Performance For CO2 Conversion Research Articles

Comparative analysis of electrolyzers for electrochemical carbon dioxide conversion

Electrochemical carbon dioxide (CO2) conversion to fuels and chemicals provides a long-term and large-scale storage solution for intermittent renewable electricity. In the last few decades, most of the effort has been devoted to developing new catalysts to improve CO2 reduction performance. Very recently, advances in system design, including electrochemical cell design and electrochemical operating conditions, have led to a significant improvement in CO2 conversion efficiency. In this review, we describe system design strategies in the context of boosting key performance metrics in CO2 conversion: current density, Faradaic efficiency, energy efficiency, stability, reactant utilization and product concentration, carbonate formation and CO2 crossover. The advantages and limitations of each strategy, in terms of overall CO2 conversion performance, are discussed. This review offers guidelines for developing a high-performance electrochemical CO2 conversion system to bring this technology closer to practical implementation.

Efficient visible-light-driven CH4 reforming by covalent organic frameworks: Enhancing the activity of cadmium-based catalyst

Dry reforming of methane to prepare synthesis gas is an innovative and practical solution to the current energy crisis as well as environmental issues such as the greenhouse effect. However, the traditional thermocatalytic methane reforming process has limitations, such as high energy consumption and harsh reaction conditions. Here, a novel strategy for the conversion of CO2 and CH4 is reported: the fast and efficient preparation of CO and H2 using solar energy at ambient temperature. In this work, the covalent organic framework (COF) composite is prepared with the hydrothermal method, and its physicochemical properties are studied using different characterization methods. Then, CdS@COF (CCF) is creatively used in the photocatalytic system of CO2-CH4, and the interaction law between the coupling of different mass fractions of COF and CdS and the performance of photocatalytic CH4 reforming is explored. Notably, the CdS@COF (5/5) catalyst shows the best performance in the photocatalytic conversion of CO2 and CH4, with CO and H2 yields of 640μ mol g−1 and 113.24μ mol g−1, respectively. Additionally, the structure–activity relationship between CdS@COF and the photocatalytic conversion of CO2 and CH4 is studied by density functional theory calculation (DFT), including the demonstration of Z-shaped heterojunctions, the adsorption and activation of CO2 and CH4, and the state density of the composites. Finally, based on isotopic tracer experiments, a possible mechanism for CdS@COF photocatalytic reforming of CH4 is proposed. This work provides new research ideas for designing organic semiconductor composites and achieving carbon neutrality.

Nanoarchitecture engineering of crumpled polymeric carbon nitride nanosheets for efficient visible-light photocatalytic CO2 reduction

Polymeric carbon nitride nanosheets with few layers have emerged as a new category of semiconductor materials which are promising for photocatalytic applications because of their unique optical and electronic characteristics. The texture and optical–electronic properties of the nanosheets significantly influence the photocatalytic activities. In this study, a series of crumpled polymeric carbon nitride nanosheets was prepared via a facile stepwise pyrolytic strategy and a time-dependent pyrolysis process. The as-obtained nanosheets exhibit a sequential change in morphology from a continuous-aggregation architecture to discrete nanosheets with prolonged thermal-treatment time. The nanosheets with the continuous-aggregation architecture, consisting of small curved nanosheet subunits are laterally large; thus, they can provide numerous reactive sites for surface reactions and awaken intrinsic n → π* electron transitions to promote photocatalytic activity. The optimum crumpled polymeric carbon nitride nanosheet is formed after 2 h of thermal condensation, and it demonstrates efficient CO2-conversion performance with the highest CO-evolution rate of 1287 µmol g−1h−1, which is 7 times more than that of pristine polymeric carbon-nitride nanosheets. This work provides an opportunity to significantly understand the roles of texture and optical–electronic properties in improving the photocatalytic activities of polymeric carbon-nitride nanosheets.

