Electrocatalytic Conversion of CO2 to Syngas

Technologies for the capture and subsequent conversion of CO2 into useful products have received significant attention in recent years. Among the conversion technologies available today, the electroreduction of CO2 is particularly interesting because of three main reasons. Firstly, it can be carried out at room temperature and with high efficiency. Secondly, it can make use of renewable electricity and lastly the extent of the reduction process can be modulated to produce a wide variety of interesting chemicals, with syngas (i.e. a mixture of H2 and CO with high chemical value) being particularly relevant. This chapter summarizes the most important electroreduction technologies allowing the conversion of CO2/water mixtures into syngas mixtures. The effect of the cathode composition, the configuration of the electrochemical cell, and the reaction conditions on the syngas production performance have been analyzed in detail. Finally, some examples on how the electrochemical promotion of catalysis (EPOC) effect can be used to enhance the CO2 hydrogenation reaction and drive the process to the production of syngas mixtures have been described

Low-temperature electrocatalytic conversion of CO2 to liquid fuels: effect of the Cu particle size

A novel gas-phase electrocatalytic system based on a low-temperature proton exchange membrane (Sterion) was developed for the gas-phase electrocatalytic conversion of CO2 to liquid fuels. This system achieved gas-phase electrocatalytic reduction of CO2 at low temperatures (below 90 °C) over a Cu cathode by using water electrolysis-derived protons generated in-situ on an IrO2 anode. Three Cu-based cathodes with varying metal particle sizes were prepared by supporting this metal on an activated carbon at three loadings (50, 20, and 10 wt %; 50% Cu-AC, 20% Cu-AC, and 10% Cu-AC, respectively). The cathodes were characterized by N2 adsorption–desorption, temperature-programmed reduction (TPR), and X-ray diffraction (XRD) and their performance towards the electrocatalytic conversion of CO2 was subsequently studied. The membrane electrode assembly (MEA) containing the cathode with the largest Cu particle size (50% Cu-AC, 40 nm) showed the highest CO2 electrocatalytic activity per mole of Cu, with methyl formate being the main product. This higher electrocatalytic activity was attributed to the lower Cu–CO bonding strength over large Cu particles. Different product distributions were obtained over 20% Cu-AC and 10% Cu-AC, with acetaldehyde and methanol being the main reaction products, respectively. The CO2 consumption rate increased with the applied current and reaction temperature

Electrochemical Activation of Ni Catalysts with Potassium Ionic Conductors for CO2 Hydrogenation

Three different kind of Ni-based catalysts were prepared on a K-β″Al2O3 solid electrolyte by combining the annealing of an organometallic paste and the addition of a catalyst powder. The different catalysts films were tested in the CO2 hydrogenation reaction under electrochemical promotion by K+ ions, and were characterized by XRD and SEM. The catalyst film derived from the addition of an α-Al2O3 powder to the Ni catalyst ink presented the highest catalytic activity as a result of the increase in Ni catalyst film porosity. The influence of the applied potential and other operation variables were evaluated on the Ni catalytic activity and selectivity. Hence, the CO production rate was enhanced either by decreasing the applied potential (with the consequent supply of K+ ions to the catalyst surface) or by increasing the CO2 (electron acceptor) feed concentration. On the other hand, CH4 production rate was favoured at positive potentials (removing K+ from the catalyst surface) or by increasing the H2 (electron donor) feed concentration. The global CO2 consumption rate increased upon negative polarization in all experiments and the electrochemical promotion of catalysis effect showed to be reversible and reproducible. Hence, the electrochemical promotion phenomena demonstrated to be a very useful technique to in situ modify and control the catalytic activity and selectivity of a non-noble metal such as Ni for the production of CH4 or syngas via CO2 valorization.Es la versión preprint del artículo. Se puede consultar la versión final en https://doi.org/10.1007/s11244-015-0488-

Direct production of flexible H2/CO synthesis gas in a solid electrolyte membrane reactor

