Electron Conduit Research Articles

Trimetallic alloy nanoparticles as cocatalyst for improving the photocatalytic performance of graphitic carbon nitride for H2 production

Trimetallic alloy nanoparticles (NPs) hybridized with graphitic carbon nitride (g-C3N4) nanosheets show potential as photocatalysts owing to their multicomponent interactions, increased catalytic efficiency, and enhanced stability. Herein, a NiCoAg–CN nanocomposite comprising NiCoAg alloy NPs deposited on g-C3N4 nanosheets was synthesized via photoreduction using simulated solar light. X-ray photoelectron spectroscopy revealed the metallic properties of Ni, Co, and Ag within the NiCoAg–CN nanocomposite, and the high-resolution transmission electron microscopy image showed alloy NPs on the surface of g-C3N4. The as-formed Schottky junction accelerated the separation and transfer of photoinduced charge carriers in NiCoAg–CN. NiCoAg–CN exhibited a remarkable photocatalytic hydrogen (H2) yield of 4896 μmol/g, surpassing the performance of NiAg–CN and CoAg–CN by 1.9- and 1.8-fold, respectively. This is attributed to the enhanced catalytically active sites, facilitating rapid charge carrier transfer between the NiCoAg alloy and the g-C3N4 nanosheets. Photoluminescence spectra indicated that NiCoAg NPs served as efficient electron conduits, suppressing charge carrier recombination and promoting direct electron transfer. Alloy NPs synthesized via the proposed strategy efficiently harness solar radiation, facilitate charge carrier transfer, and mitigate recombination, thus advancing efficient photocatalytic H2 generation.

Biological Self-Assembled Transmembrane Electron Conduits for High-Efficiency Ammonia Production in Microbial Electrosynthesis.

Usually, CymA is irreplaceable as the electron transport hub in Shewanella oneidensis MR-1 bidirectional electron transfer. In this work, biologically self-assembled FeS nanoparticles construct an artificial electron transfer route and implement electron transfer from extracellular into periplasmic space without CymA involvement, which present similar properties to type IV pili. Bacteria are wired up into a network, and more electron transfer conduits are activated by self-assembled transmembrane FeS nanoparticles (electron conduits), thereby substantially enhancing the ammonia production. In this study, we achieved an average NH4+-N production rate of 391.8 μg·h-1·L reactor-1 with the selectivity of 98.0% and cathode efficiency of 65.4%. Additionally, the amide group in the protein-like substances located in the outer membrane was first found to be able to transfer electrons from extracellular into intracellular with c-type cytochromes. Our work provides a new viewpoint that contributes to a better understanding of the interconnections between semiconductor materials and bacteria and inspires the exploration of new electron transfer chain components.

MmcA is an electron conduit that facilitates both intracellular and extracellular electron transport in Methanosarcina acetivorans

Methanogens are a diverse group of Archaea that obligately couple energy conservation to the production of methane. Some methanogens encode alternate pathways for energy conservation, like anaerobic respiration, but the biochemical details of this process are unknown. We show that a multiheme c-type cytochrome called MmcA from Methanosarcina acetivorans is important for intracellular electron transport during methanogenesis and can also reduce extracellular electron acceptors like soluble Fe3+ and anthraquinone-2,6-disulfonate. Consistent with these observations, MmcA displays reversible redox features ranging from −100 to −450 mV versus SHE. Additionally, mutants lacking mmcA have significantly slower Fe3+ reduction rates. The mmcA locus is prevalent in members of the Order Methanosarcinales and is a part of a distinct clade of multiheme cytochromes that are closely related to octaheme tetrathionate reductases. Taken together, MmcA might act as an electron conduit that can potentially support a variety of energy conservation strategies that extend beyond methanogenesis.

Shallow conductance decay along the heme array of a single tetraheme protein wire.

