Browsing by Author "Pardal, T."
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- Conversion of carbon dioxide into fuel by electrochemical reduction in aqueous solventsPublication . Pardal, T.; Fernandes, T. R. C.; Machado, Ana; Rangel, C. M.he mission of Omnidea, a Portuguese SME is to perform leading edge R&D in innovative energy concepts. In collaboration with Research Institutes Omnidea is developing a technology based upon a regenerative energy storage cycle. In this cycle the recharge system converts CO2 into hydrocarbons using a renewable source of power. The discharge system produces electrical energy when hydrocarbons and oxygen from the recharge system are directly supplied to a device such as a Solid Oxide Fuel Cell (SOFC). This work focuses on the challenges involved in the task of bringing this technology closer to the market. A key feature of this technology is the use of copper which is known to have unique properties for converting CO2 electrochemically into hydrocarbons. The modification of copper electrodes with copper deposits to improve the catalytic activity and selectivity of the cathodes in the production of hydrocarbons in aqueous solvents is also described.
- Electrochemical CO2 reduction at room temperature and mild pressuresPublication . Messias, Sofia; Sousa, Miguel M.; Ponte, Manuel Nunes; Rangel, C. M.; Pardal, T.; Machado, AnaABSTRACT: Carbon capture and utilization technologies (CCU) and electrolytic hydrogen production are closely interconnected technologies and necessary for a sustainable energy system. This work describes the development of a process for room temperature co-electrolysis of CO2 and water to produce syngas, at mild pressures. The influence of several parameters in the performance of the process is reported.
- Electrochemical production of syngas from CO2 at pressures up to 30 bar in electrolytes containing ionic liquidPublication . Messias, Sofia; Sousa, Miguel M.; Ponte, Manuel Nunes; Rangel, C. M.; Pardal, T.; Machado, AnaABSTRACT: Electrochemical CO2 reduction in a reactor that can operate up to 100 bar and 80 degrees C, with a configuration similar to that of an alkaline electrolyser, for hydrogen production suitable to be used industrially is reported for the first time. The effect of pressure on the co-electrolysis of CO2 and water was studied. The successful scale-up from a previously reported batch process to electrodes of ca. 30 cm(2) geometrical area (30-fold factor) that combines the use of pressure and an ionic liquid-based electrolyte is presented. Also for the first time, the potential of the system under study to achieve high conversions of CO2 to avoid a purification step of syngas from unreacted CO2 is shown. An inexpensive commercial foil of the common metal zinc was employed. A semi-continuous operation yielded syngas productivities in the range of 0.02-0.04 mmol cm(-2) h(-1) at ca. -1.2 V vs. QRE Ag/Ag+. When an electrolyte consisting of 90 wt% H2O and 10 wt% 1-ethyl-3-methylimidazolium trifluoromethanesulfonate was used, selectivities for CO in the range of 62% to 72% were obtained at 10 bar pressure, whereas selectivities of 82% were obtained at 30 bar pressure. H-2/CO ratios in the range of 1/1 to 4/1 at 10 bar pressure suitable for the synthesis of a variety of fuels, such as hydrocarbons, methanol, methane and chemical building blocks, were observed. An energy efficiency of 44.6% was calculated for a H-2/CO ratio of 2.2 suitable for the synthesis of methanol.
