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The study of the electrochemical CO2 reduction to obtain formate (HCOO–) or formic acid (HCOOH) is receiving much attention as a promising technology. Since continuous–mode operation has become necessary for practical implementation of electrochemical CO2 reduction, recent years have seen a rapid increase in the number of research approaches focusing on this aspect. This Focus Review provides a unified discussion of the available studies on the continuous electroreduction of CO2 to HCOO–/HCOOH, considering the different important features of process design. Moreover, this paper quantitatively assesses the performance of different studies that involve continuous electrochemical reactors for converting CO2 to HCOOH/HCOO–, comparing relevant typically used figures of merit, including energy consumption. Although some relevant trade-offs have already been achieved, the simultaneous optimization of all the figures of merit remains a challenge. Finally, concluding remarks highlight the detected trends and discuss relevant aspects that will have to be tackled by future studies in this field. The authors acknowledge the financial support from the Spanish State Research Agency (AEI) through the projects PID2019-108136RB-C31 and PID2020-112845RB-I00 (MCIN/AEI/10.13039/501100011033).

CO2 electroreduction has been considered a promising alternative to simultaneously reduce CO2 emissions and produce value-added products. Among others, the production of formic acid/formate is particularly attractive. Although promising results have already been obtained in the literature, one of the recent approaches to improve the process deals with the use of an alternative reaction at the anode instead of the traditional oxygen evolution reaction (OER). In this context, this work reports, for the first time, the study of the CO2 electroreduction to formate coupled with the electrooxidation of glycerol to high-added value products where both half-reactions operate in a continuous mode with a single pass of the reactants through the electrochemical cell. Interestingly, at the cathode, similar results to those previously reported were obtained, reaching formate concentrations of about 18 g·L-1 at a 200 mA·cm-2. In addition, at the anode, promising dihydroxyacetone productions of 196 µmol·m-2·s-1 were simultaneously achieved in the output stream of the anodic compartment. These findings represent a significant step forward for the development and application of the technology. The authors gratefully acknowledge financial support through projects PID2019–108136RB-C31, PID2019–108136RB-C32 and PID2020–112845RB-I00 (AEI/10.13039/501100011033).

A series of CuBi catalysts were prepared with different Bi loadings and tested for the electrochemical reduction of CO2 (ERCO2). The developed catalysts were tested on a filter-press cell, and the influence of the catholyte on the catalytic performance was assessed. Catalyst #20C was found to be very selective for formate production, with a faradaic efficiency (FE) of 86.4 %, when Cl– ions are present in the catholyte solution. The presence of weak CO2 adsorption sites on the catalyst surface favors the formation of non-coordinated and monodentate carbonates after CO2 adsorption, resulting in enhanced formate formation through an outer-sphere mechanism. For catalyst #50C, an unprecedented propane selectivity was recorded (FE of 85.4 %), being the first high-efficiency catalyst for the ERCO2 to propane ever reported. This remarkable catalytic behavior was attributed to strong CO2 adsorption sites on the catalyst surface and higher CO2 and CO adsorption capacity. It is also proposed that a bidentate carbonate is a key intermediate for the ERCO2 to propane, which is preferably formed when strong Lewis acid and base sites are present on the catalyst surface. C. Azenha is grateful to the Portuguese Foundation for Science and Technology (FCT) for the doctoral grant (reference SFRH/BD/128768/2017). This work was financially supported by: LA/P/0045/2020 (ALiCE), UIDB/00511/2020 and UIDP/00511/2020 (LEPABE), funded by national funds through FCT/MCTES (PIDDAC); and was performed under the project “SunStorage - Harvesting and storage of solar energy”, POCI-01-0145-FEDER-016387, funded by FEDER funds through COMPETE2020 – Programa Operacional Competitividade e Internacionalização (POCI) and by national funds (PIDDAC) through FCT/MCTES

CO2 electroreduction to formic acid and formate has been focus of great research attention in the last years. Thus, considerable and relevant efforts have been accomplished in this field, mainly by operating with different types of catalysts and electrode configurations in the cathodic compartment. Still, Pt-based anodes, which are expensive and scarce, are typically the preferred materials to carry out the oxygen evolution reaction in alkaline medium. However, it is crucial to search for new materials of lower prices, with high stability, and good performances able to be competitive with traditional Pt-based electrodes. Hence, we study hand-made NiO-based anodes for the continuous CO2 electroreduction for formate in a filter press reactor with a single pass of the reactants through the electrochemical reactor. The use of the NiO-based anodes enhances the results obtained in previous studies with DSA/O2 anodes, combining excellent values of Faradaic Efficiency for formate of 100 %, and energy consumptions values close to only 200 kWh·kmol-1. In addition, employing Sustainion® as a binder in the fabrication of the anode results in a significant improvement in the durability, maintaining similar performance in terms of key metrics. Authors fully acknowledge the financial support received from the Spanish State Research Agency (AEI) through the projects PID2019-108136RB-C31 and PID2020-112845RB-I00 (AEI/10.13039/501100011033). We are also grateful for the Bi carbon-supported nanoparticles prepared and provided by the group of Prof. V. Montiel and Dr. José Solla-Gullón from the Institute of Electrochemistry of the University of Alicante. Guillermo Díaz-Sainz would like to thank the Academic Planning and Teaching Staff Vice-chancellorship of University de Cantabria and the Young Chemical Researchers Group, belonging to the Royal Spanish Society of Chemistry (JIQ-RSEQ) for financial help to carry out the research stay at the Faculty of Engineering of the University of Porto in which the present work was developed.

