Rate Of Oxygen Reduction Research Articles

Lanthanide Voltammetry: Electrocatalysis and Electrochemistry in Acetonitrile

An electrochemical method has been developed to allow voltammetric interrogation of lanthanides in common organic, electrochemical solvents [1, 2]. Lanthanide electrochemistry was enabled in acetonitrile at an ion exchange polymer (Nafion) modified platinum electrode with triflate ligands. Under these conditions, formal potentials of the lanthanides are shifted into the potential window of acetonitrile and voltammetry is enabled. Here, voltammetry of lanthanides on the benchtop and evidence of electrocatalysis of reactions important in energy and environment are presented. For several lanthanide triflate complexes, the voltammetry is reviewed. For five lanthanides, two reductions are observed under cyclic voltammetric conditions. For each lanthanide triflate complex, LN(OTf)3 where LN is a lanthanide, two well resolved reduction waves are observed. The first is for LN3+ to LN2+. The second wave about a volt negative of the first is for reduction of the LN(II) triflate. Under cyclic voltammetric conditions, the reverse sweep to positive potentials is less well resolved. The mechanistic path for the LN(OTf)3 is considered. Electrochemical reactions of small molecule, ubiquitous species play important roles in energy and the environment. This includes the oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), carbon dioxide reduction, and the chemistry of other organic species that contain one carbon, such as methanol, formic acid, formaldehyde, and carbon monoxide. Many of these reactions are kinetically limited. ORR limits performance of many fuel cell and air batteries. Increased rates of HER facilitate energy generation. The sequence of single carbon species both maps the thermodynamic advantages of organic electrochemical fuels and identifies the dominant kinetic limitations of their exploitation in practical, low temperature electrochemical energy systems. Carbon dioxide is the highest oxidation state of carbon and so the focus of study for reduction to regenerate fuels and value added products as well as to remediate greenhouse gases. Voltammetry undertaken in the presence of some of these species will be presented. For example, there is clear cyclic voltammetric evidence of increased rates of oxygen reduction in acetonitrile when lanthanide triflates are present in solution and the Nafion film on the electrode.

A Study on Workability and Durability of Different Plating Thickness of Silver on Monel As a Cathode Material for Oxygen Reduction

The higher overvoltage for the oxygen reduction reaction (ORR) limits the performance of electrochemical system such as alkaline fuel cell, deoxygenation cell, etc. where the higher oxygen reduction rate is desirable. Silver, having similar mechanism for oxygen reduction as platinum, is one of the cheaper alternative as oxygen reduction. Silver plated on suitable substrate can significantly decrease the cost of oxygen reduction material. The study focuses on the cathodic property of four different silver plating thickness (0.2, 0.5, 1.0, 2.0 µm) on monel, high nickel-copper alloy, for oxygen reduction, and their durability in oxygen reduction process. A special two chamber electrochemical cell separated by cation exchange membrane (CEM), is constructed for conducting the electrochemical experiments. The experiments were performed at room temperatures and 0.5 M NaCl solution and seawater was used as electrolyte. The potentiodynamic and potentiostatic test were performed for the analysis of oxygen reduction property of different thickness of silver on monel. The anodic polarization and scanning electron microscope (SEM) were used for studying the durability of the specimen, with focus on erosion and erosion induced corrosion of the silver plated monel. The electrochemical experiments were performed with the dimensionally stable anode (DSA) and the saturated calomel electrode (SCE) as counter electrodes. The current density for oxygen reduction for four different thickness silver layer was similar, and the oxygen reduction to water by 4- electron pathways was evident in on all samples. The plated layer of 0.2 µm was observed to be the most affected sample and there was observation of small pits throughout the surface. There was no significant effect on 0.5, 1.0 and 2.0 µm silver plated layer. Energy-dispersive x-ray spectroscopy (EDS) showed the formation calcium hydroxide on the surface of the cathode material after 48 hours potentiostatic test on seawater. The result indicate that the durability is of more concern than electrochemical property for oxygen reduction on different thickness silver plated layer on monel.

