Ceria Zirconia Solid Solutions Research Articles

Comprehensive recycling of slag from the smelting of spent automotive catalysts

Spent automotive catalyst is a valuable source of platinum group metals (PGMs), making them crucial secondary resources. Currently, the main process for recovering PGMs from these catalysts is metal capture method. The smelting process would produce a significant amount of residual slags containing various components like SiO2, Al2O3, CaO, Fe2O3, Na2O, as well as high levels of heavy metals including Cr, Pb, and Ni. These slags are considered either solid waste or hazardous waste and usually disposed of in landfills, which can have detrimental effects on the environment. Furthermore, the smelting slags also contain approximately 2–5 % rare earth elements and trace amounts of precious metal elements. In this study, vacuum carbothermal reduction is employed to pretreat the smelting slags. This method not only successfully removes the heavy metal element lead, but also efficiently achieves the recovery of rare earths, and the enrichment of platinum group metals by mineral phase transformation of cerium-zirconium solid solution and in-situ iron capture. The lead removal rate exceeded 99 %, and the grade of precious metals in the enrichment process was approximately 12 times higher than the original material, with a recovery rate more than 90 %. The leaching rate of rare earths also increased from less than 50 % to more than 95 % after vacuum carbothermal reduction. The effect of vacuum carbothermal reduction pretreatment on the smelting slag phase was systematically studied, and the mechanism behind the increasing rare earth leaching rate due to this pretreatment was further analyzed.

Assembling bifunctional ceria-zirconia electrocatalyst for efficient electrochemical conversion of methane at room temperature

The electrochemical conversion of methane to C2 compounds at room temperature is reported using CeO2-ZrO2 electrocatalysts. The mixed oxide electrocatalysts produced methanol, ethanol, and acetone, along with traces of acetaldehyde and isopropanol, under a polarization of 1.2 V with ∼ 50 % Faradaic efficiency. Detailed characterization of the CeO2-ZrO2 revealed the formation of nanoparticles (7–9 nm mean size) composed of ceria-zirconia solid solution or a mixture of ceria with both tetragonal and monoclinic zirconia polymorphs depending on the assembling configuration of the electrocatalyst. Samples with separated phases and limited solid solution formation showed the highest electrochemical activity, indicating that an optimal assembly of ceria and zirconia was crucial to achieving efficient conversion with high Faradaic efficiency and selectivity. Such high electrochemical activity observed for the phase separated CeO2-ZrO2 electrocatalyst suggests that a synergic effect between ceria and zirconia is required for the critical reaction steps, such as the activation and partial oxidation of methane. The experimental results point to credible routes to efficiently convert methane into valuable chemicals in mild conditions.

The Effect P Additive on the CeZrAl Support Properties and the Activity of the Pd Catalysts in Propane Oxidation.

The properties of a catalyst support are closely related to the catalyst activity, yet the focus is often placed on the active species, with little attention given to the support properties. In this work, we specifically investigated the changes in support properties after the addition of P, as well as their impact on catalyst activity when used for catalyst preparation. We prepared the CeO2-ZrO2-P2O5-Al2O3 (CeZrPAl) composite oxides using the sol-gel, impregnation, and mechanical mixing methods, and characterized the support properties using techniques such as XRD, XPS, SEM-EDS, N2 adsorption-desorption, and Raman spectra. The results showed that the support prepared using the sol-gel method can exhibit a more stable phase structure, larger surface area, higher adsorption capacity for oxygen species, and greater oxygen storage capacity. The addition of an appropriate amount of P is necessary. On the one hand, the crystallization and growth of CePO4 can lead to a decrease in the Ce content in the cubic phase ceria-zirconia solid solution, resulting in a phase separation of the ceria-zirconia solid solution. On the other hand, CePO4 can lock some of the Ce3+/Ce4+ redox pairs, leading to a reduction in the adsorption of oxygen species and a decrease in the oxygen storage capacity of the CeZrPAl composite oxides. The research results indicated that the optimal P addition is 6 wt.% in the support. Therefore, we prepared a Pd/CeZrPAl catalyst using CeZrAl with 6 wt.% P2O5 as the support and conducted the catalytic oxidation of C3H8. Compared with the support without P added, the catalyst activity of the support loaded with P was significantly improved. The fresh and aged (1000 °C/5 h) catalysts decreased by 20 °C and 5 °C in T50 (C3H8 conversion temperature of 50%), and by 81 °C and 15 °C in T90 (C3H8 conversion temperature of 90%), respectively.

