A photoelectrochemical approach to splitting carbon dioxide for a manned mission to Mars

Infrared spectroelectrochemical and electrochemical kinetics studies of the reaction of nickel cluster radicals [Ni 3( μ2-dppm) 3( μ3-L) ( μ3I)] •(L = CNR, R = CH 3, i-C 3H 7, C 6H 11, CH 2C 6H 5, t-C 4H 9, 2,6-Me 2C 6H 3; L = CO) with carbon dioxide

Chem-bio interface design for rapid conversion of CO2 to bioplastics in an integrated system

HI-Light: A Glass-Waveguide-Based "Shell-and-Tube" Photothermal Reactor Platform for Converting CO2 to Fuels.

Introduction To reduce the carbon dioxide concentration in the atmosphere and to solve the energy shortage issue, CO2 converting technologies, such as electrochemical, photoelectrochemical, and photocatalytic CO2 reduction, have been paid big attention in the last several decades. Researches in this field aim to convert CO2 into useful fuels such as formic acid, carbon monoxide, methane and methanol using electric or solar energy by means of CO2 reduction catalysis, in which the products can be directly used or easily stored. To achieve high conversion efficiency, the development of CO2reduction catalyst is essential. In the present research, a Cu-Zn intermetallic catalyst was developed on the basis of the understanding of the reaction mechanism of CO2 reduction on the metal surface in an aqueous media. It was reported that the adsorption or desorption strength of CO2 and CO anion radicals on the surface of the metal is the essential factor on the reaction pathway of CO2 reduction. 1,2 Among numerous candidates for catalyst materials, the Cu-Zn intermetallic catalyst is supposed to have a very appropriate adsorption-desorption strengths to achieve high efficiency and selectivity for converting CO2into formic acid. Besides, the Cu-Zn intermetallic catalyst is consisted of abundant and eco-friendly metals, also the synthesis method is very simple and low-cost. Experimental and Evaluation A Cu-Zn intermetallic electrode was prepared by sputtering and vacuum sealing methods. Its electrocatalytic properties were evaluated in an electrochemical cell and the composition was optimized according to the electrochemical performance. The optimized Cu-Zn electrode was then used to construct a photoelectrochemical (PEC) cell with a mesoporous SrTiO3photoanode prepared by screen printing method. According to the performance in the PEC cell, Cu-Zn intermetallic nanoparticles loaded SrTiO3powder photocatalyst was also synthesized by chemical reduction and vacuum sealing methods and its photocatalytic property was evaluated. Results and Discussion According to the electrochemical evaluation, the Cu-Zn intermetallic electrode behaved lower onset potential than pure copper and pure zinc. After the optimization of the Zn concentration, we measured the lowest onset potential (-0.65V vs. Ag/AgCl) when the Zn mass ratio was 53%. In the PEC cell, the optimized Cu-Zn electrode was used as the cathode in a CO2 purged KHCO3 electrolyte. When the SrTiO3 photoanode was irradiated by UV light, CO2 reduction was catalyzed on the surface of Cu-Zn electrode. Figure 1 shows the products detected at the rest potential, and HCOOH, CO, CH4 and H2 were produced. When we purged Ar gas in the electrolyte solution at cathodic side, the products amount was much lower than that of CO2 purged condition, indicating that most of the products were originated from catalytic CO2reduction. Further, products amounts from Cu-Zn intermetallic were two times higher than those from pure Cu. It is noteworthy that the faradic efficiency for HCOOH was as high as 79.72%. The turnover number (TON) of this electrode reached 1458.9, which proved that the Cu-Zn electrode performed high stability. In the photocatalytic evaluation, the Cu-Zn intermetallic nanoparticles loaded SrTiO3 powder was dispersed into CO2 purged KHCO3 solution and irradiated under UV light. Significant amount of HCOOH was also detected, while H2 production was almost negligible, indicating that the Cu-Zn also behaves high selectivity as co-catalyst in a CO2photocatalytic reduction system. The carbon source of the products was also confirmed by our isotope tracing experiment. Conclusion The Cu-Zn intermetallic electrode can catalyze CO2 reduction under low bias-potential in electrochemical and photoelectrochemical CO2 reduction systems with high conversion efficiency and selectivity for HCOOH. Our Cu-Zn electrode was very stable under bias application as well as photon irradiation conditions. The Cu-Zn intermetallic nanoparticles loaded STO powder can also convert CO2into HCOOH and other products under UV irradiation. Acknowledgement This work has been supported by a grant from Advanced Catalytic Transformation program for Carbon utilization (ACT-C), Japan Science and Technology Agency (JST). References Kuhl, Kendra P., et al. J. Am. Chem. Soc., 136,14107-14113 (2014)Hori, Y. Modern aspects of electrochemistry. Springer New York, 2008. 89-189. Figure 1

