Limited Electron Transfer Research Articles

Electrode/Electrolyte Synergy for Concerted Promotion of Electron and Proton Transfers toward Efficient Neutral Water Oxidation

AbstractNeutral water oxidation is a crucial half‐reaction for various electrochemical applications requiring pH‐benign conditions. However, its sluggish kinetics with limited proton and electron transfer rates greatly impacts the overall energy efficiency. In this work, we created an electrode/electrolyte synergy strategy for simultaneously enhancing the proton and electron transfers at the interface toward highly efficient neutral water oxidation. The charge transfer was accelerated between the iridium oxide and in situ formed nickel oxyhydroxide on the electrode end. The proton transfer was expedited by the compact borate environment that originated from hierarchical fluoride/borate anions on the electrolyte end. These concerted promotions facilitated the proton‐coupled electron transfer (PCET) events. Due to the electrode/electrolyte synergy, Ir−O and Ir−OO− intermediates could be directly detected by in situ Raman spectroscopy, and the rate‐limiting step of Ir−O oxidation was determined. This synergy strategy can extend the scope of optimizing electrocatalytic activities toward more electrode/electrolyte combinations.

Bioinduced Surface Oxygen Vacancies on Bismuth Trioxide Nanocrystals for Photocathodic Bioassays

Cathodic photoelectrochemistry with superior photostability and anti-interference capability has been shown to be appealing in the field of bioanalysis. However, a major challenge regarding this technology is the limited photoinduced electron transfer signal transduction mechanism. Herein, we disclose a finding of the bioinduced surface oxygen vacancy (VO) on bismuth trioxide (Bi2O3) nanocrystals, which underlies an innovative mechanism for cathodic photoelectrochemical (PEC) bioanalysis. The protocatechuic acid engendered from the tandem enzymatic reaction of p-hydroxybenzoate hydroxylase (PHBH) and glucose-6-phosphate dehydrogenase (G6PD) can coordinate with the surface of Bi2O3 nanocrystals through forming binary Bi–O–C bonds, which breaks the initial Bi–O bonds and enables the escape of O2– from the lattice to form surface VO in situ. The surface VO can function as a separation center for charge carriers, which is favorable to the generation of cathodic photocurrent. In such a system, the cathodic signal is linearly correlated with the targets, glucose-6-phosphate (G-6-P) and G6PD, in concentration ranges of 8.0 to 8.0 × 105 μM and 0.1 to 1.0 × 104 U/L, achieving detection limits of 2.0 μM and 0.03 U/L, respectively. This study not only offers a way of introducing surface VO in situ but also enriches the current toolbox of cathodic PEC bioassays and promises to stimulate further interest in exploring surface effect engineering in other fields.

Bicarbonate activation of the monomeric photosystem II-PsbS/Psb27 complex.

In thylakoid membranes, photosystem II (PSII) monomers from the stromal lamellae contain the subunits PsbS and Psb27 (PSIIm-S/27), while PSII monomers (PSIIm) from granal regions lack these subunits. Here, we have isolated and characterized these 2 types of PSII complexes in tobacco (Nicotiana tabacum). PSIIm-S/27 showed enhanced fluorescence, the near absence of oxygen evolution, and limited and slow electron transfer from QA to QB compared to the near-normal activities in the granal PSIIm. However, when bicarbonate was added to PSIIm-S/27, water splitting and QA to QB electron transfer rates were comparable to those in granal PSIIm. The findings suggest that the binding of PsbS and/or Psb27 inhibits forward electron transfer and lowers the binding affinity for bicarbonate. This can be rationalized in terms of the recently discovered photoprotection role played by bicarbonate binding via the redox tuning of the QA/QA•- couple, which controls the charge recombination route, and this limits chlorophyll triplet-mediated 1O2 formation. These findings suggest that PSIIm-S/27 is an intermediate in the assembly of PSII in which PsbS and/or Psb27 restrict PSII activity while in transit using a bicarbonate-mediated switch and protective mechanism.