Tin oxide nanoparticles (SnO2 NPs) as electrocatalyst for the production of formate from CO2 reduction reaction (CO2RR). We synthesize, characterize and evaluate high surface area SnO2 NPs (2.4 nm and 299 m2 g-1 in diameter size and surface area, respectively), for the continuous production of formate at high current density within a flow electrolyzer. SnO2 NPs under Ar and CO2 reduction conditions were studied by cyclic voltammetry. SnO2-based gas diffusion electrodes (SnO2-GDEs) were manufactured to perform continuous CO2RR. A maximum formate concentration value of 27 g L-1 was achieved with a Faradaic efficiency (FE) of 44.9 % at 300 mA cm-2, which was significantly stable and reproducible when operated up to 10 h. Nevertheless, ohmic drop contribution due to the semiconducting properties of SnO2 was not negligible. The low total FE (< 60 %) of products pointed out a leakage of formate by crossover migration through the membrane from the catholyte towards the anolyte. The authors gratefully acknowledge the financial sources from the Spanish Ministry of Economy and Competitiveness (MINECO), through the project CTQ2016-76231-C2-1-R (AEI/FEDER, UE). Moreover, I.M.- G. and C.M. S.-S would like to thank the MINECO for the postdoctoral period in Paris of the predoctoral research contract (BES-2014-070081) and J. A. for the Ramón y Cajal programme (RYC-2015-17080), respectively. L.T. and O.D. acknowledge the support of French governmental funds managed by the ANR within the Investissements d’Avenir programme under reference ANR-11-IDEX-0004-02, and more specifically within the framework of the Cluster of Excellence MATISSE led by Sorbonne Universit´e. Dr. G. Gouget is strongly acknowledge for HR-TEM images.

A highly efficient copper-catalyst (noble-metal free) was developed for the electrochemical reduction of CO2 (ERCO2) to methanol. Due to the nanowire structure of the catalyst, a remarkable ERCO2 selectivity was achieved, while the competing H2 evolution reaction (HER) was significantly suppressed for the overall range of potential tested. The developed copper-catalyst (CuO NWs) outperforms the single metal Cu-catalysts in aqueous environment. Under atmospheric conditions, methanol was produced at an overpotential of 410 mV with a faradaic efficiency (FE) of 66%, and 1.27 × 10−4 mol m−2 s−1 of production yield; which represents a 6.7% improvement over the previously reported value of 1.19 × 10−4 mol m−2 s−1. Interestingly, when the developed CuO NWs was used as a gas diffusion electrode (GDE) in a filter-press cell (more real industrial configuration), methanol remained as the major ERCO2 product with the same FE (66%). Azenha, C., is grateful to the Portuguese Foundation for Science and Technology (FCT) for the doctoral grant (refer- ence SFRH/BD/128768/2017 ). This work was performed under the project “SunStorage - Harvesting and storage of solar energy”, with reference POCI-01-0145-FEDER-016387, funded by European Regional Development Fund (ERDF), through COMPETE 2020 - Operational Programme for Competitiveness and internationalisation (OPCI), and by national funds, through FCT - Fundação para a Ciência e a Tecnologia I.P. The authors are thankful to POCI-01- 0145-FEDER-006939 (Laboratory for Process Engineering, Environ- ment, Biotechnology and Energy – UID/EQU/00511/2013) funded by the European Regional Development Fund (ERDF), through COM- PETE2020 - Programa Operacional Competitividade e Internacional- ização (POCI) and by national funds, through FCT - Fundação para a Ciência e a Tecnologia and NORTE-01-0145-FEDER-0 0 0 0 05 –LEPABE-2-ECO-INNOVATION, supported by North Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement, through the European Regional Develop- ment Fund (ERDF).

It is widely known that the Learning-by-Doing (LbD) pedagogical tool is not the most common form of education in Chemical Engineering nowadays. The aim of this work is to describe the application of LbD considering as case of study the participation of undergraduate students from the Chemical Engineering Degree of the University of Cantabria (UC) from Spain in the Chem-E-Car Competition® in the 10th World Congress of Chemical Engineering (WCCE10). The Chem-E-Car Competition® is a world-known student event run by AIChE, which provides chemical engineering undergraduate students with the opportunity to participate in a team-oriented hands-on design and construction of a small prototype car powered by a chemical reaction. Within the context of the WCCE10, the competition gathered 18 teams from different countries all around the world. The UC team ended in the 6th position and won the award to the best inherent safety design. Overall, the benefits outpaced the time cost both for students and the teaching staff. This situation was not clear at the beginning of the project. Prior to this competition, LbD was used as an innovative pedagogical tool for the requested acquisition of competences. The proposal of a multi-annual Final Degree Programme was a win–win situation for all the stakeholders. From a teaching point of view, the LbD let transferable and core competences to be evaluated not only internally, but also externally thanks to the competition. A survey was completed among the students that participated in the project. Competences such as “Problem-solving” and “Adaptation to new situations” were pointed out as those which were developed in a higher level by the students.

The carbon dioxide (CO2) electroreduction to formate is nowadays considered as a promising approach to convert CO2 into a value-added product and simultaneously, in the context of strategies for mitigating climate change. However, there is a scarce number of studies published in the literature operating with a current density higher than 200 mA cm- 2 , and there is the need of operating at higher current densities, with acceptable performance and low penalty in terms of energy consumption, for future implementation at industrial scale. Thus, in this work, a novel configuration is studied using a filter press reactor in a continuous mode, with a single pass of the reactants through the cell, employing a Sustainion anion exchange membrane and working with a current density up to 600 mA cm-2 . Using the same electrocatalysts, the configuration shows a similar performance to the GDE configuration with liquid electrolyte, but with the advantage of operating only with a vapour input to the cathode and avoiding the need for a liquid catholyte. Although at the expense of obtaining a more diluted product, excellent combinations of Faradaic Efficiency for formate (73.7 %), energy consumptions (342 kWh-kmol-1), and product rates (22.9 mmol m- 2 -s -1) can be achieved at high current densities. Therefore, the configuration with Sustainion membranes reported in this manuscript can be particularly interesting for future applications that do not involve a very concentrated formate product. Authors fully acknowledge the financial support received from the Spanish State Research Agency (AEI) through the projects PID2019-108136RB-C31 (AEI/10.13039/501100011033) and PID2020-112845RB-I00 (AEI/10.13039/501100011033). We are also grateful for the nanoparticles prepared and provided by the group of Prof. V. Montiel and Dr. José Solla-Gullón from the Institute of Electrochemistry of the University of Alicante. The authors also thank BioRender.com online software as this science illustration tool has allowed to create some of the figures of this manuscript.

