CO2 Reduction Research Articles

Photosynthesis of CH3OH via oxygen-atom-grafting from CO2 to CH4 enabled by AuPd/GaN

The direct co-conversion of methane and carbon dioxide into valuable chemicals has been a longstanding scientific pursuit for carbon neutrality and combating climate change. Herein, we present a photo-driven chemical process that reforms these two major greenhouse gases together to generate green methanol and CO, two high-valued industrial chemicals. Isotopic labeling and control experiments indicate an oxygen-atom-graft occurs, wherein CO2 transfers one O into the C–H bond of CH4 via photo-activated interfacial catalysis with AuPd nanoparticles supported on GaN. The photoexcited AuPd/GaN interface effectively orchestrates the CH4 oxidation and the CO2 reduction producing 13.66 mmol g−1 of CH3OH yield over 10 h. This design provides a solid scientific basis for the photo-driven oxygen-atom-grafting process to be further extended to visible light region.

Transition-Metal-Doped CeO2 for the Reverse Water-Gas Shift Reaction: An Experimental and Theoretical Study on CO2 Adsorption and Surface Vacancy Effects.

Transition metal-doped ceria (M-CeO2) catalysts (M = Fe, Co, Ni and Cu) with multiple loadings were experimentally investigated for reverse water gas shift (RWGS) reaction. Density functional theory (DFT) calculations were performed to benchmark the properties that impact catalytic activity of CO2 reduction. Temperature-programmed desorption (TPD) was conducted to study the CO2 binding strength on doped CeO2 surfaces; the trend of the energy along increasing metal loading agrees with the DFT calculations. Notably, CO2 dissociative adsorption energy and oxygen vacancy (OV) formation energy are key descriptors obtained from both DFT and experiments, which can be used to evaluate catalytic performance. Results show the effectiveness of transition metal doping in enhancing CO2 adsorption and reducibility of the surfaces, with Fe showing particularly promising results, i.e., CO2 conversion higher than 56% at 600 °C and 100% selectivity to CO. Cu exhibits 100% selectivity to CO but low CO2 conversion, while Co and Ni showed notable ability of methanation, particularly at high loadings. This study finds that an effective CeO2 based RWGS catalyst corresponds to OV sites that have low OV formation energies for surface reduction, and moderate CO2 adsorption energies for strong interaction with the surface to promote C-O bond scission.

Role of environmental awareness & self-identification expressiveness in electric-vehicle adoption

AbstractGlobal warming is a serious threat to humanity, and greenhouse gases are behind it. CO2 is one of the main greenhouse gasses that cause global warming. The second most important reason behind CO2 emission is the transport sector. Electric-powered Vehicles introduced by the automobile sector are regarded as the main alternative to cope with this issue. Despite their advantages, EV adoption rates vary by country, and the expected reductions in energy shortages and pollution are not fully achieved. We took the opportunity to assess the consumer EV adoption intention by using the Value-based technology adoption model. We integrated Environmental awareness (EA) and Self-identification expressiveness (SIE) as new factors in this model to assess the role of EA and SIE in EV adoption intentions. We have collected the response of 704 EV users from China and applied the SEM-ANN dual-stage hybrid model to test proposed hypotheses and rank the variables according to their importance. Study findings revealed that Environmental awareness is a significant predictor of EV adoption but is not the most important factor. Study results also revealed that the perceived benefits of EV adoption and perceived sacrifices for its adoption have a significant impact on the perceived value of EV, and this value leads to the adoption intentions. PV is revealed as a significant mediator in our proposed model. We conclude that people need to educate about environmental issues and the benefits of using EVs to achieve the CO2 reduction and EV sale target. The study has several theoretical and practical implications for the government and the electric vehicle manufacturing industry.

Sulfur-doped Bi2O2CO3 nanosheet for enhanced visible-light-driven photocatalytic CO2 reduction to CO with ultra-high selectivity.