(Invited) Challenges with Ceria Diffusion Barrier Layer

Sr-doped perovskite has been the most commonly used oxygen electrode material for solid oxide cells due to their high conductivity and catalytic activity for oxygen reduction and oxygen evolution reactions. Direct contact of the electrode material with the doped zirconia electrolyte leads to formation of resistive Sr- and La-zirconate phases during cell fabrication and long-term operation leads to performance loss. A doped ceria barrier layer is applied between the electrolyte and the oxygen electrode to avoid the reactions that form the resistive phase. The ceria layer is applied using a variety of processes and screen printing is the preferred method as the oxygen electrode also uses the same fabrication option. The barrier layer is sintered at high temperature to target a thin, dense layer. The barrier layer sintering temperature needs to balance good resulting density without any reaction with the electrolyte. The ceria-zirconia solid solution is more resistive than the end members. Thus, it is accepted to limit the sintering temperature which results in a porous barrier layer.OxEon stacks tested for several thousand hours were post-test analyzed at the Pacific Northwest National Laboratory using an array of electron microscopes, and Sr migration to the zirconia interface through pores and discontinuity in the barrier layer was confirmed. The use of Sr-free electrode composition between the barrier layer and the Sr-containing electrode layer did not prevent Sr migration to the electrolyte interface when discontinuities are present in the barrier layer.In addition, the dopant in ceria, samaria in this case, also migrates into zirconia during long-term operation while as fabricated cells do not show migration of samaria.Investigations are ongoing to improve the density of the barrier layer without deleterious interdiffusion during fabrication.

In-situ formation of carbon-doped cerium-zirconium solid solution as a superacid catalyst for the removal of NOx

Defects engineering in nanomaterials can be used to precisely and effectively modulate catalysts’ reactivity. Here we report a highly efficient NH3-SCR catalyst constructed with in-situ formation of carbon-doped CeZrO2−x with dual defects, in which O atoms are substituted by C atoms to generate surface oxygen vacancies and subsurface oxygen substitutions. The carbon-doped CeZrO2−x exhibit superior activity and better SO2/H2O resistance compared with traditional bulk CeZrOx and V2O5-WO3/TiO2. The related characterization results reveal that the surface oxygen vacancy and subsurface oxygen substitution resulted in the formation of a large number of unsaturated coordination Ce and Zr species on catalyst’s surface, which contributed to the adsorption and activation of NH3, thus promoting the catalytic activity. Meanwhile, the abundant oxygen vacancy also stimulated the E-R reaction pathway over carbon-doped CeZrO2−x. In addition, it was proved that more zirconium sulfate and unstable ammonium sulfate species were exposed over carbon-doped CeZrO2−x, benifiting the better SO2-tolerance.

Order and disorder in cerium-rich ceria-zirconia solid solutions revealed from reverse Monte Carlo analysis of neutron and x-ray total scattering

A reverse Monte Carlo analysis of neutron and x-ray total scattering data from two ceria-zirconia samples of composition Ce0.75Zr0.25O2 is performed to analyze the distribution of cations and to examine the possibility of oxide-ion disorder. For the first material, heated in air under moderate conditions (800 °C), the structure is a single-phase solid-solution with the statistical distribution of cations, but a local tetragonal symmetry is found, consistent with the different coordination preferences of Ce and Zr. For the second material, heated under H2 at 1050 °C followed by reoxidation at 400 °C, the structure shows a considerable disorder, with evidence for oxygen interstitials (Frenkel-ion defects) and a non-statistical distribution of cations with significantly higher concentrations of like–like cation nearest neighbors, highlighting the existence of cation-rich nano-domains. The results highlight the dynamic nature of this solid-solution, with structural evolution upon thermal treatment, which is of relevance to understanding its stability under redox catalytic conditions in practical applications.

