Direct Electrochemical Reduction Research Articles

Study on the Direct Electrochemical Reduction of Fe2O3 in NaCl-CaCl2 Melt

Study on the Direct Electrochemical Reduction of Fe2O3 in NaCl-CaCl2 Melt

Removal and Recovery of Uranium from Groundwater Using Direct Electrochemical Reduction Method: Performance and Implications.

Removal of uranium from groundwater is of great significance as compared to in situ bioimmobilization technology. In this study, a novel direct electro-reductive method has been developed to efficiently remove and recover uranium from carbonate-containing groundwater, where U(VI)O2(CO3)34- and Ca2U(VI)O2(CO3)3 are the dominant U species. The transferred electron calculations and XPS, XRD analyses confirmed that U(VI) was reduced to U(IV)O2 and accumulated on the surface of the Ti electrode (defined as Ti@U(IV)O2 electrode) with high current efficiencies (over 90.0%). Moreover, over 98.0% of the accumulated U(IV)O2 could be recovered by soaking the Ti@U(IV)O2 electrode in the dilute nitric acid. Results demonstrated that the accumulated U(IV)O2 on the surface of the Ti electrode played a key role in the removal of U(VI), which can promote the electro-reduction of U(VI). Therefore, the electrode could be used repeatedly and has a high removal capacity of U(VI) due to the continuous accumulation of active U(IV)O2 on the surface of the electrode. Significantly, the uranium in both real and high salinity groundwater can be efficiently removed. This study implies that the proposed direct electro-reductive method has great potential for the removal and recovery of uranium from groundwater and uranium-containing wastewater.

Highly sensitive and rapid determination of sunset yellow in drinks using a low-cost carbon material-based electrochemical sensor.

Starting from simple graphite flakes, an electrochemical sensor for sunset yellow monitoring is developed by using a very simple and effective strategy. The direct electrochemical reduction of a suspension of exfoliated graphene oxide (GO) onto a glassy carbon electrode (GCE) surface leads to the electrodeposition of electrochemically reduced oxide at the surface, obtaining GCE/ERGO-modified electrodes. They are characterized by cyclic voltammetry (CV) measurements and field emission scanning electron spectroscopy (FE-SEM). The GCE/ERGO electrode has a high electrochemically active surface allowing efficient adsorption of SY. Using differential pulse voltammetry (DPV) technique with only 2min accumulation, the GCE/ERGO sensor exhibits good performance to SY detection with a good linear calibration for concentration range varying 50-1000nM (R2 = 0.996) and limit of detection (LOD) estimated to 19.2nM (equivalent to 8.9μgL-1). The developed sensor possesses a very high sensitivity of 9μA/μM while fabricated with only one component. This electrochemical sensor also displays a good reliability with RSD value of 2.13% (n = 7) and excellent reusability (signal response change < 3.5% after 6 measuring/cleaning cycles). The GCE/ERGO demonstrates a successful practical application for determination of sunset yellow in commercial soft drinks. Graphical abstract.

Water Oxidation Catalysts from Waste Metal Resources: A Facile Metal-Organic Electrochemical Approach

Abstract A fabrication route is presented by a novel metal-organic electrochemical approach, allowing facile preparation of electrocatalytic metal and metal oxide thin films from solid metals at room temperature: divalent transition metals such as iron, nickel and cobalt can be deposited as amorphous oxyhydroxide films. Among them, nickel- and cobalt-prepared samples are showing high activity as water oxidation catalysts in alkaline electrolytes. The applicability to waste metal material is exemplified using one of the most abundant waste metal alloys, i.e. steel: with a suitable multi-layer architecture, comprising, a large surface-area iron oxyhydroxide core-geometry and a steel-derived catalytic overlayer, the overpotential for oxygen evolution (at 10 mA cm−2) could be improved to only 370 mV. Chemical analysis is provided to elucidate the reaction pathway, encompassing metal halogenation, formation of meta-stable metal-organic intermediates or direct electrochemical reduction, respectively. Structural peculiarities of the derived films are finally demonstrated upon development of a photoactive nickel oxyhydroxide/silicon junction realizing a photocurrent of 1 mA cm−2 at the thermodynamic potential for oxygen evolution and short-term stabilization in the range of several hours.

