Sunlight‐driven hydrogen production via photoreforming of aqueous solutions containing renewable compounds is an attractive option for sustainable energy generation with reduced carbon footprint. ...Nevertheless, the absence of photocatalysts combining high efficiency and stability upon solar light activation has up to date strongly hindered the development of this technology. Herein, two scarcely investigated iron(III) oxide polymorphs, β‐ and ε‐Fe2O3, possessing a remarkable activity in sunlight‐activated H2 generation from aqueous solutions of renewable oxygenates (i.e., ethanol, glycerol, glucose) are reported. For β‐Fe2O3 and ε‐Fe2O3, H2 production rates up to 225 and 125 mmol h−1 m−2 are obtained, with significantly superior performances with respect to the commonly investigated α‐Fe2O3.
Sunlight‐activated photoreforming of renewable oxygenates promoted by Fe2O3 nanosystems is a very attractive process for hydrogen production. In this context, scarcely investigated β‐ and ε‐Fe2O3 polymorphs, fabricated by chemical vapor deposition, show very promising performances for photocatalytic solar hydrogen generation. The present approach holds a remarkable potential even for the synthesis of added‐value by‐products, paving the way to manifold technological applications.
Transition metal complexes with β-diketonate and diamine ligands are valuable precursors for chemical vapor deposition (CVD) of metal oxide nanomaterials, but the metal-ligand bond dissociation ...mechanism on the growth surface is not yet clarified in detail. We address this question by density functional theory (DFT) and ab initio molecular dynamics (AIMD) in combination with the Blue Moon (BM) statistical sampling approach. AIMD simulations of the Zn β-diketonate-diamine complex Zn(hfa)
TMEDA (hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; TMEDA =
,
,
,
-tetramethylethylenediamine), an amenable precursor for the CVD of ZnO nanosystems, show that rolling diffusion of this precursor at 500 K on a hydroxylated silica slab leads to an octahedral-to-square pyramidal rearrangement of its molecular geometry. The free energy profile of the octahedral-to-square pyramidal conversion indicates that the process barrier (5.8 kcal/mol) is of the order of magnitude of the thermal energy at the operating temperature. The formation of hydrogen bonds with surface hydroxyl groups plays a key role in aiding the dissociation of a Zn-O bond. In the square-pyramidal complex, the Zn center has a free coordination position, which might promote the interaction with incoming reagents on the deposition surface. These results provide a valuable atomistic insight on the molecule-to-material conversion process which, in perspective, might help to tailor by design the first nucleation stages of the target ZnO-based nanostructures.
Water is the renewable, bulk chemical that nature uses to enable carbohydrate production from carbon dioxide. The dream goal of energy research is to transpose this incredibly efficient process and ...make an artificial device whereby the catalytic splitting of water is finalized to give a continuous production of oxygen and hydrogen. Success in this task would guarantee the generation of hydrogen as a carbon-free fuel to satisfy our energy demands at no environmental cost. Here we show that very efficient and stable nanostructured, oxygen-evolving anodes are obtained by the assembly of an oxygen-evolving polyoxometalate cluster (a totally inorganic ruthenium catalyst) with a conducting bed of multiwalled carbon nanotubes. Our bioinspired electrode addresses the one major challenge of artificial photosynthesis, namely efficient water oxidation, which brings us closer to being able to power the planet with carbon-free fuels.
NiO-based nanomaterials have attracted considerable interest for different applications, which have stimulated the implementation of various synthetic approaches aimed at modulating their ...chemico-physical properties. In this regard, their bottom-up preparation starting from suitable precursors plays an important role, although a molecular-level insight into their reactivity remains an open issue to be properly tackled. In the present study, we focused on the fragmentation of Ni(II) diketonate-diamine adducts, of interest as vapor-phase precursors for Ni(II) oxide systems, by combining electrospray ionization mass spectrometry (ESI-MS) with multiple collisional experiments (ESI-MS
) and theoretical calculations. The outcomes of this investigation revealed common features in the fragmentation pattern of the target compounds: (i) in the first fragmentation, the three complexes yield analogous base-peak cations by losing a negatively charged diketonate moiety; in these cations, Ni-O and Ni-N interactions are stronger and the Ni positive charge is lower than in the parent neutral complexes; (ii) the tendency of ligand electronic charge to migrate towards Ni further increases in the subsequent fragmentation, leading to the formation of a tetracoordinated Ni environment featuring an interesting cation-π intramolecular interaction.
Hy wire: Supported Cu2O nanosystems and CuO nanowires obtained by chemical vapor deposition were used in the photocatalytic splitting of methanol/water solutions to produce hydrogen. The results ...obtained with these systems open appealing perspectives for the clean conversion of sunlight into storable chemical energy.
Hy wire: Supported Cu2O nanosystems and CuO nanowires obtained by chemical vapor deposition were used in the photocatalytic splitting of methanol/water solutions to produce hydrogen. The results obtained with these systems open appealing perspectives for the clean conversion of sunlight into storable chemical energy.
