Reversible Oxygen Redox With Enhanced Structural Stability Through Covalency Modulation for Layered Oxide Cathodes.

P2-type Mn-based layered oxides have emerged as one of the most promising cathode materials for sodium-ion batteries owing to their advantages of facile preparation and high theoretical capacity. However, challenges such as phase transition and irreversible oxygen release during cycling often lead to rapid structural distortion and the formation of oxygen vacancies, ultimately resulting in rapid capacity decay. Herein, a covalency modulation strategy is adopted to address these challenges and successfully achieved a stable P2-type Mn-based layered oxide by introducing strong covalent Ni─O bonds. The robust Ni─O motif plays a crucial role in maintaining the rigidity of transition metal (TM) layered frameworks, which efficiently alleviates the structural distortion and degradation of the coordination environments of local TM sites, thereby achieving durable structural stiffness over extended cycles. In addition, the strong covalent Ni─O bonds can also stabilize the local oxygen environment, effectively suppressing the irreversible oxygen release. Benefiting from these advancements, the as-designed Na0.6Mg0.15Mn0.7Ni0.15O2 cathode displays a full solid-solution behavior with a low volume change of only 0.9% and an enhanced reversibility of lattice oxygen redox (OR) reaction. This investigation emphasizes the crucial role of covalency modulation in regulating OR chemistry and structural integrity to achieve high-energy-density Mn-based layered oxides.

Interfacial Engineering of Nickel Oxide-Perovskite Interface with Amino Acid Complexed NiO to Improve Perovskite Solar Cell Performance.

The interface between NiO and perovskite in inverted perovskite solar cells (PSCs) is a major factor that can limit device performance due to defects and inappropriate redox reactions, which cause nonradiative recombination and decrease in open-circuit voltage (VOC). In the present study, a novel approach is used for the first time, where an amino acid (glycine (Gly), alanine (Ala), and aminobutyric acid (ABA))-complexed NiO are used as interface modifiers to eliminate defect sites and hydroxyl groups from the surface of NiO. The Ala-complexed NiO suppresses interfacial non-radiative recombination, improves the perovskite layer quality and better energy band alignment with the perovskite, resulting in improved charge transfer and reduced recombination. The incorporation of the Ala-complexed NiO leads to a PCE of 20.27% with enhanced stability under the conditions of ambient air, light soaking, and heating to 85 °C, as it retains over 82%, 85%, and 61% of its initial PCE after 1000, 500, and 350 h, respectively. The low-temperature technique also leads to the fabrication of a NiO thin film that is suitable for flexible PSCs. The Ala-complexed NiO is fabricated on the flexible substrate and achieved 17.12% efficiency while retaining 71% of initial PCE after 5,000 bending.

Organic Electrolyte Additive: Dual Functions Toward Fast Sulfur Conversion and Stable Li Deposition for Advanced Li-S Batteries.

Lithium-sulfur (Li-S) battery is of great potential for the next generation energy storage device due to the high specific capacity energy density. However, the sluggish kinetics of S redox and the dendrite Li growth are the main challenges to hinder its commercial application. Herein, an organic electrolyte additive, i.e., benzyl chloride (BzCl), is applied as the remedy to address the two issues. In detail, BzCl can split into Bz· radical to react with the polysulfides, forming a Bz-S-Bz intermediate, which changes the conversion path of S and improves the kinetics by accelerating the S splitting. Meanwhile, a tight and robust solid electrolyte interphase (SEI) rich in inorganic ingredients namely LiCl, LiF, and Li2O, is formed on the surface of Li metal, accelerating the ion conductivity and blocking the decomposition of the solvent and lithium polysulfides. Therefore, the Li-S battery with BzCl as the additive remains high capacity of 693.2 mAh g-1 after 220 cycles at 0.5 C with a low decay rate of 0.11%. This work provides a novel strategy to boost the electrochemical performances in both cathode and anode and gives a guide on the electrolyte design toward high-performance Li-S batteries.

