Alumina-supported Pt is one of the major industrial catalysts for light alkane dehydrogenation. This catalyst loses activity during reaction, with coke formation often considered as the reason for ...deactivation. As we show in this study, the amount and nature of carbon deposits do not directly correlate with the loss of activity. Rather, it is the transformation of subnanometer Pt species into larger Pt nanoparticles that appears to be responsible for the loss of catalytic activity. Surprisingly, a portion of the Sn remains atomically dispersed on the alumina surface in the spent catalyst and helps in the redispersion of the Pt. In the absence of Sn on the alumina support, the larger Pt nanoparticles formed during reaction are not redispersed during oxidative regeneration. It is known that Sn is added as a promoter in the industrial catalyst to help in achieving high propene selectivity and to minimize coke formation. This work shows that an important role of Sn is to help in the regeneration of Pt, by providing nucleation sites on the alumina surface. Aberration-corrected scanning transmission electron microscopy helps to provide unique insights into the operating characteristics of an industrially important catalyst by demonstrating the role of promoter elements, such as Sn, in the oxidative regeneration of Pt on γ-Al2O3.
The growth of lithium (Li) dendrites and the huge volume change are the critical issues for the practical applications of Li‐metal anodes. In this work, a spatial control strategy is proposed to ...address the above challenges using lotus‐root‐like Ni–Co hollow prisms@carbon fibers (NCH@CFs) as the host. The homogeneously distributed bimetallic Ni–Co particles on the N‐doped carbon fibers serve as nucleation sites to effectively reduce the overpotential for Li nucleation. Furthermore, the 3D conductive network can alter the electric field. More importantly, the hierarchical lotus‐root‐like hollow fibers provide sufficient void space to withstand the volume expansion during Li deposition. These structural features guide the uniform Li nucleation and non‐dendritic growth. As a result, the NCH@CFs host enables a very stable Li metal anode with a low voltage hysteresis during repeated Li plating/stripping for 1200 h at a current density of 1 mA cm−2.
Lotus‐root‐like carbon fibers embedded with Ni–Co nanoparticles (NCH@CFs) are designed as a lithium (Li) host via facile electrospinning and the subsequent thermal annealing. Benefitting from the 3D conductive framework and the internal hollow structure with highly dispersed lithiophilic sites, the NCH@CF host can spatially regulate the electric field to effectively suppress the Li‐dendrite growth and withstand severe volume expansion for long‐term cycling performance in both symmetric and full cells.
Uncontrolled growth of Zn dendrites and side reactions are the major restrictions for the commercialization of Zn metal anodes. Herein, we develop a TiOx/Zn/N‐doped carbon inverse opal (denoted as ...TZNC IO) host to regulate the Zn deposition. Amorphous TiOx and Zn/N‐doped carbon can serve as the zincophilic nucleation sites to prevent the parasitic reactions. More importantly, the highly ordered IO host homogenizes the local current density and electric field to stabilize Zn deposition. Furthermore, the three‐dimensional open networks could regulate Zn ion flux to enable stable cycling performance at large current densities. Owing to the abundant zincophilic sites and the open structure, granular Zn deposits could be realized. As expected, the TZNC IO host guarantees the steady Zn plating/stripping with a long‐term stability over 450 h at the current density of 1 mA cm−2. As a proof‐of‐concept demonstration, a TZNC@Zn||V2O5 full cell shows long lifespan over 2000 cycles at 5.0 A g−1.
A TiOx/Zn/N‐doped carbon inverse opal (TZNC IO) structure is designed through a multi‐step method to regulate Zn deposition for Zn metal anodes. Benefitting from the ordered open structure with abundant zincophilic sites, the TZNC host can realize a preferential Zn nucleation and growth in the confined space. As expected, the dendrite‐free TZNC@Zn composite anode enables long‐term cycling in both symmetric and full cells.
