Emerging applications of metal-TCNQ based organic semiconductor charge transfer complexes for catalysis

Computational investigation of the perylene-TCNQ complex: effects of chalcogen and fluorine substitutions

CONTEXT

Donor-acceptor (D-A) complexes, formed between two or more molecules held together by intermolecular forces, show interesting tunable properties and found applications in diverse fields, including semiconductors, catalysis, and sensors. In this study, we investigated the D-A complexes formed between perylene and 7,7,8,8-tetracyanoquinodimethane (TCNQ) and their chalcogen (S, Se) and fluorine derivatives. It was observed that interaction energies due to complex formation increase while the HOMO-LUMO gaps decrease with chalcogen substitutions. A redshift in the electronic absorption spectra of the complexes was observed with chalcogen substitutions. The substitution of fluorine further enhanced these changes without altering the trend. These changes were found to be more for substitution with selenium compared to that of sulfur.

METHODS

The ωB97X-D/6-311+G(2df,p) level of theory was used to optimize the individual geometries, complexes, and for the frequency calculation. Atoms-in-molecule and reduced density gradient analyses were employed for the interaction study. Time-dependent density functional theory with the same level was used to analyze the electronic excitation for complexes.

TCNQ and Its Derivatives as Electrode Materials in Electrochemical Investigations-Achievement and Prospects: A Review

7,7',8,8'-tetracyanoquinodimethane (TCNQ) is one of the most widely used effective surface electron acceptors in organic electronics and sensors, which opens up a very interesting field in electrochemical applications. In this review article, we outline the historical context of electrochemically stable selective electrode materials based on TCNQ and its derivatives and their development, their electrochemical characteristics, and the experimental aspects of their electrochemical applications. TCNQ-modified electrodes are characterized by long-term stability, reproducibility, and a low detection limit compared to other sensors; thus, their use can increase determination speed and flexibility and reduce investigation costs. TCNQ and its derivatives can also be successfully combined with other detector materials for cancer-related clinical diagnostic testing. Examples of simple, rapid, and sensitive detection procedures for various analytes are provided. Applications of new electrochemically stable TCNQ-based metal/covalent-organic hybrid frameworks, with exceptionally large surface areas, tunable pore sizes, diverse functionality, and high electrical conductivity, are also presented. As a result, they also offer enormous potential as revolutionary catalysts, drug carrier systems, and smart materials, as well as for use in gas storage. The use of TCNQ compounds as promising active electrode materials in high-power organic batteries/energy storage devices is discussed. We hope that the information featured in this review will provide readers with a good understanding of the chemistry of TCNQ and, more importantly, help to find good ways to prepare new micro-/nanoelectrode materials for rational sensor design.

Charge-Transfer Complexes: Fundamentals and Advances in Catalysis, Sensing, and Optoelectronic Applications

Supramolecular assemblies, formed through electronic charge transfer between two or more entities, represent a rich class of compounds dubbed as charge-transfer complexes (CTCs). Their distinctive formation pathway, rooted in charge-transfer processes at the interface of CTC-forming components, results in the delocalization of electronic charge along molecular stacks, rendering CTCs intrinsic molecular conductors. Since the discovery of CTCs, intensive research has explored their unique properties including magnetism, conductivity, and superconductivity. Their more recently recognized semiconducting functionality has inspired recent developments in applications requiring organic semiconductors. In this context, CTCs offer a tuneable energy gap, unique charge-transport properties, tailorable physicochemical interactions, photoresponsiveness, and the potential for scalable manufacturing. Here, an updated viewpoint on CTCs is provided, presenting them as emerging organic semiconductors. To this end, their electronic and chemical properties alongside their synthesis methods are reviewed. The unique properties of CTCs that benefit various related applications in the realms of organic optoelectronics, catalysts, and gas sensors are discussed. Insights for future developments and existing limitations are described.

Organic Donor-Acceptor Complexes As Potential Semiconducting Materials

In this review article, the synthesis, characterization and physico-chemical properties of the organic donor-acceptor complexes are highlighted and a special emphasis has been placed on developing them as semiconducting materials. The electron-rich molecules, i. e., donors have been broadly grouped in three categories, namely polycyclic aromatic hydrocarbons, nitrogen heterocycles and sulphur containing aromatic donors. The reactions of these classes of the donors with the acceptors, namely tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE), tetracyanobenzene (TCNB), benzoquinone, pyromellitic dianhydride and pyromellitic diimides, fullerenes, phenazine, benzothiadiazole, naphthalimide, DMAD, maleic anhydride, viologens and naphthalene diimide are described. The potential applications of the resulting DA complexes for physico-electronic purposes are also included. The theoretical investigation of many of these products with a view to rationalise their observed physico-chemical properties is also discussed.

