Electron Mediator Research Articles

Efficient H2 evolution over MoS2-NiS2/g-C3N4 S-scheme photocatalyst with NiS2 as electron mediator

Low-cost transition metal sulfides are commonly utilized as photocatalysts for H2 production owing to their exceptional conductivity and superior specific surface area. In this study, MoS2-NiS2 nanoflowers with multidimensional space structure was obtained through the sulphuration reaction between S2- and NiMoO4 under Kirkendall effect during hydrothermal reaction. Subsequently, MoS2-NiS2 was loaded on the surface of g-C3N4 nanosheets using a solvent self-assembly strategy to form 3D MoS2-NiS2/g-C3N4 heterojunctions. The experimental results demonstrate that the H2 production rate of 20 wt% MoS2-NiS2/g-C3N4 reaches 22153 μmol·g-1·h-1 under a 300 W Xe lamp irradiation, which is 59.5 and 201.4-folds than MoS2-NiS2 and g-C3N4, and surpasses 20 wt% MoS2/g-C3N4 (211 μmol·g-1·h-1) and 20 wt% NiS2/g-C3N4 (6183 μmol·g-1·h-1). The XPS and Superoxide radical capture experiments demonstrate that the charge transfer between MoS2-NiS2 and g-C3N4 follows the S-scheme route, and NiS2 functions as an electron mediator, facilitating the transfer of electrons from MoS2 to g-C3N4 to consume the holes, which enhances the efficiency of H2 evolution reaction on g-C3N4. Furthermore, the S-scheme heterojunction of MoS2-NiS2/g-C3N4 with the multidimensional geometric structure can provide abundant active sites for catalytic reactions, this presents a promising approach for the development of cost-effective and high-performance g-C3N4-based heterojunctions. This work offers distinctive perspectives on the trajectory of renewable H2 energy development.

Enhancement of stress resistance of electroactive biofilms against hypersaline shock via exogenous electron mediator addition

Unexpected hypersaline shock from saline wastewater poses a common challenge in the biological treatment processes of WWPTs. Bioelectrochemical systems (BESs) possess an inherent advantage for treating hypersaline wastewater. The elevated salinity enhances the wastewater’s conductivity, which in turn significantly accelerates the electron and proton transfer within the system. However, excessive increases in salinity can impede electron transport capacity, potentially resulting in cell plasmolysis and system failure in severe instances. Here, we investigated the impact of electron mediator (EM) addition on the resilience of electroactive biofilms (EB) to hypersaline environments in BESs. The EB developed under anthraquinone-2,6-disulphonic disodium salt (AQDS) addition obtained preferable electrochemical properties (e.g., current output, redox peak current, conductivity, electron transfer capacity) under hypersaline shock and showed superior recovery post-hypersaline stress. Partial least squares path modeling (PLS-PM) analysis indicated that the enhanced secretion of extracellular polymeric substances (EPS) and the elevated ratio of proteins to polysaccharides are likely pivotal in the formation of EB with high electrochemical activity. Meanwhile, AQDS addition constructed more complex microbial network and enriched halotolerant bacteria (e.g., Solibacillus). Higher mean function abundance of replication & repair, stress tolerance, and biofilm formation were achieved by EM addition. The results of this study present a promising approach to augment the pressure tolerance of EBs, thereby broadening the practical applications of BESs.

Hydrogen Evolution Catalysis by Cobalt Complexes of an Aza‐Bridged Bis‐1,10‐Phenanthroline Ligand Bearing Pendant Basic Sites

