Dynamic Interchain Motion in 1D Tetrathiafulvalene-Based Coordination Polymers for Highly Sensitive Molecular Recognition.

The application of electrically conductive 1D coordination polymers (1D CPs) in nanoelectronic molecular recognition is theoretically promising yet rarely explored due to the challenges in their synthesis and optimization of electrical properties. In this regard, two tetrathiafulvalene-based 1D CPs, namely [Co(m-H2TTFTB)(DMF)2(H2O)]n (Co-m-TTFTB), and {[Ni(m-H2TTFTB)(CH3CH2OH)1.5(H2O)1.5]·(H2O)0.5}n (Ni-m-TTFTB) are successfully constructed. The shorter S···S contacts between the [M(solvent)3(m-H2TTFTB)]n chains contribute to a significant improvement in their electrical conductivities. The powder X-ray diffraction (PXRD) under different organic solvents reveals the flexible and dynamic structural characteristic of M-m-TTFTB, which, combined with the 1D morphology, lead to their excellent performance for sensitive detection of volatile organic compounds. Co-m-TTFTB achieves a limit of detection for ethanol vapor down to 0.5 ppm, which is superior to the state-of-the-art chemiresistive sensors based on metal-organic frameworks or organic polymers at room temperature. In situ diffuse reflectance infrared Fourier transform spectroscopy, PXRD measurements and density functional theory calculations reveal the molecular insertion sensing mechanism and the corresponding structure-function relationship. This work expands the applicable scenario of 1D CPs and opens a new realm of 1D CP-based nanoelectronic sensors for highly sensitive room temperature gas detection.

Construction of a stable radical hydrogen-bonded metal-organic framework with functionalized tetrathiafulvalene linkers.

A stable two-dimensional radical hydrogen-bonded metal-organic framework, constructed using a modified tetrathiafulvalene-tetrabenzoate ((2-Me)-H4TTFTB) linker and Cd2+ ions, exhibits a high electrical conductivity of 4.1 × 10-4 S m-1 and excellent photothermal conversion with a temperature increase of 137 °C in 15 s under the irradiation of a 0.7 W cm-2 808 nm laser.

Versatile synthesis of nano-icosapods via cation exchange for effective photocatalytic conversion of biomass-relevant alcohols.

Branched metal chalcogenide nanostructures with well-defined composition and configuration are appealing photocatalysts for solar-driven organic transformations. However, precise design and controlled synthesis of such nanostructures still remain a great challenge. Herein, we report the construction of a variety of highly symmetrical metal sulfides and heterostructured icosapods based on them, in which twenty branches were radially grown in spatially ordered arrangement, with a high degree of structure homogeneity. Impressively, the as-obtained CdS-PdxS icosapods manifest a significantly improved photocatalytic activity for the selective oxidation of biomass-relevant alcohols into corresponding aldehydes coupled with H2 evolution under visible-light irradiation (>420 nm), and the apparent quantum yield of the benzyl alcohol reforming can be achieved as high as 31.4% at 420 nm. The photoreforming process over the CdS-PdxS icosapods is found to be directly triggered by the photogenerated electrons and holes without participation of radicals. The enhanced photocatalytic performance is attributed to the fast charge separation and abundant active sites originating from the well-defined configuration and spatial organization of the components in the branched heterostructures.

On-chip electrocatalytic microdevices.

On-chip electrocatalytic microdevices (OCEMs) are an emerging electrochemical platform specialized for investigating nanocatalysts at the microscopic level. The OCEM platform allows high-precision electrochemical measurements at the individual nanomaterial level and, more importantly, offers unique perspectives inaccessible with conventional electrochemical methods. This protocol describes the critical concepts, experimental standardization, operational principles and data analysis of OCEMs. Specifically, standard protocols for the measurement of the electrocatalytic hydrogen evolution reaction of individual 2D nanosheets are introduced with data validation, interpretation and benchmarking. A series of factors (e.g., the exposed area of material, the choice of passivation layer and current leakage) that could have effects on the accuracy and reliability of measurement are discussed. In addition, as an example of the high adaptability of OCEMs, the protocol for in situ electrical transport measurement is detailed. We believe that this protocol will promote the general adoption of the OCEM platform and inspire further development in the near future. This protocol requires essential knowledge in chemical synthesis, device fabrication and electrochemistry.

