CO2 valorisation towards alcohols by Cu-based electrocatalysts: challenges and perspectives

Advances and strategies of electrocatalytic CO2 conversion to alcohols on Cu-based catalysts is assessed with an outlook of current challenges for a practical application of this technology

Electrochemical and impedance characterization of Microbial Fuel Cells based on 2D and 3D anodic electrodes working with seawater microorganisms under continuous operation

A mixed microbial population naturally presents in seawater was used as active anodic biofilm of two Microbial Fuel Cells (MFCs), employing either a 2D commercial carbon felt or 3D carbon-coated Berl saddles as anode electrodes, with the aim to compare their electrochemical behavior under continuous operation. After an initial increase of the maximum power density, the felt-based cell reduced its performance at 5months (from 7 to 4μWcm(-2)), while the saddle-based MFC exceeds 9μWcm(-2) (after 2months) and maintained such performance for all the tests. Electrochemical impedance spectroscopy was used to identify the MFCs controlling losses and indicates that the mass-transport limitations at the biofilm-electrolyte interface have the main contribution (>95%) to their internal resistance. The activation resistance was one order of magnitude lower with the Berl saddles than with carbon felt, suggesting an enhanced charge-transfer in the high surface-area 3D electrode, due to an increase in bacteria population growth

Influence of sonication on co-precipitation synthesis of copper oxide catalyst for CO2 electroreduction

The need to reduce greenhouse gas emissions and increase our energy supply makes the electrochemical reduction of CO2 (CO2R) a very attractive alternative to produce non-fossil-based fuels or chemicals. Copper-based catalysts is one of the catalyst that most efficiently promote the formation of species with one or more carbon-carbon bonds from the electrochemical reduction of CO2 [1]. Because the catalyst preparation method has an influence on the physicochemical properties and on the electrocatalytic performance[2], in this work, it was decided to evaluate the effect of the ultrasound application (US) on the shape and size of the particles obtained, its electrocatalytic activity and its selectivity to products of interest. For this purpose, sonication was carried out at different percentage amplitudes of ultrasonic power (23, 30 and 37%) during the aging time of the synthesis. Physical characterization was carried out by using different techniques including X-ray diffraction, BET and filed-emission scanning electron microscopy (FESEM). Electrochemical tests for CO2 reduction were done under ambient conditions. Regarding the physical characteristics, we found that pore size distribution is narrower by increasing the US amplitude. On the other hand, there is no significant difference in morphology and dimension of particles. However, the surface area increased with the use of ultrasound, this is attributed to a better dispersion created by acoustic cavitation. Ultrasound has also an effect on Copper-based catalysts performance; in this case, the selectivity towards H2 and C1 products (CO and formate) was enhanced. In addition, an increase in productivity of CO2R products was obtained with respect to the synthesized catalysts that were not assisted by ultrasound (> 3-fold). These results motivate us to further explore in what other ways acoustic cavitation phenomenon can influence the physical characteristics of the catalysts and, in turns, their performance for the electrochemical reduction of CO2

Optimization of Cu-based catalyst for the electrocatalytic reduction of CO2 to fuels

In the last century, with the intensification of human industrial activities, carbon dioxide levels in the environment increased, making global warming and greenhouse effect pressing issues. In this sense, the electroreduction of CO2 is an interesting strategy, also if coupled with renewable energy sources to store the intermittent electric energy in form of chemical bonds [1]. Catalysts composed of a mixture of commercial copper nanoparticles (NPs) were studied. NPs with particles sizes of 25nm, 40-60nm and ZnO: 20-25 nm, named CZ 25_B and CZ_40-60_B. The molar ratio between copper and ZnO is equal to 65/35. Another commercial catalyst that was analysed because it is active for the CO2 hydrogenation is composed of CuO/ZnO/Al2O3 and traces of MgO (named CZA CC_B). These catalytic mixtures were prepared in a planetarian ball mill. Another sample was prepared by pre-oxidation of the Cu NPs and then by manual mixing with the ZnO (called CZ calc 2h). Carbon Nanotubes (CNT) was used as carbon substrate to increase the conductivity and allow a better catalytic ink dispersion. All the samples were characterized by BET analysis, FESEM microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and electrochemical analysis. The electrocatalytic activity was tested by using a rotating disk electrode (RDE) at ambient conditions. The best conditions were appreciated at a potential equal to -2 V vs Ag/AgCl, with the lowest FE for H2 and the highest current density (mA/cm2) in absolute value. In Figure 1, the FE % of gaseous and liquid products are reported for the different prepared catalysts. From all test, the best catalytic activity with the lowest FEH2 was obtained with the Cu/ZnO peroxidised material (CZ calc 2h) at -2 V vs Ag/AgCl. In conclusion, it can be said that Cu-based catalysts were confirmed to be active towards CO2RR via the electrochemical method, with the advantage of performing the reactions at ambient conditions