AbstractA novel series of molecular Co(II) complexes with aza‐bridged bis‐1,10‐phenanthroline (bpa) ligands have been synthesized and reported for the catalytic hydrogen evolution reaction (HER). Various nitrogen donor substituents are introduced at the aza‐bridge of the bis‐phenanthroline moieties render intramolecular basic sites in the complexes’ second‐coordination sphere. Modifying the pendant nitrogen donor significantly influences the catalytic HER performance. Among these, the cobalt complex with the (2‐pyridyl)methyl substituted bis‐phenanthroline ligand (L3) exhibits the most photocatalytic HER efficiency in both organic and aqueous media. Under optimized conditions with [Ru(bpy)3]2+ as a sensitizer and ascorbic acid as an electron donor, [CoII(L3)(TfO−)2] achieves an initial turnover frequency (TOF) of 1882±65 h−1 per catalyst and a turnover number (TON) of 4842±122 in a 3 hour reaction period under the irradiation of visible light. Combined experimental and theoretical evidences illustrate that phenanthroline moieties of the bpa ligands act as electron mediators during the HER catalysis, while the pendant nitrogen donor substituents mediate proton transfer. This work provides a unique example for understanding the activity‐structure relationship of homogeneous HER catalyst concerning the redox‐active properties and second coordination sphere basic sites of organic ligand platforms.

Sunlight-Driven Direct/Mediated Electron Transfer for Cr(VI) Reductive Sequestration on Dissolved Black Carbon-Ferrihydrite Coprecipitates.

Surface runoff horizontally distributed chromium (Cr) pollution into various surface environments. Sunlight is a vital factor for the Cr cycle in the surface environment, which may be affected by photoactive substances such as ferrihydrite (Fh) and dissolved black carbon (DBC). Herein, sunlight-driven transformation dynamics of Cr species on DBC-Fh coprecipitates were studied. Under sunlight, the removal of aqueous Cr(VI) by DBC-Fh coprecipitates occurred through sunlight-driven reductive sequestration including adsorption, followed by surface reduction (pathway 1) and aqueous reduction, followed by precipitation (pathway 2). Additionally, coprecipitates with a higher DBC content exhibited a more effective reduction of both adsorbed (kapp,S_red) and aqueous Cr(VI) (kapp,A_red). Photoelectrons facilitated Cr(VI) reduction through direct electron transfer; notably, electron donating DBC promoted the production of photoelectrons by consuming photogenerated holes. Photogenerated Fe(II) species (mineral-phase and aqueous Fe(II)) mediated electron transfer for Cr(VI) reduction, which was reinforced via a ligand-to-metal charge transfer (LMCT) process between DBC-organic ligands and mineral Fe(III). Furthermore, ·O2- also mediated Cr(VI) reduction, although this impact was limited. Overall, this study demonstrates that photoelectrons and photogenerated electron mediators play a crucial role in Cr(VI) reductive sequestration on DBC-Fh coprecipitates, providing new insights into the geochemical cycle of Cr pollution in sunlight-influenced surface environments.

Elevating photocatalytic H2 evolution over ZnIn2S4@Au@Cd0.7Zn0.3S multilayer nanotubes via Au-mediating H–S antibonding-orbital occupancy

Metal sulfides have been considered as an important category of photocatalysts for photocatalytic hydrogen evolution because of their low cost, simple preparation process and abundance of active sites. However, the atomic hydrogen is generally adsorbed on the sulfide photocatalysts to form strong H–S bond, which impedes the release of generated H2 molecules from the photocatalyst surface, severely limiting the H2 evolution efficiency. To address this issue, herein we have designed an interesting type of ZnIn2S4@Au@Cd0.7Zn0.3S (ZIS@Au@CZS) multilayer nanotubes with Au medium sandwiched between inner CZS layer and outer ZIS layer. The Au medium serves as the electron mediator to provide free electrons to fill the H–S antibonding orbitals in CZS and ZIS; this process decreases the adsorption capability of the S sites towards atomic hydrogen, thus facilitating the release of generated H2 molecules. This study provides an important guidance for modifying the photocatalysts to maximize their photocatalytic H2 evolution.