The photocatalytic reduction of carbon dioxide (CO2) has emerged as a compelling strategy for the conversion of renewable energy. However, the expeditious recombination of photogenerated charge carriers and the inadequate light absorption capabilities are currently predominant challenges. Herein, we developed a facile hydrothermal approach to synthesize a sulfur doped Bi2O2CO3 nanosheet with a tunable energy band structure designed to enhance visible light absorption. Our findings indicate that the incorporation of sulfur into the catalytic sites induces an electron sink effect, significantly improving the separation efficiency of photogenerated charge carriers. Consequently, this sulfur-doped Bi2O2CO3 catalyst exhibits a remarkable carbon monoxide (CO) yield of 16.64 μmol gcat-1 h-1 with nearly 100 % selectivity under illumination ranging from 420 to 780 nm. Through in-situ characterization techniques and theoretical calculations, it was revealed that sulfur-coordinated bismuth sites greatly enhance CO2 adsorption and decrease the energy barrier for critical intermediates formation (*COOH), thus selectively driving the reaction towards CO production. This work not only advances our understanding of mechanisms underlying photocatalytic reduction of CO2 on sulfur-doped bismuth-based catalysts but also sets a precedent for developing sophisticated photocatalytic systems for enhanced photoreduction reactions.

Strategic Siting of Direct Air Capture Facilities in the United States

Direct air capture (DAC) systems that capture carbon dioxide (CO2) directly from the atmosphere are garnering considerable attention for their potential role as negative emission technologies in achieving net-zero CO2 emission goals. Common DAC technologies are based either on liquid–solvent (L-DAC) or solid–sorbent (S-DAC) to capture CO2. A comprehensive multi-factor comparative economic analysis of the deployment of L-DAC and S-DAC facilities across various United States (U.S.) cities is presented in this paper. The analysis considers the influence of various factors on the favorability of DAC deployment, including local climatic conditions such as temperature, humidity, and CO2 concentrations; the availability of energy sources to power the DAC system; and costs for the transport and storage of the captured CO2 along with the consideration of the regional market and policy drivers. The deployment analysis in over 70 continental U.S. cities shows that L-DAC and S-DAC complement each other spatially, as their performance and operational costs vary in different climates. L-DAC is more suited to the hot, humid Southeast, while S-DAC is preferrable in the colder, drier Rocky Mountain region. Strategic deployment based on regional conditions and economics is essential for promoting the commercial adoptability of DAC, which is a critical technology to meet the CO2 reduction targets.

Precisely Constructing Molecular Junctions in Hydrogen-Bonded Organic Frameworks for Efficient Artificial Photosynthetic CO2 Reduction.

The development of artificial photocatalysts to convert CO2 into renewable fuels and H2O into O2 is a complex and crucial task in the field of photosynthesis research. The current challenge is to enhance photogenerated charge separation, as well as to increase the oxidation capability of materials. Herein, a molecular junction-type porphyrin-based crystalline photocatalyst (Ni-TCPP-TPyP) was successfully self-assembled by incorporating a nickel porphyrin complex as a reduction site and pyridyl porphyrin as an oxidation site via hydrogen bonding and π-π stacking interactions. The resulting material has a highly crystalline structure, and the formation of inherent molecular junctions can accelerate photogenerated charge separation and transport. Thus, Ni-TCPP-TPyP achieved an excellent CO production rate of 309.3 μmol g-1 h-1 (selectivity, ~100%) without the use of any sacrificial agents, which is more than ten times greater than that of single-component photocatalyst (Ni-TCPP) and greater than that of the most organic photocatalysts. The structure-function relationship was investigated by femtosecond transient absorption spectroscopy and density functional theory calculations. Our work provides new insight for designing efficient artificial photocatalysts, paving the way for the development of clean and renewable fuels through the conversion of CO2 using solar energy.

A red-light-powered silicon nanowire biophotochemical diode for simultaneous CO2 reduction and glycerol valorization

A red-light-powered silicon nanowire biophotochemical diode for simultaneous CO2 reduction and glycerol valorization

Liquid Metal-Enabled Tunable Synthesis of Nanoporous Polycrystalline Copper for Selective CO2-to-Formate Electrochemical Conversion.