Catalytic properties of nickel bis(phosphinite) pincer complexes in the reduction of CO 2 to methanol derivatives

The trinuclear nickel clusters [Ni3(µ3-L)(µ3-I)(µ2-dppm)3]+ (L = CO (1); CNR, R = CH3 (2), i-C3H7 (3), C6H11 (4), t-C4H9 (5), CH2C6H5 (6), C6H5 (7), p-C6H4I (8), p-C6H4F (9), p-C6H4CH3 (10), p-C6H4CF3 (11), p-C6H4OCH3 (12), p-C6H4CN (13), 2,6-(CH3)2C6H3 (14); dppm = Ph2PCH2PPh2) all contain a triply bridging π-acceptor (carbonyl or isocyanide) ligand. Compounds 1–14 all undergo single electron reductions over a relatively narrow range of E1/2( +/0) (−1.08 V to –1.18 V vs. SCE in acetonitrile) and are known electrocatalysts for the reduction of carbon dioxide. Specular reflectance infrared spectroelectrochemical (SEC) measurements on 1–14 indicate that the capping isocyanide or carbonyl ligand remains triply bridging (µ3,η1) upon single electron reduction. The magnitude of the ν(C≡O) or ν(C≡N) absorption band shift upon reduction is related to both the electronic and steric properties of the capping π-acceptor ligand. Spectroelectrochemical studies with UV–visible detection revealed a hypsochromic shift upon reduction of the clusters. The SEC cell and spectrometer utilized are extremely versatile and allow for data from 600 to 22 000 cm−1 to be acquired without modifying the SEC cell and making only minor configuration changes to the spectrometer. Key words: nickel, cluster, carbonyl, isocyanide, spectroelectrochemical.

A detailed electrochemical investigation of Ni(cyclam)^(2+) and its derivatives is described, especially with regard to the aqueous electrocatalytic reduction of CO_2 at mercury. Detailed chronocoulometric studies which quantify the extent of the adsorption of the active catalytic species Ni(cyclam)^+_(ads) are discussed. Ni(cyclam)^(2+) is only weakly adsorbed at mercury and in quantities substantially less than a monolayer. In contrast, Ni(cyclam)+ is adsorbed over a wide potential range and the adsorption process occurs in two potential dependent stages. An analysis of the kinetics of the adsorption process is discussed. In the presence of CO, Ni(cyclam)^(2+) is electrochemically reduced to Ni(cyclam)^+-CO and Ni(cyclam)^0-CO. This latter species is insoluble and precipitates on the electrode surface. Both of these species are chemically unstable and slowly react to form Ni(cyclam)^(2+) in the presence of oxidizing agents. Ni(cyclam)^+_(ads) catalyzes the reduction of CO_2 to exclusively CO. In unbuffered solutions, the OH- ion produced as a result of the reduction of CO_2 can decrease the flux of CO_2 molecules to the electrode surface by direct reaction with CO_2 to form HCO-^_3 or CO^(2-)_3,both of which are catalytically inactive towards reduction by Ni(cyclam)^+_(ads). In both buffered and unbuffered solutions, the precipitate Ni(cyclam)^0-CO which is formed on the electrode surface under all conditions where CO_2 is reduced causes a slow passivation of the electrode surface towards further catalytic reduction of CO_2. The binding of CO_2 and CO to Ni(cyclam)^(2+), Ni(cyclam)^+, and Ni(cyclam)^+_(ads) is discussed. The active catalyst, Ni(cyclam) )^+_(ads), is able to coordinate CO_2, but not the product of the reduction, CO. Both Ni(cyclam)^(2+) and Ni(cyclam)+ are unable to coordinate CO_2 and thus solution species are not important in the catalytic cycle. A comparison of these results with previous studies is given and an overall mechanism for the electrocatalytic reduction of CO_2 is proposed. This mechanism contains several important modifications from earlier studies.

