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Addressing the limitations arising from the consistent catalytic behavior observed for various intermediates during the electrochemical carbon dioxide reduction reaction (CO2RR) poses a significant challenge in the optimization of catalytic activity. In this study, we aimed to address this challenge by constructing an asymmetric coordination Fe single atom catalyst (SCA) with a dynamically evolved structure. Our catalyst, consisting of a Fe atom coordinated with one S atom and three N atoms (Fe−S1N3), exhibited exceptional selectivity (CO Faradaic efficiency of 99.02 %) and demonstrated a high intrinsic activity (TOF of 7804.34 h−1), and remarkable stability. Using operando XAFS spectra and Density Functional Theory (DFT) calculations, we elucidated the self‐relaxation of geometric distortion and dynamic evolution of bond lengths within the catalyst. These structure changes enabled independent regulation of the *COOH and *CO intermediate adsorption energies, effectively breaking the linear scale relationship and enhancing the intrinsic activity of CO2RR. This study provides valuable insights into the dynamic evolution of SACs and paves the way for targeted catalyst designs aimed to disrupt the linear scaling relationships. [ABSTRACT FROM AUTHOR]

Highlights: A unique atomic dispersed hetero-pair was successfully synthesized, consisting of Mo-Fe di-atoms anchored on N-doped carbon carrier. This strategy breaks the linear scaling relationships of electrocatalytic CO2 reduction by simultaneously regulating the *COOH adsorption energy and *CO desorption energy. The as-prepared MoFe–N–C exhibits excellent performance for CO2RR to CO with a high turnover frequency (TOF) of 3336.21 h−1, CO Faradaic efficiency (FECO) of 95.96% at − 0.60 V (versus RHE) and outstanding stability. Electrochemical carbon dioxide reduction reaction (CO2RR) involves a variety of intermediates with highly correlated reaction and ad-desorption energies, hindering optimization of the catalytic activity. For example, increasing the binding of the *COOH to the active site will generally increase the *CO desorption energy. Breaking this relationship may be expected to dramatically improve the intrinsic activity of CO2RR, but remains an unsolved challenge. Herein, we addressed this conundrum by constructing a unique atomic dispersed hetero-pair consisting of Mo-Fe di-atoms anchored on N-doped carbon carrier. This system shows an unprecedented CO2RR intrinsic activity with TOF of 3336 h−1, high selectivity toward CO production, Faradaic efficiency of 95.96% at − 0.60 V and excellent stability. Theoretical calculations show that the Mo-Fe diatomic sites increased the *COOH intermediate adsorption energy by bridging adsorption of *COOH intermediates. At the same time, d-d orbital coupling in the Mo-Fe di-atom results in electron delocalization and facilitates desorption of *CO intermediates. Thus, the undesirable correlation between these steps is broken. This work provides a promising approach, specifically the use of di-atoms, for breaking unfavorable relationships based on understanding of the catalytic mechanisms at the atomic scale. [ABSTRACT FROM AUTHOR]

To enable an efficient and cost‐effective electrocatalytic N2 reduction reaction (NRR) the development of an electrocatalyst with a high NH3 yield and good selectivity is required. In this work, Ti3C2Tx MXene‐derived quantum dots (Ti3C2Tx QDs) with abundant active sites enable the development of efficient NRR electrocatalysts. Given surface functional groups play a key role on the electrocatalytic performance, density functional theory calculations are first conducted, clarifying that hydroxyl groups on Ti3C2Tx offer excellent NRR activity. Accordingly, hydroxyl‐rich Ti3C2Tx QDs (Ti3C2OH QDs) are synthesized as NRR catalysts by alkalization and intercalation. This material offers an NH3 yield and Faradaic efficiency of 62.94 µg h−1 mg−1cat. and 13.30% at −0.50 V, respectively, remarkably higher than reported MXene catalysts. This work demonstrates that MXene catalysts can be mediated through the optimization of both QDs sizes and functional groups for efficient ammonia production at room temperature. [ABSTRACT FROM AUTHOR]

