There are tens of industrial producers claiming to sell graphene and related materials (GRM), mostly as solid powders. Recently the quality of commercial GRM has been questioned, and procedures for GRM quality control were suggested using Raman Spectroscopy or Atomic Force Microscopy. Such techniques require dissolving the sample in solvents, possibly introducing artefacts.A more pragmatic approach is needed, based on fast measurements and not requiring any assumption on GRM solubility. To this aim, we report here an overview of the properties of commercial GRM produced by selected companies in Europe, USA and Asia. We benchmark: (A) size, (B) exfoliation grade and (C) oxidation grade of each GRM versus the ones of 'ideal' graphene and, most importantly, versus what reported by the producer. In contrast to previous works, we report explicitly the names of the GRM producers and we do not re-dissolve the GRM in solvents, but only use techniques compatible with industrial powder metrology.A general common trend is observed: products having low defectivity (%sp 2 bonds >95%) feature low surface area (<200 m 2 g −1 ), while highly exfoliated GRM show a lower sp 2 content, demonstrating that it is still challenging to exfoliate GRM at industrial level without adding defects. PAPEROriginal content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence.

Large area van der Waals (vdW) thin films are assembled materials consisting of a network of randomly stacked nanosheets. The multiscale structure and the twodimensional (2D) nature of the building block mean that interfaces naturally play a crucial role in the charge transport of such thin films. While single or few stacked nanosheets (i.e., vdW heterostructures) have been the subject of intensive works, little is known about how charges travel through multilayered, more disordered networks. Here, we report a comprehensive study of a prototypical system given by networks of randomly stacked reduced graphene oxide 2D nanosheets, whose chemical and geometrical properties can be controlled independently, permitting to explore percolated networks ranging from a single nanosheet to some billions with roomtemperature resistivity spanning from 10 −5 to 10 −1 Ω•m. We systematically observe a clear transition between two different regimes at a critical temperature T*: Efros−Shklovskii variable-range hopping (ES-VRH) below T* and power law behavior above. First, we demonstrate that the two regimes are strongly correlated with each other, both depending on the charge localization length ξ, calculated by the ES-VRH model, which corresponds to the characteristic size of overlapping sp 2 domains belonging to different nanosheets. Thus, we propose a microscopic model describing the charge transport as a geometrical phase transition, given by the metal−insulator transition associated with the percolation of quasi-one-dimensional nanofillers with length ξ, showing that the charge transport behavior of the networks is valid for all geometries and defects of the nanosheets, ultimately suggesting a generalized description on vdW and disordered thin films.

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Light absorption and charge transport in oxide semiconductors can be tuned by the introduction, during deposition, of a small quantity of foreign elements, leading to the improvement of the photoelectrocatalytic performance. In this work, both unmodified and vanadium-modified TiO 2 thin films deposited by radio-frequency magnetron sputtering are investigated as photoanodes for photoelectrochemical water splitting. Following a structural characterization by X-ray diffraction, atomic force microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy, photoelectrocatalysis is discussed based on ultrafast transient absorbance spectroscopy measurements. In particular, three different pump wavelengths from UV to the visible range are used (300, 390, and 530 nm) in order to cover the relevant photoactive spectral range of modified TiO 2 . Incident photon-to-current conversion efficiency spectra show that incorporation of vanadium in TiO 2 extends water splitting in the visible range up to ≈530 nm, a significant improvement compared to unmodified TiO 2 that is active only in the UV range ≲390 nm. However, transient absorbance spectroscopy clearly reveals that vanadium accelerates electron−hole recombination upon UV irradiation, resulting in a lower photon-to-current conversion efficiency in the UV spectral range with respect to unmodified TiO 2 . The new photoelectrocatalytic activity in the visible range is attributed to a V-induced introduction of intragap levels at ≈2.2 eV below the bottom of the conduction band. This is confirmed by long-living transient signals due to electrons photoexcited into the conduction band after visible light (530 nm) pulses. The remaining holes migrate to the semiconductor−electrolyte interface where they are captured by long-lived traps and eventually promote water oxidation under visible light.

Graphene and related 2D material (GRM) thin films consist of 3D assembly of billions of 2D nanosheets randomly distributed and interacting via van der Waals forces. Their complexity and the multiscale nature yield a wide variety of electrical characteristics ranging from doped semiconductor to glassy metals depending on the crystalline quality of the nanosheets, their specific structural organization ant the operating temperature. Here, the charge transport (CT) mechanisms are studied that are occurring in GRM thin films near the metal‐insulator transition (MIT) highlighting the role of defect density and local arrangement of the nanosheets. Two prototypical nanosheet types are compared, i.e., 2D reduced graphene oxide and few‐layer‐thick electrochemically exfoliated graphene flakes, forming thin films with comparable composition, morphology and room temperature conductivity, but different defect density and crystallinity. By investigating their structure, morphology, and the dependence of their electrical conductivity on temperature, noise and magnetic‐field, a general model is developed describing the multiscale nature of CT in GRM thin films in terms of hopping among mesoscopic bricks, i.e., grains. The results suggest a general approach to describe disordered van der Waals thin films.