KHCO3 Solution Research Articles

Experimental Evaluation of Protecting High-Voltage Electrical Transformers Using Water Mist with and without Additives

Suppression of high-voltage (HV) electrical fires is difficult because it requires fire-extinguishing agents with good isolation properties as well as high fire-suppression efficiency. In the work presented herein, water mist with and without various water mist additives (WMAs) was utilized to suppress HV transformer oil fires. The WMAs included ionic alkali-metal salt and fluorocarbon surfactant, and nonionic hydrocarbon and fluorocarbon surfactants. At the same concentration, the surfactants were more efficient at extinguishing fires compared with the alkali-metal salt. The fluorocarbon surfactant was more efficient at extinguishing fires than the hydrocarbon surfactant, achieving flame extinction in 18 % of the time required when using natural water (NW). Besides, the effects of WMAs on the insulating properties of the water mist were studied. The gap breakdown test showed that the NW mist could increase the breakdown voltage of air by up to 5 % at 70-cm gap distance. Comparatively, the nonionic WMAs did not affect the insulating property of the NW mist, with the mist containing 1.0 % ionic KHCO3 solution enabling a reduction of up to 16 % in the breakdown at 70-cm gap distance while increasing the leakage current of the simulated insulator by up to 250 % at its nominal voltage. Finally, field tests were performed where NW mists were discharged onto a charged 220-kV high-voltage transformer. This study proves that NW mist and mists with nonionic WMAs are suitable for protecting HV electrical equipment, having important implications for extending the applications of water mist.

ZrO2 nanoparticles anchored on nitrogen-doped carbon nanosheets as efficient catalyst for electrochemical CO2 reduction

Electrochemical reduction of CO2 to produce value-added feedstock chemicals using high-performance electrocatalysts is a promising protocol to address the excessive CO2 in the atmosphere and the energy crisis. However, the high overpotential, low current density, and poor product selectivity for CO2 electroreduction greatly impede their practical applications. In this work, we develop an efficient catalyst for CO2 reduction to CO consisting of well-dispersed ZrO2 nanoparticles tightly anchored on nitrogen-doped carbon nanosheets (ZrO2/N-C) for the first time. Importantly, the ZrO2 nanoparticles possess oxygen vacancies and defects, which regulate the electronic structure of catalyst and thus greatly enhance the electrocatalytic activity. Specifically, ZrO2/N-C demonstrates a high CO Faradaic efficiency (FE) of 64% at −0.4 V vs. the reversible hydrogen electrode (RHE) and a respectable current density of ∼2.6 mA cm−2 in CO2-saturated 0.5 M KHCO3 solution. This work opens a new avenue for developing excellent catalysts for CO2 electroreduction with metal oxide/heteroatom-doped carbon composite structure.

Effects of Co3O4 Cocatalyst on InTaO4 for Photocatalytic Reduction of CO2 to CH3OH under Visible Light Irradiation

InTaO4 was synthesized by a solid-state reaction method using metal oxide as the starting materials. Co was added by incipient-wetness impregnation. The sample was pretreated by H2 (200 Torr) reduction at 500?C for 2 h and subsequent O2 (100 Torr) oxidation at 200?C for 1 h. The core-shell structure of metallic Co and Co3O4 was formed by this reduction-oxidation procedure. The catalysts were characterized by powder X-ray diffraction, scanning electron microscope, and ultraviolet-visible spectroscope. The photocatalytic reduction was carried out in a Pyrex reactor with KHCO3 or NaOH aqueous solution bubbled with ultra pure CO2 gas under visible light illumination. SEM micrographs show many small Co3O4 particles on the surface of InTaO4. The band gap of Co3O4-InTaO4 was 2.7 eV, confirming that these catalysts have the ability to reduce CO2 to methanol. The methanol yield increased with the amount of Co3O4 cocatalysts. The catalyst had a higher activity in KHCO3 aqueous solution than in NaOH solution. The InTaO4 catalyst with 1 wt% Co3O4 cocatalyst had the highest activity among all catalysts. Co3O4 was incorporate into the surface structure of InTaO4 to form CoxInTaO4-x. It resulted in more defect sites on the surface of InTaO4 and changed the valence band structure. It formed a Schottky barrier to suppress the electron-hole recombination.

