Kinetics Of CO2 Reduction Research Articles

Highly Efficient CO2 Reduction at Steady 2 A cm-2 by Surface Reconstruction of Silver Penetration Electrode.

Electroreduction of CO2 to CO is a promising route for greenhouse gas resource utilization, but it still suffers from impractical current density and poor durability. Here, a nanosheet shell (NS) vertically standing on the Ag hollow fiber (NS@Ag HF) surface formed by electrochemical surface reconstruction is reported. As-prepared NS@Ag HF as a gas penetration electrode exhibited a high CO faradaic efficiency of 97% at an ultra-high current density of 2.0 A cm-2 with a sustained performance for continuous >200h operation. The experimental and theoretical studies reveal that promoted surface electronic structures of NS@Ag HF by the nanosheets not only suppress the competitive hydrogen evolution reaction but also facilitate the CO2 reduction kinetics. This work provides a feasible strategy for fabricating robust catalysts for highly efficient and stable CO2 reduction.

Enhancing puncture voltage of La0.8Sr0.2Ga0.8Mg0.2O3-δ solid electrolyte membrane by improving CO2 reduction kinetics

Solid oxide electrolyte membrane is the core component of solid oxide cells and determines the efficiency of energy conversion. Identifying the failure mechanism of electrolyte membrane and the corresponding strategy to sustain its function at high voltages are significant to promote the development of solid oxide electrolysis cells (SOECs). In this study, we thermodynamically predict that the Ga–O bond of octahedral GaO6 in La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM22) electrolyte membrane is prone to be electro-reduced during the electro-driven CO2 reduction reaction (CO2RR). Our experimental results verify that the LSGM22 electrolyte membrane is electro-reduced at 1.4 V and 800 °C, decomposing into LaSrGaO4, La2O3, SrO, MgO and Ga. The inadequate supply of oxygen ions flux, due to the sluggish kinetics of CO2RR, is the inducing factor for the functional failure of LSGM22 electrolyte membrane. Therefore, applying a highly active cathode is proposed to increase the puncture voltage via facilitating CO2RR kinetics and avoiding the reduction of Ga–O bond. La0.5Sr0.5FeO3-δ is employed as an example to show the validity of this strategy, and improves the puncture voltage from 1.4 to 1.6 V.

Group 6 (Cr, Mo, W) and Group 7 (Mn, Re) bipyridyl tetracarbonyl complex for electrochemical CO2 conversion: DFT and DLPNO-CCSD(T) study for effects of the central metal on redox potential, thermodynamics, and kinetics

To reveal the effects of central metal on the catalytic efficiency, we estimated the thermodynamics and kinetics of CO2 reduction by Group 6 and Group 7 metal bpy tetracarbonyl complexes using DLPNO-CCSD(T) method. The applied potential V1 required for the formation of the two-electron reduced species of the metal bpy tetracarbonyl complex is greater than the applied potential V2 required for the formation of the two-electron reduced species of the metal bpy tricarbonyl complex, and for each applied potential, the effect of the central metal on the reaction process was investigated. At applied potential V1, CO2 binding to metal center was the rate-limiting step in CO2 reduction by the Group 6 complex, while the second proton transfer was the rate-limiting step for CO2 reduction by the Group 7 complex. At applied potential V2, the rate-limiting step was the dissociation of the CO ligand from the central metal, except for Cr.

Highly Efficient Cu-Porphyrin-Based Metal-Organic Framework Nanosheet as Cathode for High-Rate Li-CO2 Battery.

The lithium-carbon dioxide (Li-CO2 ) battery as a novel metal-air battery has a high specific energy density and unique CO2 conversion ability. However, its further development is limited by incomplete product decomposition resulting in poor cycling and rate performance. In this work, Cu-tetra(4-carboxyphenyl) porphyrin (Cu-TCPP) nanosheets are prepared through the solvothermal method successfully. An efficient Li-CO2 battery with Cu-TCPP as catalyst achieves a high discharge capacity of 20393 mAh g-1 at 100mA g-1 , a long-life cycle of 123 at 500mA g-1 , and a lower overpotential of 1.8V at 2000mA g-1 . Density functional theory calculation reveals that Cu-TCPP has higher adsorption energy of CO2 and Li2 CO3 compared with TCPP, and a large number of electrons gather near the Cu-N4 active sites in Cu-TCPP. Therefore, the excellent CO2 capture ability of the porphyrin ligand and the synergic catalytic effect of Cu atom in Cu-TCPP promote the thermodynamics and kinetics of CO2 reduction and evolution processes.

