Anodic Zone Research Articles

Understanding the Effect of Corrosion Resistance in Welded AA2198‐T8 Alloy: Microstructural‐Electrochemical Insights

ABSTRACTIn this study, we explore the corrosion resistance of AA2198‐T8 alloy in friction stir‐welded zones, focusing on microstructure changes and resulting corrosion susceptibility. Macrogalvanic coupling effects are observed in weldment under corrosive conditions, particularly in the welding joint (WJ), heat‐affected zones, and base metal (BM). Severe localized corrosion is prevalent in anodic zones, revealing intricate trenching patterns around micrometric particles in cathodic domains. Investigating isolated zones exposes SLC across all welding‐affected regions and BM, underscoring the involvement of microgalvanic cells in corrosion. The novel utilization of a syringe cell as an electrochemical tool proves to be instrumental in delineating the electrochemical characteristics of welding testing zones. Notably, stir zone within WJ emerges as the region depicting the lowest corrosion resistance, a critical finding substantiated by localized electrochemical impedance spectroscopy. These insights into the interplay of electrochemical phenomena and microstructural attributes have implications for advancing corrosion mitigation strategies and alloy engineering in materials science.

The electric double layer structure and interface energy of uranium electrode in molten LiCl-KCl-UCl3 mixture: A molecular dynamics simulation study

The electric double layer structure and interface energy of uranium electrode in molten LiCl-KCl-UCl3 mixture, as well as the surface energies of metallic uranium and molten salts, were investigated using molecular dynamics simulations. The surface energies were calculated, respectively, from the pressure tensor and the energy difference for molten salt and uranium, and interface energy was evaluated from the Gibbs free energy difference between systems with and without interface. The surface energies of molten alkali halides are between 76.4 and 201.8 mJ·m−2 and decrease with the increase of radius of the halide anion or the alkali cation for molten salt with the same alkali cation or the same halide anion. The surface energy of uranium depends on the allotrope morphology and crystal facet, and the surface energies of α-U, β-U, and γ-U are 2.36, 1.45, and 1.69 J·m−2 in average for the seven low index crystal facets. The interface energy of uranium and molten LiCl-KCl-UCl3 mixture is about 2.71 J·m−2 and increases with the increase of charge density on the uranium slabs. The molten LiCl-KCl-UCl3 mixture in anodic zone has higher coordination number than that in cathodic zone but similar coordination distance.

Lateral 1200V SiC schottky barrier diode with single event burnout tolerance

For a power device to be used in space, it must be able to recover from a single event effect caused by heavy ion radiation. Conventional vertical silicon carbide (SiC) power devices such as automotive diodes and MOSFETs, can only meet this requirement if they are heavily derated, a 1200 V device typically unusable above 200 V. In this paper, a lateral RESURF Schottky diode has been designed in TCAD simulation using a radiation-hard (rad-hard) by design methodology. By preventing anode-to-cathode shorting that occurs in a vertical drift region, the lateral design is shown to recover after a heavy ion traverses the device with a linear energy transfer (LET) of 60 MeV·cm2/mg, while the device is blocking 1200 V. The design splits the drift region into a higher doping zone closer to the cathode (Zone 2) of 1.5×1017 cm−3 and a lower doping zone closer to the anode (Zone 1) of 1×1016 cm−3. The electric field spikes were reduced while the device was recovering. This design keeps the local temperature in the device to under 1000 K if the heavy ion penetrates the device in a direction perpendicular to the surface. Other entry positions and directions are also simulated and a maximum temperature of 1733 K occurs when the ion path is horizontal, entering at 1 μm below the surface. However, this temperature peak occurs at the cathode, which is not expected to lead to lasting leakage damage. A deep P+ pillar embedded into the anode acts as a collector for holes generated during the single event. Simulations show that a deeper P+ pillar, to a depth of up to 5 μm, reduces the hole density in the N-drift region and P-epi layer during recovery. This also allows the Zone 1 doping to be increased to as much as 5×1016 cm−3, thereby reducing on-state losses.