Synergy of oxygen vacancy and piezoelectricity effect promotes the CO2 photoreduction by BaTiO3

Great efforts have been devoted to developing efficient visible-light-driven photocatalysts for the conversion CO2 into clean fuels. Nevertheless, the photoreduction of CO2 is hampered by inadequate surface-active sites and ineffective electron-hole pair separation. Herein, we explore the wheat-heading BaTiO3 with high surface area and piezoelectricity to facilitating their bulk charge separation. Meanwhile, oxygen vacancies were fabricated to extending the visible light absorption range and increasing the active sites of the wheat-heading BaTiO3, thus promoting the photocatalytic performance of CO2. Among the wheat-heading BaTiO3-X (X = 0, 0.5, 1.0, 1.5, 2.0) catalysts, BaTiO3-1.5 affords the optimal photocatalytic performance of CO, 6.41 μmol·g−1 under light, 9.17 μmol·g−1 under light and ultrasound, which were 3.22 and 1.86 times higher for pristine wheat-heading BaTiO3, respectively. This synergetic strategy sheds a new light on piezoelectric properties and surface defect engineering, while emphasizing the importance of surface properties in enhancing CO2 conversion performance.

A highly efficient and stable TiO2@NH2-MIL-125 material for enhanced photocatalytic conversion of CO2 and CH4

At present, there are many difficulties in accomplishing the effective and efficient chemical utilization of CO2, such as low catalyst stability, high energy consumption, limited conversion of CH4 by reforming due to thermal reaction kinetics, high reaction temperature and high demand on reactor material. Here, a novel composite catalyst TiO2/NH2-MIL-125, prepared by three different methods, was applied to the photocatalytic conversion of CO2 with CH4 under visible-light irradiation. The experimental results showed that NH2-MIL-125@TiO2-40 catalyst prepared by ultrasonic impregnation method achieved rapid conversion of CO2 and CH4 at room temperature, and the yield of CO was up to 159 μ mol/g, which was 510% great than the catalytic performance of TiO2. In addition, the photocatalytic reduction efficiency of NH2-MIL-125@TiO2-40 material held stay at 93.7% after continuous operation for 28 h, showing excellent photocatalytic stability. Moreover, a series of characterization techniques were used to study the structure, morphology and photoelectric chemical properties of the photocatalyst. As well, the relationship between the physical and chemical properties of the material and the catalytic performance of CO2 conversion is discussed. Based on the above studies, a possible catalytic mechanism for the photocatalytic conversion of CO2 by NH2-MIL-125@TiO2 hybrid materials is proposed.

Semiconductor facet junctions for photocatalytic CO2 reduction

Abstract Photocatalytic carbon dioxide (CO2) conversion has been recognized as one of the promising strategies for unraveling current environmental and energy problems attributed to the growing fossil fuel consumption of the human society because it can directly harness incident sunlight energy for converting waste CO2 into valuable compounds. Increasing attention has been provoked to the semiconductor facet junction photocatalysts due to their unique feature in enhancing the photogenerated electron–hole pair utilization toward improving the photocatalytic CO2 conversion performance. In the past decade, significant breakthroughs in the semiconductor facet junction photocatalysts for photocatalytic CO2 conversion. In this review, we give a brief introduction on the development and the idea of the semiconductor facet junction photocatalysts. Then, the unique advantages of the semiconductor facet junction photocatalysts for photocatalytic CO2 conversion are summarized. Subsequently, the recent development of semiconductor facet junction photocatalysts in photocatalytic CO2 conversion is overviewed. We end this review by presenting the perspectives and challenges in this field for its future advancement toward practical applications. This review is expected to push forward the development of not only photocatalytic CO2 conversion but also other energy and environmental photocatalytic applications.

Highly-selective CO2 conversion through single oxide CuO enhanced NiFe2O4 thermal catalytic activity

