Anodic Sulfide Research Articles

Deciphering the microbial interactions and metabolic shifts at different COD/sulfate ratios in electro-assisted anaerobic digestion

This research aims to investigate the influence of sulfate on the performance of microbial electrolysis cell-assisted anaerobic digester (MEC-AD) across varying sulfate conditions, including no sulfate and reduced COD/sulfate ratios from 20 to 1. The principal results indicate a gradual decline in methane yield in the MEC-AD from 78.7 ± 2.3 % under no sulfate conditions to 56.2 ± 2.0 % at a COD/sulfate ratio of 1, contrasting with a more substantial decrease in the control reactor (69.9 ± 3.6 % to 32.8 ± 1.5 %). The MEC-AD reactor exhibits heightened resilience to sulfide toxicity, showcasing higher specific methanogenic activities. Key findings suggest that the MEC-AD reactor maintains lower free sulfide concentrations, attributed to its higher pH and potential anodic sulfide oxidation. Additionally, the study reveals the promotion of syntrophic partnerships in the MEC-AD reactor, particularly between sulfate-reducing bacteria (SRB) such as Desulfovibrio, Desulfomicrobium, and Desulfobulbus, and other microbial groups, including hydrogenotrophic methanogens and electroactive bacteria. The integration of these mechanisms highlights the MEC-AD reactor's ability to effectively mitigate sulfate-induced challenges and enhance overall anaerobic digestion performance. This study presents a significant step forward in the development of resilient anaerobic digestion systems capable of efficiently handling sulfate stress.

Room-temperature sulfur doped NiMoO4 with enhanced conductivity and catalytic activity for efficient hydrogen evolution reaction in alkaline media

Transition metal oxides have been acknowledged for their exceptional water splitting capabilities in alkaline electrolytes, however, their catalytic activity is limited by low conductivity. The introduction of sulfur (S) into nickel molybdate (NiMoO4) at room temperature leads to the formation of sulfur-doped NiMoO4 (S-NiMoO4), thereby significantly enhancing the conductivity and facilitating electron transfer in NiMoO4. Furthermore, the introduction of S effectively modulates the electron density state of NiMoO4 and facilitates the formation of highly active catalytic sites characterized by a significantly reduced hydrogen absorption Gibbs free energy (ΔGH*) value of −0.09 eV. The electrocatalyst S-NiMoO4 exhibits remarkable catalytic performance in promoting the hydrogen evolution reaction (HER), displaying a significantly reduced overpotential of 84 mV at a current density of 10 mA cm−2 and maintaining excellent durability at 68 mA cm−2 for 10 h (h). Furthermore, by utilizing the anodic sulfide oxidation reaction (SOR) instead of the sluggish oxygen evolution reaction (OER), the assembled electrolyzer employing S-NiMoO4 as both the cathode and anode need merely 0.8 V to achieve 105 mA cm−2, while simultaneously producing hydrogen gas (H2) and S monomer. This work paves the way for improving electron transfer and activating active sites of metal oxides, thereby enhancing their HER activity.

Reduction of surface leakage current of InAs/GaSb long-wavelength superlattice detectors using SiO2 and anodic sulfide composite passivation

We investigate two passivation methods for long-wavelength infrared type-II InAs/GaSb superlattice (T2SL) photodiodes with the PπBN structure containing an InAs/AlSb hole barrier layer. In order to eliminate the surface defects of T2SL better to further reduce the surface dark current, anodic vulcanization and SiO2 composite passivation method is adopted to optimize the original SiO2 passivation method. At 77 K, the I–V curve of the devices under the two passivation methods are obtained. Compared with passivation-only SiO2, the dark current density of the anode sulfide and SiO2 composite passivation detector is reduced by one order of magnitude, and the surface resistivity is effectively improved by an order of magnitude. Additionally, the composite passivation method not only improves the uniformity of the device, but also prevents the peeling of the S layer to improve the quality of passivation. This work offers a stable and high-quality passivation method, and it could be popularized passivation in the field of optics, electronics, optoelectronics, and switching devices.