The development of novel configurations for the production of synthesis gas (syn-gas) of flexible H2/CO ratio is of great importance to reduce the cost for the synthesis of synfuels and high-value chemicals. In this work, we propose a radically novel approach to the direct production of syn-gas with flexible H2/CO ratio based on the solid electrolyte membrane reactor (SEMR). For that purpose, a single-chamber solid electrolyte membrane reactor based on yttria-stabilized zirconia (YSZ) has been developed (Pt/YSZ/Pt), where both active Pt catalysts–electrodes were exposed to the same reaction atmosphere (C2H5OH/H2O = 0.7 %/2 %). The application of different polarizations at temperature range (600–700 °C) allows to control the H2/CO ratio of the obtained syn-gas, i.e., the ratio was varied between 1.5 and 12 under polarization conditions. Unlike conventional catalytic partial oxidation processes, the H2/CO adjustment was managed without the requirement of external O2 feeding to the reactor. An increase in the applied current or potential caused the H2/CO ratio to increase vs. the open-circuit conditions where ethanol reforming occurred on the Pt catalyst–electrodes which is due to an increase in the rate of the electro-catalytic processes. On the other hand, a decrease in the H2/CO ratio at a fixed potential was achieved at higher temperatures due to the further reaction of the produced H2 with the rest of the species present in the gas phase, leading to a decrease in the faradaic efficiency. The proposed configuration may be of great interest especially for biorefinery applications where H2, syn-gas and electricity may be produced from bioethanol.Es la versión preprint del artículo. Se puede consultar la versión final en https://doi.org/10.1007/s10008-015-2922-

Electrochemical reforming vs. Catalytic reforming of ethanol: A process energy analysis for hydrogen production

This work reports an energetic analysis for hydrogen production via catalytic steam and electrochemical ethanol reforming processes. For both systems, a complete flow diagram process was proposed and simulated by Aspen HYSYS according to literature data. Besides hydrogen, other byproducts such as acetaldehyde (electrochemical reforming) and ethylene and methane (catalytic reforming) were also considered. The energy requirement of the different process units was calculated according to the operating parameters. Just process energy (thermal energy and electrical energy) consumption was considered in the study of the steam reforming whereas both energy process and electrical energy consumption were considered in the study of the electrochemical reforming. Material balances revealed electrochemical reforming to present higher hydrogen yields. (0.0436 vs. 0.0304 kg H2/kg C2H5OH of the classical catalytic reforming). In addition to its higher simplicity, simulation results showed a lower energy consumption in the H2 production by the electrochemical approach (29.2 vs. 32.70 k Wh/Kg of H2). These results demonstrated the interest of the electrochemical reforming of ethanol to obtain high purity hydrogen in a single reaction/separation step, thereby representing an interesting alternative to classical catalytic reforming.Es la versión preprint del artículo. Se puede consultar la versión final en https://doi.org/10.1016/j.cep.2015.05.00

Electrochemical vs. chemical promotion in the H2 production catalytic reactions

The addition of electronic promoters chemically (chemical promotion) or electrochemically (electrochemical promotion or EPOC) induces very significant and similar effects on catalytic hydrogen production reactions such as CH4 and CH3OH conversion reactions, water-gas shift or ammonia decomposition. Both kinds of promotional phenomena follow the same general mechanism but the usefulness of the latter is highlighted. In this paper, the most important and recent contributions of the electrochemical promotion in different hydrogen production reactions are reviewed and compared to those based on conventional chemical promotion methods, mostly focusing on alkali promoters. The functional similarities and operational differences between both promotion ways are pointed out, and their impact on the hydrogen production technology is discussed. By this way the possibility of in-situ controlling the promoter coverage on the catalyst under working conditions and the in-situ catalyst regeneration from carbon deposition, among other novel contributions, lead EPOC to new opportunities for both: development of tailored effective catalysts and operation of hydrogen catalytic processes.La adición de promotores electrónicos químicamente (promoción química) o electroquímicamente (promoción electroquímica o EPOC) induce efectos muy significativos y similares en las reacciones catalíticas de producción de hidrógeno , como las reacciones de conversión de CH 4 y CH 3 OH, el desplazamiento agua-gas o la descomposición del amoníaco .. Ambos tipos de fenómenos promocionales siguen el mismo mecanismo general pero se destaca la utilidad del último. En este trabajo se revisan las contribuciones más importantes y recientes de la promoción electroquímica en diferentes reacciones de producción de hidrógeno y se comparan con aquellas basadas en métodos de promoción química convencionales, centrándose principalmente en promotores alcalinos. Se señalan las similitudes funcionales y las diferencias operativas entre ambas formas de promoción y se discute su impacto en la tecnología de producción de hidrógeno. De esta manera, la posibilidad de controlar in situ la cobertura del promotor sobre el catalizador en condiciones de trabajo y la regeneración in situ del catalizador a partir de la deposición de carbono ., entre otras contribuciones novedosas, llevan a EPOC a nuevas oportunidades para ambos: desarrollo de catalizadores efectivos personalizados y operación de procesos catalíticos de hidrógeno

Development of an operation strategy for hydrogen production using solar PV energy based on fluid dynamic aspects