The solar-driven thermochemical CO2 conversion is an effective way to achieve the mission of carbon peaking and carbon neutrality. However, finding a material with excellent thermal stability, oxygen exchange capacity, and CO selectivity is one of the most important challenges in the thermochemical CO2 conversion approach. This study investigated the solar thermochemical CO2-splitting characteristics through the synergistic thermal catalytic activity of CuO and NiFe2O4 and the effect of SiC photothermal properties. The thermochemical redox cycling performance of CO2 conversion through thermally activated catalysts was experimentally investigated via thermogravimetric combined quantum chemical calculations to provide comprehensive insights into the physicochemical principles underlying the thermochemical catalytic CO2-splitting. The X-ray diffraction, scanning electron microscopy, and energy spectrum detector technics were developed to gain detail on the crystal structure, surface morphology, and chemical composition changes in the reacting media. The newly synthesized composite material consisting of 25%CuO and 75%NiFe2O4 (CNF-13) coated SiC porous skeleton resulted in higher CO2-splitting catalytic activity with an instantaneous CO production of 10.98mL ⋅ min‐1gCNF‐13−1 and direct CO2-to-CO conversion rate of 33.9% at 1000–1200 K reaction temperature. The thermochemical CO2-splitting activity and redox stability of CNF-13@SiC was promoted by the photothermal properties of SiC support and the formation of Cu2O and Fe3O4 new active material phases easing CO2 reduction at low energy. This study provided experimental and theoretical findings that can be used as guidance for the fundamental research and application of CO2 catalytic conversion into fuels through a solar thermochemical driven strategy.

Rh/ZrO2@C(MIL) catalytic activity and TEM images. CO2 conversion performance and structural systematic evaluation of novel catalysts derived from Zr-MOF metallated with Ru, Rh, Pd or In

A set of novel materials, denoted M/ZrO2@C(MIL) (M = Ru, Rh, Pd & In), were prepared by thermal transformation of MIL-140C containing 10% bipyridine linkers (MIL-140C-10), to provide sites for metal coordination within the framework. These materials were transformed into active catalysts for CO2 hydrogenation when heated in a gas mixture of H2 and CO2 (3:1), at 500 °C. The thermal treatment provided high surface area catalysts with high stability and high Ru or Rh metal dispersion which were very effective for the hydrogenation of CO2 to CH4, giving a CH4 production of 3.0–3.7 mol/g Ru/h or 4.2–4.3 mol/g Rh/h (at 400 °C, 33 bar and WHSV 23 L/h/g cat.). PXRD, XPS and TEM indicated that the effective catalysts consisted of nanoparticles of Ru0 (2–5 nm) or Rh0 (6 nm) associated with larger ZrO2 nanoparticles (10–20 nm), which were dispersed upon carbonaceous ribbons. Interestingly, at 250-350 °C, Pd/ZrO2@C(MIL) yielded mainly CO rather than CH4, with some CH3OH. The CH4 and CO production were not stable at 400 °C. TEM results for this catalyst indicated Pd0 and ZrO2 nanoparticles (initially 20 nm and 10–20 nm diameter, respectively). The lower, unstable activity compared to Ru and Rh could have been due to the initially larger Pd particles and their tendency to grow in size with reaction time. In/ZrO2 has mainly been used to catalyse CH3OH production, but In/ZrO2@C(MIL) gave less CH3OH than In/monoclinic ZrO2 and was less selective. At 400 °C In/ZrO2@C(MIL) was a stable, reverse-water-gas-shift catalyst (producing 0.9 mol CO/g In/h at WHSV 20 L/g cat/h). The In was well dispersed in the ZrO2–C and of small particle size. The poor selectivity for methanol may have been due to the tetragonal phase of the ZrO2 and the low surface In concentration.

Rationally design and in-situ fabrication of ultrasmall pomegranate-like CdIn2S4/ZnIn2S4 Z-scheme heterojunction with abundant vacancies for improving CO2 reduction and water splitting

Exploring efficient and robust CO2 photoreduction and water splitting photocatalysts are critical for closing the anthropogenic carbon cycle and developing H2 energy source. Herein, ultrasmall pomegranate-like Z-scheme CdIn2S4/ZnIn2S4 heterojunctions with abundant vacancies were rationally designed and in-situ constructed though L-cysteine assisted solvothermal method with precipitation conversion strategy. The obtained CdIn2S4/ZnIn2S4-3 photocatalyst displays the highest performance in the photocatalytic conversion of CO2 and H2O into CO and H2 with yields of 1194.5 and 475.7 μmolg−1h−1, respectively, which increase respectively by 62.2% and 123.1% compared to CdIn2S4 under the visible light irradiation. In addition, CdIn2S4/ZnIn2S4-4 hybrid exhibits excellent stability and activity during the 23-hour continuous HER, the average yield of H2 in 23-hour is up to 10286.6 μmolg−1h−1. This study provides a practical method for in-situ fabrication of ultrasmall pomegranate-like Z-scheme nano-heterostructures with abundant vacancies, which are valuable for efficient and robust implementation in a wide range of environmental and energy applications.