This research aimed to evaluate chitosan (CTS) and carboxymethyl chitosan (CMCS) as polysaccharides that could mimic the role of bacterial extracellular polymeric substance (EPS) in the ...biomineralization process through bionic experiments. The introduction of COOH resulted in higher calcium precipitation efficiency of CMCS (65.07%) than CTS (55.66%). CaCO3 nucleation on the surface of CTS and CMCS was triggered through the binding of Ca2+ to NH2, OH, COOH and NHCOCH3 groups. Moreover, the experiment of polysaccharides mediated biomineralization was conducted. The maximum calcium precipitation efficiency reached 96.07% with the addition of 0.15% CMCS. Combining the characterization results, the synergetic mineralization mechanisms between polysaccharides and bacteria were proposed. Among them, bacterial metabolic by-products (alkalinity), active groups and adhesion of polysaccharides played a significant role. This work provides a reference for further understanding of the biomineralization mechanism, and gives a new insight into the intensified strategies of MICP technology.
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•Polysaccharides may act as the nucleation sites in the biomineralization process.•The feasibility of polysaccharides and bacteria co-mineralization was assessed.•CMCS had a higher compatibility as compared to CTS with strain WZ39.•The MICP efficiency was improved by 28.28% with the addition of 0.15% CMCS.•This work provides a new insight into the intensified strategies of MICP technology.
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•Prepared three-dimensional (3D) host can alleviate the volume expansion.•TiO2 nanowire arrays guide the uniform deposition of zinc ions.•High cyclic stability is achieved for ...symmetric cells.•Performance of full cells is greatly improved via using the 3D host as the anode.
Aqueous rechargeable Zn-metal batteries have great potential in the field of energy storage owing to high theoretical capacity, low electrochemical potential, low cost, and good safety performance of the Zn anodes. However, Zn anode has a series of problems such as dendrite growth, surface passivation and corrosion, which limits its further development. To address these issues, a new zinc anode with a 3D porous host compounded with TiO2 nanowire arrays (NWAs) decorated with rGO and CNTs (TGC) was constructed. Density functional theory result demonstrates that the TiO2 exhibits superior binding energies of zinc, as the super-zincophilic nucleation sites, which can be conducive to a uniform deposition of the zinc and give an effective guidance to construct 3D novel dendrite-free Zn metal anodes. The 3D porous conductive network formed by rGO and CNTs homogenized the electric field and alleviated the volume expansion during the cycle. As expected, the TGC host guarantees the steady Zn plating/stripping with a long-term stability over 3000 h at the current density of 1 mA cm−2. As a validation, a Zn@TGC//MnO2 full cell shows long lifespan over 1000 cycles at 1.0 A g−1.
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•The mechanism study of pool boiling through the diameter, frequency and nucleation sites of the bubbles.•Comparing the BHTC of electrolyte and alcoholic solutions considering the ...bubble dynamic in pool boiling.•Enhancing the BHTC through the ultrasonic waves’ irradiation.•Effective role of the ultrasonic waves in improving the bubble dynamic and preventing the sediments.•Validation of the experimental data through the conventional models.
In this work, a comparison study was implemented on the pool boiling heat transfer coefficient (BHTC) between the copper sulfate and isopropanol solutions. To precise investigate; the bubble dynamic including departure diameter, departure frequency and active nucleation sites were examined. In addition, ultrasonic waves’ irradiation (25 kHz) was employed to intensive the solutions and improve the dynamic parameters due to cavitation phenomenon. First, although the cooper sulfate had a bigger bubble departure diameter and more active nucleation sites than isopropanole, its heat transef coefficient was lower due to great bubble departure frequency of isopropanol. Finally, Calus model with an average error of 12.8% for isopropanol and Palen with 13.1% for copper sulfate had the lowest errors. Moreover, the isoropanole at 20 V.% with 15% power of ultrasonic irradiation and the cooper sulfate at 10.5 V.% with 35% had the maximum increase in the BHTC as 10.549% and 18.238%, respectively.
Bubble evolution plays a vital role in the photoelectrochemical (PEC) water-splitting process. However, quantitatively relating nucleation site distribution to bubble dynamics and reaction current ...remains elusive. Here, we investigate the coalescence and detachment processes of double bubbles with different nucleation site spacing (S) using electrochemical measurements and high-speed microscopic imaging. The study reveals three types of detachment mode: the periodic buoyancy-driven detachment mode, the transition mode, and the periodic coalescence-driven detachment mode. These modes are influenced by the coalescence process, which alters the S and results in changes to the bubble detachment radius and detachment frequency. Meanwhile, significant differences in the average reaction current can be obtained by changing S at the same potential. This study elucidates the fundamental relationship between bubble coalescence and detachment characteristics, which provides guidance for optimal design of the electrode morphology in a PEC water-splitting system.