Reduction of S0 deposited on electroactive biofilm under an oxidative potential

The inevitable deposition of S0 on the electroactive biofilm (EAB) via anodic sulfide oxidation affects the stability of bioelectrochemical systems (BESs) when an accidental discharge of sulfide occurred, leading to the inhibition of electroacitivity, because the potential of anode (e.g., 0 V versus Ag/AgCl) is ~500 mV more positive than the redox potential of S2−/S0. Here we found that S0 deposited on the EAB can be spontaneously reduced under this oxidative potential independent of microbial community variation, leading to a self-recovery of electroactivity (> 100 % in current density) with biofilm thickening (~210 μm). Transcriptomics of pure culture indicated that Geobacter highly expressed genes involving in S0 metabolism, which had an additional benefit to improve the viability (25 % – 36 %) of bacterial cells in biofilm distant from the anode and the cellular metabolic activity via electron shuttle pair of S0/S2−(Sx2−). Our findings highlighted the importance of spatially heterogeneous metabolism to its stability when EABs encountered with the problem of S0 deposition, and that in turn improved the electroactivity of EABs.

Controlling the thickness and composition of stainless steel surface oxide film for anodic sulfide removal

Hydrogen sulfide is hazardous and toxic, and is present at many waste streams of industry processes. Anodic sulfide oxidation is a potentially effective approach to remove sulfide in aqueous media. This study therefore prepared and optimized surface oxide film on AISI 304 stainless steel (SS) as active and stable anode for sulfide removal. Among stainless steel samples of different anodization pretreatment duration, the anode with 15 min pretreatment (SS-15) resulted in the best sulfide removal at the same testing conditions, and achieved 48% and 18% improvement in terms of sulfide removal efficiency compared with the untreated SS and graphite, respectively. ANOVA-based tests (overall and for pairwise comparisons) also suggest the data are indeed valid. When anode potential was set no more than 1.62 V vs. reversible hydrogen electrode (RHE), direct sulfide oxidation dominated; and further increase in anode potential would initiate oxygen evolution reaction (OER) which contributed to indirect sulfide oxidation. Surface characterization found that the varying corrosion pretreatment duration led to oxide films of different thickness and chemical composition. The pretreatment duration from 15 min to 90 min increased the oxide film thickness from 178 nm to 264 nm and decreased the composition of FeOOH and NiOOH, which were most likely the catalytic active species for sulfide oxidation revealed by high-resolution XPS. Electrochemical analysis confirmed that the smaller thickness and enriched FeOOH/NiOOH composition in SS-15 led to a lower charge transfer resistance, a lower mass transfer resistance, and meanwhile a greater material stability. Depth profiling via high-resolution XPS identified metallic Fe inside oxide films and its presence may also promote the conductivity of the oxide film. This study demonstrated that anodization pretreatment of stainless steel was able to prepare effective and stable anode for electrochemical sulfide removal by controlling the thickness and composition of oxide films.

New Insights into the Anodic Sulfide Oxidation to Polysulfide by Electrodeposited Nickel Phosphide Catalyst on Stainless Steel

New Insights into the Anodic Sulfide Oxidation to Polysulfide by Electrodeposited Nickel Phosphide Catalyst on Stainless Steel

Effective anodic sulfide removal catalyzed by single nickel atoms on nitrogen-doped graphene with stainless steel substrate