Boosting CO2 methanation on ceria supported transition metal catalysts via chelation coupled wetness impregnation

The incipient wetness impregnation (IWI) method is widely used in the preparation of supported transition metal catalysts for its high throughput and cost-effective synthesis, yet suffers from poor metal-support interaction, restricting its further application at an industrial scale. Herein, a universal strategy of chelation coupled impregnation (CCI) is presented. The as-prepared Ni/CeO2(CCI) showed superior catalytic performance for CO2 conversion (84.3%) and CH4 selectivity (100%) under the experimental conditions (WGHSV = 24,000 mL g−1 h−1 and H2/CO2 = 4:1) even at low temperatures (T = 275 °C). The surface characterization results confirmed that the agglomeration of metal active sites in Ni/CeO2(CCI) was restricted and more surface oxygen vacancies were generated on CeO2. Further, the in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS) analysis suggested that the surface oxygen vacancies that served as active sites could facilitate the direct dissociation of CO2 more favorably than the associative route, thus significantly promoting CO2 methanation activity.

Ag@Pd bimetallic structures for enhanced electrocatalytic CO2 conversion to CO: an interplay between the strain effect and ligand effect.

Electrochemical CO2 reduction reactions provide a promising path to effectively convert CO2 into valuable chemicals and fuels for industries. Among the many CO2 conversion catalysts, Pd stands out as a promising catalyst for effective CO2 to CO conversion. Here, using the misfit strain strategy, Ag@Pd bimetallic nanoparticles with different Pd overlayer contents were prepared as CO2 reduction catalysts. By varying the Pd overlayer content, all the Ag@Pd bimetallic nanoparticles exhibited superior CO2 conversion performance over their Pd and Ag nanoparticle counterparts. An optimal Pd-to-Ag ratio of 1.5 : 1 yielded the highest CO faradaic efficiency of 94.3% at -0.65 V vs. RHE with a high CO specific current density of 3.9 mA cm-2. It was found that the Pd content can substantially affect the interplay between the strain effect and ligand effect, resulting in optimized binding properties of the reaction intermediates on the catalyst surface, thereby enhancing the CO2 reduction performance.

Sustained CO2-photoreduction activity and high selectivity over Mn, C-codoped ZnO core-triple shell hollow spheres

Solar conversion of CO2 into energy-rich products is one of the sustainable solutions to lessen the global energy shortage and environmental crisis. Pitifully, it is still challenging to attain reliable and affordable CO2 conversion. Herein, we demonstrate a facile one-pot approach to design core-triple shell Mn, C-codoped ZnO hollow spheres as efficient photocatalysts for CO2 reduction. The Mn ions, with switchable valence states, function as “ionized cocatalyst” to promote the CO2 adsorption and light harvesting of the system. Besides, they can capture photogenerated electrons from the conduction band of ZnO and provide the electrons for CO2 reduction. This process is continuous due to the switchable valence states of Mn ions. Benefiting from such unique features, the prepared photocatalysts demonstrated fairly good CO2 conversion performance. This work is endeavoured to shed light on the role of ionized cocatalyst towards sustainable energy production.

Unique Z-scheme carbonized polymer dots/Bi4O5Br2 hybrids for efficiently boosting photocatalytic CO2 reduction

Constructing heterojunctions with matched band semiconductor is regarded as effective strategy to promote high-efficiency photocatalytic CO2 reduction. Herein, 0D/2D direct Z-scheme heterojunction involving carbonized polymer dots and Bi4O5Br2 nanosheets (CPDs/Bi4O5Br2) is designed and fabricated, which effectively facilitate migration and separation efficiency of photogenerated carriers and retain more negative electron reduction potential of CPDs and more positive hole oxidation potential of Bi4O5Br2. Moreover, CPDs promote adsorption of CO2 and intermediate COOH* as well as desorption of product CO. The direct Z-scheme mechanism of CPDs/Bi4O5Br2 is collaboratively confirmed by theory calculation, X-ray photoelectron spectroscopy and time-resolved transient absorption spectroscopy. The 8 wt% CPDs/Bi4O5Br2 exhibits the maximal CO production of 132.42 μmol h−1g−1 under Xe lamp irradiation, 5.43 fold higher than that of Bi4O5Br2 nanosheets. The CPDs with up-conversion properties can broaden light utilization range, so that composite material also show better CO2 conversion performance when excitation wavelength is greater than 580 nm.