Green, safe, fast, and inexpensive removal of CO2 from aqueous KHCO3 solutions using a nanostructured catalyst TiO(OH)2: A milestone toward truly low-cost CO2 capture that can ease implementation of the Paris Agreement

With great effort, the Paris Agreement set goals designed to address climate change, but far more effort will be necessary to meet those goals due to the lack of transformational CO2 capture technologies that are cost-effective. This research is designed to overcome the shortcomings of conventional CO2 capture technologies (i.e. the cost, health impacts, and environmental impacts of amines) by using a titanium oxyhydroxide (TiO(OH)2) catalyst and a potassium carbonate/bicarbonate sorbent (K2CO3/KHCO3, respectively). Nanostructured TiO(OH)2 as a catalyst is able to accelerate desorption processes; the acceleration of CO2 desorption is of greater significance because the process consumes more energy than the sorption process. Experimental results show that the use of nanostructured TiO(OH)2 increases the amounts of desorbed CO2 by as much as 1200%, if not higher. Cyclic sorption-desorption testing combined with material characterization shows that both catalyst and sorbent are stable even after 50 cycles. One major benefit of the kinetic enhancement from this catalyst/sorbent system is the reduction of temperature needed to desorb CO2; waste heat may be sufficient to provide all or most of the energy required for CO2 capture. Thus, the energy cost of CO2 capture will be significantly reduced, which may keep electricity prices low, avoiding a decrease in the global economy in order to avert global climate change impacts. Another significant benefit of this system is that this inorganic system is environmentally safe, clean, and non-carcinogenic.

CuO Nanoparticles Supported on TiO2 with High Efficiency for CO2 Electrochemical Reduction to Ethanol

Non-noble metal oxides consisting of CuO and TiO2 (CuO/TiO2 catalyst) for CO2 reduction were fabricated using a simple hydrothermal method. The designed catalysts of CuO could be in situ reduced to a metallic Cu-forming Cu/TiO2 catalyst, which could efficiently catalyze CO2 reduction to multi-carbon oxygenates (ethanol, acetone, and n-propanol) with a maximum overall faradaic efficiency of 47.4% at a potential of −0.85 V vs. reversible hydrogen electrode (RHE) in 0.5 M KHCO3 solution. The catalytic activity for CO2 electroreduction strongly depends on the CuO contents of the catalysts as-prepared, resulting in different electrochemistry surface areas. The significantly improved CO2 catalytic activity of CuO/TiO2 might be due to the strong CO2 adsorption ability.

(Invite) Prospective Investigations of Tungsten and Molybdenum Carbide-Containing Materials As Catalysts for Electrochemical Energy Conversion Processes: Proton, Oxygen, and CO/CO2 Reduction Reaction