Hydrogen sulfide is hazardous and life-threatening gas emission in anaerobic digestion and degradation. Electro-oxidation technology is a promising process for sulfide removal in aqueous media due to its high efficiency, cost effectiveness and easy operation. This study employed atomic nickel dispersed on nitrogen-doped graphene catalyst (A-Ni-NG) with stainless steel (SS) substrate for efficient sulfide removal. The results showed that the highest sulfide removal efficiency of 85.02±1.25% was achieved on SS/A-Ni-NG anode at 1.98 V (vs. RHE) in 48 h, which was 11.17% and 24.18% higher than that of bare SS and FTO/A-Ni-NG, respectively. SS/A-Ni-NG catalyst achieved a first-order rate constant of 0.036±0.001 h−1, improved by 24% compared with bare SS. The main products of sulfide oxidation were thiosulfate and elemental sulfur with Faradic efficiency of 32.37±3.20% and 18.99±0.05%, respectively. Electrochemical analysis showed the sulfide oxidation anodic peak potential on SS/A-Ni-NG anode was 280 mV (vs. RHE), lower than most of the reported graphite or Ni anodes. SS/A-Ni-NG improved the interface electric conductivity and the charge transfer rate, and directly catalyzed sulfide oxidation at applied voltage below oxygen evolution reaction (OER) onset potential. A-Ni-NG also indirectly removed sulfide by boosting OER at higher voltage. The superior sulfide oxidation catalytic activity of SS/A-Ni-NG anode was mainly attributed to the atomic dispersed Ni(I) generating NiOOH that boosted OER process and to the dopant N that induced activation region. A-Ni-NG coated on SS substrate is demonstrated to be a promising material for electrochemical sulfide removal.

Kinetic investigation of galvanic dissolution of ZnS and PbS with FeS2 from hydrothermal sulfides in seawater

Sulfide mineral dissolution is an important reaction controlling geochemical and environmental chemical processes in aqueous environments. In this study, we quantitatively evaluated the kinetic influence of galvanic interactions between different sulfide minerals on their dissolution in seawater. Four hydrothermal sulfides with different amounts of Fe disulfide minerals (pyrite) were reacted with artificial seawater for 144 h, and the dissolution rates of Zn and Pb were determined by an extraction method. The Zn dissolution rates from samples with high Fe/Zn molar ratios (>0.26) were 1.3–1.5 × 10−10 mol m−2 s−1; approximately one order of magnitude higher than those of samples with low Fe/Zn molar ratios (<0.002; 1.6–1.8 × 10−11 mol m−2 s−1). The Pb dissolution rates from a sample with high Fe disulfide were approximately nine orders of magnitude higher (8.4× 10−10 mol m−2 s−1) than reference data of the single galena dissolution rate (8.9 × 10−19 mol m−2 s−1). The higher solubility of PbSO4 than PbS and PbCO3 could explain the intense release of Pb from the other samples. These results and mineralogical observations with X-ray diffraction, X-ray photoelectron spectroscopy, and electron probe micro-analysis of sulfide mineral particulates provide evidence for the selective dissolution of anodic sulfide minerals (e.g., sphalerite and galena) at a higher reaction rate than cathodic sulfide minerals of Fe disulfide (e.g., pyrite).

Kabelbakterien ermöglichen neue geochemische Prozesse

The discovery of long-distance electron transfer by cable bacteria over centimetre distances was ground-breaking in environmental microbiology in recent years. Cable bacteria transfer electrons between anodic sulphide oxidation and cathodic oxygen reduction–the only example known so far for an organism separating redox half-reactions into different locations. The discovery of cable bacteria in contaminated aquifers pronounces their importance in different habitats.

Improved Na Storage Performance with the Involvement of Nitrogen-Doped Conductive Carbon into WS2 Nanosheets.