The use of bismuth‐based catalysts is promising for formate production by the electroreduction of CO2 captured from waste streams. However, compared to the extensive research on catalysts, only a few studies have focused on electrochemical reactor performance. Hence, this work studied a continuous‐mode gas–liquid–solid reaction system for investigating CO2 electroreduction to formate using Bi‐catalyst‐coated membrane electrodes as cathodes. The experimental setup was designed to analyze products obtained in both liquid and gas phases. The influence of relevant variables (e.g., temperature and input water flow) was analyzed, with the thickness of the liquid film formed over the cathode surface being a key parameter affecting system performance. Promising results, including a high formate concentration of 34 g/L with faradaic efficiency for formate of 72%, were achieved. The authors of this work would like to acknowledge the financial support from the MINECO through the projects CTQ2016-76231-C2-1-R and CTQ2016-76231-C2-2-R (AEI/FEDER, UE). JSG acknowledges financial support from VITC (Vicerrectorado de Investigación y Transferencia de Conocimiento) of the University of Alicante (UTALENTO16-02).

The electrochemical conversion of CO2 is gaining increasing attention because it could be considered as an appealing strategy for making value-added products at mild conditions from CO2 captured. In this work, we report a process for the electrocatalytic reduction of CO2 to formate (HCOO-) operating in a continuous way, employing a single pass of the reactants through the electrochemical reactor and using Bi carbon supported nanoparticles in the form of a membrane electrode assembly composed by a Gas Diffusion Electrode, a current collector and a cationic exchange membrane. This contribution presents the best trade-off between HCOO- concentration, Faradaic Efficiency and energy consumption in the literature. We also show noteworthy values of energy consumption required of only 180 kWh·kmol-1 of HCOO-, lower than previous approaches, working at current densities that allow achieving formate concentration higher than 300 g·L-1 and simultaneously, a Faradaic Efficiency close to 90%. The results here displayed make the electrochemical approach closer for future implementation at the industrial scale. The authors of this work would like to acknowledge to the financial support from the MINECO, through the projects CTQ2016-76231-C2-1-R and CTQ2016-76231-C2-2-R (AEI/FEDER, UE). J.S.G acknowledges financial support from VITC (Vicerrectorado de Investigación y Transferencia de Conocimiento) of the University of Alicante (UTALENTO16-02). G.D.S, M.A.G and A.I filed a patent application on the experimental reaction system discussed here.

Electrocatalytic reduction of CO2 has been taken into consideration as a fascinating option to store energy from intermittent renewable sources in the form of chemical value-added products. Among the different value-added products, formic acid or formate is particularly attractive since it can be used as a fuel for low-temperature fuel-cells and as a renewable hydrogen carrier. Very recently, a rapidly increasing number of studies have revealed Bi as a promising electrocatalytic material for the CO2 electroreduction to formate, but the performance of Bi electrodes operating in a continuous mode and high current density (j) has been hardly investigated yet. Thus, this work aims at studying the CO2 electroreduction to formate working in a continuous mode in a filter-press-reactor at a j up to 300 mA·cm−2 using Bi electrodes. Bismuth Gas Diffusion Electrodes (Bi-GDEs) were fabricated from carbon-supported Bismuth-nanoparticles. The influence of j and the electrolyte flow/area ratio in the performance of the Bi-GDEs towards formate were evaluated. Working at j of 300 mA·cm−2, a concentration of 5.2 g formate·L−1 with a faradaic efficiency (FE) and rate of 70% and 11 mmol·m−2·s−1, respectively were achieved. Lowering the j to 90 mA·cm−2, formate concentrations of up to 7.5 g·L−1 could be obtained with an excellent FE of 90%. Interestingly, the highest concentration of formate obtained was 18 g·L−1, but at expenses of an important decrease in FE. Although the results of this study are interesting and promising, further research is required to increase formate concentration for a future implementation at industrial scale. The authors of this work would like to show their gratitude to the financial support from the MINECO, through the projects CTQ2016-76231-C2-1-R and CTQ2016-76231-C2-2-R (AEI/FEDER, UE). Jose Solla-Gullón also acknowledges the financial support from VITC of the University of Alicante (UTALENTO16-02).

The electrochemical valorisation of captured CO2 is an attractive option to obtain value-added products, and at the same time, to chemically store energy from intermittent renewable sources. Among the different products, formic acid/formate is particularly interesting since it is one of the most promising materials for hydrogen storage and candidate fuel for low-temperature fuel cells. In this work, a process for CO2 electroreduction to formate is studied on a continuous filter-press cell using an innovative electrode: Sn Catalyst Coated Membrane Electrodes (Sn-CCMEs) - comparing with previous approaches based on Sn Gas Diffusion Electrodes (Sn-GDEs), using the same synthesised tin nanoparticles (Sn NPs) and operating conditions. The Sn-CCME is prepared by depositing Sn NPs directly over a Nafion 117 membrane, and it allows working with a gaseous CO2 flow humidified with water as the input of the electrochemical cell, avoiding the use of the liquid catholyte. Sn-CCME operates at lower current densities (45 mA cm-2) than previous Sn-GDEs (200 mA cm-2), which resulted in lower rates of formate production. However, the proposed Sn-CCME, allowed achieving even higher formate concentrations with an energy consumption 50% lower than with the Sn-GDEs. The influence of key variables such as temperature and water input flow on the performance of the process using Sn-CCMEs was also analysed in a controlled experimental set-up specifically designed and built for this goal. Increasing the temperature of the gaseous stream did not improve the performance. The best results were obtained at ambient conditions of temperature (20 °C) and with the amount of water in the CO2 stream at 0.5 g h-1, giving the highest formate concentration (19.2 g L-1) with a Faradaic efficiency close to 50% and an energy consumption of 244 kW h kmol-1. More research is still required to further improve CCME configuration in order to increase formate rate and efficiency without increasing energy consumption. This work was conducted under the framework of the Spanish Ministry of Economy, Industry and Competitiveness (MINECO), projects CTQ2016-76231-C2-1-R (AEI/FEDER, UE) and CTQ2016-76231-C2-2-R (AEI/FEDER, UE). JSG acknowledges financial support from VITC (Vicerrectorado de Investigación y Transferencia de Conocimiento) of the University of Alicante (UTALENTO16-02).