How the Support Defines Properties of 2D Metal-Organic Frameworks: Fe-TCNQ on Graphene versus Au(111)

The functionality of 2D metal-organic frameworks (MOFs) is crucially dependent on the local environment of the embedded metal atoms. These atomic-scale details are best ascertained on MOFs supported on well-defined surfaces, but the interaction with the support often changes the MOF properties. We elucidate the extent of this effect by comparing the Fe-TCNQ 2D MOF on two weakly interacting supports: graphene and Au(111). We show that the Fe-TCNQ on graphene is nonplanar with iron in quasi-tetrahedral sites, but on Au(111) it is planarized by stronger van der Waals interaction. The differences in physical and electronic structures result in distinct properties of the supported 2D MOFs. The dz2 center position is shifted by 1.4 eV between Fe sites on the two supports, and dramatic differences in chemical reactivity are experimentally identified using a TCNQ probe molecule. These results outline the limitations of common on-surface approaches using metal supports and show that the intrinsic MOF properties can be partially retained on graphene.

Efficient Standalone Flexible Small Molecule Organic Solar Cell Devices: Structure-Performance Relation Among Tetracyanoquinodimethane Derivatives

Currently, very few dicyano and tetracyanoquinodimethane (TCNQ) based molecules are utilized as active layers, sandwiched between the electron and hole transport layer in organic solar cell (OSC) devices. Nevertheless, simple mono- and disubstituted TCNQ derivatives as exclusively active layers are yet unexplored and provide scope for further investigation. In this study, TCNQ derivatives with varying amine substituents, namely, AEPYDQ (1), BMEDDQ (2), MATBTCNQ (3), and MITATCNQ (4), were explored as efficient standalone, flexible, all small molecule OSC devices. Particularly, 1 resulted in the highest device efficiency of 11.75% with an aromatic amine, while 2 possessing an aliphatic amine showed the lowest power conversion efficiency (PCE; 2.12%). Notably, the short circuit current density (JSC) of device 1 increased from 2 mA/cm2 in the dark to 9.12 mA/cm2 under light, indicating a significant boost in the current generation. Further, 1 manifested more crystallinity than others. Interestingly, 4 exhibited a higher PCE (5.90%) than 3 (PCE is 2.58%), though 3 is disubstituted with an aromatic amine, probably attributed to the electron-withdrawing effects of the -CF3 and -CN groups in 3 reducing the available π-electron density for stacking. Therefore, this study emphasizes crystallinity, significantly on the PCE, offering insights into the design of many such efficient OSCs.

Fluorine Substitution of TCNQ Alters the Redox-Driven Catalytic Pathway for the Ferricyanide-Thiosulfate Reaction

