Temperature can govern morphologies, structures and properties of products from synthesis in solution. A reaction in solution at low temperature may result in different materials than at higher ...temperature due to thermodynamics and kinetics of nuclei formation. Here, we report a low-temperature solution synthesis of atomically dispersed cobalt in a catalyst with superior performance. By using a water/alcohol mixed solvent with low freezing point, liquid-phase reduction of a cobalt precursor with hydrazine hydrate is realized at -60 °C. A higher energy barrier and a sluggish nucleation rate are achieved to suppress nuclei formation; thus atomically dispersed cobalt is successfully obtained in a catalyst for oxygen reduction with electrochemical performance superior to that of a Pt/C catalyst. Furthermore, the atomically dispersed cobalt catalyst is applied in a microbial fuel cell to obtain a high maximum power density (2550 ± 60 mW m
) and no current drop upon operation for 820 h.
Particulate matter (PM) pollution has caused many serious public health issues. Whereas indoor air protection usually relies on expensive and energy-consuming filtering devices, direct PM filtration ...by window screens has attracted increasing attention. Recently, electrospun polymer nanofiber networks have been developed as transparent filters for highly efficient PM2.5 removal; however, it remains challenging to uniformly coat the nanofibers on window screens on a large scale and with low cost. Here, we report a blow-spinning technique that is fast, efficient, and free of high voltages for the large-scale direct coating of nanofibers onto window screens for indoor PM pollution protection. We have achieved a transparent air filter of 80% optical transparency with >99% standard removal efficiency level for PM2.5. A test on a real window (1 m × 2 m) in Beijing has proven that the nanofiber transparent air filter acquires excellent PM2.5 removal efficiency of 90.6% over 12 h under extremely hazy air conditions (PM2.5 mass concentration > 708 μg/m3). Moreover, we show that the nanofibers can be readily coated on the window screen for pollution protection and can be easily removed by wiping the screen after hazardous days.
Photochemical solution-phase reactions have been widely applied for the syntheses of nanocrystals. In particular, tuning of the nucleation and growth of solids has been a major area of focus. Here we ...demonstrate a facile approach to generate atomically dispersed platinum via photochemical reduction of frozen chloroplatinic acid solution using ultraviolet light. Using this iced-photochemical reduction, the aggregation of atoms is prevented, and single atoms are successfully stabilized. The platinum atoms are deposited on various substrates, including mesoporous carbon, graphene, carbon nanotubes, titanium dioxide nanoparticles, and zinc oxide nanowires. The atomically dispersed platinum on mesoporous carbon exhibits efficient catalytic activity for the electrochemical hydrogen evolution reaction, with an overpotential of only 65 mV at a current density of 100 mA cm
and long-time durability (>10 h), superior to state-of-the-art platinum/carbon. This iced-photochemical reduction may be extended to other single atoms, for example gold and silver, as demonstrated in this study.
Oxygen vacancies implantation is an efficient way to adjust the physical and chemical properties of metal oxide nanomaterials to meet the requirements for particular applications. Through reasonable ...defects design, oxygen-deficient metal oxides with excellent optical and electrical properties are widely applied for environmental protection and energy uses. This review discusses recent advances in synthetic approaches of oxygen-deficient metal oxides and their applications in photocatalysis, electrocatalysis, and energy storage devices. The perspectives of oxygen-deficient metal oxides for increased energy demand and environmental sustainability are also examined.
SrTiO3 is an important photocatalyst for hydrogen evolution under solar light, a promising way to solve energy shortage. However, a rapid and efficient method to synthesize high-performance SrTiO3 ...used for this purpose still remains a challenge. In this work, we successfully prepared SrTiO3 catalyst with narrowed band gap through a rapid laser-melting method of a limited reaction time to seconds. The prepared SrTiO3 catalyst, which has a band gap of 3.05 eV, presents enhanced photocatalytic performance for hydrogen evolution under visible light. The evolution rate of laser-melted SrTiO3 is approximately 3.5 times higher than that of pristine SrTiO3. In addition, the magnetism in laser-melted SrTiO3 is also enhanced, which could not be observed in pristine SrTiO3, confirming the defective structure of the obtained laser-melted SrTiO3. The proposed laser-melting method will be a promising way to rapidly and efficiently synthesize homogeneous, solar-driven SrTiO3 photocatalyst for hydrogen evolution with rich defects and thus high-performance.
To promote the performance of metal oxides, introducing oxygen vacancies is an effective strategy. Oxygen vacancies can tailor the atomic arrangement and band structure, thus optimizing the physical ...and chemical properties of metal oxides. Herein, we prepared oxygen‐deficient black ZrO2 nanoparticles via molten lithium (Li) reduction. Massive oxygen vacancies were introduced into ZrO2 nanoparticles as well as defective disorder domains formed in ZrO2 lattice during the molten lithium treatment process. Benefitting from the defective structure, black ZrO2 with enhanced light absorption demonstrated increased photocatalytic hydrogen generation rate, which was ~5 times higher than that of pristine ZrO2. Moreover, molten lithium reduction provides a powerful way to not only implant oxygen vacancies to metal oxides but also extend their applications.