Multiheme cytochromes (MHCs) are the building blocks of highly conductive micrometre-long supramolecular wires found in so-called electrical bacteria. Recent studies have revealed that these proteins possess a long supramolecular array of closely packed heme cofactors along the main molecular axis alternating between perpendicular and stacking configurations (TST = T-shaped, stacked, T-shaped). While TST arrays have been identified as the likely electron conduit, the mechanisms of outstanding long-range charge transport observed in these structures remain unknown. Here we study charge transport on individual small tetraheme cytochromes (STCs) containing a single TST heme array. Individual STCs are trapped in a controllable nanoscale tunnelling gap. By modulating the tunnelling gap separation, we are able to selectively probe four different electron pathways involving 1, 2, 3 and 4 heme cofactors, respectively, leading to the determination of the electron tunnelling decay constant along the TST heme motif. Conductance calculations of selected single-STC junctions are in excellent agreement with experiments and suggest a mechanism of electron tunnelling with shallow length decay constant through an individual STC. These results demonstrate that an individual TST motif supporting electron tunnelling might contribute to a tunnelling-assisted charge transport diffusion mechanism in larger TST associations.

Bacterial extracellular electron transfer components are spin selective.

Metal-reducing bacteria have adapted the ability to respire extracellular solid surfaces instead of soluble oxidants. This process requires an electron transport pathway that spans from the inner membrane, across the periplasm, through the outer membrane, and to an external surface. Multiheme cytochromes are the primary machinery for moving electrons through this pathway. Recent studies show that the chiral-induced spin selectivity (CISS) effect is observable in some of these proteins extracted from the model metal-reducing bacteria, Shewanella oneidensis MR-1. It was hypothesized that the CISS effect facilitates efficient electron transport in these proteins by coupling electron velocity to spin, thus reducing the probability of backscattering. However, these studies focused exclusively on the cell surface electron conduits, and thus, CISS has not been investigated in upstream electron transfer components such as the membrane-associated MtrA, or periplasmic proteins such as small tetraheme cytochrome (STC). By using conductive probe atomic force microscopy measurements of protein monolayers adsorbed onto ferromagnetic substrates, we show that electron transport is spin selective in both MtrA and STC. Moreover, we have determined the spin polarization of MtrA to be ∼77% and STC to be ∼35%. This disparity in spin polarizations could indicate that spin selectivity is length dependent in heme proteins, given that MtrA is approximately two times longer than STC. Most significantly, our study indicates that spin-dependent interactions affect the entire extracellular electron transport pathway.

Dihydropyrimidine dehydrogenase from Escherichia coli: Transient state analysis reveals both reductive activation prior to turnover and diminished substrate effector roles relative to the mammalian form

Dihydropyrimidine dehydrogenase (DPD) is an enzyme that uses an elaborate architecture to catalyze a simple net reaction: the reduction of the vinylic bond of uracil and thymine. Known DPDs have two active sites separated by approximately 60 Å. One active site has an FAD cofactor and binds NAD(P) and the other has an FMN cofactor and binds pyrimidines. The intervening distance is spanned by four Fe4S4 centers that act as an electron conduit. Recent advancements with porcine DPD have revealed unexpected chemical sequences where the enzyme undergoes reductive activation by transferring two electrons from NADPH to the FMN via the FAD such that the active form has the cofactor set FAD•4(Fe4S4)•FMNH2. Here we describe the first comprehensive kinetic investigation of a bacterial form of DPD. Using primarily transient state methods, DPD from E. coli (EcDPD) was shown to have a similar mechanism to that observed with the mammalian form in that EcDPD is observed to undergo reductive activation before pyrimidine reduction and displays half-of-sites activity. However, two distinct aspects of the EcDPD reaction relative to the mammalian enzyme were observed that relate to the effector roles for substrates: (i) the enzyme will rapidly take up electrons from NADH, reducing a flavin in the absence of pyrimidine substrate, and (ii) the activated form of the enzyme can become fully oxidized by transferring electrons to pyrimidine substrates in the absence of NADH.