Alkaline water electrolysis powered by renewable energy sources is one of the most promising strategies for environmentally friendly hydrogen production. However, wind and solar energy sources are highly dependent on weather conditions. As a result, power fluctuations affect the electrolyzer and cause several negative effects. Considering these limiting effects which reduce the water electrolysis efficiency, a novel operation strategy is proposed in this study. It is based on pumping the electrolyte according to the current density supplied by a solar PV module, in order to achieve the suitable fluid dynamics conditions in an electrolysis cell. To this aim, a mathematical model including the influence of electrode-membrane distance, temperature and electrolyte flow rate has been developed and used as optimization tool. The obtained results confirm the convenience of the selected strategy, especially when the electrolyzer is powered by renewable energies.La electrólisis del agua alcalina alimentada por fuentes de energía renovables es una de las estrategias más prometedoras para la producción de hidrógeno respetuosa con el medio ambiente. Sin embargo, las fuentes de energía eólica y solar dependen en gran medida de las condiciones meteorológicas. En consecuencia, las fluctuaciones de energía afectan al electrolizador y provocan varios efectos negativos. Teniendo en cuenta estos efectos limitantes que reducen la eficiencia de la electrólisis del agua, en este estudio se propone una novedosa estrategia de funcionamiento. Se basa en el bombeo del electrolito en función de la densidad de corriente suministrada por un módulo solar fotovoltaico, con el fin de conseguir las condiciones de dinámica de fluidos adecuadas en una célula de electrólisis. Para ello, se ha desarrollado un modelo matemático que incluye la influencia de la distancia electrodo-membrana, la temperatura y el caudal de electrolito y se ha utilizado como herramienta de optimización. Los resultados obtenidos confirman la conveniencia de la estrategia seleccionada, especialmente cuando el electrolizador es alimentado por energías renovables

Electrochemical promotion for hydrogen production via ethanol steam reforming reaction

In this work we have investigated for the first time the electrochemical activation of a catalyst for the ethanol reforming reaction. For that purpose, a Pt-KβAl2O3 electrochemical catalyst has been prepared, characterized and tested under ethanol reforming reaction conditions. The electrochemically supply of potassium ions under negative polarization step, strongly increased the hydrogen production rates leading to a reversible and controllable promotional effect. It has been attributed to the enhancement of the kinetic of ethanol dehydrogenation reaction, due to the strengthening of the chemisorptive bond of intermediate ethoxy molecules. It will increase the stability of this intermediate, thus favoring its formation, which initiates the ethanol reforming process. However, a large amount of carbonaceous species were formed on the catalyst surface during the negative polarization step that causes a continuous decrease in the catalytic activity under long polarization times. Under these conditions, the application of a catalyst potential of 2 V leads to a complete removal of the previous deposited carbonaceous molecules which allows further electrochemical activation steps. The obtained catalytic results have been supported by in-situ temperature programmed oxidation analysis and ex-situ Raman spectroscopy and Scanning Electron Microscopy. These techniques, in conjunction with the obtained catalytic results, have demonstrated the interest of the EPOC phenomenon for in-situ tuning the adsorption of reactants molecules on catalyst surface and its application in the hydrogen production technology, improving catalyst conversion and selectivity.En este trabajo hemos investigado por primera vez la activación electroquímica de un catalizador para la reacción de reformado de etanol. Para ello, un Pt-KβAl 2 O 3El catalizador electroquímico ha sido preparado, caracterizado y probado en condiciones de reacción de reformado de etanol. El suministro electroquímico de iones de potasio en el paso de polarización negativa aumentó considerablemente las tasas de producción de hidrógeno, lo que condujo a un efecto promocional reversible y controlable. Se ha atribuido a la mejora de la cinética de la reacción de deshidrogenación del etanol, debido al fortalecimiento del enlace quimisortivo de las moléculas etoxi intermedias. Aumentará la estabilidad de este intermedio, favoreciendo así su formación, que inicia el proceso de reformado del etanol. Sin embargo, se formó una gran cantidad de especies carbonáceas en la superficie del catalizador durante el paso de polarización negativa que causa una disminución continua en la actividad catalítica bajo largos tiempos de polarización. Bajo estas condiciones, la aplicación de un potencial de catalizador de 2 V conduce a una eliminación completa de las moléculas carbonosas depositadas anteriormente, lo que permite más pasos de activación electroquímica. Los resultados catalíticos obtenidos han sido respaldados por análisis de oxidación a temperatura programada in situ y espectroscopía Raman ex situ y microscopía electrónica de barrido. Estas técnicas, junto con los resultados catalíticos obtenidos, han demostrado el interés del fenómeno EPOC para ajustar in situ la adsorción de moléculas de reactivos en la superficie del catalizador y su aplicación en la tecnología de producción de hidrógeno, mejorando la conversión y selectividad del catalizador. Los resultados catalíticos obtenidos han sido respaldados por análisis de oxidación a temperatura programada in situ y espectroscopía Raman ex situ y microscopía electrónica de barrido. Estas técnicas, junto con los resultados catalíticos obtenidos, han demostrado el interés del fenómeno EPOC para ajustar in situ la adsorción de moléculas de reactivos en la superficie del catalizador y su aplicación en la tecnología de producción de hidrógeno, mejorando la conversión y selectividad del catalizador. Los resultados catalíticos obtenidos han sido respaldados por análisis de oxidación a temperatura programada in situ y espectroscopía Raman ex situ y microscopía electrónica de barrido. Estas técnicas, junto con los resultados catalíticos obtenidos, han demostrado el interés del fenómeno EPOC para ajustar in situ la adsorción de moléculas de reactivos en la superficie del catalizador y su aplicación en la tecnología de producción de hidrógeno, mejorando la conversión y selectividad del catalizador

