Search

We report here an electrolysis optical coherence tomography (eOCT) platform to visualize the chemical reactions occurring in a CO2 electrolyzer. The eOCT platform was designed to capture three dimensional images and videos at high spatial (~1 µm) and temporal (3 to reduce CO2 into CO at applied current densities of 50-800 mA cm−2. This video resolved the nucleation and formation of CO2 in the cathode compartment upon reaction of HCO3– with H+ delivered through the membrane, the formation of CO at the cathode|electrolyte interface, and H2 throughout the cathode compartment. The video captured the strikingly dynamic movement of the cathode and membrane components during electrolysis, and linked CO production to regions of the electrolyzer in which CO2 were in direct contact with both the membrane and the catalyst layers. This visualization enabled us to correlate the decrease in CO production to a buildup of CO2, CO, and H2, and (bi)carbonate salts at the cathode layer. The statistical analysis of phase distribution images allowed us to understand the competition between main (CO2 reduction) and side (hydrogen evolution) reactions in both time and space domains. We also show how a pulsing current liberates these residual bubbles and (bi)carbonates to recover CO production. These results highlight the power of using an eOCT platform to temporally and spatially resolve CO2RR electrolysis.

Electrolyzers are now capable of reducing carbon dioxide (CO

We report here an electrochemical flow reactor that converts limestone (CaCO3(s)) into Ca(OH)2(s) at a high production rate and co-produces pure CO2(g).

The manufacture of cement from limestone is the single largest industrial source of CO2(g) emissions into the atmosphere. We report here an electrochemical flow reactor (electrolyser) that continuously converts limestone (CaCO3(s)) into Ca(OH)2(s) at a high rate of product formation (486 mg h-1 at 100 mA cm-2). The Ca(OH)2(s) product (slaked lime) is a chemical precursor to cement clinker, the main component of Portland cement, and other cement varieties. This three-compartment electrolyser operates with ~100% current efficiency at a cell voltage of 2.9 V and generates pure O2(g), H2(g), and CO2(g) streams that can be utilized downstream without purification. To demonstrate this feature, we feed the CO2(g) released from limestone directly to a second electrolyser that valorizes CO2(g) into higher value carbon-containing products (e.g., CO). A life-cycle analysis indicates that the proposed electrochemical process can decrease CO2 emissions per tonne of cement by 75% and achieve cost-parity with incumbent cement manufacturing processes with a carbon tax of $50/tonne CO2.

Electrochemical conversion of CO2 to useful products at temperatures below 100 °C is nearing the commercial scale. Pilot units for CO2 conversion to CO are already being tested. Units to convert CO2 to formic acid are projected to reach pilot scale in the next year. Further, several investigators are starting to observe industrially relevant rates of the electrochemical conversion of CO2 to ethanol and ethylene, with the hydrogen needed coming from water. In each case, Faradaic efficiencies of 80% or more and current densities above 200 mA cm−2 can be reproducibly achieved. Here we describe the key advances in nanocatalysts that lead to the impressive performance, indicate where additional work is needed and provide benchmarks that others can use to compare their results. This Perspective describes the key advances in nanocatalysts that have led to the impressive electrochemical conversion of CO2 to useful products and provides benchmarks that others can use to compare their results.

We report an electrochemical reactor that converts 3.0 M KHCO3 into methane at the cathode, and oxidizes water at the anode. The molar ratio of methane product to unreacted CO2 gas (defined herein as "methane yield") was measured to be 34% at a partial current density of 120 mA cm-2. The highest previously reported CO2-to-methane yield is 3%. Our reactor achieved this improvement in methane yield because it is fed with 3.0 M KHCO3, a type of reactive carbon solution, rather than gaseous CO2. The reactor uses H+ delivered by a bipolar membrane to form CO2 at the cathode. This CO2 is subsequently reduced into methane. A cationic surfactant added to the catholyte suppressed hydrogen evolution and increased methane formation. A 1D continuum model confirmed that H+ from the membrane promotes the formation of methane over multicarbon products at the cathode. These findings present design principles for electrochemical methane synthesis.

Electrolysis is a potentially useful approach for converting carbon dioxide into chemicals and fuels. The most active electrocatalysts for efficiently mediating the carbon dioxide reduction reactio...

Gas diffusion electrodes (GDEs) mediate the transport of reagents, products, and electrons in electrochemical reactors designed to reduce CO2 into fuels or chemicals. While the ratio of ionomer to electrocatalyst in the precursor catalyst ink is typically assumed not to change after being deposited on the GDE, we show herein that this assumption is likely not valid. Moreover, we discovered that the faradaic efficiency for formate, which is considered to be inconsequential relative to CO when using Ag electrocatalysts, can be modulated by 20% by a mere 5 wt% change in GDE Nafion® content. We were able to resolve these small differences in GDE composition by developing an X-ray fluorescence (XRF) spectroscopic protocol that quantifies the sulfonate groups appended to the polytetrafluoroethylene (PTFE) backbone of Nafion®. Using this protocol, we were able to determine how to precisely control the relative amount of ionomer to electrocatalyst for each GDE. We also found that maintaining a uniform ionomer–catalyst composition across the entire GDE can likely be done more effectively with automated spray coating than with manual deposition methods. We recommend following these procedures in order to generate reproducible CO2RR performance parameters in flow cells.