Engineering cell-electrode interfacial electron transfer to boost power generation of electroactive biofilm

Electroactive biofilm plays a crucial rule in the electron transfer efficiency of bio-electrochemical systems (BES). However, the slow rate of interfacial electron transfer (IET) restricts practical applications of various BES. Here, a modular engineering strategy was developed to enhance IET rate. Firstly, to accelerate the low transmembrane electron transfer rate caused by insulative cell membrane of Shewanella oneidensis, pili-based artificial conductive nanowires and outer-membrane c-cytochrome OmcF from Geobacter sulfurreducens were heterologously expressed to construct transmembrane electron conduits. Secondly, to improve the low electron transfer rate from S. oneidensis to anode owing to the poor electron collection ability of the anode, N-doped carbon nanotubes and polyriboflavin were used to increase the surface area and active sites of the anode. Thirdly, to further reduce the resistance due to the low conductivity of biofilm, the polydopamine was coated in situ to construct high-speed conductive networks, obtaining an unprecedented power density of 5233.7 ± 364.7 mW/m2, ∼83.1-fold higher than that of the wild-type strain (62.2 ± 5.5 mW/m2), and the maximum coulomb efficiency of ESR1 @PDA was 85.4%, which, to the best of our knowledge, is one of the highest output power densities and coulomb efficiencies that have ever reported in the genetically engineered Shewanella strains. This study demonstrated an integrated biotic-electrode modular engineering strategy to boost power generation of electroactive biofilm via synthetic biology and material engineering.

Polypyrrole Electrodes Show Strain‐Specific Enhancement of Photocurrent from Cyanobacteria

AbstractThe discovery of extracellular electron conduits has spurred new applications in microbial electronics. Except for a limited number of exoelectrogens, most microbes are surrounded by insulating membranes that impair extracellular electron transfer. This study focuses on the fabrication of a conductive polypyrrole (PPy) coating for enhancing microbial charge extraction. The polymer deposition is characterized and optimized using a combination of potentiodynamic and potentiostatic measurements as well as scanning electron microscopy (SEM), energy dispersive X‐Ray (EDX) analysis, and Raman spectroscopy. The electrodes are used to extract photosynthetic electrons from the cyanobacteria Synechocystis sp. PCC6803 (Synechocystis) and Synechococcus Elongatus PCC7942 (Elongatus). The PPy electrode shows a sixfold increase in extracted photocurrent for Synechocystis under unmediated conditions compared to bare graphite electrodes. This enhancement is attributed to the decreased resistance and increased electroactive surface area of the PPy electrode. By contrast, Elongatus shows no substantial difference in photocurrent between the PPy and bare electrodes. Compared to Synechocystis cells, the Elongatus cells show limited electrode adherence with weaker charge interactions. These findings lay the framework for designing customized polymer electrodes for strain‐specific charge extraction.

Enhanced photocatalytic CO2 reduction on biomineralized CdS via an electron conduit in bacteria.

There is an increasing trend in semi-artificial photosynthesis systems that combine living cells with inorganic semiconductors to activate a bacterial catalytic network. However, these systems face various challenges, including electron-hole recombination, photocorrosion, and the generation of photoexcited radicals by semiconductors, all of which impair the efficiency, stability, and sustainability of biohybrids. We first focus on a reverse strategy to improve highly efficient CO2 photoreduction on biosynthesized inorganic semiconductors using an electron conduit in the electroactive bacterium S. oneidensis MR-1. Due to the suppressed charge recombination and photocorrosion on CdS, the maximum photocatalytic production rate of formate in water was 2650 μmol g-1 h-1 (with a selectivity of ca.100%), which ranks high among all photocatalysts and is the highest for inorganic-biological hybrid systems in an all-inorganic aqueous environment. The reverse enhancement effect of electrogenic bacteria on photocatalysis on semiconductors inspires new insight to develop a new generation of bio-semiconductor catalysts for solar chemical production.

