CO2 Reduction Potential Research Articles

Scenario-based Assessment of Decarbonized Transport Sector in Thailand towards Carbon Neutrality 2050

Thailand's transport sector has been one of the highest CO2 emitters for several decades in the country due to the excessive increase in transport service demand and the high reliance on high-carbon-intensity petroleum fuels. This article discusses the potential of CO2 reduction in the transport sector in Thailand to achieve carbon neutrality by 2050. The Low Emissions Analysis Platform (LEAP) is adopted to estimate the future energy demand and CO2 emission between 2020 and 2050. This study designs two main scenarios, namely the Baseline (BAS) and the Decarbonization (DEC) scenarios. The BAS scenario is developed in a business-as-usual approach with frozen technologies, while the DEC scenario is constructed as a CO2 countermeasure by including multiple low carbon technologies such as i) improving fuel economy efficiency of engines, ii) promoting electric vehicles (EVs), iii) utilizing fuel cell electric vehicles (FCEVs), and iv) promoting mass transportation. The results indicate that by 2050, the transport sector's total energy demand will significantly increase to approximately 49,906 ktoe, with diesel, gasoline, and jet kerosene accounting for the majority of fuel consumption. In the BAS scenario, total CO2 emissions in the transport sector are estimated to be 119,737 ktCO2eq. By full implementation of the CO2 countermeasures and low carbon technologies in the decarbonization scenario, the total carbon emission in the transport sector is estimated to be 30,582 ktCO2 by 2050, which is in line with carbon neutrality pathways of Thailand. However, the nation-wide transport action plan should be developed in order to promote such sustainable transport technologies.

Enhanced Charge Transfer in Poly(Heptazine Imide) Synergistically Induced by Donor-Acceptor Motifs and Ohmic Junctions for Efficient Photocatalytic CO2 Reduction.

Poly(heptazine imide) (PHI) has received widely interest in the photocatalytic CO2 reduction due to its good crystallinity and complete in-plane structure. However, its poor photo-induced carrier separation and migration efficiency and insufficient active sites results in undesirable photocatalytic CO2 reduction performance. Herein, we designed and constructed a novel ohmic junction photocatalyst by integrating melamine edge-modified PHI (mel-PHI) with extended π-conjugated system with TiN (TiN/mel-PHI) for enhancing the photocatalytic CO2 reduction activity. Strikingly, the photocatalytic CO2 reduction yield of the optimal TiN/mel-PHI is 62.64 μmol g-1 h-1, which is 5.6 and 2.8 times higher than PHI (11.26 μmol g-1 h-1) and mel-PHI (22.32 μmol g-1 h-1), respectively. The superior photocatalytic CO2 reduction activity is attributed not only to the formation of D-A structure by the introduction of melamine, which extends the π-conjugation system, alters the electronic structure of PHI, and accelerates the charge separation and migration, but also to the induced internal electric field by ohmic junction further enhances the charge separation and migration efficiency. Meanwhile, the synergistic effect of mel-PHI and TiN enriched the electron number of TiN, reducing the CO2 reduction potential. This work highlights the synergistic enhancement of charge transfer between D-A motifs and ohmic junctions, confirming their potential in optimizing photocatalysts.

Advancing sustainability in e-commerce packaging: A simulation-based study for managing returnable transport items

As e-commerce grows, tackling its environmental impacts, including those of packaging, becomes increasingly challenging. This study explores the benefits of reusable industrial packaging systems in the e-commerce industry, addressing ecological and financial perspectives. We contribute by formulating a generalized balancing problem for returnable transport items (RTIs) and developing a discrete-event simulation model and a heuristic to solve the problem. One methodological novelty is our modeling of network nodes that are simultaneously senders and recipients of RTIs. By applying the methodology to a case study of a large European e-commerce retailer, we address the need for industry-specific empirical studies comparing single-use and reusable packaging and RTI management in e-commerce.The case study reveals that reusing packaging and balancing its inventory across the network, even with packaging materials designed for single use, coupled with harmonizing packaging solutions, may produce substantial financial and ecological benefits. Furthermore, ours is the first study to include a CO2 price in optimizing RTI management. We find that while this does not have a positive effect on operational decision-making, it does steer strategic decisions towards more ecologically sustainable logistics systems. Our results indicate a savings potential of 30 to 75% of industrial packaging costs and an industry-wide CO2 reduction potential of 200,000 to 600,000 tons annually in Europe alone. Our research contributes to theoretical and practical understanding of sustainable packaging in e-commerce, offering a model and strategies for industry adaptation amidst growing environmental and regulatory pressures.