N-doped carbon-coated CoSe2/ZnIn2S4 Z-scheme heterojunction for enhanced visible-light photocatalytic performances

N-doped carbon (NC)/CoSe2/ZnIn2S4 Z-scheme heterojunction was constructed by growing ZnIn2S4 on N-doped carbon-coated CoSe2 derived from the metal-organic framework (ZIF-67) via the self-sacrificing template method and hydrothermal method. X-ray photoelectron spectroscopy, electron paramagnetic resonance, and density-functional theory (DFT) calculations demonstrate that NC/CoSe2/ZnIn2S4 (NSZ) Z-scheme heterojunction was constructed with CoSe2 as an electron mediator. The optimal 5NSZ composite achieved 97.3% in photocatalytic degradation efficiency of tetracycline hydrochloride (TCH) within 30 min, and H2O2 production of 645.3 μM under visible light for 60 min. Moreover, the top-flight photocatalytic hydrogen evolution (PHE) rate of 6772.9 μmol g−1 h−1 is 19.1 folds and 2.2 folds higher than pure ZnIn2S4 and Pt–ZnIn2S4, respectively. The photoreduction CO2 gas produces rates of CO (53.7 μmol g−1 h−1), C2H4 (7.0 μmol g−1 h−1), and C2H6 (6.4 μmol g−1 h−1) products were obtained within 10 h under visible light. This work provides an effective strategy for designing unique noble-metal-free Z-scheme heterojunction photocatalysts to purify the environment and produce clean energy.

Constructing Tandem Fenton-like Reaction Systems Based on Structure Adaption to Boost Water Contaminant Mineralization Efficiency.

Mineralization of emerging contaminants by using advanced oxidation processes (AOPs) is a desirable option to ensure water safety, but still challenged by the excessive chemical and/or energy input. Here, we conceptually proposed the tandem reaction system (TRS) of different reactive oxygen species (ROS) based on structure adaption of target contaminants. To construct a model TRS, we first realized highly selective generation of three classical ROS (1O2, HO• and SO4•-) by peroxymonosulfate activation in an electrochemical Fenton-like system, where three replaceable Fe-centered cathodes were rationally designed as electronic mediator. The 1O2+SO4•--TRS exhibited nearly 100% mineralization of sulfamethoxazole (SMX), whereas only 34.2%, 56.2% and 60.8% for each of the single 1O2/HO•/SO4•--AOP systems. Mechanism exploration of SMX degradation in TRS evidenced that the initial reaction with 1O2 selectively destructed the sulfonamide bridge of SMX to form p-aminobenzenesulfonic acid, which will be vulnerable to sequent SO4•- attack to facilitate mineralization. Successful extendibility of 1O2+SO4•--TRS to other sulfonamide antibiotics and 1O2+HO•-TRS to phenolic and arylcarboxylic compounds, as well as the demonstration of 1O2+SO4•--TRS in treatment of three actual pharmaceutical wastewaters strongly support that TRS is a powerful and sustainable strategy to enhance the mineralization of emerging contaminants in water.

Constructing Tandem Fenton‐like Reaction Systems Based on Structure Adaption to Boost Water Contaminant Mineralization Efficiency

Mineralization of emerging contaminants by using advanced oxidation processes (AOPs) is a desirable option to ensure water safety, but still challenged by the excessive chemical and/or energy input. Here, we conceptually proposed the tandem reaction system (TRS) of different reactive oxygen species (ROS) based on structure adaption of target contaminants. To construct a model TRS, we first realized highly selective generation of three classical ROS (1O2, HO• and SO4•–) by peroxymonosulfate activation in an electrochemical Fenton‐like system, where three replaceable Fe‐centered cathodes were rationally designed as electronic mediator. The 1O2+SO4•–‐TRS exhibited nearly 100% mineralization of sulfamethoxazole (SMX), whereas only 34.2%, 56.2% and 60.8% for each of the single 1O2/HO•/SO4•–‐AOP systems. Mechanism exploration of SMX degradation in TRS evidenced that the initial reaction with 1O2 selectively destructed the sulfonamide bridge of SMX to form p‐aminobenzenesulfonic acid, which will be vulnerable to sequent SO4•– attack to facilitate mineralization. Successful extendibility of 1O2+SO4•–‐TRS to other sulfonamide antibiotics and 1O2+HO•‐TRS to phenolic and arylcarboxylic compounds, as well as the demonstration of 1O2+SO4•–‐TRS in treatment of three actual pharmaceutical wastewaters strongly support that TRS is a powerful and sustainable strategy to enhance the mineralization of emerging contaminants in water.