CNTs Bridged Basal-Plane-Active 2H-MoS2 Nanosheets for Efficient Robust Electrocatalysis.

2D 2H-phase MoS2 is promising for electrocatalytic applications because of its stable phase, rich edge sites, and large surface area. However, the pristine low-conductive 2H-MoS2 suffers from limited electron transfer and surface activity, which become worse after their highly likely aggregation/stacking and self-curling during applications. In this work, these issues are overcome by conformally attaching the intercalation-detonation-exfoliated, surface S-vacancy-rich 2H-MoS2 onto robust conductive carbon nanotubes (CNTs), which electrically bridge bulk electrode and local MoS2 catalysts. The optimized MoS2 /CNTs nanojunctions exhibit outstanding stable electroactivity (close to commercial Pt/C): a polarization overpotential of 79mV at the current density of 10mAcm-2 and the Tafel slope of 33.5mVdec-1 . Theoretical calculations unveil the metalized interfacial electronic structure of MoS2 /CNTs nanojunctions, enhancing defective-MoS2 surface activity and local conductivity. This work provides guidance on rational design for advanced multifaceted 2D catalysts combined with robust bridging conductors to accelerate energy technology development.

Synthesis and Peroxide Activation Mechanism of Bimetallic MOF for Water Contaminant Degradation: A Review.

Metal-organic framework (MOF) materials possess a large specific surface area, high porosity, and atomically dispersed metal active sites, which confer excellent catalytic performance as peroxide (peroxodisulfate (PDS), peroxomonosulfate (PMS), and hydrogen peroxide (H2O2)) activation catalysts. However, the limited electron transfer characteristics and chemical stability of traditional monometallic MOFs restrict their catalytic performance and large-scale application in advanced oxidation reactions. Furthermore, the single-metal active site and uniform charge density distribution of monometallic MOFs result in a fixed activation reaction path of peroxide in the Fenton-like reaction process. To address these limitations, bimetallic MOFs have been developed to improve catalytic activity, stability, and reaction controllability in peroxide activation reactions. Compared with monometallic MOFs, bimetallic MOFs enhance the active site of the material, promote internal electron transfer, and even alter the activation path through the synergistic effect of bimetals. In this review, we systematically summarize the preparation methods of bimetallic MOFs and the mechanism of activating different peroxide systems. Moreover, we discuss the reaction factors that affect the process of peroxide activation. This report aims to expand the understanding of bimetallic MOF synthesis and their catalytic mechanisms in advanced oxidation processes.

Production of renewable fuel from CO2 by Co3O4/Cr doped MgAl–LDH p-n heterojunction catalyst

Converting CO2 into renewable fuel via photocatalysis is of significance to solving the energy crisis and climate change. However, the limited electron transfer in single catalysts always limits the reduction reaction. In this work, a p-n heterojunction was constructed between Cr doped MgAl–LDH (abbreviated as LDH) and Co3O4 for visible-light-driven fuel production. Since LDH and Co3O4 both have the sufficient potentials to drive CO2 photoreduction, the constructed type-II heterojunction is more favorable for electron utilization efficiency. The optimal Co3O4/LDH heterojunction exhibited the highest CO evolution rate of 7.42 μmol•g−1•h−1 and a CO selectivity of 90.5% with TEOA as sacrificial agent. The further characterizations highlight that the addition of Co3O4 greatly improves the light absorption and the heterojunction effectively promotes the reverse migration of electrons and holes. This work investigates and verifies the designed type-II heterojunction based on MgAl–LDH, which has the guidance for the design of heterojunction catalysts and promotes the practical application of MgAl–LDH in photocatalytic region.