Directed self-assembly strategy of a DET complex based on the application of artificial electron channeling

Custom exogenous ferredoxin (Fdx) created a new conduit for electrons to travel from the reductase to the oxygenase, which increased the 4-androstene-3,17-dione (AD) conversion rate.

Direct extracellular electron transfer from Escherichia coli through modified carbon nanoparticles

Direct electron transfer (DET) from bacteria to the electrode is one of the key factors in developing microbial electrochemical technology. While extensive study has been made for exoelectrogens, DET for nonexoelectrogens has not been seriously taken. Here we report our preliminary results on DET in which Escherichia coli (E. coli) was chosen as a model nonexoelectrogen and carbon nanoparticles (CNPs) as an electron conduit connecting E. coli and the electrode. To improve accessibility of CNPs to the bacterium and the carbon electrode, CNPs were modified with 4-aminophenyl groups (4AP) and the carbon surface with carboxyl groups. Thus modified 4AP-CNPs were positively charged in neutral pH that induces electrostatic interaction both with the negatively charged cell surface and with the electrode. When glucose was used as a substrate, oxidation current was observed at -110 mV vs. Ag/AgCl, indicating that electrons generated from the glucose oxidation were captured by 4AP-CNPs and directly transferred to the electrode, which was confirmed under various conditions. It was found that oxidation current increased with glucose concentration and without E. coli, no oxidation was observed. This work shows DET is possible even from nonexoelectrogens and opens a possibility for utilizing those bacteria.

Enhanced methane production in anaerobic digestion: A critical review on regulation based on electron transfer

Anaerobic digestion (AD) is a potential bioprocess for waste biomass utilization and energy conservation. Various iron/carbon-based CMs (e.g., magnetite, biochar, granular activated carbon (GAC), graphite and zero valent iron (ZVI)) have been supplemented in anaerobic digestors to improve AD performance. Generally, the supplementation of CMs has shown to improve methane production, shorten lag phase and alleviate environmental stress because they could serve as electron conduits and promote direct interspecies electron transfer (DIET). However, the CMs dosage varied greatly in previous studies and CMs wash out remains a challenge for its application in full-scale plants. Future work is recommended to standardize the CMs dosage and recover/reuse the CMs. Moreover, additional evidence is required to verify the electrotrophs involved in DIET.

Pyrogenic carbon facilitated microbial extracellular electron transfer in electrogenic granular sludge via geobattery mechanism

Electroactive pyrogenic carbon (PC) is an intriguing candidate for realizing the ambitious goals of large-scale applications of microbial electrochemical technologies (METs). In this study, PC was employed to promote the extracellular electron transfer (EET) within the electrogenic granular sludge (EGS) by acting as an electron conduit. The pecan shell-derived PC prepared at three temperatures (600, 800, and 1000 ˚C) contained rich oxygenated-functional moieties (mainly quinone) on the surface, endowing a good electron transfer capacity (EEC). The maximum current density (Jmax) of EGS with PC amendment outperformed the control EGS without PC amendment, i.e., 100-132 times higher than Jamx of EGS in the absence of PC. Among various pyrolysis temperatures, the PC derived from 600 ˚C produced the highest Jmax (0.40 A/ m2), 0.67-times, and 0.33-times higher than that of PC derived from 800 and 1000 ˚C, respectively. Furthermore, more polysaccharides were secreted in extracellular polymeric substance with PC amendments. The microbial community analysis demonstrated that the PC favored the growth of electroactive bacteria over methanogens. The metabolic pathway revealed that PC induced more functional enzymes in the quinone biosynthesis and cytochrome c and heme synthesis, resulting in an enhanced EET. The EEC of PC was responsible for the EET enhancement effect via PC acting as a geobattery to wire up the EGS and electrodes. Overall, this study pinpoints the finding of PC role in a mixed electroactive biofilm and provides a wide scenario of the PC applications in MET at large scales.

Iodate Reduction by Shewanella oneidensis Requires Genes Encoding an Extracellular Dimethylsulfoxide Reductase.