Regional oxygen reduction and denitrification rates in groundwater from multi-model residence time distributions, San Joaquin Valley, USA

Summary Rates of oxygen and nitrate reduction are key factors in determining the chemical evolution of groundwater. Little is known about how these rates vary and covary in regional groundwater settings, as few studies have focused on regional datasets with multiple tracers and methods of analysis that account for effects of mixed residence times on apparent reaction rates. This study provides insight into the characteristics of residence times and rates of O 2 reduction and denitrification (NO 3 − reduction) by comparing reaction rates using multi-model analytical residence time distributions (RTDs) applied to a data set of atmospheric tracers of groundwater age and geochemical data from 141 well samples in the Central Eastern San Joaquin Valley, CA. The RTD approach accounts for mixtures of residence times in a single sample to provide estimates of in-situ rates. Tracers included SF 6 , CFCs, 3 H, He from 3 H (tritiogenic He), 14 C, and terrigenic He. Parameter estimation and multi-model averaging were used to establish RTDs with lower error variances than those produced by individual RTD models. The set of multi-model RTDs was used in combination with NO 3 − and dissolved gas data to estimate zero order and first order rates of O 2 reduction and denitrification. Results indicated that O 2 reduction and denitrification rates followed approximately log-normal distributions. Rates of O 2 and NO 3 − reduction were correlated and, on an electron milliequivalent basis, denitrification rates tended to exceed O 2 reduction rates. Estimated historical NO 3 − trends were similar to historical measurements. Results show that the multi-model approach can improve estimation of age distributions, and that relatively easily measured O 2 rates can provide information about trends in denitrification rates, which are more difficult to estimate.

The Mechanisms of Oxygen Reduction in the Terminal Reducing Segment of the Chloroplast Photosynthetic Electron Transport Chain.

The review is dedicated to ascertainment of the roles of the electron transfer cofactors of the pigment-protein complex of PSI, ferredoxin (Fd) and ferredoxin-NADP reductase in oxygen reduction in the photosynthetic electron transport chain (PETC) in the light. The data regarding oxygen reduction in other segments of the PETC are briefly analyzed, and it is concluded that their participation in the overall process in the PETC under unstressful conditions should be insignificant. Data concerning the contribution of Fd to the oxygen reduction in the PETC are examined. A set of collateral evidence as well as results of direct measurements of the involvement of Fd in this process in the presence of isolated thylakoids led to the inference that this contribution in vivo is negligible. The increase in oxygen reduction rate in the isolated thylakoids in the presence of either Fd or Fd plus NADP+ under increasing light intensity was attributed to the increase in oxygen reduction executed by the membrane-bound oxygen reductants. Data are presented which imply that a main reductant of the O2 molecule in the terminal reducing segment of the PETC is the electron transfer cofactor of PSI, phylloquinone. The physiological significance of characteristic properties of oxygen reductants in this segment of the PETC is discussed.

Carbon Material Optimized Biocathode for Improving Microbial Fuel Cell Performance.

To improve the performance of microbial fuel cells (MFCs), the biocathode electrode material of double-chamber was optimized. Alongside the basic carbon fiber brush, three carbon materials namely graphite granules, activated carbon granules (ACG) and activated carbon powder, were added to the cathode-chambers to improve power generation. The result shows that the addition of carbon materials increased the amount of available electroactive microbes on the electrode surface and thus promote oxygen reduction rate, which improved the generation performance of the MFCs. The Output current (external resistance = 1000 Ω) greatly increased after addition of the three carbon materials and maximum power densities in current stable phase increased by 47.4, 166.1, and 33.5%, respectively. Additionally, coulombic efficiencies of the MFC increased by 16.3, 64.3, and 20.1%, respectively. These results show that MFC when optimized with ACG show better power generation, higher chemical oxygen demands removal rate and coulombic efficiency.

Oxygen Reduction on Ag(100) in Alkaline Solutions--A Theoretical Study.

