IN PRESS - Selected, just-accepted articles

Néstor Merino-Díez, Jorge Lobo-Checa, Pawel Nita, Aran Garcia-Lekue, Andrea Basagni, Guillaume Vasseur, Federica Tiso, Francesco Sedona, Pranab K. Das, Jun Fujii, Ivana Vobornik, Mauro Sambi, José Ignacio Pascual, J. Enrique Ortega and Dimas G. de Oteyza

J. Phys. Chem Lett.

I.F. 9.353

Publication date (online): April 24, 2018

DOI: 10.1021/acs.jpclett.8b00796

The challenge of synthesizing graphene nanoribbons (GNRs) with atomic precision is currently being pursued along a one-way road, based on the synthesis of adequate molecular precursors that react in predefined ways through self-assembly processes. The synthetic options for GNR generation would multiply by adding a new direction to this readily successful approach, especially if both of them can be combined. We show here how GNR synthesis can be guided by an adequately nanotemplated substrate instead of by the traditionally designed reactants. The structural atomic precision, unachievable to date through top-down methods, is preserved by the self-assembly process. This new strategy´s proof-of-concept compares experiments using 4,4´´-dibromo-para-terphenyl as molecular precursor on flat Au(111) and stepped Au(322) substrates. As opposed to the former, the periodic steps of the latter drive the selective synthesis of 6 atom-wide armchair GNRs, whose electronic properties have been further characterized in detail by scanning tunneling spectroscopy, angle resolved photoemission and density functional theory calculations.

Tomasz Kosmala, Dario Mosconi, Giuseppe Giallongo, Gian Andrea Rizzi*, and Gaetano Granozzi

ACS Sustainable Chemistry & Engineering

DOI: 10.1021/acssuschemeng.8b00840

IF = 5.951

An efficient photo-electrocatalyst for Hydrogen Evolution Reaction (HER) was prepared by electrochemical deposition of MoS2 on the Ag nanostructured surface of a commercial writable
Digital Versatile Disc (DVD). The deposition was performed by reduction of MoS42- ions and the concomitant production of HS- ions led to the formation of Ag2S nanoparticles. The result
was a composite material MoS2/Ag2S/Ag characterized by the formation of uniformly distributed n-p nanojunctions that make the performances of this easy to prepare and cheap electrocatalyst comparable or better than those of similar MoS2 based systems. This study suggests a viable opportunity to turn an abundant waste into an added-value material.

Tomasz Kosmala, Horacio Coy Diaz, Hannu‐Pekka Komsa, Yujing Ma, Arkady V. Krasheninnikov, Matthias Batzill, and Stefano Agnoli

Advanced Energy Materials

DOI: 10.1002/aenm.201800031

I.F.: 16.721

The hydrogen evolution reaction (HER) is a fundamental process that impacts several important clean energy technologies. Great efforts have been taken to identify alternative materials that could replace Pt for this reaction or that may present additional functional properties such as optical activity and advanced electronic properties. We report a comparative study of the HER activity for ultrathin films of MoTe2, MoSe2, and their solid solutions on highly oriented pyrolytic graphite. Combining advanced characterization techniques (STM, AFM, XPS, UPS) and density functional theory calculations with electrochemical measurements, we demonstrate that the chemical activity of the scarcely reactive 2H phases can be boosted by the presence of metallic twin boundaries that are obtained when these materials are deposited by MBE as thin films. This novel strategy is similar to the exploitation of 1T polymorphs in WS2 and MoS2 that have metallic properties and therefore show HER activity not only at edges but also in the basal plane. However, these phases are metastable and inevitably degrade with time. Metallic twin boundaries on the contrary, are the most thermodynamically stable defects in slightly Mo-enriched MoTe2 and therefore are expected to provide materials with better stability. Their special electronic structure and versatile geometry made them quite interesting to impart TMCs at the nano- or macroscale, with special functional properties such as metallic conductions and unprecedented chemical activity. For the first time, we demonstrated their potential for boosting the HER activity in tellurides, however their presence in several chalcogenides (i.e. MoSe2, MoS2, WSe2, WS2) suggests that the same effect can be reproduced on several other materials. Therefore, the control of MTBs offers a quite versatile tool for the development of advanced multifunctional materials with improved electronic properties and special chemical activity. 