Atomic iridium species anchored on porous carbon network support: An outstanding electrocatalyst for CO2 conversion to CO

Converting CO2 into valuable chemicals using electrocatalysis is an attractive approach for sustainable energy storage and artificial carbon cycle. In this study, atomically dispersed Ir species (Ad-Ir) that are supported on three-dimensional (3D) porous carbon networks are proposed as electrocatalysts for highly efficient CO2 conversion. The resulting catalysts can preferentially and rapidly produce CO with a high Faradaic efficiency of 95.6 % and a very high turnover frequency (TOF) value of 33,365 h−1. Furthermore, it shows no obvious decay in both FE for CO and current density over 20 h of continuous operation. Based on detailed experimental studies and density functional theory (DFT) calculations, such outstanding catalytic performance for CO2 conversion to CO production can be attributed to the structural advantages of 3D network of porous carbon and atomically dispersed Ir species on the 3D carbon support.

Low-Dimensional Nanostructured Photocatalysts for Efficient CO2 Conversion into Solar Fuels

The ongoing energy crisis and global warming caused by the massive usage of fossil fuels and emission of CO2 into atmosphere continue to motivate researchers to investigate possible solutions. The conversion of CO2 into value-added solar fuels by photocatalysts has been suggested as an intriguing solution to simultaneously mitigate global warming and provide a source of energy in an environmentally friendly manner. There has been considerable effort for nearly four decades investigating the performance of CO2 conversion by photocatalysts, much of which has focused on structure or materials modification. In particular, the application of low-dimensional structures for photocatalysts is a promising pathway. Depending on the materials and fabrication methods, low-dimensional nanomaterials can be formed in zero dimensional structures such as quantum dots, one-dimensional structures such as nanowires, nanotubes, nanobelts, and nanorods, and two-dimensional structures such as nanosheets and thin films. These nanostructures increase the effective surface area and possess unique electrical and optical properties, including the quantum confinement effect in semiconductors or the localized surface plasmon resonance effect in noble metals at the nanoscale. These unique properties can play a vital role in enhancing the performance of photocatalytic CO2 conversion into solar fuels by engineering the nanostructures. In this review, we provide an overview of photocatalytic CO2 conversion and especially focus on nanostructured photocatalysts. The fundamental mechanism of photocatalytic CO2 conversion is discussed and recent progresses of low-dimensional photocatalysts for efficient conversion of CO2 into solar fuels are presented.

CO2 conversion promoted by potassium intercalated g-C3N4 catalyst in DBD plasma system

The direct conversion of CO2 to CO and O2 has attracted extensive attention as CO is a key C1 feedstock for chemical synthesis. The CO2 conversion promoted by γ-Al2O3 supported potassium intercalated g-C3N4 (KuCN/AO) catalyst in a packed-bed dielectric barrier discharge (DBD) plasma system was investigated. A coaxial cylinder DBD plasma reactor was used with Cu powder as the high voltage electrode. Reactor temperature showed converse effect on CO2 conversion. As the reactor temperature decreased from 120 ℃ to 50 ℃, CO2 conversion rate and energy efficiency both increased by ca. 50%. After the catalyst was filled into the discharge area, the discharge mode changed from filamentary discharge to the combination of filamentary-surface discharge. The morphology and structure of KuCN was characterized by SEM, XRD, FTIR and XPS. KuCN kept a porous structure and K element distributed uniformly between CN interlayer spacing. In KuCN/AO assisted DBD plasma system, the highest CO2 conversion rate, CO yield and energy efficiency were increased from 11.1%, 10.0% and 9.41% to 19.3%, 18.1% and 20.6% compared with pure DBD/γ-Al2O3 system, respectively. The main mechanism of KuCN assisted enhancing CO2 conversion in packed-bed DBD reactor was analyzed. The larger specific surface area, layers bridging and charge redistribution enabled KuCN/AO to obtain good plasma-catalytic CO2 conversion performance.