Analysis of defect mechanisms in nonstoichiometric ceria–zirconia by the microwave cavity perturbation method

AbstractIn this microwave study, the defect chemistry of ceria–zirconia solid solutions (CZO, Ce1−yZryO2−δ) was investigated at high temperatures by a resonant microwave method. Specifically, the effects of temperature and Zr content on the dielectric properties and defect chemistry mechanisms in CZO were analyzed. Experiments were performed on a series of different CZO powders (y = 0.2, 0.33, 0.50, 0.67). Measurements at 600°C and different oxygen partial pressures (pO2 = 10−26–0.2 bar) confirm a dominant n‐type conduction of small‐polarons in CZO due to the preferred formation of oxygen vacancies, which is also supported by a multimodal analysis. Polarization losses were found to be negligible in the GHz range. Furthermore, an increased relative permittivity was observed in CZO, which correlates with the concentration of oxygen vacancies in CZO. Our microwave study is the first to provide a comprehensive data set for the dielectric properties of CZO powder sample in a wide range of different conditions. In addition, the connection of dielectric properties to CZO defect chemistry mechanisms is presented. The results are in good agreement with findings in the literature and may contribute to a better understanding of microwave‐based state diagnosis of CZO‐based materials, as it discussed for three‐way catalysts.

Influence of Oxidative Properties of CexZr1−xO2 Catalyst on Partial Oxidation of Dimethyl Ether

Partial oxidation of dimethyl ether (DME) to hydrogen is an efficient route for hydrogen production for application in SOFC. However, quite a large amount of CO2 as a byproduct has been an important obstacle. In this work, cerium–zirconium solid solution (CexZr1−xO2) was applied to determine how the oxidative properties of the catalyst affect the production of CO2 in the partial oxidation of DME. The results show that the catalyst with more adsorbed oxygen (Oads) rather than the lattice oxygen has stronger oxidizability and gives higher DME conversion as well as higher CO2 yield, due to the overoxidation of CO.

Possible Fine-Tuning of Methane Activation toward C2 Oxygenates by 3d-Transition Metal-Ions Doped Nano-Ceria-Zirconia.

In this work, we demonstrate a simple sol-gel technique to prepare metal-ion(s)-doped ceria-zirconia solid solution for efficient catalytic methane activation. The cation-depicting formula units are Ce0.80Zr0.20 (CZ), Ce0.79Zr0.20M0.01 (CZM), and Ce0.79Zr0.20M0.005M10.005 (CZMM1) (M and M1 = V, Mn, Fe, Co, and Cu), employed for undoped, mono-metal-ion-doped, and bi-metal-ion-doped solid solutions, respectively. Methane activation with Mn, Fe, Cu mono-metal-ion-doped CZ favors the C1 product, while CZCo assists C-C coupling with the formation of acetaldehyde. On the other hand, the Co- and Fe-doped bi-metal-ion combination catalyst (CZCoFe) shows significant ethanol but predominant formic acid formation. This is further promoted by the Co + V bi-metal-ion combination (CZCoV) catalyst, and it shows ethanol as the major product along with methyl hydrogen peroxide, methanol, and formic acid as minor products. An impressive ethanol yield of 93 μmol/g h with 76% selectivity obtained with the CZCoV catalyst is at par with that obtained with noble-metal-based catalysts under comparable reaction conditions. When Co and V content was increased two and four times from 0.005 to 0.01 and 0.02, ethanol yield increased at the expense of formic acid. The 213 μmol/g h ethanol yield (86% selectivity) observed with Ce0.76Zr0.20Co0.02V0.02 is probably the highest observed. The partial oxidation of CH4 in Co-based bi-metal combinations (Co + V or Co + Fe) suggests the synergistic effect of doped metal ions owing to the heterogeneous near-neighbor environment. The present results are attributed to the surface heterogeneity between the host and the dopants, which selectively promotes methane activation as well as C-C coupling. This indicates a large scope to tune the activity of partial oxidation of methane and product selectivity with different metal-ion(s) combinations.

