Towards the improvement of methane production in CO2 photoreduction using Bi2WO6/TiO2 heterostructures

Russelite bismuth tungstate (Bi2WO6) has been widely reported for the photocatalytic degradation and mineralization of a myriad of pollutants as well as organic compounds. These materials present perovskite-like structure with hierarchical morphologies, which confers excellent optoelectronic properties as potentials candidates for photocatalytic solar fuels production. Here, we propose the development of Bi2WO6/TiO2 heterojunctions for CO2 photoreduction, as a promising solution to produce fuels, alleviate global warming and tackle fossil fuel shortage. Our results show an improvement of the photocatalytic activity of the heterojunctions compared to the pristine semiconductors. Near Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS) experiments reveals a preferential CO2 adsorption over TiO2. On the other hand, transient absorption spectroscopy measurements show that the charge transfer pathway in Bi2WO6/TiO2 hybrids leads to longer-lived photogenerated carriers in spatially separated redox active sites, which favor the reduction of CO2 into highly electron demanding fuels and chemicals, such as CH4 and C2H6Financial support has been received from the European Research Council (ERC), through HYMAP project (grant agreement No. 648319), under the European Union's Horizon 2020 research and innovation program, as well as from the Marie Sklodowska-Curie grant agreement No. 754382. L.C. acknowledges funding from the project ARMONIA (PID2020–119125RJ-I00) funded by MCIN/AEI/10.13039/ 501100011033. Financial support has also been received from AEIMINECO/FEDER (Nympha Project, PID2019–106315RB-I00), "Comunidad de Madrid" regional government, and the European Structural Funds (FotoArt-CM project, S2018/NMT-4367). Authors also acknowledge financial support from the grant PLEC2021–007906 funded by MCIN/AEI/10.13039/501100011033 and the "European Union NextGenerationEU/PRTR"

Holy Water: Photo-Brightening in Quasi-2D Perovskite Films under Ambient Enables Highly Performing Light-Emitting Diodes

Quasi-2D perovskites provide new opportunities for lighting and display applications due to their high radiative recombination and excellent stability. However, seldom attention has been placed on their self-stability/working operation under ambient storage. Herein, quasi-2D perovskites/Polyethylene oxide (PEO) films are studied, showing an unforeseen photo-brightening effect under ambient storage (i.e., an increase of the photoluminescence quantum yield from 55% to 74% after 100 days). In stark contrast, those stored under a dark/inert atmosphere show a significant decrease down to 38%. This counterintuitive phenomenon responds to the increasing radiative recombination rate caused by the passivation of the surface Br vacancies in the presence of physically adsorbed water molecules, as corroborated by in situ/ex situ X-ray photoelectron spectroscopy and density functional theory calculations. Capitalizing on this surprising effect, stable light-emitting diodes (LEDs) using quasi-2D perovskites/PEO color filters are fabricated, realizing high stabilities of ≈400 h@10 mA under operating ambient conditions, representing a 20-fold enhancement compared to LEDs with 3D counter partners. Hence, this study reveals a unique insight into the impact of water passivation on the optical/structural properties of quasi-2D perovskite films, broadening their applications under operating ambient conditions.Y.D. thanks the financial support from the China Scholarship Council (CSC, no. 201808440326). Financial support has been received from AEI-MINECO/FEDER, UE through the Nympha Project (PID2019-106315RB-I00), the regional government of "Comunidad de Madrid" and the European Structural Funds through FotoArt-CM Project (S2018/NMT-4367). F.O. acknowledges funding from the Marie Skłodowska-Curie grant agreement no 754382. M.U.K. and G.N. thank ELI-ALPS, which is supported by the European Union and co-financed by the European Regional Development Fund (GI-NOP-2.3.6-15-2015-00001). This publication has also received funding from PANOSC, the European Union's Horizon 2020 research and innovation programme under grant agreement no 823852. M.U.K. and G.N. also acknowledge Project no. 2019-2.1.13-TÉT-IN-2020-00059 which has been implemented with the support provided from the National Research, Development and Innovation Fund of Hungary, financed under the 2019-2.1.13-TÉT-IN funding scheme. O.A.R. has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 899987. R.D.C. and L.M.C. acknowledge the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 956923

Bringing Earth-Abundant Plasmonic Catalysis to Light : Gram-Scale Mechanochemical Synthesis and Tuning of Activity by Dual Excitation of Antenna and Reactor Sites