Tungsten disulfide (WS2) material is regarded as one of the most promising anode candidates for sodium ion batteries (SIBs). However, the exploration of this material still remains a great challenge to improve its cycling capacity. In this paper, nitrogen-doped conductive carbon/WS2 nanocomposites (WS2-NC) were fabricated based on the synthesis of the pure WS2 and conductive carbon/WS2 (WS2-C) nanocomposites. The reversible capacity of the as-prepared WS2-NC is stabilized at ∼360 mA h g(-1) at the density of 100 mA g(-1), even ∼200 mA h g(-1) at 1 A g(-1), presenting much better cycling performance than pure WS2 and conductive carbon/WS2 (WS2-C) samples. This excellent performance is further attributed to obviously promoted interfacial reaction in WS2 nanosheets at a low voltage platform (0.3-0.0 V), which is considered to closely relate to the incorporation of nitrogen-doped conductive carbon into WS2 nanosheets. Generally, this work presents an obviously enhanced Na storage performance by the incorporation of N-doped carbon into WS2 nanosheets to promote their interfacial reaction at low voltage platform. It could provide guidelines to create other high-capacity anode sulfide materials for SIBs.

Electrochemical sulfide removal and caustic recovery from spent caustic streams

Spent caustic streams (SCS) are produced during alkaline scrubbing of sulfide containing sour gases. Conventional methods mainly involve considerable chemical dosing or energy expenditures entailing high cost but limited benefits. Here we propose an electrochemical treatment approach involving anodic sulfide oxidation preferentially to sulfur coupled to cathodic caustic recovery using a two-compartment electrochemical system. Batch experiments showed sulfide removal efficiencies of 84 ± 4% with concomitant 57 ± 4% efficient caustic production in the catholyte at a final concentration of 6.4 ± 0.1 wt% NaOH (1.6 M) at an applied current density of 100 A m−2. Subsequent long-term continuous experiments showed that stable cell voltages (i.e. 2.7 ± 0.1 V) as well as constant sulfide removal efficiencies of 67 ± 5% at a loading rate of 47 g(S) L−1 h−1 were achieved over a period of 77 days. Caustic was produced at industrially relevant strengths for scrubbing (i.e. 5.1 ± 0.9 wt% NaOH) at current efficiencies of 96 ± 2%. Current density between 0 and 200 A m−2 and sulfide loading rates of 50–200 g(S) L−1 d−1 were tested. The higher the current density the more oxidized the sulfur species produced and the higher the sulfide oxidation. On the contrary, high loading rate resulted in a reduction of sulfide oxidation efficiency. The results obtained in this study together with engineering calculations show that the proposed process could represent a cost-effective approach for sodium and sulfur recovery from SCS.

Fabrication of type-II InAs/GaSb superlattice long-wavelength infrared focal plane arrays

In this paper, we present an InAs/GaSb type-II superlattice (SL) with the M-structure for the fabrication of a long-wavelength (10μm range) infrared (LWIR) focal plane arrays (FPA), which are grown by molecular beam epitaxy (MBE). The M-structure is named for the shape of the band alignment while the AlSb layer is inserted into the GaSb layer of InAs/GaSb SL. A 320×256 LWIR FPA has been fabricated with low surface leakage and high R0A product of FPA pixels by using anodic sulfide and SiO2 physical passivation. Experiment results show that the devices passivated with anodic sulfide obviously have higher R0A than the un-sulphurized one. The 50% cutoff wavelength of the LWIR FPA is 9.1μm, and the R0A is 224Ωcm2 with the average detectivity of 2.3×1010cmHz1/2W−1.

Cable Bacteria in Freshwater Sediments.

In marine sediments cathodic oxygen reduction at the sediment surface can be coupled to anodic sulfide oxidation in deeper anoxic layers through electrical currents mediated by filamentous, multicellular bacteria of the Desulfobulbaceae family, the so-called cable bacteria. Until now, cable bacteria have only been reported from marine environments. In this study, we demonstrate that cable bacteria also occur in freshwater sediments. In a first step, homogenized sediment collected from the freshwater stream Giber Å, Denmark, was incubated in the laboratory. After 2 weeks, pH signatures and electric fields indicated electron transfer between vertically separated anodic and cathodic half-reactions. Fluorescence in situ hybridization revealed the presence of Desulfobulbaceae filaments. In addition, in situ measurements of oxygen, pH, and electric potential distributions in the waterlogged banks of Giber Å demonstrated the presence of distant electric redox coupling in naturally occurring freshwater sediment. At the same site, filamentous Desulfobulbaceae with cable bacterium morphology were found to be present. Their 16S rRNA gene sequence placed them as a distinct sister group to the known marine cable bacteria, with the genus Desulfobulbus as the closest cultured lineage. The results of the present study indicate that electric currents mediated by cable bacteria could be important for the biogeochemistry in many more environments than anticipated thus far and suggest a common evolutionary origin of the cable phenotype within Desulfobulbaceae with subsequent diversification into a freshwater and a marine lineage.

