High Efficiency Alkaline Iodine Batteries with Multi-Electron Transfer Enabled by Bi/Bi2O3 Redox Mediator.

The multi-electron transfer I-/IO3- redox couple is attractive for high energy aqueous batteries. Shifting from an acidic to an alkaline electrolyte significantly enhances the IO3- formation kinetics due to the spontaneous disproportionation reaction, while the alkaline environment also offers more favorable Zn anode compatibility. However, sluggish kinetics during the reduction of IO3- persists in both acidic and alkaline electrolytes, compromising the energy efficiency of this glorious redox couple. Here, we establish the fundamental redox mechanism of the I-/IO3- couple in alkaline electrolytes for the first time and propose that Bi/Bi2O3 acts as a redox mediator (RM) to "catalyze" the reduction of IO3-. This mediation significantly reduces the voltage gap between charge/discharge from 1.6 V to 1 V with improved conversion efficiency and rate capability. By pairing the Zn anode and the Bi/Bi2O3 RM cathode, the full battery with I-/IO3- redox mechanism achieves high areal capacity of 12 mAh cm-2 and stable operation at 5 mAh cm-2 for over 400 cycles.

Fulvic acid mediated highly efficient heterotrophic nitrification-aerobic denitrification by Paracoccus denitrificans XW11 with reduced C/N ratio.

Reducing the C/N ratio requirements for heterotrophic nitrification-aerobic denitrification (HNAD) is crucial for its practical application; however, it remains underexplored. In this study, a highly efficient HNAD bacterium, Paracoccus denitrificans XW11, was isolated. The HNAD characteristics of XW11 were studied, and the redox mediator fulvic acid (FA) was used to reduce the C/N requirements. Whole-genome sequencing revealed multiple denitrification genes in XW11; however, nitrification genes were not identified, because heterotrophic nitrification-related gene sequences were not included in the database. However, the nitrogen removal related enzyme activity test revealed complete nitrification and denitrification pathways. Reverse transcription PCR showed that the membrane-bound nitrate reductase (NarG), rather than the periplasmic nitrate reductase, was responsible for aerobic denitrification. The conventional nitrite reductase (NirS) also does not mediate nitrite denitrification. When the C/N ratio was 10, the ammonia removal efficiency of the Control was 71.71 % and the addition of FA increased it to 86.12 %. Transcriptomic analysis indicated electron flow from the carbon source to FA without proton transmembrane transport, and the presence of FA constructs another electron transfer system. The redox potential of oxidized FA/reduced FA is 0.3679 V, avoiding competition for electrons from Complex III. Thus, ammonia monooxygenase obtains electrons more easily, thereby promoting nitrification. The enzyme activity test of the nitrification process confirmed this view. In addition, NarG expression increased, and the denitrification process was enhanced. Overall, FA improved HNAD efficiency by facilitating electron transfer to the nitrogen dissimilation process, offering a novel approach to reduce the C/N requirement of HNAD.

Cutting-Edge Progress in Aqueous Zn-S Batteries: Innovations in Cathodes, Electrolytes, and Mediators.

Rechargeable aqueous zinc-sulfur batteries (AZSBs) are emerging as prominent candidates for next-generation energy storage devices owing to their affordability, non-toxicity, environmental friendliness, non-flammability, and use of earth-abundant electrodes and aqueous electrolytes. However, AZSBs currently face challenges in achieving satisfied electrochemical performance due to slow kinetic reactions and limited stability. Therefore, further research and improvement efforts are crucial for advancing AZSBs technology. In this comprehensive review, it is delved into the primary mechanisms governing AZSBs, assess recent advancements in the field, and analyse pivotal modifications made to electrodes and electrolytes to enhance AZSBs performance. This includes the development of novel host materials for sulfur (S) cathodes, which are capable of supporting higher S loading capacities and the refinement of electrolyte compositions to improve ionic conductivity and stability. Moreover, the potential applications of AZSBs across various energy platforms and evaluate their market viability based on recent scholarly contributions is explored. By doing so, this review provides a visionary outlook on future research directions for AZSBs, driving continuous advancements in stable AZSBs technology and deepening the understanding of their charge-discharge dynamics. The insights presented in this review signify a significant step toward a sustainable energy future powered by renewable sources.