Silver is much more reactive to oxygen than gold; nevertheless, in alkaline solutions, the rates of oxygen reduction on both metals are similar. To explain this phenomenon, the first, rate-determining step of oxygen reduction on Ag(100) is determined by a combination of DFT, molecular dynamics, and electrocatalysis theory. In vacuum, oxygen is adsorbed on Ag(100), but in the electrochemical environment, the adsorption energy is offset by the loss of hydration energy as the molecule approaches the surface. As a result, the first electron transfer should take place in an outer-sphere mode. Previously, the same mechanism for oxygen reduction on Au(100) has been predicted, and these calculations have been repeated by using a more advanced version of the electrocatalysis theory discussed herein to confirm previous conclusions. The theoretical results compare well with experimental data.

Effects of magnitude and duration of cathodic voltage-controlled electrical stimulation of titanium for prevention of biofilm infections

Event Abstract Back to Event Effects of magnitude and duration of cathodic voltage-controlled electrical stimulation of titanium for prevention of biofilm infections Mary Canty1*, Anthony Campagnari2* and Mark Ehrensberger1, 3* 1 SUNY at Buffalo, Biomedical Engineering, United States 2 SUNY at Buffalo, Microbiology and Immunology, United States 3 SUNY at Buffalo, Orthopaedics Surgery, United States Introduction: Periprosthetic joint infection (PJI) is a devastating outcome of total joint arthroplasty (TJA). Gram-positive methicillin-resistant Staphylococcus aureus (NRS70) and gram-negative Acinetobacter baumanni (Ab307) develop biofilms on the surface of titanium implants. This study evaluated the effects of applying cathodic voltage-controlled electrical stimulations (CVCES) of -1.5V and -1.8V for 2, 4, and 8hrs to commercially pure titanium (cpTi) incubated in NRS70 and Ab307 as a method of preventing bacterial attachment to the surface. Materials and Methods: cpTi coupons were wet sanded to a 600-grit finish, sonicated in deionized water for 10mins, and sterilized under ultraviolet light for 30mins. Experiments were conducted with NRS70 (respiratory isolate) and Ab307 (blood isolate). Fresh cultures of NRS70 were incubated in 5mL of tryptic soy broth with 0.25% glucose (TSBG). This was repeated for Ab307 in Muller Hinton (MH) broth. Solutions were adjusted to an OD600 of 0.1 (~107 CFU/mL) and placed in a shaking water bath at 180rpm and 37°C. Cultures were grown to mid-log, diluted to an OD600 of 0.1, and then 2.75mL of this solution was added to a sterile cpTi coupon in a custom stimulation chamber[1]. The agar chamber uses a standard three-electrode system with a cpTi working electrode, a graphite counter electrode and an Ag/AgCl reference electrode. With respect to Ag/AgCl, voltages of -1.8V for 2, 4 and 8hrs, and -1.5V for 4 and 8hrs were applied to the working electrode at room temperature using a potentiostat (Interface 1000, Gamry Instruments). Control experiments were conducted at open circuit potential (OCP). After incubation, cpTi coupons were washed in sterile PBS, sonicated and dilution plated for colony forming units (CFU). The media was collected for pH measurement and dilution plated for CFU. Potentiostatic EIS was performed on cpTi in sterile media for each CVCES condition. EIS Impedance results were fit to a modified Randles circuit (EIS 300 software, Gamry Instruments) with a complex-non-linear-least-squares method. The media pH was assessed following EIS. Four independent samples were evaluated in all conditions. For 4 and 8hrs, a one-way ANOVA followed by Tukey post-hoc compared log-transformed CFU, Rp, and C across CVCES conditions. If the Levene’s test was significant, a Welch’s test followed by a Games-Howell post-hoc test was performed. Student’s t-tests compared the log-transformed CFU, Rp, and C for 2hr CVCES. Results and Discussion: As compared to OCP, CVCES for 4hrs at -1.8V significantly reduced coupon-associated NRS70 and Ab307 CFU by 99.9% (p=0.029 and p<0.001). It also completely eradicated all planktonic CFU in media for NRS70 and Ab307 (p<0.001). CVCES at -1.8V for 8hrs completely eradicated both coupon-associated and planktonic CFU in media for NRS70 and Ab307. CVCES at -1.5V for 4 and 8hrs, and -1.8V for 2hrs, did not result in clinically relevant CFU reductions compared to OCP. For 4 and 8hr CVCES with and without bacteria, the current density was significantly higher at -1.8V than -1.5V (6.56x10-4 vs. 5.60x10-5 A/cm2) and resulted in increases in pH. Conclusions: CVCES of cpTi implants may provide effective prevention of PJI. Stimulation increases the pH and reduces viable CFU. This is directly related to the rates of water and oxygen reduction on the cpTi. The voltage-dependent properties of cpTi are a suspected factor in the observed antimicrobial effects of CVCES.