Engineering Cu+/CeZrOx interfaces to promote CO2 hydrogenation to methanol

Cu-based catalysts are widely employed for CO2 hydrogenation to methanol, which is expected as a promising process to achieving carbon neutrality. However, most Cu-based catalysts still suffer from low methanol yield with a passable CO2 conversion and lack insight into its reaction mechanism for guiding the design of catalysts. In this work, Cu+/CeZrOx interfaces are engineered by employing a series of ceria-zirconia solid solution catalysts with various Ce/Zr ratios, forming a Cu+-Ov-Ce3+ structure where Cu+ atoms are bonded to the oxygen vacancies (Ov) of ceria. Compared to Cu/CeO2 and Cu/ZrO2, the optimized catalyst (i.e., Cu0.3Ce0.3Zr0.7) exhibits a much higher mass-specific methanol formation rate (192 gMeOH/kgcat/h) at 240 °C and 3 MPa. Through a series of in-situ and ex-situ characterization, it is revealed that oxygen vacancies in solid solutions can effectively assist the activation of CO2 and tune the electronic state of copper to promote the formation of Cu+/CeZrOx interfaces, which stabilizes the key *CO intermediate, inhibits its desorption and facilitates its further hydrogenation to methanol via the reverse water–gas-shift (RWGS) + CO-Hydro pathway. Therefore, the concentration of *CO or the apparent Cu+/(Cu++Cu0) ratio could be employed as a quantitative descriptor of the methanol formation rate. This work is expected to give a deep insight into the mechanism of metal/support interfaces in CO2 hydrogenation to methanol, offering an effective strategy to develop new catalysts with high performance.

A novel alkylation process of benzene with CO2 and H2 over bifunctional ZnxCeyZrzO/Z5 catalyst

The synergy between the two active sites in Zn 3 Ce 1 Zr 3 O that the active hydrogen atoms provided by ZnO species hydrogenated the adsorbed CO 2 at adjacent oxygen vacancy of cerium zirconium solid solution effectively improved the CO 2 hydrogenation selectivity. While the HZSM-5 zeolite with moderate acidity was beneficial to the rapidly alkylation of methoxy intermediate with benzene. Coupling Zn x Ce y Zr z O with HZSM-5 could contribute to the well kinetic matching between CO 2 activation and alkylation, thus affording an effective bifunctional catalyst Zn x Ce y Zr z O/Z5 for highly selective conversion of benzene with CO 2 and H 2 into toluene and xylene. • In situ alkylation process of benzene with CO 2 and H 2 to produce TX is proposed. • The synergy in Zn x Ce y Zr z O promoted the CO 2 hydrogenation kinetics. • Zn x Ce y Zr z O/Z5 contribute to the well matching of CO 2 activation and alkylation. • The mechanism of the alkylation of benzene with CO 2 and H 2 is proposed. Alkylation of benzene using CO 2 and H 2 to toluene and xylene (TX) can not only give value-added chemical products but also alleviate the greenhouse effect. The key to achieving this goal is to develop a highly efficient catalyst. Herein, a class of bifunctional catalysts containing series of Zn x Ce y Zr z O metal oxide and HZSM-5 was prepared and studied for the catalytic properties. Higher CO 2 conversion and alkylation utilization were achieved using the Zn x Ce y O coupling with HZSM-5 compared to its counterpart ZnO and CeO 2 , revealing synergy between the ZnO and CeO 2 . More strikingly, the Zn x Ce y Zr z O, synthesized by insertion of Zirconia (Zr) atoms into CeO 2 , can not only improve the concentration of oxygen vacancy but also facilitate CO 2 adsorption. After coupling with HZSM-5, the alkylation utilization of CO 2 was significantly improved and the unwanted CO selectivity was obviously reduced by hindering the RWGS reaction. The optimal bifunctional catalyst Zn 3 Ce 1 Zr 3 O/Z5 showed alkylation utilization of 24%, unwanted CO selectivity of only 64% and the TX selectivity as high as 82%. In situ DRIFTS results confirmed that the methanol generated on the Zn x Ce y Zr z O metal oxide via the formate-methoxy intermediates mechanism was rapidly alkylated on HZSM-5 with benzene to produce TX.

Experimental and theoretical study on the complete phase separation of ceria-zirconia solid solution into two end members, ceria and zirconia

Solid solution CeO2–ZrO2 has long been used as a non-noble metal oxide promoter for three-way catalysts owing to its high oxygen storage capacity. However, the stability issue of the CeO2–ZrO2 has been controversial for a long time. In particular, the phenomena observed by phase instability are so diverse and inconsistent that the related causal analysis is still a matter of debate. In this study, for the first time, it was demonstrated theoretically and experimentally that a Ce0.75Zr0.25O2 (CZO) solid solution must be completely separated into CeO2 and ZrO2 phases owing to its inherent thermodynamic instability. According to an extensive evaluation via defect chemical calculations and well-controlled model experiments with grain-boundary-free epitaxial thin film samples, CZO materials undergo phase separation until they are completely separated, and the separation rate is particularly high in a reducing atmosphere. The underlying inherent stability problem and enhanced phase separation kinetics of the CZO material are attributed to the enhanced cation diffusion in a reducing atmosphere, where more mobile cationic defects (interstitial cations) are generated and an easier pathway with a lower migration energy is available.