Design of Photocatalysts for Efficient Heterogeneous and Heterogeneous/Homogeneous Photocatalytic Carbon Dioxide Reduction Systems

Electrocatalytic carbon dioxide (CO2) reduction using water is the key of artificial photosynthesis systems designed to produce fuels. However, a lot of catalysts for CO2 reduction have been studied using organic solvent, because hydrogen production is competitive reaction in the aqueous solution.We have improved the CO2 reduction selectivity of inorganic semiconductor (SC) material by combining SC with metal complex catalyst (MC) (SC/[MC] hybrid photocatalyst).1,2 In addition, by conjugating the SC/[MC] hybrid photocatalyst for CO2 reduction with a SC capable of H2O oxidation, we have successfully achieved an artificial photosynthesis system, which reduces CO2 to HCOOH with no external electrical bias using H2O as electron and proton source.3,4 However, the device requires noble metal catalysts, such as a ruthenium complex polymer as a CO2 reduction catalyst, and iridium oxide as a water oxidation catalyst. In view of future practical applications, such a system requires efficient catalysts that consist of inexpensive and abundant elements. The system can be applied to many other SCs and MCs. Thus, development of MC is an important factor for improvement in reaction rates and product selectivity of the artificial photosynthesis.Electrocatalytic CO2 reduction can be conducted using molecular catalysts (metal-complexes) under certain electrical biases. These electrocatalysts require a large electrical potential to achieve catalytic CO2 reduction, because the first step in the CO2 conversion is formation of a CO2 - radical anion intermediate during single-electron reduction. Therefore, hydrogen is likely to be generated preferentially by water splitting in aqueous solution. Current electrocatalysts facilitate proton-coupled multi-electron reactions (for example, CO2 + 2H+ + 2e- ➝ CO + H2O, -0.11 V vs. RHE), which require lower potentials than those for the single-electron reaction. However, many metal complex catalysts for CO2 reduction are limited by low product selectivity in the presence of water, due to preferential hydrogen generation which occurs at 0.0 V (vs. RHE).Mn complex catalysts for CO2 reduction have been researched by a lot of researchers, because Mn is one of earth abundant elements. However, because of the high overpotential for CO2 reduction, the limited operation conditions in organic solvents with H2O additives only, and the instability under irradiation, new catalysts need to be developed. Therefore, we tried to develop a new metal complex catalyst for CO2 reduction even in an aqueous solution. As a result, we have successfully developed a new Mn complex electrocatalyst with carbon material support for CO2 reduction in water.5 The developed Mn complex/carbon electrode catalyzed selective CO2 reduction even in aqueous solution, at very low overpotential under room light conditions. On the other hand, without carbon material support, this Mn complex electrode cannot act as CO2 reduction catalyst. Therefore, we have developed a noble method to improve the CO2 reduction activity of Mn complex catalysts by carbon materials, both high CO2 selectivity and low reaction overpotential in aqueous solutions. We also confirmed that the carbon support effect can be applied to other metal complex catalysts.We will discuss research progress of the new Mn complex electrocatalyst and development of new SC/[MC] hybrid photocatalyst for the artificial photosynthesis system. S. Sato, et al. Angew. Chem. Int. Ed. 2010, 49, 5101.T. Arai, et al. Chem. Commun. 2010, 46, 6944.S. Sato, et al. J. Am. Chem. Soc. 2011, 133, 15240.T. Arai, et al. Energy. Environ. Sci. 2015, 8, 1998.S. Sato et al. ACS Catal. 2018, 8, 4452.

