Ce Oxides Research Articles

Influence of Ce and Ti oxides doping on the PMMA polymer: structural, optical, THz, dielectric, and antimicrobial characteristics

Influence of Ce and Ti oxides doping on the PMMA polymer: structural, optical, THz, dielectric, and antimicrobial characteristics

The adsorption of cerium on synthetic δ-MnO2: Implications for Ce uptake behavior of hydrogenetic and early diagenetic ferromanganese nodules from the Western Pacific

Cerium (Ce) anomalies can be used to distinguish diagenetic and hydrogenetic nodules, making them an important discriminator for the genesis of marine ferromanganese nodules. To understand the enrichment and adsorption mechanisms of Ce in different types of ferromanganese nodules, we conducted mineralogical and geochemical studies on ferromanganese nodule layers formed through both hydrogenetic and early diagenetic processes as well as adsorption experiments on synthetic δ-MnO2 to monitor the Ce uptake during the different processes. The major and trace element contents of natural ferromanganese nodule layers were investigated by SEM, EPMA and LA-ICP-MS analysis. The marine nodule studied in this study consisted of a core of fish tooth and a rim that could be divided into the hydrogenetic (type I) and early diagenetic (type II) layers based on their mineralogy and Mn/Fe ratios. The Mn oxide mineral assemblage is composed of todorokite, buserite, birnessite, and vernadite (δ-MnO2) and occurred in both type I and II layers. The type I layer has laminated structures with a low Mn/Fe ratio (1.1–3.2; averaging at 1.7), and low Cu, Ni and Mg contents consistent with a hydrogenetic genesis. The type II layer has a columnar and stromatolitic structure with a high Mn/Fe ratio (5.1–54.0; averaging at 23.3) and high Cu, Ni and Mg contents that are similar to early diagenetic nodules. The ΣREE contents in type I and type II layers are 1405–3506 ppm (averaging at 2091 ppm) and 199–1232 ppm (averaging at 674 ppm), respectively, indicating that the REE is enriched in the hydrogenetic type I layers. Strong positive Ce anomalies are present type I layers ranging from 1.2 to 2.5 (averaging 1.9), but only slightly positive are seen in type II ranging from 0.4 to 2.4 (averaging at 1.0). Synthetic experiments to monitor the Ce uptake process show that Ce can be adsorbed onto δ-MnO2 with the XRD and FTIR patterns suggesting that the structure of δ-MnO2 did not change significantly, consistent with Ce behavior in hydrogenetic nodules. The results suggest that Ce is predominantly concentrated in hydrogenetic nodules in an oxic environment, whereas in the early diagenetic layer, there is less oxidation and fixation of Ce due to the suboxic conditions. Our findings are consistent with Ce anomalies in marine Fe-Mn nodules being the result of Mn oxide oxidation adsorption and then fixation (oxidation) after adsorption.

A Gd-doped ceria/TiOx nanocomposite as the active layer in a three terminal electrochemical resistivity switch.

Coupling between an electrochemical reaction and a functional material property has been termed electro-chemo-X, or EC-X, where X can refer to mechanical, optical, magnetic or thermal properties. Recently, our group has demonstrated a two-terminal electro-chemo-mechanical (ECM) membrane actuator operating under ambient conditions and containing a Ce0.8Gd0.2O1.9 solid electrolyte layer sandwiched between two Gd-doped ceria/TiOx nanocomposite thin films. Reducing one nanocomposite film while oxidizing the other was observed to produce reversible volume change thereby driving membrane actuator operation. Here, we use the same electrolyte and nanocomposite layer pair (the upper one as the ion reservoir and the lower, as the active layer) to further explore the EC-X effect. We demonstrate the suitability of the nanocomposite for a three-terminal, thin film-based resistivity switch. We find that application of ±6 V (<60 kV/cm) bias to the gate terminal for two hours under ambient conditions changes the nanocomposite conductivity in the channel between the source and drain by at least 40%. When the bias is negative, the active layer remains in a more highly conductive state for approximately twenty-four hours. Impedance spectroscopy and cyclic voltammetry reveal oxygen ion migration taking place between the active layer and the reservoir. X-ray photoelectron spectroscopy indicates that, in the absence of negative gate bias, thermal oxidation of Ce+3 - > Ce+4 is similarly effective in leading to increased nanocomposite conductivity, while reduction produces the opposite effect. With the expectation that the response time can be significantly shortened, the proposed resistivity switch may be suitable for future applications such as sensors, neuromorphic computing or spintronics.