Optimizing microbial electrolysis cell performance: strategies to mitigate electron mediator degradation on membranes.

This investigation probes the role of the electron mediator, neutral red (NR), in the electrosynthesis process, specifically examining its effect on the production of succinic acid by Actinobacillus succinogenes. Our findings reveal that NR, when integrated into the cell membrane, is pivotal for sustaining MEC efficiency. Nevertheless, it is susceptible to both intrinsic and MECs-induced degradation. Notably, during the exponential growth phase of the bacteria, NR is readily incorporated into the cell membrane. However, the supplemental addition of NR fails to significantly enhance the MEC's capacity for succinic acid synthesis, no matter what stage of bacterial growth. And significant depletion of membrane-associated NR is not adequately compensated by the NR present in the fermentation liquid. The ORP feedback-regulated MECs adeptly conserve the NR on the cell membrane, which is essential for maintaining the efficiency of long-term electrosynthesis. The presence of NR on the cell membrane is essential for the functionality of MECs, yet its external replenishment hard. Implementing precise electro-potential regulation strategies can effectively diminish the degradation of NR, thus maintaining the system's efficiency.

Regulation of extracellular electron transfer by sustained existence of Fe²⁺/Fe³⁺ redox couples on iron oxide-functionalized woody biochar anode surfaces in bioelectrochemical systems

Sluggish extracellular electron transfer between the exoelectrogens and anode interface limits the application of bioelectrochemical systems (BECs) for energy generation. In this study, an innovative anode coated with oxidized biochar and co-functionalized with iron nanoparticles (FBC/Fe2O3) was developed to enhance microbial reactions through tuned physicochemical and electrical properties. The designed anode features a highly porous, heterogeneous structure with a large accessible surface area of 10.141 m²/g, promoting better habitation and metabolism of exoelectrogens. The synergistic effect of iron nanoparticles and oxidized functional groups increased the hydrophilicity of the anode surface, augmenting its affinity for bacterial outer membrane c-cysts and facilitating microbial adhesion at a density of 3.106 × 10⁹ CFU/cm². The iron moieties on the FBC/Fe2O3 electrode surface act as electron mediators, utilizing Fe²⁺/Fe³⁺ redox couples, as evidenced by X-ray photoelectron spectroscopy (XPS) data. This enhancement improved extracellular electron transfer (EET) between bacterial cells and the anode surface, resulting in a faster and bifurcated EET process through both direct transfer via outer membrane c-cysts and mediated transfer via the redox couples of Fe moieties. The assembled double-chamber microbial fuel cell (DC-MFC) with the FBC/Fe2O3 anode achieved a maximum power density of 528.75 mW/m² and a chemical oxygen demand (COD) removal efficiency of 47.5 % within 24 h of operation.

Signal amplification strategy based on target-controlled release of mediator for ultrasensitive self-powered biosensing of acetamiprid