In the last decade, transition metal carbides, particularly based of molybdenum and tungsten, have emerged as novel materials with promising catalytic properties toward several important practical electrochemical reactions. In this presentation, the activity of such materials will be discussed for the following electrochemical approaches/reactions: i) the electrocatalysis of oxygen reduction reaction (ORR) in acid media on Pt- and Pt2Ni-nanoparticles supported on carbon forming composites with tungsten and molybdenum carbides with cubic (α) and hexagonal (β) structures; ii) the hydrogen evolution reaction (HER) in acid and alkaline media on TM-modified molybdenum carbide (TM-Mo2C) catalysts, where TM is a transition metal, such as, Fe, Co, Ni and Cu; iii) the CO2 and CO electro-reduction reactions in 0.1 M NaClO4 and 0.5 and 1 M KHCO3 solutions on carbon supported tungsten and molybdenum carbides. Syntheses of the carbide-based catalysts have been conducted employing different procedures, after which the produced material are characterized by X-Ray diffraction (XRD), energy dispersive X-ray spectroscopy, (EDS), X-ray photoelectron spectroscopy (XPS), in situ X-ray absorption near edge structure (XANES), and transmission electron microscopy (TEM). Cyclic voltammetry and polarization measurements on stationary and rotation disk electrodes have been employed for the electrochemical investigations. For the CO/CO2 reduction, reaction products were analyzed by differential electrochemical mass spectrometry (DEMS) and high performance liquid chromatography (HPLC) analyses. Enhanced mass and specific ORR activities are seen for Pt–molybdenum carbide-derived composites compared to Pt-α-WC/C, which in turn presents specific activity for the ORR similar to that of a standard carbon supported Pt catalyst (Pt/C). For Pt-β-WC1-x/C composites, the specific activity is also higher than that of Pt/C when a carbide-to carbon load of 40 wt.% is used. In the case of the HER, high activities are observed for all TM-Mo2C catalysts in acid and alkaline media. Nonetheless, while in acid there is a decrease in the activity upon metal doping, with an activity trend of α-Mo2C > Fe-Mo2C > Co-Mo2C > Ni-Mo2C > Cu-Mo2C, the opposite tendency is found in alkaline solutions. In situ near-edge X-ray adsorption analysis reveals different oxidation states of the TM inside the carbide in both solutions. In acid, a positive charge of the TM in the materials in the electrochemical environment is possibly at the origin of the deleterious effect of Fe, Co, Ni and Cu. In addition, catalysts stability against dissolution in acid media is increased by doping of molybdenum carbide with TM. Regarding of CO and CO2 electro-reductions in 0.1 M NaClO4 and 0.5 and 1 M KHCO3 solutions, results suggest that neither molybdenum nor tungsten carbides can be considered as active catalysts, in contrast to reported results in gas phase. It appears that both the aqueous environment and their activity toward the HER surpass the reactivity toward these latter reactions. Acknowledgements: Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP - Procs. 2013/16930-7 and 2014/23486-9) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) (Procs. 1423454), Brazil, for financial supports.

Metal Sulfides As Catalysts for the Electrochemical Reduction of Carbon Dioxide

Electrochemical reduction of carbon dioxide (ERC) is a promising way to solve the greenhouse effect and energy issues. We look forward to finding efficient, durable and cost-effective catalysts for the practical application of ERC. Metal sulfides can be used as desirable catalysts for ERC. Sulfides of transition metals are considered as catalyst candidates for the ERC in this study. Selected metal sulfides are coated on carbon paper to get the gas diffusion electrode (GDE), which are then used to catalyze the ERC in KHCO3 solution. Their electrocatalystic activity, product selectivity and durability for ERC were evaluated by cyclic voltammetry and linear sweep voltammetry. The structures of them are investigated by using SEM, TEM, etc. To confirm the influence of different synthesis methods on the performance, we used hydrothermal and chemical synthesis to prepare the metal sulfides. The results indicated the desirable electrochemical catalytic performance.

A catalyst based on copper-cadmium bimetal for electrochemical reduction of CO2 to CO with high faradaic efficiency

Electrochemical reduction carbon dioxide (CO2) can produce value-added chemicals such as carbon monoxide and hydrocarbon. However, the sluggish kinetic process and complex reaction routes of CO2 electro-reduction reaction (CO2RR) largely limit the conversion efficiency and products selectivity. Herein, a Cu2Cd/Cd/Cu bimetallic catalyst by imbedding Cd bulks onto Cu substrate surface was designed and applied for the CO2RR. This catalyst presents good conductivity and selectivity toward the CO2RR. Particularly, the catalyst shows CO conversion faradaic efficiency of 84% with a current density of 8 mA cm-2 at −1.0 V vs. RHE in CO2-saturated 0.1 M KHCO3 solution. Detailed investigation has revealed that the electrocatalytic capability of this catalyst can be attributed to the boundaries between Cu and Cd that could provide sufficient active sites for the CO2RR and the formation of Cu2Cd alloy that could enhance the binding energy between the catalyst and the intermediate.

