Proper design and simple preparation of nonnoble bifunctional electrocatalysts with high cost performance and strong durability for the oxygen reduction reaction (ORR) and the oxygen evolution ...reaction (OER) is highly demanded but still full of enormous challenges. In this work, a spontaneous gas‐foaming strategy is presented to synthesize cobalt nanoparticles confined in 3D nitrogen‐doped porous carbon foams (CoNCF) by simply carbonizing the mixture of citric acid, NH4Cl, and Co(NO3)2·6H2O. Thanks to its particular 3D porous foam architecture, ultrahigh specific surface area (1641 m2 g−1), and homogeneous distribution of active sites (C–N, Co–Nx, and Co–O moieties), the optimized CoNCF‐1000‐80 (carbonized at 1000 °C, containing 80 mg Co(NO3)2·6H2O in precursors) catalyst exhibits a remarkable bifunctional activity and long‐term durability toward both ORR and OER. Its bifunctional activity parameter (ΔE) is as low as 0.84 V, which is much smaller than that of noble metal catalyst and comparable to state‐of‐the‐art bifunctional catalysts. When worked as an air electrode catalyst in rechargeable Zn–air batteries, a high energy density (797 Wh kg−1), a low charge/discharge voltage gap (0.75 V), and a long‐term cycle stability (over 166 h) are achieved at 10 mA cm−2.
Co nanoparticles confined in 3D N‐doped porous carbon foams are fabricated by a spontaneous gas‐foaming strategy. Owing to the synergistic effect of the particular 3D porous foam architecture, ultrahigh specific surface area, and homogeneous distribution of active sites, the optimized CoNCF delivers a remarkable bifunctional activity and long‐term charge/discharge cycling stability.
Developing low-cost and high-performance metal-free oxygen reduction reaction (ORR) catalysts for fuel cells is highly desirable but still full of challenges. In this study, nitrogen and phosphorus ...co-functionalized three-dimensional (3D) porous carbon networks (NPCN) have been prepared by pyrolysis the zero-dimensional carbon quantum dots (CQDs) and a supermolecular gel of self-assembled melamine and amino trimethylene phosphonic acid (ATMP). The resultant NPCN catalysts possess unique 3D networks-like porous architecture, large specific surface area (743 m2 g−1) and abundant edge defects. As a catalyst for ORR, the optimized NPCN-900 (pyrolyzed at 900 °C) displays positive onset potential at 0.92 V and 0.74 V (vs. RHE) in alkaline and acidic media respectively, which are roughly close to those of Pt/C (0.93 V and 0.80 V). Additionally, the NPCN-900 exhibits longer-term stability and strong endurance to methanol over a wide pH range of aqueous media, which is much superior to that of Pt/C. Considering the outstanding activity of NPCN-900, it can be worked as a prospective metal-free catalyst to substitute commercial Pt/C for ORR in fuel cells.
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Abstract
Iron phthalocyanine (FePc) is a promising non-precious catalyst for the oxygen reduction reaction (ORR). Unfortunately, FePc with plane-symmetric FeN
4
site usually exhibits an ...unsatisfactory ORR activity due to its poor O
2
adsorption and activation. Here, we report an axial Fe–O coordination induced electronic localization strategy to improve its O
2
adsorption, activation and thus the ORR performance. Theoretical calculations indicate that the Fe–O coordination evokes the electronic localization among the axial direction of O–FeN
4
sites to enhance O
2
adsorption and activation. To realize this speculation, FePc is coordinated with an oxidized carbon. Synchrotron X-ray absorption and Mössbauer spectra validate Fe–O coordination between FePc and carbon. The obtained catalyst exhibits fast kinetics for O
2
adsorption and activation with an ultralow Tafel slope of 27.5 mV dec
−1
and a remarkable half-wave potential of 0.90 V. This work offers a new strategy to regulate catalytic sites for better performance.
A high porosity Mo doped BiVO4 film was synthesized by excess Mo doping and following vanadium re-substitution, which exhibited great photoelectrochemical performance.