Highly Active Large Au Clusters and Even More Active Ag Nanoparticles Supported on Ceria-Zirconia: Impact of Particle Size and Potassium Ion Loading on Activity in Catalytic Transfer Hydrogenation

Although heterogeneous monometallic gold catalysts are commonly more active when the gold particles are smaller, this study shows that the reverse is true in the case of liquid phase catalytic transfer hydrogenation of acetophenone with 2-pentanol. Higher catalytic activity of larger gold particles, i.e., over 30 nm in diameter, than of smaller particles of average 4 nm in size was observed. Moreover, this effect was contradictory to that observed for supported monometallic silver catalysts in which the interaction with the support and hence particle size was shown to cause drastic changes in the activity in this reaction, with the large particles being completely inactive and tiny ones being the most active system studied. In this reaction, the ceria-zirconia solid solutions were used as the supports for the catalysts and both zirconium doped ceria, as well as cerium doped zirconia carriers were tested. The supports themselves exhibited little activity in this reaction. It was shown that the activity of the supports and catalysts depends on the Ce/Zr ratio and potassium content. Both types of catalysts showed excellent selectivity to 1-phenylethanol and conversion of acetophenone, although it was noted that a high loading of potassium carbonate in the gold catalysts propelled undesired reactions, thereby reducing the selectivity to 1-phenylethanol.

Conversion of CO2 to Value-Added C1 Products over Mesoporous Ceria–Zirconia Solid Solution with a Homogeneous Structure

Conversion of CO₂ to Value-Added C₁ Products over Mesoporous Ceria–Zirconia Solid Solution with a Homogeneous Structure

Synthesis of hollow ceria-zirconia solid solution particles by spray pyrolysis with organic ligands and its oxygen storage capacity

CeO2-based materials have been explored as oxidative catalysts owing to the reversible oxygen absorption and release behavior. The catalytic property is stabilized by addition of ZrO2 to form the solid solution. Hollow CeO2-ZrO2 solid solution particles were prepared by a spray pyrolysis method with organic additives, characterized by SEM, XRD and TEM, and evaluated for oxygen storage capacity (OSC). Spherical hollow particles with a size of about 500 nm formed, which were composed of about 10 nm nanoparticles. CeO2-rich particles had cubic crystal structure, while tetragonal phase was included in ZrO2-rich particles. The addition of organic ligands was effective to form uniform solid solution and increase specific surface area. The spray-pyrolysis temperature should be low to keep the specific surface area. At 50 mol% ZrO2, although the specific surface area was not so high as 20 m2/g, the maximum OSC of 650 μmol-O2/g was achieved. It was found that the OSC depends on ZrO2 content and the oxygen release rate increases with specific surface area.

The dependence of high catalytic performance on the tunable oxygen vacancy in the CZxS/Zn‐HZSM‐5 bifunctional catalyst for alkylation of benzene and syngas

AbstractA bifunctional catalyst (CZxS/Zn‐HZSM‐5) with tunable oxygen vacancy was prepared by coupling ceria–zirconia solid solution (CZxS) and zinc‐modified HZSM‐5 zeolite (Zn‐HZSM‐5). The characterization results indicated that the formation of CZxS by insertion of zirconia (Zr) atoms into cerium oxide (CeO2) could generate more oxygen vacancy due to the structural distortion. With the increasing of Zr content, the oxygen vacancy concentration on the surface of CZxS increased as well, which reached a maximum for a Zr/Ce ratio of 4 and then decreased by further increase of Zr content. The dependence of oxygen vacancy concentration in the CZxS/Zn‐HZSM‐5 bifunctional catalyst on their catalytic performance in the benzene alkylation with syngas was further investigated. The result exhibited that the oxygen vacancy was the site for CO activation, and the more oxygen vacancy, the better catalytic performance. The best catalytic activity, with a CO conversion of 33%, the benzene conversion of 30% and the total toluene and xylene selectivity of 92% was obtained over the bifunctional catalyst CZ4S/Zn‐HZSM‐5 with the highest oxygen vacancy concentration.