Magnetic field-assisted adsorption of phosphate on biochar loading amorphous Zr–Ce (carbonate) oxide composite

For metal-based phosphate adsorbents, the dispersity and utilization of surface metal active sites are crucial factors in their adsorption performance and synthesis cost. In this study, a biochar material modified with amorphous Zr–Ce (carbonate) oxides (BZCCO-13) was synthesized for the phosphate uptake, and the adsorption process was enhanced by magnetic field. The beside-magnetic field was shown to have a better influence than under-magnetic field on adsorption, with maximum adsorption capacities (123.67 mg P/g) 1.14-fold greater than that without magnetic field. The beside-magnetic field could also accelerate the adsorption rate, and the time to reach 90% maximum adsorption capacity decreased by 83%. BZCCO-13 has a wide range of application pHs from 5.0 to 10.0, with great selectivity and reusability. The results of XPS and ELNES showed that the "magnetophoresis" of Ce3+ under the magnetic field was the main reason for the enhanced adsorption performance. In addition, increased surface roughness, pore size and oxygen vacancies, enhanced mass transfer by Lorentz force under a magnetic field, all beneficially influenced the adsorption process. The mechanism of phosphate adsorption by BZCCO-13 could be attributed to electrostatic attraction and CO32–dominated ligand exchange. This study not only provided an effective strategy for designing highly effective phosphate adsorbents, but also provides a new light on the application of rare earth metal-based adsorbent in magnetic field.

Thermal decomposition behavior of Mountain Pass rare earth concentrate in air/CO2 atmosphere

The Mountain Pass mine is recognized as one of the world’s primary sources of rare earth minerals. These rare earth minerals mainly consist of bastnaesite and a small amount of monazite phosphate, which cannot be decomposed and recovered through conventional oxidative roasting and hydrochloric acid leaching process. An efficient, clean, and economical process called the "combined method" was proposed for the utilization of the Mountain Pass mine to extract rare earths from Mountain Pass rare earth concentrate (MPREC). The main steps of this process include weak oxidation atmosphere roasting, step leaching of hydrochloric acid, solid-liquid separation, the monazite slag with sulfuric acid roasting water leaching, etc. In this paper, the roasting process of MPREC under a weak oxidation atmosphere was investigated. The study examines the thermal decomposition kinetics, phase transition process, and leaching behavior of MPREC in air/CO2 atmosphere. Results show that, the activation energy (Ea) for MPREC thermal decomposition in air and CO2 atmosphere are 146 and 320 kJ/mol, respectively. At temperature above 500 °C in air or above 700 °C in CO2 atmosphere, REOF are generated from bastnaesite through an in-situ reaction with CaO, which is decomposed from CaCO3, to form CaF2 and rare earth oxide (REO). Thus, F is regulated into solid phase. In an oxidizing atmosphere, the thermal decomposition of bastnaesite is accompanied by the rapid oxidation of Ce(Ⅲ). In contrast, the oxidation of Ce(Ⅲ) in a CO2 atmosphere is significantly inhibited. At 700 °C, the oxidation rate of Ce in air is 74.09%, while in a CO2 atmosphere, it is only 33.83%. The hydrochloric acid leaching experiment shows that, the leaching rate of rare earth after roasting at 600 °C under an air atmosphere reaches to 82.9%, and it reaches 87% after roasting at 800 °C under a CO2 atmosphere. The reduction of Ce oxidation in a weak oxidizing atmosphere significantly improves the leaching rate of Ce.