Highly Efficient Electrochemical Nitrate Reduction to Ammonia in Strong Acid Conditions with Fe2 M-Trinuclear-Cluster Metal-Organic Frameworks.

Nitrate-containing industrial wastewater poses a serious threat to the global food security and public health safety. As compared to the traditional microbial denitrification, electrocatalytic nitrate reduction shows better sustainability with ultrahigh energy efficiency and the production of high-value ammonia (NH3 ). However, nitrate-containing wastewater from most industrial processes, such as mining, metallurgy, and petrochemical engineering, is generally acidic, which contradicts the typical neutral/alkaline working conditions for both denitrifying bacteria and the state-of-the-art inorganic electrocatalysts, leading to the demand for pre-neutralization and the problematic hydrogen evaluation reaction (HER) competition and catalyst dissolution. Here, we report a series of Fe2 M (M=Fe, Co, Ni, Zn) trinuclear cluster metal-organic frameworks (MOFs) that enable the highly efficient electrocatalytic nitrate reduction to ammonium under strong acidic conditions with excellent stability. In pH=1 electrolyte, the Fe2 Co-MOF demonstrates the NH3 yield rate of 20653.5 µg h-1 mg-1 site with 90.55 % NH3 -Faradaic efficiency (FE), 98.5 % NH3 -selectivity and up to 75 hr of electrocatalytic stability. Additionally, successful nitrate reduction in high-acidic conditions directly produce the ammonium sulfate as nitrogen fertilizer, avoiding the subsequent aqueous ammonia extraction and preventing the ammonia spillage loss. This series of cluster-based MOF structures provide new insights into the design principles of high-performance nitrate reduction catalysts under environmentally-relevant wastewater conditions.

Integrating Tetrathiafulvalene and Nickel-Bis(dithiolene) Units into Donor-Acceptor Covalent Organic Frameworks for Stable and Efficient Photothermal Conversion.

Tetrathiafulvalene (TTF) and Ni-bis(dithiolene) are typical conductive units widely studied in electronics, optics, and photochemistry. However, their applications in near-infrared (NIR) photothermal conversion are often limited by insufficient NIR absorption and low chemical/thermal stability. Herein, we integrate TTF and Ni-bis(dithiolene) into a covalent organic framework (COF) with stable and efficient NIR and solar photothermal conversion performance. Two isostructural COFs, namely Ni-TTF and TTF-TTF, are successfully isolated which are composed of TTF and Ni-bis(dithiolene) units as donor-acceptor (D-A) pairs or TTF units only. Both COFs show high BET surface areas and good chemical/thermal stability. Notably, compared with TTF-TTF, the periodic D-A arrangement in Ni-TTF significantly lowers the bandgap, leading to unprecedented NIR and solar photothermal conversion performance.

Spinel-Derived Formation and Amorphization of Bimetallic Oxyhydroxides for Efficient Electrocatalytic Biomass Oxidation.

Replacing the oxygen evolution reaction (OER) with water-assisted oxidation of organic molecules represents a promising approach for achieving sustainable electrochemical biomass utilization. Among numerous OER catalysts, spinels have received substantial attention due to their manifold compositions and valence states, yet their application in biomass conversions remains rare. Herein, a series of spinels were investigated for the selective electrooxidation of furfural and 5-hydroxymethylfurfural, two model substrates for versatile value-added chemical products. Spinel sulfides universally exhibit superior catalytic performance compared to that of spinel oxides, and further investigations show that the replacement of oxygen with sulfur led to the complete phase transition of spinel sulfides into amorphous bimetallic oxyhydroxides during electrochemical activation, serving as the active species. Excellent values of conversion rate (100%), selectivity (100%), faradaic efficiency (>95%), and stability were achieved via sulfide-derived amorphous CuCo-oxyhydroxide. Furthermore, a volcano-like correlation was established between their BEOR and OER activities based on an OER-assisted organic oxidation mechanism.