The localized surface plasmon resonance (LSPR) excitation in plasmonic nanoparticles (NPs) in the visible and near-infrared ranges is currently at the forefront of improving photocatalytic performances via plasmonic photocatalysis. One bottleneck of this field is that the NPs that often display the best optical properties in the visible and near-infrared ranges are based on expensive noble metals such as silver (Ag) and gold (Au). While earth-abundant plasmonic materials have been proposed together with catalytic metals in antenna-reactor systems, their performances remain limited by their optical properties. Importantly, the synthesis of plasmonic photocatalysts remains challenging in terms of scalability while often requiring several steps, high temperatures, and special conditions. Herein, we address these challenges by developing a one-pot, gram-scale, room-temperature synthesis of earth-abundant plasmonic photocatalysts while improving their activities beyond what has been dictated by the LSPR excitation of the plasmonic component. We describe the mechanochemical synthesis of earth-abundant plasmonic photocatalysts by using MoO3 (antenna) and Au (reactor) NPs as a proof-of-concept example and demonstrate that the dual plasmonic excitation of antenna and reactor sites enables the tuning of plasmonic photocatalytic performances toward the reductive coupling of nitrobenzene to azobenzene as a model reaction. In addition to providing a pathway to the facile and gramscale synthesis of plasmonic photocatalysts, the results reported herein may open pathways to improved activities in plasmonic catalysis.Peer reviewe

An Fe stabilized metallic phase of NiS2 for the highly efficient oxygen evolution reaction.

This work reports a fundamental study on the relationship of the electronic structure, catalytic activity and surface reconstruction process of Fe doped NiS2 (FexNi1-xS2) for the oxygen evolution reaction (OER). A combined photoemission and X-ray absorption spectroscopic study reveals that Fe doping introduces more occupied Fe 3d6 states at the top of the valence band and thereby induces a metallic phase. Meanwhile, Fe doping also significantly increases the OER activity and results in much better stability with the optimum found for Fe0.1Ni0.9S2. More importantly, we performed detailed characterization to track the evolution of the structure and composition of the catalysts after different cycles of OER testing. Our results further confirmed that the catalysts gradually transform into amorphous (oxy)hydroxides which are the actual active species for the OER. However, a fast phase transformation in NiS2 is accompanied by a decrease of OER activity, because of the formation of a thick insulating NiOOH layer limiting electron transfer. On the other hand, Fe doping retards the process of transformation, because of a shorter Fe-S bond length (2.259 Å) than Ni-S (2.400 Å), explaining the better electrochemical stability of Fe0.1Ni0.9S2. These results suggest that the formation of a thin surface layer of NiFe (oxy)hydroxide as an active OER catalyst and the remaining Fe0.1Ni0.9S2 as a conductive core for fast electron transfer is the base for the high OER activity of FexNi1-xS2. Our work provides important insight and design principle for metal chalcogenides as highly active OER catalysts

Thermally Induced Oxygen Vacancies in BiOCl Nanosheets and Their Impact on Photoelectrochemical Performance**

Oxygen vacancies (OVs) have been reported to significantly alter the photocatalytic properties of BiOCl nanosheets. However, their formation mechanism and their role in the enhancement of photoelectrochemical performance remain unclear. In this work, thermally induced oxygen vacancies are introduced in BiOCl nanosheets by annealing in He atmosphere at various temperatures and their formation mechanism is investigated by in‐situ diffuse reflectance infrared (DRIFTS) measurements. The influence of OVs on band offset, carrier concentrations and photoelectrochemical performance are systematically studied. The results show that (1) the surface of BiOCl nanosheets is extremely sensitive to temperature and defects are formed at temperatures as low as 200 °C in inert atmosphere. (2) The formation of surface and bulk OVs in BiOCl is identified by a combination of XPS, in‐situ DRIFTS, and EPR experiments. (3) The photocurrent of BiOCl is limited by the concentration of charge carriers and shallow defect states induced by bulk oxygen vacancies, while the modulation of these parameters can effectively increase light absorption and carrier concentration leading to an enhancement of photoelectrochemical performance of BiOCl

Highly Active and Stable Ni/La-Doped Ceria Material for Catalytic CO2Reduction by Reverse Water-Gas Shift Reaction

[EN] The design of an active, effective, and economically viable catalyst for CO2 conversion into value-added products is crucial in the fight against global warming and energy demand. We have developed very efficient catalysts for reverse water-gas shift (rWGS) reaction. Specific conditions of the synthesis by combustion allow the obtention of macroporous materials based on nanosized Ni particles supported on a mixed oxide of high purity and crystallinity. Here, we show that Ni/La-doped CeO2 catalysts─with the "right"Ni and La proportions─have an unprecedented catalytic performance per unit mass of catalyst for the rWGS reaction as the first step toward CO2 valorization. Correlations between physicochemical properties and catalytic activity, obtained using a combination of different techniques such as X-ray and neutron powder diffraction, Raman spectroscopy, in situ near ambient pressure X-ray photoelectron spectroscopy, electron microscopy, and catalytic testing, point out to optimum values for the Ni loading and the La proportion. Density functional theory calculations of elementary steps of the reaction on model Ni/ceria catalysts aid toward the microscopic understanding of the nature of the active sites. This finding offers a fundamental basis for developing economical catalysts that can be effectively used for CO2 reduction with hydrogen. A catalyst based on Ni0.07/(Ce0.9La0.1Ox)0.93 shows a CO production of 58 × 10-5 molCO·gcat-1·s-1 (700 °C, H2/CO2 = 2; selectivity to CO > 99.5), being stable for 100 h under continuous reaction.We acknowledge the financial support of the Spanish Ministry of Science and Innovation (PID2021-123287OB-I00, PID2021-122477-OB-I00, PID2021-128915NB-I00, and RTI2018-101604-B-I00) and of the CSIC through the i-LINK 2021 program (LINKA20408). Financial support has also been received from AEI-MINECO/FEDER (Nympha Project, PID2019-106315RB-I00), “Comunidad de Madrid” regional government, and the European Structural Funds (FotoArt-CM project, S2018/NMT-4367). Authors also acknowledge financial support from the grant PLEC2021-007906 funded by MCIN/AEI/10.13039/501100011033 and the “European Union NextGenerationEU/PRTR”. We are grateful to ILL (France) for making all facilities available. This project also received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 832121. Computer time provided by the RES (Red Española de Supercomputación) resources at the MareNostrum 4 (BSC, Barcelona) node and the DECI resources at the BEM cluster of the WCSS based in Poland with the support from PRACE aislb is acknowledged