Probing the Buried Metal-Organic Coating Interfacial Reaction Kinetic Mechanisms by a Hydrogen Permeation Based Potentiometric Approach

Corrosion driven delamination of coatings is crucially determined by the rate of the cathodic oxygen reduction reaction at the buried metal-organic coating interface. Quantitative measurement of this rate at such interfaces by conventional techniques is impeded due to the blocking of ion transport by the coating. A new approach where hydrogen permeation is used as a tool to measure the oxygen reduction rate underneath coatings has been recently introduced. This permeation based potentiometry approach measures the rate of the oxygen reduction reaction by correlating the open circuit potential established as a consequence of the dynamic electrochemical equilibrium between hydrogen oxidation and oxygen reduction reactions on the coated exit side with the hydrogen uptake rate on the entry side. In this work, the interfacial reaction kinetics of the oxygen reduction reaction causing delamination of the coating are investigated by this hydrogen permeation based potentiometric approach. Moreover, thus performed prolonged cathodic polarizations of the palladium/coating interface have been found to destroy the interface, just like it is the case in the cathodic delamination process. Initial results obtained on ultra-thin films of iron on palladium are also presented, showing that the technique is applicable also on technically more relevant metal surfaces.

Effect of Low-Concentration Alloying in Titanium on Reduction Reaction Kinetics in Alkaline Environments

The electrochemical behavior of oxides of three Ti-based binary alloys, Ti99Co1, Ti99Sn1, and Ti99Cr1, are investigated using electrochemical impedance spectroscopy, Mott-Schottky analysis and cyclic voltammetry. It is found that native amorphous TiO2 can be doped in order to change the oxide's electronic properties and thereby reduce oxygen reduction rates in an alkaline solution, with the greatest reduction seen for the Ti99Sn1 alloy.

A biosynthetic model of cytochrome c oxidase as an electrocatalyst for oxygen reduction.

Creating an artificial functional mimic of the mitochondrial enzyme cytochrome c oxidase (CcO) has been a long-term goal of the scientific community as such a mimic will not only add to our fundamental understanding of how CcO works but may also pave the way for efficient electrocatalysts for oxygen reduction in hydrogen/oxygen fuel cells. Here we develop an electrocatalyst for reducing oxygen to water under ambient conditions. We use site-directed mutants of myoglobin, where both the distal Cu and the redox-active tyrosine residue present in CcO are modelled. In situ Raman spectroscopy shows that this catalyst features very fast electron transfer rates, facile oxygen binding and O–O bond lysis. An electron transfer shunt from the electrode circumvents the slow dissociation of a ferric hydroxide species, which slows down native CcO (bovine 500 s−1), allowing electrocatalytic oxygen reduction rates of 5,000 s−1 for these biosynthetic models.

Effect of cathodic polarisation on the corrosion behaviour of 316L stainless steel under static and dynamic conditions

AbstractThe role of cathodic polarisation on the corrosion of 316L stainless steel was investigated under static and dynamic conditions. The results reveal that the applied flow regime during the cathodic polarisation process has a direct effect on the corrosion behaviour of steel. The cathodic polarisation of steel under static conditions increases the oxygen reduction rate and shifts the corrosion potential towards nobler potentials. Under dynamic conditions, depending on the regime of the applied fluid flow during cathodic and anodic polarisation, the oxygen reduction rate can increase, causing the corrosion potential of the cathodically polarised steel to shift towards more positive direction. On the contrary, the oxygen reduction rate can decrease and the corrosion potential of the cathodically polarised steel shifts towards more negative potentials.