Tuning of catalytic activity by thermoelectric materials for carbon dioxide hydrogenation

An innovative use of a thermoelectric material (BiCuSeO) as a support and promoter of catalysis for CO2 hydrogenation is reported here. It is proposed that the capability of thermoelectric materials to shift the Fermi level and work function of a catalyst lead to an exponential increase of catalytic activity for catalyst particles deposited on its surface. Experimental results show that the CO2 conversion and CO selectivity are increased significantly by a thermoelectric Seebeck voltage. This suggests that the thermoelectric effect can not only increase the reaction rate but also change chemical equilibrium, which leads to the change of thermodynamic equilibrium for the conversion of CO2 in its hydrogenation reactions. It is also shown that this thermoelectric promotion of catalysis enables BiCuSeO oxide itself to have a high catalytic activity for CO2 hydrogenation. The generic nature of the mechanism suggests the possibility that many catalytic chemical reactions can be tuned in situ to achieve much higher reaction rates, or at lower temperatures, or have better desired selectivity through changing the backside temperature of the thermoelectric support

Electrochemical promotion of a dispersed Ni catalyst for H2 production via partial oxidation of methanol

This study reports the electrochemical promotion (EPOC) of Ni particles dispersed in a diamond-like carbon (DLC) matrix. A Ni-DLC (Ni/C molar ratio of 0.1) catalyst film was prepared on a K-βAl2O3 (K+-conductor) solid electrolyte by cathodic arc deposition (CAD). This physical vapour deposition (PVD) technique allows to decrease the metal loading used in the solid electrolyte cell and to electrochemically activate dispersed Ni particles in the methanol partial oxidation (POM) reaction by in-situ controlling the coverage of K+ ions electrochemically transferred to the catalyst surface. As compared with a pure Ni layer prepared by the same technique, the Ni-DLC catalyst film shows a higher specific activity and an improved oxidation resistance under EPOC working reaction conditions. The possibility of electrochemically activate (with a negligible energy consumption) dispersed particles of a non-noble metal catalyst (closely related to commercially catalyst formulations) is of great interest for a further commercialization step of the EPOC phenomena in H2 production reactions and in other catalytic systems.Este estudio informa sobre la promoción electroquímica (EPOC) de partículas de Ni dispersas en una matriz de carbono tipo diamante (DLC). Se preparó una película catalizadora de Ni-DLC (relación molar Ni/C de 0,1) sobre un electrolito sólido de K-βAl2O3 (conductor de K+) mediante deposición por arco catódico (CAD). Esta técnica de deposición física de vapor (PVD) permite disminuir la carga metálica utilizada en la celda de electrolito sólido y activar electroquímicamente las partículas de Ni dispersas en la reacción de oxidación parcial del metanol (POM) mediante el control in situ de la cobertura de iones K+ transferidos electroquímicamente a la superficie del catalizador. En comparación con una capa de Ni pura preparada mediante la misma técnica, la película catalizadora de Ni-DLC muestra una mayor actividad específica y una mejor resistencia a la oxidación en condiciones de reacción de trabajo EPOC. La posibilidad de activar electroquímicamente (con un consumo de energía insignificante) partículas dispersas de un catalizador de metal no noble (estrechamente relacionado con las formulaciones de los catalizadores comerciales) es de gran interés para un posterior paso de comercialización del fenómeno EPOC en reacciones de producción de H2 y en otros sistemas catalíticos