Microbial iodate (IO3–) reduction is a major component of the iodine biogeochemical reaction network in anaerobic marine basins and radioactive iodine-contaminated subsurface environments. Alternative iodine remediation technologies include microbial reduction of IO3– to iodide (I–) and microbial methylation of I– to volatile gases. The metal reduction pathway is required for anaerobic IO3– respiration by the gammaproteobacterium Shewanella oneidensis. However, the terminal IO3– reductase and additional enzymes involved in the S. oneidensis IO3– electron transport chain have not yet been identified. In this study, gene deletion mutants deficient in four extracellular electron conduits (EECs; ΔmtrA, ΔmtrA-ΔmtrDEF, ΔmtrA-ΔdmsEF, ΔmtrA-ΔSO4360) and DMSO reductase (ΔdmsB) of S. oneidensis were constructed and examined for anaerobic IO3– reduction activity with either 20 mM lactate or formate as an electron donor. IO3– reduction rate experiments were conducted under anaerobic conditions in defined minimal medium amended with 250 μM IO3– as anaerobic electron acceptor. Only the ΔmtrA mutant displayed a severe deficiency in IO3– reduction activity with lactate as the electron donor, which suggested that the EEC-associated decaheme cytochrome was required for lactate-dependent IO3– reduction. The ΔmtrA-ΔdmsEF triple mutant displayed a severe deficiency in IO3– reduction activity with formate as the electron donor, whereas ΔmtrA-ΔmtrDEF and ΔmtrA-ΔSO4360 retained moderate IO3– reduction activity, which suggested that the EEC-associated dimethylsulfoxide (DMSO) reductase membrane-spanning protein DmsE, but not MtrA, was required for formate-dependent IO3– reduction. Furthermore, gene deletion mutant ΔdmsB (deficient in the extracellular terminal DMSO reductase protein DmsB) and wild-type cells grown with tungsten replacing molybdenum (a required co-factor for DmsA catalytic activity) in defined growth medium were unable to reduce IO3– with either lactate or formate as the electron donor, which indicated that the DmsAB complex functions as an extracellular IO3– terminal reductase for both electron donors. Results of this study provide complementary genetic and phenotypic evidence that the extracellular DMSO reductase complex DmsAB of S. oneidensis displays broad substrate specificity and reduces IO3– as an alternate terminal electron acceptor.

Customized exogenous ferredoxin functions as an efficient electron carrier

Ferredoxin (Fdx) is regarded as the main electron carrier in biological electron transfer and acts as an electron donor in metabolic pathways of many organisms. Here, we screened a self-sufficient P450-derived reductase PRF with promising production yield of 9OHAD (9α-hydroxy4-androstene-3,17-dione) from AD, and further proved the importance of [2Fe–2S] clusters of ferredoxin-oxidoreductase in transferring electrons in steroidal conversion. The results of truncated Fdx domain in all oxidoreductases and mutagenesis data elucidated the indispensable role of [2Fe–2S] clusters in the electron transfer process. By adding the independent plant-type Fdx to the reaction system, the AD (4-androstene-3,17-dione) conversion rate have been significantly improved. A novel efficient electron transfer pathway of PRF + Fdx + KshA (KshA, Rieske-type oxygenase of 3-ketosteroid-9-hydroxylase) in the reaction system rather than KshAB complex system was proposed based on analysis of protein–protein interactions and redox potential measurement. Adding free Fdx created a new conduit for electrons to travel from reductase to oxygenase. This electron transfer pathway provides new insight for the development of efficient exogenous Fdx as an electron carrier.Graphical

Bespoke Biomolecular Wires for Transmembrane Electron Transfer: Spontaneous Assembly of a Functionalized Multiheme Electron Conduit.