- Modified electrodes for electrochemical reduction of carbon dioxidePublication . Machado, Ana; Fernandes, T. R. C.; Pardal, T.; Rangel, C. M.The efforts to constrain greenhouse gas emissions and concerns over security of fossil fuels have led to increased attention for renewable energy for the past decade. Renewable energy is one of the key solutions to the actual energy challenges. Omnidea in collaboration with Research Institutes is developing a technology based upon a regenerative energy storage cycle that could be a contribution to a low-carbon energy future. In this cycle the recharge system, which is composed of an electrochemical cell, converts CO2 into fuel (hydrocarbons and hydrogen) using an external source of power (e.g. solar power). The discharge system produces electric energy when hydrocarbons and oxygen from the recharge system are directly supplied to a Solid Oxide Fuel Cell (SOFC). Currently state of the art systems for direct electrochemical reduction of CO2 exhibit low current densities and or low Faradaic efficiencies. Thus considerable research activity is still needed to develop electrodes with a performance suitable for an industrial application. This paper describes the progress to date and the work carried out with the aim of achieving this goal. It addresses particularly the modification of electrodes for electrochemical conversion of CO2 and reports voltammetric studies as a tool for screening and optimizing electrodes for CO2 conversion
- Pressurized electrochemical process for syngas production [Resumo]Publication . Messias, Sofia; Sousa, Miguel M.; Rangel, C. M.; Pardal, T.; Ponte, Manuel Nunes; Machado, AnaABSTRACT: Carbon Capture and Utilisation (CCU) comprise technologies that capture carbon dioxide and convert it into chemical products, such as fuels, chemicals and building materials that can replace the same products derived from fossil resources. These technologies can thus contribute to reach the ambitious 2030 targets set by the European Union for decarbonisation of the economy of 40% CO2 reduction, introduction of 27% renewable energies in the energy mix and 27% energy efficiency. CCU technologies are at different stages of maturity and some are already commercially deployed. One of these commercial technologies is the production of methanol by CO2 hydrogenation at high temperature using hydrogen produced by water electrolysis. Another CCU technology that is still at laboratory stage is electrochemical CO2 reduction. In this process carbon dioxide is co-electrolyzed with water near room temperature. Hydrogen is produced in situ. Depending on process conditions and catalysts CO2 reduction originates a series of products, such as CO, formic acid, hydrocarbons, alcohols etc. at the cathode. Oxygen is produced at the anode resulting from water oxidation reaction. Figure 1 illustrates the process. Electrochemical CO2 reduction presents several technological challenges that have not been surpassed yet, such as low CO2 conversions, poor stability of electrodes and low energy efficiencies. This work reports not yet published results of the development of a pressurized electrochemical process for producing syngas (CO + H2) by electrochemical reduction of carbon dioxide. Green syngas produced using renewable energy can be an important platform for introducing renewable energy in the chemical industry. The development of a process that works at pressures higher then atmospheric pressure seems promising to circumvent the aforementioned challenges, namely low conversions and low energy efficiencies.
- Scale-up of a system for hydrocarbon production by electrochemical reduction of CO2Publication . Fernandes, T. R. C.; Machado, Ana; Condeço, J.; Rangel, C. M.; Pardal, T.This work addresses the scaling up of a system for electrochemical reduction of CO2 to produce hydrocarbons that can be used as fuel for a regenerative energy storage cycle. Challenges involved in such a task are mentioned. Scalingup results of a system based on electrodes of high surface area with modified copper deposits are described. Current densities around 100 mA/cm2 were obtained. This corresponds to the current density threshold that enables technological applications. At potentials as negative as -1.6 V it was observed that CO2 reduction still dominated over hydrogen evolution reaction.
- Structural features of electrodeposited copper electrodes for CO2 conversionPublication . Machado, Ana; Fernandes, T. R. C.; Pardal, T.; Rangel, C. M.Direct electrochemical reduction of CO2 is a process that could contribute to the reduction of the emission of greenhouse gases by using CO2 as a raw material for fuel production. This paper focuses on voltammetric studies of functionalized electrodes for the electrochemical conversion of CO2 and reports on its use as a tool for electrode screening and optimization. Nickel substrates modified with copper and ruthenium/copper electrodeposits were studied. Voltammetric experiments indicate that CO2 electroreduction follows a nickel type mechanism in which this electrochemical reaction occurs simultaneously and in competition with hydrogen evolution. A significant inhibition of hydrogen evolution reaction is observed in nickel modified electrodes. Inhibition characteristics and the onset of carbon dioxide conversion are dependent of the type of electrode functionalization. Voltammetry is thus a powerful tool to evaluate electrode modifications and for tuning electrodes for an optimized electrocatalytic performance.