Enhancing the nitrogen removal of anammox sludge by setting up novel redox mediators-mediated anammox process.

Anaerobic ammonium oxidizing (anammox) bacteria have been proven weak-electroactive. However, the impact of exogenous anthraquinone-2,6-disulfonate (AQDS) on the anammox activity, although it usually plays essential roles in the life activities of many other electroactive microorganisms, is still unknown. Therefore, this study further explored the influences of AQDS on the anammox activity and the interaction mechanism with anammox bacteria, as well as the behaviors of NH4+, NO2-, and NO3-. The results showed that exogenous AQDS increased the ammonium and total nitrogen removal rates by 12.8% and 10.7%, respectively. Interestingly, the conversion from NO2- to NO3- was significantly reduced after adding AQDS, resulting in a 40.1% reduction in NO3- production of anammox process. In this study, we found for the first time that anammox bacteria could not only carry out the conventional anammox process but also perform a weak redox mediator-mediated anammox process, which could achieve the 1:1 consumption of NH4+ and NO2-. The redox mediator-mediated anammox process was related to an endogenous redox mediator (ERM) synthesized and secreted by anammox bacteria, whose redox midpoint potential was around -0.26 V (vs. Ag/AgCl). After adding AQDS, not only the ERM-mediated anammox process was enhanced, but also two novel redox mediator-mediated anammox processes were introduced, including the AQDS-mediated anammox process and ERM-AQDS-mediated anammox process. These three redox mediator-mediated anammox processes significantly improved the nitrogen removal performance of anammox bacteria and reduced energy consumption. These findings will help reduce the dependence of anammox technology on NO2-, reduce the cost of subsequent treatment of NO3-, and provide new visions for optimizing and applying anammox technology.

A Novel Ferrocene-Linked Thionine as a Dual Redox Mediator for the Electrochemical Detection of Dopamine and Hydrogen Peroxide.

We introduce a novel dual redox mediator synthesized by covalently linking ferrocene dicarboxylic acid (FcDA) and thionine (TH) onto a pre-treated glassy carbon electrode. This unique structure significantly enhances the electro-oxidation of dopamine (DA) and the reduction of hydrogen peroxide (H2O2), offering a sensitive detection method for both analytes. The electrode exhibits exceptional sensitivity, selectivity, and stability, demonstrating potential for practical applications in biosensing. It facilitates rapid electron transfer between the analyte and the electrode surface, detecting H2O2 concentrations ranging from 1.5 to 60 µM with a limit of detection (LoD) of 0.49 µM and DA concentrations from 0.3 to 230 µM with an LoD of 0.07 µM. The electrode's performance was validated through real-sample analyses, yielding satisfactory results.

Solid-Liquid-Gas Three-Phase Indirect Electrolysis Enabled by Affinity Auxiliary Imparted Covalent Organic Frameworks.

The design of efficient heterogenous redox mediators with favorable affinity to substrate and electrolyte are much desired yet still challenging for the development of indirect electrolysis system. Herein, for the first time, we have developed a solid-liquid-gas three-phase indirect electrolysis system based on a covalent organic framework (Dha-COF-Cu) as heterogenous redox mediator for S-S coupling reaction. Dha-COF-Cu with the integration of high porosity, nanorod morphology, abundant hydroxyl groups and active Cu sites is much beneficial for the adsorption/activation of thiols, uniform dispersion and high wettability in electrolyte, and efficient interfacial electron transfer. Notably, Dha-COF-Cu as solid-phase redox mediator exhibits excellent electrocatalytic efficiency for the formation of value-added liquid-phase S-S bond product (yields up to 99%) coupling with the generation of gas-phase product of H2 (~1.40 mmol g-1 h-1), resulting in a powerful three-phase indirect electrolysis system. This is the first work about COFs that can be applied in three-phase indirect electrolysis system, which might promote the development of porous crystalline materials in this field.