Self-powered biosensors with high sensitivity have garnered significant interest for their potential applications in the realm of portable sensing. Herein, a self-powered biosensor with a novel signal amplification strategy was developed by integrating target-controlled release of mediator with an enzyme biofuel cell for the ultrasensitive detection of acetamiprid (ACE). Zeolitic imidazolate framework-67 was utilized as both a nanocontainer for capturing the electron mediator 2,2′-azidobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and a precursor for the synthesis of cobalt nanoparticles/nitrogen, sulfur-codoped carbon nanotubes (Co NPs/NS-CNTs), which were employed as the electrode material for constructing both the glucose oxidase-based bioanode and the laccase-based biocathode. The target analyte ACE can specifically bind to its aptamer, leading to the release of ABTS, which cyclically participates in the catalytic reaction of the biocathode, thereby amplifying the electrochemical signal. By leveraging the benefits of ABTS cyclic catalysis and the effective electrocatalysis of bioelectrodes based on Co NPs/NS-CNTs, the self-powered biosensor has a broad detection range of 0.1–1000 fM and a low detection limit of 25 aM toward ACE. The proposed signal amplification approach presents a promising strategy for enhancing sensitivity and enabling portable analysis in applications of food safety, environmental monitoring, and medical diagnostics.

Specific interaction of resorufin to outer-membrane cytochrome OmcE of Geobacter sulfurreducens: A new insight on artificial electron mediators in promoting extracellular electron transfer

Bioelectrochemical system (BES) is a unique biotechnology for wastewater treatment and energy recovery, and extracellular electron transfer (EET) between microbe and electrode is the key to optimize the performance of BESs. Resazurin is an effective artificial compound that can promote EET in BESs, but the way how it transports electrons is not fully understood. In this study differential pulse voltammetry revealed that the redox potential of resorufin (RR) (intermediate of resazurin reduction, actual electron mediator) within Geobacter sulfurreducens biofilm was positively shifted by 100 mV than that of free RR, and this shift was attenuated by the mutation of outer-membrane cytochrome gene omcE but not by omcS and omcZ mutation, indicating that RR specifically interacted with OmcE. By using heterologously expressed OmcE monomers in Escherichia coli, it was found that RR bonded with OmcE monomers with a moderate intensity (dissociation constant of 720 nM), and their interaction obviously increased the content of α helix in OmcE monomers. Biomolecular analysis indicated that heme II of OmcE monomer might be the binding site for RR (binding energy of -7.01 kJ/mol), which were favorable for electron transfer within OmcE-RR complex. Comparative transcriptomics showed that RZ addition significantly upregulated the expression of omcE, periplasmic cytochrome gene ppcB, and outer-membrane genes omaB, ombB and omcB, thus, it was hypothesized that OmcE-bound RR might serve as potential electron acceptor of OmbB-OmaB-OmcB porin complex which passes electrons across outer membrane. Our work demonstrated a new pathway of artificial electron mediators in facilitating EET in Geobacter species, which may guide the application of electron mediator in improving the performance of BESs.

Carbon Steel Corrosion Induced by Sulfate-Reducing Bacteria: A Review of Electrochemical Mechanisms and Pathways in Biofilms

Microbial metal corrosion has become an important topic in metal research, which is one of the main causes of equipment damage, energy loss, and economic loss. At present, the research on microbial metal corrosion focuses on the characteristics of corrosion products, the environmental conditions affecting corrosion, and the measures and means of corrosion prevention, etc. In contrast, the main microbial taxa involved in metal corrosion, their specific role in the corrosion process, and the electron transfer pathway research are relatively small. This paper summarizes the mechanism of microbial carbon steel corrosion caused by SRB, including the cathodic depolarization theory, acid metabolite corrosion theory, and the biocatalytic cathodic sulfate reduction mechanism. Based on the reversible nature of electron transfer in biofilms and the fact that electrons must pass through the extracellular polymers layer between the solid electrode and the cell, this paper focuses on three types of electrochemical mechanisms and electron transfer modes of extracellular electron transfer occurring in microbial fuel cells, including direct-contact electron transfer, electron transfer by conductive bacterial hair proteins or nanowires, and electron shuttling mediated by the use of soluble electron mediators. Finally, a more complete pathway of electron transfer in microbial carbon steel corrosion due to SRB is presented: an electron goes from the metal anode, through the extracellular polymer layer, the extracellular membrane, the periplasm, and the intracellular membrane, to reach the cytoplasm for sulfate allosteric reduction. This article also focuses on a variety of complex components in the extracellular polymer layer, such as extracellular DNA, quinoline humic acid, iron sulfide (FeSX), Fe3+, etc., which may act as an extracellular electron donor to provide electrons for the SRB intracellular electron transfer chain; the bioinduced mineralization that occurs in the SRB biofilm can inhibit metal corrosion, and it can be used for the development of green corrosion inhibitors. This provides theoretical guidance for the diagnosis, prediction, and prevention of microbial metal corrosion.