Copper-based catalysts exhibit high activity in electrochemical CO2 conversion to value-added chemicals. However, achieving precise control over catalysts design to generate narrowly distributed products remains challenging. Herein, a gallium (Ga) liquid metal-based approach is employed to synthesize hierarchical nanoporous copper (HNP Cu) catalysts with tailored ligament/pore and crystallite sizes. The nanoporosity and polycrystallinity are generated by dealloying intermetallic CuGa2 formed after immersing pristine Cu foil in liquid Ga in a basic or acidic solution. The liquid metal-based approach allows for the transformation of monocrystalline Cu to the polycrystalline HNP Cu with enhanced CO2 reduction reaction (CO2RR) performance. The dealloyed HNP Cu catalyst with suitable crystallite size (22.8nm) and nanoporous structure (ligament/pore size of 45nm) exhibits a high Faradaic efficiency of 91% toward formate production under an applied potential as low as -0.3 VRHE. The superior CO2RR performance can be ascribed to the enlarged electrochemical catalytic surface area, the generation of preferred Cu facets, and the rich grain boundaries by polycrystallinity. This work demonstrates the potential of liquid metal-based synthesis for improving catalysts performance based on structural design, without increasing compositional complexity.

Precisely Constructing Molecular Junctions in Hydrogen‐Bonded Organic Frameworks for Efficient Artificial Photosynthetic CO2 Reduction

The development of artificial photocatalysts to convert CO2 into renewable fuels and H2O into O2 is a complex and crucial task in the field of photosynthesis research. The current challenge is to enhance photogenerated charge separation, as well as to increase the oxidation capability of materials. Herein, a molecular junction‐type porphyrin‐based crystalline photocatalyst (Ni‐TCPP‐TPyP) was successfully self‐assembled by incorporating a nickel porphyrin complex as a reduction site and pyridyl porphyrin as an oxidation site via hydrogen bonding and π–π stacking interactions. The resulting material has a highly crystalline structure, and the formation of inherent molecular junctions can accelerate photogenerated charge separation and transport. Thus, Ni‐TCPP‐TPyP achieved an excellent CO production rate of 309.3 μmol g‐1 h‐1 (selectivity, ~100%) without the use of any sacrificial agents, which is more than ten times greater than that of single‐component photocatalyst (Ni‐TCPP) and greater than that of the most organic photocatalysts. The structure‐function relationship was investigated by femtosecond transient absorption spectroscopy and density functional theory calculations. Our work provides new insight for designing efficient artificial photocatalysts, paving the way for the development of clean and renewable fuels through the conversion of CO2 using solar energy.

Hierachical Aerogel-Supported Cu-Sn-Ox Solid Solutions for Highly Selective CO2 Electroreduction and Zn-CO2 Batteries.

The electrochemical CO2 reduction reaction (CO2RR) into high-value carbon compounds such as CO and HCOOH is a promising strategy for the utilization and conversion of emitted CO2. However, the selectivity of the CO2RR for HCOOH is typically less than 90% and operates within a narrow voltage range, which limits its practical application. Herein, we propose a novel heterostructural aerogel as a highly efficient electrocatalyst for CO2RR to HCOOH. This catalyst consists of Cu-Sn-Ox solid solutions embedded in a reduced graphene oxide matrix (Cu-Sn-Ox/rGO). The incorporation of Cu2+ into the SnO2 matrix enhances HCOOH production by improving the adsorption of the *OCHO intermediate and inhibiting H2 evolution, as confirmed by in situ measurements and computational studies. As a result, Cu-Sn-Ox/rGO achieves a remarkable Faradaic efficiency (FE) of up to 91.4% for HCOOH and maintains high selectivity over a broad operating voltage range (-0.8 to -1.1 V). Additionally, the assembled Zn-CO2 batteries demonstrated an excellent power density of 1.14 mW/cm2 and exceptional stability for over 25 h.

In situ reconstructured alloy nanosheets heterojunction for highly selective electrochemical CO2 reduction to formate.