Climate change mitigation requires the development of new processes to reduce the amount of carbon dioxide in the atmosphere. The products of CO2 utilization can supplement or replace chemical feedstocks, fine chemicals, pharmaceutical, and polymers. Carbon capture and utilization based on innovative electroreduction processes is one of the suggested routes to reduce the use of coal and oil as carbon sources due to the recycling of carbon. Some chemicals may be produced using carbon dioxide, decreasing the use of natural resources. The electrocatalytic processes to obtain formate and methanol as derived products from CO2 are discussed in this chapter, taking into account the electro-catalysts and the reactor design in the development of innovative processes.

Various strategies have been proposed to date in order to mitigate the concentration of CO2 in the atmosphere, such as the separation, storage, and utilization of this gas. Among the available technologies, the electrochemical valorisation of CO2 appears to be an innovative technology, in which electrical energy is supplied to establish a potential between two electrodes, allowing CO2 to be transformed into value-added chemicals under mild conditions. It provides a method to recycle CO2 (in a carbon neutral cycle) and, at the same time, a way to chemically store the excess of renewable energy from intermittent sources, thus reducing our dependence on fossil fuels. Among the useful products that can be obtained, methanol is particularly interesting as a platform chemical, and it has gained renewed and growing attention in the research community. Accomplishments to date in the electroreduction of CO2 to methanol have been encouraging, although substantial advances are still needed for it to become a profitable technology able to shift society to renewable energy sources. This review presents a unified discussion of the significant work that has been published in the field of electrocatalytic reduction of CO2 to methanol. It emphasizes the aspects related to process design at different levels: cathode materials, reaction media, design of electrochemical cells, as well as working conditions. It then extends the discussion to the important conclusions from different electrocatalytic routes, and recommendations for future directions to develop a catalytic system that will convert CO2 to methanol at high process efficiencies.

BACKGROUND The valorization of CO2 into added-value products appears to be a promising strategy for reducing CO2 emissions. Dimethyl carbonate (DMC) is an environmentally friendly valuable product, with multiple applications, suggested as a potential gasoline additive. However, DMC has traditionally been produced from hazardous phosgene and CO routes, which encourages the interest in developing new processes. The purpose of this work is to study the influence of the membrane in a filter-press electrochemical cell for the valorization of CO2 by the electrosynthesis of DMC from methanol in the presence of the ionic liquid [bmim][Br] and CH3OK and avoiding the addition of carcinogens. RESULTS The performance of the process has been studied using six different anion exchange membranes in comparison with an undivided configuration and our previous study using a cationic exchange membrane. A significant increase in the initial reaction rate is achieved when no membrane is employed. Regardless of which membrane is used, an additional resistance seems to be introduced. A final concentration of 85 mmol L−1 was obtained up to 48 h without membrane, which is a 6-fold increase over our previous work. CONCLUSIONS Although better results were obtained when no membrane was used, study of the divided cell has provided experimental evidence that can serve as a reference for the evaluation of future improvements in this electrosynthesis. © 2014 Society of Chemical Industry

Electrochemical valorization may be a strategy for mitigating climate change, as the process allows for CO2 to be converted into industrially useful chemicals. The aim of this work is to study the influence of key variables on the performance of an experimental system for continuous electroreduction of CO2 to formate with a gas diffusion electrode (GDE) loaded with Sn. A 23 factorial design of experiments at different levels of current density (j), electrolyte flow rate/electrode area ratio (Q/A ratio) and GDE Sn load was followed. Higher rates and concentrations (i.e., 1.4·10−3 mol m−2 s−1 and 1348 mg L−1 with efficiencies of approximately 70%) were obtained with GDEs than with plate electrodes. The statistical design of experiments demonstrated that the Sn load had the most significant effect on rate and efficiency. However, despite these promising results, further research is required to optimize the process. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3557–3564, 2014

BACKGROUND The electrochemical valorization of CO2 into added-value products appears a promising strategy for reducing CO2 emissions and mitigating climate change. Dimethyl carbonate (DMC) is an environmentally friendly valuable chemical, with multiple applications, and has been suggested as a potential gasoline additive. However, DMC has traditionally been produced from hazardous phosgene and CO routes, which encourages the interest in developing new processes. The aim of this work is to study the valorization process for the direct electrosynthesis of DMC from CO2 and methanol using CH3OK and the ionic liquid 1-butyl-3-methylimidazolium bromide, avoiding the addition of carcinogenic compounds. RESULTS The evolution of the concentration of DMC was studied in a filter-press electrochemical cell with anodic and cathodic compartments separated by a Nafion 117 membrane, operating for 48 h. A final DMC concentration of 15.07 mmol L−1 was observed. Analysis of the by-products obtained in the process revealed the formation of tetramethyl orthocarbonate and dimethoxymethane, which were detected and quantified in the liquid phase. A simplified reaction scheme was also proposed based on the results obtained. CONCLUSION Unlike all previous work that used an undivided cell, the new experimental results of this study using a divided cell can serve as a reference for further research to overcome current limitations. © 2014 Society of Chemical Industry

Robert Hamers replied: One can think of water as being like an amorphous semiconductor, in that there are strong interactions between adjacent atoms but there is no long-range order. J.V. Coe published several important papers in which he describes the water conduction band. Terminology is important, as one can refer to an optical conduction band and an adiabatic conduction band. The optical conduction band is determined by nding the position of the valence band relative to vacuum, and then using the optical bandgap (onset of optical absorption) to dene the position of the conduction band. For our purposes, the more important denition is that of the adiabatic conduction band, which is essentially determined by the electron affinity level of the water. That is, it refers to a state in which there is an excess electron, but the water molecules have not yet polarized around it to form a solvated electron. In this limit, the electron is essentially a plane wave and water behaves like a continuum dielectric, with the electron stabilized with respect to vacuum by ~0.1 V due to the long-range polarization forces that the electron exerts. A key aspect of the ‘adiabatic conduction band’ is that it has been used to explain how electrons created in water (usually created by high-energy ionizing radiation) are able to travel signicant distances in water before the water nally polarizes around them to form solvated electrons, which then have much lower mobility. In our studies, the conduction band may be important in establishing how far the solvated electrons are located away from the electrode surface. If they enter the water with ~1 eV of kinetic energy (roughly the energy difference between the conduction band of diamond and the conduction band of water), then they may be able to travel some