Monitoring the Activation of a Aucu Aerogel Catalyst for Electrochemical CO2 Reduction via in Situ XAS

To drive the further development of electrochemical CO2 reduction technologies, there is an urgent need for highly active catalysts that minimize unwanted side reactions and that also possess a large specific surface area. While nanostructured catalysts typically fulfill the latter requirement, they often use porous carbon supports that improve the nanoparticles’ dispersion but can shift the product selectivity towards undesirable H2 formation.[1] This challenge could be solved by using unsupported aerogels consisting of interconnected nanodomain networks of highly porous materials such as nano-wires or -particles, which provide a large surface area while minimizing unwanted side reactions.[2] So far, precious metals such as gold (Au) and silver (Ag) have shown remarkable activity and selectivity as CO2-reduction catalysts for CO production.[3] However, due to the high cost of such noble metals, improving their mass-specific activity is essential. One strategy to attain this, especially for Au, is to reduce the adsorption energy of the catalyst’s surface towards CO by changing the electronic structure of the d-band through alloying with other metals. In this context, ordered AuCu structures have proven to be promising candidates for improving the CO2-to-CO activity and selectivity.[4] With the motivation to combine both of the above approaches (i.e., Au-alloying with Cu and the absence of a C-support), in this study we present an AuCu aerogel with an average domain size of ≈ 7 nm that exhibits an exceptionally high faradaic efficiency of 87 % for CO at -0.6 V versus the reversible hydrogen electrode (RHE). This corresponds to a ≈ 2-fold higher Au-mass-specific partial current density for CO when compared to an equivalent, monometallic Au aerogel. Notably, this enhanced activity and selectivity are achieved by performing a potential cycling procedure prior to the CO2 reduction potential hold that involves cyclic voltammetry (CV) between 0.1 and 1.7 V vs. RHE at a scan rate of 50 mV/s until a stable voltammogram is achieved. To investigate the changes in the electronic and structural properties which have happened to the catalyst during this potential cycling, we performed an in situ grazing incidence X-ray absorption spectroscopy (XAS) measurements in the course of these CVs. Chiefly, these spectroelectrochemcial tests were carried out in the same cell used for the assessment of the CO2 reduction performance, ensuring for the first time that the mass-transport conditions encountered by the catalyst during these XAS measurements are identical to those in the CO2-reduction activity and selectivity tests. Figure 1 illustrates the changes observed throughout the potential cycling procedure in the Cu K- and Au L3-absorption edges, whereby the acquired spectra were submitted to a multivariate curve resolution (MCR) analysis. For the Cu K spectra, a total of three components were identified to describe the whole dataset, and it becomes evident that as the number of cycles increases, the copper oxide phase (component 1 in Figs. 1b and 1c) diminishes while a metallic phase (component 2, identified as an AuCu alloy through EXAFS fitting) becomes more prominent. In the case of the Au L3 data, only two components were discerned to describe the dataset, and both of them were identified as distinct AuCu alloy phases through EXAFS fitting. With an increasing number of cycles, component 2 (featuring a higher oxide content than component 1) becomes dominant at positive potentials, suggesting an increasing Au content on the aerogel’s surface as the potential cycling procedure progresses.In summary, in this contribution we present an AuCu aerogel catalyst exhibiting a high activity and selectivity for CO production that is achieved by cyclic voltammetry treatment prior to holding CO2 reduction potential. The results derived from the in situ XAS measurements on this material indicate that this process effectively removes the copper oxide domains initially present in the catalyst, forming a novel AuCu alloy phase while simultaneously enriching the aerogel’s surface with Au. References Baturina, O.A., et al., CO2 Electroreduction to Hydrocarbons on Carbon-Supported Cu Nanoparticles. ACS Catalysis, 2014. 4(10): p. 3682-3695. Cai, B. and A. Eychmuller, Promoting Electrocatalysis upon Aerogels. Adv Mater, 2019. 31(31): p. e1804881. Hori, Y.M., A.; Kikuchi, K.; Suzuki, S, Electrochemical Reduction of Carbon Dioxides to Carbon Monoxide at a Gold Electrode in Aqueous Potassium Hydrogen Carbonate. J. Chem. Soc., Chem. Commun., 1987. 10: p. 728-729. Liu, K., et al., Electronic Effects Determine the Selectivity of Planar Au-Cu Bimetallic Thin Films for Electrochemical CO(2) Reduction. ACS Appl Mater Interfaces, 2019. 11(18): p. 16546-16555. Figure 1