Enhanced visible light-assisted photocatalytic activity of g-C3N4 decorated with ZIF-8 and AgI ternary heterojunctions

Fabrication of a suitable photocatalyst system that responds to visible light has become a requirement for photocatalytic environmental remediation processes. For better transfer/separation of photogenerated-charges, successful interfacial engineering to build photocatalytic heterojunctions is essential for improving the photodegradation performance. Herein, ternary composites of zeolitic-imidazolate-framework-8 (ZIF-8) coupled with AgI nanoparticles assembled on g-C3N4 have been fabricated, characterized using XRD, FESEM, EDX, TEM, PL, UV–visible DRS, and N2-adsorption–desorption, and used as visible-light-driven photocatalysts for photocatalytic destruction of methylene blue (MB). The ternary AgI/ZIF-8/g-C3N4 photocatalyst achieved superb photodestruction activity (94.2 %) within 120 min. Besides, the first-order degradation rate constant reached 0.02431 min−1, which was nearly 1.5, 2.5, 4.5, and 5.5 times greater than that reached by ZIF-8/g-C3N4 (0.01628 min−1), g-C3N4 (0.00941 min−1), AgI (0.00542 min−1) and ZIF-8 (0.00441 min−1), respectively. The improved photocatalytic behavior was accredited to the synergistic influence of the photo-charge carrier transfer/separation pathway and the electron mediation assisted by ZIF-8. The trapping tests supported the recommended photocatalytic mechanism, which suggested that the O2− radicals were the main reacting agents in this process. The parameters affecting the photodegradation, including the AgI/ZIF-8/g-C3N4 dose, the solution pH, and the MB concentration were systematically tested in this work. Furthermore, the AgI/ZIF-8/g-C3N4 demonstrated good degradation stability after multi-consecutive rounds (only 1 % deduction in its activity after 5 rounds), and thus, it is projected to be a promising photocatalyst in wastewater treatment.

Implementation of Supreme Court Regulation Number 3 of 2022 concerning electronic mediation in the jurisdiction of The Denpasar District Court

The integration of electronic systems into the judicial process represents a significant advancement in legal practice. The advent of e-Court and electronic mediation represent a broader trend towards integrating technology to improve the efficiency and reach of judicial processes. This study aims to find out the stages of implementation of Supreme Court Regulation Number 3 of 2022 concerning Electronic Mediation in the jurisdiction of the Denpasar District Court, and the inhibiting factors of the implementation of the regulation in this jurisdiction. The study provides valuable insights into the practical application of electronic mediation, highlights challenges faced in the field, and offers recommendations for improving the regulatory process and overcoming obstacles. This research could evaluate how legal representatives support parties in fulfilling their rights and obligations during electronic mediation. Additionally, investigating the specific obstacles related to software and human resources could provide insights into how these challenges impact the mediation process.