Enhancing microbial fuel cell performance for distillery wastewater treatment and bioelectricity generation: harnessing niacin as a redox mediator.

The role of redox mediators in improving electron transport from electrochemically active bacteria to the anode is crucial for enhanced bioelectricity output from microbial fuel cells (MFCs), which makes the selection of an ideal mediator very important. This study aims at exploring a new redox mediator niacin (vit B3) for enhanced bioelectricity generation in MFC while treating distillery wastewater through facile modification of anode electrode by niacin doping (MFC-NME) and simple application of niacin to the anolyte (MFC-NAA). Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) of NME confirmed the effective adsorption of niacin onto the carbon felt surface. Notably, MFC-NME exhibited a significantly higher power density (PD) of 6.36 W/m3 compared to MFC-NAA (4.59 W/m3) and control MFC (3.49W/m3). The charge transfer resistance (RCT) in MFC-NME (1.73 Ω) and MFC-NAA (2.06 Ω) were lowered by more than half than that in control MFC (4.33 Ω), which underscores the efficacy of niacin as a redox mediator. SEM analysis revealed improved bacterial attachment over the bioanode in the MFC-NME as compared to that of MFC-NAA and control MFC. Removal of chemical oxygen demand (COD) was higher in MFC-NAA (85%) and MFC-NME (80%) than in control MFC (73%) suggesting that niacin in the anolyte supported greater organic matter removal due to enriched microbial activity. Niacin used in anode modification shows great potential for improved electron transfer and enhanced bioelectricity production and supports greater wastewater treatment performance. The modified bioanode NME exhibits excellent stability.

Systems biology of electrogenic Pseudomonas putida - multi-omics insights and metabolic engineering for enhanced 2-ketogluconate production.

BACKGROUND: Pseudomonas putida KT2440 has emerged as a promising host for industrial bioproduction. However, its strictly aerobic nature limits the scope of applications. Remarkably, this microbe exhibits high bioconversion efficiency when cultured in an anoxic bio-electrochemical system (BES), where the anode serves as the terminal electron acceptor instead of oxygen. This environment facilitates the synthesis of commercially attractive chemicals, including 2-ketogluconate (2KG). To better understand this interesting electrogenic phenotype, we studied the BES-cultured strain on a systems level through multi-omics analysis. Inspired by our findings, we constructed novel mutants aimed at improving 2KG production. RESULTS: When incubated on glucose, P. putida KT2440 did not grow but produced significant amounts of 2KG, along with minor amounts of gluconate, acetate, pyruvate, succinate, and lactate. 13C tracer studies demonstrated that these products are partially derived from biomass carbon, involving proteins and lipids. Over time, the cells exhibited global changes on both the transcriptomic and proteomic levels, including the shutdown of translation and cell motility, likely to conserve energy. These adaptations enabled the cells to maintain significant metabolic activity for several weeks. Acetate formation was shown to contribute to energy supply. Mutants deficient in acetate production demonstrated superior 2KG production in terms of titer, yield, and productivity. The ∆aldBI ∆aldBII double deletion mutant performed best, accumulating 2KG at twice the rate of the wild type and with an increased yield (0.96 mol/mol). CONCLUSIONS: By integrating transcriptomic, proteomic, and metabolomic analyses, this work provides the first systems biology insight into the electrogenic phenotype of P. putida KT2440. Adaptation to anoxic-electrogenic conditions involved coordinated changes in energy metabolism, enabling cells to sustain metabolic activity for extended periods. The metabolically engineered mutants are promising for enhanced 2KG production under these conditions. The attenuation of acetate synthesis represents the first systems biology-informed metabolic engineering strategy for enhanced 2KG production in P. putida. This non-growth anoxic-electrogenic mode expands our understanding of the interplay between growth, glucose phosphorylation, and glucose oxidation into gluconate and 2KG in P. putida.

Photoelectrochemical Two-Dimensional Electronic Spectroscopy (PEC2DES) of Photosystem I: Charge Separation Dynamics Hidden in a Multichromophoric Landscape.

