Well-defined hybrid Copper-based nanoreactors for electrocatalytic CO2 reduction

In the perspective of drastically reducing anthropogenic CO2 emissions and mitigating the effects of global warming, the electrochemical CO2 reduction reaction (CO2RR) powered by renewable sources and catalyzed by transition metal-based catalysts represents an attractive strategy to produce fuels and commodity chemicals. However, further improvement in the catalyst design is required to tackle the main bottlenecks that currently limit the performances of the state-of-the-art catalysts. Although several transition metal-based systems have been reported to catalyze CO2RR, catalyst durability and selectivity still represent major challenges to achieve an efficient CO2RR, mainly due to catalyst deactivation and to competitive Hydrogen evolution reaction (HER) and/or alternative pathways leading to multiple carbon-based products. The combination of molecular chemistry and heterogeneous catalysis has recently revealed to be an effective strategy to improve the overall efficiency and selectivity of the CO2RR process. In particular, the formation of hybrid catalysts based on the integration of organic molecules or reticular frameworks with heterogeneous metal or metal-oxide surfaces allowed to tune the stability of key reaction intermediates or the local microenvironment of the catalyst, resulting in a significant improvement of the CO2RR performances. In this contribution, we highlight a modular and versatile strategy to synthesize well-defined hybrid nanomaterials, based on the in situ growth of polymeric matrices around a well-defined metal nanoparticle core in a controlled manner. For instance, well-defined Cu2O nanocubes (NCs) are used as both templates and catalysts for an in situ polymerization based on a Cu-catalyzed azide–alkyne cycloaddition reaction (CuAAC) in the presence of the corresponding monomeric building blocks. This approach results in a series of hybrid nanoreactors with well-defined shape and size, which are active electrocatalysts for CO2 reduction in neutral-pH electrolyte. The composition of the molecular layer was found to be critical for the catalytic performances. The data herein presented provide a proof-of-concept of the potential offered by a molecular perspective towards a rational design of heterogeneous electrocatalysts

Laying the Foundations for a Human-Predator Conflict Solution: Assessing the Impact of Bonelli's Eagle on Rabbits and Partridges

BACKGROUND: Predation may potentially lead to negative effects on both prey (directly via predators) and predators (indirectly via human persecution). Predation pressure studies are, therefore, of major interest in the fields of theoretical knowledge and conservation of prey or predator species, with wide ramifications and profound implications in human-wildlife conflicts. However, detailed works on this issue in highly valuable--in conservation terms--Mediterranean ecosystems are virtually absent. This paper explores the predator-hunting conflict by examining a paradigmatic, Mediterranean-wide (endangered) predator-two prey (small game) system. METHODOLOGY/PRINCIPAL FINDINGS: We estimated the predation impact ('kill rate' and 'predation rate', i.e., number of prey and proportion of the prey population eaten, respectively) of Bonelli's eagle Aquila fasciata on rabbit Oryctolagus cuniculus and red-legged partridge Alectoris rufa populations in two seasons (the eagle's breeding and non-breeding periods, 100 days each) in SE Spain. The mean estimated kill rate by the seven eagle reproductive units in the study area was c. 304 rabbits and c. 262 partridges in the breeding season, and c. 237 rabbits and c. 121 partridges in the non-breeding period. This resulted in very low predation rates (range: 0.3-2.5%) for both prey and seasons. CONCLUSIONS/SIGNIFICANCE: The potential role of Bonelli's eagles as a limiting factor for rabbits and partridges at the population scale was very poor. The conflict between game profitability and conservation interest of either prey or predators is apparently very localised, and eagles, quarry species and game interests seem compatible in most of the study area. Currently, both the persecution and negative perception of Bonelli's eagle (the 'partridge-eating eagle' in Spanish) have a null theoretical basis in most of this area

Applications of Carbon Dots for the Photocatalytic and Electrocatalytic Reduction of CO2