Significantly enhanced low-temperature activity and SO2/H2O tolerance of Mn–Ce-Ox/TiO2 catalyst prepared by a facile citric acid assisted impregnation method

Two different Mn–Ce-Ox/TiO2 catalysts were prepared by ordinary impregnation (denoted as MCT) and citric acid assisted impregnation (denoted as MCT-CA) methods, respectively. Excellent NOx removal is achieved over MCT-CA for selective catalytic reduction with NH3 (NH3-SCR), and 100% NOx conversion is obtained at 125 °C under weight hour space velocity (WHSV) of 80000 mL/(gcat·h). Particularly, 100% NOx is converted on MCT-CA in the presence of 10 vol% H2O at 175 °C. As H2O and SO2 coexist in the reaction system for 9 h, NOx conversion can still be maintained >90%, much higher than that (22%) of MCT. A series of characterization results indicates that MCT-CA exhibits a larger BET specific surface area, pore volume, and pore size, which enhances the dispersion of Mn and Ce oxides and promotes the rapid adsorption of reactants and desorption of products. Additionally, MCT-CA possesses more Mn4+, Ce3+, chemisorbed oxygen species, and stronger reducibility, facilitating the conversion of NO to NO2. Specially, the amount of active NH3 species and active nitrate species on MCT-CA is much more than that over MCT. The combined effect of the aforementioned factors devotes to the excellent low-temperature SCR performance and tolerance to H2O/SO2 over MCT-CA.

Effective Promotion of the Activity and Stability of Cathodes for Protonic Ceramic Fuel Cells

AbstractProtonic ceramic fuel cells (PCFCs) are emerging as effective devices for their excellent capability of converting energy. However, the sluggish oxygen reduction reaction (ORR) and poor durability of cathodes greatly limit their widespread commercialization. Herein, a multi‐cationic oxide nano‐catalyst with a nominal composition of Pr0.2Ce0.2Ni0.2Co0.2Fe0.2Ox (denoted as PCNCFO) is designed and reported, which significantly enhanced the ORR activity and durability of a typical PrBaCo2O5+δ (PBC) cathode. The PCNCFO‐coated PBC cathode delivered impressive cell performance with a small polarization resistance of only 0.18 Ω cm2 at 600 °C on symmetrical cells and a high peak power density (PPD) of 1.31 W cm−2 at 650 °C on single cells. Meanwhile, the PCNCFO‐coated PBC cathode exhibits excellent operational stability both on symmetrical and single cells. It is indicated that the Ce oxide in the nano‐catalyst coating can react with the segregated Ba to form active species, while others can activate the surface of the cathode, as indicated by the transmission electron microscope (TEM) and distribution of relaxation time (DRT) analyses.

Facile Oxidation of Ce(III) to Ce(IV) Using Cu(I) Salts.

The synthesis, luminescence, and electrochemical properties of the Ce(III) compound, [(C5Me5)2(2,6-iPr2C6H3O)Ce(THF)], 1, were investigated. Based on the electrochemical data, treatment of 1 with CuX (X = Cl, Br, I) results in the formation of the corresponding Ce(IV) complexes, [(C5Me5)2(2,6-iPr2C6H3O)Ce(X)]. Each complex has been characterized using NMR, IR, and UV-vis spectroscopy as well as structurally determined using X-ray crystallography. Additionally, the treatment of [(C5Me5)2(2,6-iPr2C6H3O)Ce(Br)] with AgF results in the formation of the putative [(C5Me5)2(2,6-iPr2C6H3O)Ce(F)]. The electronic structure of these Ce(IV)-X complexes was investigated by bond analyses and the Ce(IV)-F moiety using quantum chemistry NMR calculations.