We present a nonlinear spectroelectrochemical technique to investigate photosynthetic protein complexes. The PEC2DES setup combines photoelectrochemical detection (PEC) that selectively probes the protein photogenerated charges output with two-dimensional electronic spectroscopy (2DES) excitation that spreads the nonlinear optical response of the system in an excitation-detection map. PEC allows us to distinguish the contribution of charge separation (CS) from other de-excitation pathways, whereas 2DES allows us to disentangle congested spectral bands and evaluate the exciton dynamics (decays and coherences) of the photosystem complex. We have developed in operando phase-modulated 2DES by measuring the photoelectrochemical reaction rate in a biohybrid electrode functionalized with a plant photosystem complex I-light harvesting complex I (PSI-LHCI) layer. Optimizing the photoelectrochemical current signal yields reliable linear spectra unequivocally associated with PSI-LHCI. The 2DES signal is validated by nonlinear features like the characteristic vibrational coherence at 750 cm-1. However, no energy transfer dynamics is observed within the 450 fs experimental window. These intriguing results are discussed in the context of incoherent mixing resulting in reduced nonlinear contrast for multichromophoric complexes, such as the 160 chlorophyll PSI. The presented PEC2DES method identifies generated charges unlike purely optical 2DES and opens the way to probe the CS channel in multichromophoric complexes.

Rescue of dead MnO2 for stable electrolytic Zn-Mn redox-flow battery: a metric of mediated and catalytic kinetics.

The virtues of electrolytic MnO2 aqueous batteries are high theoretical energy density, affordability and safety. However, the continuous dead MnO2 and unstable Mn2+/MnO2 electrolysis pose challenges to the practical output energy and lifespan. Herein, we demonstrate bifunctional cationic redox mediation and catalysis kinetics metrics to rescue dead MnO2 and construct a stable and fast electrolytic Zn-Mn redox-flow battery (eZMRFB). Spectroscopic characterizations and electrochemical evaluation reveal the superior mediation kinetics of a cationic Fe2+ redox mediator compared with the anionic ones (e.g. I- and Br-), thus eliminating dead MnO2 effectively. With intensified oxygen vacancies, density functional theory simulations of the reaction pathways further verify the concomitant Fe-catalysed Mn2+/MnO2 electrolysis kinetics via charge delocalization and activated O 2p electron states, boosting its rate capability. As a result, the elaborated eZMRFB achieves a coulombic efficiency of nearly 100%, ultra-high areal capacity of 80 mAh cm-2, rate capability of 20 C and a long lifespan of 2500 cycles. This work may advance high-energy aqueous batteries to next-generation scalable energy storage.

Natural redox mediator anthraquinone aloe-emodin facilitated the in-situ mineralized γ-FeO(OH) membrane for the removal of tannic acid through photocatalytic-PMS activation.

The growing utilization of Traditional Chinese Medicine (TCM) has resulted in an increase in wastewater. Herein, a new kind of organic-inorganic redox mediator membrane by immobilizing γ-FeO(OH) and aloe-emodin(AE) with the characteristic large π-conjugation anthraquinone structure on PVDF membrane was innovatively achieved. AE exhibiting both electron deficiency and redox activity possesses a co-catalyst role in degradation of tannic acid (TA), aiding in the separation of charge carriers through the sequential hydrogenation and dehydrogenation of AE. The removal rates of TA were 92.8 % in the tannic acid solution and 60.3 % in the simulated rhubarb wastewater by the AE-γ-FeO(OH) membrane under PMS+Vis conditions in 45 min. Also, they show a higher recovery of pure water flux and owning good fouling performance. Overall, this current work presents a novel approach for the design and preparation of organic-inorganic photocatalytic composite membrane using readily available natural products for the purification TCM wastewater.

Bifunctional Chiral Electrocatalysts Enable Enantioselective α-Alkylation of Aldehydes.