Mechanistic variation in catalysis through substituent-based redox tuning is well established. Fluorination of TCNQ (TCNQ=tetracyanoquinodimethane) provides ~850 mV variation in the redox potentials of theTCNQF n 0 / 1 - ${{{\rm {TCNQF}}}_{{\rm {n}}}^{{\rm {0/1-}}}}$ andTCNQF n 1 - / 2 - ${{{\rm {TCNQF}}}_{{\rm {n}}}^{{\rm {1-/2-}}}}$ (n=0, 2, 4) processes. WithTCNQF 4 1 - ${{{\rm {TCNQF}}}_{{\rm {4}}}^{{\rm {1-}}}}$ , catalysis of the kinetically very slow ferrocyanide-thiosulfate redox reaction in aqueous solution occurs via a mechanism in which the catalystTCNQF 4 1 - ${{{\rm {TCNQF}}}_{{\rm {4}}}^{{\rm {1-}}}}$ is reduced toTCNQF 4 2 - ${{{\rm {TCNQF}}}_{{\rm {4}}}^{{\rm {2-}}}}$ when reacting withS 2 O 3 2 - ${{{\rm {S}}}_{{\rm {2}}}{{\rm {O}}}_{{\rm {3}}}^{{\rm {2-}}}}$ which is oxidised toS 4 O 6 2 - ${{{\rm {S}}}_{{\rm {4}}}{{\rm {O}}}_{{\rm {6}}}^{{\rm {2-}}}}$ . Subsequently,TCNQF 4 2 - ${{{\rm {TCNQF}}}_{{\rm {4}}}^{{\rm {2-}}}}$ reacts with[ Fe ( CN ) 6 ]​ 3 - ${{{\rm {[Fe(CN)}}}_{{\rm {6}}}{{\rm {]}}}^{{\rm {3-}}}}$ to form[ Fe ( CN ) 6 ]​ 4 - ${{{\rm {[Fe(CN)}}}_{{\rm {6}}}{{\rm {]}}}^{{\rm {4-}}}}$ and reform theTCNQF 4 1 - ${{{\rm {TCNQF}}}_{{\rm {4}}}^{{\rm {1-}}}}$ catalyst, in another thermodynamically favoured process. An analogous mechanism applies withTCNQF 2 1 - ${{{\rm {TCNQF}}}_{{\rm {2}}}^{{\rm {1-}}}}$ as a catalyst. In contrast, since the reaction ofS 2 O 3 2 - ${{{\rm {S}}}_{{\rm {2}}}{{\rm {O}}}_{{\rm {3}}}^{{\rm {2-}}}}$ withTCNQ 1 - ${{{\rm {TCNQ}}}^{{\rm {1-}}}}$ is thermodynamically unfavourable, an alternative mechanism is required to explain the catalytic activity observed in this non-fluorinated system. Here, upon addition ofTCNQ 1 - ${{{\rm {TCNQ}}}^{{\rm {1-}}}}$ , reduction of[ Fe ( CN ) 6 ]​ 3 - ${{{\rm {[Fe(CN)}}}_{{\rm {6}}}{{\rm {]}}}^{{\rm {3-}}}}$ to[ Fe ( CN ) 6 ]​ 4 - ${{{\rm {[Fe(CN)}}}_{{\rm {6}}}{{\rm {]}}}^{{\rm {4-}}}}$ occurs with concomitant oxidation ofTCNQ 1 - ${{{\rm {TCNQ}}}^{{\rm {1-}}}}$ toTCNQ 0 ${{{\rm {TCNQ}}}^{{\rm {0}}}}$ , which then acts as the catalyst forS 2 O 3 2 - ${{{\rm {S}}}_{{\rm {2}}}{{\rm {O}}}_{{\rm {3}}}^{{\rm {2-}}}}$ oxidation. Thermodynamic data explain the observed differences in the catalytic mechanisms.CuTCNQF n ${{{\rm {CuTCNQF}}}_{{\rm {n}}}}$ (n=0, 4) also act as catalysts for the ferricyanide-thiosulfate reaction in aqueous solution. The present study shows that homogeneous pathways are available following addition of these dissolved materials. Previously, theseCuTCNQF n ${{{\rm {CuTCNQF}}}_{{\rm {n}}}}$ (n=0, 4) coordination polymers have been regarded as insoluble in water and proposed as heterogeneous catalysts for the ferricyanide-thiosulfate reaction. Details and mechanistic differences were established using UV-visible spectrophotometry and cyclic voltammetry.

Electron-Rich Diruthenium Complexes with π-Extended Alkenyl Ligands and Their F4 TCNQ Charge-Transfer Salts

The synthesis of dinuclear ruthenium alkenyl complexes with {Ru(CO)(Pi Pr3 )2 (L)} entities (L=Cl- in complexes Ru2 -3 and Ru2 -7; L=acetylacetonate (acac- ) in complexes Ru2 -4 and Ru2 -8) and with π-conjugated 2,7-divinylphenanthrenediyl (Ru2 -3, Ru2 -4) or 5,8-divinylquinoxalinediyl (Ru2 -7, Ru2 -8) as bridging ligands are reported. The bridging ligands are laterally π-extended by anellating a pyrene (Ru2 -7, Ru2 -8) or a 6,7-benzoquinoxaline (Ru2 -3, Ru2 -4) π-perimeter. This was done with the hope that the open π-faces of the electron-rich complexes will foster association with planar electron acceptors via π-stacking. The dinuclear complexes were subjected to cyclic and square-wave voltammetry and were characterized in all accessible redox states by IR, UV/Vis/NIR and, where applicable, by EPR spectroscopy. These studies signified the one-electron oxidized forms of divinylphenylene-bridged complexes Ru2 -7, Ru2 -8 as intrinsically delocalized mixed-valent species, and those of complexes Ru2 -3 and Ru2 -4 with the longer divinylphenanthrenediyl linker as partially localized on the IR, yet delocalized on the EPR timescale. The more electron-rich acac- congeners formed non-conductive 1 : 1 charge-transfer (CT) salts on treatment with the F4 TCNQ electron acceptor. All spectroscopic techniques confirmed the presence of pairs of complex radical cations and F4 TCNQ.- radical anions in these CT salts, but produced no firm evidence for the relevance of π-stacking to their formation and properties.