Eu-Based Porphyrin MOF Enables High-Performance Carbon-Based Perovskite Solar Cells.

The low power conversion efficiency (PCE) of hole transport materials (HTM) - free carbon-based perovskite solar cells (C-PSCs) poses a challenge. Here, a novel 2D Eu-TCPP MOF (TCPP; [tetrakis (4-carboxyphenyl) porphyrin]) sandwiched between the perovskite layer and the carbon electrode is used to realize an effective and stable HTM-free C-PSCs. Relying on the synergistic effect of both the metal-free TCPP ligand with a unique absorption spectrum and hydrophobicity and the EuO4(OH)2 chain in the Eu-TCPP MOF, defects are remarkably suppressed and light-harvesting capability is significantly boosted. Energy band alignment is achieved after Eu-TCPP MOF treatment, promoting hole collection. Förster resonance energy transfer results in improved light utilization and protects the perovskite from decomposition. As a result, the HTM-free C-PSCs with Eu-TCPP MOF reach a champion PCE of 18.13%. In addition, the unencapsulated device demonstrates outstanding thermal stability and UV resistance and keeps 80.6% of its initial PCE after 5500 h in a high-humidity environment (65%-85% RH).

Atomic-Level Catalyst Coupled with Metal Oxide Heterostructure for Promoting Kinetics of Lithium-Sulfur Batteries.

Despite the low competitive cost and high theoretical capacity of lithium-sulfur (Li-S) batteries, their practical application is severely hindered by the lithium polysulfide (LiPS) shuttling and low conversion efficiency. Herein, the electronic structure of hollow Titanium dioxide nanospheres is tunned by single Iron atom dopants that can cooperatively enhance LiPS absorption and facilitate desired redox reaction in practical Li-S batteries, further suppressing the notorious shuttle effect, which is consistent with theoretical calculations and in situ UV/vis investigation. The obtained electrode with massive active sites and lower energy barrier for sulfur conversions exhibits exceptional cycling stability after 500 cycles and high capacity under the sulfur loading of 10.53 mg cm-2. In particular, an Ah-level Li-S pouch cell is fabricated, further demonstrating that the synthetic strategy based on atomic-level design offers a promising route toward practical high-energy-density Li-S batteries.

Highly Selective and Reversible Detection of Simulated Breath Hydrogen Sulfide Using Fe-Doped CuO Hollow Spheres: Enhanced Surface Redox Reaction by Multi-Valent Catalysts.

The precise and reversible detection of hydrogen sulfide (H2S) at high humidity condition, a malodorous and harmful volatile sulfur compound, is essential for the self-assessment of oral diseases, halitosis, and asthma. However, the selective and reversible detection of trace concentrations of H2S (≈0.1 ppm) in high humidity conditions (exhaled breath) is challenging because of irreversible H2S adsorption/desorption at the surface of chemiresistors. The study reports the synthesis of Fe-doped CuO hollow spheres as H2S gas-sensing materials via spray pyrolysis. 4 at.% of Fe-doped CuO hollow spheres exhibit high selectivity (response ratio ≥ 34.4) over interference gas (ethanol, 1 ppm) and reversible sensing characteristics (100% recovery) to 0.1 ppm of H2S under high humidity (relative humidity 80%) at 175 °C. The effect of multi-valent transition metal ion doping into CuO on sensor reversibility is confirmed through the enhancement of recovery kinetics by doping 4 at.% of Ti- or Nb ions into CuO sensors. Mechanistic details of these excellent H2S sensing characteristics are also investigated by analyzing the redox reactions and the catalytic activity change of the Fe-doped CuO sensing materials. The selective and reversible detection of H2S using the Fe-doped CuO sensor suggested in this work opens a new possibility for halitosis self-monitoring.

Suppressing Redox Reactions at the Perovskite-Nickel Oxide Interface with Zinc Nitride to Improve the Performance of Perovskite Solar Cells.