Shewanella oneidensis exchanges electrons between cellular metabolism and external redox partners in a process that attracts much attention for production of green electricity (microbial fuel cells) and chemicals (microbial electrosynthesis). A critical component of this pathway is the outer membrane spanning MTR complex, a biomolecular wire formed of the MtrA, MtrB, and MtrC proteins. MtrA and MtrC are decaheme cytochromes that form a chain of close-packed hemes to define an electron transfer pathway of 185 Å. MtrA is wrapped inside MtrB for solubility across the outer membrane lipid bilayer; MtrC sits outside the cell for electron exchange with external redox partners. Here, we demonstrate tight and spontaneous in vitro association of MtrAB with separately purified MtrC. The resulting complex is comparable with the MTR complex naturally assembled by Shewanella in terms of both its structure and rates of electron transfer across a lipid bilayer. Our findings reveal the potential for building bespoke electron conduits where MtrAB combines with chemically modified MtrC, in this case, labeled with a Ru-dye that enables light-triggered electron injection into the MtrC heme chain.

Engineering Cells, Membranes and Light Harvesting/Photosystem II Super-Complexes in Bio-Photoelectrochemical Cells

Photosynthetic organisms, membranes and complexes are attractive starting materials for solar energy conversion (SEC). Our overall goal is to develop methods to perform SEC using these materials in simple, inexpensive and a fashion that will be non-polluting and will not compete with the growth of food materials. I will describe here how the remarkable photocatalytic activity of the photosynthetic apparatus can provide overall water splitting with oxygen and hydrogen production in Bio-Photo-Electro-Chemical (BPEC) cells via the simplest and cleanest of processes wither in the absence or presence of added electron transport molecules. With plant thylakoids, electrons are shuttled by FeCN to a transparent FTO electrode, yielding a photocurrent density of 0.5 mA·cm-2. Hydrogen evolution occurs at the cathode at a bias as low as 0.8 V. A tandem cell comprising the BPEC cell with the thylakoid membranes and a Si photovoltaic module achieves overall water splitting with solar to hydrogen conversion efficiency of 0.3% (Pinhassi et al. Nature Communications 2016). With cyanobacterial cells, electrons from the respiratory system are energized by the photosynthetic system and transferred directly to a graphite electrode, utilizing endogenous electron carriers, especially NADPH (Saper et al. Nature Communications 2018 and Shlosberg et al. iScience 2020). The current produced can be used for hydrogen production at low additional bias for significantly longer durations than the plant thylakoids.Another route is to use isolated photosynthetic complexes and chemically connect them to the electrochemical cell. One of the issues with this strategy is the small number of light absorbing chromophores connected to the complex, lowering the photochemical efficiency. Connection of isolated light harvesting (LH) complexes can help to overcome this deficiency. Photosystem II (PSII) is the only enzyme that catalyzes light-induced water oxidation being the basis for its application as a biophotoanode in various bio-photovoltaics and photo-bioelectrochemical cells. However, the absorption spectrum of PSII limits the quantum efficiency in the range of visible light, due to a gap in the green absorption region of chlorophylls (500 - 600 nm). To overcome this limitation, we have used two strategies: stabilizing the interaction between PSII and Phycobilisomes (PBSs) –LH complex or direct connection to modified gold-nanoparticles (Au-NPs) that serve both as LH and electron conduit. Integration of the PBS-PSII super-complexes within an Os-complex-modified hydrogel on macro-porous indium tin oxide electrodes (MP-ITO) resulted in notably improved, wavelength dependent, incident photon-to-electron conversion efficiencies (Hartmann et al. J. Mat. Chem. A. 2020). With the Au-NPs, record currents were obtained, with strong improvement in the SPR range of wavelengths that are not absorbed by chlorophylls.