The highest performance flow cells capable of electrolytically converting CO2 into higher value chemicals and fuels pass a concentrated hydroxide electrolyte across the cathode. A major problem for CO2 electrolysis is that this strongly alkaline medium converts the majority of CO2 into unreactive HCO3– and CO32– rather than CO2 reduction reaction (CO2RR) products. The electrolysis of CO (instead of CO2) does not suffer from this same problem because CO does not react with hydroxide. Moreover, CO can be more readily converted into products containing two or more carbon atoms (i.e., C2+ products). While several solid-state electrocatalysts have proven competent at converting CO into C2+ products, we demonstrate here that molecular electrocatalysts are also effective at mediating this transformation in a flow cell. Using a molecular copper phthalocyanine (CuPc) electrocatalyst, CO was electrolyzed into C2+ products at high rates of product formation (i.e., current densities J ≥200 mA/cm2), and at high Faradaic efficiencies for C2+ production (FEC2+; 72% at 200 mA/cm2). These findings present a new class of electrocatalysts for making carbon-neutral chemicals and fuels.

Molecular catalysts that combine high product selectivity and high current density for CO2 electrochemical reduction to CO or other chemical feedstocks are urgently needed. While earth-abundant metal-based molecular electrocatalysts with high selectivity for CO2 to CO conversion are known, they are characterized by current densities that are significantly lower than those obtained with solid-state metal materials. Here, we report that a cobalt phthalocyanine bearing a trimethyl ammonium group appended to the phthalocyanine macrocycle is capable of reducing CO2 to CO in water with high activity over a broad pH range from 4 to 14. In a flow cell configuration operating in basic conditions, CO production occurs with excellent selectivity (ca. 95%), and good stability with a maximum partial current density of 165 mA cm−2 (at −0.92 V vs. RHE), matching the most active noble metal-based nanocatalysts. These results represent state-of-the-art performance for electrolytic carbon dioxide reduction by a molecular catalyst., Molecular electrocatalysts reducing CO2 to CO with high selectivity and high rate are urgently needed. A cobalt phthalocyanine complex is capable of reducing CO2 to CO in water with a maximum partial current density up to 165 mA cm−2, matching the most active noble metal-based nanocatalysts.

Electrolyzers that reduce carbon dioxide (CO2) into chemicals and fuels often use high-purity gaseous CO2 feedstocks that need to be isolated from upstream carbon capture units. If CO2 were to be captured directly from air, the eluent is likely to be an aqueous solution rich in bicarbonate ions (HCO3-). This scenario provides the impetus to electrolytically reduce these bicarbonate-rich carbon capture solutions into the same products as a CO2 electrolyzer. We report here an electrolyzer configuration that couples the conversion of bicarbonate to CO at the cathode with hydrogen oxidation at an anode. This unique system is capable of reaching a commercially-relevant current density of 500 mA cm-2 at merely 2.2 V, which is >0.5 V more efficient than any other reported electrolyzer that reduces HCO3- or CO2 at these current densities.

Electrolyzers that reduce carbon dioxide (CO2) into chemicals and fuels often use high-purity gaseous CO2 feedstocks that need to be isolated from upstream carbon capture units. If CO2 were to be captured directly from air, the eluent is likely to be an aqueous solution rich in bicarbonate ions (HCO3-). This scenario provides the impetus to electrolytically reduce these bicarbonate-rich carbon capture solutions into the same products as a CO2 electrolyzer. We report here an electrolyzer configuration that couples the conversion of bicarbonate to CO at the cathode with hydrogen oxidation at an anode. This unique system is capable of reaching a commercially-relevant current density of 500 mA cm-2 at merely 2.2 V, which is >0.5 V more efficient than any other reported electrolyzer that reduces HCO3- or CO2 at these current densities.

The highest performance flow cells capable of electrolytically converting CO2 into higher value chemicals and fuels pass a concentrated hydroxide electrolyte across the cathode. A major problem for CO2 electrolysis is that this strongly alkaline medium converts the majority of CO2 into unreactive HCO3– and CO32– rather than CO2 reduction reaction (CO2RR) products. The electrolysis of CO (instead of CO2) does not suffer from this same problem because CO does not react with hydroxide. Moreover, CO can be more readily converted into products containing two or more carbon atoms (i.e., C2+ products). While several solid-state electrocatalysts have proven competent at converting CO into C2+ products, we demonstrate here that molecular electrocatalysts are also effective at mediating this transformation in a flow cell. Using a molecular copper phthalocyanine (CuPc) electrocatalyst, CO was electrolyzed into C2+ products at high rates of product formation (i.e., current densities J ≥200 mA/cm2), and at high Faradaic efficiencies for C2+ production (FEC2+; 72% at 200 mA/cm2). These findings present a new class of electrocatalysts for making carbon-neutral chemicals and fuels.

Electrochemical conversion of CO

Flowing CO 2 boosts a molecular catalyst Molecular electrocatalysts for CO 2 reduction have often appeared to lack sufficient activity or stability for practical application. Ren et al. now show that design of the surrounding electrochemical cell can substantially boost both features. They directly exposed a known molecular catalyst, cobalt phthalocyanine, to gaseous CO 2 in a flow cell architecture, rather than an aqueous electrolyte. The configuration accommodated current densities exceeding 150 milliamperes per square centimeter, with longevity limited by local proton concentration rather than catalyst stability. Science , this issue p. 367

Practical electrochemical carbon dioxide (CO

The ant colony algorithm is an intelligence-optimized algorithm introduced by simulating ants searching for food by seeking the shortest route through pheromone. It is very useful in solving certain complicated optimization. This paper solves task allocation problem that an underwater glider deals with multiple tasks according to their situations, finished time and importance. The simulation results show that the ant colony algorithm is feasible and effective in solving tasks allocation.

Path planning of intelligent underwater robot is a key problem in robot research field. This article puts forward a method of underwater robot path planning based on immunization genetic algorithms. This method combines genetic algorithms and artificial immunization, which makes the path planning best. Emulation result proved it to be effective.