Herein, we describe an innovative approach to the asymmetric electrochemical α-alkylation of aldehydes facilitated by a newly designed bifunctional chiral electrocatalyst. The highly efficient bifunctional chiral electrocatalyst combines a chiral aminocatalyst with a redox mediator. It plays a dual role as a redox mediator for electrooxidation, while simultaneously providing remarkable asymmetric induction for the stereoselective α-alkylation of aldehydes. Additionally, this novel catalyst exhibits enhanced catalytic activity and excellent stereoselective control comparable to conventional catalytic systems. As a result, this strategy provides a new avenue for versatile asymmetric electrochemistry. The electrooxidation of diverse phenols enables the C-H/C-H oxidative α-alkylation of aldehydes in a highly chemo- and stereoselective fashion. Detailed mechanistic studies by control experiments and cyclic voltammetry analysis demonstrate possible reaction pathways and the origin of enantio-induction.

Oxidation of Ammonia Catalyzed by a Molecular Iron Complex: Translating Chemical Catalysis to Mediated Electrocatalysis.

Ammonia is a promising candidate in the quest for sustainable, clean energy. With its capacity to serve as an energy carrier, the oxidation of ammonia opens avenues for carbon-neutral approaches to address worldwide growing energy needs. We report the catalytic chemical oxidation of ammonia by an Earth-abundant transition metal complex, trans-[LFeII(MeCN)2][PF6]2, where L is a macrocyclic ligand bearing four N-heterocyclic carbene (NHC) donors. Using triarylaminium radical cations in MeCN, up to 182 turnovers of N2 per Fe were obtained from chemical catalysis with an extremely low loading of the Fe catalyst (0.043 mM, 0.004 mol % catalyst). This chemical catalysis was successfully transitioned to mediated electrocatalysis for the oxidation of ammonia. Molecular electrocatalysis by the Fe catalyst and the mediator (p-MeOC6H4)3N exhibited a catalytic half-wave potential (Ecat/2) of 0.18 V vs [Cp2Fe]+/0 in MeCN, and achieved 9.3 turnovers of N2 at an applied potential of 0.20 V vs [Cp2Fe]+/0 at -20 °C in controlled-potential electrolysis, with a Faradaic efficiency of 75 %. Based on computational results, the catalyst undergoes sequential oxidation and deprotonation steps to form [LFeIV(NH2)2]2+, and thereafter bimetallic coupling to form an N-N bond.

Homogeneous to heterogeneous redox mediator enhancing ferrate(VI) oxidation of sulfamethoxazole: Role of ferrate(VI) activation and electron shuttle.

Ferrate (Fe(VI)) is a promising oxidant for water remediation, yet it has limited reactivity towards certain recalcitrant but important emerging contaminants, such as sulfamethoxazole. Here, this study demonstrates that nitroxide redox mediators, specifically 9-azabicyclo[3.3.1]nonasne N-oxyl (ABNO), can catalyze Fe(VI) reaction with sulfamethoxazole by functioning both as Fe(VI) activator and electron shuttle. The underlying mechanism is explained as: (i) Fe(VI) activation: a series of one-electron transfers between Fe(VI) and ABNO produces highly reactive Fe(V)/Fe(IV) and ABNO+; (ii) electron shuttle: the newly formed active ABNO+ reacts with the sulfamethoxazole, contributing to its removal. Concurrently, ABNOH is generated and subsequently converted back to ABNO by reactive species, thereby completing the redox cycle. The as-developed heterogeneous redox mediator, ABNO@SiO2, retained its catalytic properties and effectively catalyzed Fe(VI) to remove sulfamethoxazole at environmentally relevant pH levels.

A MOF-Gel Based Separator for Suppressing Redox Mediator Shuttling in Li-O2 Batteries.

Redox mediators (RMs) are widely utilized in the electrolytes of Li-O2 batteries to catalyze the formation/decomposition of Li2O2, which significantly enhances the cycling performance and reduces the charge overpotential. However, RMs have a shuttle effect by migrating to the Li anode side and inducing Li metal degradation through a parasitic reaction. Herein, a metal-organic framework gel (MOF-gel) separator is proposed to restrain the shuttling of RMs. Compared to traditional MOF nanoparticles, MOF gels form uniform and dense films on the separators. When using Ru(acac)3 (ruthenium acetylacetonate) as an RM, the MOF-gel separator suppresses the shuttling of Ru(acac)3 toward the Li anode side and significantly enhances the performance of Li-O2 batteries. Specifically, Li-O2 batteries exhibit an ultralong cycling life (410 cycles) at a current density of 0.5 A g-1. Moreover, the batteries using the MOF-gel/celgard separator exhibit significantly improved cycling performance (increase by ≈1.6 times) at a high current density of 1.0 A g-1 and a decreased charge/discharge overpotential. This result is expected to guide future development of battery separators and the exploration of redox mediators.