Correlation of electronic structure and magnetic properties of [formula omitted] nanostructure using synchrotron soft XAS

The present study reports crystalline structure, electronic structure and magnetic properties for nanoparticles undoped CeO2 and Ce1-xSmxO2 (x = 0.02 to 0.10, @ 0.02). The nanoparticle samples are synthesized by the co-precipitation method. XRD data shows the successful incorporation of Sm3+ ions at Ce4+ sites in the face-centered cubic (fcc) lattice. The soft X-ray absorption spectroscopy technique is utilized to get an insightful overview of electronic structural properties due to structural defects, chemical states and the development of oxygen vacancies in Ce1-xSmxO2 nanoparticles. The soft XAS spectra show a significant Ce and Sm peak in the M4,5 domain, along with the well-defined O K-edge peak. Analysis of Ce M4,5-edges indicates that Ce-ions have both 3 + and 4 + oxidation states. With the incorporation of Sm+3 ions, there is a reduction of Ce4+ states and oxidation of Ce3+ states, as well as a substantial increase in oxygen vacancy concentration. The room-temperature magnetic properties of Ce1-xSmxO2 nanoparticles reveal ferromagnetic behavior. The origin of ferromagnetism is explained by F-center exchange (FCE) coupling mechanisms mediated via development of oxygen vacancy and defects.

Multi‐electron Oxidation of Ce(III) Complexes Facilitated by Redox‐Active Ligands

AbstractA family of cerium complexes featuring a redox‐active ligand in different oxidation states has been synthesized, including the the iminosemiquinone (isq)1− compound, Ce(dippisq)3 (1‐Ceisq), and the amidophenolate (ap)2− species CeIII(dippap)3K3 (2‐Ceap), [CeIII(dippap)3K][K(18‐c‐6)]2 (2‐Ceap 18c6), and [CeIII(dippap)3K][K(15‐c‐5)2]2 (2‐Ceap 15c5). Treating 2‐Ceap 15c5 with dioxogen furnishes the cerium(IV) derivative [CeIV(dippap)3][K(15‐c‐5)2]2 (3‐Ceap 15c5), and an analogous synthesis can be used to generate [CeIV(dippap)3][K(crypt)]2 (3‐Ceap crypt). Similarly, addition of hexamethyldisiloxane produces an interesting bis(amidophenolate) species, [(Me3SiO)2CeIV(dippap)2][K(15‐c‐5)2]2 (4‐CeOSiMe3). Full spectroscopic and structural characterization of each derivative was performed to establish the oxidation states of both the ligands and the cerium ions.

Nb2O5 and Nb based oxides as redox photocatalysts: Partial oxidation of 2-propanol and H2 generation by photoreforming

The structural and chemical properties of niobium oxide catalysts have been under scientific scrutiny for the last fifty years; however, their application in photocatalytic processes is very recent and still little studied. In this research, pristine Nb2O5 and its composites containing Ti, Ce, or Zr oxides have been used as photocatalysts in redox reactions such as 2-propanol oxidation in gas-solid regime and in aqueous phase triethanolamine photo-reforming to yield H2. All the materials were active in the oxidation of 2-propanol under simulated sunlight irradiation. The substrate was oxidised in the presence of all of the solids resulting in formation of propanone as the major intermediate product and CO2 as the final product. In liquid solid regime, the H2 production by UV-assisted photoreforming of aqueous solution of triethanolamine reached ca. 6 μmol h−1 g−1 for the best performing material, the bare Nb2O5, which increases up to 592 μmol h−1 g−1 in the presence of 1 % of Pt co-catalyst.