Facile synthesis of cubic cuprous oxide for electrochemical reduction of carbon dioxide

Abstract High level of atmospheric carbon dioxide (CO2) concentration is considered one of the main causes of global warming. Electrochemical conversion of CO2 into valuable chemicals and fuels has promising potential to be implemented into practical and sustainable devices. In order to efficiently realize this strategy, one of the biggest efforts has been focused on the design of catalysts which are inexpensive, active and selective and can be produced through green and up-scalable routes. In this work, copper-based materials are simply synthesized via microwave-assisted process and carefully characterized by physical/chemical/electrochemical techniques. Nanoparticle with a cupric oxide (CuO) surface as well as various cuprous oxide (Cu2O) cubes with different sizes is obtained and used for the CO2 reduction reaction. It is observed that the Cu2O-derived electrodes show enhanced activity and carbon monoxide (CO) selectivity compared to the CuO-derived one. Among various Cu2O catalysts, the one with the smallest cubes leads to the best CO selectivity of the electrode, attributed to a higher electrochemically active surface area. Under applied potentials, all Cu2O cubes undergo structural and morphological modification, even though the cubic shape is retained. The nanoclusters formed during the material evolution offer abundant and active reaction sites, leading to the high performance of the Cu2O-derived electrodes. Graphic abstrac

Development of Cu-based hybrid catalysts for the electrocatalytic CO2 reduction to added value products

The simultaneous need to reduce greenhouse gas emissions and increase our energy supply makes the electrochemical reduction of CO2 a very attractive alternative [1]. In this context, science seeks effective methods to transform CO2 into chemicals of economic value. Among the possible products to obtain, we are especially interested in species with one or more carbon-carbon bonds, these types of compounds are favoured using copper as catalyst. Six catalysts were synthesized with different ratios of Cu, Zn Al and subsequently exposed to a thermal treatment to obtain the correspondent oxidized compounds. These kinds of catalyst are traditionally used in thermocatalysis for the efficient production of methanol at high temperature and pressure conditions [2]. Noting the good performance of this catalyst in thermocatalysis, it was chosen to carry out the experiment in the electrochemical reduction of CO2 at ambient conditions. Electrochemical tests were carried out in the rotating disk electrode (RDE) in order to reduce the mass transfer limitations that may exist due to the low solubility of CO2 in an aqueous medium. The chemical-physical properties of the catalyst were studied by several characterization techniques (e.g. XRD, XPS, BET, among others) to understand the role of the modification of the catalyst components during operation in the final selectivity and activity. Among the liquid products obtained are acetone, ethanol, isopropanol, formic acid and in some cases, methanol was also found. Moreover, gaseous products obtained were hydrogen, carbon monoxide and methane, being these last - gaseous products - those that present the highest faradaic efficiencies. These results were compared with the performance of the catalysts in a Gas Diffusion Electrode (GDE) cell, to obtain commercially-relevant current densities

Evaluation of the charge transfer kinetics of spin-coated BiVO4 thin films for sun-driven water photoelectrolysis

tThe present research work focuses on bismuth vanadate (BiVO4) thin films deposited on FTO-coated glasselectrodes through the spin-coating technique, and discusses the influence of different film morphologies(dense and porous) on the physicochemical properties and photoelectrochemical (PEC) performance ofthe as-prepared photoanodes, for the water splitting reaction. The surface recombination phenomenon,which is one of the main issues of BiVO4, has been quantified by means of two distinct approaches: tran-sient photocurrent measurements and electrochemical impedance spectroscopy (EIS). This phenomenonhas resulted to be higher in the porous material, thus a poorer performance has been observed than inthe dense material. In order to increase the BiVO4efficiency, a cobalt phosphate (CoPi) catalyst has beenphoto-electrodeposited onto the best BiVO4electrode, employing an optimized technique and a pho-tocurrent of up to 3 mA/cm2at 1.23 V vs. RHE under neutral pH and 1 sun irradiation (100 mW/cm2)has been achieved. The charge transfer kinetics of the BiVO4photoanodes, with and without CoPi, hasalso been quantified. The beneficial effect of this water oxidation catalyst, as well as the influence of thepreparation method on the uniformity of the film and on its actual performance, is discussed in view ofits prospective application in a real PEC device