Ferroferric oxide promotes metabolism in Anaerolineae other than microbial syntrophy in anaerobic methanogenesis of antibiotic fermentation residue

Antibiotic fermentation residue (AFR) is a kind of protein-rich biosolids that would be utilized as valuable substrates for biogas production. However, the effectiveness of conductive material supplementation and its effect on the microbiome in anaerobic digestion of AFR have not been fully elucidated. The objective of this study is to access the impact of Fe3O4 addition on anaerobic digestion of AFR and reveal its microbial mechanism. By adding Fe3O4 at concentration of 150 mg/gTS to two typical AFRs, the methane yield was decreased while the methane production rate was significantly enhanced by 48% and 21%, respectively. Genomic analyses revealed that the Fe3O4 addition altered the microbial community by selecting the unknown genus of Anaerolineae with the metabolic capacity of carbohydrate hydrolysis and proteolysis. Meanwhile, the hydrogenotrophic methanogenesis was the dominant pathway in the AFR digestion system, which was mostly contributed by the Methanoculleus and Methanolinea. More interestingly, Methanoculleus might possess fermentative capability involved in the versatile hydrolysis pathway. Although the genes related to electrically conductive pili were detected, the induction of direct interspecies electron transfer by Fe3O4 supplementation was not confirmed in this study. In summary, except the accelerated methane production rate, Fe3O4 addition functioned as biostimulator for Anaerolineae other than electron conduit in anaerobic methanogenesis in the AFR digestion system.

OMS-2 nanorods filled with Co-ion in the tunnels as efficient electron conduits and regulatory substance for oxygen reduction

Co-filled OMS-2 nanorods (Co-OMS-2) of different concentrations are synthesized by a simple hydrothermal reaction. Electrocatalytic test results indicate that Co-OMS-2 has excellent catalytic activity (Vonset: 0.905 V, Vhalf: 0.806 V vs. RHE), rapid reaction kinetics, and favorable stability. The obvious improvement in catalytic behavior correlates with the enhancement of conductivity and oxygen adsorption capacity studied by specific experiments. On the one hand, ions fill the tunnels as efficient electron conduits to accelerate the electron transfer and interconversion of Mn3+/ Mn4+ couple enhance intrinsic conductivity of OMS-2. On the other hand, ions in the tunnels act as regulatory substances to regulate the oxidation state requirements and coordination geometry of MnO6 octahedron, which is helpful to stabilize Mn3+ and enhance O2 adsorption. It is essential to understand the mechanisms that regulate the oxygen reduction activity of manganese oxides by filling the metal cation. And the roles of Co-ion in the tunnels of OMS-2 for oxygen reduction reaction (ORR) were studied in depth. All the experimental studies are confirmed by density functional theory (DFT) computations. This work shows for the first time there is an explicit correlation between OMS-2 and tunnel cation for the ORR in alkaline medium.

Stress Bearing Mechanism of Reduced Graphene Oxide in Silicon-Based Composite Anodes for Lithium Ion Batteries.

Despite the significant research that has been carried out to improve cycling performance of lithium ion batteries (LIB) with silicon (Si) based composite electrodes, limited studies have been performed on these materials to evaluate the effects of internal microstructural changes and stress evolution on the electrochemical performance. Here, combined ex situ and in situ investigations on the accommodation of volume expansion in Si-based nanocomposite electrodes are reported. This work emphasizes the importance of conductive agents in light of the poor electronic conductivity of Si. A detailed comparison between commonly used carbon black (CB) and reduced graphene oxide (rGO) shows that these materials have substantial effects on microstructural evolution and internal stress in Si based composite electrodes that are employed in lithium ion cells. This study provides the first monitoring of stress evolution in Si-rGO based composite electrode during electrochemical cycling using in situ wafer curvature measurements. The prepared Si-rGO based electrode exhibits almost 10 times lower stress generation and consequently higher cycling performance in electrochemical cells. The resulting 3D networked structure not only acts as an electronic conduit to the encapsulated active materials but also serves as a mini-electrochemical reaction chamber which hinders the formation of the solid electrolyte interphase (SEI) and limits the pulverization of active material and the evolution of severe stress during cycling. Moreover, investigations of the microstructural changes and internal charge transfer resistance in the electrodes after cycling provide further evidence that rGO produces superior structures for energy storage.