CO2 conversion and utilization

Alcohol Production from Carbon Dioxide: Methanol as a Fuel and Chemical Feedstock

Electrocatalytic CO ₂ Reduction over Bimetallic Bi-Based Catalysts: A Review

Photoelectrochemical CO2 reduction has attracted considerable attention as a route to convert CO2 into value-added products. Pyridine (Py)-catalyzed CO2 reduction on a GaP photoelectrode has been shown to be a promising photoelectrochemical system to produce methanol under the underpotential condition. However, whether the dramatic decrease in overpotential can be attributed to the CO2 activation by the formation of the zwitterionic complex PyCO2 is currently under debate. Because the alignment between the band edge positions of photoelectrodes and the redox potentials of species determines the desired redox reactions, calculations have been performed to evaluate the band edge positions of GaP and the redox potentials of relevant reactions. In these works, the water effect has been either neglected or approximated by using the dielectric continuum or a few explicit water molecules, which may not be enough to determine the accurate energy level alignment in realistic chemical environments. Moreover, calculations performed in conventional implicit solvation models suggested that PyCO2 is unstable in homogeneous aqueous, while the bonding interactions between CO2 and N species have been experimentally detected. Thus, we performed ab initio molecular dynamics to investigate the band alignment of GaP, as well as the stability and the reducibility of PyCO2 in more realistic chemical environments. Our results showed that the solvation effect and the pyridine adsorption could shift up the band edge positions of GaP significantly, and neglecting such effects could result in a serious underestimation of the activity of the photocatalysts. More importantly, we found that the interaction between pyridine and CO2 at the GaP(110)/water interface is strong due to the synergetic stabilization effect, which leads to an about 0.6 V less negative redox potential of PyCO2/PyCO2– than that of CO2/CO2– in the homogeneous aqueous. Furthermore, we compared the redox potential of PyCO2/PyCO2– at the GaP(110)/water interface with the conduction band minimum of GaP, which showed that the reduction of the adsorbed PyCO2 is thermodynamically feasible. Our results suggested that the CO2 activation by the formation of PyCO2 at the GaP(110)/water interface could be responsible for the low overpotential. This work provides valuable insights into the mechanism of pyridine-catalyzed CO2 reduction on GaP and could pave the way for the development of efficient catalysts for CO2 reduction.

Activation of carbon dioxide is the most important step in its conversion into valuable chemicals. Surfaces of stable oxide with a low work function may be promising for this purpose. Here we report that the surfaces of the inorganic electride [Ca24Al28O64]4+(e−)4 activate and split carbon dioxide at room temperature. This behaviour is attributed to a high concentration of localized electrons in the near-surface region and a corrugation of the surface that can trap oxygen atoms and strained carbon monoxide and carbon dioxide molecules. The [Ca24Al28O64]4+(e−)4 surface exposed to carbon dioxide is studied using temperature-programmed desorption, and spectroscopic methods. The results of these measurements, corroborated with ab initio simulations, show that both carbon monoxide and carbon dioxide adsorb on the [Ca24Al28O64]4+(e−)4 surface at RT and above and adopt unusual configurations that result in desorption of molecular carbon monoxide and atomic oxygen upon heating.

Photochemistry of methyl- and n1-benzyl- n5-cyclopentadienyltricarbonyltungstein(II)