New Charge Transfer Complex between 4-Dimethylaminopyridine and DDQ: Synthesis, Spectroscopic Characterization, DNA Binding Analysis, and Density Functional Theory (DFT)/Time-Dependent DFT/Natural Transition Orbital Studies

A combined experimental and theoretical study of the electron donor 4-dimethylaminopyridine (4-DMAP) with the electron acceptor 2, 3-dichloro-5, 6-dicyano-p-benzoquinone (DDQ) has been made in acetonitrile (ACN) and methanol (MeOH) media at room temperature. The stoichiometry proportion of the charge transfer (CT) complex was determined using Job's and photometric titration methods and found to be 1:1. The association constant (K _CT), molar absorptivity (ε), and spectroscopic physical parameters were used to know the stability of the CT complex. The CT complex shows maximum stability in a high-polar solvent (ACN) compared to a less-polar solvent (MeOH). The prepared complex was characterized by Fourier transform infrared, NMR, powder X-ray diffraction, and scanning electron microscopy-energy-dispersive X-ray analysis. The nature of DNA binding ability of the complex was probed using UV-visible spectroscopy, and the binding mode of the CT complex is intercalative. The intrinsic binding constant (K _b) value is 1.8 × 10⁶ M^-1. It reveals a primary indication for developing a pharmaceutical drug in the future due to its high binding affinity with the CT complex. The theoretical study was carried out by density functional theory (DFT), and the basis set is wB97XD/6-31G(d,p), with gas-phase and PCM analysis, which supports experimental results. Natural atomic charges, state dipole moments, electron density difference maps, reactivity parameters, and FMO surfaces were also evaluated. The MEP maps indicate the electrophilic nature of DDQ and the nucleophilic nature of 4-DMAP. The electronic spectrum computed using time-dependent DFT (TD-DFT) via a polarizable continuum salvation approach, PCM/TD-DFT, along with natural transition orbital analysis is fully correlated with the experimental outcomes.

Charge transfer in mixed and segregated stacks of tetrathiafulvalene, tetrathianaphthalene and naphthalene diimide: a structural, spectroscopic and computational study

We report the synthesis of novel charge transfer complexes consisting of TTF or TTN, and DPNI. A spectroscopic and computational approach is taken to elucidate charge transfer in these complexes.

Unprecedented transformation from cyclized zwitterionic oxazolidine derivatives to corresponding non-zwitterionic aromatic amides via Vilsmeier reagent in a one-pot reaction: optical property and crystallography

In situ formation of iminium intermediate in the conversion of zwitterionic oxazolidine derivatives to aromatic amides resulting in contrasting optical properties.

Coordination polymers of 5-substituted 1,2,3,4-tetracyanocyclopentadienides: structural and electrochemical properties of complex compounds of 5-amino- and 5-nitro-tetracyanocyclopentadienide

Compounds of the 5 amino (ATCC) and 5 nitro 1,2,3,4 tetracyanocyclopentadienide (NTCC) ligand with iron(II) and iron(III), silver(I) and potassium(I) were prepared and characterized by electrochemical methods using EPR, cyclic voltammetry and Mößbauer spectroscopy as well as UV-Vis spectroscopy. The investigation sheds light on the free radical activity in non- as well as transition metal compounds, and shows signs of photoinduced electron transfer in transition metal compounds of the ligands. We characterized silver(I) and potassium compounds of the compounds via X-ray diffraction, with one of the structures exhibiting a porous coordination polymer.