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•Double-bubble evolution on electrode surface is experimentally studied•Effects of nucleation site spacing on coalescence and detachment dynamics•Effects of nucleation site spacing on detachment characteristics•Average reaction current is inversely correlated with bubble detachment radius
Zhang et al. explore the effect of nucleation site spacing on double-bubble coalescence, detachment dynamics, and reaction current using electrochemical measurements and high-speed microscopic imaging. This study provides insights into gas bubble manipulation for the optimization of electrode morphology design.
The practical applications of Li metal batteries (LMBs) have long been limited by the obstacles of low Coulombic efficiency (CE) and formation of dendrites on Li metal electrode. Herein, we ...demonstrated the synthesis of a novel three-dimensional (3D) nanostructured skeleton substrate composed of nitrogen-doped hollow carbon fiber/carbon nanosheets/ZnO (NHCF/CN/ZnO) using 2-methylimidazole (2-MIZ)-coated 3D cloth as a scaffold. The mechanism of formation of this novel hierarchical structure was investigated. The multilayered hierarchical structure and abundant lithiophilic nucleation sites of the substrate provide a stable environment for the deposition and stripping of lithium metal, thus preventing the generation of lithium dendrites. Consequently, the lithium anode based on the NHCF/CN/ZnO current collector demonstrated an excellent Coulombic efficiency of 96.47% after 400 cycles at 0.5 mA cm–2. The prepared NHCF/CN/ZnO/Li electrode also showed outstanding cycling performance of over 800 h and an ultralow voltage hysteresis of less than 30 mV in a symmetric cell at 5 mA cm–2 and 5 mAh cm–2. Even at a high loading of the cathode with 10.4 mg cm–2, the full cell of NHCF/CN/ZnO/Li anode with LiFePO4 can also work very well. Our work offers a path toward the facial preparation of 3D hierarchical structure for high-performance lithium metal batteries.
Bone extracellular matrix (ECM) is a unique organic-inorganic composite material derived from highly mineralized liquid crystal (LC) organic substrate. However, it remains a substantial challenge to ...design bone ECM-like LC materials with sufficient available nucleation sites to mimic the mineralization process of natural bone. Herein, we designed a bioinspired hydrogel with bone ECM-like LC organic substrate and inorganic phosphate mineralization nucleation sites for robust cell biomineralization and bone regeneration. Black phosphorus (BP) nanosheet was firstly loaded by bioactive layered double hydroxide (LDH) based on electrostatic attraction to improve the stability and photothermal performance of BP. Then, the LDH@BP was creatively added into chitin whisker/poly (ethylene glycol) diacrylate (CHW/PEGDA) LC hydrogel, abbreviated as LCgel, to fabricate LCgel/LDH@BP to highly mimic the mineralization microenvironment of bone ECM. The bone ECM-like LC topology of LCgel/LDH@BP is conducive to facilitating cell adhesion, proliferation and osteogenic differentiation. More importantly, the in-situ phosphate mineralization nucleation sites combined with mild hyperthermia induced by BP can further synergistically reinforce biomineralization of cells adhered on bone ECM-like LC substrate, thus substantially promoting cell biomineralization-mediated osteogenesis in vitro and in vivo. This study opens a new insight for the design of bioinspired hydrogel for cell biomineralization-mediated osteogenesis.
Enlighted by bone extracellular matrix (ECM) mineralization microenvironment, herein, a bioinspired LDH@BP-incorporated liquid crystal (LC) hydrogel was designed. The LCgel/LDH@BP hydrogel has bone ECM-like LC organic substrate and durable phosphate mineralization nucleation sites that can synergistically promote cell biomineralization. Notably, BP-mediated mild hyperthermia can further reinforce the cell biomineralization-mediated osteogenesis. Display omitted
•A bioinspired hydrogel highly mimics the mineralization microenvironment of bone ECM.•Bone ECM-like LC matrix and phosphate nucleation site enhance cell biomineralization.•BP is firstly loaded by LDH to improve stability and photothermal performance of BP.•Mild hyperthermia reinforces cell biomineralization-mediated osteogenesis.
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