Constructing Triple-Atom sites for H2O Participated Electrocatalytic CO2 Reduction

After single and dual atoms catalysts (SACs and DACs), triple-atom catalysts (TACs) have been recently reported to possess great potential for electrocatalytic CO2 reduction (CO2RR). However, these expectations are all extracted from theoretical studies, and have not been verified experimentally. Here, we constructed a N-doped carbon-supported Zn-Ni bimetallic triple-atom catalyst (ZnNi-TACs) to fill the gap. It was found from operando IR spectroscopy and DFT calculations that in ZnNi-TACs, the Zn atom promotes the dissociation of H2O into protons and their participate in the activation of CO2 adsorbed at the Ni atom, while Zn and its adjacent Ni atom cooperatively optimize the formation of *COOH intermediate and the final desorption of *CO intermediate, thus leading to the remarkable catalytic activity for CO2RR. As such, this catalyst exhibited a CO Faradaic efficiency of 98.9 % and a current density of 485 mA cm−2 at −0.90 V (vs. RHE). In H-cell, the CO partial current density of ZnNi-TACs is 2 and 10 times higher than that of Ni-SAC and Zn-SAC prepared under the same conditions. This work provides the first example for studying the structure-performance relationship of TACs in CO2RR.

CO2 Electrolysis Coupled with Hydrogen Oxidation Reaction in Non-Aqueous Aprotic Electrolytes

CO2 electrolysis (CO2E) coupled with renewable energy is an important strategy to mitigate the effects of the green house gas in the atmosphere. By effectively transforming CO2 into higher value chemicals and fuels, the carbon cycle can be closed.[1] In order to produce C2+ products, most of the studies have been done in aqueous electrolytes, using Cu based catalysts. Nevertheless, these systems show different critical problems. First, in low temperature CO2E, CO2 carbonation in water is the primary source of energy and carbon losses.[2] Moreover, these systems rely on low faradaic efficiencies (FE) towards the single C2+ products (ethylene, ethanol, propanol). CO2E in organic aprotic electrolyte is gaining more and more attention due to the possibility of controlling the proton dynamics and the higher FE towards target products, mainly CO and oxalate. One challenge of these systems is the counter reaction. Many are using sacrificial anodes, which are not suitable for continuous industrial application.[3] Hydrogen oxidation reaction (HOR) is a promising reaction that could lower down the overall cell voltage, and, at the same time, produce more protonated products. This approach is not new in these systems, lithium mediated ammonia electrosynthesis, for example, has achieved relevant results using HOR at the anode and aprotic based electrolytes.[4] Based on these prerogatives, this study investigates the feasibility of couple CO2E with HOR in organic aprotic systems with controlled water content. A DMF/TBAPF6 electrolyte was used due to the good CO2 solubility (194 mmol L-1)[5] and conductivity. The rotating disk electrode experiments set up in a glovebox proved the stability of the chosen electrolyte, with a potential window of 3.6V, a HOR’s onset potential at -0.5V vs Ag/AgCl, and an onset potential for CO2 reduction at around -1.5V vs Ag/AgCl. A gas diffusion electrode (GDE) cell was used to perform CA or CP studies. A sputtered Cu GDE was used at the cathode. At the anode, an electrochemical deposited Pt/Au GDE was implemented for the HOR. [4] From the gas analysis, CO, H2 and ethylene have been detected at current densities of 10 mA/cm2. To investigate further the catalyst stability, XPS and SEM were used on the catalyst before and after the electrochemical reaction. ICP-MS analyses were done on the electrolyte to assess the eventual metal leaching during reaction.

