Developing high-efficiency electrocatalysts based on non-precious transition metal compounds alternative to noble metal for oxygen evolution reaction (OER) is crucial for renewable energy storage ...technologies. Herein we designed a novel OER electrocatalyst by incorporating transition metal oxide (TMO) and sulfide (TMS) into a hierarchical nanoporous structure. Hierarchical porous Co3O4 nanosheet-assembled microspheres (HPMS Co3O4) were fabricated by a facile solvothermal method followed by an annealing process, and the Co3O4/CoS2 composite was easily obtained by a simple subsequent sulfurization process, which maintained the HPMS structure. Due to rapid surface diffusion and mass transfer, increased active sites, improved conductivity and strong synergetic coupling effects, the prepared HPMS Co3O4/CoS2 composite showed significantly enhanced electrocatalytic OER activities with a current density of 10 mA cm−2 at a low overpotential of 280 mV, a small Tafel slope of about 63 mV dec−1 and satisfactory stability at 20 mA cm−2. Notablely, it was non-durable at high current density. We expect that more active TMS functionalized hierarchical porous TMO will open a new avenue to innovate non-precious OER electrocatalysts.
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•OER electrocatalyst on hierarchical porous Co3O4/CoS2 was facilely synthesized.•Co3O4 and CoS2 synergistically electro-catalyzed oxidation of H2O.•The nano-composite showed better OER activity with 10 mA cm−2 at 0.28 V overpotential.•The unique HPMS structure provided fast surface diffusion and mass transfer.
In this paper, a consensus based fully distributed optimization algorithm is proposed for solving economic dispatch problem (EDP) in smart grid. Since the incremental cost of all buses reach ...consensus when the optimal solution is achieved, it is selected as a consensus variable. An additional variable at each bus, called “surplus” is added to record the local power mismatch, which is used as a feedback variable to purse the balance between power supply and demand. Different from most of the existing distributed methods which require the communication network to be balanced, the algorithm uses a row random matrix and a column random matrix to precisely steer all the agents to asymptotically converge to a global optimal solution over a time‐varying directed communication network. Due to the use of a fixed step size, the proposed algorithm also outperforms other algorithms in terms of convergence speed. The graph and eigenvalue perturbation theories are employed for the algorithm convergence analysis, and the upper bound of the parameters required for convergence is given theoretically. Finally, the performance and scalability of the proposed distributed algorithm are verified by several case studies conducted on the IEEE 14‐bus power system and a 200‐node test system.
A consensus based fully distributed optimization algorithm is proposed for solving EDP in smart grid. Our algorithm uses a row random matrix and a column random matrix to precisely steer all the agents to asymptotically converge to a global optimal solution over a time‐varying directed communication network. Experimental results show that the proposed distributed algorithm has good performance and scalability.
•The porosity of Co3O4 arrays were regulated by constructing and oxidizing of ZIF-67 on their surface.•The porous Co3O arrays with the highest porosity and surface area exhibited the highest response ...to acetone.•This strategy can pave a new way to improve the gas-sensing properties of array film-based sensors.
Array-based sensors have been regarded as excellent candidates for the gas-sensing elements owing to their low-cost preparation, great miniaturization potential as well as stable performance. However, it still remains a great challenge to prepare porous arrays and regulate their porosity to increase pores for gas transport and active sites for surface reactions. To solve this problem, the porosity of metal oxide arrays (Co3O4) that had grown directly in-situ on the surface of ceramic substrates was regulated by the constructing and oxidizing of MOFs (ZIF-67) that coated on the surface cobalt-containing precursor arrays. It was found that the porosity and surface area of Co3O4 nanowire arrays increased with the content of ZIF-67. The porous Co3O arrays with the highest porosity and surface area exhibited the highest response value (Rg/Ra = 16.7), the lowest optimal operating temperature (200 °C) as well as the fastest response/recovery time (4/39 s) towards acetone. These porous Co3O4 arrays are thus promising gas-sensing materials for acetone detection with excellent performances. This novel strategy to enhance the porosity of arrays can pave a new way to improve the gas-sensing properties of array film-based sensors.
Active {1 1 1}-faceted ultra-thin NiO single-crystalline porous nanosheets supported highly dispersed Pt nanoparticles were designed and synthesized for efficient gas sensing and photocatalytic ...applications.
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•Ultra-thin NiO single-crystalline porous nanosheet with {1 1 1}-facet were prepared.•Highly dispersed Pt nanoparticles with tunable sizes were decorated on NiO surface.•Enhanced formaldehyde sensing and methyl orange degradation activity were shown.•The activity was related to the morphology, surface and interface structure design.•The work was important for the practical use of metal oxides in environmental issues.
