Design Of Catalysts For CO2 Reduction Research Articles

Quantitative Structure–Electrochemistry Relationship (QSER) Studies on Metal–Amino–Porphyrins for the Rational Design of CO2 Reduction Catalysts

The quantitative structure-electrochemistry relationship (QSER) method was applied to a series of transition-metal-coordinated porphyrins to relate their structural properties to their electrochemical CO2 reduction activity. Since the reactions mainly occur within the core of the metalloporphyrin catalysts, the cluster model was used to calculate their structural and electronic properties using density functional theory with the M06L exchange-correlation functional. Three dependent variables were employed in this work: the Gibbs free energies of H*, C*OOH, and O*CHO. QSER, with the genetic algorithm combined with multiple linear regression (GA-MLR), was used to manipulate the mathematical models of all three Gibbs free energies. The obtained statistical values resulted in a good predictive ability (R2 value) greater than 0.945. Based on our QSER models, both the electronic properties (charges of the metal and porphyrin) and the structural properties (bond lengths between the metal center and the nitrogen atoms of the porphyrin) play a significant role in the three Gibbs free energies. This finding was further applied to estimate the CO2 reduction activities of the metal-monoamino-porphyrins, which will prove beneficial in further experimental developments.

Meta-analysis approach for understanding the characteristics of CO2 reduction catalysts for renewable fuel production

The conversion of CO2 into renewable fuels by thermo-catalytic hydrogenation has been attempted by several researchers as this overcomes two significant problems, namely, greenhouse gas CO2 mitigation and renewable fuel production. Numerous experimental data have been reported in carbon-neutral methanol production using various copper, copper-zinc, copper-zinc-aluminium and also non-copper based catalysts in the past two decades. However, the lack of comprehensive data extraction and undefined data structure have concealed the property-performance correlations in catalyst design, which may have given a significant breakthrough in scaling up this carbon-neutral technology. This work attempts to review the literature data on this catalytic reaction considering various important catalyst descriptors starting from an elemental composition followed by correlating all the catalyst properties with performance using a meta-analysis approach. Herein, data for CO2 hydrogenation to C1 alcohol, methanol, was collected from 110 literature publications, and a comprehensive, structured interpretation of the catalysts' features that enhance their activity in this reaction is interpreted using meta-analysis. All the property groups, which are the key performance indicators, are analysed by testing their statistical significance across a wide range of reaction conditions under which the experimental data are collected from the literature. The developed machine learning model reveals that the promising catalyst must have the functionality to form stable carbonates. The adequacy of the model was validated through experimental data collected over eight different reaction conditions in a laboratory-scale tubular reactor. Thus, the meta-analysis tool is used to its full potential of exploring experimental data reported in past decades for the accurate design of CO2 reduction catalysts.

Elucidating the Role of Strain in Promoting C-C Coupling on Cu Surfaces

The design of CO2 reduction catalysts with high selectivity toward energy-dense, multi-carbon products remains a challenge. In this study we demonstrate a substantial correlation between surface strain and selectivity in aqueous CO2 reduction on model Cu (001) surfaces. By tuning the thickness of epitaxially-grown Cu layers on Si (001) substrates, we vary the lattice mismatch-derived tensile strain that remains. In-plane X-ray diffractometry indicates an increasing in-plane strain, up to 0.48%, is achieved in Cu epitaxial layers as layer thickness decreases from 100 nm to 20 nm. A roughly order-of-magnitude enhancement in selectivity to multi-carbon products (C2H4, acetate, EtOH, and n-PrOH) as compared to single-carbon products (formate, CO, and CH4) in 0.1M KHCO3 electrolyte is seen with this increase in built-in strain, evidencing the tuning of the adsorption energy of key reaction intermediates. Moreover, the strained 20 nm epitaxially-grown Cu thin films exhibit 4.8x and 68.3x higher selectivity to multi-carbon products as compared with bulk single-crystal Cu(100) and polycrystalline Cu surfaces. The enhanced selectivity toward energy-dense products can be attributed to an increased adsorption energy of selectivity-determining intermediates such as *CO and *CHO on the strained surface and promotion of C-C coupling reaction. These findings indicate the opportunity for rigorous strain engineering to modify adsorption energy of key intermediates for enhanced selectivity in CO2 reduction. Figure. Characteristics and CO2 reduction performance of epitaxially grown Cu (001) thin film on Si (001) substrate. (a) Bulk in-plane tensile strain as a function film thickness. Selectivity ratio of (b) C2H4 to CH4 and (c) multi-carbon products to single-carbon products as a function of bulk in-plane tensile strain at -0.9V vs RHE in CO2-saturated 0.1 M KHCO3 electrolyte. Figure 1

The role of reticular chemistry in the design of CO2 reduction catalysts.