Plasma-induced, N-doped, and reduced graphene oxide-incorporated NiCo-layered double hydroxide nanowires as a high-capacity redox mediator for sustainable decoupled water electrolysis.

Although the recent emergence of decoupled water electrolysis prevents typical H2/O2 mixing, the further development of decoupled water electrolysis has been confined by the lack of reliable redox mediator (RM) electrodes to support sustainable H2 production. As energy storage electrodes, layered double hydroxides (LDHs) possess inherently poor conductivity/stability, which can be improved by growing LDHs on graphene substrates in situ. The proper modification of the graphene surface structure can improve the electron transport and energy storage capacity of composite electrodes, while current methods are usually cumbersome and require high temperatures/chemical reagents. Therefore, in this study, dip coating was adopted to grow graphene oxide (GO) on nickel foam (NF). Then, the GO was reduced using nonthermal plasma (NTP) to reduced GO (rGO) in situ while simultaneously implementing N doping to obtain plasma-assisted N-doped rGO on NF (PNrGO/NF). The uniform conductive substrate ensured the subsequent growth of less-aggregated NiCo-LDH nanowires, which improved the conductivity and energy storage capacity (5.93 C/cm2 at 5 mA/cm2) of the NiCo-LDH@PNrGO/NF. For the decoupled system, the composite RM electrode exhibited a high buffering capacity for 1300 s during the decoupled H2/O2 evolution, and in the conventional coupled system, the necessary input voltage of 1.67 V was separated into two lower ones, 1.42/0.33 V for H2/O2 evolutions, respectively. Simultaneously, the RM possessed outstanding redox reversibility and structural stability during long-term cycling. This work could offer a feasible strategy for using NTP to synthesize excellent RM electrodes for application to decoupled water electrolysis.

Overlooked interaction between redox-mediator and bisphenol-A in permanganate oxidation.

Research efforts on permanganate (Mn(VII)) combined with redox-mediator (RM), have received increasing attention due to their significant performance for bisphenol-A (BPA) removal. However, the mechanisms underpinning BPA degradation remain underexplored. Here we show the overlooked interactions between RM and BPA during permanganate oxidation by introducing an RM-N-hydroxyphthalimide (NHPI). We discovered that the concurrent generation of MnO2 and phthalimide-N-oxyl (PINO) radical significantly enhances BPA oxidation within the pH range of 5.0-6.0. The detection of radical cross-coupling products between PINO radicals and BPA or its derivatives corroborates the pivotal role of radical cross-coupling in BPA oxidation. Intriguingly, we observed the formation of an NHPI-BPA complex, which undergoes preferential oxidation by Mn(VII), marked by the emergence of an electron-rich domain in NHPI. These findings unveil the underlying mechanisms in the Mn(VII)/RM system and bridge the knowledge gap concerning BPA transformation via complexation. This research paves the way for further exploration into optimizing complexation sites and RM dosage, significantly enhancing the system's efficiency in water treatment applications.

Effects of Central Metal Ion on Binuclear Metal Phthalocyanine-Based Redox Mediator for Lithium Carbonate Decomposition.