Electrochemical reduction of CO2 has been pointed out as an interesting strategy to convert CO2 into useful chemicals. In addition, coupling CO2 electroreduction with renewable energies would allow storing electricity from intermittent renewable sources such as wind or solar power. In this work, an easy and fast method is adapted for the synthesis of pure and carbon supported Sn nanoparticles. The resulting nanoparticles have been characterized by transmission electron microscopy and their electrocatalytic properties towards CO2 reduction evaluated by cyclic voltammetry. Carbon supported Sn nanoparticles have been subsequently used to prepare Gas Diffusion Electrodes (Sn/C-GDEs). The electrodes have been characterized by scanning electron microscopy and also by cyclic voltammetry. Finally, the electrodes were tested on a continuous and single pass CO2 electroreduction filter-press type cell system in aqueous solution, to obtain formate at ambient pressure and temperature. These Sn/C-GDEs allow working at high current densities with low catholyte flow. Thus, for instance, at 150 mA cm−2, a 70% Faradaic Efficiency (FE) was obtained with a formate concentration of 2.5 g L−1. Interestingly, by increasing the current density to 200 mA cm−2 and decreasing the flow rate, a concentration over 16 g L−1 was reached. Despite the high concentrations obtained, further research is still required to keep high FE operating at high current densities. This work was conducted under the framework of the Spanish Ministry of Economy and Competitiveness projects CTQ2013-48280-C3-1-R and CTQ2013-48280-C3-3-R. Andrés Del Castillo also acknowledges the research grant from University of Cantabria, co-financed by the Regional Government of Cantabria.

Life cycle assessment (LCA) has been used at an early design stage to evaluate the environmental sustainability of a novel process for synthesizing dimethyl carbonate (DMC) from waste CO2. The process involves an electrochemical reaction of CO2 and methanol in the presence of potassium methoxide and the ionic liquid 1-butyl-3-methylimidazolium bromide to produce DMC. Experimental data and process simulation have been combined to estimate the environmental impacts and compare them to the conventional commercial "Eni" process based on oxidative carbonylation of methanol. Eleven environmental impact categories have been assessed from "cradle to gate", including global warming potential (GWP), toxicity potentials, and resource depletion. For example, GWP of DMC produced in the electrochemical process ranges from 63.3 to 94.5 kg CO2 eq./kg DMC, depending on a process configuration. This is around 25 times higher than GWP of the commercial process estimated in this study at 3.2 kg CO2 eq./kg DMC. This is because of the low conversion achieved in the current design of the electrochemical process (0.7%), requiring high energy consumption in the separation process. The results suggest that the process yield must be increased to at least 20% to reduce the GWP to a level comparable with the commercial process. At this yield, the electrochemical process also becomes more sustainable than the commercial system for most other impacts considered. The study demonstrates how LCA can play a key role in the development of environmentally more sustainable processes during design by combining experimental data and process simulation at an early stage of technology development. This work was funded by the Spanish Ministry of Economy and Competitiveness (MINECO) project CTQ2013-48280-C3-1-R and by the UK Engineering and Physical Sciences Research Council under the 4CU Programme Grant (EP/K001329/1). The authors are grateful for this funding. I.G.-H. would also like to acknowledge the FPI postgraduate research grant (BES-2011-047906) and thank A. Dominguez-Ramos and M. Margallo for their inestimable help.

Among the different strategies for CO 2 emissions reduction and climate change mitigation that are being considered, valorisation of CO 2 appears as a more interesting option than carbon storage, since it allows the recycling of CO 2 into added-value products. The purpose of this work is to study the influence of key variables on the performance of an experimental system for continuous electro-reduction of CO 2 to formate in aqueous solutions under ambient conditions, using a filter-press electrochemical reactor with a lead plate as cathode. A 2 2 factorial design of experiments at different levels of current density (“ j ”) and electrolyte flow rate/electrode area ratio (“ Q / A ratio”) was followed by additional tests at the mean level of each variable. The obtained results confirmed general suggested trends in previous works, but they also offered a detailed analysis of the influence of these variables. Regarding j , it should be emphasised that a significant increase of the rate of formate production was observed at the expense of lowering the Faradaic efficiency when increasing j up to a limit value of 10.5 mA cm −2 , where a Faradaic efficiency of 57% was maintained. The influence of Q / A turned out to be more limited than that of j , since the results revealed that increasing the catholyte flow to overcome mass transport limitations only had beneficial effects for the lowest Q / A ratios (i.e. ⩽0.76 mL min −1 cm −2 ). This study is a reference for the evaluation of future improvements in the development of these continuous electro-reduction processes for CO 2 valorisation, derived from further research to overcome current limitations.

Decision-making for sediment management is a complex task that requires the consideration of temporal and spatial impacts of several remedial alternatives as well as the associated economic, social and political impact. Multicriteria decision analysis (MCDA) is becoming increasingly recognized as an important environmental management tool that can be used to support the selection of suitable remediation alternatives and prioritization of management units in space and time. This paper proposes an MCDA framework for prioritizing sediment management alternatives. This framework involves identifying of a set of feasible options, as well as defining and evaluating criteria which integrate relevant technical, economic, social and environmental aspects of remedies. The methodology allows an explicit consideration of uncertainty in criteria scores and weights by assigning probability distributions and analyzing subsequent Monte-Carlo simulations. The consideration of different stakeholder simulated values is used to assess the robustness of alternative rankings and to guide the selection of remediation options. An application of this methodology to a case study in the Bay of Santander, Spain, is presented. An assessment is conducted for the case of unknown preferences as well as for hypothetical preferences profiles for four types of stakeholders: Idealist, Politician, Environmentalist and Balanced. The results are used to visualize stakeholder positions and potential disagreements, allowing for the identification of a group of least preferred alternatives for each stakeholder. Stakeholder involvement has the potential to ease the remedy selection process during all stages of the decision-making process and to eventually remedy implementation.