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•High porosity ...structure was constructed via dissolution of excess Mo in BiVO4 film.•The contact area of photoanode and electrolyte is increased.•The VMo-BiVO4 photoanode exhibits great photoelectrochemical performance.•The separation efficiency for VMo-BiVO4 reaches to 96%.
Bismuth vanadate (BiVO4) is one of the most studied photoanodes whose photoelectrochemical (PEC) performance is limited by the sluggish charge mobility and substantial recombination losses. Here, a high porosity Mo doped BiVO4 film was synthesized by excess Mo doping and following vanadium re-substitution. The as-prepared BiVO4 based photoanode has large contact area between the electrolyte and the film due to the dissolution of excess Mo, shown by the results of electrochemically active surface area tests. As a result, the photocurrent of VMo-BiVO4 is 6.12 mA/cm2 at 1.23 V vs. the reversible hydrogen electrode (RHE) in 0.2 M KPi + 0.2 M Na2SO3 with the charge separation efficiency of ~96%, and the photocurrent of VMo-BiVO4 (3.18 mA/cm2 at 1.23 V vs. RHE) is 6.91 times of pristine BiVO4 in 0.2 M KPi. This approach demonstrated that a reasonable doping structure design could guarantee PEC water splitting with high performance.
The photoreduction of CO2 to hydrocarbon products has attracted much attention because it provides an avenue to directly synthesize value‐added carbon‐based fuels and feedstocks using solar energy. ...Among various photocatalysts, graphitic carbon nitride (g‐C3N4) has emerged as an attractive metal‐free visible‐light photocatalyst due to its advantages of earth‐abundance, nontoxicity, and stability. Unfortunately, its photocatalytic efficiency is seriously limited by charge carriers′ ready recombination and their low reaction dynamics. Modifying the local electronic structure of g‐C3N4 is predicted to be an efficient way to improve the charge transfer and reaction efficiency. Here, boron (B) is doped into the large cavity between adjacent tri‐s‐triazine units via coordination with two‐coordinated N atoms. Theoretical calculations prove that the new electron excitation from N (2px, 2py) to B (2px, 2py) with the same orbital direction in B‐doped g‐C3N4 is much easier than N (2px, 2py) to C 2pz in pure g‐C3N4, and improves the charge transfer and localization, and thus the reaction dynamics. Moreover, B atoms doping changes the adsorption of CO (intermediate), and can act as active sites for CH4 production. As a result, the optimal sample of 1%B/g‐C3N4 exhibits better selectivity for CH4 with ≈32 times higher yield than that of pure g‐C3N4.
Graphitic carbon nitride (g‐C3N4) exhibits unsatisfactory photocatalytic CO2 reduction activity due to its low charge transfer and reaction dynamics. Modifying the local electronic structure of g‐C3N4 is predicted to improve the charge transfer and reaction efficiency. In this work, B atoms are doped into g‐C3N4 for improving charge transfer and localization, and boosting the photocatalytic activity.
Recent studies have shown platelet to lymphocyte ratio (PLR) to be a potential inflammatory marker in cardiovascular diseases. We performed a meta-analysis to systematically evaluate the prognostic ...role of PLR in acute coronary syndrome (ACS). A comprehensive literature search up to May 18, 2016 was conducted from PUBMED, EMBASE and Web of science to identify related studies. The risk ratio (RR) with 95% confidence interval (CI) was extracted or calculated for effect estimates. Totally ten studies involving 8932 patients diagnosed with ACS were included in our research. We demonstrated that patients with higher PLR level had significantly higher risk of in-hospital adverse outcomes (RR = 2.24, 95%CI = 1.81-2.77) and long-term adverse outcomes (RR = 2.32, 95%CI = 1.64-3.28). Sensitivity analyses confirmed the stability of our results. We didn't detect significant publication bias by Begg's and Egger's test (p > 0.05). In conclusion, our meta-analysis revealed that PLR is promising biomarker in predicting worse prognosis in ACS patients. The results should be validated by future large-scale, standard investigations.
► Nitrogen doping of self-organized anodic nanoporous WO3 photoelectrodes obtained by one step annealing in a NH3/N2 gas mixture. ► Nitrogen-doped nanoporous WO3 photoelectrodes show a significant ...enhancement in conversion efficiency in the visible light. ► Nitrogen-doped nanoporous WO3 photoelectrodes were used for photocatalytic and photoelectrocatalytic degradation of methyl orange. ► Nitrogen-doped samples exhibited higher levels of activity under visible light irradiation.