Biogenic sulfur recovery from sulfate-laden antibiotic production wastewater using a single-chamber up-flow bioelectrochemical reactor

The high-concentration sulfate (SO42−) in the antibiotic production wastewater hinders the anerobic methanogenic process and also proposes possible environmental risk. In this study, a novel single-chamber up-flow anaerobic bioelectrochemical reactor (UBER) was designed to realize simultaneous SO42− removal and elemental sulfur (S0) recovery. With the carbon felt, the cathode was installed underneath and the anode above to meet the different biological niches for sulfate reducing bacteria (SRB) and sulfur oxidizing bacteria (SOB). The bio-anode UBER (B-UBER) demonstrated a much higher average SO42− removal rate (SRR) of 113.2 ± 5.7 mg SO42−−S L−1 d−1 coupled with a S0 production rate (SPR) of 54.4 ± 5.8 mg S0-S L−1 d−1 at the optimal voltage of 0.8 V than that in the abio-anode UBER (control reactor) (SRR = 86.6 ± 13.4 mg SO42−−S L−1 d−1; SPR = 25.5 ± 9.7 mg S0-S L−1 d−1) under long-term operation. A large amount of biogenic S0 (about 72.2 mg g−1 VSS) was recovered in the B-UBER. The bio-anode, dominated by Thiovirga (SOB genus) and Acinetobacter (electrochemically active bacteria genus), exhibited a higher current density, lower overpotential, and lower internal resistance. C-type cytochromes mainly served as the crucial electron transfer mediator for both direct and indirect electron transfer, so that significantly increasing electron transfer capacity and biogenic S0 recovery. The reaction pathways of the sulfur transformation in the B-UBER were hypothesized that SRB utilized acetate as the main electron donor for SO42− reduction in the cathode zone and SOB transferred electrons to the anode or oxygen to produce biogenic S0 in the anode zone. This study proved a new pathway for biogenic S0 recovery and sulfate removal from sulfate-laden antibiotic production wastewater using a well-designed single-chamber bioelectrochemical reactor.

Prevalence of Escherichia coli in electrogenic biofilm on activated carbon in microbial fuel cell.

For a better understanding of the distribution of depth-dependent electrochemically active bacteria at in the anode zone, a customized system in a microbial fuel cell (MFC) packed with granular activated carbon (GAC) was developed and subsequently optimized via electrochemical tests. The constructed MFC system was sequentially operated using two types of matrice solutions: artificially controlled compositions (i.e., artificial wastewater, AW) and solutions obtained directly from actual sewage-treating municipal plants (i.e., municipal wastewater, MW). Notably, significant difference(s) of system efficiencies between AW or MW matrices were observed via performance tests, in that the electricity production capacity under MW matrices is < 25% that of the AW matrices. Interestingly, species of Escherichia coli (E. coli) sampled from the GAC bed (P1: deeper region in GAC bed, P2: shallow region of GAC near electrolytes) exhibited an average relative abundance of 75 to 90% in AW and a relative abundance of approximately 10% in MW, while a lower relative abundance of E. coli was found in both the AW and MW anolyte samples (L). Moreover, similar bacterial communities were identified in samples P1 and P2 for both the AW and MW solutions, indicating a comparable distribution of bacterial communities over the anode area. These results provide new insights into E. coli contribution in power production for the GAC-packed MFC systems (i.e., despite the low contents of Geobacter (> 8%) and Shewanella (> 1%)) for future applications in sustainable energy research. KEY POINTS: • A microbial community analysis for depth-dependence in biofilm was developed. • The system was operated with two matrices; electrochemical performance was assessed. • E. coli spp. was distinctly found in anode zone layers composed of activated carbon.

