich atmosphere; 3) ball milling; 4) etching the silica template using harsh acids environment; 5) the second pyrolysis in ammonia rich atmosphere; 6) final ball milling. Three independent batches were fabricated following the same procedure. The effect of each synthetic parameters on the surface chemistry and the electrocatalytic performance in neutral media was studied. Rotating ring disk electrode (RRDE) experiment showed an increase in half wave potential and limiting current after the pyrolysis steps. The additional improvement was observed after etching and performing the second pyrolysis. A similar trend was seen in microbial fuel cells (MFCs), in which the power output increased from 167 ± 2 μW cm−2 to 214 ± 5 μW cm−2. X-ray Photoelectron Spectroscopy (XPS) was used to evaluate surface chemistry of catalysts obtained after each synthetic step. The changes in chemical composition were directly correlated with the improvements in performance. We report outstanding reproducibility in both composition and performance among the three different batches

A family of Fe-N-C oxygen reduction electrocatalysts for microbial fuel cell (MFC) application: Relationships between surface chemistry and performances

© 2016 The Author(s) Different iron-based cathode catalysts have been studied for oxygen reduction reaction (ORR) in neutral media and then applied into microbial fuel cells (MFC). The catalysts have been synthesized using sacrificial support method (SSM) using eight different organic precursors named Niclosamide, Ricobendazole, Guanosine, Succinylsulfathiazole, Sulfacetamide, Quinine, Sulfadiazine and Pyrazinamide. Linear Sweep Voltammetry (LSV) curves were obtained for the catalysts using a O2 saturated in 0.1M potassium phosphate buffer and 0.1M KCl solution and a Rotating Ring Disk Electrode (RRDE) setup in order to study the ORR characteristics. Additionally, we analyze the peroxide yield obtained for each catalyst which helps us determine the reaction kinetics. Those catalysts have been mixed with activated carbon (AC), carbon black (CB) and PTFE and pressed on a metallic mesh forming a pellet-like gas diffusion electrode (GDE). Results showed that Fe-Ricobendazole, Fe-Niclosamide and Fe-Pyrazinamide had the highest cathode polarization curves and highest power densities output that was above 200μWcm−2. Fe-Ricobendazole, Fe-Niclosamide, Fe-Pyrazinamide, Fe-Guanosine Fe-Succinylsulfathiazole and Fe-Sulfacetamide outperformed compared to Pt cathode. Fe-Sulfadiazene and Fe-Quinine performed better than AC used as control but less than Pt. Correlation of surface composition with performance showed that power density achieved is directly related to the total amount of nitrogen, and in particularly, N coordinated to metal and pyridinic and pyrrolic types while larger amounts of graphitic nitrogen result in worse performance

Clonal chromosomal mosaicism and loss of chromosome Y in elderly men increase vulnerability for SARS-CoV-2

The pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, COVID-19) had an estimated overall case fatality ratio of 1.38% (pre-vaccination), being 53% higher in males and increasing exponentially with age. Among 9578 individuals diagnosed with COVID-19 in the SCOURGE study, we found 133 cases (1.42%) with detectable clonal mosaicism for chromosome alterations (mCA) and 226 males (5.08%) with acquired loss of chromosome Y (LOY). Individuals with clonal mosaic events (mCA and/or LOY) showed a 54% increase in the risk of COVID-19 lethality. LOY is associated with transcriptomic biomarkers of immune dysfunction, pro-coagulation activity and cardiovascular risk. Interferon-induced genes involved in the initial immune response to SARS-CoV-2 are also down-regulated in LOY. Thus, mCA and LOY underlie at least part of the sex-biased severity and mortality of COVID-19 in aging patients. Given its potential therapeutic and prognostic relevance, evaluation of clonal mosaicism should be implemented as biomarker of COVID-19 severity in elderly people. Among 9578 individuals diagnosed with COVID-19 in the SCOURGE study, individuals with clonal mosaic events (clonal mosaicism for chromosome alterations and/or loss of chromosome Y) showed an increased risk of COVID-19 lethality

Nurses' perceptions of aids and obstacles to the provision of optimal end of life care in ICU