Li2CO3 is the most tenacious parasitic solid-state product in lithium-air batteries (LABs). Developing suitable redox mediators (RMs) is an efficient way to address the Li2CO3 issue, but only a few RMs have been investigated to date, and their mechanism of action also remains elusive. Herein, we investigate the effects of the central metal ion in binuclear metal phthalocyanines on the catalysis of Li2CO3 decomposition, namely binuclear cobalt phthalocyanine (bi-CoPc) and binuclear cobalt manganese phthalocyanine (bi-CoMnPc). Density functional theory (DFT) calculations indicate that the key intermediate peroxydicarbonate (*C2O62-) is stabilized by bi-CoPc2+ and bi-CoMnPc3+, which is accountable for their excellent catalytic effects. With one central metal ion substituted by manganese for cobalt, the bi-CoMnPc's second active redox couple shifts from the second Co(II)/Co(III) couple in the central metal ion to the Pc(-2)/Pc(-1) couple in the phthalocyanine ring. In artificial dry air (N2-O2, 78:22, v/v), the LAB cell with bi-CoMnPc in electrolyte exhibited 261 cycles under a fixed capacity of 500 mAh g-1carbon and current density of 100 mA g-1carbon, significantly better than the RM-free cell (62 cycles) and the cell with bi-CoPc (193 cycles).

Engineering FeOOH/Fe2O3@Carbon Interfaces With Biomass-Derived Carbon Nanodot/Iron Colloids for Efficient Redox-Modulated Dopamine Voltammetric Detection.

The Fe2+/Fe3+ redox couple is effective for voltammetric detection of trace dopamine (DA). However, achieving adequate concentrations with high electroactive surface area (ECSA), DA affinity, and fast interfacial charge transfer is challenging. Consequently, most reported Fe-based sensors have a high nanomolar range detection limit (LOD). Herein, we address these limitations by manipulating the phase and morphology of FeOOH/Fe2O3 heterojunctions anchored on sp2-carbon. FeOOH/Fe2O3 is synthesized by variable temperature aging of unique Fe5H9O15/Fe2O3@sp2-carbon colloidal nanoparticles, which form via chelation between biomass-derived carbon nanodots (CNDs) and Fe2+ ions. At 27 °C and 120 °C, Fe5H9O15/Fe2O3@sp2-carbon transforms into ß-FeOOH/Fe2O3 nanoparticles and α-FeOOH/Fe2O3 nanosheet, respectively. The ß-FeOOH/Fe2O3 interface exhibits higher eg orbital electron occupancy than α-FeOOH/Fe2O3, thereby facilitating oxygen adsorption and the generation of Fe2+/Fe3+ sites near the polarization potential of DA. This facilitates interfacial electron transfer between Fe3+ and DA. Moreover, its nanoparticle morphology enhances ECSA and DA adsorption compared to α-FeOOH/Fe2O3 nanosheets. With a LOD of ~3.11 nM, ß-FeOOH/Fe2O3 surpasses the lower threshold in humans (~10 nM) and matches noble-metal sensors. Furthermore, it exhibits selective detection of DA over 10 biochemicals in urine. Therefore, the ß-FeOOH/Fe2O3@sp2-C platform holds promise as a low-cost, easy-to-synthesize, and practical voltammetric DA monitor.

Single-Atom Iron Catalyst as an Advanced Redox Mediator for Anodic Oxidation of Organic Electrosynthesis.

Homogeneous electrocatalysts can indirect oxidate the high overpotential substrates through single-electron transfer on the electrode surface, enabling efficient operation of organic electrosynthesis catalytic cycles. However, the problems of this chemistry still exist such as high dosage, difficult recovery, and low catalytic efficiency. Single-atom catalysts (SACs) exhibit high atom utilization and excellent catalytic activity, hold great promise in addressing the limitations of homogeneous catalysts. In view of this, we have employed Fe-SA@NC as an advanced redox mediator to try to change this situation. Fe-SA@NC was synthesized using an encapsulation-pyrolysis method, and it demonstrated remarkable performance as a redox mediator in a range of reported organic electrosynthesis reactions, and enabling the construction of various C-C/C-X bonds. Moreover, Fe-SA@NC demonstrated a great potential in exploring new synthetic method for organic electrosynthesis. We employed it to develop a new electro-oxidative ring-opening transformation of cyclopropyl amides. In this new reaction system, Fe-SA@NC showed good tolerance to drug molecules with complex structures, as well as enabling flow electrochemical syntheses and gram-scale transformations. This work highlights the great potential of SACs in organic electrosynthesis, thereby opening a new avenue in synthetic chemistry.