The Feasibility of Electrochemical Ammonia Synthesis in Molten LiCl-KCl Eutectics.

Molten LiCl and related eutectic electrolytes are known to permit direct electrochemical reduction of N2 to N3- with high efficiency. It had been proposed that this could be coupled with H2 oxidation in an electrolytic cell to produce NH3 at ambient pressure. Here, this proposal is tested in a LiCl-KCl-Li3 N cell and is found not to be the case, as the previous assumption of the direct electrochemical oxidation of N3- to NH3 is grossly over-simplified. We find that Li3 N added to the molten electrolyte promotes the spontaneous and simultaneous chemical disproportionation of H2 (H oxidation state 0) into H- (H oxidation state -1) and H+ in the form of NH2- /NH2 - /NH3 (H oxidation state +1) in the absence of applied current, resulting in non-Faradaic release of NH3 . It is further observed that NH2- and NH2 - possess their own redox chemistry. However, these spontaneous reactions allow us to propose an alternative, truly catalytic cycle. By adding LiH, rather than Li3 N, N2 can be reduced to N3- while stoichiometric amounts of H- are oxidised to H2 . The H2 can then react spontaneously with N3- to form NH3 , regenerating H- and closing the catalytic cycle. Initial tests show a peak NH3 synthesis rate of 2.4×10-8 mol cm-2 s-1 at a maximum current efficiency of 4.2 %. Isotopic labelling with 15 N2 confirms the resulting NH3 is from catalytic N2 reduction.

The Feasibility of Electrochemical Ammonia Synthesis in Molten LiCl–KCl Eutectics

AbstractMolten LiCl and related eutectic electrolytes are known to permit direct electrochemical reduction of N2 to N3− with high efficiency. It had been proposed that this could be coupled with H2 oxidation in an electrolytic cell to produce NH3 at ambient pressure. Here, this proposal is tested in a LiCl–KCl–Li3N cell and is found not to be the case, as the previous assumption of the direct electrochemical oxidation of N3− to NH3 is grossly over‐simplified. We find that Li3N added to the molten electrolyte promotes the spontaneous and simultaneous chemical disproportionation of H2 (H oxidation state 0) into H− (H oxidation state −1) and H+ in the form of NH2−/NH2−/NH3 (H oxidation state +1) in the absence of applied current, resulting in non‐Faradaic release of NH3. It is further observed that NH2− and NH2− possess their own redox chemistry. However, these spontaneous reactions allow us to propose an alternative, truly catalytic cycle. By adding LiH, rather than Li3N, N2 can be reduced to N3− while stoichiometric amounts of H− are oxidised to H2. The H2 can then react spontaneously with N3− to form NH3, regenerating H− and closing the catalytic cycle. Initial tests show a peak NH3 synthesis rate of 2.4×10−8 mol cm−2 s−1 at a maximum current efficiency of 4.2 %. Isotopic labelling with 15N2 confirms the resulting NH3 is from catalytic N2 reduction.

Electrochemical reduction of hematite-based ceramics in alkaline medium: Challenges in electrode design

Electrochemical reduction of low-conductive hematite-based ceramics represents a novel approach for iron recovery and waste valorisation. The process itself allows a flexible switching between hydrogen generation and iron reduction, important for the intermittent renewable-energy-powered electrolytic process. The present study focuses on the direct electrochemical reduction of aluminium-containing hematite in strong alkaline media. Within this scope, the reduction mechanisms of porous and dense cathodes, with 60%, 37% and 3% of open porosity, were investigated using different types of electrodes configuration: nickel-foil and Ag-modified nickel-foil supported configuration (cathodes facing or against the counter electrode), and nickel-mesh supported configuration. The efficiency of the iron reduction was compared for different electrode concepts. The results highlight the importance of electrolyte access to the interface between the metallic current collector and ceramic cathode for attaining reasonable electroreduction currents. Both excessively porous and dense ceramic cathodes are hardly suitable for such reduction process, showing a necessity to find a compromise between mechanical strength of the electrode and its open porosity, essential for the electrolyte access.

Mechanistic reaction pathways of enhanced ethylene yields during electroreduction of CO2-CO co-feeds on Cu and Cu-tandem electrocatalysts.