Redox-Active Mixed-Linker Metal-Organic Frameworks with Switchable Semiconductive Characteristics for Tailorable Chemiresistive Sensing.

Metal-organic frameworks (MOFs), with diverse metal nodes and designable organic linkers, offer unique opportunities for the rational engineering of semiconducting properties. In this work, we report a mixed-linker conductive MOF system with both tetrathiafulvalene and Ni-bis(dithiolene) moieties, which allows the fine-tuning of electronic structures and semiconductive characteristics. By continuously increasing the molar ratio between tetrathiafulvalene and Ni-bis(dithiolene), the switching of the semiconducting behaviors from n-type to p-type was observed along with an increase in electrical conductivity by 3 orders of magnitude (from 2.88×10-7  S m-1 to 9.26×10-5  S m-1 ). Furthermore, mixed-linker MOFs were applied for the chemiresistive detection of volatile organic compounds (VOCs), where the sensing performance was modulated by the corresponding linker ratios, showing synergistic and nonlinear modulation effects.

Understanding the electrocatalytic mechanism of self-template formation of hierarchical Co9S8/Ni3S2 heterojunctions for highly selective electroreduction of nitrobenzene.

Aqueous electrochemical nitroarene reduction reaction using H2O as the sustainable hydrogen source is an emerging technology to produce functionalized anilines. However, the development of low-cost electrocatalysts and the fundamental mechanistic understanding of the selective NO-RR still remain challenging. Herein, self-supporting hierarchical nanosheets consisting of high-density Co9S8/Ni3S2 heterojunctions on Ni foam (Co9S8/Ni3S2-NF) are constructed via an in situ self-template strategy. With combined advantages of high-loading, high surface exposure, efficient conductivity and unique electronic structure of the Co9S8/Ni3S2 interface, the as-prepared Co9S8/Ni3S2-NF exhibits efficient electrocatalytic NO-RR performance, including up to 99.0% conversion and 96.0% selectivity towards aniline, and outstanding functional group tolerance. Mechanistic investigations and theoretical calculations reveal that electron transfer from Ni3S2 to Co9S8 is beneficial for the co-adsorption of H2O and nitrobenzene molecules at the interfacial sites, promoting the formation of active hydrogen and subsequent reduction of nitrobenzene. Additionally, the interfacial charge transfer breaks the symmetry of two active Co sites at the Co9S8/Ni3S2 interface, which markedly reduces the energy barrier for reduction of nitrobenzene to aniline. This work offers a successful example for the interfacial engineering of metal sulfide-based heterojunctions with excellent electrocatalytic nitroarene reduction performance, and also paves the way for the in-depth understanding of the corresponding mechanism.

Critical role of hydrogen sorption kinetics in electrocatalytic CO2 reduction revealed by on-chip in situ transport investigations.

Precise understanding of interfacial metal-hydrogen interactions, especially under in operando conditions, is crucial to advancing the application of metal catalysts in clean energy technologies. To this end, while Pd-based catalysts are widely utilized for electrochemical hydrogen production and hydrogenation, the interaction of Pd with hydrogen during active electrochemical processes is complex, distinct from most other metals, and yet to be clarified. In this report, the hydrogen surface adsorption and sub-surface absorption (phase transition) features of Pd and its alloy nanocatalysts are identified and quantified under operando electrocatalytic conditions via on-chip electrical transport measurements, and the competitive relationship between electrochemical carbon dioxide reduction (CO2RR) and hydrogen sorption kinetics is investigated. Systematic dynamic and steady-state evaluations reveal the key impacts of local electrolyte environment (such as proton donors with different pKa) on the hydrogen sorption kinetics during CO2RR, which offer additional insights into the electrochemical interfaces and optimization of the catalytic systems.

The Critical Role of Initial/Operando Oxygen Loading in General Bismuth-Based Catalysts for Electroreduction of Carbon Dioxide.

