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3D structured Mn2O3 with flower-like (Mn2O3-F), globe-like (Mn2O3-G) or rhombohedral (Mn2O3-R) morphologies were successfully synthesized by solvothermal method by controlling the amounts of Tween surfactant. These Mn2O3 oxides enhance the catalytic activity for the oxygen reduction reaction (ORR) in direct methanol fuel cells (DMFCs) significantly, while PtRu/C works as the anode catalyst and polymer fiber membrane (PFM) functions as the electrolyte film. Mn2O3-G shows higher ORR catalytic activity than Mn2O3-F and Mn2O3-R. The maximum power density (Pmax) of Mn2O3-F-, Mn2O3-G- and Mn2O3-R-based DMFCs are 11.44, 21.03 and 10.22 mW cm−2 at room temperature, respectively. The influence of the Tween surfactant on the microstructure and ORR properties were also studied systematically. Compared with Mn2O3-F and Mn2O3-R, the Raman and XPS results indicate that Mn2O3-G has more oxygen vacancies, which can promote the electrical conductivity and act as an active center to absorb and store available O2 for stable ORR properties. [ABSTRACT FROM AUTHOR]

Exploring an efficient non-enzymetic electrochemical sensor towards the detection of H2O2 is of great significance for the practical health monitoring and environmental analysis. In this study, four Preyssler-type polyoxometalate-based organic–inorganic hybrid materials were synthesized as non-enzymatic H2O2 electrochemical sensors having the formulae (H2bimb)6H4[(Mn(H2O)3)2(μ-bimb)(Mn(H2O)4(Mn(H2O)5)0.75(Mn(H2O)4)0.25(Na(H2O)P5W30O110))2]·30.5H2O (1), (H2bimb)3H4[(Co(H2O)4)2(μ-bimb)(Na(H2O)P5W30O110)]·10H2O (2), {[(Cu(Hbimb)(H2O)(μ-bimb)Cu(Hbimb)(H2O))(Cu(H2O)2(μ-bimb)Cu(H2O)2)((Cu(H2O)2)0.5(μ-bimb)(Cu(H2O)3)0.5)H2(Na(H2O)P5W30O110)]·12H2O}n (3) and (H2bimb)2H[((Zn(Hbimb)(H2O)2)0.5)2(Zn(Hbimb)(H2O)4)2(Na(H2O)P5W30O110)]·8H2O (4) (bimb = 1,4-bis(1H-imidazol-1-yl)benzene). In the compounds 1–4, Preyssler {P5W30} clusters show abundant coordination modes, and support the transition metal–organic fragments to give fascinating diverse networks. When used as electrochemical sensors for H2O2 detection, compounds 1–4 exhibited good electrocatalytic activities with high sensitivity and low detection limit. Among them, compound 2 showed the lowest limit of detection of 0.13 mM with a high sensitivity of 4.35 μA mM−1 and fast response time of 1 s. Moreover, compound 2 displayed excellent electrochemical operational stability and anti-interference capacity. This study provides a good choice for the development of promising electrochemical non-enzymatic H2O2 sensors by employing Preyssler {P5W30}-based materials. [ABSTRACT FROM AUTHOR]

Aromatic amino compounds are important and universally used chemical intermediates in a wide range of industrial fields. Thus, their production with high efficiency and selectivity under ambient conditions is expected and demanded in modern industry. Herein, a series of superfine CoNi alloy nanoparticles embedded in Al2O3 nanosheet (CoxNi1−x/Al2O3, where x represents the content of Co in the precursor) catalysts was fabricated from CoNiAl-LDH and used to catalyze the tandem dehydrogenation of ammonia borane (AB) and hydrogenation of nitroaromatics to the corresponding amines. Systematic experiments indicate that the composition, size, morphology and catalytic performance of the CoxNi1−x/Al2O3 catalysts can be easily controlled by changing the content of Ni in the CoNiAl-LDH precursor. Particularly, Co0.67Ni0.33/Al2O3 exhibited the best tandem catalytic performance among the six samples. This as-prepared catalyst not only showed a moderate turn-over-frequency value (TOF: 34.5 molH2 molCo0.67Ni0.33−1 min−1 at 298 K without base or additives) and relatively low activation energy (32.4 kJ mol−1) for the dehydrogenation of AB, but also superior catalytic activity (conversion yield reaching up to 100%) and selectivity (>99%) for the tandem reductive transformation of in excess of sixteen types of nitroaromatics to aromatic amines. Density functional theory (DFT) calculations suggest that the construction of the CoNi alloy optimized the electronic structure with respect to the pure component, promoting its activity for AB hydrolysis and nitroaromatics hydrogenation. Finally, the catalyst could be easily recycled using a magnet due to the magnetic properties of the Co0.67Ni0.33 alloy. [ABSTRACT FROM AUTHOR]