Integrating plant microbial fuel cells and permeable O2-releasing rods to enhance copper removal and electricity generation in sediment

The high mass transfer resistance of the sediment limits the migration of copper (Cu) ions generated from the operation of a sediment microbial fuel cell (SMFC), causing difficulty in obtaining high removal efficiencies of Cu ions through the SMFC. Therefore, approaches are required to reduce the internal resistance of the system and to increase the power generation of the SMFC. In this study, the anode zone of SMFCs was planted with water spinach, which produces root exudates to activate the microorganisms. A permeable oxygen release rod (POR) was installed in the cathode zone of the SMFC to slowly release a small amount of oxygen to enhance power generation, prompting copper ions to migrate to the cathode for a reduction reaction to remove copper. Under the condition of growing water spinach and setting POR simultaneously, the power density (94.9 mW/m3) of SMFC was increased by 14.1 times, significantly increasing the removal efficiency of Cu ions (from 20.9 % to 84.9 %). The abundance of electro-producing bacteria (e.g., Clostridium, Bacillus, and Thiobacillus) was increased when the anode zone of the SMFC was planted with water spinach. This suggests that the root exudates of water spinach and trace oxygen from POR promoted the electricity production of SMFC and accelerated the migration of Cu ions.

Preparation of ovarian fluid (caviar sol) of sturgeons for the use as physiological and functional ingredients in new generation food products

The development of the modern market for food functional ingredients involves the search for new raw materials, increasing efficiency and developing innovative technological processes for their production and introduction into fortified products, and the development of marketing promotion strategies. Considering this, we have conducted the research to assess physical, chemical and technological properties of secondary resources for the production of black caviar of sturgeon fish grown in the conditions of sturgeon farms in the Krasnodar Territory. It has been shown that ovarian fluid (caviar sol) has a high biological value, which is confirmed by the presence of all essential amino acids in caviar proteins. Caviar sol also contains a complex of basic macro- and micronutrients. The results obtained confirm that this product is a physiologically functional ingredient for the production of new generation food products. A technology has been developed for disinfecting caviar sol to increase its shelf life and of the products obtained from it. The processing of ovarian fluid (caviar sol) in the anode zone during electrolysis of an aqueous solution of table salt was carried out followed by its placement in the structure of a multiple emulsion sauce. Analysis of microbiological indicators has indicated that the processing of caviar sol and the production of sauce in the form of a multiple emulsion makes it possible to ensure microbiological indicators of the finished product that meet the requirements of TR CU 021/2011.

Concentration of sodium chloride solutions in the processing of concentrates for reverse osmotic water desalification

The paper examines the processes of concentrating sodium chloride solutions by the electrodialysis method. Given the shortage of reagents and their high prices, this electrodialysis method can be implemented to obtain acid and alkali from solutions of sodium sulfate, alkali, aluminum and iron coagulants. Today, the technologies that, as a result of the process, allow us to obtain valuable materials, substances, products, coagulants as a secondary product, are very justified, economically feasible and, most importantly, allow us to successfully implement the principles of low-waste production. The essence of the process is the use of sodium chloride solutions, which are formed during the desalination of water by reverse osmosis in the form of concentrates. The concentration process was implemented in a three-chamber electrolyzer, in the cathode, anode and working areas, a sodium chloride solution with a concentration of 360 mmol/dm3 was placed. An alkali solution with a concentration of 480 mg-eq/dm3 was used in the anode area. During electrolysis, alkali was formed in the cathode area, due to the diffusion of sodium in the working area and the cathodic reduction of water. Chlorides from the working area moved to the anode area. Hydroxide anions on the anode were oxidized to oxygen, chlorides with sodium formed sodium chloride, the concentration of which increased to 660 mg-eq/dm3. Alkalinity decreased to 68-70 mg-eq/dm3. When changing cathodes and anodes, the process was repeated in some places until the alkalinity in the cathode zone and the concentration of chlorides in the anode zone increased. . A solution of sodium chloride with a concentration of 360 mmol/dm3 was added to the working area where water desalination took place. After nine cycles of electrolysis, a sodium chloride solution with a concentration of 100-150 g/dm3 was obtained. The residual content of sodium chloride in desalinated water reached 50-100 mg/dm3. Sodium chloride solutions with a concentration of 4 to 30 g/dm3 can be used for concentration. It should be noted that after conducting nine cycles of the experiment, we can state that the process of concentration by this electrodialysis method does not lead to an increase in system resistance and energy consumption.