Nanocomposite Fe2O3Co3O4 photoanodes for photoelectrochemical H2O splitting were prepared by a plasma‐assisted route. Specifically, Fe2O3 nanostructures were grown by plasma enhanced‐chemical vapor ...deposition, followed by cobalt sputtering for different process durations. The systems were annealed in air after, or both prior and after, sputtering of Co, to analyze the treatment influence on functional performances. The interplay between processing conditions and chemico‐physical features was investigated by a multi‐technique characterization. Photocurrent density measurements in sunlight‐assisted H2O splitting revealed a performance improvement upon Co3O4 loading. A cathodic shift of the onset potential was also observed, highlighting Co3O4 activity as catalyst for the oxygen evolution reaction.
Fe2O3Co3O4 nanomaterials are fabricated on FTO substrates by means of a two‐step strategy, consisting in the plasma enhanced‐CVD of Fe2O3 followed by cobalt sputtering. A thorough characterization of the obtained systems as a function of thermal treatment conditions and cobalt loading is presented, followed by functional testing in photoelectrochemical water splitting activated by solar light.
ZnO−TiO2 nanocomposites were synthesized by an innovative chemical vapor deposition (CVD) strategy, based on the initial growth of ZnO nanoplatelets (host) and the subsequent dispersion of TiO2 ...nanoparticles (guest). Ti(O i Pr)2(dpm)2 and Zn(hfa)2·TMEDA (O i Pr: iso-propoxy; dpm: 2,2,6,6-tetramethyl-3,5-heptanedionate; hfa: 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; and TMEDA: N,N,N‘,N‘-tetramethylethylenediamine) were adopted as Ti and Zn molecular sources, respectively. The syntheses were performed in nitrogen plus wet oxygen atmospheres at relatively low temperatures (350−400 °C) on Si(100) and Al2O3 substrates, avoiding ex-situ thermal treatment to preserve the chemical identity of the host and guest phases. The process resulted in the formation of ZnO−TiO2 nanocomposite deposits with an average thickness of 140 nm, whose characteristics were directly affected by the host matrix porosity and the guest amount and dispersion, tailored by varying the TiO2 deposition time. In this framework, particular attention was devoted to the investigation of the composite chemico-physical properties as a function of the adopted processing parameters. Furthermore, the gas sensing performances of the nanocomposites in the detection of volatile organic compounds (CH3COCH3, CH3CH2OH, and CO) resulted in being directly dependent on their composition and morphology, revealing better performances than the pristine ZnO systems. These results disclose intriguing perspectives for the development of sensing devices for environmental purposes and food control monitoring.
The artificial leaf project calls for new materials enabling multielectron catalysis with minimal overpotential, high turnover frequency, and long-term stability. Is graphene a better material than ...carbon nanotubes to enhance water oxidation catalysis for energy applications? Here we show that functionalized graphene with a tailored distribution of polycationic, quaternized, ammonium pendants provides an sp2 carbon nanoplatform to anchor a totally inorganic tetraruthenate catalyst, mimicking the oxygen evolving center of natural PSII. The resulting hybrid material displays oxygen evolution at overpotential as low as 300 mV at neutral pH with negligible loss of performance after 4 h testing. This multilayer electroactive asset enhances the turnover frequency by 1 order of magnitude with respect to the isolated catalyst, and provides a definite up-grade of the carbon nanotube material, with a similar surface functionalization. Our innovation is based on a noninvasive, synthetic protocol for graphene functionalization that goes beyond the ill-defined oxidation–reduction methods, allowing a definite control of the surface properties.
A single-step plasma enhanced-chemical vapor deposition (PE-CVD) route for the synthesis of F-doped iron(III) oxide nanomaterials is presented. Growth experiments, performed from a fluorinated Fe(II) ...β-diketonate precursor on Indium Tin Oxide (ITO) between 200 and 400 °C, yielded columnar β-Fe2O3 arrays with a preferential (100) growth direction. The fluorine content in the deposits could be adjusted by the sole variation of the deposition temperature controlling, in turn, the optical absorption and energy bandgap. Photocurrent measurements and Mott–Schottky analyses, carried out in Na2SO4 solution under one sun illumination, evidenced a conductivity switch from n- to p-type upon increasing fluorine amount in the obtained nanomaterials. The sample photocurrent density, donor content and flatband potential support the hypothesis that a progressive substitution of oxygen by fluorine in the iron(III) oxide lattice can alter electronic structure and extend charge carrier lifetimes, making anion-doped β-Fe2O3 an efficient water oxidation catalyst.
•Novel PE-CVD approach to β-Fe2O3 nanomaterials on ITO substrates.•Fabrication of columnar arrays with an homogeneous in-depth fluorine doping.•First example of β-Fe2O3 application in photoelectrochemical water splitting.•Modulation of optical and photoelectrochemical properties as a function of fluorine content.
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