Proper morphology, surface and interface structure designing are required to obtain efficient gas sensing and photocatalytic materials. In the present work, ultra-thin NiO single-crystalline porous nanosheets with dominant {1 1 1} crystal facets (denoted as SP-NiO) and hierarchical NiO porous microspheres (denoted as HP-NiO) supported highly dispersed Pt nanoparticles with controllable sizes were designed and synthesized. Their gas sensing and photocatalytic performance were investigated. It was found that both the formaldehyde sensing and methyl orange photocatalytic degradation performance were greatly enhanced by decorating Pt nanoparticles on SP-NiO, while Pt nanoparticles decoration contributed little to the improved photocatalytic performance of HP-NiO. The results indicated that surface structure of the NiO support could also produce significant impact on the activity of Pt/NiO heterojunctions. Moreover, Pt decorated SP-NiO with stable structure showed a marked long-term stability with negligible attenuation of gas sensitivity (less than 5%) for 45 days, while Pt decorated HP-NiO exhibited obvious attenuation of gas sensitivity (more than 30%) due to the structural collapse. The work not only offers promising materials for gas sensing and photocatalytic application, but also brings new dawn for the designing of efficient p-type metal oxides gas sensing and photocatalytic materials through the synergistic effect of single-crystalline porous structures modulation, crystal facets engineering and facet-selective deposition of highly-dispersed Pt nanoparticles.
As inspired by a novel materials-sensor integration fabrication strategy, nanowire-like network (NWN) structured ZnO, Co3O4, In2O3 and SnO2 films are synthesized directly onto an alumina substrate by ...the screen printing combined with micro-injecting and calcination (SPMIC) to fabricate a flat-type coplanar gas sensor array based on these four sensors. The gas-sensing properties of the sensor array are investigated at different operating temperatures (150–350°C), and the best selectivity is interestingly found among the four indoor pollution gases including toluene (C7H8), formaldehyde (HCHO), acetone (CH3COCH3) and ammonia (NH3) at 300°C. This is also confirmed by the principal component analysis (PCA) result that the four gases can be discriminated and recognized by the sensor array. The enhancement in the selectivity is attributed to the combination of special nanostructures with large surface area and sensor array based on the four different metal oxides. Furthermore, the SPMIC method is demonstrated to be an effective route not only to synthesize NWN structured metal oxides directly onto an alumina substrate without being destroyed, but also to fabricate coplanar sensor array based on various NWN structured metal oxide films.
In this study, one-dimensional (1D) zinc oxide was loaded on the surface of cobalt oxide microspheres, which were assembled by single-crystalline porous nanosheets, via a simple heteroepitaxial ...growth process. This elaborate structure possessed an excellent transducer function from the single-crystalline feature of Co
O
nanosheets and the receptor function from the zinc oxide nanorods. The structure of the as-prepared hybrid was confirmed via a Scanning Electron Microscope (SEM), X-ray diffraction (XRD), and a Transmission Electron Microscope (TEM). Gas-sensing tests showed that the gas-sensing properties of the as-designed hybrid were largely improved. The response was about 161 (R
/R
) to 100 ppm ethanol, which is 110 and 10 times higher than that of Co
O
(R
/R
= 1.47) and ZnO (R
/R
= 15), respectively. And the as-designed ZnO/Co
O
hybrid also showed a high selectivity to ethanol. The superior gas-sensing properties were mainly attributed to the as-designed nanostructures that contained a super transducer function and a super receptor function. The design strategy for gas-sensing materials in this work shed a new light on the exploration of high-performance gas sensors.
•Scalable synthesis of 1–3 layers SnS2 with a typical size of 200–300 nm.•The 2D SnS2 based NH3 sensors exhibited high gas sensing at room temperature.•The sensing mechanism behind the largely ...enhanced sensitivity was also revealed.
Recently, tin sulfide (SnS2) with different structures has been widely used for NH3 detection. However, the low sensitivity and high operating temperatures severely limit its potential application. Here, we demonstrate enhanced room temperature NH3 sensing using scalable SnS2 nanosheets, which are facily synthesized by chemical exfoliation. Structural and morphological characterization revealed that the as-prepared two-dimensional (2D) SnS2 is composed of 1–3 layers (0.6 nm–1.8 nm). Compared with the bulk SnS2 that shows none response to NH3, the gas sensors based on the as-prepared 2D SnS2 exhibit excellent ammonia gas sensing performance at room temperature. When exposed to 500 ppm ammonia, the response time, i.e., 16 s, is the shortest among all the NH3 gas sensors based on transition metal dichalcogenides (TMDs). We attribute this enhanced sensitivity mainly to the effective NH3 gas adsorption is dominated by the high energy defect sulfur vacancies on the surface of 2D SnS2. The easily synthesized 2D SnS2 with sulfur vacancies are expected to find a vast application in gas sensing.
•Co3O4@NiMoO4 nanowire arrays were fabricated in-situ on flat alumina substrates without seed layers.•The Co3O4@NiMoO4 composite arrays showed the highest response towards trimethylamine.•The ...mechanism was ascribed to the array structures that offered high surface area and additional resistance modulation.