Graphite-Conjugated Pyrazines as Molecularly Tunable Heterogeneous Electrocatalysts.

Condensation of ortho-phenylenediamine derivatives with ortho-quinone moieties at edge planes of graphitic carbon generates graphite-conjugated pyrazines (GCPs) that are active for oxygen reduction electrocatalysis in alkaline aqueous electrolyte. Catalytic rates of oxygen reduction are positively correlated with the electrophilicity of the active site pyrazine unit and can be tuned by over 70-fold by appending electron-withdrawing substituents to the phenylenediamine precursors. Discrete molecular analogs containing pyrazine moieties display no activity above background under identical conditions. This simple bottom up method for constructing molecularly well-defined active sites on ubiquitous graphitic solids enables the rational design of tunable heterogeneous catalysts.

In-Situ Surface Analysis of SOFC Cathode Degradation Using High Temperature Environmental Scanning Electron Microscopy

Solid Oxide Fuel Cell (SOFC) cathode materials rely on the catalytic processes at their surfaces to reduce and incorporate oxygen. For many common cathode materials surface passivation occurs through 'A site' segregation at common operating temperatures [1]. These processes have a negative effect upon the oxygen reduction rates and therefore overall cell performance. Quantifying the true extent these segregation effects have on the exchange properties has not been fully explored but it is clear that the properties of the surface are essential. Many techniques have been employed to study cell properties in-situ, however, surface studies are typically restricted to post mortem or ex-situ analysis due to the necessity of a high vacuum. In this study High Temperature Environmental Scanning Electron Microscopy (HT-ESEM) has been employed to analyse the morphology changes of common SOFC cathode materials in-situ. Samples of La0.6Sr0.4Co0.2Fe0.8O3-x (LSCF) and La0.6Sr0.4CoO3-x (LSC) were annealed from room temperature to 1000oC at pressure ranges between 3 – 6mbar in atmospheres of Oxygen and Water. Using secondary electron imaging during the thermal annealing cycle morphological and compositional changes were able to be documented at temperature for the first time (Figure 1). This technique has enabled detailed analysis of the surface degradation that occurs during SOFC fuel cell operation. Secondary phase precipitation rate and formation behaviour has been quantified over a range of temperatures and time scales furthering the understanding of SOFC cathode surfaces significantly. [1] M. Kubicek, A. Limbeck, T. Fromling, H. Hutter, and J. Fleig, "Relationship between cation segregation and the electrochemical oxygen reduction kinetics of La0.6Sr0.4Co0.2Fe0.8O3 thin film electrodes" Journal of The Electrochemical Society, vol. 158, no. 6, pp. B727–B734, 2011. Figure 1 - Showing in-situ growth of secondary phase particulates on a polished surface of LSCF Figure 1

The Role of Chromium (III) in the Corrosion Inhibition of AA2024-T3 By Trivalent Chromium Process Coatings