Unlike energy efficiency and selectivity challenges, the kinetic effects of impure or intentionally mixed CO2 feeds on the catalytic reactivity of the direct electrochemical CO2 reduction reaction (CO2RR) have been poorly studied. Given that industrial CO2 feeds are often contaminated with CO, a closer investigation of the CO2RR under CO2/CO co-feed conditions is warranted. Here, we report mechanistic insights into the CO2RR reactivity of CO2/CO co-feeds on Cu-based nanocatalysts. Kinetic isotope-labelling experiments-performed in an operando differential electrochemical mass spectrometry capillary flow cell with millisecond time resolution-showed an unexpected enhanced production of C2H4, with a yield increase of almost 50%, from a cross-coupled 12CO2-13CO reactive pathway. The results suggest the absence of site competition between CO2 and CO molecules on the reactive surface at the reactant-specific sites. The practical significance of sustained local interfacial CO partial pressures under CO2 depletion is demonstrated by metallic/non-metallic Cu/Ni-N-doped carbon tandem catalysts. Our findings show the mechanistic origin of improved C2 product formation under co-feeding, but also highlight technological opportunities of impure CO2/CO process feeds for H2O/CO2 co-electrolysers.

Preparation of Metal Lead from Waste Lead Paste by Direct Electrochemical Reduction in NH3-NH4Cl Solution

Metal lead was first prepared from waste lead paste by direct electrochemical reduction in NH3-NH4Cl solution. Cyclic voltammetry of waste lead paste powders indicated that waste lead paste could be directly electrochemically reduced to metal lead. After constant cell voltage electrolysis for 3 h, waste lead paste pellets were almost completely converted into metal containing 98.3% lead, and the current efficiency and energy consumption were approximately 86.3% and 689.4 kW h/t, respectively. In addition, an empirical model of direct electrochemical reduction of waste lead paste pellets in NH3-NH4Cl solution has been proposed. Metal lead was initially formed at a three-phase interface of the current collector, waste lead paste and electrolyte; then, the newly formed three-phase interface of the metal lead, waste lead paste and electrolyte quickly expanded along the surface of the pellets and eventually extended into the interior of the pellets.

Tuning the preferentially electrochemical growth of carbon at the “gaseous CO2-liquid molten salt-solid electrode” three-phase interline

It has been widely accepted that the electrochemical reduction of CO2 in molten carbonate is implemented by the reduction of CO32− at the cathode that releases O2− to capture CO2 and replenish CO32−. This paper aims to reveal the direct electrochemical reduction of gaseous CO2 in molten salts and the growth behaviors of carbon at the CO2/molten salt/electrode interline. The electrochemical reduction of gaseous CO2 takes place at the three-phase interline of gaseous CO2/liquid molten salt/solid electrode (GLS-3PI) when the temperature is over 700 °C. The reduction of CO2 at the GLS-3PI results in the preferential growth of carbon, posing a potential risk to short-circuiting the electrolysis cell. An insulative sheath can prevent the CO2 contacting the GLS-3PI, thereby avoiding the preferential growth of carbon and getting rid of the risk of the short circuit. This paper offers new insights into understanding the direct electrochemical reduction of CO2 at the GLS-3PI and provides an isolation strategy to engineer the molten salt electrolysis cells.

Optimizing FeNC Materials as Electrocatalysts for the CO2 Reduction Reaction: Heat‐Treatment Temperature, Structure and Performance Correlations

AbstractThe direct CO2 electrochemical reduction reaction (CO2RR) into carbon‐based chemicals has attracted tremendous attention as a sustainable process for CO2 utilization. The viability of the process, however, is contingent on finding efficient catalysts based on earth abundant elements. Carbon‐based solid catalyst materials doped with nitrogen and transition metals (M−N−C) have emerged as a cost‐efficient alternative for the direct electrochemical reduction of CO2 into CO. These materials contain different N functionalities and MNx moieties which could be involved in the catalytic process. With the aim of gaining insight into the role of these different active sites and how to control their concentration we have prepared 5 polyaniline derived FeNC catalysts by changing the temperature of the heat treatment (750–1050 °C). We observed that it is possible to tune the ratio of the different N functionalities by changing the pyrolysis temperature. Furthermore, this had a clear impact on the catalytic performance of this family of FeNC materials. In particular, a higher temperature correlated with a larger FeNx concentration resulting in a high selectivity toward the CO2RR. These results indicate that FeNx moieties play a predominant role in the catalytic process and that the incorporation of such sites to the carbon structure is enhanced by the heat‐treatment temperature.