Array-based sensors are considered as potential candidates for gas detection due to their low cost and great miniaturization potential. However, the fabrication process of array-based sensors is complex and time-consuming since it usually contains the formation and growth processes of seed layers on the surface of alumina substrates. In addition, the gas-sensing materials for the fabrication of array-based sensors are mainly confined to n-type semiconductors such as ZnO, TiO2 and WO3. In this work, a kind of p-type heterostructures arrays composed of NiMoO4 nanosheets and Co3O4 nanowire (Co3O4@NiMoO4) was fabricated in-situ on flat alumina substrates via a simple hydrothermal method without seed layers. SEM and TEM characterizations revealed that the Co3O4 nanowire arrays were fully covered with NiMoO4 nanosheets. The gas-sensing measurements revealed that the Co3O4@NiMoO4 composite arrays showed the highest response (Rg/Ra = 17.12) towards 100 ppm trimethylamine at its optimal operating temperature of 250 °C. This response value was 3.91 times higher than that of Co3O4 arrays (Rg/Ra = 4.39) and 9.25 times higher than that of NiMoO4 nanosheets (Rg/Ra = 1.85) at their optimal operating temperatures of 250 and 350 °C, respectively. Meanwhile, the enhanced sensing mechanism of the Co3O4@NiMoO4 composite arrays was also discussed. It could be explained by the special heterojunction structure of the Co3O4@NiMoO4 composite arrays, which offered a high surface area and an additional modulation in resistance. Our studies shed a new light to design p-type heterostructure arrays in-situ for fabricating sensing device by a facile method. Moreover, the as-designed Co3O4@NiMoO4 composite arrays are potential candidates in the fabricating of high performance trimethylamine sensors.
The growth of Fe2O3 on the surface of Co3O4 nanocrystals can remarkably improve their gas-sensing performances. The response value of Fe2O3 growing on Co3O4 truncated nanocubes can reach as high as ...318.7 (Ra/Rg) towards 100 ppm triethylamine which is 6–7 and 1.6 times higher than its pristine counterparts and Fe2O3 on Co3O4 nanocubes, respectively.
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•Heterostructures composed of well-defined Co3O4 and Fe2O3 nanorods were prepared.•The exposed facets of Co3O4 in the composite were varied from nanocubes to truncated nanocubes.•The Fe2O3/Co3O4 {111} exhibited the highest response towards triethylamine among Co3O4, Fe2O3 and Fe2O3/Co3O4 {100}.
In this work, Co3O4 enclosed with specific facets that anchored with Fe2O3 nanorods was prepared by a facile hydrothermal method. To reveal the role of heterojunctions on their gas-sensing performances, the exposed facets of Co3O4 crystals were varied from nanocubes enclosed with six {100} (denoted as Fe2O3/C-Co3O4) to truncated nanocubes enclosed with six {100} and eight {111} (denoted as Fe2O3/TC-Co3O4). It revealed that the growth of Fe2O3 on the surface of Co3O4 nanocrystals can remarkably improve their gas-sensing performances. The response value of Fe2O3/TC-Co3O4 can reach as high as 318.7 (Ra/Rg) towards 100 ppm triethylamine (TEA) which is 6–7 and 1.6 times higher than its pristine counterparts and Fe2O3/C-Co3O4, respectively. The highly facet-dependent gas-sensing performances of these p-n heterostructures were contributed to the effect of hetero-contact on charge transfer as well as gas adsorption which were confirmed by First-principles calculation. This study opens an avenue to investigate the effect of p-n heterojunctions on gas-sensing properties by designing interfacial contact with defined crystal facets, as well as guidance for the preparation of sensing materials with super performances.
Because of their ultra-high surface area, large porosity and excellent structural tailorability, metal-organic frameworks (MOFs) are considered as outstanding candidates among sensing materials for ...hazardous gas detection. However, most of MOFs-based sensing films show weak film adhesion and low conductivity due to the poor formation ability of MOFs films by traditional sensor fabrication methods as well as the intrinsic insulating character of these MOFs. In this work, we propose a novel strategy to directly grow robust gas-sensing films based on pristine MOFs arrays (ZIF-67 nanosheets) in-situ on the surface of ceramic substrates. To improve the conductivity of MOFs arrays, anion-exchange method is applied to couple Prussian blue analogue (PBA) on the surface of ZIF-67 arrays. Structural characterization revealed that this permutation reaction can significantly improve the conductivity of the MOF films while their sheet-like structures can be mainly remained. Benefiting from the robust structure and improved conductivity, the as-designed ZIF-67/PBA films exhibited superior sensing performances such as good reproducibility, high response value (Rg/Ra=11.7), and fast response/recovery speed (5/182 s) towards triethylamine. This work provides a new strategy to fabricate MOFs gas sensors and paves a new way to modulate the conductivity of MOF films.
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•Robust MOFs films (ZIF-67) were grew in-situ on the surface of ceramic substrate.•The conductivity of MOFs films (ZIF-67/PBA) was regulated by a facile anion-exchange method.•The modified MOFs films exhibited excellent gas-sensing performances at low operating temperature.
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