Reticular polarization engineering of covalent organic frameworks for accelerated generation of superoxide anion radicals

The exploration of type I mechanism remains a great challenge in photodynamic therapy (PDT) due to the limited electron transfer from the photosensitizer to ground state oxygen to form superoxide anion radical (O2−). In this study, we design three kinds of nanoscale covalent organic frameworks (COFs) with tunable local polarization for accelerating the generation of O2−. Among three COFs, the tetrakis-(4-formylphenyl)benzene-based COF (TB-COF) exhibits highly aggravated local polarization with 3.29 Debye of the dipole moment, and thus drives the photoinduced e− reduction of O2/O2−, which matches with the energy level of TB-COF. The elongated charge-separated state of TB-COF is also identified by femtosecond transient absorption spectra and time-dependent density functional theory calculation. Significantly, the inhibited electron-hole recombination of COFs further improves the O2− production efficiency upon protonation and thus strengthens anti-cancer effect in the acidic microenvironment of tumor cell or in vivo. The reticular polarization engineering of COFs provides a new type I PDT paradigm in biomedical applications.

Synergistic of yeast Saccharomyces cerevisiae and glucose oxidase enzyme as co-biocatalyst of enzymatic microbial fuel cell (EMFC) in converting sugarcane bagasse extract into electricity

The microbial fuel cell (MFC) is an ecologically friendly alternative energy source. Due to the typically limited electron transfer in MFC systems, co-biocatalysts are necessary to enhance their performance. Enzymes are used as co-biocatalysts due to their superior ability to generate energy, and the system is known as an enzymatic microbial fuel cell (EMFC). One of the substrates that may be used is bagasse waste extracted from sugarcane. Saccharo­myces cerevisiae and the enzyme glucose oxidase (GOx) serve as co-biocatalysts in the breakdown of sugarcane bagasse waste in this study, which uses single-chamber EMFCs. In EMFC using sugarcane bagasse waste extract employing S. cerevisiae biocatalyst and glucose oxidase enzyme co-biocatalyst, the open circuit voltage was 0.56 V and the maximum power density was 146.65 mW m-2, an increase of 10.4 times to MFCs that solely employed only yeast biocatalyst. In addition, the chemical oxygen demand (COD) reduction achieved by this technology is 75 %. In addition, the pH of sugarcane bagasse waste extract samples treated with Saccharomyces cerevisiae yeast and GOx enzyme decreased from 4.6 to 4.2. This research demonstrates that adding the co-biocatalyst GOx enzyme may boost the performance of the traditional yeast MFC.

Electrical stimulation accelerated phenanthrene biodegradation coupling with nitrate reduction in groundwater

Phenanthrene (PHE) and nitrate co-contamination widely exists in the groundwater. Anaerobic bioremediation of the two suffered from the slow removal rate and limited electron transfer within microbes. Herein electrical stimulation (ES) was proved to stimulate the simultaneous removal of PHE and nitrate anaerobically. High removal of PHE and nitrate (90.94 % and 100 %, respectively) was obtained within 24 h in the ES-bioreactor, two times higher than the control anaerobic bioreactor (32.16 %). ES-bioreactor exhibited a good PHE removal performance within initial PHE ranging from 5 to 25 mg/L. In ES-bioreactor, extracellular polymeric substances increased PHE bioavailability and acted as protective capsules. Nicotinamide adenine dinucleotide (NADH) and cytochrome C (cyt-C) facilitated the extracellular and intracellular electron exchange during PHE biotransformation. ES significantly selected Acetobacterium, PHE-degraders (f_Bacteroidetes_vadin HA17, Limnobacter and Stenotrophomonas) and electrogens (Clostrium_sensu_stricto_13) to participate in PHE decomposition. Acetobacterium decomposed complex organics to acetate, proving accessible substrates for electrogens to maintain an efficient electron flow. Enzymes regulating bacterial chemotaxis, flagellar assembly and carbohydrate metabolism were up-regulated with ES, suggesting the indispensable role of such enzymatic processes in ES-bioreactor. Overall, this work demonstrates ES can promote anaerobic bioremediation of PHE and nitrate in groundwater and, thus, opens up a new bioelectrochemistry application scenario.