The development of highly active and stable electrocatalysts for HER has been received extensive attention. Among these, minimizing the Pt usage and promoting its utilization efficiency are essential prerequisites for a future hydrogen economy. Herein, we use a new ε-Keggin-type polyoxometalate-based metal–organic framework H3[Zn4(bimb)2][PMoV8MoVI4O40]·12H2O (POMOF-1) as a support to load a low amount of ultrasmall Pt nanoparticles (NPs), and then mix this material with Ketjenblack carbon (KB) to form a new composite catalyst (Pt@POMOF-1/KB). This composite catalyst shows a low Pt loading amount of 0.43 wt% and the average size of the Pt NPs is 1.5 nm. Pt@POMOF-1/KB exhibits a remarkable HER performance in 0.5 M H2SO4. It only requires an overpotential to of 23 mV to observe a current density of 10 mA cm−2, which is superior to that of 20% Pt/C. The mass activity of Pt@POMOF-1/KB is almost 100 and 37 times that of 20% Pt/C at overpotentials of 50 and 100 mV, respectively, as a consequence of the very low noble-metal loading. This result may provide an approach to meet the cost requirements for large-scale applications. [ABSTRACT FROM AUTHOR]

Transition metal (TM) oxides and hydroxides are one of the important candidates for the development of durable and low-cost electrocatalysts towards water splitting. The key issue is exploring effective methods to improve their electrocatalytic activity. Herein, we report a new type of P-doped Ni(OH)2/NiMoO4 hierarchical nanosheet array (abbr. P-Ni(OH)2/NiMoO4) grown on Ni foam (NF), which can act as a highly efficient electrocatalyst towards overall water splitting. Such a composite was obtained by a three-step preparation process. In the first two hydrothermal reactions, the crystalline Ni(OH)2 hierarchical nanosheet arrays were grown on NF and then the low crystallinity NiMoO4 was grafted on the Ni(OH)2 nanosheets. In the third phosphorization step, P element was doped into the composite Ni(OH)2/NiMoO4. Electrocatalytic experiments show that P-Ni(OH)2/NiMoO4 possesses a smaller overpotential (60 mV) and lower Tafel slope (130 mV dec−1) toward HER in 1 M KOH. When it was employed as an integrated water splitting catalyst, only a potential of 1.55 V was required to achieve a current density of 10 mA cm−2. This catalytic activity is even better than those of electrolyzers constructed with noble metals Pt/CIrO2. The superior electrocatalytic performance of P-Ni(OH)2/NiMoO4 can be attributed to the high quality of crystalline Ni(OH)2 nanosheet arrays grown on NF, which dramatically improve the conductivity. Furthermore, the hierarchical structure not only increases the surface area and exposes more catalytically active sites, but also provides a superaerophobic surface, which helps to accelerate the release of generated bubbles. Moreover, the synergistic effects between P-Ni(OH)2 and P-NiMoO4 efficiently promote the HER and OER processes also. This work may suggest new a way to explore TM oxide/hydroxide-based durable electrocatalysts with highly efficient electrocatalytic activities towards overall water splitting. [ABSTRACT FROM AUTHOR]

Carbon nitride (g-C3N4), as a rising star of metal-free photocatalysts, has received considerable attention. However, for practical application, the photocatalytic efficiency of g-C3N4 remains to be further improved. Herein, a series of Keggin-type polyoxoanion (polyoxoanions = SiW12O404−, PW12O403−, PMo12O403−) modified g-C3N4 (POM/C3N4) composites have been successfully prepared. The results of XRD, TEM, XPS and EDAX reveal that a small amount of polyoxoanions was modified on the surface of g-C3N4 with electrostatic and hydrogen bonding interactions. Photocatalytic experiments indicate that these composites exhibit enhanced methyl orange (MO) degradation photocatalytic activity and water splitting H2 production under visible light irradiation. The loading amount and the type of polyoxoanion can tune the photocatalytic performance of the composites. Among these catalysts, 5% SiW12O404− (SiW12)-modified g-C3N4 has the best photocatalytic performance, which is 4.4 times higher than that of pure g-C3N4 for the degradation of MO. The photocatalytic mechanism reveals that polyoxoanions can act as electron traps, which can efficiently promote the separation of photogenerated electrons and holes of C3N4, thus resulting in the enhanced photocatalytic performance of the composites. [ABSTRACT FROM AUTHOR]

A series of 2D sheet Bi2OxS3−x/Nb6O17 (Bi/Nb) heterostructure photocatalysts were synthesized through a facile hydrothermal vulcanization method between Bi3+ exchanged K4Nb6O17 and thiourea (NH2CSNH2). XRD results confirm that the heterostructures were composed of Bi2OxS3−x and Nb6O17. HRTEM indicates that Bi2OxS3−x was successfully intercalated into layers of K4Nb6O17. Such large interfacial contacts can be beneficial to the transfer and separation of photogenerated charge carriers. Thus the composites exhibit good photocatalytic performance for the degradation of methyl orange (MO) under visible light irradiation (λ ＞ 400 nm), which is superior to that of both precursors, pure Bi2S3 and K4Nb6O17. Radical capture tests reveal that photogenerated holes h+ and ṖO2− play important roles in the photodegradation of MO. And based on the UV-visible diffuse reflectance spectra (DRS) and the band gap of the semiconductors, the mechanism of the enhanced visible light photocatalytic activity of these composites has been proposed. [ABSTRACT FROM AUTHOR]