Electrolyte Effects on Reactive Carbon Capture in Ionic Liquids

Reactive carbon capture (RCC), or integrated CO2 capture and electrochemical conversion, is a promising strategy to improve the energy efficiency and technoeconomics of the electrochemical reduction of CO2 from dilute sources. Ionic liquids are a class of functional solvents for RCC that can have high CO2 solubility and complex with CO2 to make an adduct species that lowers the activation energy and associated onset potential for CO2 reduction. Work is ongoing at the Center for Closing the Carbon Cycle, a DOE Energy Frontier Research Center, to understand which aspects of direct aqueous electrochemical CO2 reduction are translatable knowledge for RCC using ionic liquids. RCC behavior in imidazolium ionic liquids has been studied on exemplar catalysts including Ag and Sn as a function of variable electrolyte properties including ionic liquid concentration, solvent, supporting electrolyte cation, and pH. In particular, the effect of alkali cations was notably different from the behavior reported for aqueous-only CO2 reduction, with alkali species inhibiting CO2 reduction product selectivity in the presence of ionic liquid. In addition, the reduction of imidazolium carboxylate compounds has been investigated for further insight into the reduction of ionic liquid imidazolium cation-CO2 adducts.

Growth and Photoelectrochemical Characterization of Epitaxial ZnTe Photocathodes for Carbon Dioxide Reduction

We report on the growth and photoelectrochemical (PEC) characterization of single crystal, epitaxial zinc telluride (ZnTe) thin film photocathodes. ZnTe is a II-VI semiconductor that has promising photocathode characteristics, including its suitable band gap alignments to CO2 reduction potentials, chemical stability, strong p-type character, and is theorized to have surface sites suitable for CO2 reduction. To gain a deeper understanding of the fundamental charge transport of the reactivity mechanism for ZnTe, we utilized molecular beam epitaxy (MBE) to grow single crystal thin film photocathodes. This work focuses largely on the synthesis and characterization of degenerately-doped ZnTe films on three different gallium arsenide (GaAs) substrate orientations: (100), (110), and (111)A. ZnTe thin films with a thickness of 300 nm, grown in the temperature range of 340–360ºC, were doped with nitrogen via an in situ RF plasma source and characterized by RHEED, XRD, AFM, and Hall effect measurements. The epitaxial films exhibited p-type characteristics with doping concentrations of 1018 to 1020 cm-3. Photoelectrochemical stability and catalytic selectivity of the ZnTe photocathodes were investigated in a three-electrode compression cell in a CO2-saturated electrolyte (0.1 M KHCO3). Utilizing degenerately doped (100) ZnTe, we have demonstrated high (60%) selectivity for CO2 reduction to CO in the absence of cocatalysts. Overall, we showed the correlation between the CO2R selectivity and ZnTe orientation and this work can be leveraged for developing catalyst-free tandem ZnTe-based photocathodes for carbon dioxide reduction.

The diffusion of prefabrication technology and its potential for CO2 emissions reduction in China: A combined system dynamics and agent-based study

The building sector is one of the largest CO2 emitters. Prefabrication technology (PT) shows remarkable potential for reducing CO2 emissions during the material and construction phases of the building life cycle. However, the diffusion of PT in China is still in its infancy, and more targeted policies are necessary to accelerate the adoption of PT. This study proposes a combined system dynamics and agent-based modeling approach to include the technology adoption behavior of enterprises at the micro level, and the market effects and policies at the macro level. This approach provides a more comprehensive modeling approach and analysis for technology diffusion. Results show that the diffusion of PT has experienced three phases: (i) an initial phase that lasted until 2016, (ii) a mandatory adoption phase from 2016 to 2025, and (iii) a mandatory and market adoption phase that will last from 2025 to 2035 under appropriate policy mixes. A policy mix with moderate intensity is the most efficient in terms of balancing the policy effect and feasibility. The potential of CO2 reduction depends on both the diffusion rate of PT and the floor area of new buildings. Mandatory adoption is more effective than incentive-based policies in reducing CO2 emissions.