Optimization of the cathodic protection system for the main pipelines

This study investigated the multi-criteria task of optimizing the operating modes of cathodic protection stations (CPS), considering monitoring data, geological conditions at the pipeline installation site, climatic or seasonal changes, and other factors. The relevance of this research is associated with a comprehensive solution to the problem of increasing the durability and reliability of trunk pipelines to reduce accidents at their facilities by ensuring the efficiency of electrochemical protection (EChP) systems. The problems of existing EChP systems are analyzed, where the elimination of anode zones ("lack of protection") due to cathodic polarization is carried out without operational consideration of environmental conditions, as a rule, with a margin in terms of protective potential, which often leads to "overprotection", resulting in increased power consumption, gas formation on the metal surface, and detachment and wear insulation of pipelines. The aim of this research is to create a method for optimal regulation of the operation modes of the main pipelines and an adaptive electrochemical protection system that provides control and parameter management of cathodic protection stations, considering changes in external conditions on individual linear sections of main pipelines. Tasks: to develop an adjustment method for finding the effect of the CPS on the value of potentials at control points along the pipeline route; to develop a multicriteria optimization model for regulating the operation modes of the CPS; and to provide an example of testing the method of optimal regulation on the objects of the linear part of the existing main gas pipeline. The following results were obtained. A method is proposed for determining the effect of CPS operating modes on the value of potentials at control points in the mode of interrupting the protection current of other stations. An optimization model was formed according to the criterion of uniformity of the distribution of the protective potential "pipe-ground" along the pipeline route and according to the criterion of the minimum total protective current of all CPSs on a given section of the main pipeline. Conclusions. The scientific novelty of the results obtained is associated with the development of an original optimization method that allows scientifically determining the operation modes of the CPS to ensure the protection of the main pipeline both in time and length with reduced operating costs and adaptability to changes in climatic, seasonal, and geological conditions at the pipeline installation site. The effectiveness of the proposed approach is illustrated by the regulation of the parameters of the CPS based on the monitoring data of the section of the main gas pipeline of the oil and gas complex of the Republic of Kazakhstan.

Enhancement of energy recovery from caffeine wastewater in constructed wetland-microbial fuel cell through operating conditions.

The enhancement of up-flow constructed wetland-microbial fuel cell (UFCW-MFC) performance in energy retrieval from caffeine containing wastewater has been explored via various operating conditions (hydraulic retention time (HRT), multianode (MA), multicathode current collector (MC), external resistance). The anaerobic decaffeination and COD removal improved by 37 and 12% as the HRT extended from 1 to 5 d. The increment in contact time between the microbes and organic substrates promoted the degradation and contributed to higher power output (3.4-fold), CE (eightfold), and NER (14-16-fold). The MA and MC connections facilitated the electron transfer rate and the degradation rate of organic substrates in the multiple anodic zones, which enhanced the removal efficiency in the anaerobic compartment (Caffeine: 4.2%; COD: 7.4%) and led to higher electricity generation (Power: 4.7-fold) and energy recovery (CE: 1.4-fold; NER: 2.3-2.5-fold) compared to SA. The lower external resistance favored the growth of electrogens and induced higher electron flux, where the best treatment performance and electricity production was obtained when the external resistance approached the internal resistance. Overall, it was noteworthy that the optimum operating conditions were achieved with 5 d HRT, MA, and MC connection along with external resistance of 200 Ω, which significantly outperformed the initial conditions (1 d HRT, SA connection, and 1000 Ω) by 43.7 and 29.8% of caffeine and COD removal in the anaerobic compartment, respectively as well as 14-fold of power generation.