The application of mathematical tools can be necessary to provide an integrated analysis and interpretation of the abundant information that can be collected in air quality monitoring networks. This article develops a methodology based on the use of Self-Organizing Map (SOM) artificial neural networks for integrating data about multiple measured pollutants to group monitoring stations according to their similar air quality. The proposed method considers the subsequent geographical mapping of the clusters of stations observed with the SOM, which can make it possible to detect geographically different areas but that share similar air pollution problems. This methodology is illustrated with its application to a case study in which 517 stations of the Spanish air quality monitoring network were classified considering simultaneously their levels of regulated pollutants in 2005, highlighting some implications of data normalization in the process. In particular, the use of legal limit values to normalize the concentrations of pollutants proved to be especially advisable. Results obtained with the SOM-based methodology, when compared to classifications based directly on legislation, provided more useful classifications for further air quality management actions, and revealed that these types of tools can facilitate the design of air pollution reduction programs by discovering different areas with similar problems. © 2010 American Institute of Chemical Engineers Environ Prog, 2011.

Decision-making for sediment management is a complex task that incorporates the selections of areas for remediation and the assessment of options for any mitigation required. The application of Multicriteria Analysis (MCA) to rank different areas, according to their need for sediment management, provides a great opportunity for prioritisation, a first step in an integrated methodology that finally aims to assess and select suitable alternatives for managing the identified priority sites. This paper develops a methodology that starts with the delimitation of management units within areas of study, followed by the application of MCA methods that allows ranking of these management units, according to their need for remediation. This proposed process considers not only scientific evidence on sediment quality, but also other relevant aspects such as social and economic criteria associated with such decisions. This methodology is illustrated with its application to the case study area of the Bay of Santander, in northern Spain, highlighting some of the implications of utilising different MCA methods in the process. It also uses site-specific data to assess the subjectivity in the decision-making process, mainly reflected through the assignment of the criteria weights and uncertainties in the criteria scores. Analysis of the sensitivity of the results to these factors is used as a way to assess the stability and robustness of the ranking as a first step of the sediment management decision-making process. Keywords: Sediment, Management, Multicriteria Analysis, Site prioritisation

The application of mathematical tools in initial steps of sediment quality assessment frameworks can be useful to provide an integrated interpretation of multiple measured variables. This study reveals that the Self-Organizing Map (SOM) artificial neural network can be an effective tool for the integration of multiple physical, chemical and ecotoxicological variables in order to classify different sites under study according to their similar sediment quality. Sediment samples from 40 sites of 3 estuaries of Cantabria (Spain) were classified with respect to 13 physical, chemical and toxicological variables using the SOM. Results obtained with the SOM, when compared to those of traditional multivariate statistical techniques commonly used in the field of sediment quality (principal component analysis (PCA) and hierarchical cluster analysis (HCA)), provided a more useful classification for further assessment steps. Especially, the powerful visualization tools of the SOM, which offer more information and in an easier way than HCA and PCA, facilitate the task of establishing an order of priority between the distinguished groups of sites depending on their need for further investigations or remediation actions in subsequent management steps. Keywords: Sediment, Quality assessment, Self-Organizing Map, Multivariate statistical techniques

Ionic Liquid-based Aqueous Two Phase Systems (ILATPS) are an innovative technique to separate biomolecules that combines the advantages of liquid–liquid extraction and hydrophilic ionic liquids. Most ILATPS are based on ionic liquids and conventional inorganic salts, and the phase envelope, described by the binodal curve, is usually modeled by empirical equations that are used to determine the phase compositions and assess the ionic liquid recyclability. However, these empirical equations may provide a poor extrapolation ability or low accuracy at the extreme regions of the binodal curve or suffer from problems of convergence. Therefore, the aim of this work is the analysis of the binodal curve equations, comparing the models reported in the literature to describe ILATPS and proposing alternative equations to improve accuracy or to reduce the mathematical complexity. For this purpose, a database compiling binodal experimental data of 100 ILATPS has been built, so that the analysis could make it possible to obtain representative conclusions for all these systems. Several models were developed, and different statistical criteria were used to assess the advantages and disadvantages of each one of these models for the binodal curve. The results show that, when accuracy is critical, a proposed model with just an additional parameter reduced more than 25% the residual mean squared error (RMSE) with respect to the commonly used equation, without losing the statistical significance of the parameters. For complex problems where an explicit equation in both the concentration of ionic liquid and of salt is needed, the use of an explicit model developed with 3 adjusted parameters that kept high accuracy (R2 > 0.996 and RMSE < 0.66) is proposed. Finally, the analysis also revealed that a fitting method based on the minimization of relative errors is recommended to increase the accuracy of the binodal curve at high salt concentrations, which is the crucial region for assessing the recyclability of the ionic liquid. This work was developed in the scope of the project CICECO Aveiro Institute of Materials (Ref. FCT UID/CTM/50011/2013), financed by national funds through the FCT/MEC and co-financed by FEDER under the PT2020 Partnership Agreement. The authors also acknowledge FCT for the Post-doctoral grant SFRH/BPD/79263/2011 of S.P.M. Ventura.

Members of the INTERSED network initiated several efforts to coordinate management activities, information, priorities and approaches in research and technological development (RTD) with respect to sediments at a national level in Spain. The present work summarizes the results of a database search (1995–2005) carried out within the INTERSED framework; we found 250 international and national publications of Spanish groups related to the study of sediments located in the Spanish coast and river basins using different approaches. The results show the statistics of RTD groups involved, the main objectives of the publications, the types of sediment and their location, and the analytical method and parameters. We describe the state of the art on the field of research in sediments at the national level in Spain over a period of 10 years.