Ce/N @BC prepared based on plant metallurgy strategy: A novel activator of peroxymonosulfate for the degradation of sulfamethoxazole

A novel carbon catalyst was created based on plant metallurgy strategy for organic pollutants removal. Plants rich in CeO2 NPs in water were used as carbon precursors and pyrolyzed with urea to obtain Ce/N co-doped carbon catalysts, which were used in the degradation of sulfamethoxazole (SMX) by active peroxymonosulfate (PMS). The results showed that the Ce/N @BC/PMS system achieved to 94.5% degradation of SMX in 40 min at a rate constant of 0.0602 cm−1. The activation center of PMS is widely dispersed Ce oxide nanocrystals, and CeO2 NPs promote the formation of oxygen centered PFR with enhanced catalytic ability and longer half-life. In addition, N-doping facilitates the transfer of π-electrons within the sp2 carbon of biochar, increasing active sites and thus improving PMS activation efficiency. The degradation process was contributed to by both radical and non-radical activation mechanisms including 1O2 and direct electron transfer, with O2•- serving as 1O2's precursor. Through the DFT calculations, LC-MS and toxicological analyses, the degradation pathway of pollutants and the toxicity changes throughout the entire degradation process were further revealed, indicating that the degradation of SMX could effectively reduce ecological toxicity.

Operando Tracking the Interactions between CoOx and CeO2 during Oxygen Evolution Reaction

AbstractCeO2 greatly enhances the electrocatalytic oxygen evolution reaction (OER) activity of CoOx, though the enhancement mechanism beyond this synergy is yet to be understood. Here, operando hard X‐ray absorption spectroscopy (hXAS) is applied to monitor the Co K edge and Ce L3 edge in CoOx/CeO2 to shed light on the evolution of the Co and Ce oxidation states during OER. In addition, ex situ soft XAS (sXAS) characterizations provide information on the irreversible surface‐specific transformations of the Co L3 edge as well as of the O K edge. Combining the operando and ex situ spectroscopic characterizations with comprehensive electrochemical analyses, it is confirmed that CeO2 is not the active center for the OER. However, coupling CeO2 with CoOx introduces significant modifications in the Co and O species at the CoOx surface and alters the flat band potential (Efb), leading to more favorable Co oxidation state transformations during OER and possibly modifying the preferential reaction pathway. This work establishes the connections between electronic structures, Co oxidation state and the OER reaction mechanism for CoOx/CeO2 composites electrodes.

High-Pressure Die Casting of Al–Ce–La–Ni–Fe Alloys

The effects on phase equilibria of La and Fe additions to the Al–Ce–Ni-based alloy system are explored under high-pressure die casting conditions. The addition of La to Al–Ce–Ni-based alloy system only reacts with Ce synergistically to promote the formation of the Al11(Ce,La)3 intermetallic phase as predicted by CALculation of PHAse Diagrams (CALPHAD) and verified experimentally. High Fe additions react with Ni to form the Al9FeNi intermetallic phase, which is an additional eutectic former. The targeted co-precipitation type eutectic morphology is achieved in the alloys studied. Additional coarse particles of Al11(Ce,La)3, present in the alloys studied and not predicted by CALPHAD, are attributed to possible inclusions of Ce and La oxide, present in the mischmetal feedstock used. Both alloys exhibit exceptional mechanical stability after 10 hours at 400 °C due to the stability of the phases formed during solidification. The alloy with high Fe additions possessed better mechanical properties after heat treatment based on the higher eutectic content and more substantial improvement to the morphology of secondary phases after treatment.

Ni/CeZr deposition on metallic mesh supports for CO2 methanation. Adherence and morphology

Structured supports suitable for highly demanding reactions in heat and mass transfer such as the Sabatier reaction were synthesised. The use of a metallic mesh as the support is promising. In this work, a treatment strategy for the metallic substrate and deposition of the support and the catalytic phase was proposed to obtain a thin, homogeneous, and crack-free layer that avoid the attack of the metallic substrate under the reaction conditions. The metallic surface of the meshes was thermally pre-treated under different conditions to generate roughness. A layer of Ce and Zr oxides was deposited from Nyacol® to generate the catalyst support that act, at the same time, as a barrier between the reaction atmosphere and the surface of the meshes. Subsequently, nickel was deposited as an active phase by impregnation. The elimination of the excess was studied by air blowing and centrifugation. The morphology, phase structure and adhesion of the layer were investigated by SEM, EDX and adherence test. The results showed that the load and the adhesion of the layer were affected by the mesh size and the conditions of the excess removal as well as the concentration of the slurry. The adhesion of the active phase was excellent under severe conditions.