DEVELOPMENT OF IDEAS ABOUT ELECTRICAL CORROSION OF RAILWAY TRACK STRUCTURES AND IMPROVEMENT OF THEIR PROTECTION METHODS USING ELECTRICALLY CONDUCTIVE COMPOSITIONS

Research is devoted to the development of ideas about the mechanism of the flow of corrosion currents through the structures of railway tracks and buildings and the justification of methods of their protection against electrical corrosion. As a result of theoretical studies and field tests, the electric circuits of the leakage currents from the pulsating unidirectional electric potential of the POEP, which arise during the passage of the electric rolling stock along the electrified direct current railway tracks, have been clarified. Current carriers are installed in the elements and structures of the track and buildings. In concrete, soil, which are conductors of the second kind, these carriers are mainly cations Ca2+, Na+, anions OH-. It was found that in reinforced concrete sleepers, supports of passenger platforms due to the influence of POEP, zones of neutralization and leaching of concrete, cathode and anode zones of steel reinforcement are formed. Corresponding chemical and electrochemical reactions of leaching and carbonization of lime, oxidation of iron, etc. occur in these zones. It is proposed to prevent corrosion processes in these zones by diverting currents with grounded screens-coatings made of electrically conductive compositions based on mineral binders -Portland cement with a complex chemical additive or sodium silicate and a filler - dispersed graphite. The proposed indicator of the effectiveness of these screens-coatings, which is the degree of reduction of the current strength through the structure. As a result of experimental studies, it was established that it depends on the share of the contact area of the steel grounding device with the screen from the area of the screen itself, and the corresponding dependencies were obtained. New methods of protecting track structures and structures from electrical corrosion are substantiated, and appropriate structural and technological solutions are developed.

Assessment of the Impressed Current Cathodic Protection system after 4 years operation: Case study of the Saint-Cloud Viaduct (France)

Impressed Current Cathodic Protection (ICCP) is an electrochemical technique widely used, especially for repairing reinforced concrete structures contaminated with chlorides. This paper represents the results of the feedback of the ICCP system implemented on a road bridge, the Viaduct of Saint-Cloud in France. In 2012, a field trial was conducted in order to evaluate the effectiveness and the reliability of an ICCP system with embedded anodes designed for impressed current. The full-scale ICCP system was energized in 2018. Results of the four years monitoring including the variations of the applied current density and the polarization of the various anodic zones are presented. The ICCP data analysis is performed taking into consideration the initial degradation level of the span segments and the presence of prestressed tendons ducts. The electrical resistance of the circuit is influenced by several factors, the most important of which is the temperature. Considerations about the heterogeneity of the concrete resistivity are discussed.

Innovative pilot-scale constructed wetland-microbial fuel cell system for enhanced wastewater treatment and bioelectricity production

In this study, a unique configuration of pilot scale constructed wetland-microbial fuel cell (CW-MFC) system was evaluated in terms of chemical oxygen demand (COD) removal from synthetic wastewater and bioelectricity generation. The system consists of nine individual CW-MFC units and two aerobic chambers configured in a fibre-reinforced rectangular tank (Total working volume-135.5 L). Typha angustifolia was used as wetland plant. To enhance electrical performance of the system, two auxiliary MFCs equipped with terracotta-based separator-electrode-assembly (SEA) were integrated into the anodic zone of each CW-MFC unit in addition to the conventional sediment-configured MFC. The system was evaluated in fed-batch and continuous up-flow modes of operations. All the CW integrated MFCs were studied individually without any combinations (parallel/series). In fed-batch mode, the CW-MFC unit of the system removed a maximum of 97.56 ± 1.6 % of COD from wastewater. The highest power and current densities achieved by the auxiliary MFCs were 58.55 mW/m2 and 229.6 mA/m2 respectively. In the continuous up-flow mode, the pilot-scale system treated around 4100 L of wastewater and exhibited a maximum of 82.8 ± 1.9 % COD removal efficiency. Whereas, the auxiliary MFCs attained the maximum power and current densities of 41.44 mW/m2 and 283.3 mA/m2 respectively. In both modes, the internal resistance of the auxiliary MFCs was found to be two times lower than that of the conventional sediment-configured MFCs of the system. The overall results manifested that the inclusion of SEAs and aerobic chambers in this innovative pilot-scale CW-MFC shows merit and improved the energetics of the system.