In-situ grown nanoporous Zn-Cu catalysts on brass foils for enhanced electrochemical reduction of carbon dioxide

In-situ grown nanoporous Zn-Cu catalysts were prepared by simply annealing a commercial brass foil at 500 °C in air, followed by electrochemical reduction. During the annealing process, Zn preferentially melted and migrated out of the framework of the alloy to form a thin layer of ZnO on its surface. Subsequent electroreduction created nanoporous Zn-enriched surface. The Zn concentration increased from 36% to 50% by 10 min, to 81% by 3 h, and to 87% by 12 h annealing treatment while the average pore size decreased from 290 nm to 120 nm as the annealing time increased from 1 h to 12 h. Faradaic efficiency of CO2 reduction to CO and HCOOH was enhanced by nearly 4 and 6 times, respectively, as compared to untreated brass foils. The nanoporous Zn-Cu catalyst presented a stable ratio of CO/H2 and a steady working current density in a continuous electrolysis of 18 h in 0.5 M KHCO3 solution.

Stepped surface-rich copper fiber felt as an efficient electrocatalyst for the CO2RR to formate

We developed a novel biomass carbon-templated route to synthesize stepped surface-rich Cu fiber felt as an efficient and stable electrocatalyst for the CO2RR to formate, whose FE reaches 71.1 ± 3.1% in KHCO3 solution.

Electrodeposition of tin on Nafion-bonded carbon black as an active catalyst layer for efficient electroreduction of CO2 to formic acid

Electroreduction of CO2 to formic acid (ERCF) based on gas diffusion electrodes (GDEs) has been considered as a promising method to convert CO2 into value-added chemicals. However, current GDEs for ERCF suffer from low efficiency of electron transfer. In this work, a novel Sn-based gas diffusion electrode (ESGDE) is prepared by electrodepositing Sn on Nafion-bonded carbon black as catalyst layer to enhance electron transfer and thus the efficiency of ERCF. The highest Faraday efficiency (73.01 ± 3.42%), current density (34.21 ± 1.14 mA cm−2) and production rate (1772.81 ± 59.08 μmol m−2 s−1) of formic acid are obtained by using the ESGDE with electrodeposition time of 90 s in 0.5 M KHCO3 solution, which are one of the highest values obtained from Sn-based gas diffusion electrodes under similar conditions. The notable efficiency of ERCF achieved here should be attributed to the enhancement in the reactants transfer as well as the three-dimensional reaction zone. This work will be helpful for the industrial application of GDEs in EFCF.

Selective Electrochemical Reduction of CO2 to Ethylene on Nanopores-Modified Copper Electrodes in Aqueous Solution.

Electrochemical reduction of carbon dioxide was carried out on copper foil electrodes modified with nanopores on the surface. Such nanopores modified structure was obtained through an alloying-dealloying process. Scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy confirmed the formation of alloy layer and the final nanoporous morphology of such copper electrodes. When used in electrolysis process, the as-prepared nanopores-modified electrodes can suppress the Faradaic efficiency toward methane to less than 1%, while keeping that of ethylene in a high level of 35% in aqueous 0.1 M KHCO3 solution under -1.3 V (vs reversible hydrogen electrode), thus revealing a remarkable selectivity toward ethylene production. The high yield of ethylene can be ascribed to the exposed specific crystalline orientations.