H-Cell Vs Gas Diffusion Electrolyzer for Evaluating Intrinsic Activity of Nanocatalysts for Electrochemical CO2 Reduction

Anthropogenic CO2 emissions are a leading contributor toward climate change, making closing the carbon cycle of the utmost importance to the research community.1 One potential technique to do this effectively is via the sustainable electrochemical conversion of CO2. By using energy from intermittent sources (such as wind and solar) and protons from water, CO2 can be converted to a variety of useful products (i.e. CO and C2H4).2 However, controlling the selectivity towards which particular product is formed and preventing the parasitic hydrogen evolution reaction is a crucial challenge that must be overcome before commercial implementation can occur.3 Typically, when exploring fundamental mechanisms and new catalyst materials to overcome this challenge, preliminary studies begin in an H-type cell (Figure 1a) where CO2 and gas products diffuse to and from the catalyst surface through the liquid electrolyte.4 However, this can place a considerable restriction on the electrochemical selectivity and current due to the low solubility (~34.2 mmol/L) and diffusivity (~2x10-9 m2/s) of CO2 in the liquid electrolyte.5,6 Furthermore, the H-cell configuration is restricted to laboratory scale experiments. Potential commercial processes for electrochemical CO2 reduction rely on the use of gas-diffusion layers, which greatly increases the diffusivity of CO2 and gas products by enabling transport through the gas phase (Figure 1d).7,8 When a catalyst or system of catalysts are evaluated solely in the H-cell the selectivity and activity for products of electrochemical CO2 reduction can misrepresent a catalyst’s intrinsic capability for electrochemical CO2 reduction. We present a comparison between a series of nanoparticle (NP) based electrodes, prepared similarly, in a liquid H-type cell vs. a gas-diffusion electrolyzer (GDE) for electrochemical reduction of CO2. In the case of Au NPs (Figure 1 a-b) we found ~45% faradaic efficiency and ~0.5 A/g current density towards CO at -0.5 V vs. RHE (the only electrochemical CO2 product), which would suggest that these particular Au NPs are an ineffective catalyst. However, when reevaluated in the GDE the selectivity and activity are much higher (~80% and ~220 A/g) at the same potential and with the same electrolyte. The stark contrast in both selectivity and activity for the catalyst’s capability of converting CO2 to CO depending on the reactor chosen demonstrates the importance of considering operational conditions when evaluating a class of materials true potential to carry out electrochemical CO2 reduction in commercially relevant systems. (1) Olah, G. A.; Prakash, G. K. S.; Goeppert, A. Anthropogenic Chemical Carbon Cycle for a Sustainable Future. J. Am. Chem. Soc. 2011, 133 (33), 12881–12898. https://doi.org/10.1021/ja202642y. (2) Whipple, D. T.; Kenis, P. J. A. Prospects of CO2 Utilization via Direct Heterogeneous Electrochemical Reduction. J. Phys. Chem. Lett. 2010, 1 (24), 3451–3458. https://doi.org/10.1021/jz1012627. (3) Verma, S.; Kim, B.; Jhong, H.-R. “Molly”; Ma, S.; Kenis, P. J. A. A Gross-Margin Model for Defining Technoeconomic Benchmarks in the Electroreduction of CO2. ChemSusChem 2016, 9 (15), 1972–1979. https://doi.org/10.1002/cssc.201600394. (4) Raciti, D.; Mao, M.; Ha Park, J.; Wang, C. Mass Transfer Effects in CO 2 Reduction on Cu Nanowire Electrocatalysts. Catalysis Science & Technology 2018, 8 (9), 2364–2369. https://doi.org/10.1039/C8CY00372F. (5) Gupta, N.; Gattrell, M.; MacDougall, B. Calculation for the Cathode Surface Concentrations in the Electrochemical Reduction of CO2 in KHCO3 Solutions. J Appl Electrochem 2006, 36 (2), 161–172. https://doi.org/10.1007/s10800-005-9058-y. (6) Raciti, D.; Mao, M.; Wang, C. Mass Transport Modelling for the Electroreduction of CO2 on Cu Nanowires. Nanotechnology 2018, 29 (4), 044001. https://doi.org/10.1088/1361-6528/aa9bd7. (7) Weng, L.-C.; Bell, A. T.; Weber, A. Z. Modeling Gas-Diffusion Electrodes for CO2 Reduction. Phys. Chem. Chem. Phys. 2018, 20 (25), 16973–16984. https://doi.org/10.1039/C8CP01319E. (8) Wu, K.; Birgersson, E.; Kim, B.; Kenis, P. J. A.; Karimi, I. A. Modeling and Experimental Validation of Electrochemical Reduction of CO2 to CO in a Microfluidic Cell. J. Electrochem. Soc. 2015, 162 (1), F23–F32. https://doi.org/10.1149/2.1021414jes. Figure 1