Breathing oscillations excitation mechanism and influence factors in Hall thrusters

Breathing oscillations as one of the low frequency, large amplitude discharge instabilities have serious influence on the performance and lifetime of Hall thrusters. In order to acquire a better understanding of the breathing-oscillation in the Hall thrusters and provide the effective suppression methods for breathing-oscillation, the excitation mechanism and influence factors of the breathing oscillations are investigated by utilizing the two-zone predator-prey (P-P) model in this paper. The two-zone P-P model divides the discharge channel of Hall thruster into two parts according to the working principle of Hall thruster: one is the near anode zone and the other e is the ionization zone. The model includes the ion radial diffusion effect and electrons-wall interaction effect. The four-order Range-Kuttle method is utilized to solve the nonlinear two-zone P-P model equation. The research results show that the interaction of electrons with the wall has the inhibition effect on the breathing oscillations caused by the energy consumption due to the colliding with discharge channel wall. However, ion radial diffusion effect which is near anode has an excitation effect on the breathing oscillation. The ion and neutral atom dynamic behaviors obviously show the P-P feature in the phase space. In other words, there is a phase difference between the change of ion density and the change of neutral particle density. Relying on the intensity of the ions radial diffusion effect, the mode oscillation frequency and oscillation amplitude of discharge current present non monotonic change trend. More specifically, with the increase of intensity of ion radial diffusion effect, the oscillation frequency first increases and then decreases. However, the discharge peak current first decreases and then increases. Furthermore, the breathing oscillations excitation is irrelevant to the length of ionization zone, and the oscillation frequency increases (oscillation period) with length of ionization zone increasing (decreasing), provided that the length of discharge channel is constant. The research results of this paper will provide support to make clear the excitation mechanism and propose the new method of suppressing the breathing oscillations in the hall thrusters.

Promoting removal of copper from sediment and production of bioelectricity by sediment microbial fuel cells using tea extracts

In a sediment microbial fuel cell (SMFC) in which both the cathode and the anode are embedded in the sediment, copper is removed from the anode zone by its migration to the cathode. However, the removal of copper in an SMFC is often limited by poor mass transfer in the sediment environment. Tea extracts are rich in tea polyphenols, which are antioxidizing and transfer electrons. Adding tea extract to the electrodes of an SMFC can not only increase the efficiency of reduction of copper but also minimize the internal resistance of the SMFC, increasing its power output and the migration of copper. The results herein reveal that (1) the peak redox current of tea extract that was obtained using 50 % ethanol as the extractant was 60 μA, which was 1.39 and 1.69 times those obtained using DI water and 75 % ethanol, respectively; (2) adding tea extract reduced the internal resistance of the SMFC by 12.5 %; (3) the SMFC to whose anode tea extract was added removed 70.7 % of copper and had a maximum power density of 19.45 mW/m3, which was 1.66 times that of the SMFC without the tea extract. The SMFC with added tea extract can potentially be used to remediate heavy metal-contaminated sediment.

Research on the difference of characteristics at Steel/electrolyte interface under cathodic protection and in High-pH alkaline solution

• In situ spectroelectrochemistry is used to compare steel/electrolyte interfaces under CP to those at high-pH. • No protective passive film with high impedance formed under CP conditions. • Anodic excursions can induce unstable passivition on steel surfaces under high CP. In situ spectroelectrochemistry measurements, including electrochemical impedance spectroscopy (EIS) and UV–vis light reflecting spectroscopy, were conducted simultaneously to compare the characteristics at the steel/electrolyte interface under cathodic protection (CP) to that in high-pH alkaline solution. The results show that the electrochemical characteristics and optical light reflectance of the steel/electrolyte interface under CP are significantly different from those with a passive film formed in high-pH alkaline solution. These data indicate that no protective passive film is formed under the CP potential of −1.2V SSC , presumably because of the continuous supply of CP current to the cathodic interface and subsequent cathodic reduction reactions. The essence of the cathodic protection mechanism is to eliminate the anodic and cathodic zones by cathodic polarization, not to produce passive film on the steel surface. Another interesting phenomenon observed in the experiments was for the steel specimen under CP potentials equal to or more negative than −1.2 V SSC , for which the interruption of CP current and anodic excursions could induce passivation on the steel surface for a certain time. Analyses indicate that the occurrence of passivation in this case is related to the high pH environment produced by previous cathodic reactions and the positive potential shift caused by the anodic excursion; whereas the disappearance of passivation correlates with a decreasing pH and the subsequent electrochemical reactions, which could provide some insights for understanding the effect of dynamic stray current on cathodically protected steel.