Tin (Sn)-based materials are expected to realize efficient CO2 electroreduction into formate. Herein, we constructed a heterojunction by depositing Cu on Cu-doped SnS2 nanosheets. During the electrochemical reaction, this heterojunction evolves to a highly active phase of Cu2O@Cu6Sn5 while maintaining its two-dimensional morphology. Specifically, a partial current density of 35 mA cm-2 with an impressive faradaic efficiency of 93% for formate production was achieved over the evolved heterojunction. In situ and ex situ experiments elucidated the formation mechanism of the Cu2O@Cu6Sn5 heterojunction. Cu6Sn5 nanosheets were formed via a stepwise desulfurization process, while Cu2O was generated through its reaction with hydroxyl radicals. This evolved heterojunction with a high electrochemically active surface area synergistically stabilized the *OCHO intermediate, thereby significantly enhancing the selectivity and activity. Our findings provide insight into the structural evolution process and guide the development of selective electrocatalysts for CO2 reduction.

One-pot hydrothermal synthesis of transition metal sulfides-decorated CuS microflower-like structures for electrochemical CO2 reduction to CO

Electrochemical CO2 reduction (ECR) to value-added products is regarded as a sustainable strategy to mitigate global warming and energy crisis, and designing highly efficient and robust catalysts is essential. In this work, transition metal sulfides (TMS)-decorated CuS microflower-like structures were prepared via the one-pot hydrothermal synthesis method for ECR to CO, and the influence of TMS doping on ECR performance was demonstrated. Characterization of the catalysts was performed using XRD, FESEM-EDS, N2 physisorption, and XPS, revealing the successful loading of TMS, the formation of microflower-like architectures and the generation of sulfur vacancies. Electrochemical tests demonstrated that doping ZnS, Bi2S3, CdS and MoS2 improved the intrinsic CO2 reduction activity of the CuS catalyst. Particularly, the MoS2-CuS composite catalyst with imperfect petal-like structure showed uniform distribution of edge Mo sites, which worked synergistically with the formed grain boundaries (GBs) and undercoordinated S vacancy sites in promoting CO2 activation, stabilizing *COOH adsorption, facilitating *CO desorption, and lowering the energy barrier of the potential-limiting step for improved CO selectivity. The MoS2-CuS catalyst achieved a maximum CO selectivity of 83.2% at –0.6 V versus the reversible hydrogen electrode (RHE) and a high CO cathodic energetic efficiency of 100%. At this potential, the catalyst maintained stable catalytic activity and CO selectivity during a 333-min electrolysis process. The findings will offer a promising avenue for the development of efficient and stable catalysts for CO production from ECR.

Confinement Synthesis of Atomic Copper-Anchored Polymeric Carbon Nitride in Crystalline UiO-66-NH2 for High-Performance CO2-to-CH3OH Photocatalysis.

Photocatalytic CO2 reduction to value-added fuels displays an attractive scenario to enhance energy supply and reduce global warming. We report herein the confinement synthesis of polymeric carbon nitride (PCN) incorporating with Cu single atoms (CuSAs) inside the crystalline UiO-66-NH2, which combines the merits of heterojunction photocatalysis and single-atom catalysis (SAC) to achieve high-performance CO2-to-CH3OH conversion. A series of spectral studies displays the formation of CuSAs@PCN inside the crystalline UiO-66-NH2. Remarkably, the ternary composite shows an excellent photocatalytic turnover frequency of 4.15 mmol·h-1·g-1 for CO2-to-CH3OH conversion. Theoretical and experimental studies demonstrate the doping of CuSAs, as well as the formation of type-II heterojunction, are causal factors to achieve CH3OH generation. The study provides new insights designing high-performance photocatalyst for CO2 conversion to fuels at atomic scale.

Electrocatalysis of CO2 Reduction by Immobilized Formate Dehydrogenase without a Metal Redox Center.