Surface hydroxyls mediated CO2 methanation at ambient pressure over attapulgite-loaded Ni-TiO2 composite catalysts with high activity and reuse ability

Here we report a Ni/TiO2 loaded on attapulgite (ATP) composite catalyst with fairly good CO2 conversion performance amd outstanding reusability (up to 80 h re-use circles) at ambient pressure. The composite was prepared by sol-gel method using ATP powder as the matrix to load TiO2 and Ni nanocrystals in an equivalent impregnation process. Catalytic activity of the newly synthesized catalysts was investigated towards hydrogenation of CO2 at atmospheric pressure in varied temperature between 200 and 450 °C. And in the reaction process, the flow rate of CO2 gas was 2.5 mL/min and the concentration ratio of H2 : CO2 is always 4. The GHSV was 30,000 h−1. Among the investigated catalysts, the 8 % Ni-TiO2-ATP catalyst showed preferable activity at 450 ℃. Improved activity and reducibility were found when adding 8 % Ni due to the enhanced CO2 activation compared with the pure TiO2 or ATP matrix, as well as with the other Ni dosages. These improvements were obtained probably due to its higher surface area than TiO2 catalyst, more surface hydroxyls, and better dispersion on the ATP matrix.

Ionic liquid-based electrolytes for CO2 electroreduction and CO2 electroorganic transformation.

CO2 is an abundant and renewable C1 feedstock. Electrochemical transformation of CO2 can integrate CO2 fixation with renewable electricity storage, providing an avenue to close the anthropogenic carbon cycle. As a new type of green and chemically tailorable solvent, ionic liquids (ILs) have been proposed as highly promising alternatives for conventional electrolytes in electrochemical CO2 conversion. This review summarizes major advances in the electrochemical transformation of CO2 into value-added carbonic fuels and chemicals in IL-based media in the past several years. Both the direct CO2 electroreduction (CO2ER) and CO2-involved electroorganic transformation (CO2EOT) are discussed, focusing on the effect of electrocatalysts, IL components, reactor configurations and operating conditions on catalytic activity, selectivity and reusability. The reasons for the enhanced CO2 conversion performance by ILs are also discussed, providing guidance for the rational design of novel IL-based electrochemical processes for CO2 conversion. Finally, the critical challenges remaining in this research area and promising directions for future research are proposed.

Construction of BiO2−x/Bi2O2.75 heterojunction for highly efficient photocatalytic CO2 reduction

Nowadays, using solar energy to convert CO2 into hydrocarbon fuels such as CO and methanol is considered as an attractive approach to alleviate environmental pollution and the energy crisis. However, the easy recombination of photo-generated carriers and holes of photocatalyst is still the main factor that inhibits photocatalytic performance for CO2 conversion. In this study, the BiO[Formula: see text]/Bi2O[Formula: see text] heterojunction complex was successfully synthesized via a facile hydrothermal method. The BiO[Formula: see text]/Bi2O[Formula: see text] heterogeneous catalyst shows greatly improved photocatalytic performance for CO2 reduction, and the CO and CH4 yields obtained on BiO[Formula: see text]/Bi2O[Formula: see text] are 6.8 and 16 times compared with pure BiO[Formula: see text]. The improved photocatalytic performance can be ascribed to the rapid charge separation on BiO[Formula: see text]/Bi2O[Formula: see text] interface, thereby providing a favorable surface with suitable electronic structure for CO2 reduction. Subsequently, a possible photocatalytic mechanism was proposed to explain the improved performance of photocatalytic CO2 reduction.

Charge separation in hybrid metal–organic framework films for enhanced catalytic CO2 conversion

A three-dimensional porous metal–organic framework-based hybrid film is prepared through a solid conversion process, demonstrating high photocatalytic performance for CO2 conversion under mild conditions.