 

Paolo Dolcet, Stefano Diodati, Federico Zorzi, Pascal Voepel, Christoph Seitz, Bernd M. Smarsly, Simone Mascotto, Fabrizio Nestola, and Silvia Gross

Green Chemistry, Just accepted (DOI: 10.1039/C8GC00086G)
I. F. : 9.125

MFe2O4 spinel ferrites (M=Co, Mn, Ni, Zn) were synthesised through a low-temperature aqueous route combining co-precipitation of oxalates and hydrothermal treatment at 135°C. To gain a deeper understanding of the structural evolution of the compounds to crystalline material during the synthetic process, samples were characterised through several time-resolved state-of-the-art analytical techniques, both on the atomic (XAS) and mesoscopic (XRPD, SAXS) scale. Experimental outcomes reveal that in most cases a fully crystalline habit already forms after short treatment times. By varying the thermal treatment duration is it possible to modulate the inversion degree of the ferrites. In parallel, temperature-programmed characterisation was carried out to investigate the evolution of the compounds during the heating process.

Laura Calvillo, Francesco Carraro, O. Vozniuk, V. Celorrio, L. Nodari, A. E. Russell, D. Debellis, D. Fermin, F. Cavani, S. Agnoli and G. Granozzi

Journal of Materials Chemistry A
DOI: 10.1039/C7TA10892C
(I.F.= 8.867)

Co-Fe spinels (CoxFe3-xO4, x = 0.6, 1, 2) are prepared both as model (ultrathin film) and realistic (powder) catalysts. Elemental reorganisation and oxidation state changes of key active sites in Co-Fe spinels are investigated by in situ X-ray photoemission spectroscopy (XPS) and operando X-ray absorption spectroscopy (XAS) under oxygen evolution operating conditions. The combination of these two in situ techniques and post-mortem XPS, TEM and Mössbauer spectroscopy, allow to identify both the surface and bulk modifications on the oxides and relate them to the activity loss during extended cycling. The results show that Co-Fe spinels experience a surface irreversible phase evolution under oxygen evolution reaction (OER) conditions, resulting in the formation of an amorphous layer composed of Co3O4, CoOOH and Fe2O3. The extension of this oxidation depends on the composition and cation distribution of the spinel oxides, since the Co(II) cations in Td sites are those that experience the modifications. Accelerated ageing tests show that the durability, intended as the performance loss during cycling treatments, is not directly related to the structural/chemical stability of the spinels but to the new species formed at the surface due to the electrochemical work. Thus, the material that experienced more significant changes was also the most durable one, demonstrating that the understanding of the chemical and/or structural evolution of the materials during the catalytic process can be the key for the design of highly active and stable catalysts.

Martin Pilarski, Roland Marschall, Silvia Gross, Michael Wark

Appl. Cat. B: Environmental, Just accepted manuscript

I. F.: 9.446

Layered cesium copper titanate as well as the unmodified cesium titanate Cs0.68Ti1.830.17O4 (□: vacancy) were synthesized by a solution-based approach. The insertion of small amounts of copper into the vacancies of Cs0.68Ti1.830.17O4 led to a significant red shift of the band gap energy from 3.4 eV to 2.9 eV. During photocatalytic H2 production experiments, a steady increase in the evolution rate was detected, which can be referred to the in-situ reduction of incorporated copper ions to metallic Cu. As shown by XPS, the reduced copper ions leach out of the lattice to the catalyst surface and act as co-catalyst for H2 formation, considerably exceeding the activity achieved with Cs0.68Ti1.830.17O4 modified with 0.075 wt.-% of Rh as co-catalyst.

Tomasz Kosmala, Laura Calvillo, Stefano Agnoli and Gaetano Granozzi

ACS Catalysis 2018, DOI: 10.1021/acscatal.7b02690 (I.F.= 10.614)