Buildings in Hot Climate Zones—Quantification of Energy and CO2 Reduction Potential for Different Architecture and Building Services Measures

Reducing energy and associated greenhouse gas emissions in buildings is one of the key aspects of climate change on a global level. To put the building sector on a low carbon development path, policies and adequate financing play a crucial role in each region. In the global South, policies and regulations related to the decarbonization of the building stock are increasingly being implemented. For policy and decision makers, adequate data on the status quo of the building stock, as well as the quantification of energy reduction measures, are essential to make informed decisions on the building regulatory and funding framework. The objective of this study is to provide data-driven insights into the potential for energy and CO2 reduction in buildings across various hot climate zones in the Global South. A simulation-based approach was employed to model five different building types, ranging from residential homes to office buildings, under a variety of architectural and building services scenarios. The simulations were conducted using the dynamic building energy simulation tool EnergyPlus, which assessed the impact of various energy-saving measures under both current and projected future climate conditions. This study concludes that optimizing passive design features, such as improved windows, solar shading, and reflective surfaces, in conjunction with active systems like decentralized cooling units and renewable energy integration, can result in a notable reduction in energy demand and emissions. Our findings provide a robust basis for policymakers to develop targeted energy efficiency strategies for buildings in hot climate zones, which will play a crucial role in achieving climate goals in the Global South.

Enhanced photoelectrocatalytic CO2 reduction to CO via structure-induced carrier separation in coral-like CuBi2O4-Bi2O3

Significant carrier recombination has severely limited the development of the most potential photoelectrocatalytic CO2 reduction reaction (PEC-CO2 RR). Herein, coral-like CuBi2O4-Bi2O3 photocathodes are prepared using the strategy of the construction of heterojunction to improve the efficiency of carrier separation. As expected, its faradic efficiency of CO (FECO) at the lower potential (0.1 V vs. RHE) is 86.03 %, which is about 1.49 times higher than that of the original CuBi2O4 film. The increased catalytic activity of CuBi2O4-Bi2O3 can be attributed to the high surface area of the distinctive coral-like structure of Bi2O3, which enhances light absorption efficiency. Additionally, the higher degree of band bending in CuBi2O4-Bi2O3 and the built-in electric field can speed up the transport rate of electrons, slow down the recombination of photogenerated electrons with holes and extend the lifetime of photogenerated electrons, allowing electrons to continuously participate in the reaction. This study proposes a novel strategy to optimize the efficiency of photoelectrocatalytic CO2 reduction by CuBi2O4-based photocathodes.

Potentiostatic electrodeposition of copper, indium, and cadmium sulfides for CO2 electroreduction: A path toward sustainable hydrogen generation

This study focuses on the potentiostatic electrodeposition of copper indium and cadmium sulfide (CuS, In2S3, and CdS) thin films on copper substrates, aiming to develop efficient electrocatalysts for the electrochemical reduction of CO2 and sustainable hydrogen generation. Utilizing Cu Kα radiation for X-ray diffraction (XRD) analysis, the crystal structures of the electrodeposited films were confirmed, revealing well-defined crystalline phases. The films exhibited average particle sizes of 55.99 nm for CuS, 50.37 nm for In2S3, and 63.51 nm for CdS. Cyclic voltammetry and chronoamperometry were employed to optimize the deposition parameters, ensuring efficient nucleation and growth of the metal sulfide films. The electrochemical performance of the synthesized electrocatalysts was rigorously tested, demonstrating their potential for CO2 reduction under optimized conditions with the highest efficiency for CdS electrodes. Additionally, the electrodeposited CuS and CdS are of the p-type, and In2S3 is of the n-type semiconductor were studied and verified by the Mott–Schottky test. CuS, In2S3, and CdS were found to have donor and acceptor concentrations (ND) of 1.68 × 106, 1.44 × 105, and 8.9 × 105 cm3, respectively. The photoelectrochemical measurements of the electrodeposited metal sulfides were studied at ambient temperature and under illumination, providing higher photocurrent responses for CdS and demonstrating its strong potential as a photoelectrode material for CO2 reduction. This work underscores the significance of facile electrochemical synthesis methods in developing cost-effective and scalable electrocatalysts, paving the way for their integration into photoelectrochemical systems for green energy applications.