Cable bacteria activity and impacts in Fe and Mn depleted carbonate sediments

The metabolic activities of cable bacteria enable the oxidation of sulfide to sulfate in anoxic sediment at depth through long distance electron transport coupled to the reductions of O2 and NO3−/NO2− in surface sediment. The spatial separation of oxidation and reduction half reactions requires modification of diagenetic models that assume electron donors and acceptors are coupled with each other locally within sedimentary deposits. In this study, we show that cable bacteria can become established and remain metabolically active in sulfidic, but Fe, Mn, and solid phase sulfide-depleted, carbonate muds from Florida Bay, USA. Sediment surface pH maxima reflecting electrogenic metabolism developed between 1 and 3 weeks in sediment incubated in laboratory microcosms with oxic overlying water. Cable filament cell abundances varied over time, with the increase initially focused within the subsurface, but by the end of experiments, cell abundances increased both in subsurface and oxic surface sediment. The development of cable bacteria activity in carbonate muds demonstrates that long-distance electron transport metabolism can utilize subsurface dissolved sulfide (e.g., H2S) as a sole reductant source for sustained periods without transition to Fe-sulfide and apparently without formation of an intermediate suboxic region associated with Fe and Mn cycling. H2S consumption occurs initially within the O2-NO3− rich oxic – suboxic zone and transitions to a dominant, but not exclusive, subsurface cable bacteria anodic zone. Once established, cable bacteria significantly altered sediment carbonate cycling. Thermodynamic calculations demonstrated that aragonite and hi-Mg-calcites were supersaturated (Ω ∼2.0–3.2) in the surface sediment layer (< 0.25 cm depth) and were undersaturated (Ω ∼ 0.2) in the anodic zone (1–2 cm depth). Hi-Mg-calcites and aragonite likely precipitated in the surface sediment and dissolved in the anodic region, the dissolution confirmed by elevated porewater Ca2+, Mg2+ concentrations. P cycling was coupled to remineralization of organic matter, carbonate mineral cycling, and apparently intracellular accumulation of polyphosphates. Thus, cable bacteria may play an important role in the acquisition of P by seagrasses in carbonate deposits where P is otherwise limited by irreversible adsorption and authigenic mineral precipitation.

The in-depth revelation of the mechanism by which a downflow Leersia hexandra Swartz constructed wetland-microbial fuel cell synchronously removes Cr(VI) and p-chlorophenol and generates electricity

The composite pollution by Cr(VI) and p-chlorophenol (4-CP) has high toxicity and harms water safety. However, research on the effective removal of Cr(VI) and 4-CP composite-polluted wastewater (C&P) and efficient synchronous electricity generation with reclaimed resources is limited. In this study, a downflow Leersia hexandra constructed wetland-microbial fuel cell (DLCW-MFC) was builded to treat C&P, as well as wastewater singularly polluted by Cr(VI) (SC) and 4-CP (SP), respectively, to reveal the mechanism by which DLCW-MFC treats C&P and synchronously generates electricity. The results demonstrate that the cathode layer had a stronger removal effect on pollutants than the middle layer and anode zone layer. Moreover, SC and SP had stronger pollutant removal effects than C&P. Cr(VI) had more competitive with electrons than 4-CP, and they had a synergistic effect on efficient electricity generation. The L.hexandra in SC and SP had a better growth state and lower Cr enrichment concentration than that in C&P. Cr existed in the DLCW-MFC mainly in the form of Cr(III). Gas chromatography-mass spectrometry was used to investigate the degradation pathway of 4-CP in C&P, and indicated that Phenol, 2,4-bis(1,1-dimethylethyl)- and benzoic acid compounds were the main intermediates formed at the cathode, and further mineralized to form medium-long-chain organic compounds to form CO2. The microbial community distribution results revealed that Simplicispira, Cloacibacterium, and Rhizobium are associated with Cr(VI) removal and 4-CP degradation, and were found to be rich in the cathode of C&P. The anode of C&P was found to have more Acinetobacter (1.34%) and Spirochaeta (4.83%) than SC and SP, and the total relative abundance of electricigens at the anode of C&P (7.46%) was higher than that at the anodes of SC and SP. This study can provide a theoretical foundation for the DLCW-MFC to treat heavy metal and chlorophenol composite-polluted wastewater and synchronously generate electricity.