The photocatalytic and electrocatalytic conversion of CO2 has the potential to provide valuable products, such as chemicals or fuels of interest, at low cost while maintaining a circular carbon cycle. In this context, carbon dots possess optical and electrochemical properties that make them suitable candidates to participate in the reaction, either as a single component or forming part of more elaborate catalytic systems. In this review, we describe several strategies where the carbon dots participate, both with amorphous and graphitic structures, in the photocatalysis or electrochemical catalysis of CO2 to provide different carbon-containing products of interest. The role of the carbon dots is analyzed as a function of their redox and light absorption characteristics and their complementarity with other known catalytic systems. Moreover, detailed information about synthetic procedures is also reviewed

Copper-based hybrid nanomaterials for the electrocatalytic reduction of CO2

Global warming, worldwide energy crisis and the issues related to increasing levels of carbon dioxide (CO2) have prompted the research of new catalysts to transform CO2 back to fuels and value-added chemicals [1]. Copper (Cu)-based nanocatalysts have attracted increasing interest in CO2 reduction over the last decades, due to their unique capability to promote an electrochemical reduction of CO2 into multicarbon C2+ products. Nevertheless, an efficient Cu-catalyst is required to face the typical high overpotentials required for the process and the low selectivity, which results in obtaining a mixture of several products (C1-C3) [2]. Combining molecular with heterogeneous chemistry has revealed to be an efficient approach to improve the efficiency of the CO2RR processes [3]. In fact, the formation of hybrid materials combining heterogeneous Cu-based nanoreactors with organic or metal-organic frameworks allowed to tune stability of key reaction intermediates, enhancing selectivity towards some specific product [4]. In this work, we developed hybrid molecular-heterogeneous Cu-based nanomaterials for CO2RR, with the aim of tunning the selectivity of the nanostructured Cu catalysts by combining them with a purely organic molecularly defined polymer. The design of these systems is based on a novel strategy, whereby cuprous oxide (Cu2O) nanoparticles with a well-defined cubic geometry are used as both, templates and catalyst, for an in-situ polymerization reaction based on azide-alkyne ‘’click’’ reaction between the molecular building blocks. The catalytic performances of the hybrid nanomaterials were tested in a H-type electrochemical cell setup with an online gas-chromatographic quantification analysis (NMR was used for the liquid quantification analysis) and found to be efficient electrocatalysts for CO2RR obtaining a mixture of C1-C2 gaseous products (primarily CO, C2H4, CH4 in addition to H2) and C1-C3 liquids products (primarily C2H6O and CHOO-) in neutral pH electrolyte

FROM MOLECULES TO NANOSTRUCTURED MATERIALS: NOVEL OPPORTUNITIES FOR ELECTROCATALYTIC CO2 REDUCTION

The electrocatalytic CO2 reduction reaction (CO2RR) powered by renewable energy and promoted by transition metal catalysts, will play an important role in the global decarbonization process of the chemical industry, since represents a sustainable route for the production of value-added chemicals using CO2 as a feedstock. [1]-[2] However, despite the significant progress made in the field, selectivity, durability and intrinsic activity of the catalysts are still key challenges to achieve an efficient CO2RR. For organometallic molecular systems, characterized by a well-defined chemical environment of the active site, a rational tuning of the CO2RR efficiency and selectivity can be precisely controlled through a rational modification of the ligand scaffold. [3]-[5] Moreover, the encapsulation of molecularly defined active units into reticular frameworks was recently shown as an effective strategy to boost the CO2RR performances of molecular catalysts, but also to alter their redox behavior. [6] In recent years, the synergy between molecules and nanostructured materials has been proposed as a promising approach to design efficient heterogeneous catalysts for CO2 electroreduction. For instance, the presence of organic modifiers on metallic surfaces was found to tune the stability of key reaction intermediates or the local surface microenvironment, thus altering the product selectivity. [7]-[8] In this contribution, we will discuss novel strategies and approaches to form hybrid electrocatalysts based on the utilization of reticular or molecular chemistry as tools to steer the CO2RR selectivity and activity of transition metal-based nanostructured catalysts. The discussion will focus on providing a molecular perspective towards a rational design of heterogeneous catalysts