(Corrosion Division Morris Cohen Graduate Student Award Address) Active Metallic Corrosion in Weak Acid Solutions: A Unified Mechanistic View to Cathodic Reactions

Metallic corrosion in an aqueous acidic solution is one of the most common corrosion scenarios in industrial applications and energy sector, in particular the oil and gas extraction and transmission facilities. In such systems corrosion is usually caused by the presence of the co-produced aqueous phase, acid gases, and other dissolved acidic compounds. The three major compounds that are conventionally believed to be causing the high corrosivity in such environments are carboxylic acids, carbon dioxide (CO2), and hydrogen sulfide (H2S). The presence of these species in the aqueous phase form an acidic, highly corrosive solution. Nevertheless, mild steel remains the inevitable choice of material due to practical and economical limitations of such large scale infrastructures. The use of mild steel, with its low resistance to corrosion, makes the understanding, prediction, detection, and mitigation of corrosion an essential aspect of this industry. The exceptionally higher corrosivity of the aqueous solutions containing CO2, H2S and carboxylic acids (e.g. acetic acid or HAc in short) as compared to solutions of strong acids (e.g. HCl) with the same pH, has been known for decades. Species like carbonic acid (H2CO3), bicarbonate ion (HCO3 -), H2S, and HAc, as weak acids, are only partially dissociated in the solution. Hence, they are present both in their dissociated and undissociated forms. In the conventional mechanistic view, the higher corrosivity of these solutions have been associated with the additional reduction reactions of the undissociated weak acids (to hydrogen and their corresponding anion) including H2CO3, and HCO3 - in CO2 corrosion, as well as HAc, and H2S. With the focus on the cathodic reactions, the mechanism of corrosion in aqueous solutions containing HAc, CO2, and H2S are revisited in a series of investigations. In all three cases the experimental data and the quantitative evaluations showed that the direct electrochemical reduction of H2CO3, HCO3 -, HAc, and H2S are not occurring to any appreciable extend, in contrast to the conventional mechanistic understanding. Furthermore, the deficiencies in previous studies both in the experimental approaches and quantification of the results leading to misinterpretation of the data, were discussed. In the mechanistic view developed in these studies, the corrosion of mild steel in all of the abovementioned scenarios is an extension of simple acidic corrosion of steel with only two electrochemical reactions: hydrogen ion (H+) reduction as the sole cathodic reaction, and iron dissolution as the sole anodic reaction. However, the combined effect of the coupled chemical reactions along with solution pH, and other environmental conditions such as temperature and fluid flow on the surface concentration of H+, leads to a great diversity in the observed behavior of the cathodic polarization curves and corrosion rate trends, as have been observed in the previous studies. In its simplest form, the chemical dissociation of the weak acid at the vicinity of the metal surface acts as an additional source of H+, hence, results in increased limiting currents. Nevertheless, the results of this study showed that depending on the chemical properties of the involved weak acid and other environmental conditions, the same mechanism may lead to more complex polarization behavior. The reduction of HCO3 - and H2S are examples of such scenario, where the cathodic polarization curves show two “waves”, as demonstrated in Figure 1. Even though the existence of this “double wave” was considered as solid proof of the direct reduction of these weak acid until very recently, the mathematical simulations based on the newly proposed mechanism showed that this behavior is also merely another example of the effect of solution chemistry on the surface concentration of H+. In light of this cumulative knowledge, a unifying and generic mechanistic view for Active corrosion in weak acid solutions can now be put forward. Based on this mechanistic view a generic categorization of weak acids, simply based on their pKa values, is developed to represent their extent of influence on the cathodic polarization and corrosion rates. Such a framework can be used to assess the expected behavior of any given species and provides the guidelines for any future research in this field of study. Figure 1