Operando reconstruction of solid catalyst into a distinct active state frequently occurs during electrocatalytic processes. The correlation between initial and operando states, if ever existing, is critical for the understanding and precise design of a catalytic system. Inspired by recently established intermediate metallic state of Bi-based catalysts during electrocatalytic carbon dioxide reduction (CO2RR), here we investigate a series of Bi oxide catalysts (Bi, Bi2O3, BiO2) and demonstrate that the operando surface/subsurface oxygen loading, positively correlated to the initial oxygen content, plays a critical role in determining Bi-based CO2RR performance. Higher initial oxygen loading indicates a better electrocatalytic efficiency. Further analysis shows that this conclusion generally applies to all Bi-based electrocatalysts reported up to date. Following this principle, cost-effective BiO2 nanocrystals demonstrated the highest formate Faradaic efficiency (FE) and current density compared to Bi/Bi2O3, further allowing a pair-electrolysis system with 800 mA/cm2 current density and an overall 175% FE for formate production.

On-Chip Investigation of Electrocatalytic Oxygen Reduction Reaction of 2D Materials.

The on-chip electrocatalytic microdevice (OCEM) is an emerging platform specialized in the electrochemical investigation of single-entity nanomaterials, which is ideal for probing the intrinsic catalytic properties, optimizing performance, and exploring exotic mechanisms. However, the current catalytic applications of OCEMs are almost exclusively in electrocatalytic hydrogen/oxygen evolution reactions with minimized influence from the mass transfer. Here, an OCEM platform specially tailored to investigate the electrocatalytic oxygen reduction reaction (ORR) at a microscopic level by introducing electrolyte convection through a microfluidic flow cell is reported. The setup is established on gold microelectrodes and later successfully applied to investigate how Ar-plasma treatment affects the ORR activities of 2H MoS2 . This study finds that Ar-plasma treatment significantly enhances the ORR performance of MoS2 nanosheets owing to the introduction of surface defects. This study paves the way for highly efficient microscopic investigation of diffusion-controlled electrocatalytic reactions.

Highly Selective Electrocatalytic Oxidation of Amines to Nitriles Assisted by Water Oxidation on Metal-Doped α-Ni(OH)2.

Selective oxidation to synthesize nitriles is critical for feedstock manufacturing in the chemical industry. Current strategies typically involve substitutions of alkyl halides with toxic cyanides or the use of strong oxidation reagents (oxygen or peroxide) under ammoxidation/oxidation conditions, setting considerable challenges in energy efficiency, sustainability, and production safety. Herein, we demonstrate a facile, green, and safe electrocatalytic route for selective oxidation of amines to nitriles under ambient conditions, assisted by the anodic water oxidation on metal-doped α-Ni(OH)2 (a typical oxygen evolution reaction catalyst). By controlling the balance between co-adsorption of the amine molecule and hydroxyls on the catalyst surface, we demonstrate that Mn doping significantly promotes the subsequent chemical oxidation of amines, resulting in Faradaic efficiencies of 96% for nitriles under ≥99% conversion. This anodic oxidation is further coupled with cathodic hydrogen evolution for overall atomic economy and additional green energy production.

Boosting the performance of single-atom catalysts via external electric field polarization.

Single-atom catalysts represent a unique catalytic system with high atomic utilization and tunable reaction pathway. Despite current successes in their optimization and tailoring through structural and synthetic innovations, there is a lack of dynamic modulation approach for the single-atom catalysis. Inspired by the electrostatic interaction within specific natural enzymes, here we show the performance of model single-atom catalysts anchored on two-dimensional atomic crystals can be systematically and efficiently tuned by oriented external electric fields. Superior electrocatalytic performance have been achieved in single-atom catalysts under electrostatic modulations. Theoretical investigations suggest a universal "onsite electrostatic polarization" mechanism, in which electrostatic fields significantly polarize charge distributions at the single-atom sites and alter the kinetics of the rate determining steps, leading to boosted reaction performances. Such field-induced on-site polarization offers a unique strategy for simulating the catalytic processes in natural enzyme systems with quantitative, precise and dynamic external electric fields.

Single-Atom Tailoring of Two-Dimensional Atomic Crystals Enables Highly Efficient Detection and Pattern Recognition of Chemical Vapors.