For p-i-n perovskite solar cells (PSCs), nickel oxide (NiOx) hole transport layers (HTLs) are the preferred interfacial layer due to their low cost, high mobility, high transmittance, and stability. However, the redox reaction between the Ni≥3+ and hydroxyl groups in the NiOx and perovskite layer leads to oxidized CH3NH3 + and reacts with PbI in the perovskite, resulting in a large number of non-radiative recombination sites. Among various transition metals, an ultra-thin zinc nitride (Zn3N2) layer on the NiOx surface is chosen to prevent these redox reactions and interfacial issues using a simple solution process at low temperatures. The redox reaction and non-radiative recombination at the interface of the perovskite and NiOx reduce chemically by using interface modifier Zn3N2 to reduce hydroxyl group and defects on the surface of NiOx. A thin layer of Zn3N2 at the NiOx/perovskite interface results in a high Ni3+/Ni2+ ratio and a significant work function (WF), which inhibits the redox reaction and provides a highly aligned energy level with perovskite crystal and rigorous trap-passivation ability. Consequently, Zn3N2-modified NiOx-based PSCs achieve a champion PCE of 21.61%, over the NiOx-based PSCs. After Zn3N2 modification, the PSC can improve stability under several conditions.

Bi-Directional Modification to Quench Detrimental Redox Reactions and Minimize Interfacial Energy Offset for NiOX/Perovskite-Based Solar Cells.

The quality of the buried heterojunction of nickel oxide (NiOX)/perovskite is crucial for efficient charge carrier extraction and minimizing interfacial non-radiative recombination in inverted perovskite solar cells (PSCs). However, NiOX has limitations as a hole transport layer (HTL) due to energy level mismatch, low conduction, and undesirable redox reactions with the perovskite layer, which impede power conversion efficiency (PCE) and long-term stability. In this study, para-amino 2,3,5,6-tetrafluorobenzoic acid (PATFBA) is proposed as a bifacial defect passivator to tailor the NiOX/perovskite interface. The acid group and adjacent fluorine atoms of PATFBA effectively passivate NiOX surface defects, thereby improving its Ni3+/Ni2+ ratio, hole extraction capability, and energy band alignment with perovskite, while also providing active sites for homogenous nucleation. Meanwhile, the amine and adjacent fluorine atomsstabilize the buried perovskite interface by passivating interfacial defects, resulting in higher crystalline perovskite films with supressed non-radaitive recombination. Furthermore, the PATFBA buffer layer prevents redox reactions between Ni3+ and perovskite.These synergistic bi-directional interactions lead to optimized inverted PSCs with a PCE of 20.51% compared to 16.89% for pristine devices and the unencapsulated PATFBA-modified devices exhibit outstanding thermal and long-term stability. This work provides a new engineering approach to buried interfaces through the synergy of functional groups.

Single-step purification and characterization of Pseudomonas aeruginosa azurin.

Azurin is a small periplasmic blue copper protein found in bacterial strains such as Pseudomonas and Alcaligenes where it facilitates denitrification. Azurin is extensively studied for its ability to mediate electron-transfer processes, but it has also sparked interest of the pharmaceutical community as a potential antimicrobial or anticancer agent. Here we offer a novel approach for expression and single-step purification of azurin in Escherichia coli with high yields and optimal metalation. A fusion tag strategy using an N-terminal GST tag was employed to obtain pure protein without requiring any additional purification steps. After the on-column cleavage by HRV 3C Protease, azurin is collected and additionally incubated with copper sulphate to ensure sufficient metalation. UV-VIS absorption, mass spectroscopy, and circular dichroism analysis all validated the effective production of azurin, appropriate protein folding and the development of an active site with an associated cofactor. MD simulations verified that incorporation of the N-terminal GPLGS segment does not affect azurin structure. In addition, the biological activity of azurin was tested in HeLa cells.

Ion valence-gated photochromism of an aza-crowned diarylethene.