A Facile Electrochemical Synthesis for Nanostructured Au for Improved Photo- and Electrochemical CO2 Reduction Activity

Direct CO2 conversion using renewable energy source (e.g. solar energy) to value-added chemicals has attracted much attention for alternative fuel production. An efficient and durable electrocatalyst is essential to achieve practical level of CO2 conversion. In the recent years, nanostructuring of metal catalysts (e.g. Au, Ag, Cu) has been reported for enhancing CO2 reduction reaction (CO2RR) activity in aqueous solutions. In particular, nanostructured Au formed on a thick Au foil by electrochemical treatment has been intensively focused due to the superior properties regarding low overpotential and enhanced stability.[1] However, the utilization of thick Au foils can increase the cost and is also unavailable for photoelectrochemical (PEC) CO2RR which is the simplest approach for solar CO2 conversion. Accordingly, we recently demonstrated that mild electrochemical treatment enabling the formation of nanoporous Au thin film on Si photocathode for PEC CO2RR.[2] Although it shows exceptional CO2RR activity with only 20 nm-thick nanoporous Au layer, stability issue still remains to be solved for practical CO2 conversion. Here, we propose a novel electrochemical synthesis strategy to form Au nanostructured thin film for further improved CO2RR activity. The electrochemical synthesis is simply performed with 160 nm-thick Au thin film on Si substrate by anodization of Au thin films to grow Au oxide at constant potential (2.5 V (vs. RHE) for 40 min) followed by electro-reduction of the grown Au oxide at constant current density (-0.5 mA cm-2 for 10 min) in 0.2 M KHCO3 solution. Nanoporous Au nanostructures with height of ~180 nm were formed as a result of the electrochemical treatment. The CO2RR activities (overpotential, durability) for the nanostructured Au is significantly improved as compared to bare Au thin film. For example, our CO selectivity is to 66% and 98% at -0.35V and -0.39V, respectively, (bare Au: 0 and 20%, respectively). Nanostructured Au also shows better stability at -0.49V (~2 hours for over 90% selectivity) as compared to bare Au (20% selectivity at an hour). In order to further improve the stability of our nanostructured Au during CO2RR, we introduce additional electrochemical oxidation and reduction cycles. Interestingly, declined CO2RR activity (CO selectivity: ~70%) is revived to have 97% CO selectivity after an additional cycle. Furthermore, after the 4th electrochemical cycles, our Au nanostructures are stable over 6 hours while producing over 90% CO selectivity. We performed a systematic morphological and microstructural investigation of Au nanostructures during the repeated electrochemical treatment cycles. In particular, the height of Au nanostructured increases to about 390 nm and roughness factor is doubled after the 4th treatment. TEM investigations confirmed that remarkably increased number of grain boundaries (GBs) on the 4th treated Au samples. In addition, most GBs disappear after 15 hours of CO2RR. These results indicate that extended stability by repeating cycle of electrochemical synthesis is attributed to increased GBs on a roughened Au nanostructure. Finally, we applied our Au nanostructures to Si photocathodes for PEC CO2RR with Si photocathodes by forming Au micro-mesh. Micro-mesh Au on Si enables electrochemical treatments selectively on Au surface without deteriorating the underlying Si. Our Si photocathode with nanostructured Au co-catalyst remarkably achieves ~82% CO selectivity at -0.07 V which is more positive than CO2/CO redox potential under 1 sun illumination with extended stability. Therefore, our electrochemical synthesis would provide an efficient strategy to improve and recycle nanostructured Au activity for photo- and electrochemical CO2reduction. [1] Yihong Chen, Christina W. Li, and Matthew W. Kanan, J. Am. Chem. Soc. 134, 19969 (2012) [2] Jun Tae Song, Hyewon Ryoo, Minhyung Cho, Jaehoon Kim, Jin-Gyu Kim, Sung-Yoon Chung, and Jihun Oh, Adv. Energy Mater. 7, 1601103 (2017)

Electrocatalytic Reduction of Carbon Dioxide on Tin Oxide-Based Nanoparticles: Indirect Detection of Formate Ions Via on-Line Dems

