Highly effective electrocatalysts promoting CO
reduction reaction (CO
RR) is extremely desirable to produce value-added chemicals/fuels while addressing current environmental challenges. Herein, we ...develop a layer-stacked, bimetallic two-dimensional conjugated metal-organic framework (2D c-MOF) with copper-phthalocyanine as ligand (CuN
) and zinc-bis(dihydroxy) complex (ZnO
) as linkage (PcCu-O
-Zn). The PcCu-O
-Zn exhibits high CO selectivity of 88%, turnover frequency of 0.39 s
and long-term durability (>10 h), surpassing thus by far reported MOF-based electrocatalysts. The molar H
/CO ratio (1:7 to 4:1) can be tuned by varying metal centers and applied potential, making 2D c-MOFs highly relevant for syngas industry applications. The contrast experiments combined with operando spectroelectrochemistry and theoretical calculation unveil a synergistic catalytic mechanism; ZnO
complexes act as CO
RR catalytic sites while CuN
centers promote the protonation of adsorbed CO
during CO
RR. This work offers a strategy on developing bimetallic MOF electrocatalysts for synergistically catalyzing CO
RR toward syngas synthesis.
Abstract
Various platinum-free electrocatalysts have been explored for hydrogen evolution reaction in acidic solutions. However, in economical water-alkali electrolysers, sluggish water dissociation ...kinetics (Volmer step) on platinum-free electrocatalysts results in poor hydrogen-production activities. Here we report a MoNi
4
electrocatalyst supported by MoO
2
cuboids on nickel foam (MoNi
4
/MoO
2
@Ni), which is constructed by controlling the outward diffusion of nickel atoms on annealing precursor NiMoO
4
cuboids on nickel foam. Experimental and theoretical results confirm that a rapid Tafel-step-decided hydrogen evolution proceeds on MoNi
4
electrocatalyst. As a result, the MoNi
4
electrocatalyst exhibits zero onset overpotential, an overpotential of 15 mV at 10 mA cm
−2
and a low Tafel slope of 30 mV per decade in 1 M potassium hydroxide electrolyte, which are comparable to the results for platinum and superior to those for state-of-the-art platinum-free electrocatalysts. Benefiting from its scalable preparation and stability, the MoNi
4
electrocatalyst is promising for practical water-alkali electrolysers.
While X-ray computed tomography (XCT) is pushed further into the micro- and nanoscale, the limitations of various tool components and object motion become more apparent. For high-resolution XCT, it ...is necessary but practically difficult to align these tool components with sub-micron precision. The aim is to develop a novel reconstruction methodology that considers unavoidable misalignment and object motion during the data acquisition in order to obtain high-quality three-dimensional images and that is applicable for data recovery from incomplete datasets. A reconstruction software empowered by sophisticated correction modules that autonomously estimates and compensates artefacts using gradient descent and deep learning algorithms has been developed and applied. For motion estimation, a novel computer vision methodology coupled with a deep convolutional neural network approach provides estimates for the object motion by tracking features throughout the adjacent projections. The model is trained using the forward projections of simulated phantoms that consist of several simple geometrical features such as sphere, triangle and rectangular. The feature maps extracted by a neural network are used to detect and to classify features done by a support vector machine. For missing data recovery, a novel deep convolutional neural network is used to infer high-quality reconstruction data from incomplete sets of projections. The forward and back projections of simulated geometric shapes from a range of angular ranges are used to train the model. The model is able to learn the angular dependency based on a limited angle coverage and to propose a new set of projections to suppress artefacts. High-quality three-dimensional images demonstrate that it is possible to effectively suppress artefacts caused by thermomechanical instability of tool components and objects resulting in motion, by center of rotation misalignment and by inaccuracy in the detector position without additional computational efforts. Data recovery from incomplete sets of projections result in directly corrected projections instead of suppressing artefacts in the final reconstructed images. The proposed methodology has been proven and is demonstrated for a ball bearing sample. The reconstruction results are compared to prior corrections and benchmarked with a commercially available reconstruction software. Compared to conventional approaches in XCT imaging and data analysis, the proposed methodology for the generation of high-quality three-dimensional X-ray images is fully autonomous. The methodology presented here has been proven for high-resolution micro-XCT and nano-XCT, however, is applicable for all length scales.
