Effect of the structure of Pt–Ru/C particles on COad monolayer vibrational properties and electrooxidation kinetics

Unusual Effect of Trace Water on the Structure and Activity of Nix Co1-x Electrocatalysts for the Methanol Oxidation Reaction

Highly active Ni-based catalysts have attracted much attention but are still facing challenges owing to the immature synthetic method. Herein, polyhedral Ni_x Co_1-x alloy was prepared by a facile modified polyol method in which a trace amount of water could halve the particle size of the alloy. The Ni/Co ratios in Ni_x Co_1-x alloy strictly depended on the used amount of water owing to the different solubilities of the precursors. Among them, the Ni_0.6 Co_0.4 nanoparticles obtained with 70 μL of deionized water exhibited the best performance in the methanol oxidation reaction with a peak current density of 116 mA cm^-2 in the presence of 1 m NaOH+0.5 m CH₃ OH solution, which is higher than those of Ni_0.7 Co_0.3 (80 mA cm^-2 ) and Ni_0.5 Co_0.5 (33 mA cm^-2 ). The excellent performance of Ni_0.6 Co_0.4 is attributed to the unique structure with appropriate Ni/Co ratio, which elongates the C-O bond in methanol and lowers the reaction free energy according to DFT calculations.

Bimetallic alloy and semiconductor support synergistic interaction effects for superior electrochemical catalysis

The design and fabrication of economically viable anode catalysts for the methanol oxidation reaction (MOR) have been challenging issues in direct methanol fuel cells (DMFCs) over the decades. In this work, a composite electrochemical catalyst of Pd-coupled Ag and ZnO for the possible replacement of expensive Pt catalysts in DMFCs is successfully prepared. The as-made Pd@Ag/ZnO exhibits specific activity, which is 1.8-fold, 2.8-fold, and 4.6-fold higher than that of a Pd/ZnO catalyst, 20% Pd/C catalyst and Pd black, respectively. The improvement of the catalytic mechanism is likely due to the synergistic interaction between Pd@Ag and ZnO. The density functional theory (DFT) calculation results confirm that Ag doped into Pd weakens the adsorption of CO, dramatically improving the capability to resist CO poisoning.

Vanadium Dioxide-Graphene Composite with Ultrafast Anchoring Behavior of Polysulfides for Lithium-Sulfur Batteries

The lithium-sulfur (Li-S) battery has been deemed as one of the most promising energy-storage systems owing to its high energy density, low cost, and environmental benignancy. However, the capacity decay and kinetic sluggishness stemming from polysulfide shuttle effects have by far posed a great challenge to practical performance. We herein demonstrate the employment of low-cost, wet-chemistry-derived VO₂ nanobelts as the effective host additives for the graphene-based sulfur cathode. The VO₂ nanobelts displayed an ultrafast anchoring behavior of polysulfides, managing to completely decolor the polysulfide solution in 50 s. Such a fast and strong anchoring ability of VO₂ was further investigated and verified by experimental and theoretical investigations. Benefitting from the synergistic effect exerted by VO₂ in terms of chemical confinement and catalytic conversion of polysulfides, the Li-S batteries incorporating VO₂ and graphene manifested excellent cycling and rate performances. Notably, the batteries delivered an initial discharge capacity of 1405 mAh g^-1 when cycling at 0.2 C, showed an advanced rate performance of ∼830 mAh g^-1 at 2 C, and maintained a stable cycling performance at high current densities of 1, 2, and 5 C over 200 cycles, paving a practical route toward cost-effective and environmentally benign cathode design for high-energy Li-S batteries.

Phosphorene as a Polysulfide Immobilizer and Catalyst in High-Performance Lithium-Sulfur Batteries

Theoretical and experimental studies together show phosphorene as a highly potent polysulfide immobilizer for lithium-sulfur batteries, enabling a high capacity, good rate capability, and excellent cycling stability.

Ni- and Mn-Promoted Mesoporous Co3O4: A Stable Bifunctional Catalyst with Surface-Structure-Dependent Activity for Oxygen Reduction Reaction and Oxygen Evolution Reaction

Efficient bifunctional catalysts for electrochemical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are highly desirable due to their wide applications in fuel cells and rechargeable metal air batteries. However, the development of nonprecious metal catalysts with comparable activities to noble metals is still challenging. Here we report a one-step wet-chemical synthesis of Ni-/Mn-promoted mesoporous cobalt oxides through an inverse micelle process. Various characterization techniques including powder X-ray diffraction (PXRD), N2 sorption, transmission electron microscopy (TEM), and scanning electron microscopy (SEM) confirm the successful incorporation of Ni and Mn leading to the formation of Co-Ni(Mn)-O solid solutions with retained mesoporosity. Among these catalysts, cobalt oxide with 5% Ni doping demonstrates promising activities for both ORR and OER, with an overpotential of 399 mV for ORR (at -3 mA/cm(2)) and 381 mV (at 10 mA/cm(2)) for OER. Furthermore, it shows better durability than precious metals featuring little activity decay throughout 24 h continuous operation. Analyses of cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), Raman, and O2-temperature-programmed desorption (O2-TPD) reveal that redox activity of Co(3+) to Co(4+) is crucial for OER performance, while the population of surface oxygen vacancies and surface area determine ORR activities. The comprehensive investigation of the intrinsic active sites for ORR and OER by correlating different physicochemical properties to the electrochemical activities is believed to provide important insight toward the rational design of high-performance electrocatalysts for ORR and OER reactions.