Passivation of InAs/GaSb type II superlattice photodiodes

One of the major challenges faced by antimonide-based devices is a result of the large number of surface states that are generated. Surface passivation and subsequent capping of the surfaces are essential for any practical applicability of this material system, as evidenced by the comparison of unpassivated and passivated InAs/GaSb superlattice mid-infrared photodiodes herein. The surface passivation methods include silicon dioxide (SiO2) coating after anodic sulfide, SiO2 coating after anodic oxide, SiO2 coating only, zinc sulfide (ZnS) coating after anodic sulfide, and ZnS coating after ammonium sulfide [(NH4)2S] chemical passivation. The leakage current as a function of bias voltage (I–V) for superlattice diodes obtained using different passivation methods has been examined at 77 K. The best performance was demonstrated by the SiO2 after anodic sulfide passivation. The leakage current of the passivated diode is four orders of magnitudes less than that of the unpassivated diode.

Growth and electrical characterization of type II InAs/GaSb superlattices for midwave infrared detection

Herein, we report a type II InAs/GaSb superlattice structure (SLS) grown on GaSb(100) substrates by molecular beam epitaxy (MBE) and its electrical characterization for mid-wavelength infrared detection. A GaSb buffer layer was grown under optimized SLS growth conditions, which can decrease the occurrence of defects for similar pyramidal structures. The complications associated with these conditions include oxide desorption of the substrate, growth temperature of the SLS, the V/III ratio during superlattice growth and the shutter sequence. High-resolution X-ray diffraction (HRXRD) shows the sixth satellite peak, and the period of the SLS was 52.9Å. The atomic force microscopy (AFM) images indicated that the roughness was less than 2.8nm. High-resolution transmission electron microscopy (HRTEM) images indicated that the SLS contains few structural defects related to interface dislocations or strain relaxation during the growth of the superlattice layer. The photoresponse spectra indicated that the cutoff wavelength was 4.8μm at 300K. The SLS photodiode surface was passivated by a zinc sulfide (ZnS) coating after anodic sulfide.

Electric coupling between distant nitrate reduction and sulfide oxidation in marine sediment

Filamentous bacteria of the Desulfobulbaceae family can conduct electrons over centimeter-long distances thereby coupling oxygen reduction at the surface of marine sediment to sulfide oxidation in deeper anoxic layers. The ability of these cable bacteria to use alternative electron acceptors is currently unknown. Here we show that these organisms can use also nitrate or nitrite as an electron acceptor thereby coupling the reduction of nitrate to distant oxidation of sulfide. Sulfidic marine sediment was incubated with overlying nitrate-amended anoxic seawater. Within 2 months, electric coupling of spatially segregated nitrate reduction and sulfide oxidation was evident from: (1) the formation of a 4–6-mm-deep zone separating sulfide oxidation from the associated nitrate reduction, and (2) the presence of pH signatures consistent with proton consumption by cathodic nitrate reduction, and proton production by anodic sulfide oxidation. Filamentous Desulfobulbaceae with the longitudinal structures characteristic of cable bacteria were detected in anoxic, nitrate-amended incubations but not in anoxic, nitrate-free controls. Nitrate reduction by cable bacteria using long-distance electron transport to get privileged access to distant electron donors is a hitherto unknown mechanism in nitrogen and sulfur transformations, and the quantitative importance for elements cycling remains to be addressed.