The problem with current state-of-the-art catalysts for CO2 photo- or electroreduction is rooted in the notion that no single system can independently control, and thus optimize, the interplay between activity, selectivity and efficiency. At its core, reticular chemistry is recognized for its ability to control, with atomic precision, the chemical and structural features (activity and selectivity) as well as the output optoelectronic properties (efficiency) of porous, crystalline materials. The molecular building blocks that are in a reticular chemist's toolbox are chosen in such a way that the structures are rationally designed, framework chemistry is performed to integrate catalytically active components, and the manner in which these building blocks are connected endows the material with the desired optoelectronic properties. The fact that these aspects can be fine-tuned independently lends credence to the prospect of reticular chemistry contributing to the design of next-generation CO2 reduction catalysts.

Selective CO2 Reduction with Catalyst-Assembled Electrodes in an Aqueous Solution

Suppression of CO2 emission is an urgent and important issue to be solved global warming problem. When one recycles emitted CO2 from burned fossil fuels as useful carbon resources, such as CO, the overall amount of emitted CO2 in air will be reduced by keeping the usefulness of carbon-containing fuels and materials as key chemicals in industries without increase of CO2 emission. On the design of CO2 reduction catalysts, overpotential (η), turnover frequency (TOF), and robustness are major issues for highly efficient catalytic reaction. Our strategy is based on mimicking the active site structures of metalloenzyms, carbon monoxide dehydrogenases (CODHs), which contain Ni-Fe bimetallic center in a Fe-S cluster.1 These enzymes can convert CO2-to-CO at a quite low η, < 100 mV.2 However, the enzymes easily lose their activity due to the lack of their robustness. On the other hand, reported metal complexes applied for CO2 reduction, different from the enzymes, involve single metal ion in their active centers and require relatively higher η  than those of the enzymes. On this context, we have developed efficient electrocatalysts and their reaction systems, which fulfill all essential requisites for catalytic CO2 reduction. We applied the bimetallic motif in the enzymes for the structures of CO2 reduction catalysts and synthesized Fe porphyrin dimers by linking two Fe porphyrins through a phenylene group.3 As expected, the catalytic activity is very sensitive on the Fe-Fe separation. As the results, we demonstrated homogeneous catalytic CO2-to-CO reaction with Fe meso-tris(perfluorophenyl)porphyrin dimer bearing o-phnylene linker in very high TOF, 25,000 s-1, at η = 0.42 V and 93% CO selectivity in a wet DMF. Controlled potential electrolysis under the same conditions keeps current density, ≈1 mA cm-2 for 12 h without any loss of the activity.4 Since CO2-to-CO reaction couples with water splitting, heterogeneous electrocatalytic system is important. When one uses a coordination catalyst-assembled electrode in an aqueous solution, following issues should be solved: 1. When one modifies a flat electrode with a coordination catalyst, catalyst coverage on the electrode is limited. In order to increase current density or reaction velocity, the surface coverage should be several orders higher than the modified flat electrode. 2. The standard reduction potential of proton is less negative than those of many CO2 reduction reaction. Thus, an electrode protected by a suitable material is required in order to avoid preferential proton reduction over CO2. To overcome these issues, we use (1) nano tin oxide-sintered film on an electrode in order to increase the electrode surface area and (2) co-modification of a SAM layer for the protection of the metal oxide surface from water. By application of these methods, we attained selective CO2 reduction over hydrogen formation at zero overpotential in an aqueous solution in ten times higher current density than one with the ordinary flat electrode. References J.-H. Jeoung and H. Dobbek, Science, 2007, 318, 1461; J. Fesseler, J.-H. Jeoung, and H. Dobbek, Angew. Chem. Int. Ed., 2015, 54, 8560.W. Shin et al., J. Am. Chem. Soc., 2003, 125, 14688.E. A. Mohamed, Z. N. Zaharan, and Y. Naruta, Chem. Commun, 2015, 51, 16900.Z. N. Zahran, E. A. Mohamed, and Y. Naruta, Sci. Reports, 2016, 6, 24533.