Chloride Ion Adsorption Enables Ampere-Level CO2 Electroreduction over Silver Hollow Fiber.

Electrochemical conversion of CO2 into valuable feedstocks is a promising strategy for carbon neutrality. However, it remains a challenge to possess a large current density, a high faradaic efficiency and excellent stability for practical applications of CO2 utilization. Herein, we report a facile tactic that enables exceedingly efficient CO2 electroreduction to CO by virtue of low-coordination chloride ion (Cl- ) adsorption on a silver hollow fiber (Ag HF) electrode. A CO faradaic efficiency of 92.3 % at a current density of one ampere per square centimeter (1 A cm-2 ) in 3.0 M KCl with a sustained performance observed during a 150-hour test was achieved, which is better than state-of-the-art electrocatalysts. The electrochemical results and density functional theory (DFT) calculations suggested a low-coordination Cl- adsorption on surface of Ag HF, which not only suppressed the competitive hydrogen evolution reaction (HER), but also facilitated the CO2 reduction kinetics.

Chloride Ion Adsorption Enables Ampere‐Level CO 2 Electroreduction over Silver Hollow Fiber

Electrochemical conversion of CO2 into valuable feedstocks is a promising strategy for carbon neutrality. However, it remains a challenge to possess a large current density, a high faradaic efficiency and excellent stability for practical applications of CO2 utilization. Herein, we report a facile tactic that enables exceedingly efficient CO2 electroreduction to CO by virtue of low-coordination chloride ion (Cl−) adsorption on a silver hollow fiber (Ag HF) electrode. A CO faradaic efficiency of 92.3 % at a current density of one ampere per square centimeter (1 A cm−2) in 3.0 M KCl with a sustained performance observed during a 150-hour test was achieved, which is better than state-of-the-art electrocatalysts. The electrochemical results and density functional theory (DFT) calculations suggested a low-coordination Cl− adsorption on surface of Ag HF, which not only suppressed the competitive hydrogen evolution reaction (HER), but also facilitated the CO2 reduction kinetics.

Efficient CO2 Electroreduction over Silver Hollow Fiber Electrode

Electrocatalytic reduction of CO2 to fuels and chemicals is one of the most attractive routes for CO2 utilization. However, low efficiency and poor stability restrict the practical application of most conventional electrocatalysts. Here, a silver hollow fiber electrode is presented as a novel self-supported gas diffusion electrode for efficient and stable CO2 electroreduction to CO. A CO faradaic efficiency of over 92% at current densities of above 150 mA∙cm−2 is achieved in 0.5 M KHCO3 for over 100 h, which is comparable to the most outstanding Ag-based electrocatalysts. The electrochemical results suggest the excellent electrocatalytic performance of silver hollow fiber electrode is attributed to the unique pore structures providing abundant active sites and favorable mass transport, which not only suppresses the competitive hydrogen evolution reaction (HER) but also facilitates the CO2 reduction kinetics.

Steering the Pathway of Plasmon-Enhanced Photoelectrochemical CO2 Reduction by Bridging Si and Au Nanoparticles through a TiO2 Interlayer.

Photoelectrochemical (PEC) conversion of CO2 in an aqueous medium into high-energy fuels is a creative strategy for storing solar energy and closing the anthropogenic carbon cycle. However, the rational design of catalytic architectures to selectively and efficiently produce a target product such as CO has remained a grand challenge. Herein, an efficient and selective Si photocathode for CO production is reported by utilizing a TiO2 interlayer to bridge the Au nanoparticles and n+ p-Si. The TiO2 interlayer can not only effectively protect and passivate Si surface, but can also exhibit outstanding synergies with Au nanoparticles to greatly promote CO2 reduction kinetics for CO production through stabilizing the key reaction intermediates. Specifically, the TiO2 layer and Au nanoparticles work concertedly to enhance the separation of localized surface plasmon resonance generated hot carriers, contributing to the improved activity and selectivity for CO production by utilizing the hot electrons generated in Au nanoparticles during PEC CO2 reduction. The optimized Au/TiO2 /n+ p-Si photocathode exhibits a Faradaic efficiency of 86% and a partial current density of -5.52mA cm-2 at -0.8 VRHE for CO production, which represent state-of-the-art performance in this field. Such a plasmon-enhanced strategy may pave the way for the development of high-performance PEC photocathodes for energy-efficient CO2 utilization.

