Cylindrical C96 Fullertubes: A Highly Active Metal-Free O2 -Reduction Electrocatalyst.

A new isolation protocol was recently reported for highly purified metallic Fullertubes D5h -C90 , D3d -C96 , and D5d -C100, which exhibit unique electronic features. Here, we report the oxygen reduction electrocatalytic behavior of C60 , C70 (spheroidal fullerenes), and C90 , C96 , and C100 (tubular fullerenes) using a combination of experimental and theoretical approaches. C96 (a metal-free catalyst) displayed remarkable oxygen reduction reaction (ORR) activity, with an onset potential of 0.85 V and a halfway potential of 0.75 V, which are close to the state-of-the-art Pt/C benchmark catalyst values. We achieved an excellent power density of 0.75 W cm-2 using C96 as a modified cathode in a proton-exchange membrane fuel cell, comparable to other recently reported efficient metal-free catalysts. Combined band structure (experimentally calculated) and free-energy (DFT) investigations show that both favorable energy-level alignment active catalytic sites on the carbon cage are responsible for the superior activity of C96 .

Tailoring the Interfacial Interactions of van der Waals 1T-MoS2/C60 Heterostructures for High-Performance Hydrogen Evolution Reaction Electrocatalysis.

Fullerene-based low-dimensional (LD) heterostructures have emerged as excellent energy conversion materials. We constructed van der Waals 1T-MoS2/C60 0D-2D heterostructures via a one-pot synthetic approach for catalytic hydrogen generation. The interfacial 1T-MoS2-C60 and C60-C60 interactions as well as their electrocatalytic properties were finely controlled by varying the weight percentages of the fullerenes. 1T-MoS2 platforms provided a novel template for the formation of C60 nanosheets (NSs) within a very narrow fullerene concentration range. The heterostructure domains of 1T-MoS2 and C60 NSs exhibited excellent hydrogen evolution reaction (HER) performances, with one of the lowest onset potentials and ΔGH* values for LD non-precious nanomaterials reported to date.

Crystal Chemistry, Band-Gap Red Shift, and Electrocatalytic Activity of Iron-Doped Gallium Oxide Ceramics.

This work for the first time unfurls the fundamental mechanisms and sets the stage for an approach to derive electrocatalytic activity, which is otherwise not possible, in a traditionally known wide band-gap oxide material. Specifically, we report on the tunable optical properties, in terms of wide spectral selectivity and red-shifted band gap, and electrocatalytic behavior of iron (Fe)-doped gallium oxide (ß-Ga2O3) model system. X-ray diffraction (XRD) studies of sintered Ga2-x Fe x O3 (GFO) (0.0 ≤ x ≤ 0.3) compounds provide evidence for the Fe3+ substitution at Ga3+ site without any secondary phase formation. Rietveld refinement of XRD patterns reveals that the GFO compounds crystallize in monoclinic crystal symmetry with a C2/m space group. The electronic structure of the GFO compounds probed using X-ray photoelectron spectroscopy data reveals that at lower concentrations, Fe exhibits mixed chemical valence states (Fe3+, Fe2+), whereas single chemical valence state (Fe3+) is evident for higher Fe content (x = 0.20-0.30). The optical absorption spectra reveal a significant red shift in the optical band gap with Fe doping. The origin of the significant red shift even at low concentrations of Fe (x = 0.05) is attributed to the strong sp-d exchange interaction originated from the 3d5 electrons of Fe3+. The optical absorption edge observed at ≈450 nm with lower intensity is the characteristic of Fe-doped compounds associated with Fe3+-Fe3+ double-excitation process. Coupled with an optical band-gap red shift, electrocatalytic studies of GFO compounds reveal that, interestingly, Fe-doped Ga2O3 compound exhibits electrocatalytic activity in contrast to intrinsic Ga2O3. Fe-doped samples (GFO) demonstrated appreciable electrocatalytic activity toward the generation of H2 through electrocatalytic water splitting. An onset potential and Tafel slope of GFO compounds include ∼900 mV, ∼210 mV dec-1 (x = 0.15) and ∼1036 mV, ∼290 mV dec-1 (x = 0.30), respectively. The electrocatalytic activity of Fe-doped Ga-oxide compounds is attributed to the cumulative effect of different mechanisms such as doping resulting in new catalytic centers, enhanced conductivity, and electron mobility. Hence, in this report, for the first time, we explored a new pathway; the electrocatalytic behavior of Fe-doped Ga2O3 resulted due to Fe chemical states and red shift in the optical band gap. The implications derived from this work may be applicable to a large class of compounds, and further options may be available to design functional materials for electrocatalytic energy production.

Designing Metallic MoO2 Nanostructures on Rigid Substrates for Electrochemical Water Activation.

In situ growth of metallic MoO2 films on fluorine-doped tin oxide (FTO) and MoO2 powder in solution was achieved simultaneously by a simple hydrothermal process employing citric acid as the surfactant. The growth mechanism of MoO2 nanostructures (NSs) at the heterogeneous interface and in homogeneous medium proceeds in a different manner in which seeds grow in a preferred orientation on FTO, whereas they propagate in all directions in solution. The high lattice matching of FTO and MoO2 favours the film growth which could not be obtained on other conventional substrates. The disc morphology of MoO2 nanostructures was changed to other diverse morphology by varying the synthesis conditions, particularly by the addition of nitric acid. A competitive effect of nitric acid and citric acid on the structure direction produced various shapes. The electrochemical water activation studies show that hydrogen-annealed MoO2 is an excellent hydrogen evolution reaction (HER) catalyst with good stability. H-MoO2 film/FTO displays a low onset overpotential of72 mV with a Tafel slope of 84.1 mV dec-1 , whereas the powder form exhibits an onset overpotential of 46 mV with a Tafel slope of 71.6 mV dec-1 . The large active surface area, exposure of fringe facets of (110) and the lesser electrochemical charge-transfer resistance offered by the hydrogen-annealed MoO2 NSs play a major role in the enhanced HER activity.