A non-photochromic diarylethene 2o with an N-phenylaza-15-crown-5 was synthesized. When the nitrogen atom in the aza-crown ring was protonated, it became photochromic due to the prevention of a twisted intramolecular charge transfer (TICT). Although addition of a monovalent metal cation (Li+, Na+, K+, Rb+, Cs+, Cu+, Ag+) in acetonitrile could not stop the TICT so that it was not photochromic, the addition of a multivalent metal cation (Mg2+, Ca2+, Sr2+, Ba2+, Fe2+, Ni2+, Al3+, Sb5+) changed 2o to be photochromic due to the strong attraction of the lone pair on the nitrogen atom. In the presence of excess Cu2+, 2o was oxidized to be EPR-detectable 2o·+, which was thermally unstable as well as inert towards visible-light irradiation. However, 2o·+ was further oxidized to be fairly stable 2o2+ by the irradiation of 365-nm light in the presence of Cu2+. ESI-MS measurements strongly suggested the generation of 2o·+ by mixing 2o with Cu(ClO4)2 in acetonitrile, and the transformation of 2o·+ to 2o2+ by successive 365-nm light irradiation. Fe3+ similarly worked as the oxidant, but the two-step oxidation of 2o to 2o2+ occurred more easily.

Regulating the Selectivity of Nitrate Photoreduction for Purification or Ammonia Production by Cooperating Oxidative Half-Reactions.

The removal and conversion of nitrate (NO3-) from wastewater has become an important environmental and health topic. The NO3- can be reduced to nontoxic nitrogen (N2) for environmental remediation or ammonia (NH3) for recovery, in which the tailoring of the selectivity is greatly challenging. Here, by construction of the CuOx@TiO2 photocatalyst, the NO3- conversion efficiency is enhanced to ∼100%. Moreover, the precise regulation of selectivity to NH3 (∼100%) or N2 (92.67%) is accomplished by the synergy of cooperative redox reactions. It is identified that the selectivity of the NO3- photoreduction is determined by the combination of different oxidative reactions. The key roles of intermediates and reactive radicals are revealed by comprehensive in situ characterizations, providing direct evidence for the regulated selectivity of the NO3- photoreduction. Different active radicals are produced by the interaction of oxidative reactants and light-generated holes. Specifically, the introduction of CH3CHO as the oxidative reactant results in the generation of formate radicals, which drives selective NO3- reduction into N2 for its remediation. The alkyl radicals, contributed to by the (CH2OH)2 oxidation, facilitate the deep reduction of NO3- to NH3 for its upcycling. This work provides a technological basis for radical-directed NO3- reduction for its purification and resource recovery.

Alginate-derived carbon dots for "turn off-on" anti-neoplastic 5-fluorouracil sensing in biological samples.

As a chemotherapy drug, 5-fluorouracil (5-FU) has been used for colon cancer for decades. Excessive levels of 5-FU in the human body can lead to notable adverse effects, including severe diarrhea, infection, mouth sores, skin peeling, skin inflammation, and ulcers, which are important and relatively common digestive side effects. In addition, 5-FU is an analog of uracil and also has similarities to pyrimidines. Therefore, it is not easy to separate them. This research presented a sensor capable of detecting drugs in minimal amounts. An alginate-derived carbon dot (CD) was synthesized by unique optical properties that obey an on-off fluorescence mechanism for 5-FU sensing. Introducing copper (Cu(I)) to CDs results in fluorescence quenching through electron transfer. However, when 5-FU is added to the system as an oxidizing agent, a redox reaction occurs on the surface of the CDs, which leads to the restoration of fluorescence as Cu(I) is altered to Cu(II). Experimental results showed a strong linear correlation (R2 = 0.99) in the concentration range of 1.00-45.00 nM, with the following linear regression, and revealed the relative standard deviation (RSD%) and detection limit of 2.57%, and 1.00 nM, respectively. These results validated the excellent detection capability of the proposed method even at low concentrations of 5-FU and in the presence of other drugs and interfering substances. Also, the recovery of 5-FU (varies from 100.46% to 113.7%, with RSD equal to 1.89-3.63) in serum samples indicates the absence of matrix interference in the determination of 5-FU. In summary, this novel approach to developing a cost-effective and sensitive sensor holds great potential for future applications in healthcare and related fields.