Increased Crystallization of CuTCNQ in Water/DMSO Bisolvent for Enhanced Redox Catalysis

Controlling the kinetics of CuTCNQ (TCNQ = 7,7,8,8-tetracyanoquinodimethane) crystallization has been a major challenge, as CuTCNQ crystallizing on Cu foil during synthesis in conventional solvents such as acetonitrile simultaneously dissolves into the reaction medium. In this work, we address this challenge by using water as a universal co-solvent to control the kinetics of crystallization and growth of phase I CuTCNQ. Water increases the dielectric constant of the reaction medium, shifting the equilibrium toward CuTCNQ crystallization while concomitantly decreasing the dissolution of CuTCNQ. This allows more CuTCNQ to be controllably crystallized on the surface of the Cu foil. Different sizes of CuTCNQ crystals formed on Cu foil under different water/DMSO admixtures influence the solvophilicity of these materials. This has important implications in their catalytic performance, as water-induced changes in the surface properties of these materials can make them highly hydrophilic, which allows the CuTCNQ to act as an efficient catalyst as it brings the aqueous reactants in close vicinity of the catalyst. Evidently, the CuTCNQ synthesized in 30% (v/v) water/DMSO showed superior catalytic activity for ferricyanide reduction with 95% completion achieved within a few minutes in contrast to CuTCNQ synthesized in DMSO that took over 92 min.

Electrochemical Detection of Electrolytes Using a Solid-State Ion-Selective Electrode of Single-Piece Type Membrane

This study aimed to develop simple electrochemical electrodes for the fast detection of chloride, sodium and potassium ions in human serum. A flat thin-film gold electrode was used as the detection electrode for chloride ions; a single-piece type membrane based solid-state ion-selective electrode (ISE), which was formed by covering a flat thin-film gold electrode with a mixture of 7,7,8,8-tetracyanoquinodimethane (TCNQ) and ion-selective membrane (ISM), was developed for sodium and potassium ions detection. Through cyclic voltammetry (CV) and square-wave voltammetry (SWV), the detection data can be obtained within two minutes. The linear detection ranges in the standard samples of chloride, sodium, and potassium ions were 25-200 mM, 50-200 mM, and 2-10 mM, with the average relative standard deviation (RSD) of 0.79%, 1.65%, and 0.47% and the average recovery rates of 101%, 100% and 96%, respectively. Interference experiments with Na+, K+, Cl-, Ca2+, and Mg2+ ions demonstrated that the proposed detection electrodes have good selectivity. Moreover, the proposed detection electrodes have characteristics such as the ability to be prepared under relatively simple process conditions, excellent detection sensitivity, and low RSD, and the detection linear range is suitable for the Cl-, Na+ and K+ concentrations in human serum.

Non-invasive detection of glucose in human urine using a color-generating copper NanoZyme

Renal complications are long-term effect of diabetes mellitus where glucose is excreted in urine. Therefore, reliable glucose detection in urine is critical. While commercial urine strips offer a simple way to detect urine sugar, poor sensitivity and low reliability limit their use. A hybrid glucose oxidase (GOx)/horseradish peroxidase (HRP) assay remains the gold standard for pathological detection of glucose. A key restriction is poor stability of HRP and its suicidal inactivation by hydrogen peroxide, a key intermediate of the GOx-driven reaction. An alternative is to replace HRP with a robust inorganic enzyme-mimic or NanoZyme. While colloidal NanoZymes show promise in glucose sensing, they detect low concentrations of glucose, while urine has high (mM) glucose concentration. In this study, a free-standing copper NanoZyme is used for the colorimetric detection of glucose in human urine. The sensor could operate in a biologically relevant dynamic linear range of 0.5-15 mM, while showing minimal sample matrix effect such that glucose could be detected in urine without significant sample processing or dilution. This ability could be attributed to the Cu NanoZyme that for the first time showed an ability to promote the oxidation of a TMB substrate to its double oxidation diimine product rather than the charge-transfer complex product commonly observed. Additionally, the sensor could operate at a single pH without the need to use different pH conditions as used during the gold standard assay. These outcomes outline the high robustness of the NanoZyme sensing system for direct detection of glucose in human urine. Graphical abstract.