Rational Design of Nanostructured Metal/C Interface in 3D Self‐Supporting Cellulose Carbon Aerogel Facilitating High‐Performance Li‐CO2 Batteries

AbstractThe sluggish kinetics of CO2 reduction and evolution reaction (CRR and CER) on the Li–CO2 battery cathode seriously hindered its practical application. Rational design of the Ru/C interface is expected to simultaneously decrease the free energy barrier of intermediate species and create a favorable electronic structure, effectively promoting the catalytic reaction kinetics of the CRR and CER. Herein, a 3D self‐supporting cellulose carbon aerogel (CCA) with well‐defined Ru/C interfaces (Ru@CCA) is synthesized as an advanced CO2‐breathing cathode for Li–CO2 batteries. The results show that the energy efficiency significantly improves to 80% with a high discharge capacity of 10.71 mA h cm−2 at 20 µA cm−2, and excellent cyclic stability of 421 cycles at 100 µA cm−2. These outstanding performances are highly competitive compared with state‐of‐art Li–CO2 cathodes. In addition, the unique interface design strategy is applied to other non‐noble metal@CCA cathodes, which confirms the advantages of constructing nanostructure metal/C interfaces for improving the kinetics of CRR and CER. This fundamental understanding of the structure–performance relationship provides new inspiration for designing highly efficient cathode catalysts for Li–CO2 batteries.

Reaction mechanism and kinetics for carbon dioxide reduction on iron–nickel Bi-atom catalysts

The electrocatalytic reaction mechanism and kinetics of CO2 reduction at the Ni–Fe dual-site were determined based on the grand canonical potential kinetics (GCP-K) method, and a new CO-passivating mechanism was revealed.

Enhancing Puncture Voltage of La0.8sr0.2ga0.8mg0.2o3-Δ Solid Electrolyte Membrane by Improving Co2 Reduction Kinetics

Enhancing Puncture Voltage of La0.8sr0.2ga0.8mg0.2o3-Δ Solid Electrolyte Membrane by Improving Co2 Reduction Kinetics

Comparing interfacial cation hydration at catalytic active sites and spectator sites on gold electrodes: understanding structure sensitive CO2 reduction kinetics.

Hydrated cations present in the electrochemical double layer (EDL) are known to play a crucial role in electrocatalytic CO2 reduction (CO2R), and numerous studies have attempted to explain how the cation effect contributes to the complex CO2R mechanism. CO2R is a structure sensitive reaction, indicating that a small fraction of total surface sites may account for the majority of catalytic turnover. Despite intense interest in specific cation effects, probing site-specific, cation-dependent solvation structures remains a significant challenge. In this work, CO adsorbed on Au is used as a vibrational Stark reporter to indirectly probe solvation structure using vibrational sum frequency generation (VSFG) spectroscopy. Two modes corresponding to atop adsorption of CO are observed with unique frequency shifts and potential-dependent intensity profiles, corresponding to direct adsorption of CO to inactive surface sites, and in situ generated CO produced at catalytic active sites. Analysis of the cation-dependent Stark tuning slopes for each of these species provides estimates of the hydrated cation radius upon adsorption to active and inactive sites on the Au electrode. While cations are found to retain their bulk hydration shell upon adsorption at inactive sites, catalytic active sites are characterized by a single layer of water between the Au surface and the electrolyte cation. We propose that the drastic increase in catalytic performance at active sites stems from this unique solvation structure at the Au/electrolyte interface. Building on this evidence of a site-specific EDL structure will be critical to understand the connection between cation-dependent interfacial solvation and CO2R performance.

Electrochemical CO2 Reduction at Silver from a Local Perspective

The electrochemical reduction of CO2 to chemical fuels and value-added chemicals is a viable pathway to store renewably generated electrical energy and to mitigate the negative impact of anthropogenic CO2 production. Herein, we study how the local reaction environment dictates the mechanism and kinetics of CO2 reduction to CO at an Ag electrode. The local reaction environment is determined using a hierarchical model that accounts for multistep reaction kinetics, specific surface charging state at a given electrode potential, and mass transport phenomena. The model reveals vital mechanistic insights into the reaction behavior. The increasing Tafel slope with overpotential is seen to be influenced by the surface charging relation and mass transport effects. In addition, the decrease of the CO current density at high overpotentials is found to be caused not only by the decrease in CO2 concentration due to mass transport, surface charge effects, and pH increase but also by lateral interactions between HCOOad, COOHad, and Had. Moreover, we explore how the electrolyte properties, including bicarbonate concentration, solvated cation size, and CO2 partial pressure, tune the local reaction environment.