Evaluating the potential of different crop straw biochar to capture carbon dioxide and increase the growth of Zea mays L.

The roles of biochar in capturing CO2 and ensuring food security are intertwined. Thus, a comprehensive understanding of these roles is crucial for optimizing the environmental benefits of biochar. Six crop straws: non-legumes (rice straw-RS, maize straw-MS, and wheat straw-WS), and legumes (chickpea straw-CS, mustard straw-MTS, and peanut straw-PS), were used to prepare biochar (RB, MB, WB, CB, MTB, and PB, respectively) at 700 °C and their ability to capture CO2, improve soil fertility, and enhance maize plant growth was evaluated. Our results revealed that the CO2 reduction potential (CRP) differed significantly, with CB being more efficient in retaining CO2. The CRP showed a significant polynomic relationship with ΔpH (R2 = 0.9646) and Δexchangeable acidity (R2 = 0.6356) but not with Δsoil organic carbon (R2 = 0.4181). Due to the differences in their physicochemical properties, straws and biochar had significantly different effects on soil pH, exchangeable acidity, nutrient uptake, maize growth, and maize biomass accumulation. Also, the N uptake potential of maize plants grown in biochar-amended soils was significantly larger than that of the respective straw. This significant difference in nutrient uptake between biochar and straw treatments was also observed for K, Ca, and Mg, and corroborates the significant differences recorded in plant growth parameters. Thus, converting crop residues to biochar sequesters carbon through the storage of captured CO2 thereby mitigating climate change. Also, by incorporating biochar in soil, soil acidity decreases, soil fertility increases, and the growth of maize plants improves. Nevertheless, it is important to carefully select biochar feedstock so as to achieve the optimal effects of carbon sequestration and soil fertility improvement when applied to agricultural soils.Graphical

Glycine modified copper promotes CO2 electroreduction to multi-carbon products: a computational study.

Molecular modification strategy exhibits great potential for electrocatalytic CO2 reduction. Here, DFT calculations were applied to study the mechanism of CO2 electroreduction on glycine modified copper. The results indicate that the interaction between the modified molecule and the intermediate could change the reaction energy of CO2 electroreduction.

Domestication of halotolerant methanogens for energy-efficient microbial electrosynthesis of methane from CO2

Microbial electrosynthesis (MES) has great potential for CO2 reduction and renewable energy storage. However, high energy consumption and investment costs constrained the practical application of MES. Here, the domestication of halotolerant methanogens was proposed to improve the energy efficiency of MES, and methane metabolism under low and high Na+ concentrations was explored by metagenomic analysis. The Na+ concentration of the catholyte was increased from 4.07 g·L-1 to 23.01 g·L-1, and the reactor maintained great performance after initial inhibition. High-salinity catholyte improved the energy efficiency to 47% and reduced the cathode voltage consumption. Increasing Na+ concentration, microorganisms resisted damage by secreting more extracellular polymers, and maintained methane production through community evolution. The relative abundance of Euryarchaeota increased from 50% to 80%. Methanobrevibacter and Methanobacterium were dominant genera at Na+ of 23.01 g·L-1. Incorporating metagenomic analysis, the methane metabolism at the initial period (Na+:4.07 g·L-1) included a CO2-reduction pathway and acetoclastic pathway. However, when Na+ concentration increased to 23.01 g·L-1, the CO2-reduction pathway with 4Fe–4S ferredoxin and common pathways was significantly enhanced, in addition, the acetyl metabolism pathway using CO2 as substrate was also enhanced. Overall, methane metabolism was enhanced, and the metabolic pathways changed with increasing Na⁺ concentration.