Polycyclic Aromatic Hydrocarbons (PAHs) in inland aquatic ecosystems: Perils and remedies through biosensors and bioremediation

Polycyclic Aromatic Hydrocarbons (PAHs) are among the most ubiquitous environmental pollutants of high global concern. PAHs belong to a diverse family of hydrocarbons with over one hundred compounds known, each containing at least two aromatic rings in their structure. Due to hydrophobic nature, PAHs tend to accumulate in the aquatic sediments, leading to bioaccumulation and elevated concentrations over time. In addition to their well-manifested mutagenic and carcinogenic effects in humans, they pose severe detrimental effects to aquatic life. The high eco-toxicity of PAHs has attracted a number of reviews, each dealing specifically with individual aspects of this global pollutant. However, efficient management of PAHs warrants a holistic approach that combines a thorough understanding of their physico-chemical properties, modes of environmental distribution and bioaccumulation, efficient detection, and bioremediation strategies. Currently, there is a lack of a comprehensive study that amalgamates all these aspects together. The current review, for the first time, overcomes this constraint, through providing a high level comprehensive understanding of the complexities faced during PAH management, while also recommending future directions through potentially viable solutions. Importantly, effective management of PAHs strongly relies upon reliable detection tools, which are currently non-existent, or at the very best inefficient, and therefore have a strong prospect of future development. Notably, the currently available biosensor technologies for PAH monitoring have not so far been compiled together, and therefore a significant focus of this article is on biosensor technologies that are critical for timely detection and efficient management of PAHs. This review is focussed on inland aquatic ecosystems with an emphasis on fish biodiversity, as fish remains a major source of food and livelihood for a large proportion of the global population. This thought provoking study is likely to instigate new collaborative approaches for protecting aquatic biodiversity from PAHs-induced eco-toxicity.

Oxygen-deficient photostable Cu2O for enhanced visible light photocatalytic activity

Oxygen vacancies in inorganic semiconductors play an important role in reducing electron-hole recombination, which may have important implications in photocatalysis. Cuprous oxide (Cu2O), a visible light active p-type semiconductor, is a promising photocatalyst. However, the synthesis of photostable Cu2O enriched with oxygen defects remains a challenge. We report a simple method for the gram-scale synthesis of highly photostable Cu2O nanoparticles by the hydrolysis of a Cu(i)-triethylamine [Cu(i)-TEA] complex at low temperature. The oxygen vacancies in these Cu2O nanoparticles led to a significant increase in the lifetimes of photogenerated charge carriers upon excitation with visible light. This, in combination with a suitable energy band structure, allowed Cu2O nanoparticles to exhibit outstanding photoactivity in visible light through the generation of electron-mediated hydroxyl (OH˙) radicals. This study highlights the significance of oxygen defects in enhancing the photocatalytic performance of promising semiconductor photocatalysts.

Nanostructured silver fabric as a free-standing NanoZyme for colorimetric detection of glucose in urine

Enzyme-mimicking catalytic nanoparticles, more commonly known as NanoZymes, have been at the forefront for the development of new sensing platforms for the detection of a range of molecules. Although solution-based NanoZymes have shown promise in glucose detection, the ability to immobilize NanoZymes on highly absorbent surfaces, particularly on free-standing substrates that can be feasibly exposed and removed from the reaction medium, can offer significant benefits for a range of biosensing and catalysis applications. This work, for the first time, shows the ability of Ag nanoparticles embedded within the 3D matrix of a cotton fabric to act as a free-standing peroxidase-mimic NanoZyme for the rapid detection of glucose in complex biological fluids such as urine. The use of cotton fabric as a template not only allows high number of catalytically active sites to participate in the enzyme-mimic catalytic reaction, the absorbent property of the cotton fibres also helps in rapid absorption of biological molecules such as glucose during the sensing event. This, in turn, brings the target molecule of interest in close proximity of the NanoZyme catalyst enabling accurate detection of glucose in urine. Additionally, the ability to extract the free-standing cotton fabric-supported NanoZyme following the reaction overcomes the issue of potential interference from colloidal nanoparticles during the assay. Based on these unique characteristics, nanostructured silver fabrics offer remarkable promise for the detection of glucose and other biomolecules in complex biological and environmental fluids.

Two-dimensional iron–tetracyanoquinodimethane (Fe–TCNQ) monolayer: an efficient electrocatalyst for the oxygen reduction reaction

The Fe–TCNQ monolayer exhibit superior catalytic performance for oxygen reduction and can serve as a promising alternative to Pt-based catalysts.