Vacancy-strengthened Cu/Co composite oxides for efficient removal of methylene blue via peroxymonosulfate activation: Synergism of multiple Lewis acid sites

The development of suitable catalysts poses a challenge for the peroxymonosulfate (PMS) activation system used in decontamination process. Here we constructed a series of vacancy-strengthened Cu/Co composite oxides (CuCoO) composed of CuCo2O4 and CuO containing multiple Lewis acid sites. The results demonstrate that the as-prepared CuCoO-2 exhibited exceptional activation performance, broad-ranging degradation capacity, remarkable reusability and stability. The optimized CuCoO-2+PMS system achieved complete removal of methylene blue (MB) in 40 min, while maintaining a degradation efficiency of above 86 % even after 5 cycles. A comprehensive survey revealed that hydroxyl radical (·OH), sulfate radical (SO4.-) and singlet oxygen (1O2) collectively contribute to the degradation of MB in the CuCoO-2+PMS system. Especially, 1O2 was the dominant active species. The synergism of various Lewis acid sites (Cu+/2+, Co2+/3+ and VO/N) as unsaturated surface-bound centers played a pivotal role in promoting non-radical-driven activation of PMS. Meanwhile, the generated VO/N facilitated enhanced metallic valence circulation in CuCoO-2, strengthening electron mediation between PMS and MB. Additionally, possible degradation pathways and toxicity evaluations of MB and its intermediates were proposed. In conclusion, this work offers valuable insights into PMS activation by vacancy-strengthened CuCoO and is of great significance for water purification.

Highly efficient photoenzymatic CO2 reduction dominated by 2D/2D MXene/C3N5 heterostructured artificial photosynthesis platform

Photoenzyme-coupled catalytic systems offer a promising avenue for selectively converting CO2 into high-value chemicals or fuels. However, two key challenges currently hinder their widespread application: the heavy reliance on the costly coenzyme NADH, and the necessity for metal-electron mediators or photosensitizers to address sluggish reaction kinetics. Herein, we present a robust 2D/2D MXene/C3N5 heterostructured artificial photosynthesis platform for in situ NADH regeneration and photoenzyme synergistic CO2 conversion to HCOOH. The efficiencies of utilizing and transmitting photogenerated charges are significantly enhanced by the abundant π-π conjugation electrons and well-engineered 2D/2D hetero-interfaces. Noteworthy is the achievement of nearly 100 % NADH regeneration efficiency within just 2.5 h by 5 % Ti3C2/C3N5 without electron mediators, and an impressive HCOOH production rate of 3.51 mmol g−1h−1 with nearly 100 % selectivity. This study represents a significant advancement in attaining the highest NADH yield without electron mediator and provides valuable insights into the development of superior 2D/2D heterojunctions for CO2 conversion.

Integrating Mo2C/C as cocatalyst into S-scheme Mo2C/C/Co0.5Cd0.5S heterojunction with spatial photocarrier separation for photocatalytic synergistic H2 evolution

Reasonable design and production of potent photocatalysts for sustainable H2 production from solar energy is one of the necessary strategies in the photocatalysis process. The S-scheme heterojunction exposes remarkable superiority in boosting light harvesting and progressing photocarrier separation efficiency in the photocatalyst. Here, new S-scheme heterojunction Mo2C/C/Co0.5Cd0.5S photocatalysts, including different weights of noble metal-free Mo2C/C nanostructures as cocatalysts, were successfully synthesized. As expected, the nanocomposite structures exhibited increased photocatalytic activity relative to single Co0.5Cd0.5S. The nanocomposite containing 5 wt% Mo2C/C exhibited an increased hydrogen production efficiency of 83.86 mmol g−1 h−1, which was 8.4 times higher than single Co0.5Cd0.5S (10.06 mmol g−1 h−1). This implies that for Co0.5Cd0.5S, Mo2C/C increases visible light absorption, facilitates photocarrier separation, and boosts the H2 evolution rate. Moreover, conductive carbon nanoparticles, electron mediators with strong interfacial interaction, serve as rapid photocarrier transfer bridges between Co0.5Cd0.5S and Mo2C. In summary, the superb efficiency of Mo2C/C/Co0.5Cd0.5S is accredited to the synergistic effect between Co0.5Cd0.5S and Mo2C/C, the creation of S-scheme heterojunction, which assists the separation of photocarriers and declines the recombination possibilities. This research ensures a reference and new profound insight for understanding and designing noble metal-free cocatalyst-assisted S-scheme heterojunctions for immensely efficient photocatalytic H2 production.