IONIC LIQUIDS FOR CAPTURE AND ELECTROCHEMICAL CONVERSION OF CO2 - ISE 2021

The exponential increase in the concentration of greenhouse gasses in the atmosphere is considered one of the most important reasons for climate change. Carbon Dioxide is the most significant anthropogenic gas that contributes to global warming. CO2 capture and storage (CCS) has been proposed as one of the most important invention to mitigate CO2 emissions. Moreover, conversion of carbon dioxide into energy-rich chemicals is a viable approach to reducing the global carbon footprint. The most common techniques to remove CO2 from gas streams are the chemical and physical adsorption by liquid solvents. Traditionally, aqueous amine solutions have been used as chemical solvents because of their high selectivity, high reactivity and low price. Unfortunately, they present also many disadvantages associated with the high energy demand required for the solvent regeneration, corrosion issues and loss of solvent because of their high volatility. Hence, in the need to find more efficient solvents for CO2 capture and conversion, Ionic Liquids (ILs) have been highlighted as very good alternatives to common amine solution.[1] Within this field lies this research, which in turn is part of a much broader European project called SunCoChem. For this project we are testing the stability and performance of various ionic liquids, provided by Iolitec, Ionic Liquids Technologies GmbH, and in particular their ability to capture and electrochemically convert a pure CO2 stream to CO with high efficiencies. The ionic liquids were tested in a two-compartment H-type electrochemical cell. In the anodic chamber a nickel mesh electrode was immersed in a solution of potassium hydroxide and in the cathodic one a silver foil cathode was employed in a solution of acetonitrile and ionic liquid. An organic solvent was used to favor the dissolution of the ionic liquid and the homogenization of the solution. Other organic solvents such as propylene carbonate, ethylene glycol and 1-butanol were also tested with the aim of finding the best compromise between low viscosity, good conductivity and high electrochemical stability window. The Ionic Liquids (ILs) tested so far have a cationic part based on imidazole, which is expected to stabilize and lower the activation energy for the reduction of CO2. During Linear Sweep Voltammetry (LSV) tests this trend was confirmed by a shift to more positive potentials of the onset (~ 0.5V) for the CO2 reduction reaction in the presence of these Ionic Liquid and interesting value of current density were reached. Throughout the Chronopotentiometry (CP) studies, some ILs evidenced a decrease in the applied potential indicating the increase of the electrolyte conductivity. Our results evidence relevant current density values, a good stability during chronopotentiometry (CP) tests and a high selectivity towards the target product: CO, which however change depending on the used IL. AKCNOWLEDGMENT: The research leading to these results has received funding from the European Union’s Horizon 2020 Research and Innovation Action programme under the SunCoChem project (Grant Agreement No 862192). REFERENCES: [1] Shokat Sarmad et al, Carbon Dioxide Capture with Ionic Liquids and Deep Eutectic Solvents: A New Generation of Sorbents, 2016, https://doi.org/10.1002/cssc.20160098

Enhanced electrochemical oxidation of phenol over manganese oxides under mild wet air oxidation conditions

Low-cost manganese oxide, MnOx-based electrocatalysts, containing a-MnO2 and mixed a-Mn2O3/a- MnO2 phases, were synthesized by scalable anodic and cathodic electrodeposition methods, respectively. Their morphological and chemical composition were characterized by means of Field Emission Scanning Electronic Microscopy (FESEM), X-Ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). These electrodes were tested for the electro-oxidation of a recalcitrant molecule (i.e. phenol) in a lab- scale high temperature and high pressure (HTHP) batch electrocatalytic reactor. Their electrocatalytic activity was compared with that of state-of-the-art anodes for phenol electro-oxidation: antimony- doped tin oxide (SnO2eSb5þ) and ruthenium oxide (RuO2): first, under standard ambient conditions, and then, under the conditions of a Polymeric Electrolyte Membrane (PEM) electrolyzer (i.e. 85 C and 30 bar) and of mild Catalytic Wet Air Oxidation (CWAO, i.e. 150 C and 30 bar). Both reaction time and current density were varied to investigate their effect in the performances of the system as well as on the re- action mechanism. Both MnOx electrodes reported enhanced conversion efficiencies, up to ~75%, at the highest pressure and temperature, and at the lowest applied current density, which influenced the process by improving dissolution of the O2 evolved, the reaction kinetics and thermodynamics, and by minimizing irreversibilities, respectively. The here reported MnOx films achieved conversion and mineralization efficiencies comparable to Sb-SnO2 (that is the more toxic) and RuO2 (that is more expensive) materials, operating under mild CWAO operation conditions, which demonstrate the po- tential of the electrocatalytic HTHP process as a sustainable advanced oxidation technology for waste- water treatment or electrosynthesis applications