A critical evaluation of the mode of incorporation of nitrogen in doped anatase photocatalysts

A range of sol-gel synthesis conditions were used to prepare high surface area N-doped TiO(2) in the anatase phase. The N dopant was derived either from NH(3) in solution or from NH(3) gas bubbled through solution. Bulk N doping levels were determined by an inert gas fusion method and were compared with surface N doping levels determined by X-ray photoelectron spectroscopy. Comparison was also made with the concentration of paramagnetic species measured by electron spin resonance spectroscopy. It was found that both surface and bulk doping levels were typically around 3 orders of magnitude higher than the concentration of paramagnetic N-containing species. All N-doped samples showed higher visible region (lambda > 395 nm) photocatalytic activity than undoped anatase itself. It is argued that catalytic activity is associated with the presence of nitrogen bound to lattice oxygen to give (NO)'O which can be photoexcited to give (NO)(O)(X)

Influence of polyvinylpyrrolidone as stabilizing agent on Pt nanoparticles in Pt/H-BEA catalyzed hydroconversion of n-hexadecane

Colloidal Pt particles prepared using polyvinylpyrrolidone (PVP) as a capping agent were loaded on acidic Beta zeolite, with the aim of obtaining bifunctional catalysts with controllable dispersion for the hydroconversion of n-hexadecane (n-C16). Among the different approaches to remove PVP, reduction was the most effective whilst maintaining the initial Pt particle size after deposition on the zeolite. The presence of small amounts of nitrogen- and carbon-containing products from PVP decomposition affected the acidity stronger than the Pt metal function. Therefore, it was not possible to establish the effect of Pt particle size on the performance of the Pt/Beta zeolites in n-C16 hydroconversion and the performance trends were dominated by the acidity differences. Small Pt particles on zeolite obtained by using high PVP/Pt ratios during the colloidal synthesis step presented lower Brønsted acidity than catalysts containing larger Pt particles. The resulting variations in Pt/H+ ratios led to a transition of observed ideal cracking behavior for weakly acidic catalysts (small Pt particles, larger amount of PVP residuals) to overcracking behavior for catalysts with stronger acidity. We find that the Pt/H+ ratio and the number of acid-catalyzed steps extrapolated to zero conversion are better indicators of ideal cracking behavior than the isomers yield

Improved Methane Production by Photocatalytic CO2 Conversion over Ag/In2O3/TiO2 Heterojunctions

In this work, the role of In2O3 in a heterojunction with TiO2 is studied as a way of increasing the photocatalytic activity for gas-phase CO2 reduction using water as the electron donor and UV irradiation. Depending on the nature of the employed In2O3, different behaviors appear. Thus, with the high crystallite sizes of commercial In2O3, the activity is improved with respect to TiO2, with modest improvements in the selectivity to methane. On the other hand, when In2O3 obtained in the laboratory, with low crystallite size, is employed, there is a further change in selectivity toward CH4, even if the total conversion is lower than that obtained with TiO2. The selectivity improvement in the heterojunctions is attributed to an enhancement in the charge transfer and separation with the presence of In2O3, more pronounced when smaller particles are used as in the case of laboratory-made In2O3, as confirmed by time-resolved fluorescence measurements. Ternary systems formed by these heterojunctions with silver nanoparticles reflect a drastic change in selectivity toward methane, confirming the role of silver as an electron collector that favors the charge transfer to the reaction medium.This research was funded by the European Union’s Horizon 2020 research and innovation program under the European Research Council (ERC) through the HyMAP project, grant agreement No. 648319. Additional funding by the Spanish MCIN/AEI/10.13039/501100011033/FEDER through the Nympha Project (PID2019-106315RB-I00), the regional government of “Comunidad de Madrid” and the European Structural Funds through FotoArt-CM program (S2018/NMT-4367), and Fundación Ramón Areces through the ArtLeaf project is gratefully acknowledged.Peer reviewe