The electrochemical reduction of carbon dioxide is an important route for producing valuable chemical compounds and industrial feedstock. Additionally, this molecule can be used in regenerative cycles of electrochemical energy conversion and storage. In the last case, carbon dioxide can be selectively reduced to formate ions, which can be used as fuel in direct formate or formic acid fuel cells. As presented before [1,2], metals with high hydrogen evolution reaction (HER) overpotential, such as Pd, Sn, Hg, In, and Sn, tend to catalytically convert carbon dioxide to formate ions. In this study, we have synthesized carbon-supported Sn-based nanoparticles and tested them as electrocatalysts for the CO2 electro-reduction in aqueous KHCO3 electrolyte. The generated formate ions were indirectly and quantitatively determined via cyclic voltammetry on a porous sputtered platinum electrode, for the electro-oxidation of the formate ions, with on-line and instantaneous detection of CO2 (electro-oxidation product of formate) by Differential Electrochemical Mass Spectrometry (DEMS). For this, after potentiostatic polarizations for the CO2 electro-reduction, the CO2-saturated KHCO3 electrolyte was acidified with sulfuric acid (to reach pH close to zero) in order to decompose the bicarbonate ions, and it was purged with argon for 30 min. The acidification is necessary because the protons generated from the formate ions electro-oxidation in the near-neutral pH KHCO3 solution attack the bicarbonate ions, producing CO2. So, this procedure guarantees that all detected CO2 comes exclusively from the electro-oxidation of the generated formic acid molecules and not from the decomposition of the bicarbonate ions (the acid addition also induces the protonation of the formate species producing formic acid). This procedure offers, therefore, an alternative method for quantitative determination of formate ions during the CO2 reduction. The results showed that the production of the formate ions linearly increases with the decrease of the electrochemical potential in the potential domain from -0.9 to -1.8 V vs. Ag/AgCl, for SnO2/C nanoparticles. The maximum faradaic current efficiency for formate ions production was 23 %, achieved at -1.2 V. Interestingly, the modification of tin with other transition metals, such as cobalt, completely inhibited the production of formate. Contrarily, by synthetizing non-alloyed bimetallic Sn-Co nanoparticles, the formate ions generation was maintained. The discussion concerning the parameters that govern the selectivity to formate ions will be addressed in this presentation. The faradaic current efficiency-electrocatalyst composition/structure correlation, determined by DEMS, followed the tendencies of surface hydroxide formation, and this will also be presented and discussed. [1] Y. Hori, H. Wakebe, T. Tsukamoto, O. Koga, Electrochim. Acta 39 (1994) 1833 – 1839. [2] Y. Chen, M. W. Kanan, J. Am. Chem.Soc. 2012, 134, 1986−1989 Acknowledgements The authors gratefully acknowledge financial support from FAPESP (2016/13323-0 and 2013/16930-7) and CNPq (306469/20162).

(Keynote) Investigation the Effect of CO2 Absorption in Anion Exchange Membrane By Electrical Conductivity and NMR

