Boosting oxygen reduction and hydrogen evolution at the edge sites of a web-like carbon nanotube-graphene hybrid

Identifying catalytically active sites in graphene-based catalysts is critical to improved oxygen reduction reaction (ORR) electrocatalysts for fuel-cell applications. To generate abundant active edge sites on graphene-based electrocatalysts for superior electrocatalytic activity, rather than at their basal plane, has been a challenge. A new type of ORR electrocatalyst produced using fluidization process and based on a three-dimensional hybrid consisting of horizontally-aligned carbon nanotube and graphene (CNT-G), featured abundant active edge sites and a large specific surface area (863\ua0m\ua0g). The Pt-doped CNT-G exhibited an increase of about 55% in mass activity over the state-of-the-art commercial Pt/C and about 164% over Pt/N-graphene in acidic medium, and approximately 54% increase in kinetic limiting current than the Pt/C at low overpotential in alkaline medium. The higher mass activity indicates that less Pt is required for the same performance, reducing the cost of fuel cell electrocatalyst. In hydrogen evolution reaction (HER), both the metal-free CNT-G and Pt/CNT-G exhibited superior electrocatalytic activity compared to N-doped graphene and commercial Pt/C, respectively

Metal-support interface of a novel Ni-CeO2 catalyst for dry reforming of methane

Simultaneous treatment of both the loaded metal and the ceria support under plasma led to the generation of clean metal-support interface. This novel synthesis route prevents the tendency of Ni atoms migrating into the bulk of the supports, thereby avoiding a diffused interfacial region. The plasma treated sample showed excellent stability and higher catalytic activity than the thermally calcined sample in dry reforming of methane. The high activity of the plasma treated sample is attributed to the clean metal-support interface generated by exposing both the support and the loaded metal to microwave plasma treatment

Flower-like perovskite LaCr(0.9)Ni(0.1)O(3-delta)-NiO nanostructures: a new candidate for CO2 reforming of methane

We have developed a facile low-cost approach to the fabrication of large-scale flower-like perovskite-type oxides: orthorhombic LaCr 0.9Ni0.1O3-δ nanowires. The nanowires (∼76.2%) exhibited higher CO2 conversion than their conventional bulk counterpart (∼40.1%) due to exposure of more active sites. The unique morphological structure of the nanowires enhanced the dispersion of Pd nanoparticles on its edges and surfaces, resulting in excellent performance and stability in CO2 reforming of methane. The Pd decorated LaCr 0.9Ni0.1O3-δ nanowires exhibit optimum CO2 and CH4 conversions of ∼98.6% and ∼75.4% at 800 °C. The high turnover frequency (TOF) of CH4 (6.04 s -1) on 1 wt% Pd decorated LaCr0.9Ni0.1O 3-δ might be attributed to high dispersion of Pd species on the nanowires. This journal i

Synthesis of Supported Nickel Nanoparticles via a Nonthermal Plasma Approach and Its Application in CO₂ Reforming of Methane

A microwave plasma treatment was applied to obtain not only a desired strong metal–support interaction but also well-dispersed nickel nanoparticles supported on ceria. The catalytic properties of these supported nanoparticles were tested in CO₂ reforming of methane. The plasma-treated Ni/CeO₂ catalysts showed enhanced turnover frequencies (TOFs), normalized by Ni on the surface, as compared with the thermally calcined samples. The Ni/CeO₂ treated under plasma with low Ni loading gave an enhanced TOF of 9.5 s^–1 (700 °C, 50% CH₄ and 50% CO₂, and 1 atm) as compared with the thermally calcined catalyst (8.7 s^–1). Increasing the Ni loading on the plasma-treated Ni/CeO₂ catalysts gave an improved TOF (10.4 s^–1) which was stable with time, while the TOF was observed to drop by a factor of 2 relative to the optimal TOF on the thermally calcined catalyst after 5 h. For the plasma-treated samples, concurrent treatment of both the uncalcined ceria support and the loaded metal precursor generated strong metal–support interaction and formation of well-dispersed Ni particles, resulting in a superior and stable TOF with time. In the case of thermally calcined catalysts, the weak metal–support interaction and the agglomeration of Ni clusters together with the migration of the Ni particles into the ceria support hindered the accessibility of active nickel sites, resulting in deactivation of the materials during reaction. Moreover, high-resolution transmission electron microscopy, high-angle annular dark-field scanning transmission electron microscopy, H₂ temperature-programmed reduction, and X-ray photoelectron spectroscopy yielded a clear picture of the impact of microwave plasma treatment on the nickel particle size, shape, distribution, and interaction with the ceria support

Hexagonal sphericon hematite with high performance for water oxidation

A cost-effective hexagonal sphericon hematite with predominant (110) facets for the oxygen evolution reaction (OER) is demonstrated. Sequential incorporation of near-atomic uniformly distributed Ce species and Ni nanoparticles into selected sites of the hematite induces a complex synergistic integration phenomenon that enhances the overall catalytic OER performance. This cheap hexagonal sphericon hematite (Fe ≈ 98%) only needs a small overpotential (η) of 0.34 V to reach 10 mA cm−2, superior to commercial IrO2 and more expensive Co-, Ni-, and Li-based electrocatalysts

Activated carbon becomes active for oxygen reduction and hydrogen evolution reactions

We utilized a facile method for creating unique defects in the activated carbon (AC), which makes it highly active for the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER). The ORR activity of the defective AC (D-AC) is comparable to the commercial Pt/C in alkaline medium, and the D-AC also exhibits excellent HER activity in acidic solution

Influences of doping Cr/Fe/Ta on the performance of Ni/CeO2 catalyst under microwave irradiation in dry reforming of CH4

The structure of Ni/CeO2 catalyst with doping of Cr, Fe and Ta was investigated with XRD, N2 physisorption, XPS and HRTEM and the catalytic activity of the catalysts under microwave irradiation in dry reforming of methane was tested in a microwave reactor. The results show that the introduction of Cr and Ta to Ni/CeO2 can enhance the interaction between Ni and the support/promoter and inhibit the enlargement of NiO particles during the synthesis. The CH4 conversions in dry reforming on the catalysts follow the order: Ni/CeO2<2Fe–Ni<2Ta–Ni<2Cr–Ni. The superior performance of 2Ta–Ni and 2Cr–Ni may be attributed to the locally-heated Ni particles caused by the strong microwave absorption of the in-situ grown graphene attached on them under microwave irradiation