Nicotinamide adenine dinucleotide-dependent formate dehydrogenase from Candida boidinii was immobilized in a 1,2-dimyristoyl-sn-glycero-3-phosphocholine/cholesterol floating lipid bilayer on the gold surface as a biocatalyst for electrochemical CO2 reduction. We report that, in contrast to common belief, the enzyme can catalyze the electrochemical reduction of CO2 to formate without the cofactor protonated nicotinamide adenine dinucleotide. The electrochemical data indicate that the enzyme-catalyzed reduction of CO2 is diffusion-controlled and is a reversible reaction. The orientation and conformation of the enzyme were investigated by surface-enhanced infrared reflection absorption spectroscopy. The α-helix of the enzyme adopts an orientation nearly parallel to the surface, bringing its active center close to the gold surface. This orientation allows direct electron transfer between CO2 and the gold electrode. The results in this paper provide a new method for the development of enzymatic electrocatalysts for CO2 reduction.

Selection of suitable organic electrolyte for CO2 electro-reduction to CO in three-compartment electrolysis cell with NaOH and Cl2 yielded as byproducts

Developing high performance electrolyte is essential in improving the performance of CO2 electro-reduction. In this work, we have constructed a three-compartment electrolysis cell for CO2 reduction to CO in organic electrolyte, with NaOH and Cl2 produced as byproducts. The generated CO and Cl2 can be served as feedstock for the production of phosgene, which is a widely used acylating agent for producing valuable downstream products. In order to improve the performance of the electrolysis cell, various commonly used organic solvents and supporting electrolytes were investigated. Consequently, 0.72 M Bu4NCF3SO3 in propylene carbonate (PC) was selected due to its high CO2 solubility. This electrolyte enabled the achievement of a current density of 27 mA/cm2 at a potential of −2.0 V (vs. SHE), with a stable Faradaic efficiency of 93 % for CO production. Compared with an aqueous catholytes, the altered double electric layer in the organic electrolyte prevents cathode poisoning, which is crucial for practical applications.

Efficient CO2 Conversion through a Novel Dual-Fiber Reactor System.

Carbon dioxide (CO2) can be converted to valuable organic chemicals using light irradiation and photocatalysis. Today, light-energy loss, poor conversion efficiency, and low quantum efficiency (QE) hamper the application of photocatalytic CO2 reduction. To overcome these drawbacks, we developed an efficient photocatalytic reactor platform for producing formic acid (HCOOH) by coating an iron-based metal-organic framework (Fe-MOF) onto side-emitting polymeric optical fibers (POFs) and using hollow-fiber membranes (HFMs) to deliver bubble-free CO2. The photocatalyst, Fe-MOF with amine-group (-NH2) decoration, provided exceptional dissolved inorganic carbon (DIC) absorption. The dual-fiber system gave a CO2-to-HCOOH conversion rate of 116 ± 1.2 mM h-1 g-1, which is ≥18-fold higher than the rates in photocatalytic slurry systems. The 12% QE obtained using the POF was 18-fold greater than the QE obtained by a photocatalytic slurry. The conversion efficiency and product selectivity of CO2-to-HCOOH were up to 22 and 99%, respectively. Due to the dual efficiencies of bubble-free CO2 delivery and the high QE achieved using the POF platform, the dual-fiber system had energy consumption of only 0.60 ± 0.05 kWh mol-1, 3000-fold better than photocatalysis using slurry-based systems. This innovative dual-fiber design enables efficient CO2 valorization without the use of platinum group metals or rare earth elements.

Twist angle-driven photoreduction of carbon dioxide on bilayer black phosphorus – A first-principles study

Utilizing first principles calculations, the product selectivity in photocatalytic CO2 reduction was modulated by manipulating the twisted angle in bilayer black phosphorus. Four twisted angles, 0° (AA stacking), 15.40°, 19.00° and 24.66°, were constructed. Comprehensive investigations revealed enhanced carrier mobility and lifetime, especially at a 24.66° twist. Furthermore, an in-depth analysis of the CO2 reduction processes in these four systems was undertaken. Our simulations indicate that in the AA stacking, the photocatalytic CO2 reduction yields multiple products, including HCHO, CH3OH, and CH4, demonstrating limited product selectivity. However, when the surface is twisted at 15.40°, 19.00°, or 24.66°, the sole product is CH4. Remarkably, the 24.66° configuration exhibits the lowest energy barrier for the rate-determining step, measuring just 1.29 eV. These observations suggest that by carefully adjusting the twisted angle in bilayer black phosphorus, we can significantly improve both the activity and selectivity of CO2 photoreduction.