Nicotinamide Riboside: What It Takes to Incorporate It into RNA.

Nicotinamide is an important functional compound and, in the form of nicotinamide adenine dinucleotide (NAD), is used as a co-factor by protein-based enzymes to catalyze redox reactions. In the context of the RNA world hypothesis, it is therefore reasonable to assume that ancestral ribozymes could have used co-factors such as NAD or its simpler analog nicotinamide riboside (NAR) to catalyze redox reactions. The only described example of such an engineered ribozyme uses a nicotinamide moiety bound to the ribozyme through non-covalent interactions. Covalent attachment of NAR to RNA could be advantageous, but the demonstration of such scenarios to date has suffered from the chemical instability of both NAR and its reduced form, NARH, making their use in oligonucleotide synthesis less straightforward. Here, we review the literature describing the chemical properties of the oxidized and reduced species of NAR, their synthesis, and previous attempts to incorporate either species into RNA. We discuss how to overcome the stability problem and succeed in generating RNA structures incorporating NAR.

Reaction of Partially Methylated Polygalacturonic Acid with Iron(III) Chloride and Characterization of a New Mixed Chloride-Polygalacturonate Complex.

We have described a new route for the preparation of partially methylated polygalacturonic acid containing hydrolyzed (acidic) and unhydrolyzed (methyl esterified) carboxylate groups in a ratio of 1:1 (PGA, compound 1), and one of its basic FeIII-salts (compound 2) with a ~1:2 FeIII:GA stoichiometry (GA means galacturonic acid and methylated galacturonic acid units). The partially hydrolyzed pectin was transformed into compound 1 with the use of double ion exchange with a strongly acidic macroreticular sulfonated styrene-divinylbenzene copolymer as a hydrogen ion source. The reaction of compound 1 with FeCl3 resulted in compound 2. Compound 2 has a polymeric nature and contains binuclear FeIII(µ-O)(µ-OH)FeIII core units with two kinds of distorted octahedral iron geometries. The salt-forming acidic and methylated GA units of compound 1 are coordinated to FeIII centers in asymmetric bidentate-chelating and -bridging (via C=O group and glycosidic oxygen) modes, respectively. Two kinds of outer-sphere chloride anions were also detected by XPS in various chemical environments fixed by different sets of hydrogen bonds. We also observed a partial reduction of FeIII into FeII due to the ring-opening of the chain-end GA units of compound 1. This reaction provides a new route to determine the number of chain-ends in compound 2, and with the use of the number of GA units calculated from charge neutrality, the average length of these chains and the average molecular weight were also determined. The average molecular weight of the partially methylated polygalacturonic acid used in the industrial-scale production of commercial anti-anemic iron-polygalacturonate agents was ~50,000 g/mol. Compound 2 was also characterized by IR, Mössbauer, and X-ray photoelectron spectroscopy, and magnetic susceptibility measurements. These results on the structure and average molecular weight of basic iron(III) polygalacturonate provide a tool to design Fe-PGA complexes with tuned iron-releasing properties.

Unlocking Double Redox Reaction of Metal-Organic Framework for Aqueous Zinc-Ion Battery.

Metal-organic frameworks (MOFs) show wide application as the cathode of aqueous zinc-ion batteries (AZIBs) in the future owning to their high porosity, diverse structures, abundant species, and controllable morphology. However, the low energy density and poor cycling stability hinder the feasibility in practical application. Herein, an innovative strategy of organic/inorganic double electroactive sites is proposed and demonstrated to obtain extra capacity and enhance the energy density in a manganese-based metal-organic framework (Mn-MOF-74). Simultaneously, its energy storage mechanism is systematically investigated. Moreover, profiting from the coordination effect, the Mn-MOF-74 features with stable structure in ZnSO4 electrolyte. Therefore, the Zn/Mn-MOF-74 batteries exhibit a high energy density and superior cycling stability. This work aids in the future development of MOFs in AZIBs.