Electron transfer is the most crucial step in several electrochemical reactions, therefore finding alternative ways for its control represents a huge step toward the design of advanced electrocatalytic materials. We demonstrate that the electrons from an oxide-buried metal interface can be efficiently exploited in electrochemical reactions. This is proven by studying the electrochemical activity of model systems constituted by cobalt oxide ultrathin (<2nm) films epitaxially grown on Pd(100). Metal/metal oxide interfacial hybridization and electron tunnelling from the metal substrate through the oxide endow CoOx ultrathin films with exceptional electrochemical activity and improved methanol poison tolerance. In situ XPS and Raman measurements indicate that during the oxygen reduction reaction, CoOx films are oxidized by oxygen: Co3O4/CoO is fully converted to a spinel phase, whereas CoO is transformed via the transient formation of Co(OH)2 to a mixed Co3O4/CoOOH phase. The study of different oxide film thickness shows the crucial role of the substrate. At the UT regime, the performance of cobalt oxide is essentially analogous to that of Pd(100), because the electrons from the metal substrate can tunnel through the oxide and reduce the oxygen on the electrode surface. On the other hand, as the oxide thickness increases, tunnelling is suppressed and the ORR activity is significantly reduced. Therefore, UT oxide films supported on metals represent an innovative class of materials for electrochemistry applications that show properties not available in a single material. These results demonstrate that the in situ study of ultrathin films on single crystals is a powerful method for the identification of materials active phase and of novel phenomena such as electron tunnelling.

 

T. Gatti, E. Menna, M. Meneghetti, M. Maggini, A. Petrozza, F. Lamberti

Journal: Nano Energy (IF: 12.343)

DOI: 10.1016/j.nanoen.2017.09.016

Fullerenes have been extensively used for more than two decades for the development of organic photovoltaics (OPV). While OPV seems to be a technology almost ready for the market, in the last few years fullerenes are attracting a big interest for the improvement they afford on the already well-performing perovskite solar cells (PSCs). Thanks to PSC integration, interest in fullerenes is rising again, opening up new exciting perspectives for photovoltaics. This review article aims at analyzing the landmark contributions that gave birth to the novel application of fullerenes in PSCs and to the technological solutions that are emerging with them.

 

T. Gatti, N. Manfredi, C. Boldrini, F. Lamberti, A. Abbotto, E. Menna

Journal: Carbon (IF: 6.337)

DOI: 10.1016/j.carbon.2017.01.081

We report here the first example of a covalent functional nanocarbon hybrid based on a benchmark metal-free donor-π-acceptor (D-π-A) dye and reduced graphene oxide (RGO). The dyad, prepared by direct arylation of the RGO surface by means an aniline derivative of the D-π-A species, has been thoroughly characterized in terms of dye loading percentage and spectroscopic properties, in comparison with the reference free dye, pristine RGO, and with an analogous non-covalent dye-RGO hybrid. When used as a photosensitizing agent in dye-sensitized solar cells (DSSC), the covalent hybrid demonstrated lower photovoltaic performances compared to the cell with the reference dye, a result that was mostly ascribed to the lower dye content of the former. Furthermore, the RGO based sensitizer showed stronger binding to the semiconductor oxide in comparison to the reference dye, paving the way to a new generation of DSSC photoanodes with improved chemical stability. This work demonstrates the full potential of the new class of hybrid sensitizers to equal or even exceed the photovoltaic performances achieved by standard organic photovoltaic sensitizers once molecular engineering of the functional nanocarbon hybrid has been refined.

 

T. Gatti, S. Casaluci, M. Prato, M. Salerno, F. Di Stasio, A. Ansaldo, E. Menna, A. Di Carlo, F. Bonaccorso

Adv. Funct. Mater. (IF: 12.124)

DOI: 10.1002/adfm.201602803

Perovskite solar cells (PSCs) are demonstrating great potential to compete with second generation photovoltaics. Nevertheless, the key issue hindering PSCs full exploitation relies on their stability. Amongst the strategies devised to overcome this problem, the use of carbon nanostructures (CNSs) as hole transporting materials (HTMs) has given impressive results in terms of solar cells stability to moisture, air oxygen and heat. In this work, we propose the use of a HTM based on a poly(3-hexylthiophene) (P3HT) matrix doped with organic functionalized single walled carbon nanotubes (SWCNTs) and reduced graphene oxide in PSCs to achieve higher η (11% and 7.3%, respectively) and prolonged shelf-life stabilities (480 h) in comparison with a benchmark PSC fabricated with a bare P3HT HTM (η = 4.3% at 480 h). Further endurance test, i.e., up to 3240 h, have shown the failure of all the PSCs based on un-doped P3HT, while, on the contrary, a η of ~ 8.7% is still detected from devices containing 2wt% SWCNT-doped P3HT as HTM. We attribute the increase in photovoltaic performances and stabilities of the P3HT-CNSs-based solar cell with respect to the standard P3HT-based one to the improved interfacial contacts between the doped HTM and the adjacent layers.