Enhanced activity of CexZr1-xO2 solid solutions supported Cu-based catalysts for hydrogenation of CO2 to methanol

Hydrogenation of CO2 to methanol is one of the promising environmentally and economically technologies which can convert CO2 to sustainable fuels. A series of CexZr1-xO2 solid solutions were synthesized by solvent evaporation self-assembly method and employed as the supports of Cu-based catalysts for CO2 hydrogenation to methanol. The obtained catalysts were systematically characterized by N2 physisorption, XRD, CO2-TPD, TEM, N2O titration, XPS and H2-TPR techniques. It is found that the reduction performance, the adsorption and activation ability for CO2 are enhanced by the formation of ceria-zirconia solid solution. The Ce/Zr ratio of the catalysts and the feature of the supports are crucial for tuning the catalytic activity. The Cu/CexZr1-xO2 catalysts display much higher methanol selectivity than Cu/ZrO2 and the improved methanol selectivity stems from inhibition of the RWGS activity.

Insights into the promotion mechanism of ceria-zirconia solid solution to ethane combustion over Pt-based catalysts

Pt/Ce0.5Zr0.5O2 (denoted as Pt/CZ11) and Pt/Al2O3 with identical Pt loading and dispersion were prepared and evaluated for ethane catalytic combustion. Pt/CZ11 exhibited higher activity than Pt/γ-Al2O3 even with similar Pt dispersion. Combined with various characterizations, it was revealed that the enrichments of surface active oxygen and oxygen vacancy on Pt/CZ11 facilitated ethane combustion owing to the strong interaction between Pt and Ce-Zr solid solution. Moreover, in situ DRIFT results demonstrated that different reaction mechanisms were followed over Pt/CZ11 and Pt/Al2O3. The front followed the single-site Langmuir-Hinshelwood (L-H), in which C2H6 and O2 were absorbed and activated on Pt sites. While the coupled reaction mechanism involving L-H and Mars-van Krevelen (MvK) were illustrated over Pt/CZ11, on which ethane can be activated on Pt sites and CZ11 support. More mechanistic insights into ethane combustion provided the guidelines for the developments of catalysts with superior performance for light-carbon alkane volatile organic compounds.

Synthesis of flowerlike ceria–zirconia solid solution for promoting dry reforming of methane

Using a newly developed two-step hydrothermal process, flowerlike Ce0.5Zr0.5O2 with an oxygen storage capacity (OSC) of 536 μmol O2 g−1, almost twice as high as that of pure flowerlike CeO2 (284 μmol O2 g−1), can be synthesized. The synthesized ceria-based oxide supports loaded with Ni are dispersed in a ceramic fiber network to form paper-structured catalysts (PSCs). Among the prepared PSCs, the PSC with the flowerlike Ce0.5Zr0.5O2 exhibits the highest catalytic performance for dry reforming of methane (DRM) at 750 °C with the initial methane conversion of 88.4%, degradation rate of 0.1% h−1 and amount of deposited carbon of 0.04 g per gram catalyst, whereas for the Ce0.5Zr0.5O2 synthesized by the one-step hydrothermal process, the values are 83.7%, 0.62% h−1 and 0.07 g per gram catalyst, respectively. This is attributed to the Ni anti-sintering on the petals of the flowerlike structure and the coking tolerance resulting from the high OSC.

Cerium Zirconium Solid Solution with High Faradaic Efficiency for Electrochemical Nitrogen Reduction Reaction under Ambient Condition

AbstractIndustrial synthesis of ammonia (NH3) involves high energy consumption resulting in intense pollution. Alternatively, electrochemical nitrogen reduction reaction (NRR) to NH3 can be carried out under mild conditions, which is a new green NH3 synthesis method. Herein, cerium zirconium solid solutions (ZrxCe1‐xO2) with different proportions were synthesized by NH3 precipitation method and employed as electrocatalysts for NRR. The performance of the different catalysts in 0.1 mol L−1 Na2SO4 was evaluated with H2O and N2 as reactants. The results show that Zr0.9Ce0.1O2 has the highest Faraday efficiency (FE) of 62.68 % at −1.3 V (vs. Ag/AgCl) and the highest yield rate of NH3 −9.34×10−11 mol cm−2 s−1 at −1.35 V (vs. Ag/AgCl). The impressive FE is due to more oxygen vacancies in Zr0.9Ce0.1O2 introduced by Ce3+, which is more prone to the adsorption of N2 on the catalyst surface and facilitates the electrochemical reaction.