High strength aluminum alloys (e.g., AA2024-T3) are widely used as aircraft structural components. The inclusion of two major alloying elements, Cu and Fe, make the metal more susceptible to localized damage in the form of pitting and intergranular corrosion. The susceptibility of the alloy to localized corrosion is due to the fact that galvanic cells form between the Cu- and Fe-rich intermetallic phases, sites that support relatively rapid oxygen reduction reaction kinetics, and the aluminum, which undergoes dissolution. The intermetallic phases are more noble than the surrounding aluminum matrix leading to the localized pitting or dissolution of the aluminum near the intermetallics. Inhibiting this localized corrosion is essential for achieving long performance lifetime of these structural components. Conversion pretreatment coatings are one component of a multilayer coating system that is typically used to protect aerospace aluminum alloys from corrosion. The multi-layer coating system consists of a conversion coating, a primer and an organic topcoat. The focus of current research in our group is on the application of alternate, more environmentally-friendly conversion coatings that serve as suitable replacements for the currently-used chromate conversion coatings (CCC). The corrosion inhibition provided by the multilayer coating system depends on the chemical composition, physical structure and thickness and uniformity of the conversion coating. The need for some level of corrosion inhibition by the conversion coating arises when there is coating breakthrough, in other words a scratch through the coating system that exposes some bare metal. Conversion coating thicknesses are generally in the 50-200 nm range and they provide corrosion inhibition, at least in part, by providing a barrier to oxygen and water/electrolyte accessibility to the metal surface. The trivalent chromium process (TCP) conversion coating is an environmentally-friendly potential replacement for the currently used chromate conversion coating. TCP is regarded as one of the leading drop-in replacements for CCC. Prior work has shown that the TCP coating inhibits corrosion on aluminum alloys, in part, by serving as a barrier layer. A key question with regard to the mechanism of corrosion inhibition is the role of Cr(III) or the transiently formed Cr(VI) that has been shown to form in the coating. We conducted studies using a trivalent chromium conversion coating from Henkel Corp., named Alodine® T5900™ , and a formulation of the same coating devoid of Cr(III). The formation, structure and corrosion inhibition of the coatings was investigated on AA2024-T3. The coating was formed by immersion on a polished, degreased and deoxidized specimen. These conversion coatings are about 100 nm thick when formed by immersion and consist of a biphasic structure with a hydrated zirconia (ZrO2·nH2O) top layer and a fluoroaluminate (e.g., KxAlF3+x) interfacial layer. Electrochemical methods were used to assess the degree of corrosion inhibition. Despite having the same physical structure, the conversion coating containing the Cr(III) exhibited a polarization resistance 10x greater than that for the coating devoid of it. Polarization curves revealed that the TCP coating provided cathodic inhibition. Rotating disk voltammetry was to assess the effect of the coating on the oxygen reduction reaction (ORR) kinetics. The results demonstrated that the TCP coating, as formed, inhibits the ORR. The reduced rate of oxygen reduction is attributed to (i) the formation of a poorly conducting layer on the Cu-rich intermetallics that blocks sites for O2 chemisorption and serves as a barrier to electron transfer and (ii) the formation of diffisusion barrier layer for O2 to the reaction sites.

Lactococcus lactis thioredoxin reductase is sensitive to light inactivation.

Thioredoxin, involved in numerous redox pathways, is maintained in the dithiol state by the nicotinamide adenine dinucleotide phosphate-dependent flavoprotein thioredoxin reductase (TrxR). Here, TrxR from Lactococcus lactis is compared with the well-characterized TrxR from Escherichia coli. The two enzymes belong to the same class of low-molecular weight thioredoxin reductases and display similar kcat values (∼25 s(-1)) with their cognate thioredoxin. Remarkably, however, the L. lactis enzyme is inactivated by visible light and furthermore reduces molecular oxygen 10 times faster than E. coli TrxR. The rate of light inactivation under standardized conditions (λmax=460 nm and 4 °C) was reduced at lowered oxygen concentrations and in the presence of iodide. Inactivation was accompanied by a distinct spectral shift of the flavin adenine dinucleotide (FAD) that remained firmly bound. High-resolution mass spectrometric analysis of heat-extracted FAD from light-damaged TrxR revealed a mass increment of 13.979 Da, relative to that of unmodified FAD, corresponding to the addition of one oxygen atom and the loss of two hydrogen atoms. Tandem mass spectrometry confined the increase in mass of the isoalloxazine ring, and the extracted modified cofactor reacted with dinitrophenyl hydrazine, indicating the presence of an aldehyde. We hypothesize that a methyl group of FAD is oxidized to a formyl group. The significance of this not previously reported oxidation and the exceptionally high rate of oxygen reduction are discussed in relation to other flavin modifications and the possible occurrence of enzymes with similar properties.