Enhancement of electrode properties using carbon dots functionalized magnetite nanoparticles for azo dye decolorization in microbial fuel cell

Technology integration of nanomaterials with microbial fuel cell (MFC) have led to simultaneous degradation of recalcitrant dyes and energy extraction from textile wastewater. Limited electron transfer capacity and hydrophobicity of electrode are the bottlenecks for enhancing the performance of MFC. Nanomaterials can provide surface functionalities for electron transfers and serve as catalyst for pollutant degradation. In this paper, magnetite nanoparticles functionalized with carbon dots (Fe3O4@CDs) were used to enhance the electron transfer capacity of the electrodes due to numerous surface-active functional groups of CDs and the reversible redox reaction of Fe2+/Fe3+. Polydopamine (PDA) was used as binder to coat Fe3O4@CDs onto the surface of carbon felt (CF) electrodes in a sono-chemical reaction, favoring to form biocompatible electrodes. Charge transfer resistance of Fe3O4@CDs@PDA-CF was 5.02Ω as compared to 293.34Ω of unmodified CF. Fe3O4@CDs@PDA-CF installed MFC could achieve almost 98% dye degradation efficiency within 48 h and 18.30 mW m−2 power output as compared to 77% dye degradation and 0.34 mW m−2 power output by unmodified CF electrode MFC. Moreover, metagenomic analysis of microbial consortia developed in Fe3O4@CDs@PDA-CF MFC showed enrichment of electrogenic and dye degrading microbial communities of Achromobacter. Delftia, Geobacter and Pseudomonas.

Coupling multifunctional catalytic active sites into metal carbide catalysts to promote the multipath bidirectional conversion of Li-S redox

Li-S batteries are hampered by sluggish liquidsolid redox and shuttle effects. Herein, a strategy of coupling multifunctional catalytic sites is proposed to fabricate bidirectional catalysts to promote multipath bidirectional Li-S redox conversion. By engineering Co or Zr dopants into Ni3C/C, the obtained Co0.30Ni2.70C/C and Zr0.30Ni2.70C/C electrocatalysts play different roles in polysulfide adsorption and multipath bidirectional conversion. During the discharging/charging process, due to limited electron transfer between the Co3+/Co2+ pair and polysulfides, Co sites themselves are catalytically inactive for the conversion of polysulfides and only act as promoters to improve the catalytic activity of Ni sites. In contrast, in addition to being promoters, Zr sites serve as electron acceptors and donors to catalyze bidirectional Li-S redox due to the flexible electron transfer between the Zr4+/Zr2+ pair and polysulfides. Such bidirectional electron transfer is accompanied by thiosulfate-mediated redox. Therefore, Zr doping not only accelerates the inherent solid (S8)-liquid (polysulfide)-solid (Li2S) conversion pathway but also propels the reversible thiosulfate-mediated conversion pathway. As a result, when the Zr0.30Ni2.70C/C nanosheets were used to modify the commercial PP separator, the Li-S batteries exhibit improved electrochemical performance (a decay of 0.0756 % over 200 cycles with a sulfur loading of 5.0 mgs cm−2).

MnCe/GAC-CNTs catalyst with high activity, SO2 and H2O tolerance for low-temperature NH3-SCR

SO2 and H2O tolerance is a crucial issue for low-temperature selective catalytic reduction of NO with NH3 (NH3-SCR) in practical application. In the present work, MnCe/GAC-CNTs catalysts were prepared and showed high activity, SO2 and H2O tolerance for low-temperature NH3-SCR. The catalysts were characterized by SBET, XPS, XRD, NH3−TPD, and DRIFTs. MnCe/GAC-CNTs exhibited higher catalytic activity and H2O + SO2 tolerance than CeO2/GAC-CNTs due to electron transfer between Ce and Mn species (Ce4+ + Mn3+ ↔ Ce3+ + Mn4+) accompanied with higher proportion Ce3+, and the improvement of surface acidity concentration and strength. Besides, Mn addition inhibited the oxygen inhibitory effect, enhanced the adsorption of NO, and increased the proportion diameter, which were beneficial to SO2/H2O resistance. Furthermore, the presence of Mn suppressed the formation of hydroxyl group, inhibited the adsorption of SO2, ultimately limited electron transfer between SO2 and Ce4+, which led to high SO2 tolerance of the MnCe/GAC–CNTs catalyst. Therefore, MnCe/GAC-CNTs catalyst with high deNOx performance and SO2/H2O tolerance, showed the potential of practical low-temperature deNOx application.