Contains fulltext : 172380.pdf (publisher's version ) (Open Access

ACTIVITY OF PGM-FREE ELECTROCATALYSTS FOR OXYGEN REDUCTION REACTION: PH AND CO-CATALYSIS EFFECTS

Fuel cells offer a source to the current and always increasing demand for electric power. But as any new technology, there are challenges that need to be addressed to render it feasible for the market place. One of this challenges is finding the appropriate materials to catalyze the oxygen reduction reaction (ORR) that occurs in the cathode. Oxygen is used as an oxidant in a significant portion of the fuel cells due to its readily availability and high reduction potential. Now, one the bottlenecks that stops the large-scale adoption is the expensive and rare metals that have been used as catalysts for this reaction. One solution to this issue came with the development of platinum-metal group free (PGM-free) catalysts, which are composed of abundant and low cost elements like carbon, nitrogen and transition metals. These PGM-free catalysts have demonstrated their ability to effectively catalyze the ORR in highly alkaline and highly acidic media, as these have been the usual operating conditions for fuel cells that they were developed for. Due to this success, these PGM-free catalysts have attracted the attention for other applications, like the use in physiological devices or in microbial fuel cells, where the pH is far away from acid or alkaline. This has led to the need to understand how to introduce PGM-free catalyst in fuel cells that operate at pHs around neutrality and to learn about the way their activity towards the ORR is affected by changes in the concentration of hydronium and hydroxyl ions. The current study addresses these two issues. To begin with, four different transition metals were used in the synthesis of the PGM-free catalysts and tested at neutral pH. It was found that the iron containing PGM-free catalyst provides the highest current densities and lower hydrogen peroxide production. This same PGM-free catalyst was compared against platinum at neutral pH and demonstrated to have higher ORR performance and stability than the precious metal catalyst. Enzymes like bilirubin oxidase (BOx) catalyze the ORR at pH around neutrality, as they were developed by the biological systems to facilitate this reaction within them. The next achievement in this study was to successfully integrate BOx onto the PGM-free catalyst, obtaining a co-catalytic effect. This led to the next discovery, which consisted in unveiling what are the chemical and morphological characteristics of the PGM-free catalyst that make the integration of the BOx optimal. The closing component of this study is the exploration of the pH effect on the surface chemistry and the electrochemical activity towards the ORR of a PGM-free catalyst. It was found that the pH has an effect in surface chemistry of the PGM-free catalyst and this leads to a change in the kinetic and electron transfer parameters of the catalytic process

Effect of pH on the activity of platinum group metal-free catalysts in oxygen reduction reaction

© 2018 American Chemical Society. The impact of the electrolyte's pH on the catalytic activity of platinum group metal-free (PGM-free) catalysts toward the oxygen reduction reaction (ORR) was studied. The results indicate that the ORR mechanism is determined by the affinity of protons and hydroxyls toward multiple functional groups present on the surface of the PGM-free catalyst. It was shown that the ORR is limited by the proton-coupled electron transfer at pH values below 10.5. At higher pH values (>10.5), the reaction occurs in the outer Helmholtz plane (OHP), favoring hydrogen peroxide production. Using a novel approach, the changes in the surface chemistry of PGM-free catalyst in a full pH range were studied by X-ray photoelectron spectroscopy (XPS). The variations in the surface concentration of nitrogen and carbon species are correlated with the electron transfer process and overall kinetics. This study establishes the critical role of the multitude of surface functional groups, presented as moieties or defects in the carbonaceous "backbone" of the catalyst, in mechanism of oxygen reduction reaction. Understanding the pH-dependent mechanism of ORR provides the basis for rational design of PGM-free catalysts for operation across pH ranges or at a specific pH of interest. This investigation also provides the guidelines for developing and selecting ionomers used as "locally-confined electrolytes", by taking into account affinities and possible interactions of specific functional groups of the PGM-free catalysts with protons or hydroxyls facilitating the overall ORR kinetics

Chemistry of Multitudinous Active Sites for Oxygen Reduction Reaction in Transition Metal–Nitrogen–Carbon Electrocatalysts

Development and optimization of non-platinum group metal (non-PGM) electrocatalysts for oxygen reduction reaction (ORR), consisting of transition metal–nitrogen–carbon (M–N–C) framework, is hindered by the partial understanding of the reaction mechanisms and precise chemistry of the active site or sites. In this study, we have analyzed more than 45 M–N–C electrocatalysts synthesized from three different families of precursors, such as polymer-based, macrocycles, and small organic molecules. Catalysts were electrochemically tested and analyzed structurally using exactly the same protocol for deriving structure-to-property relationships. We have identified possible active sites participating in different ORR pathways: (1) metal-free electrocatalysts support partial reduction of O₂ to H₂O₂; (2) pyrrolic nitrogen acts as a site for partial O₂ reduction to H₂O₂; (3) pyridinic nitrogen displays catalytic activity in reducing H₂O₂ to H₂O; (4) Fe coordinated to N (Fe–N_<i>x</i>) serves as an active site for four-electron (4e^–) direct reduction of O₂ to H₂O. The ratio of the amount of pyridinic and Fe–N_<i>x</i> to the amount of pyrrolic nitrogen serves as a rational design metric of M–N–C electrocatalytic activity in oxygen reduction reaction occurring through the preferred 4e^– reduction to H₂O

Enabling Efficient Water Splitting with Advanced Materials Designed for High pH Membrane Interface

This research focuses on durable, high-performance materials and interfaces for advanced water splitting, enabling a clear pathway for achieving &lt;$2/KgH2 (on scale) via anion exchange membrane (AEM)-based electrolysis. We aim to advance this goal via an improved fundamental understanding of both hydrogen and oxygen evolution reactions (HER/OER) leading to platinum group metal (PGM)-free catalyst materials. Here, we use NiFeCo and NiMo as OER and HER catalysts, respectively, in a full alkaline electrolysis cell. A thermally stable, multi-cation AEM is used to operate the cell at elevated temperatures thereby lowering the operating potential by increasing the kinetics of the respective catalytic reactions. The transition metal catalysts, paired with this novel AEM, have been used to achieve an operating potential of 1.79 V at 1 A/cm2. This potential is 300 mV lower than similar electrolysis cells equipped with PGM-based catalysts. We have also demonstrated the efficacy of the less caustic potassium carbonate solution as a replacement for potassium hydroxide as an electrolyte. By using a carbonate-based electrolyte, the hydroxide ion required for the anodic reaction is continuously replenished by re-establishing an equilibrium with water. This consideration, coupled with the reduced alkalinity of the carbonate solution, yields an electrolysis cell capable of sustained operation with minimal increase in operating potential