The anion exchange membrane (AEM) has attracted considerable attention in the application of fuel cell technology. Compared with proton exchange membrane fuel cells, AEM fuel cells (AEMFCs) have advantages in cost, catalyst stability, efficiency and system size1. However, one challenge in the application of AEMFCs is the absorption of CO2 from the cathode air supply, which forms carbonate and bicarbonate species and reduces the ionic conductivity of membrane. In this study, to better understand the effect induced by CO2 on AEM performance, the ion transport mechanism was investigated by using electrical conductivity and Nuclear Magnetic Resonance (NMR) techniques. A typical commercial anion exchange membrane Tokuyama A201 has been used for all experiments. OH- form membranes are prepared by soaking in low concentration (10-4 M) KOH solution. CO3 2- and HCO3 - form membranes are used after soaking in 1M K2CO3 or KHCO3 solution. Both electrical conductivity and NMR experiments have been performed on a series of OH- form, CO3 2- and HCO3 - form samples with different water contents from 20 °C to 80 °C. Figure 1 shows the electrical conductivity of HCO3 - form A201 at different relative humility as a function of temperature, which displays an increasing trend as the relative humility and temperature increase. Also note the low values of conductivity relative to that expected from a hydroxyl ion conductor. This is in accord with previous reports that indicate a significant decrease in conductivity upon uptake of CO2 into hydroxide-form membranes. 1H and 13C pulse-field-gradient NMR are used to characterize the speciation and diffusion coefficient D(NMR) of water, CO3 2- and HCO3 - respectively. Difference in ionic conductivity and diffusion coefficient of each species in the membrane between three different forms can be observed. The estimated diffusion coefficient D(σ) from ionic conductivity obtained by using Nernst-Einstein equation is sometimes different from that measured by NMR. The comparison between D(NMR) and D(σ) provides valuable information on ionic transport mechanism 2. Obtaining dynamic information on the behavior of CO2– derived species in the membrane will allow modeling to the distribution of such species in the membrane. Acknowledgement. We gretefully acknowledge the support of this work by the Office of Naval Research. We also appreciate the assistance of Tokuyama Soda in providing A201 membrane samples. Reference: 1. X. M. Ren, S. C. Price, A. C. Jackson, N. Pomerantz and F. L. Beyer, Acs Appl Mater Inter, 6, 13330 (2014). 2. S. Ochi, O. Kamishima, J. Mizusaki and J. Kawamura, Solid State Ionics, 180, 580 (2009). Figure 1

Electrochemical Reduction of Carbon Dioxide to Hydrocarbons Using Copper Nanocomposite Catalyst

Increase in carbon dioxide, a greenhouse gas, emissions has resulted in widespread impact on climate and adversely affected the environment. In addition to carbon dioxide (CO2) capture and sequestration approaches, conversion of CO2 to chemical compounds has been explored as another pathway to mitigate CO2 emissions problem. Synthesis of high value hydrocarbons, such as methane (CH4) and ethylene (C2H4), and alcohols such as methanol (CH3OH) and ethanol (C2H5OH) from emitted CO2 is a worthy sustainable process. In the past few years, the electrochemical reduction of CO2 to hydrocarbons and alcohols has gained importance. Among the metal catalysts, copper (Cu) has demonstrated higher current efficiencies and selectivity towards synthesis of hydrocarbon by electrochemical reduction of CO2 in aqueous solution.1-3 Varying Cu layer thickness improved selectivity between methane and ethylene; specifically more C2H4 was formed than CH4 on monolayer Cu catalyst.4 Studies have reported use of Cu nanoparticles and high surface area catalyst supports, such as carbon nanotube, for enhanced faradic efficiency to reduce CO2 to hydrocarbons.5-6 This encouraged us to pursue graphene, a high surface area material, as support for the Cu catalyst to form a nanocomposite. The development of Cu – graphene nanocomposite as electrocatalyst for CO2 reduction reaction is one of the objectives of this investigation. Electrochemical reduction of graphene oxide (commercial solution) will be combined with Cu electrodeposition to prepare the Cu – reduced graphene oxide nanocomposite. Another objective of this investigation is determining the operating conditions for electrochemical reduction of CO2 to produce hydrocarbons at high efficiency and selectivity. The electrolysis experiments will be performed in an airtight cell with platinum (Pt) foil as anode electrode. A reference electrode (Ag/AgCl) will be used in the cell to apply different potential on Cu-based catalyst electrode (cathode) for CO2 reduction reaction. For all the electrolysis experiments, 0.1 M KHCO3 solution will be used with and without CO2 saturation. The effect of catalyst morphology, applied electrode potential, electrolysis time, and electrolysis cell configuration will be evaluated with the gaseous products formed during the CO2 reduction reaction. The gaseous products collected from the electrochemical cell will be analyzed using gas chromatograph instrument equipped with natural gas analyzer. Efficient and selective synthesis of hydrocarbon products by CO2 reduction reaction will depend on the preparation of Cu – reduced graphene oxide nanocomposite catalyst. References Y. Hori, K. Kikuchi and S. Suzuki, Chemistry Letters, 14, 1695 (1985).Y. Hori, K. Kikuchi, A. Murata and S. Suzuki, Chemistry Letters, 15, 897 (1986).R. J. Lim, M. Xie, M. A. Sk, J-M. Lee, A. Fisher, X. Wang and K. H. Lim, Catalysis Today, 233, 169 (2013).R. Reske, M. Duca, M. Oezaslan, K. J. P. Schouten, M. T. M. Koper and P. Strasser, The Journal of Physical Chemistry Letters, 4, 2410 (2013).K. Manthiram, B. J. Beberwyck and A. P. Alivisatos, Journal of the American Chemical Society, 136, 13319 (2014)C. Genovese, C. Ampelli, S. Perathoner and G. Centi, Journal of Catalysis, 308, 237 (2013).