Low-dimensional semiconductor materials, such as single-walled carbon nanotubes, two-dimensional (2D) atomic crystals, and organic frameworks, have been widely adapted as ideal platforms to construct various chemo/biosensors with satisfying sensitivity. However, the general drawbacks in chemiresistive devices, including high operation temperatures, low response to low-polarity molecules, and poor selectivity, have limited their real-world applications. In this study, 2D materials (graphene, MoS2, and WSe2) were systematically functionalized with series of monodispersed single atomic sites (Pt, Co, and Ru) through a facile approach to construct single-atom sensors (SASs) for the detection of VOCs at room temperature. The structural and catalytic characteristics of SAs successfully translated into enhanced gas-sensing performance, with a 1-2 orders of magnitude increase in relative response to ethanol (@5 ppm) and acetone (@20 ppm) vapors (in all M-2D SASs as compared to pristine substrates), high selectivity to VOCs against relative humidity (M-WSe2 SASs), and fast response/recovery time (11/58 s for Pt-Graphene and 22/48 s for Pt-MoS2 to 50 ppm ethanol, 9/57 s for Pt-Graphene and 15/75 s for Pt-MoS2 to 200 ppm acetone) that are several times faster than the pristine 2D materials. Density functional theory (DFT) calculations revealed the signaling mechanism in SASs, and the data were further trained to build machine learning (ML) models for predicting the adsorption energies and sensing performance using the features of adsorption heights, metal charge, and charge transfer between the adsorbed VOCs and SASs sites. Finally, the rich combination of the metal single atoms and 2D atomic crystal supports were converted to cross-sensitive SA sensor array that allows for detection and identification of different VOCs.

Atomically Precise Integration of Multiple Functional Motifs in Catalytic Metal-Organic Frameworks for Highly Efficient Nitrate Electroreduction.

Ammonia production plays a central role in modern industry and agriculture with a continuous surge in its demand, yet the current industrial Haber-Bosch process suffers from low energy efficiency and accounts for high carbon emissions. Direct electrochemical conversion of nitrate to ammonia therefore emerges as an appealing approach with satisfactory sustainability while reducing the environmental impact from nitrate pollution. To this end, electrocatalysts for efficient conversion of eight-electron nitrate to ammonia require collective contributions at least from high-density reactive sites, selective reaction pathways, efficient multielectron transfer, and multiproton transport processes. Here, we report a catalytic metal-organic framework (two-dimensional (2D) In-MOF In8) catalyst integrated with multiple functional motifs with atomic precision, including uniformly dispersed, high-density, single-atom catalytic sites, high proton conductivity (efficient proton transport channel), high electron conductivity (promoted by the redox-active ligands), and confined microporous environments. These eventually lead to a direct and efficient electrochemical reduction of nitrate to ammonia and record high yield rate, FE, and selectivity for NH3 production. A novel "dynamic ligand dissociation" mechanism provides an unprecedented working principle that allows for the use of a high-quality MOF crystalline structure to function as highly ordered, high-density, single-atom catalyst (SAC)-like catalytic systems and ensures the maximum utilization of the metal centers within the MOF structure. Further, the atomically precise assembly of multiple functional motifs within a MOF catalyst offers an effective and facile strategy for the future development of framework-based enzyme-mimic systems.

Silver nanoparticles boost charge-extraction efficiency in Shewanella microbial fuel cells.

Microbial fuel cells (MFCs) can directly convert the chemical energy stored in organic matter to electricity and are of considerable interest for power generation and wastewater treatment. However, the current MFCs typically exhibit unsatisfactorily low power densities that are largely limited by the sluggish transmembrane and extracellular electron-transfer processes. Here, we report a rational strategy to boost the charge-extraction efficiency in Shewanella MFCs substantially by introducing transmembrane and outer-membrane silver nanoparticles. The resulting Shewanella-silver MFCs deliver a maximum current density of 3.85 milliamperes per square centimeter, power density of 0.66 milliwatts per square centimeter, and single-cell turnover frequency of 8.6 × 105 per second, which are all considerably higher than those of the best MFCs reported to date. Additionally, the hybrid MFCs feature an excellent fuel-utilization efficiency, with a coulombic efficiency of 81%.