Strategies for Improved Electrochemical CO2 Reduction to Value-Added Products by Highly Anticipated Copper-Based Nanoarchitectures.

Uncontrolled CO2 emission from various industrial and domestic sources is a considerable threat to environmental sustainability. Scientists are trying to develop multiple approaches to not only reduce CO2 emissions but also utilize this potent pollutant to get economically feasible products. The electrochemical reduction of CO2 (ERC) is one way to effectively convert CO2 to more useful products (ranging from C1 to C5). Nevertheless, this process is kinetically hindered and less selective towards a specific product and, consequently, requires an efficient electrocatalyst with characteristics like selectivity, stability, reusability, low cost, and environmentally benign. Owing to specified commercial features, copper (Cu)-based materials are highly anticipated and widely investigated for the last two decades. However, their non-modified polycrystalline Cu forms usually lack selectivity and lower overpotential of CO2 reduction. Therefore, extensive research is in progress to induce various alterations ranging from morphological and surface chemistry tuning to structural and optoelectrical characteristics modifications. This review provides an overview of those strategies to improve the CO2 conversion efficiency through Cu-based ERC into valuable C1, C2, and higher molecular weight hydrocarbons. The thermodynamics and kinetics of CO2 reduction via Cu-based electrocatalysts are discussed in detail with the support of the first principle DFT-based models. In the last portion of the review, the reported mechanisms for various products are summarized, with a short overview of the outlook. This review is expected to provide important basics as well as advanced information for experienced as well as new researchers to develop various strategies for Cu and related materials to achieve improved ERC.

Oxidation kinetics of hercynite spinels for solar thermochemical fuel production

The development of an economically viable solar thermochemical fuel production process relies largely on identifying redox active materials with optimized thermodynamic and kinetic properties. Iron aluminate (FeAl2O4, hercynite) and cobalt-iron aluminate (CoxFe1-xAl2O4) have both been demonstrated as viable redox-active materials for this process. However, doping with cobalt creates a tradeoff between the thermodynamics and kinetics of H2 production mediated by hercynite in which the kinetics are improved at the expense of lowering the yield. In this work, we evaluate four spinel aluminate materials with varying cobalt contents (FeAl2O4, Co0.05Fe0.95Al2O4, Co0.25Fe0.75Al2O4, and Co0.40Fe0.60Al2O4) to better understand the role of cobalt in the redox mediating properties of these materials and to quantify its effect on the thermodynamic and kinetic properties for CO2 reduction. A solid-state kinetic analysis was performed on each sample to model its CO2 reduction kinetics at temperatures ranging from 1200 °C to 1350 °C. An F1 model representative of first-order reaction kinetics was found to most accurately represent the experimental data for all materials evaluated. The computed rate constants, activation energies, and pre-exponential factors all increase with increasing cobalt content. High temperature in-situ XPS was utilized to characterize the spinel surfaces and indicated the presence of metallic states of the reduced cobalt-iron spinel, which are not present in un-doped hercynite. These species provide a new site for the CO2 reduction reaction and enhance its rate through an increased pre-exponential factor.

Highly correlation of CO2 reduction selectivity and surface electron Accumulation: A case study of Au-MoS2 and Ag-MoS2 catalyst

Artificial photosynthesis from CO2 reduction to methane is severely hampered by the kinetically challenging eight-electron transfer process. Accumulated electrons has been demonstrated can decrease this kinetic barrier. However, charge accumulation were mainly reported in several homogenous systems because of its difficulties in heterogenous systems. Here we identify that highly accumulated electrons exist in Au loaded ultrathin MoS2 under light irradiation, resulting in a superior performance of CO2 reduction to methane. The selectivity for methane is up to 80 % with an average production rate of about 19.38 μmolg−1 h−1 in pure water. Further detailed studies reveal that plasmon-excited hot electrons transfer from Au to charged excitons in ultrathin MoS2 promotes electron accumulation and multi-electron CO2 reduction kinetics for methane generation. This is further supported by the CO2 reduction performance of Ag-MoS2. Along with the vanished accumulated electrons, CO is the main product with a selectivity of 98 %.