The role of clay minerals in the concentration and distribution of critical metals in lateritic palaeosols from NE Iberia

The intense chemical weathering processes that lead to the formation of laterites and bauxites result in the enrichment of critical metals (Sc, V, Co, Ga, Ge, Nb, In, Hf, Ta, W, and REEs), which are of great economic interest and are directly involved in the manufacture of various devices essential for the technology transition. This work focuses on combined geochemical and scanning transmission electron microscopy (STEM) studies of lateritic palaeosols developed in continental profiles (Lower Cretaceous, NE Iberia) in order to evaluate the distribution and concentration of critical metals and their possible relationship with weathering processes. In this study, we show that during the process of laterization the highest weathering produces the highest critical metal concentrations (reaching concentrations of 1914.80 ppm in the lateritic palaeosols and 926.30 ppm in the ferruginous macropisoids). Concentrations normalized to the upper continental crust (Taylor and McLennan, 1985) indicate that both the lateritic palaeosols and the macropisoids are enriched in LREEs (256.81 and 223.01 ppm, respectively) and HREEs (107.11and 110.53, respectively). In the lateritic palaeosols, the (La/Sm)c values are higher than those of (Gd/Yb)c, indicating that the LREEs exhibit higher fractionation with weathering, whereas the opposite occurs for the macropisoids, in which the HREEs have higher fractionation. These data indicate that the HREEs are less mobile than the LREEs during laterization. The critical metals present a good positive correlation with Fe, Ti, and Al, but a good negative correlation with K. STEM images and EDS analyses allowed us to identify REE-phases (including monazite, xenotime, and La, Ce and Nd oxides) and nanoparticles of gold adsorbed on the surface of kaolinite crystals. This shows not only that during the laterization process Fe and Ti oxides act as scavengers for the critical metals, but also that kaolinite controls their distribution.

Effect of impregnation strategy on structural characteristics of Ce-Mn/Al2O3 and its catalytic ozonation of benzoic acid.

Ce-Mn binary oxides supported on Al2O3 (Ce-Mn/Al2O3), with enhanced activity and stability for catalytic ozonation of benzoic acid, were synthesized using a facile impregnation method. The competitive synergetic effects between cerium and manganese significantly influenced the structural characteristics and catalytic performance of the catalysts depending on the impregnation sequence. Catalysts prepared via the one-step impregnation process exhibited a higher concentration of homogeneous Ce3+ species on the catalyst surface. This led to an increase in surface oxygen vacancies, thereby enhancing catalytic activity. In contrast, the two-step impregnation process resulted in fewer oxygen vacancies due to reduced competitive effects between cerium and manganese. Overall, the optimized Ce-Mn/Al2O3 catalysts demonstrated improved catalytic performance in ozonation reactions, highlighting the importance of impregnation method and calcination conditions in tailoring catalyst properties for enhanced activity and stability. Oxygen vacancies play a crucial role as active sites for ozone adsorption and dissociation into *O2 and *O, facilitated by the reduction of Mn4+ to Mn3+ and the oxidation of Ce3+ to Ce4+. This process forms an electron closed loop that maintains electron balance. The synergistic interactions between cerium and manganese enable rapid electron transfer between Ce4+ and Mn3+, facilitating the regeneration of Ce3+ and Mn4+. Due to the increase of the dual redox conjugate pairs and the surface reactive oxygen species, the catalytic ozonation activity and stability of Ce-Mn/Al2O3 was enhanced.