Nanozyme-based colorimetry was suggested to be a rapid method for biomarker (e.g. glutathione) detection, but this method suffers from lack of efficiency and low-toxicity nanozymes till now. Herein, quantum dots of TiO2 loaded on carbon (TiO2/C-QDs) oxidase-like nanozymes were prepared via a hydrothermal treatment of tiny and few-layered Ti3C2Tx MXene nanosheets, which possess abundant thermodynamic metastable Ti atoms on MXene margins as raw materials for the preparation of TiO2/C-QDs. The oxygen vacancy in TiO2 on the surface of the carbon matrix can facilitate O2 adsorption in the solution and generate reactive oxygen species (ROS), thereby quickly oxidizing 3,3′,5,5′-tetramethylbenzidine (TMB) to its oxidized form (TMBox) in the absence of H2O2. After adding glutathione (GSH), TMBox was able to be restored to TMB, which resulted in a corresponding decrease in the UV-vis absorbance value at 652 nm. Furthermore, this assay possesses good selectivity, excellent specificity and high sensitivity (limit of detection: 0.2 μM), which made it possible to efficiently detect GSH in complex biological samples such as human serum. [ABSTRACT FROM AUTHOR]

The electrooxidation of urea holds great potential for converting urea from wastewater into hydrogen, contributing to environmental protection and sustainable energy production. This necessitates the development of highly efficient and stable catalysts for the urea oxidation reaction (UOR). In this study, a NiCoCr‐LDH/NF (nickel‐cobalt‐chromium layered double hydroxide/nickel foam) electrode is successfully synthesized via a simple hydrothermal method, demonstrating excellent electrocatalytic performance with a low work potential of 1.38 V at a high current density of 100 mA cm−2. In situ, Raman spectra analysis revealed that the incorporation of chromium (Cr) facilitated the generation of active γ‐NiOOH species and catalyst reconstruction. Density functional theory (DFT) simulations confirmed that the lower formation energy of γ‐NiOOH is due to the weakened interaction of O─H bonds because of a narrow energy range of hybridization between O‐2pz orbitals and H‐1s orbitals. The introduction of Cr also improved the adsorption energy of urea molecules and its intermediates, thereby enhancing the overall activity of UOR. With its excellent electrocatalytic performance, unique electronic states, and coordination structures, the NiCoCr‐LDH/NF electrode showcases great potential for practical applications in the field of energy catalysis. [ABSTRACT FROM AUTHOR]

To achieve the energy‐effective ammonia (NH3) production via the ambient‐condition electrochemical N2 reduction reaction (NRR), it is vital to ingeniously design an efficient electrocatalyst assembling the features of abundant surface deficiency, good dispersibility, high conductivity, and large surface specific area (SSA) via a simple way. Inspired by the fact that the MXene contains thermodynamically metastable marginal transition metal atoms, the oxygen‐vacancy‐rich TiO2 nanoparticles (NPs) in situ grown on the Ti3C2Tx nanosheets (TiO2/Ti3C2Tx) are prepared via a one‐step ethanol‐thermal treatment of the Ti3C2Tx MXene. The oxygen vacancies act as the main active sites for the NH3 synthesis. The highly conductive interior untreated Ti3C2Tx nanosheets could not only facilitate the electron transport but also avoid the self‐aggregation of the TiO2 NPs. Meanwhile, the TiO2 NPs generation could enhance the SSA of the Ti3C2Tx in return. Accordingly, the as‐prepared electrocatalyst exhibits an NH3 yield of 32.17 µg h−1 mg−1cat. at −0.55 V versus reversible hydrogen electrode (RHE) and a remarkable Faradaic efficiency of 16.07% at −0.45 V versus RHE in 0.1 m HCl, placing it as one of the most promising NRR electrocatalysts. Moreover, the density functional theory calculations confirm the lowest NRR energy barrier (0.40 eV) of TiO2 (101)/Ti3C2Tx compared with Ti3C2Tx or TiO2 (101) alone. [ABSTRACT FROM AUTHOR]