Spontaneous Polarity Flipping in a 2D Heterobilayer Induced by Fluctuating Interfacial Carrier Flows.

Polarity often refers to the charge carrier type of a semiconductor or the charging state of a functional group, generally dominating their functionality and performance. Herein we uncover a spontaneous and stochastic polarity-flipping phenomenon in monolayer WSe2, which randomly switches between the n-type and p-type states and is essentially triggered by fluctuating carrier flows from or to the adjacent WS2 monolayer. We have traced such fluctuating carrier flows by interfacial photocurrent measurements in a zero-bias two-terminal device. Such polarity flipping results in switching between the negative and positive correlations between the emission intensities of WS2 and WSe2 in the heterobilayer, which is further well-controlled by the electrostatic gate-tuning experiments in a capacitor-structure device. Our work not only demonstrates giant and intermittent carrier flows through long-range coupling in 2D heterostructures and a consequent spontaneous polarity flipping phenomenon but also provides a two-emitter system with a switchable correlation sign that could project future applications in optical logic devices.

In(III) Metal-Organic Framework Incorporated with Enzyme-Mimicking Nickel Bis(dithiolene) Ligand for Highly Selective CO2 Electroreduction.

Inspired by the exciting physical/chemical properties in metal-organic frameworks (MOFs) of the redox-active tetrathiafulvalene (TTF) ligands, nickel bis(dithiolene-dibenzoic acid), [Ni(C2S2(C6H4COOH)2)2], has been designed and developed as an inorganic analogue of the corresponding TTF-type donors (such as tetrathiafulvalene-tetrabenzoate, TTFTB), where a metal site (Ni) replaces the central C═C bond. In this work, [Ni(C2S2(C6H4COOH)2)2] and In3+ have been successfully assembled into a three-dimensional MOF, (Me2NH2+){InIII-[Ni(C2S2(C6H4COO)2)2]}·3DMF·1.5H2O (1, DMF = N,N-dimethylformamide), with satisfying chemical and thermal stabilities. With the combination of reversible redox activity and unsaturated metal sites originated from [Ni(C2S2(C6H4COOH)2)2], 1 showed a significantly enhanced performance in electrocatalytic CO2 reduction compared with the isomorphic MOF, (Me2NH2+)[InIII-(TTFTB)]·0.7C2H5OH·DMF (2, with TTFTB ligand). More importantly, by mimicking the active [NiS4] sites of formate dehydrogenase and CO-dehydrogenase, a prominently higher conversion rate and Faradaic efficiency (FE), with FEHCOO- increasing from 54.7% to 89.6% (at -1.3 V vs RHE, jHCOO- = 36.0 mA cm-2), were achieved in 1. Mechanistic investigations further confirm that [NiS4] can serve as a CO2 binding site and efficient catalytic center. This unprecedented effect of redox-active nickel dithiolene-based MOF catalysts on the performance of electroreduction of CO2 provides an important strategy for designing stable and efficient crystalline enzyme-mimicking catalysts for the conversion of CO2 into high-value chemical stocks.

Double-Exchange-Induced in situ Conductivity in Nickel-Based Oxyhydroxides: An Effective Descriptor for Electrocatalytic Oxygen Evolution.

Motivated by in silico predictions that Co, Rh, and Ir dopants would lead to low overpotentials to improve OER activity of Ni-based hydroxides, we report here an experimental confirmation on the altered OER activities for a series of metals (Mo, W, Fe, Ru, Co, Rh, Ir) doped into γ-NiOOH. The in situ electrical conductivity for metal doped γ-NiOOH correlates well with the trend in enhanced OER activities. Density functional theory (DFT) calculations were used to rationalize the in situ conductivity of the key intermediate states of metal doped γ-NiOOH during OER. The simultaneous increase of OER activity with intermediate conductivity was later rationalized by their intrinsic connections to the double exchange (DE) interaction between adjacent metal ions with various d orbital occupancies, serving as an indicator for the key metal-oxo radical character, and an effective descriptor for the mechanistic evaluation and theoretical guidance in design and screening of efficient OER catalysts.