Creating High-entropy Single Atoms on Transition Disulfides through Substrate-induced Redox Dynamics for Efficient Electrocatalytic Hydrogen Evolution.

The controllable anchoring of multiple metal single-atoms (SAs) into a single support exhibits scientific and technological opportunities, while marrying the concentration-complex multimetallic SAs and high-entropy SAs (HESAs) into one SAC system remains a substantial challenge. Here, we present a substrate-mediated SAs formation strategy to successfully fabricate a library of multimetallic SAs and HESAs on MoS2 and MoSe2 supports, which can precisely control the doping location of SAs. Specially, the contents of SAs can continuously increase until the accessible Mo atoms on TMDs carriers are completely replaced by SAs, thus allowing the of much higher metal contents. In-depth mechanistic study shows that the well-controlled synthesis of multimetallic SAs and HESAs is realized by controlling the reversible redox reaction occurred on the TMDs/TM ion interface. As a proof-of-concept application, a variety of SAs-TMDs were applied to hydrogen evolution reaction. The optimized HESAs-TMDs (Pt,Ru,Rh,Pd,Re-MoSe2) delivers a much higher activity and durability than state of-the-art Pt. Thus, our work will broaden the family of single-atom catalysts and provide a new guideline for the rational design of high-performance single-atom catalysts.

Metal Coordinated Polymer as Three-Dimensional Network Binder for High Sulfur Loading Cathode of Lithium-Sulfur Battery.

The construction of high sulfur (S) loading cathode is one of the critical parameters to obtain lithium-sulfur (Li-S) batteries with high energy density, but the slow redox reaction rate of high S loading cathode limits the development process. In this paper, a metal coordinated polymer-based three-dimensional network binder, which can improve the reaction rate and stability of S electrode. Compared with traditional linear polymer binders, the metal coordinated polymer binder can not only increase the load amount of S through the three-dimensional cross-linking, but also promote the interconversion reactions between S and lithium sulfide (Li2 S), avoiding the passivation of electrode and improving the stability of the positive electrode. At an S load of 4-5 mg cm-2 and an E/S ratio of 5.5 µL mg-1 , the discharged voltage in the second platform is 2.04 V and the initial capacity is 938 mA h g-1 with metal coordinated polymer binder. Moreover, the capacity retention rate approaches 87% after 100 cycles. In comparison, the discharged voltage in the second platform is lost and the initial capacity is 347 mA h g-1 with PVDF binder. It demonstrates the advanced properties of metal-coordinated polymer binders for improving the performance of Li-S batteries.

Superhydrophilic and Superaerophobic Ru-Loaded NiCo Bimetallic Hydroxide Achieves Efficient Hydrogen Evolution over All pH Ranges.

Realizing an effective, binder-free, and super-wetting electrocatalyst for the hydrogen evolution reaction (HER) at full pH is essential for the creation of clean hydrogen. In this study, the Ru-loaded NiCo bimetallic hydroxide (Ru@NiCo-BH) catalyst was prepared by spontaneous redox reaction. The chemical interaction between Ru NPs and NiCo-BH by the Ru-O-M (M=Ni, Co) interface bond, the electron-rich Ru active site, and the multi-channel nickel foam carrier make the superhydrophilic and superaerophobic surface advantageous for mass transfer in the HER process. Therefore, Ru@NiCo-BH has remarkable HER activity, with low overpotential of 29, 68 and 80 mV, a 10 mA cm-2 current density can be obtained in alkaline, neutral and acidic electrolytes respectively. This work provides a reference for the rational development of universal electrocatalysts for hydrogen evolution in the all pH ranges through simple design strategies.

Hybrid Functional and Plane Waves based Ab Initio Molecular Dynamics Study of the Aqueous Fe2+ /Fe3+ Redox Reaction.