English

Sediments play an important role in determining the quality of lakes, rivers and oceans as they can act as either a source or sink for pollutants. Once the input pollution is controlled, sediments as a secondary source of pollution can release the accumulated pollutants to overlying water.1 The organic matter content of sediments can also affect the structure of macroinvertebrate assemblages.2 To date, traditional sediments remediation methods include monitored natural recovery, in-situ treatment, and ex-situ treatment.3 The traditional methods are either expensive or not environmentally friendly, so it is crucial to find a cost-effective and environmentally friendly way to solve the contaminated sediments problem. Microbial fuel cell (MFC) technology is considered an environmentally friendly and promising approach for converting wastewater or solid waste into electricity.4–6 Recently, some studies have shown that sediment microbial fuel cell (SMFC) can alter the properties and enhance the removal of organic matter in sediment.7–9 Wang9 developed a three-dimensional floating biocathode to dispose river sediments, and concluded that the sediment organic matter content near the anode was removed by 29 %. Hong7 found that sediment organic matter around the electrodes became more humified, aromatic, and polydispersed, and had a higher average molecular weight, along with its partial degradation and electricity generation compared to that of the original sediment. Sajana10 studied the performance of SMFC by adding cellulose in freshwater and demonstrated effective cellulose degradation from aquaculture pond sediment and maintained the oxidized sediment top layer favourable for aquaculture. Zhou11 improved the SMFC performance by amendment of colloidal iron oxyhydroxide into sediments and concluded that high Fe(II) concentration in pore water of sediments led to high power production. Song12 found that the addition of biomass in appropriate proportions can enhance output power in SMFC. However, mass transfer limitations for electron donors to reach the anode and a low rate of oxygen reduction in cathodes were major limitations for power production.13 In freshwater environments, the maximum power densities in SMFC with felt graphite14 and carbon paper15 as cathode were 4 mW m–2 and 2 mW m–2 respectively. Song13 constructed SMFC with granule activated carbon cathode and stainless steel anode and obtained 3.5 mW m–2 maximum power density, and further increased to 11.2 mW m–2 by adding cellulose. Jiang16 built MFC with graphite fiber brush and enhanced TCOD removal rate from 11.3 % to 19.2 % for raw sludge. Removal and Changes of Sediment Organic Matter and Electricity Generation by Sediment Microbial Fuel Cells and Amorphous Ferric Hydroxide

Influence of Tetraalkylammonium Cation Chain Length on Gold and Glassy Carbon Electrode Interfaces for Alkali Metal-Oxygen Batteries.

Fundamental studies of dioxygen electrochemistry relevant to metal-air batteries commonly require conductive supporting salts, such as tetraalkylammonium, to sustain redox processes in nonaqueous electrolytes. Electrochemical analysis of the formation and oxidation of superoxide on glassy carbon and gold working electrodes has shown a decrease in reversibility and lowering of the oxygen reduction rate constant when tetraalkylammonium cation alkyl chain length is increased. Probing interfacial regions on Au using in situ surface enhanced Raman spectroscopy (SERS) provides evidence that this is caused by the changing adsorption characteristics of tetralkylammonium cations under negative potentials. These effects are heightened with longer alkyl chain lengths, therefore reducing the reversibility of superoxide formation and dioxygen evolution. From these observations it can be established that shorter chain tetraalkylammonium cations while retaining necessary conductive support: (1) enhance reversibility and rate of superoxide formation and oxidation and (2) for in situ SERS, have lower preference for adsorption, thus improving experimental detection of superoxide at the Au electrode interface.

Hybrid binuclear-cobalt-phthalocyanine as oxygen reduction reaction catalyst in single chamber microbial fuel cells

A novel hybrid binuclear-cobalt-phthalocyanine (Bi-CoPc) is developed as the cathode catalyst to replace the costly platinum (Pt) in single chamber microbial fuel cells (SCMFCs). Bi-CoPc/C is integrated with metal oxides (NiO and CoO) to form macrocyclic complex for enhanced oxygen reduction rate (ORR). The characteristics of hybrid catalysts (Bi-CoPc/C–CoO and Bi-CoPc/C–NiO) are compared with Co-contained catalysts (CoPc/C and Bi-CoPc/C) and metal oxide catalysts (NiO and CoO). The increase in O and N functional groups indicates the benefits of NiO and CoO to the cathode catalysts. The cyclic voltammetry (CV) shows the reduction peak for Bi-CoPc/C–NiO and Bi-CoPc/C–CoO at −0.12 V and −0.22 V, respectively. The power densities (368 mW m−2 and 400 mW m−2) of SCMFCs with Bi-CoPc/C–CoO and Bi-CoPc-NiO/C are the highest among the cathodes tested, and close to that of Pt (450 mW m−2). This study demonstrates that hybrid Bi-CoPc/C with metal oxides has a great potential as a cost-effective catalyst in MFCs.