Lithium-Mediated Nitrogen Reduction in a Flow Electrolyzer Cell Using Gas Diffusion Electrodes with Carbon-Based Electrocatalysts

Due to the sluggish kinetics in activating the chemically stable dinitrogen (N2) and the competing hydrogen evolution reaction in aqueous media, recent attention in the field of direct ammonia (NH3) electrosynthesis has been increasingly drawn to the lithium-mediated N2 reduction reaction (LNRR) in tetrahydrofuran (THF)-based non-aqueous electrolyte. In particular, near 100% faradaic efficiency (FE) and/or a current density (j) of 100 mA cm-2 has been demonstrated with unique electrolyte (proton-shuttle additive) and/or electrode designs (expansive electrochemical surface area) in single-compartment cells at elevated N2 pressure (5 – 20 bar).[1,2]A submerged electrode leads to electrolyte flooding and restricts to N2 mass transfer to the electrode surface where electrodeposited Li as an electron mediator is available.[3] However, flow cell electrolyzers containing gas-diffusion electrodes can improve this technology to practical relevance, which features the LNRR on the cathode and hydrogen oxidation reaction (HOR) on the anode. Differing from single-compartment cells, the HOR supplements the ethanol additive (<1 vol%) as the proton source, which not only prevents the oxidative electrolyte degradation but also reduces the energy consumption due to a lower equilibrium anode potential (E0 = 0 VRHE). Gas-diffusion electrodes (GDEs) are used in the few LNRR studies with flow cell configurations, which are prepared by electro- or electroless depositing electrocatalysts (e.g., Pt [4] or PtAu alloy [5]) onto a porous substrate.In this work, carbon-based electrocatalysts (Vulcan XC72R carbon black, battery-grade conductive carbon SUPER C45, and graphitic carbon SFG6L) as low-cost alternatives to previously studied precious metals are assessed for their LNRR performance in flow cells using an HOR anode. In comparison to Vulcan-supported Pt, XC72R and C45 can obtain similar NH3 production rates (rNH3 )and FE at the same . Continuous LNRR at -3 mA cm-2 was demonstrated with linearly increased NH3 production for over 8 h without catalyst layer detachment, which was also verified with open circuit and Ar control experiments (Fig. 1). By presenting the LNRR activity with GDEs spray-coated with carbon-based electrocatalysts, opportunities for future research are suggested, such as novel carbon materials and porous substrates other than SSC for facile N2 mass transfer and Li deposition.

Rationally Designed S-Scheme CeO2/g-C3N4 Heterojunction for Promoting Visible Light Driven CO2 Photoreduction into Syngas.

Exploring low-cost visible light photocatalysts for CO2 reduction to produce proportionally adjustable syngas is of great significance for meeting the needs of green chemical industry. A S-Scheme CeO2/g-C3N4 (CeO2/CN) heterojunction was constructed by using a simple two-step calcination method. During the photocatalytic CO2 reduction process, the CeO2/CN heterojunction can present a superior photocatalytic performance, and the obtained CO/H2 ratios in syngas can be regulated from 1 : 0.16 to 1 : 3.02. In addition, the CO and H2 production rate of the optimal CeO2/CN composite can reach 1169.56 and 429.12 μmol g-1 h-1, respectively. This superior photocatalytic performance is attributed to the unique S-Scheme photogenerated charge transfer mechanism between CeO2 and CN, which facilitates rapid charge separation and migration, while retaining the excellent redox capacity of both semiconductors. Particularly, the variable valence Ce3+/Ce4+ can act as electron mediator between CeO2 and CN, which can promote electron transfer and improve the catalytic performance. This work is expected to provide a new useful reference for the rational construction of high efficiency S-Scheme heterojunction photocatalyst, and improve the efficiency of photocatalytic reduction of CO2, promoting the photocatalytic reduction of CO2 into useful fuels.