Functional polymers such as polyvinylidene fluoride (PVDF) and its copolymers, which exhibit room-temperature piezoelectricity and ferroelectricity in two-dimensional (2D) limit, are promising ...candidates to substitute hazardous lead-based piezoceramics for flexible nanoelectronic and electromechanical energy-harvesting applications. However, realization of many polymers including PVDF in ultrathin 2D nanostructures with desired crystal phases and tunable properties remains challenging due to ineffective conventional synthesis methods. Consequently, it has remained elusive to obtain optimized piezoelectric performance of PVDF particularly in sub-10 nm regimes. Taking advantage of its high flexibility and easy processing, we fabricate ultrathin PVDF nanoflakes with thicknesses down to 7 nm by using a hot-pressing method. This thermo-mechanical strategy simultaneously induces robust thermodynamic α to electroactive β-phase transformation, with β fraction as high as 92.8% in sub-10 nm flakes. Subsequently, piezoelectric studies performed by using piezoresponse force microscopy reveal an excellent piezoelectric strain of 0.7% in 7 nm film and the highest piezoelectric coefficient (d 33) achieved is −68 pm/V for 50 nm-thick nanoflakes, which is 13% higher than the piezoresponse from 50 nm-thick PZT nanofilms. Our results further suggest thickness modulation as an effective strategy to tune the piezoelectric performance of PVDF and affirm its supremacy over conventional piezoceramics especially at nanoscale. This work aims not only to help understand fundamental piezoelectricity of pure PVDF in sub-10 nm regimes but also provides an opportunity to realize other polymer-based 2D nanocrystals.
Large-scale growth of low-cost, efficient, and durable non-noble metal-based electrocatalysts for water splitting is crucial for future renewable energy systems. Atomic layer deposition (ALD) ...provides a promising route for depositing uniform thin coatings of electrocatalysts, which are useful in many technologies, including the splitting of water. In this communication, we report the growth of a NiO/Ni catalyst directly on carbon fiber paper by atomic layer deposition and report subsequent reduction and oxidation annealing treatments. The 10-20 nm NiO/Ni nanoparticle catalysts can reach a current density of 10 mA·cm
at an overpotential of 189 mV for hydrogen evolution reactions and 257 mV for oxygen evolution reactions with high stability. We further successfully achieved a water splitting current density of 10 mA·cm
at 1.78 V using a typical NiO/Ni coated carbon fiber paper two-electrode setup. The results suggest that nanoparticulate NiO/Ni is an active, stable, and noble-metal-free electrocatalyst, which facilitates a method for future water splitting applications.
Defective TiO2 has attracted increasing attention for use in photocatalytic and electrochemical materials because of its narrowed band-gap and improved visible-light photocatalytic activity. However, ...a facile and efficient approach for obtaining defect-rich TiO2 still remains a challenge. Herein, we demonstrate such an approach to narrow its bandgap and improve visible-light absorption through implanting abundant defects by aerodynamic levitated laser annealing （ALLA） treatment. Note that the ALLA method not only provides rapid annealing, solidifying and cooling process, but also exhibits high efficiency for homogeneous and defective TiO2 nanoparticles. The laser-annealed TiO2 achieves a high hydrogen evolution rate of 8.54 mmol.h-1.g-1, excellent decomposition properties within 60 min, and outstanding recyclability and stability, all of which are superior to the corresponding properties of commercial P25.
Highly active and durable noble metal-based catalysts for electrochemical hydrogen evolution are crucial for clean and renewable energy production, however, low abundance and high price hinder their ...development at industrial scale. Herein, we synthesized carbon-supported ultrafine iridium nanoparticles (Ir NPs/C) catalyst via solvothermal method which achieved ultralow overpotentials of 13 and 57 mV at the current density of 10 and 100 mA cm−2 for hydrogen evolution reaction (HER) in acidic media, respectively. The prepared Ir NPs/C catalyst also exhibited ultrahigh mass activity of 44.5 A mg−1 at the overpotential of 40 mV and outstanding long-term stability in HER performance for 12 h, remarkably superior to state-of-the-art commercial Pt/C catalyst (3.3 A mg−1, fast decay) and commercial Ir/C catalyst (1.2 A mg−1). Furthermore, it possessed activities toward oxygen evolution reaction (OER) and overall water splitting. This work demonstrates evenly dispersed fine Ir NPs/C catalyst can facilitate highly efficient HER and provides inspiration for rational design of advanced electrocatalysts.
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•Carbon-supported ultrafine iridium nanoparticles (Ir NPs/C) were synthesized via a solvothermal method.•The Ir NPs/C catalyst showed a high mass activity for HER in acid, superior to commercial Pt/C and Ir/C catalysts.•Ultrathin Ir nanoparticles without aggregation exhibited outstanding electrocatalytic activity and durability for HER.
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