The development of electrochemical processes for the conversion of CO2 into value-added products allows innovative carbon capture & utilization (CCU) instead of carbon capture & storage (CCS). In addition, coupling this conversion with renewable energy sources would make it possible to chemically store electricity from these intermittent renewable sources. The electroreduction of CO2 to formate in aqueous solution has been performed using Sn particles deposited over a carbon support. The effect of the particle size and Sn metal loading has been evaluated using cyclic voltammetry and chronoamperometry. The selected electrode has been tested on an experimental filter-press type cell system for continuous and single pass CO2 electroreduction to obtain formate as main product at ambient pressure and temperature. Experimental results show that using electrodes with 0.75 mg Sn cm−2, 150 nm Sn particles, and working at a current density of 90 mA cm−2, it is possible to achieve rates of formate production over 3.2 mmol m−2 s−1 and faradaic efficiencies around 70% for 90 min of continuous operation. These experimental conditions allow formate concentrations of about 1.5 g L−1 to be obtained on a continuous mode and with a single pass of catholyte through the cell. This work was conducted under the framework of the Spanish Ministry of Science and Innovation Projects ENE2010-14828 and Spanish Ministry of Economy Competitiveness CTQ2013-48280-C3-1-R and CTQ2013-48280-C3-3-R. Andrés Del Castillo also acknowledges the research grant from University of Cantabria, co-financed by the Regional Government of Cantabria.

Various strategies have been proposed to date in order to mitigate the concentration of CO2 in the atmosphere, such as the separation, storage, and utilization of this gas. Among the available technologies, the electrochemical valorisation of CO2 appears to be an innovative technology, in which electrical energy is supplied to establish a potential between two electrodes, allowing CO2 to be transformed into value-added chemicals under mild conditions. It provides a method to recycle CO2 (in a carbon neutral cycle) and, at the same time, a way to chemically store the excess of renewable energy from intermittent sources, thus reducing our dependence on fossil fuels. Among the useful products that can be obtained, methanol is particularly interesting as a platform chemical, and it has gained renewed and growing attention in the research community. Accomplishments to date in the electroreduction of CO2 to methanol have been encouraging, although substantial advances are still needed for it to become a profitable technology able to shift society to renewable energy sources. This review presents a unified discussion of the significant work that has been published in the field of electrocatalytic reduction of CO2 to methanol. It emphasizes the aspects related to process design at different levels: cathode materials, reaction media, design of electrochemical cells, as well as working conditions. It then extends the discussion to the important conclusions from different electrocatalytic routes, and recommendations for future directions to develop a catalytic system that will convert CO2 to methanol at high process efficiencies.

The development of electrochemical processes for using captured CO2 in the production of valuable compounds appears as an attractive alternative to recycle CO2 and, at the same time, to store electricity from intermittent renewable sources. Among the different innovative attempts that are being investigated to improve these processes, the application of ionic liquids (ILs) has received growing attention in recent years. This paper presents a unified discussion of the significant work that involves the utilisation of ILs for the valorisation of CO2 by means of electrochemical routes. We discuss studies in which CO2 is used as one of the reactants to electrosynthesise value-added products, among which dimethyl carbonate has been the focus of particular attention in the literature. Approaches based on the electrochemical reduction of CO2 to convert it into products without the use of other carbon-based reactants are also reviewed, highlighting the remarkable improvements that the use of ILs has allowed in the CO2 electroreduction to CO. The review emphasises on different aspects related to process design, including the nature of IL anions and cations that have been used, the working conditions, the electrocatalytic materials, the electrode configurations, or the design of electrochemical cells, as well as discussing the most relevant observations, results and figures of merit that the participation of ILs has allowed to achieve in these processes. Several conclusions are finally proposed to highlight crucial challenges and recommendations for future research in this area. The financial support from the Spanish Ministry of Economy and Competitiveness Project CTQ2013-48280-C3-1-R is gratefully acknowledged. J. Albo particularly thanks Juan de la Cierva program (JCI-2012-12073).

Richard McCreery opened the discussion of the paper by Robert Dryfe: You stated that Ru(hexamine) shows a depression of the outer sphere ET rate, on graphene, possibly due to the proximity of its redox potential to the Dirac point. If so, then other redox systems with different Es should show an increasing kinetic trend as the potential moves from the Dirac point. Has anyone observed such a trend?

International audience; Discussion between experts about carbon material.

Electrochemical reduction has been pointed out as a promising method for CO2valorisation into useful chemicals. This paper studies the influence of key variables on the performance of an experimental system for continuous electro-reduction of CO2 to formate, when a tin plate is used as working electrode. Particular emphasis is placed on comparing the performance of Sn and Pb as cathodes. As was previously found with Pb, the influence of current density (“j”) using Sn was particularly noteworthy, and when j was raised up to a limit value of 8.5 mA cm−2, important increases of the rate of formate production were observed at the expense of lowering the Faradaic efficiency. However, unlike what was found with Pb, the performance using Sn improved when the electrolyte flow rate/electrode area ratio was increased within the range studied (0.57–2.3 mL min−1 cm−2). In this way, the use of Sn as cathode allowed achieving rates of formate production that were 25% higher than the maximum rates obtained with Pb, together with Faradaic efficiencies close to 70%, which were 15 points higher than those with Pb. These results reinforce the interest in Sn as electrode material in the electro-reduction of CO2 to formate. This work was conducted under the framework of the Spanish Ministry of Science and Innovation Project ENE2010-14828.

There is strong interest in developing tools to link chemical concentrations of contaminants to the potential for observing sediment toxicity that can be used in initial screening-level sediment quality assessments. This paper presents new approaches for predicting toxicity in sediments, based on 10-day survival tests with marine amphipods, from sediment chemistry, by means of the application of Partial Least Squares-Discriminant Analysis (PLS-DA) and Counter-propagation Artificial Neural Networks (CP-ANNs) to large historical databases of chemical and toxicity data. The exploration of the internal structure of the developed models revealed inherent limitations of predicting toxicity from common chemical analyses of bulk contaminant concentrations. However, the results obtained in the validation of these models combined relevant values of non-error classification rate, sensitivity and specificity of, respectively, 76, 87 and 73% with PLS-DA and 92, 75 and 97% with CP-ANNs, outperforming the results reported for previous approaches. © 2009 Elsevier Ltd. All rights reserved.