Structural Characterization and Enhanced Oxygen Reduction Activity of Chemically-Ordered Intermetallic PtFeNi Catalysts

The polymer electrolyte fuel cells (PEFCs) are excellent candidates as next-generation electric generators for vehicles, residential uses, laptop, etc. However, there are many issues to be solved to enlarge commercially uses. One of issues is related to Pt catalysts for oxygen reduction reaction (ORR) on a cathode electrode. Pt catalysts show low ORR activity and low durability, leading to lower performance in PEFCs. Our earlier studies found the chemically ordered face centered tetragonal (fct) intermetallic Pt-alloy catalysts (L10 type super-lattice structure) can satisfy both of higher ORR activity and long-term durability, whereas many of the previously-reported Pt-alloys cannot. It is considered that the high performance of fct-Pt alloy catalysts would result from the chemically-ordered structures, but it is unclear how they work to enhance ORR activity and durability. Thus, in this presentation, we will discuss the relationship between the ORR activities and surface structures in fct-Pt alloys by the detailed characterization of the catalyst’s surface structures.The fct-PtFeNi catalysts with different atomic compositions of Fe and Ni (Pt50Fe35Ni15, Pt50Fe25Ni25, Pt50Fe15Ni35) were prepared using a simple solid-state impregnation method; the mixture of metal (Pt, Fe, Ni)-salts and carbon blacks were annealed under H2/N2 at a temperature of 800°C. The prepared fct-PtFeNi catalysts exhibit about 3 times higher ORR mass activity, compared with the commercial Pt catalyst. Especially, the mass activity of Pt50Fe35Ni15 is about 0.62 A/mgPt; it is higher than that of fct-Pt50Fe25Ni25 and fct-Pt50Fe15Ni35 (about 0.5 A/mgPt). To discuss more about the enhancement of the ORR activities in the fct-PtFeNi alloys, the surface structures of the catalysts were examined by in-situ XAFS measurements. The EXAFS analysis of Pt-L3 edge reveals that the distance of Pt-Pt bonds in the fct-PtFeNi catalysts is about 2.72 nm, which is shorter than that of commercial Pt catalyst. Interestingly, the coordination number of Pt oxides (Pt-O or Pt-OH) in the fct-Pt50Fe35Ni15 is more increased at high potential of 0.8~1.2V, compared with other fct-PtFeNi catalysts with the lower content of Fe. The tendency of the formation of Pt oxides is in accord with that of the ORR activities in the fct-PtFeNi with the different compositions of Fe and Ni. Therefore, it is inferred that fct-PtFeNi with higher content of Fe would form more Pt oxides, leading to a faster reaction rate of oxygen reduction. This study brought out new insights; the surface structures of chemically-ordered fct-Pt alloys, such as the Pt-Pt bond distance and the formation of Pt oxides, strongly affect the ORR activities, as those of the previously-reported disordered Pt-alloys do as well. It is believed that our findings can aid in developing fct-Pt alloys with more enhanced catalytic activity and durability for PEFCs.

Corrosion mechanisms of Zn(Mg,Al) coated steel: 2. The effect of Mg and Al alloying on the formation and properties of corrosion products in different electrolytes

Oxygen reduction rate on galvanized steel and ZnAlMg coated steel decreased in presence of corrosion products identified as basic zinc salts (BZS) and layered double hydroxides (LDH). Under cathodic polarization of galvanized steel the transformation BZS→ZnO occurred, resulting in a loss of the inhibiting effect. It did not happen on ZnMgAl. Acid–base titrations of Zn2+-containing solutions with and without additives demonstrated that (1) Mg2+ ions delay the transformation BZS→ZnO; (2) Al3+ forms LDH which remains stable even at pH>12.5. A residual Al “skeleton” was observed in corrosion products formed on ZnMgAl. It may increase the compactness of the patinas.