In the present work, nitrogen-doped tungsten oxide (WO3) nanoporous photoelectrode was studied by photoelectrochemical and photocatalytic methods in order to evaluate the photoactivity and the possibility of its application in solar photocatalysis. WO3 nanoporous photoelectrodes were prepared by anodization of tungsten foil in NH4F/(NH4)2SO4 electrolytes, followed by annealing in NH3/N2 to incorporate N as a dopant. The crystal structure, composition and morphology of pure and nitrogen doped WO3 were compared using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM). The results indicate that nitrogen can be doped successfully into WO3 nanoporous photoelectrodes by controlling annealing temperature. Incident photon to current efficiency measurements carried out on PEC cell with N-doped WO3 nanoporous photoelectrodes as anodes demonstrate a significant increase of photoresponse in the visible region compared to undoped WO3 nanoporous photoelectrodes prepared at similar conditions. In particular, the photocatalytic and photoelectrocatalytic activity under visible light irradiation for newly synthesized N-doped WO3 nanoporous photoelectrodes were investigated by degradation of methyl orange. The photoelectrocatalytic activity of N-doped WO3 nanoporous photoelectrodes was 1.8-fold enhancement compared with pure WO3 nanoporous photoelectrodes.
A WO₃/TiO₂ composite, hollow-sphere photocatalyst with average diameter of 320nm and shell thickness of 50nm was successfully prepared using a template method. UV–vis diffuse reflectance spectra ...illustrated that the main absorption edges of the WO₃/TiO₂ hollow spheres were red-shifted compared to the TiO₂ hollow spheres, indicating an extension of light absorption into the visible region of the composite photocatalyst. The WO₃ and TiO₂ phases were confirmed by X-ray diffraction analysis. BET isotherms revealed that the specific surface area and average pore diameter of the hollow spheres were 40.95m²/g and 19nm, respectively. Photocatalytic experiments indicate that 78% MB was degraded by WO₃/TiO₂ hollow spheres under visible light within 80min. Under the same conditions, only 24% MB can be photodegraded by TiO₂. The photocatalytic mineralization of MB, catalyzed by TiO₂ and WO₃/TiO₂, proceeded at a significantly higher rate under UV irradiation than that under visible light, and more significant was the increase in the apparent rate constant with the WO₃/TiO₂ composite semiconductor material which was 3.2- and 3.5-fold higher than with the TiO₂ material under both UV and visible light irradiation. The increased photocatalytic activity of the coupled nanocomposites was attributed to photoelectron/hole separation efficiency and the extension of the wavelength range of photoexcitation.
•A simple deposition-annealing method was used to fabricate high-performance NiWO4/WO3 heterojunction photoanode.•NiWO4 serves as a functional component of the heterojunction for the ...photoelectrochemical (PEC) water splitting reaction.•Effective separation of the electron–hole pairs is achieved by the heterojunction structure.•Mechanism of the photo-generated carriers transport process was put forward and proved.
NiWO4/WO3 heterojunction photoanode was fabricated for the first time to enhance the photoelectrochemical (PEC) performance under visible light irradiation. Such a photoanode was prepared using a simple deposition-annealing method of NiWO4 nanoparticles onto the surface of porous WO3 films. It was found that the NiWO4/WO3 film synthesized with 25mM Ni(NO3)2 in ethanol exhibited the best PEC performance, which achieved a 70% increase compared with the pure WO3 film under similar conditions. The promising composite photoanode is desired to be employed for water splitting in the PEC cells. The heterojunction structure offers enhanced photoconversion efficiency and increased the density of carriers. This study reveals that introducing NiWO4 into WO3 films could facilitate the separation and restrain the recombination of photo-generated electron–hole pairs and accelerate the electrons transfer. Synthesis details are discussed, with film morphologies and structures characterized by X-ray diffraction, field emission scanning electron microscope, transmission electron microscope and X-ray photoelectron spectroscopy.
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