Chem-bio interface design for rapid conversion of CO2 to bioplastics in an integrated system

Chem-bio interface design for rapid conversion of CO2 to bioplastics in an integrated system

Influence of positive pulse voltages on structure, mechanical, and corrosion inhibition characteristics of Si/DLC coatings

In this study, Si/DLC films were effectively deposited on 2024-Al alloy using a plasma-enhanced chemical vapor method at different pulse voltages. Scanning electron microscopy, X-ray diffraction spectroscopy, 2D optical profilometer, Raman spectroscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy were used to characterize the structure of the DLC coatings. The adhesion strength was performed using Scratch Tester. Further, the Nano Indenter G200 apparatus was used to measure the hardness and Young's modulus of coatings. The Ball-on-Disk Tester was used to measure the friction coefficient of the specimens. A Potentiostat/Galvanostat electrochemical workstation was used to examine the corrosion performance and passive stability of DLC coatings in 3.5 wt% NaCl solution. The findings demonstrated that the thickness of the coatings increased with increasing the pulse voltage to 1800 V, causing an improvement in mechanical properties and corrosion resistance. This is due to an increase in the amount of sp3 hybrid in the coating, which reduces the electrical conductivity of DLC and limits electron transfer and electrical charge exchange at the coating surface. However, the corrosion rate of the coatings increased when the pulse voltage increased to 2200 V.

Microbial | electrochemical CO2 reduction: To integrate or not to integrate?

Microbial | electrochemical CO2 reduction: To integrate or not to integrate?

Assemble 2D redox-active covalent organic framework/graphene hybrids as high-performance capacitive materials

Graphene and two-dimension covalent organic frameworks (2D COFs) with a redox-active skeleton are promising potential capacitive materials for energy storage applications. However, their tendency to form thick laminates severely limits electron transfer and ion diffusion. Herein, we demonstrate graphene hybrids assembled by mixing 2D COFs and reduced graphene oxide (rGO) nanosheets to address their problems effectively. Electrochemical analysis shows that the two different 2D nanosheets prevent their restacking into thick laminates. Electrically conductive rGO nanosheets provide fast electron paths, while 2D COFs with abundant mesopores make graphene surface and redox-active sites in COFs accessible to electrolyte ions. The optimized hybrid containing 30 wt% COFs delivers a high gravimetric capacitance of 599 F g−1, much higher than the pristine rGO (203 F g−1) and COFs (110 F g−1). It also exhibits excellent rate capability with over 80% capacity retention when the charging/discharging current density increases by 40 times. This mixing strategy of different types of 2D nanosheets by hydrothermal assembly can be further extended to various graphene hybrids containing COFs and other 2D materials, creating a wide range of novel carbon composite materials for fundamental research and applications.

Electrified bioreactors: the next power-up for biometallurgical wastewater treatment.

SummaryOver the past decades, biological treatment of metallurgical wastewaters has become commonplace. Passive systems require intensive land use due to their slow treatment rates, do not recover embedded resources and are poorly controllable. Active systems however require the addition of chemicals, increasing operational costs and possibly negatively affecting safety and the environment. Electrification of biological systems can reduce the use of chemicals, operational costs, surface footprint and environmental impact when compared to passive and active technologies whilst increasing the recovery of resources and the extraction of products. Electrification of low rate applications has resulted in the development of bioelectrochemical systems (BES), but electrification of high rate systems has been lagging behind due to the limited mass transfer, electron transfer and biomass density in BES. We postulate that for high rate applications, the electrification of bioreactors, for example, through the use of electrolyzers, may herald a new generation of electrified biological systems (EBS). In this review, we evaluate the latest trends in the field of biometallurgical and microbial‐electrochemical wastewater treatment and discuss the advantages and challenges of these existing treatment technologies. We advocate for future research to focus on the development of electrified bioreactors, exploring the boundaries and limitations of these systems, and their validity upon treating industrial wastewaters.