Growth and Characterization of GaSb-Based Type-II InAs/GaSb Superlattice Photodiodes for Mid-Infrared Detection

InAs/GaSb superlattice (SL) midwave infrared photovoltaic detectors are grown by molecular beam epitaxy on GaSb(001) residual p-type substrates. A thick GaSb layer is grown under the optimized growth condition as a buffer layer. The detectors containing a 320-period 8ML/8ML InAs/GaSb SL active layer are fabricated with a series pixel area using anode sulfide passivation. Corresponding to 50% cutoff wavelengths of 5.0 μm at 77K, the peak directivity of the detectors is 1.6 × 1010 cm·Hz1/2 W−1 at 77K.

Electrochemical regeneration of sulfur loaded electrodes

Electrochemical oxidation of sulfide is a promising technique for its removal from wastewaters. Generally, the main product of this oxidation reaction is elemental sulfur. The latter deposits as a solid on the electrode and deactivates it. Therefore, an efficient and effective regeneration technique of sulfur loaded electrodes is required for the practical implementation of this technology. Here we demonstrate a method for in situ reduction of electrodeposited sulfur on carbon fibre electrodes to sulfide/polysulfides, at low energy input. The intermediary coulombic efficiency (CE) values strongly depend on pH and buffer capacity of the solution. These values were recorded up to 435 ± 5% due to simultaneous chemical dissolution of sulfur to polysulfides under alkaline conditions. This process demonstrates the potential for continuously removing dissolved sulfide from wastewaters at an anode as sulfur and recovering the deposited sulfur based on regular switching between anodic sulfide oxidation and cathodic sulfur reduction.

Sulphide stress cracking behaviour of weldments produced by indirect electric arc welding

The aim of the present study was to evaluate the corrosion resistance of weldments produced by the Indirect Electric Arc technique. The material studied was API grade X-65 steel, which was corroded in NACE solution saturated with H2S. Three different temperatures were employed, room temperature (25°C), 37°C and 50°C. The test methods used included potentiodynamic polarisation curves, hydrogen permeation measurements and slow strain rate tests. The anodic corrosion current density and sulphide stress cracking susceptibility of the weldments were found to be unaffected by temperature over the range 25–50°C. However, values of the steady-state hydrogen permeation current, hydrogen permeation rate, effective diffusion coefficient, and the concentration of hydrogen atoms at the entrance side all increased with temperature. The cracking of the X-65 weldments is explained in terms of a hydrogen embrittlement mechanism.

Optical characterisation of anodic sulphide films on Hg 1− xCd xTe (MCT) grown by the potential step method

The growth of native sulphide films on Hg 1− x Cd x Te (MCT) by potential steps to two different electrochemical growth regions has been studied by in-situ ellipsometry, photocurrent spectroscopy and second harmonic generation (SHG) rotational anisotropy. Films grown at −0.4 V versus SCE were porous and consisted mainly of cubic close packed (ccp) CdS. The photocurrent spectrum of the film exhibited a cut-off which closely conformed to the expected bandgap of CdS. The gradual increase in SH intensity as the sulphide film thickened was due to a contribution to the overall SH signal from the CdS film itself. No evidence of any hcp species was apparent in the rotational anisotropy patterns, with the four-fold pattern expected for the vicinal MCT surface being maintained even after film growth. When the potential was stepped to −0.3 V, the film grown absorbed the ellipsometer radiation once a thickness of 86 nm was reached. Photocurrent measurements showed a tail extending into the red region of the spectrum. These phenomena have been attributed to the incorporation of ccp HgS into the sulphide film as at this potential, the electrochemical reaction of the HgTe component of MCT can occur. SHG rotational anisotropy confirmed the four-fold symmetry of the ccp surface film.