Ru(II)-phthalocyanine sensitized solar cells: the influence of co-adsorbents upon interfacial electron transfer kinetics

The development of efficient red sensitizer dyes is essential for the optimization of dye-sensitized photoelectrochemical solar cells. Ru-phthalocyanines are good candidates because they show high absorbance in the red while their axial ligands hinder the formation of aggregates, a recurrent problem among phthalocyanine dyes. In this paper, we present the photophysics and photovoltaic device performance for a series of novel Ru-phthalocyanines. We focus in particular upon the origin of the enhancement in device performance observed in the presence of two additives, Li+ and chenodeoxycholic acid. The addition of Li+ lowers the conduction band edge of the TiO2 semiconductor leading to a higher electron injection yield and a higher photocurrent in the device. The increases in injection yield and photocurrent are large for these sensitizers, compared to the widely studied ruthenium bipyridyl dye N719, due to the relatively slow injection dynamics, emphasizing the importance of injection yield in limiting device performance for this Ru-phthalocyanine dye series. Of particular interest is the effect of chenodeoxycholic acid. This coadsorbent dramatically enhances the photocurrent of the studied devices without lowering the photovoltage. Unlike previous studies, in this case the photocurrent rise can not be attributed to an increment in the electron injection yield due to the effect of the coadsorbent hindering the formation of dye aggregates. Photophysical measurements instead show that the slower recombination of dye cations with the TiO2 electrons and faster regeneration of the dye cations by the electrolyte are the reasons for the enhanced photocurrent.Depto. de Química en Ciencias FarmacéuticasFac. de FarmaciaTRUEpu

Slow Electron Injection on Ru−Phthalocyanine Sensitized TiO2

Photoinduced electron injection in dye sensitized TiO2 is a critical step in the function of dye sensitized solar cells. High electron injection quantum yields are a requirement to obtain efficient devices. While high electron injection quantum yields are usually linked to ultrafast electron-transfer dynamics (in the fs−ps timescales), the latter are not a requirement. We present here a system, Ru-phthalocyanine sensitized TiO2, where slow electron injection (kinj ≈ 450 ns-1) and efficient electron injection are compatible owing to the long lifetime of the injecting state, the Ru-phthalocyanine triplet state. Ru-phthalocyanine dyes are attractive sensitizers because they absorb strongly in the red and their axial ligands hinder the formation of aggregates.European ComissionMinisterio de Educación, Cultura y Deporte (España)Comunidad de MadridDepto. de Química en Ciencias FarmacéuticasFac. de FarmaciaTRUEpu

Catalysis of Recombination and Its Limitation on Open Circuit Voltage for Dye Sensitized Photovoltaic Cells Using Phthalocyanine Dyes

In order to increase the energy efficiency of dye-sensitized solar cells beyond 10%, an improved dye needs to be developed with greater light absorption in the red and near-infrared. Many dyes have been tested for this purpose; however, no dye with significant absorption beyond 750 nm has functioned properly. We have examined a series of ruthenium phthalocyanines, a dye class with large and tunable absorption in the red. For these dyes we observe a large reduction in the output voltage of the cells relative to the benchmark dye (N719). By examination of photovoltage transients and charge density measurements, we demonstrate that this reduction in voltage is caused by a 100-fold increase in the rate constant for recombination (iodine reduction) at the TiO2/electrolyte interface. N719, however, does not seem to catalyze this reaction. By examination of the literature, we propose that catalysis of the recombination reaction may be occurring for many other classes of potentially useful dyes including porphyrins, coumarins, perylenes, cyanines, merocyanines, and azulene. This widespread ability of the dye to catalyze recombination has not been appreciated before. This finding has important implications for future work to improve the red response of dye sensitized photovoltaics.Engineering and Physical Sciences Research Council (Reino Unido)Ministerio de Educación, Cultura y Deporte (España)European CommissionMinisterio de Ciencia, Innovación y Universidades (España)Comunidad de MadridDepto. de Química en Ciencias FarmacéuticasFac. de FarmaciaTRUEpu