Sediments can act as sinks of multiple chemicals that accumulate over time and could represent a potentially significant hazard to the ecosystem and human health. The assessment of sediment quality, which is a complex task, usually involves, in its initial steps, the measurement of sediment contamination, followed by tests for assessing toxicity. This work presents a chemometric approach to tackle the challenging issue of linking concentrations of chemicals to the potential for observing toxicity in sediments. Various methods were applied to large databases of field-collected chemical and biological effects data, including linear and quadratic discriminant analysis (LDA and QDA), partial least squares-discriminant analysis (PLS-DA), extended canonical variates analysis (ECVA), classification and regression trees (CART) and counter-propagation artificial neural networks (CP-ANN). LDA, QDA, PLS-DA and ECVA showed very similar and satisfactory performances, but the best results were obtained with CP-ANNs and CART. In any case, the developed models for predicting toxicity improved the classification performance compared to previous approaches, giving non-error rates (NERs) in the range of 76.0-97.4. Moreover, the exploration of the internal structure of the models, jointly with the application of variable selection techniques, allowed the study of the importance of the 16 chemical contaminants considered, emphasizing Cu, followed by Zn, as the most discriminating variables for predicting toxicity in the developed models. Copyright © 2009 John Wiley & Sons, Ltd.

Sediments are an essential component of aquatic ecosystems that must be assessed and managed properly. The use of quantitative environmental quality standards derived from consideration of sediment quality guidelines (SQGs) can be effective as part of a tiered risk assessment approach. In Part I of this 2-part paper addressing sediment quality assessment and dredged material management in Spain, different SQG methods are used to evaluate sediment quality in the Bay of Santander, located in the Cantabric Sea along the northern coast of Spain, and to guide development of empirically derived SQGs for marine sediments. The results of the study indicate a great heterogeneity of SQGs, both with regard to the numeric values for a particular chemical and the number of substances for which SQGs have been derived. The analysis highlights the scarce development of empirical SQGs for priority substances identified in current European Union water policy. Nonetheless, the application of SQGs makes it possible to classify different zones of sediment quality in the Bay of Santander. Part II of this 2-part paper considers the environmental impacts of dredged material disposal. Legislation and criteria used to regulate dredged material disposal at sea in different European countries are reviewed, and action levels derived by different countries were used to evaluate management of dredged sediments from Cadiz Bay, located on the South Atlantic coast of Spain.

Δημοσίευση σε επιστημονικό περιοδικό Summarization: The use of Vibrio fischeri as luminescence bacteria is particularly effective in evaluating contaminated sediment. In this study, the ecotoxicity of five core sediments from the Bay of Santander, northern Spain, utilising V. fischeri as marine bacterium, was carried out. Different toxicity assay procedures were applied in order to study the influence of the mobility and bioavailability of the pollutants. Basic Solid Phase Test (BSPT) in whole sediment and acute toxicity test, using pore water and three leaching test procedures as liquid extracts, were applied. In addition, the study of the influence of the pH value on the toxicity results of the leaching tests was conducted. The obtained results show toxicity units (TU50) values in BSPT test ranging from 0.42 to 39.06 with a decrease with depth as general trend and TU50 values from 0.010 to 0.389 in the liquid extracts, where TU50 is calculated as the inverse of EC50 (%). The obtained data show the historical toxicity trends of the Bay of Santander and provides a technical database for the management of contaminated sediments. Moreover, these results showed evidence that each sediment test procedure provided independent and complementary ecotoxicological responses useful for a sediment classification. In order to analyse the correlations between chemical parameters (both organic and inorganic) and the toxicity results, the self-organising map (SOM) neural network and regression equations were applied. Satisfactory correlations (R=0.93) between chemical concentrations of sum of five heavy metals and 16 PAHs and BSPT toxicity were obtained. Presented on: Environmental Research

Ionic liquids have attracted a lot of attention as potential replacements for conventional volatile organic solvents, although they may pose environmental risks to aquatic ecosystems that have to be assessed. There is strong interest in developing mathematical models to estimate the ecotoxicity of ionic liquids, minimising the experimental investigations and the consequent consumption of time and resources. This paper presents a new approach for estimating the ecotoxicity of ILs, based on the standardised assay with the bacterium Vibrio fischeri, by means of the application of Partial Least Squares-Discriminant Analysis (PLS-DA). The PLS-DA model developed makes it possible to discriminate ionic liquids, formed by combinations of 30 anions and 64 cations, on the basis of their expected toxicity with respect to conventional solvents that they may replace. The successful results obtained in the validation of the model reveal that this approach can be useful as a screening tool to easily aid, from the early stages of the process, the design of aquatic environmentally friendly ionic liquids. This approach may also be useful for the further development of predictive models based on other aquatic organisms, for which more data are expected to be available in the near future.

When sediments are removed from aquatic bottoms, they turn into dredged material that must be managed, taking into account its environmental impact. In Part II of this 2-part paper addressing sediment quality assessment and dredged material management in Spain, legislation and criteria used to regulate dredged material disposal at sea in different European countries are reviewed, as are action levels (ALs) derived by different countries used to evaluate management of dredged sediments from Cádiz Bay located on the South Atlantic coast of Spain. Comparison of ALs established for dredged material disposal by different countries reveals orders of magnitude differences in the values established for the same chemical. In Part I of this 2-part paper, review of different sediment quality guideline (SQG) methods used to support sediment quality assessments indicated a great heterogeneity of SQGs, both with regard to the numeric values for a particular chemical and the number of substances for which SQGs have been derived. The analysis highlighted the absence of SQGs for priority substances identified in current European Union water policy. Here, in Part II, the ALs are applied to dredged sediments from Cádiz Bay (South Atlantic coast of Spain), evidencing that the heterogeneity of ALs implemented in the reviewed countries could determine different management strategies. The application of other measurements such as bioassays might offer information useful in identifying a cost-effective management option in a decision-making framework, especially for dredged material with intermediate chemical concentrations.