MXene‐derived quantum dots (MQDs) have begun to attract much attention recently, but their most attractive features (i.e., optical properties) are still explored less than expected. In the present work, Ti3C2Tx MQDs with solvent‐determined optical characteristics and size distributions are prepared through solvothermal treatment of Ti3C2Tx nanosheets in various solvents. White‐emitting photoluminescence (PL) under 365 nm UV irradiation is obtained in dimethyl sulfoxide (DMSO), while blue in dimethylformamide (DMF) and ethanol, respectively. Moreover, the average diameters and quantum yields of the MQDs are 3.3 ± 0.2 nm and 10.7%; 2.5 ± 0.2 nm and 6.9%; as well as 1.8 ± 0.1 nm and 4.1% in DMF, ethanol, and DMSO, respectively. Interestingly, among a variety of metal ions, Fe3+ shows specific quenching effect toward the PL of the MQDs in DMF rather than in the other two. Moreover, electrochemiluminescence of the MQDs is observed using persulfate as coreactant for the first time. The possible mechanisms are discussed based on the combined influences of polarity, oxidation effect, and boiling point of the different solvents and the various characterizations. White/blue‐emitting photoluminescence (PL) of MXene‐derived quantum dots (MQDs) is obtained depending on the varied solvents in solvothermal treatment of bulk Ti3C2Tx MXene. Fe3+ shows specific quenching effect toward the PL of the MQDs in dimethylformamide rather than in others. Moreover, electrochemiluminescence of the MQDs is for the first time observed using persulfate as coreactant. [ABSTRACT FROM AUTHOR]

Electrochemical carbon dioxide reduction reaction (CO 2 RR) involves a variety of intermediates with highly correlated reaction and ad-desorption energies, hindering optimization of the catalytic activity. For example, increasing the binding of the *COOH to the active site will generally increase the *CO desorption energy. Breaking this relationship may be expected to dramatically improve the intrinsic activity of CO 2 RR, but remains an unsolved challenge. Herein, we addressed this conundrum by constructing a unique atomic dispersed hetero-pair consisting of Mo-Fe di-atoms anchored on N-doped carbon carrier. This system shows an unprecedented CO 2 RR intrinsic activity with TOF of 3336 h -1 , high selectivity toward CO production, Faradaic efficiency of 95.96% at - 0.60 V and excellent stability. Theoretical calculations show that the Mo-Fe diatomic sites increased the *COOH intermediate adsorption energy by bridging adsorption of *COOH intermediates. At the same time, d-d orbital coupling in the Mo-Fe di-atom results in electron delocalization and facilitates desorption of *CO intermediates. Thus, the undesirable correlation between these steps is broken. This work provides a promising approach, specifically the use of di-atoms, for breaking unfavorable relationships based on understanding of the catalytic mechanisms at the atomic scale., (© 2023. The Author(s).)

Nanozyme-based colorimetry was suggested to be a rapid method for biomarker (e.g. glutathione) detection, but this method suffers from lack of efficiency and low-toxicity nanozymes till now. Herein, quantum dots of TiO2 loaded on carbon (TiO2/C-QDs) oxidase-like nanozymes were prepared via a hydrothermal treatment of tiny and few-layered Ti3C2Tx MXene nanosheets, which possess abundant thermodynamic metastable Ti atoms on MXene margins as raw materials for the preparation of TiO2/C-QDs. The oxygen vacancy in TiO2 on the surface of the carbon matrix can facilitate O2 adsorption in the solution and generate reactive oxygen species (ROS), thereby quickly oxidizing 3,3',5,5'-tetramethylbenzidine (TMB) to its oxidized form (TMBox) in the absence of H2O2. After adding glutathione (GSH), TMBox was able to be restored to TMB, which resulted in a corresponding decrease in the UV-vis absorbance value at 652 nm. Furthermore, this assay possesses good selectivity, excellent specificity and high sensitivity (limit of detection: 0.2 μM), which made it possible to efficiently detect GSH in complex biological samples such as human serum.

Nb 2 CT x , an emerging type of MXene, should be a promising electromagnetic wave (EMW) absorbing material to overcome the EMW pollution nowadays due to its unique layered structure and extremely thin monolayer thickness, but was lack of systematic study till now. Meanwhile, Nb 2 CT x nanosheets obtained upon HF etching of Nb 2 AlC MAX was unfortunately found with limited absorption performance due to its mainly dielectric loss mechanism herein. Therefore, the Nb 2 CT x nanosheets were further treated with solvothermal strategy in various solvents. As a result, the absorption performance of the as-treated Nb 2 CT x nanosheets could be significantly improved, while the ones in ethanol showed much more superior absorption capability, especially in the low-frequency band (2.0-4.0 GHz). The minimum reflection loss value could reach -52.2 dB at 3.93 GHz with the thickness of only 2.90 mm, indicating more than 99.999% EMW was absorbed. These should be due to the multi-loss mechanism including dielectric, interfacial, and multiple reflection ones resulting from the enlarged interlayer spacing, and increased surface functional groups on the Nb 2 CT x nanosheets upon the ethanol-based solvothermal treatment., (Copyright © 2018 Elsevier Inc. All rights reserved.)