Modelling Diffusion at Random Arrays of Active Sites: Revisiting the Voronoi Tessellation Concept

Many practical systems at micro- and nanoscale can be represented as arrays of active sites distributed randomly [1]. As shown previously these systems can be efficiently addressed theoretically by using Voronoi diagrams [2, 3] which allows facile tessellation of the system into the unit cells around each active sites. The overall current flowing in the system can then be evaluated by modelling diffusion-reaction processes inside every unit cell and summing the contributions from individual active sites. Although this approach is tempting by its simplicity and efficiency [3] one should bear in mind that Voronoi diagram representing the unit cells by polygonal prisms remains approximation and as each approximation remains valid only under certain conditions. In this work [4] we show that even for the case of diffusion limited electron transfer (ET) the actual shapes of the unit cells are more complicated and depend on the local configuration of the neighbouring active sites. This was exemplified on the small patches of the random arrays with band-like and disk-like active sites via simulations and in the case of band-like active sites confirmed by analytical derivations.Importantly, by comparing the total array current obtained by employing Voronoi tessellation and simulation of the system without any approximations we found that they agree well (relative error ca. 5% or less). At the same time, the individual contributions from the active sites are reproduced with a much larger relative error [4]. The latter suggests that in the case of kinetic control or reaction mechanisms that are more complicated than simple ET the diffusion-reaction competition between the active sites may become even stronger eventually leading to significant deviations from the total current predicted on the basis of the Voronoi approximation. This is currently investigated in our team. Fig. 1. Comparison between the Voronoi tessellation boundaries (white dashed lines) and the actual boundaries (coloured surface) of the unit cells. Three disk-type active sites are shown as white disks.

A novel near-infrared light-responsive photoelectrochemical platform for detecting microcystin-LR in fish based on Ag2S cubes and plasmonic Au nanoparticles

As a main contaminant in fish, microcystin-LR (MC-LR) leads to serious liver problems; therefore, the development of MC-LR sensors is important to guarantee aquatic food safety. In this work, a near-infrared (NIR) light-excited photoelectrochemical (PEC) immunosensor was developed through conjugation of Ag2S cubes with Au nanoparticles (NPs) to determine MC-LR residues in fish. Specifically, as a narrow-band semiconducting material, Ag2S is capable of absorbing NIR light. Taking advantage of the localized surface plasmon resonance (LSPR) effect along with good conductivity of AuNPs, the developed AuNP/Ag2S/fluorine-doped tin oxide (FTO) owns much higher photoelectric conversion efficiency, and the photocurrent is 5.3 times that of Ag2S FTO. Subsequently, the NIR-driven AuNP/Ag2S/FTO was used to immobilize antibodies (Abs) for MC-LR. Their specificity to MC-LR led to steric effects and limited surface electron transfer, causing reduce of the photocurrent. Through AuNP/Ag2S-composite amplification and immunological specificity, the PEC immunosensor can quantitatively measure MC-LR with a wide linear range, 10 pg L−1 to 10 μg L−1, and a much low detection limit, 7 pg L−1 (S/N = 3). Finally, the NIR PEC sensor was employed in the analysis of MC-LR contents in fish. This work reveals the NIR-responsive ability of Ag2S cubes and deepens understanding the role of AuNPs in the PEC process. Due to the superior properties, the developed NIR PEC immunosensor has been demonstrated as a promising method for analysis of biological samples.

An Electrochemical Study with Three Redox Substances on a Carbon Based Nanogap Electrode Array

An Electrochemical Study with Three Redox Substances on a Carbon Based Nanogap Electrode Array