Direct electrochemical reduction of copper sulfide in molten borax

In this study, for the first time, direct copper production from copper sulfide was carried out via direct electrochemical reduction method using inexpensive and stable molten borax electrolyte. The effects of current density (100–800 mA/cm2) and electrolysis time (15–90 min) on both the cathodic current efficiency and copper yield were systematically investigated in consideration of possible electrochemical/chemical reactions at 1200°C. The copper production yield reached 98.09% after 90 min of electrolysis at a current density of 600 mA/cm2. Direct metal production was shown to be possible with 6 kWh/kg energy consumption at a 600 mA/cm2 current density, at which the highest current efficiency (41%) was obtained. The suggested method can also be applied to metal/alloy production from single- and mixed-metal sulfides coming from primary production and precipitated sulfides, which are produced in the mining and metallurgical industries during treatment of process solutions or wastewaters.

Manganese Oxide Nanochips as a Novel Electrocatalyst for Direct Redox Sensing of Hexavalent Chromium

In order to maintain a healthy organisation of bionetworks, both qualitative and quantitative estimation of hexavalent chromium in food and beverage samples is required based on proper quality control and assurance. Nonetheless, conventional quantitation techniques for hexavalent chromium generally suffer from certain limitations (e.g., the need for expertise, costly equipment, and a complicated procedure). This research was performed to elaborate a novel method to quantify hexavalent chromium based on an electrochemical cyclic voltammetry technique. To this end, nanochips of manganese oxide (Mn3O4: approximately 80–90 nm diameter and 10 nm thickness) were synthesized using a chemical method and characterized with spectroscopic and microscopic approaches. These nanochips were employed as proficient electrocatalytic materials in direct redox sensing of hexavalent chromium in both real samples and laboratory samples. Manganese oxide nanochips felicitated large surface area and catalytic action for direct electrochemical reduction of hexavalent chromium at electrode surface. This fabricated nanochip sensor presented a detection limit of 9.5 ppb with a linear range of 50–400 ppb (sensitivity of 25.88 µA cm−2 ppb−1).

The synergistic interaction between sulfate-reducing bacteria and pyrogenic carbonaceous matter in DDT decay

Although 1,1,1-trichloro-2,2-di(4-chlorophenyl)ethane (DDT) was banned in the United States in 1972, it is still often detected in sediments where pyrogenic carbonaceous matter (PCM) and sulfate-reducing bacteria (SRB) co-exist. In this study, we found that 70.2 ± 0.2% of DDT disappeared in the presence of SRB and graphite powder, a model PCM, after 21 days at pH 7. Our results suggest that the observed DDT decay was due to the reaction between graphite powder and the reduced sulfur species that were produced by SRB. No biofilm formation was observed on the surface of graphite powder. Rather, the activity of SRB was inhibited by the presence of graphite powder. To understand the involvement of PCM in DDT decay, electrochemical cells and batch reactor experiments with sulfur-pretreated PCM as well as direct electrochemical reduction by a potentiostat were employed. Our results suggest that polysulfide, sulfide, sulfite, and thiosulfate could all react with PCM, forming surface-bound intermediates that subsequently led to DDT decay. The reactivity of reduced sulfur species was the highest for polysulfide, followed by sulfide, sulfite, and thiosulfate.

(Invited) Mechanistic Studies of the Direct Electrochemical CO2 Reduction on Non-Metallic MNC Single Site and MNC/Cu Hybrid Catalysts

In this talk, I will highlight some of our recent advances in the field of direct electrochemical reduction of CO2 into value-added fuels and chemicals on non-metallic carbon-based MNC electrocatalysts with molecularly-defined coordinative MNx metal-nitrogen centers as active sites. Special focus will be placed on efficient production of CO at lab-scale and industrial current densities with emphasis on a fundamental understanding of between selectivity and the nature of the MNx moiety. Furthermore, the design of hybrid electrocatalysts consisting of CO-efficient MNC backbones decorated with CuOx nanoparticles will be addressed and the molecular mechanisms of their enhanced ethylene production discussed.