Kohn-Sham density functional theory and plane wave basis set based ab initio molecular dynamics (AIMD) simulation is a powerful tool for studying complex reactions in solutions, such as electron transfer (ET) reactions involving Fe2+ /Fe3+ ions in water. In most cases, such simulations are performed using density functionals at the level of Generalized Gradient Approximation (GGA). The challenge in modelling ET reactions is the poor quality of GGA functionals in predicting properties of such open-shell systems due to the inevitable self-interaction error (SIE). While hybrid functionals can minimize SIE, standard plane-wave based AIMD at that level of theory is typically 150 times slower than GGA for systems containing ∼100 atoms. Among several approaches reported to speed-up AIMD simulations with hybrid functionals, the noise-stabilized MD (NSMD) procedure, together with the use of localized orbitals to compute the required exchange integrals, is an attractive option. In this work, we demonstrate the application of the NSMD approach for studying the Fe2+ /Fe3+ redox reaction in water. It is shown here that long AIMD trajectories at the level of hybrid density functionals can be obtained using this approach. Redox properties of the aqueous Fe2+ /Fe3+ system computed from these simulations are compared with the available experimental data for validation.

Revisiting the TCNQF4 0/1-/2- Catalysis Mechanism for the [Fe(CN)6 ]3-/4- -S2 O3 2- /S4 O6 2- Redox Reaction.