Ultrathin RuRh Alloy Nanosheets Enable High-Performance Lithium-CO2 Battery

Summary The aprotic Li-CO2 battery with high energy density is an attractive energy-storage technology. However, its development is largely impeded by the sluggish kinetics of CO2 reduction and evolution reactions. Here, we demonstrate a class of ultrathin triangular RuRh alloy nanosheets as an exceptionally active catalyst for greatly accelerating the kinetics of CO2 reduction and evolution reactions and achieving a high-performance Li-CO2 battery. The RuRh alloy nanosheets-based battery can achieve the lowest voltage gap of 1.35 V during the charge-discharge process and stably cycle for 180 cycles with a cutoff capacity of 1,000 mAh g−1 at 1,000 mA g−1. Density functional theory calculations demonstrate the pivotal roles of Rh introduction in RuRh alloy nanosheets, which evidently activate the electron-transfer ability of surface Ru and balance the CO2 binding near Ru sites. We find that the d-d correlation between Rh and Ru contributes to the energetically favorable cycle of the Li-CO2 battery.

Solar-heating boosted catalytic reduction of CO2 under full-solar spectrum

Catalytic converting CO2 into fuels with the help of solar energy is regarded as ‘dream reaction’, as both energy crisis and environmental issue can be mitigated simultaneously. However, it is still suffering from low efficiency due to narrow solar-spectrum utilization and sluggish heterogeneous reaction kinetics. In this work, we demonstrate that catalytic reduction of CO2 can be achieved over Au nanoparticles (NPs) deposited rutile under full solar-spectrum irradiation, boosted by solar-heating effect. We found that UV and visible light can initiate the reaction, and the heat from IR light and local surface-plasmon resonance relaxation of Au NPs can boost the reaction kinetically. The apparent activation energy is determined experimentally and is used to explain the superior catalytic activity of Au/rutile to rutile in a kinetic way. We also find the photo-thermal synergy in the Au/rutile system. We envision that this work may facilitate understanding the kinetics of CO2 reduction and developing feasible catalytic systems with full solar spectrum utilization for practical artificial photosynthesis.

Highly Surface‐Wrinkled and N‐Doped CNTs Anchored on Metal Wire: A Novel Fiber‐Shaped Cathode toward High‐Performance Flexible Li–CO2 Batteries

AbstractLi–CO2 batteries are regarded as a promising candidate for the next‐generation high‐performance electrochemical energy storage system owing to their ultrahigh theoretical energy density and environmentally friendly CO2 fixation ability. Until now, the majority of reported catalysts for Li–CO2 batteries are in the powder state. Thus, the air electrodes are produced in 2D rigid bulk structure and their electrochemical properties are negatively influenced by binder. The nondeformable feature and unsatisfactory performance of the cathode have already become the main obstacles that hinder Li–CO2 batteries toward ubiquity for wearable electronics. In this work, for the first time, a flexible hybrid fiber is reported comprising highly surface‐wrinkled and N‐doped carbon nanotube (CNT) networks anchored on metal wire as the cathode integrated with high performance and high flexibility for fiber‐shaped Li–CO2 battery. It exhibits a large discharge capacity as high as 9292.3 mAh g−1, an improved cycling performance of 45 cycles, and a decent rate capability. A quasi‐solid‐state flexible fiber‐shaped Li–CO2 battery is constructed to illustrate the advantages on mechanical flexibility of this fiber‐shaped cathode. Experiments and theoretical simulations prove that those doped pyridinic nitrogen atoms play a critical role in facilitating the kinetics of CO2 reduction and evolution reaction, thereby enabling distinctly enhanced electrochemical performance.

Exploiting Synergistic Effect by Integrating Ruthenium–Copper Nanoparticles Highly Co‐Dispersed on Graphene as Efficient Air Cathodes for Li–CO2 Batteries

AbstractLi–CO2 batteries are attractive electrical energy storage devices; however, they still suffer from unsatisfactory electrochemical performance, and the kinetics of CO2 reduction and evolution reactions must be improved significantly. Herein, a composite of ruthenium–copper nanoparticles highly co‐dispersed on graphene (Ru–Cu–G) as efficient air cathodes for Li–CO2 batteries is designed. The Li–CO2 batteries with Ru–Cu–G cathodes exhibit ultra‐low overpotential and can be operated for 100 cycles with a fixed capacity of 1000 mAh g−1 at 200 and 400 mA g−1. The synergistic effect between Ru and Cu not only regulates the growth of discharge products, but also promotes CO2 reduction and evolution reactions by changing the electron cloud density of the surface between Ru and Cu. This work may provide new directions and strategies for developing highly efficient air cathodes for Li–CO2 batteries, or even practical Li–air batteries.