Chemical Species Change of Radionuclides by Microorganisms: Effects of Exudated Siderophores

Microbial exudates including siderophore, which changes chemical species of actinides and lanthanides. We have investigated effects of desferrioxamine B (DFOB; one of the siderophores) and siderophore-like organic molecules (SLOM) on the adsorption of lanthanides by microbial cells, aluminium oxide (Al2O3), and manganese (Mn) oxides. When DFOB was present, the distribution coefficients of cerium (Ce) were measured to be lower than those of neighboring elements of lanthanum (La) and praseodymium (Pr) (Negative anomaly of Ce adsorption). Even though initial oxidation state of Ce in the solution was III, that was changed to IV after the addition of DFOB, indicating that Ce(III) was oxidized by forming complex with DFOB. When lanthanides were adsorbed by biogenic Mn(IV) oxides, negative anomaly of Ce adsorption was observed in the sorption in alkaline solution. Ce(III) was oxidized to forme the complexes of Ce(IV) with SLOM in the solution. These results show that siderophore possesses high performance of oxidation of Ce(III) to Ce(IV) during association, affectiong the adsorption behavior of Ce. After Fukushima accident, radioactive Cs accumulation by Eleutherococcus sciadophylloides (Koshiabura) caused by the dissolution of Fe from soil around the roots, that was dominated by siderophore releasing microorganisms (SB). These SBs may enhance dissolution of iron (Fe) and uranium (U) phases in the nuclear fuel debris formed in the nuclear reactors in Fukushima Daiichi nuclear power plant. Thus, in the interaction between microorganisms and radionuclides, SLOMs discharged by microorganisms are deeply involved in the chemical state change of radionuclides.

Cobalt oxide/cerium oxide heterogeneous interfaces as advanced durable and bifunctional electrocatalysts for robust industrially relevant overall water splitting

Non-precious mixed-phase Co oxide and Ce oxide heterostructured electrodes are investigated as bifunctional electrocatalysts for both oxygen and hydrogen evolution reactions in an alkaline medium. They are capable to operate at industrial relevant current density.

Exploring the Mechanism of the Electrochemical Polymerization of CO2 over CeO2(110)

The reduction of CO2 is a promising route for the synthesis of renewable energy carriers and the removal of CO2 from the atmosphere to limit global warming. These negative emission technologies (NETs) require the conversion of carbon dioxide into a stable and easily storable form[1]. However, despite its potential, the development of suitable CO2 reduction catalysts is still in its infancy. Indeed state of the art catalysts suffer from high overpotentials, a low selectivity between possible products and a generally low yield of post CO products with two or more carbon atoms. Catalysts which even allow for the electrochemical polymerization of CO2 and thus, the direct formation of hard carbon were completely absent until the work of Esrafilzadeh et al.[2]. Using a liquid electrocatalyst consisting of Ga, In, Sn and Ce in a n,n-dimethylformamide (DMF) electrolyte they were able to polymerize CO2 electrochemically to a carbonaceous material. They hypothesized that the active catalyst consists of a cerium oxide which is reduced to metallic Ce in the process. However, no direct proof for this hypothesis was provided. Also a possible mechanism which could lead to the reported products is so far unknown.In this contribution we will explore the reaction mechanisms for the electrochemical polymerization of CO2 using density functional theory (DFT) modelling. In the initial step, the most likely active sites at Ce oxide are identified. This is then followed by a detailed analysis of the reaction route which is based on well known mechanisms in organic chemistry. We find that an oxygen defect rich CeO2(110) surface is most likely present under reaction conditions. [3] The reaction over this surface is initialized at oxygen defect sites. Chain propagation is then achieved through an electrochemical aldol condensation type mechanism (Figure 1). [3] References 1 J. Hilaire, J. C. Minx et al., Climatic Change, 2019, 157, 189.2 D. Esrafilzadeh, A. Zavabeti et al., Nature. Commun., 2019, 10, 865.3 F. Keller, J. Döhn, A. Groß, M. Busch, in preparation. Figure 1