2D conjugated metal‐organic frameworks (2D c‐MOFs) are emerging as a novel class of conductive redox‐active materials for electrochemical energy storage. However, developing 2D c‐MOFs as flexible ...thin‐film electrodes have been largely limited, due to the lack of capability of solution‐processing and integration into nanodevices arising from the rigid powder samples by solvothermal synthesis. Here, the synthesis of phthalocyanine‐based 2D c‐MOF (Ni2CuPc(NH)8) nanosheets through ball milling mechanical exfoliation method are reported. The nanosheets feature with average lateral size of ≈160 nm and mean thickness of ≈7 nm (≈10 layers), and exhibit high crystallinity and chemical stability as well as a p‐type semiconducting behavior with mobility of ≈1.5 cm2 V−1 s−1 at room temperature. Benefiting from the ultrathin feature, the nanosheets allow high utilization of active sites and facile solution‐processability. Thus, micro‐supercapacitor (MSC) devices are fabricated mixing Ni2CuPc(NH)8 nanosheets with exfoliated graphene, which display outstanding cycling stability and a high areal capacitance up to 18.9 mF cm−2; the performance surpasses most of the reported conducting polymers‐based and 2D materials‐based MSCs.
A ball milling mechanical exfoliation of a layer‐stacked phthalocyanine‐based 2D conjugated MOF (2D c‐MOF) toward ultrathin nanosheets is explored. Benefiting from the intrinsic conductivity, porosity, and ultrathin feature, the nanosheets allow high exposure of active sites and fast ion diffusion, and therefore exhibit remarkable performance as flexible film electrode for micro‐supercapacitor.
Metal-organic frameworks (MOFs) have so far been highlighted for their potential roles in catalysis, gas storage and separation. However, the realization of high electrical conductivity (>10
S cm
) ...and magnetic ordering in MOFs will afford them new functions for spintronics, which remains relatively unexplored. Here, we demonstrate the synthesis of a two-dimensional MOF by solvothermal methods using perthiolated coronene as a ligand and planar iron-bis(dithiolene) as linkages enabling a full π-d conjugation. This 2D MOF exhibits a high electrical conductivity of ~10 S cm
at 300 K, which decreases upon cooling, suggesting a typical semiconductor nature. Magnetization and
Fe Mössbauer experiments reveal the evolution of ferromagnetism within nanoscale magnetic clusters below 20 K, thus evidencing exchange interactions between the intermediate spin S = 3/2 iron(III) centers via the delocalized π electrons. Our results illustrate that conjugated 2D MOFs have potential as ferromagnetic semiconductors for application in spintronics.
Electrocatalytic oxygen reduction reaction (ORR) is the vital process for next-generation electrochemical energy storage and conversion technologies,
e.g.
, metal-air batteries and fuel cells. During ...the ORR, the O
2
* and O* intermediates principally combine with protons to form OOH* and OH* species, respectively, which are the proton-coupled electron transfer processes. Unfortunately, under alkaline conditions, the protons are essentially generated from the sluggish water dissociation process, which unavoidably limits the ORR kinetics. Herein, we design and synthesize a nitrogen-doped hierarchically porous carbon with homogeneously distributed ultrafine α-MoC nanoparticles (α-MoC/NHPC) as a model electrocatalyst. Theoretical investigations unveil that α-MoC on NHPC could efficiently reduce the energy barrier of the water dissociation process to generate protons, eventually promoting the proton-coupled ORR kinetics. In a 0.1 M KOH aqueous solution, α-MoC/NHPC exhibits excellent ORR performance with a high half-wave potential of 0.88 V (
vs.
reversible hydrogen electrode), which outperforms those for NHPC and commercial Pt/C. Moreover, as the air electrode in a zinc-air battery, α-MoC/NHPC presents a large peak power density of 200.3 mW cm
−2
and long-term stability. Thereby, our approach to engineering proton-feeding centers paves a new avenue towards the understanding of ORR kinetics and the development of high-performance ORR electrocatalysts.
We demonstrate the important role of the water dissociation process in proton-feeding and enhancing ORR kinetics under an alkaline environment.