The Steelmaking Transformation Process and Its Consequences for Slag Utilization

The main challenge of the European steel industry for the next decade is the steel production transformation process. Many steel producers aim to avoid their CO2 emissions by substituting the CO2‐intensive blast furnace/basic oxygen furnace route by a gas‐based direct reduced iron (DRI) process combined with an electric smelting process. Thus, the well‐known latent hydraulic granulated blast furnace slag (GBS) will vanish step by step. For more than 140 years, this slag has been used as a supplementary cementitious material due to its clinker reduction potential and from there its CO2 reduction potential for the cement and concrete production. Moreover, slag cements offer some special technical advantages. Whereas the solid‐state DRI process itself does not generate any slag, the different electric smelting processes will produce liquid steel or “electric” pig iron, respectively, together with very different types of slags. However, specific slag/metal ratios, resulting slag volumes, chemical and mineralogical composition, and physical properties of the new slags are yet unknown. Therefore, their cementitious and environmental properties are also still unknown. Different current and scheduled projects aim mainly to enable the different types of new slags to substitute GBS to continue the successful cross‐industrial cooperation between steel and cement industry.

Hetero-Bimetallic Paddlewheel Complexes for Enhanced CO2 Reduction Selectivity: A First Principles Study

The reduction of carbon dioxide (CO2) into value-added feedstock materials, fine chemicals, and fuels represents a crucial approach for meeting contemporary chemical demands while reducing dependence on petrochemical sources. Optimizing catalysts for the CO2 reduction reaction can entail employing first principles methods to identify catalysts possessing desirable attributes, including the ability to form diverse products, selectively form few products, or exhibit favorable reaction kinetics. In this study, we investigate the CO2 reduction reaction on bimetallic Cu paddlewheel complexes, aiming to understand the impact metal substitution with Mn, Co, or Ni has on bimetallic paddlewheel metal-organic frameworks (MOFs). Substituting one of the Cu sites of the paddlewheel complex with Mn results in a more catalytically active Cu center, poised to produce substantial quantities of formic acid (HCOOH) and minor quantities of methane (CH4) with a suppressed production of C2 products such as ethanol (CH3CH2OH) or ethylene (C2H4). Moreover, the presence of Mn significantly reduces the limiting potential for CO2 reduction from 2.22 eV on the homo-bimetallic Cu paddlewheel complex to 1.19 eV, thereby necessitating a smaller applied potential. Conversely, within the Co-substituted paddlewheel complex, the Co site emerges as the primary catalytic center, selectively yielding CH4 as the sole reduced CO2 product, with a limiting potential of 1.22 eV. Notably, the Co site faces substantial competition from H2 production, attributed to a lower limiting potential of 0.81 eV for hydrogen reduction. Our examination of the Cu-Ni paddlewheel complex, featuring a Ni substituent site, reveals two catalytically active centers, each promoting distinct reductive processes. Both the Ni and Cu sites exhibit a propensity for HCOOH formation, with the Ni site favoring further reduction to CH4, while the Cu site directs the reaction towards methanol (CH3OH) production. The significance of this study lies in its potential to inform and streamline future experimental efforts, facilitating the synthesis and evaluation of novel catalysts with superior capabilities for CO2 reduction.

Oxidative and Reductive Manipulation of C1 Resources by Bio-Inspired Molecular Catalysts to Produce Value-Added Chemicals.