(Keynote) Electroreduction of CO2 on Pb and Bi Nanoneedles

The rise in atmospheric CO2 concentration since the beginning of the Industrial Age has raised concerns on its potential effect on global temperatures. While several factors such as natural climate changes, variations in solar activity, and volcanic eruptions may also contribute to observed variations in CO2 concentrations, it has been well established that anthropogenic emissions contribute to the annual emission of over 30 billion tonnes of CO2, only about half of which is recycled through natural pathways. CO2 conversion into value-added products is an avenue explored to mitigate environmental issues. Conversion methods appear promising, as they offer the potential to produce liquid and gaseous fuels for use either in the aeronautics industry, or as a chemical storage method for the intermittent energy produced by windmills and photovoltaic panels. Fuel synthesis may be achieved via either the production of a syngas mixture (H2 and CO) through the water gas shift reaction and subsequent conversion into hydrocarbon fuel through processes such as Fisher-Tropsch, or by direct electrochemical reduction of CO2. While all methods may result in similar conversion yields, depending on the catalyst used, direct electrochemical conversion of CO2 into value-added products is a low-temperature process, with the further advantage of requiring relatively simple equipment. Formic acid, or formate salts, are used in a variety of chemical processes such as electrowinning, leather tanning, and aircraft de-icing. Alternatively, formic acid and formate salts may be considered a hydrogen storage medium. Direct formic acid, and more recently, direct formate fuel cells, have been investigated in the literature as they demonstrate significant benefits over methanol fuel cells, including higher open circuit voltage and lower crossover. Among earth-abundant CO2 electrocatalysts, Sn, Pb and Bi are known to be highly selective for formate production, with faradic efficiency (FE) > 90%. However, several challenges need to be addressed for these materials to become viable alternatives for industrial applications based on an ERC process to become economically viable. In particular, issues related with large overpotential and low current densities need to be addressed, along with the long term stability of electrodes. In this study, we compared the activity and stability for CO2 electroreduction of high surface area metallic Bi and Pb nanoneedles (see Figure 1). In both cases, the materials films were prepared through a direct electrodeposition (potentiostatic method). Both types of films were extensively characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM) and x-ray diffraction (XRD), while electrochemical activities were characterized by cyclic voltammetry (CV), linear sweep voltammetry (LSV), and potentiostatic measurements. Figure 1

Feasibility study of electrochemical conversion of solid ZrO2 to Zr metal in LiCl-(0-1 wt%)Li2O melts with graphite and platinum anodes

Direct electrochemical reduction of solid ZrO2 to Zr metal assumes importance in the context of pyrochemical reprocessing of spent oxide nuclear fuel. In this context, electrochemical reduction experiments were carried out with powder compacted and sintered ZrO2 pellets as cathode in LiCl-x wt.% Li2O (x = 0, 0.1, 0.25 and 0.5) melts against graphite anode and in LiCl-(0.5 and 1.0) wt.% Li2O melts against platinum anode at 650 °C and the samples were analysed using XRD and SEM combined with EDS techniques. The pellets were found reduced to Zr in pure LiCl melt and to Zr and smaller amounts of Li2ZrO3 in LiCl-Li2O melts under specific experimental conditions. Similar cathodic polarization experiments carried out with Li2ZrO3 pellets converted those to a mixture of Zr and Li2ZrO3. Contrary to the results reported in the literature by earlier workers, the results of this study make it quite clear that both solid ZrO2 and Li2ZrO3 can be electro-reduced to Zr in LiCl-Li2O melts. However, the study carried out with two different cathode configurations reveal that the efficiency of electro-reduction is strongly influenced by the design of the oxide electrode and to some extent the Li2O content of the melt.

Sourcing commodity chemicals from air?

Electrochemistry Plants that grow in the ground make all their carbon-based infrastructure from carbon dioxide (CO2). By contrast, plants built by chemists use petroleum and natural gas as their carbon feedstock. In a review, De Luna et al. explore the prospective challenges and opportunities for manufacturing commodity chemicals such as ethylene and alcohols by direct electrochemical reduction of CO2. They estimate that production costs would be competitive with fossil technologies if renewable electricity costs drop below 4 cents per kilowatt-hour and electrical-to-chemical conversion efficiencies reach 60%. Science , this issue p. [eaav3506][1] [1]: /lookup/doi/10.1126/science.aav3506