Engineering conducting polymer thin films with morphological homogeneity and long-range molecular ordering is intriguing to achieve high-performance organic electronics. Polyaniline (PANI) has ...attracted considerable interest due to its appealing electrical conductivity and diverse chemistry. However, the synthesis of large-area PANI thin film and the control of its crystallinity and thickness remain challenging because of the complex intermolecular interactions of aniline oligomers. Here we report a facile route combining air-water interface and surfactant monolayer as templates to synthesize crystalline quasi-two-dimensional (q2D) PANI with lateral size ~50 cm
and tunable thickness (2.6-30 nm). The achieved q2D PANI exhibits anisotropic charge transport and a lateral conductivity up to 160 S cm
doped by hydrogen chloride (HCl). Moreover, the q2D PANI displays superior chemiresistive sensing toward ammonia (30 ppb), and volatile organic compounds (10 ppm). Our work highlights the q2D PANI as promising electroactive materials for thin-film organic electronics.
The engineering of acetylenic carbon-rich nanostructures has great potential in many applications, such as nanoelectronics, chemical sensors, energy storage, and conversion, etc. Here we show the ...synthesis of acetylenic carbon-rich nanofibers via copper-surface-mediated Glaser polycondensation of 1,3,5-triethynylbenzene on a variety of conducting (e.g., copper, graphite, fluorine-doped tin oxide, and titanium) and non-conducting (e.g., Kapton, glass, and silicon dioxide) substrates. The obtained nanofibers (with optical bandgap of 2.51 eV) exhibit photocatalytic activity in photoelectrochemical cells, yielding saturated cathodic photocurrent of ca. 10 µA cm
(0.3-0 V vs. reversible hydrogen electrode). By incorporating thieno3,2-bthiophene units into the nanofibers, a redshift (ca. 100 nm) of light absorption edge and twofold of the photocurrent are achieved, rivalling those of state-of-the-art metal-free photocathodes (e.g., graphitic carbon nitride of 0.1-1 µA cm
). This work highlights the promise of utilizing acetylenic carbon-rich materials as efficient and sustainable photocathodes for water reduction.
The realization of ferromagnetism in semiconductors is an attractive avenue for the development of spintronic applications. Here, we report a semiconducting layered metal-organic framework (MOF), ...namely K
Fe
(2,3,9,10,16,17,23,24-octahydroxy phthalocyaninato)Fe (K
Fe
PcFe-O
) with spontaneous magnetization. This layered MOF features in-plane full π-d conjugation and exhibits semiconducting behavior with a room temperature carrier mobility of 15 ± 2 cm
V
s
as determined by time-resolved Terahertz spectroscopy. Magnetization experiments and
Fe Mössbauer spectroscopy demonstrate the presence of long-range magnetic correlations in K
Fe
PcFe-O
arising from the magnetic coupling between iron centers via delocalized π electrons. The sample exhibits superparamagnetic features due to a distribution of crystal size and possesses magnetic hysteresis up to 350 K. Our work sets the stage for the development of spintronic materials exploiting magnetic MOF semiconductors.
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•A novel technique to monitor and control the microcracking process in specially designed 3D nanopatterned structures in real time is demonstrated on a technically relevant materials ...system, i.e. an on-chip interconnect stack. The three-dimensional details of the complicated physical failure mechanism are unveiled with high resolution.•The combination of X-ray microscopy and micromechanics and the ability to image microcracks in a model system with a hierarchically structured architecture is described.•The critical energy release rate at the crack tip is determined quantitatively in sub-100 nm regions.•A controlled microcrack steering into regions with high fracture toughness is demonstrated for an engineered hierarchical materials system.
An experimental approach to control the fracture behavior of 3D nanopatterned structures in real time and to describe the microcrack propagation in solids quantitatively is presented. The three-dimensional details of the complicated failure mechanism are unveiled with high resolution using a method that integrates a micro-scale fracture mechanics test into a nano X-ray computed tomography system, to allow in-situ 3D imaging of the kinetics of damage mechanisms in integrated circuits. With the unique combination of a miniaturized micro-mechanical experiment and high-resolution X-ray imaging, the critical energy release rate at the crack tip of materials is determined quantitatively in sub-100 nm dimension, which allows to reveal scale-dependent mechanical properties. The ability of controlled microcrack steering in engineered materials and structures into regions with high fracture toughness is demonstrated. This unique characterization capability promises broad applications for design and manufacturing of robust microchips in future technology nodes, and it is applicable to the study of a broad variety of 3D nanostructured material systems.
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