MXene quantum dots decorated g-C3N4/BiOI heterojunction photocatalyst for efficient NO deep oxidation and CO2 reduction

The photocatalytic performance of g-C3N4 is greatly limited by the severe charge recombination due to its s-triazine unit structure. Hence, enhancing the separation of photogenerated carriers is the pivotal factor for high-efficiency photocatalysis of g-C3N4. In this work, we construct a MXene quantum dots (MQDs) decorated BiOI/g-C3N4p-n heterojunction photocatalyst. The interfacial charge separation and transfer are substantially promoted, due to the synergistic effect of the internal electric field (IEF) of BiOI/g-C3N4 heterojunction and strong electron-withdrawing capability of MQDs. Furthermore, the introduction of BiOI with a low band gap and MQDs with large specific areas and rich surface terminals lead to enhanced light absorption and active sites. As a result, the ternary g-C3N4/MQDs/BiOI photocatalyst achieves a much higher NO removal rate of 42.23 % and discharges less NO2 intermediate than the individual and binary ones. Meanwhile, the g-C3N4/MQDs/BiOI photocatalyst also exhibits the most effective CO2 photoreduction, with a CO production rate of 57.8 μmol·g−1·h−1 and a CH4 production rate of 3.6 μmol·g−1·h−1, surpassing all other photocatalysts in this study. In addition, the designed composite photocatalyst shows remarkable stability. The photocatalytic mechanisms are studied by the trapping experiment and in-situ Fourier Transform Infrared (FTIR) Spectra. This work paves a new avenue for enhancing charge separation and thus improving performances of g-C3N4-based photocatalysts by integrating a p-n heterojunction and a co-catalyst, which would accelerate commercial deployment of emerging photocatalysts.

Electrolyte Composition-Dependent Product Selectivity in CO2 Reduction with a Porphyrinic Metal-Organic Framework Catalyst.

A copper porphyrin-derived metal-organic framework electrocatalyst, FICN-8, was synthesized and its catalytic activity for CO2 reduction reaction (CO2RR) was investigated. FICN-8 selectively catalyzed electrochemical reduction of CO2 to CO in anhydrous acetonitrile electrolyte. However, formic acid became the dominant CO2RR product with the addition of a proton source to the system. Mechanistic studies revealed the change of major reduction pathway upon proton source addition, while catalyst-bound hydride (*H) species was proposed as the key intermediate for formic acid production. This work highlights the importance of electrolyte composition on CO2RR product selectivity.

Boosting and stabilizing the electrocatalytic reduction of carbon dioxide on Bi2O2CO3 via surface modification with p-aminobenzoic acid

In the realm of electrocatalytic CO2 reduction (ECR) reactions, the challenges of instability and self-reducibility present significant obstacles to the practical application of bismuth oxide-based catalysts. Herein, Bi2O3 pre-catalyst was synthesized and surface-modified with 4-aminobenzoic acid (PABA). Theoretical studies confirmed that PABA was effectively grafted through oxygen vacancies on the Bi2O3 surface, leading to electronic rearrangement. PABA efficiently prevented surface Bi3+ on Bi2O3 from self-reducing to Bi0 during the ECR reaction. The Bi2O3PABA pre-catalyst transformed into the active Bi2O2CO3PABA ECR catalyst via electrolyte mediation. A Faraday efficiency of 98.6 % for formate was achieved at −1.1 V vs. RHE, with a wide potential window of 800 mV. The current density reached 210 mA cm–2 in a 2×2 cm2 flow cell system. Theoretical calculations illustrate that PABA facilitates stabilizing the *OCHO intermediate, diminishing the adsorption barrier. These results may provide valuable insights for designing highly selective ECR catalysts through interface engineering.