ConspectusTo tackle the energy and environmental concerns the world faces, much attention is given to catalytic reactions converting methane (CH4) and carbon dioxide (CO2) as abundant C1 resources into value-added chemicals with high efficiency and selectivity. In the oxidative conversion of CH4 to methanol, it is necessary to solve the requirement of strong oxidants due to the large bond-dissociation energy (BDE) of the C-H bonds in methane and achieve suppression of overoxidation due to the smaller BDE of the C-H bond in methanol as the product. On the other hand, to efficiently perform CO2 reduction, proton-coupled electron transfer (PCET) processes are required since the reduction potential of CO2 becomes positive by using proton-coupled processes; however, under the acidic conditions required for PCET, hydrogen evolution by the reduction of protons becomes competitive with CO2 reduction. Thus, it is indispensable to develop efficient catalysts for selective CO2 reduction. Recently, we have developed efficient catalytic reactions toward the alleviation of the concerns mentioned above. Concerning CH4 oxidation, inspired by metalloenzymes that oxidize hydrophobic organic substrates, a hydrophobic second coordination sphere (SCS) was introduced to an FeII complex bearing a pentadentate N-heterocyclic carbene ligand, and the FeII complex was used as a catalyst for CH4 oxidation in aqueous media. Consequently, CH4 was efficiently and selectively oxidized to methanol with 83% selectivity and a turnover number of 500. In contrast, when methanol was used as a substrate for catalytic oxidation by the FeII complex, oxidation products were obtained in a negligible yield, which was comparable to that of the control experiment without the catalyst. Therefore, the hydrophobic SCS of the FeII complex can capture only hydrophobic substrates such as CH4 and release hydrophilic products such as methanol to the aqueous medium for suppressing overoxidation ("catch-and-release" mechanism). On the other hand, for photocatalytic CO2 reduction, we have developed NiII complexes with N2S2-chelating ligands as catalysts, which have been inspired by carbon monoxide dehydrogenase, and have also introduced a binding site of Lewis-acidic metal ions to the SCS of the Ni complex. When Mg2+ was applied as a moderate Lewis acid, a Mg2+-bound Ni catalyst allowed us to achieve remarkable enhancement of the photocatalytic CO2 reduction to afford CO as the product with over 99% selectivity and a quantum yield of 11.4%. Divalent metal ions besides Mg2+ also showed similar positive impacts on photocatalytic CO2 reduction, whereas monovalent metal ions exhibited almost no effects and trivalent metal ions exclusively promoted hydrogen evolution. In this Account, we highlight our recent progress in the catalytic manipulations of CH4 and CO2 as C1 resources.

The Structure of Carbon Dioxide at the Air-Water Interface and its Chemical Implications.

The efficient reduction of CO2 into valuable products is a challenging task in an international context marked by the climate change crisis and the need to move away from fossil fuels. Recently, the use of water microdroplets has emerged as an interesting reaction media where many redox processes which do not occur in conventional solutions take place spontaneously. Indeed, several experimental studies in microdroplets have already been devoted to study the reduction of CO2 with promising results. The increased reactivity in microdroplets is thought to be linked to unique electrostatic solvation effects at the air-water interface. In the present work, we report a theoretical investigation on this issue for CO2 using first-principles molecular dynamics simulations. We show that CO2 is stabilized at the interface, where it can accumulate, and that compared to bulk water solution, its electron capture ability is larger. Our results suggest that reduction of CO2 might be easier in interface-rich systems such as water microdroplets, which is in line with early experimental data and indicate directions for future laboratory studies. The effect of other relevant factors which could play a role in CO2 reduction potential is discussed.

Comprehensive analysis of carbon emission reduction technologies (CRTs) in China's coal-fired power sector: A bottom-up approach

Carbon dioxide (CO2) reduction technologies (CRTs) in the coal-fired power sector play an imperative role in the mitigation of environmental challenges and reducing CO2 emissions to help achieve the 2 °C target. However, a compelling necessity persists for a unified framework that can effectively and accurately estimate the costs and potentials associated with CRTs, arising from the diversity of technologies and unit types. Therefore, this study employs a bottom-up approach to analyze the costs and potential of 25 advanced CRTs in the coal-fired power sector, excluding CO2 capture, utilization and storage (CCUS), across 19 types of coal-fired power units. This analysis amalgamates the CO2 reduction supply curve (CRSC) approach with levelized cost of CO2 reduction (LCOC) and a broken-even analysis which could reflect the sector's average carbon reduction cost. The outcomes reveal the following key insights: (1) These technologies collectively harbor a substantial CO2 conservation potential amounting to 925.61 Mt CO2, with a broken-even price of CNY 410.1/tCO2. This reduction could potentially lower 20%–25 % of CO2 emissions in China's power system in 2022, highlighting the crucial role of CRTs in achieving a low-carbon transition and national climate targets; (2)Steam turbine flow path retrofit (T8) not only offers a relatively high CO2 reduction potential (>60 Mt CO2), but also features a low cost (<CNY 150/tCO2) and high profit (>CNY 0.85/MWh). Prioritizing the development of this technology can significantly accelerate the low-carbon transition of coal power; (3) Carbon price have a paramount influence on the cost-effectiveness of CRTs and driving their adoption.