Published data suggest that sparingly soluble metal complexes of TCNQF n 1 - ${{\rm{TCNQF}}_{\rm{n}}^{{\rm{1 - }}} }$ , where n=0, 1, 2, 4, can act as heterogeneous catalysts for the kinetically very slow [ Fe ( CN ) 6 ]​ 3 - / 4 - ${{\rm{[Fe(CN)}}_{\rm{6}} {\rm{]}}^{{\rm{3 - /4 - }}} }$ - S 2 O 3 2 - ${{\rm{S}}_{\rm{2}} {\rm{O}}_{\rm{3}}^{{\rm{2 - }}} }$ / S 4 O 6 2 - ${{\rm{S}}_{\rm{4}} {\rm{O}}_{\rm{6}}^{{\rm{2 - }}} }$ reaction in aqueous solution. This study shows that the coordination polymer CuTCNQF 4 ${{\rm{CuTCNQF}}_{\rm{4}} }$ , participates as a homogeneous catalyst via an extremely small concentration of dissolved TCNQF 4 1 - ${{\rm{TCNQF}}_{\rm{4}}^{{\rm{1 - }}} }$ . This finding suggests that the generally accepted mechanism of catalysis by TCNQF 4 ${{\rm{TCNQF}}_{\rm{4}} }$ based solids needs to be revisited to ascertain the role of homogeneous pathways. In the present study, UV-visible spectrophotometry was used to examine the catalysis of the aqueous redox reaction of [ Fe ( CN ) 6 ]​ 3 - ${{\rm{[Fe(CN)}}_{\rm{6}} {\rm{]}}^{{\rm{3 - }}} }$ (1.0 mM) with S 2 O 3 2 - ${{\rm{S}}_{\rm{2}} {\rm{O}}_{\rm{3}}^{{\rm{2 - }}} }$ (100 mM) in the presence of (i) a precursor catalyst, TCNQF 4 0 ${{\rm{TCNQF}}_{\rm{4}}^{\rm{0}} }$ ; (ii) the catalyst, TCNQF 4 1 - ${{\rm{TCNQF}}_{\rm{4}}^{{\rm{1 - }}} }$ , as the water soluble Li+ salt; and (iii) CuTCNQF 4 ${{\rm{CuTCNQF}}_{\rm{4}} }$ . A homogeneous reaction scheme that utilises the TCNQF 4 1 - / 2 - ${{\rm{TCNQF}}_{\rm{4}}^{{\rm{1 - /2 - }}} }$ couple is provided. In the case of TCNQF 4 1 - ${{\rm{TCNQF}}_{\rm{4}}^{{\rm{1 - }}} }$ derived from highly soluble LiTCNQF 4 ${{\rm{LiTCNQF}}_{\rm{4}} }$ , quantitative conversion of 1.0 mM S 2 O 3 2 - ${{\rm{S}}_{\rm{2}} {\rm{O}}_{\rm{3}}^{{\rm{2 - }}} }$ to 0.50 mM S 4 O 6 2 - ${{\rm{S}}_{\rm{4}} {\rm{O}}_{\rm{6}}^{{\rm{2 - }}} }$ occurs with complete reduction of [ Fe ( CN ) 6 ]​ 3 - ${{\rm{[Fe(CN)}}_{\rm{6}} {\rm{]}}^{{\rm{3 - }}} }$ to [ Fe ( CN ) 6 ]​ 4 - ${{\rm{[Fe(CN)}}_{\rm{6}} {\rm{]}}^{{\rm{4 - }}} }$ being rapidly accelerated by sub-micomolar concentrations of TCNQF 4 1 - ${{\rm{TCNQF}}_{\rm{4}}^{{\rm{1 - }}} }$ . TCNQF 4 2 - ${{\rm{TCNQF}}_{\rm{4}}^{{\rm{2 - }}} }$ generated in the catalytic cycle, reacts with [ Fe ( CN ) 6 ]​ 3 - ${{\rm{[Fe(CN)}}_{\rm{6}} {\rm{]}}^{{\rm{3 - }}} }$ to reform TCNQF 4 1 - ${{\rm{TCNQF}}_{\rm{4}}^{{\rm{1 - }}} }$ and produce [ Fe ( CN ) 6 ]​ 4 - ${{\rm{[Fe(CN)}}_{\rm{6}} {\rm{]}}^{{\rm{4 - }}} }$ . Along with the rapid catalytic reaction, the sluggish competing reaction between TCNQF 4 1 - ${{\rm{TCNQF}}_{\rm{4}}^{{\rm{1 - }}} }$ and S 2 O 3 2 - ${{\rm{S}}_{\rm{2}} {\rm{O}}_{\rm{3}}^{{\rm{2 - }}} }$ occurs to give TCNQF 4 2 - ${{\rm{TCNQF}}_{\rm{4}}^{{\rm{2 - }}} }$ , which is protonated to HTCNQF 4 1 - ${{\rm{\;HTCNQF}}_{\rm{4}}^{{\rm{1 - }}} }$ , along with a trace amount of S 4 O 6 2 - ${{\rm{S}}_{\rm{4}} {\rm{O}}_{\rm{6}}^{{\rm{2 - }}} }$ . On addition of the precursor catalyst, TCNQF 4 0 ${{\rm{TCNQF}}_{\rm{4}}^{\rm{0}} }$ , rapid reduction with S 2 O 3 2 - ${{\rm{S}}_{\rm{2}} {\rm{O}}_{\rm{3}}^{{\rm{2 - }}} }$ occurs to form TCNQF 4 1 - ${{\rm{TCNQF}}_{\rm{4}}^{{\rm{1 - }}} }$ - the active catalyst. CuTCNQF 4 ${{\rm{CuTCNQF}}_{\rm{4}} }$ added to water is shown to be sufficiently soluble to provide adequate TCNQF 4 1 - ${{\rm{TCNQF}}_{\rm{4}}^{{\rm{1 - }}} }$ to act as the catalyst for the [ Fe ( CN ) 6 ]​ 3 - / 4 - ${{\rm{[Fe(CN)}}_{\rm{6}} {\rm{]}}^{{\rm{3 - /4 - }}} }$ - S 2 O 3 2 - ${{\rm{S}}_{\rm{2}} {\rm{O}}_{\rm{3}}^{{\rm{2 - }}} }$ / S 4 O 6 2 - ${{\rm{S}}_{\rm{4}} {\rm{O}}_{\rm{6}}^{{\rm{2 - }}} }$ reaction.