Vertically Oriented Arrays of ReS2 Nanosheets for Electrochemical Energy Storage and Electrocatalysis

Transition-metal dichalcogenide (TMD) nanolayers show potential as high-performance catalysts in energy conversion and storage devices. Synthetic TMDs produced by chemical-vapor deposition (CVD) methods tend to grow parallel to the growth substrate. Here, we show that with the right precursors and appropriate tuning of the CVD growth conditions, ReS2 nanosheets can be made to orient perpendicular to the growth substrate. This accomplishes two important objectives; first, it drastically increases the wetted or exposed surface area of the ReS2 sheets, and second, it exposes the sharp edges and corners of the ReS2 sheets. We show that these structural features of the vertically grown ReS2 sheets can be exploited to significantly improve their performance as polysulfide immobilizers and electrochemical catalysts in lithium-sulfur (Li-S) batteries and in hydrogen evolution reactions (HER). After 300 cycles, the specific capacity of the Li-S battery with vertical ReS2 catalyst is retained above 750 mA h g(-1), with only ∼0.063% capacity decay per cycle, much better than the baseline battery (without ReS2), which shows ∼0.184% capacity decay per cycle under the same test conditions. As a HER catalyst, the vertical ReS2 provides very small onset overpotential (<100 mV) and an exceptional exchange-current density (∼67.6 μA/cm(2)), which is vastly superior to the baseline electrode without ReS2.

Visual discrimination of dihydroxybenzene isomers based on a nitrogen-doped graphene quantum dot-silver nanoparticle hybrid

A room temperature reducing agent-free strategy for the synthesis of a nitrogen-doped graphene quantum dot-silver nanoparticle (N-GQD/AgNP) hybrid was presented. In this strategy, N-GQDs were used as a reducing agent and stabilizer for the formation of the N-GQD/AgNP hybrid, and the formation of the N-GQD/AgNP hybrid may result from the extraordinary reduction properties of N-GQDs, which are attributed to the nature of the surface oxygen-containing functional groups. The N-GQD/AgNP hybrid exhibits good dispersity and outstanding catalytic ability toward the oxidation of catechol (CC) and hydroquinone (HQ) by Ag(+). In the presence of the N-GQD/AgNP hybrid, the reduction of Ag(+) by CC and HQ was improved. CC enhanced the absorbance of the N-GQD/AgNP-Ag(+) system the most, and HQ followed, while resorcinol (RC) had only a little effect on the absorption intensity of the system. Thus, a sensitive and selective colorimetric sensing method based on the N-GQD/AgNP-Ag(+) system was developed for the discrimination of CC, HQ and RC. A good linear relationship was obtained from 0.1 to 15.0 μM for CC and from 0.3 to 20.0 μM for HQ. The detection limits of CC and HQ were 0.03 and 0.1 μM, respectively. In addition, the proposed method also shows a high selectivity for the detection of CC and HQ, and appreciable changes in color of the N-GQD/AgNP-Ag(+) system toward CC, RC and HQ were observed.

Development of a highly active electrocatalyst via ultrafine Pd nanoparticles dispersed on pristine graphene

A unique synthesis was developed to immobilize Pd nanoparticles on pristine graphene (PG) sheets via a facile supercritical carbon dioxide route. Pristine graphene was obtained by sonication-assisted exfoliation of graphite in an organic solvent. Finely dispersed worm-like Pd nanoparticles are homogeneously deposited on the hydrophobic graphene surfaces. The combination of pristine graphene sheets and well-dispersed Pd nanoparticles provided large electrochemically active surface areas (ECSA) for both direct formic acid fuel cell (DFAFC) and methanol fuel cell (DMFC). The ECSA values are more than twice as large as those of reduced graphene oxide and carbon nanotube based counterparts or six times those of conventional XC-72 carbon black. Significant enhancements were also observed in the electrocatalytic activity and stability measurements. The excellent electrochemical property of Pd/PG is attributable to the well-preserved graphene structure that ensures electrical conductivity and stability of the composite. Its large surface area also allows for the deposition of small size and high dispersion of the Pd nanoparticles. This straightforward synthesis offers a new pathway for developing highly active electrocatalysts based on pristine graphene with fully optimized properties.

A facile one-pot self-assembly approach to incorporate SnOx nanoparticles in ordered mesoporous carbon with soft templating for fuel cells

Unique SnO(x) (x = 1,2)/ordered mesoporous carbon nanocomposites (denoted as SnO(x)/OMC) are firstly synthesized through a 'one-pot' synthesis together with the soft template self-assembly approach. The obtained SnO(x)/OMC nanocomposites with various SnO(x) contents exhibit uniform pore sizes between 3.9 and 4.2 nm, high specific surface areas between 497 and 595 m(2) g(-1), and high pore volumes between 0.39 and 0.48 cm(3) g(-1). With loading of Pt, Pt-SnO(x)/OMC with relatively low SnO(x) content exhibits superior electrocatalytic performance, long-term durability, and resistance to CO poisoning for methanol oxidation, as compared to Pt/OMC, PtRu/C and Pt-SnO(x)/C, which may be attributed not only to the synergetic effect of embedded SnO(x), but also to the highly ordered mesostructure with high specific surface areas and large pore volumes affording plenty of surface area for support of Pt nanoparticles. This work supplies an efficient way to synthesize novel ordered mesoporous carbon self-supported metallic oxide as catalyst support and its further potential application to reduce the cost of catalysts in direct methanol fuel cells.