Cyanogel-Induced Synthesis of RuPd Alloy Networks for High-Efficiency Formic Acid Oxidation

For direct formic acid fuel cells (DFAFC), palladium (Pd)-based alloy catalysts with competitive morphology and elemental composition are essential to boost the performance of the formic acid oxidation reaction (FAOR) in the anode zone. Herein, we design and synthesize RuPdx alloy nano-network structures (ANs) via the facile wet-chemical reduction of Pd-Ru cyanogel (Pdx [Ru(CN)6]y·aH2O) as an effective electrocatalyst for the FAOR. The formation of Pd-Ru cyanogel depends on the facile coordination of K2PdCl4 and K3 [Ru(CN)6]. The unique structure of cyanogel ensures the presentation of a three-dimensional mesoporous morphology and the homogeneity of the elemental components. The as-prepared RuPd3 ANs exhibit good electrocatalytic activity and stability for the FAOR. Notably, the RuPd3 ANs achieve a mass-specific activity of 2068.4 mA mg−1 in FAOR, which shows an improvement of approximately 16.9 times compared to Pd black. Such a competitive FAOR performance of RuPd3 ANs can be attributed to the advantages of structure and composition, which facilitate the exposure of more active sites, accelerate mass/electron transfer rates, and promote gas escape from the catalyst layer, as well as enhance chemical stability.

Mechanistic investigation into flow-through electrochemical oxidation of sulfanilamide for groundwater using a graphite anode

The technical effectiveness/merit of electrochemical oxidation (EO) has been recognized. Nonetheless, its practical application to groundwater remediation has not been fully implemented due to several technical challenges. To overcome the technical incompleteness, this study adopted a graphite anode in the flow-through system and studied the mechanistic roles of a graphite anode. To this end, groundwater contaminated with sulfanilamide was remediated by means of EO, and sulfanilamide oxidation was quantitatively determined in this study. Approximately 60% of sulfanilamide was degraded at the anode zone, and such observation offered that the removal of sulfanilamide was not closely related with current variations (10–100 mA). However, this study delineated that sulfanilamide removal is contingent on the flow speed. For example, the removal of sulfanilamide was lowered from 59 to 25% owing to a short contact time when the flow velocity was increased from 0.14 to 0.55 cm/min. This study also delineated that a shorter anode-cathode distance could offer a favorable chance to enhance the removal of sulfanilamide even under an identical current. A shorter distance could offer a chance to save energy due to the lower voltage operation. This study also offered that chloride (Cl−) and sulfate (SO42−) electrolytes served a crucial role in the generation of active species. In contrast, bicarbonate (HCO3−) and synthetic groundwater electrolytes impeded the oxidation rate because HCO3− scavenged the other active species. In an effort to seek the oxidation mechanisms of a graphite anode, scavenger, cyclic voltammetry test, and electron https://en.wikipedia.org/wiki/Electron_paramagnetic_resonanceparamagnetic resonance (EPR) analysis were done. From a series of the tests, it was inferred that a graphite anode did not directly affect the generation of the active species. Thus, the prevalence of the oxygenated functional groups on an anode surface could be the main mechanism in sulfanilamide removal due to the enhanced electron transfer.