Surface-reconstructed Cu electrode via a facile electrochemical anodization-reduction process for low overpotential CO2 reduction

A high-surface-area Cu electrode, fabricated by a simple electrochemical anodization-reduction method, exhibits high activity and selectivity for CO2 reduction at low overpotential in 0.1M KHCO3 solution. A faradaic efficiency of 37% for HCOOH and 27% for CO production was achieved with the current density of 1.5mAcm−2 at −0.64V vs. RHE, much higher than that of polycrystalline Cu. The enhanced catalytic performance is a result of the formation of the high electrochemical active surface area and high density of preferred low-index facets.

A broad parameter range for selective methane production with bicarbonate solution in electrochemical CO2 reduction

Selective methane production was achieved over a broad current density range with 0.5 M KHCO3 solution and bulk, polycrystalline Cu.

Electrochemical promotion of catalysis over Pd nanoparticles for CO2 reduction.

Electrochemical promotion of catalysis (EPOC) has been shown to accelerate the rate of many heterogeneous catalytic reactions; however, it has rarely been reported in low-temperature aqueous electrochemical reactions. Herein, we report a significant EPOC effect for the CO2 reduction to generate formate over Pd nanoparticles (NPs) in a 1 M KHCO3 aqueous solution. By applying a negative potential over differently-sized Pd NPs, the rate of formate production is greatly improved as compared to that at an open-circuit voltage, with a rate enhancement ratio ranging from 10 to 143. The thermocatalytic and electrocatalytic reduction of CO2 compete with each other and are promoted by the applied negative potential and H2 in the feeds, respectively. Inspired by the EPOC effect, a composite electrode containing Pd/C and Pt/C catalysts on different sides of a carbon paper was constructed for catalyzing the CO2 reduction without adding H2 to the feeds. Water electrolysis over Pt NPs generates H2, which then effectively promotes formate production over Pd NPs.

Effect of KHCO3 Concentration on Electrochemical Reduction of CO2 on Copper Electrode

Recently, extensive investigations have been carried out on the electrochemical and photoelectrochemical reductions of CO2 into hydrocarbons to convert renewable energies into chemical fuels. In these researches, aqueous solutions of bicarbonate salts, such as NaHCO3 and KHCO3, are widely used as the supporting electrolyte. However, the effects of HCO3− on the CO2 reduction have not been studied in detail. In this research, the effects of KHCO3 concentration on CO2 reduction were studied at different applied potentials on a Cu working electrode using a potentiostatic method. The concentration of dissolved CO2 ([CO2]) and ratio of [CO2]/[K+] in the KHCO3 solution after bubbling with CO2 were studied to determine the relationship between KHCO3 concentration and CO2 reduction faradaic efficiency. The results suggest that high [CO2]/[K+] ratio in solutions with low KHCO3 concentration is probably a key factor to promote CO2 reduction faradaic efficiency. A model for the effect of [CO2]/[K+] ratio on CO2 reduction efficiency was also proposed.