Light-Induced Redox Looping of a Rhodium/Cex WO3 Photocatalyst for Highly Active and Robust Dry Reforming of Methane.

Dry reforming of methane (DRM) has provided an effective avenue to convert two greenhouse gases, CH4 and CO2 , into syngas. Here, we design a DRM photocatalyst Rh/Cex WO3 that invokes both photothermal and photoelectric processes, which overcomes the thermodynamic limitation of DRM under conventional conditions. In contrast to plasmonic or UV-response photocatalysts, our photocatalyst produces a superior light-to-chemical energy efficiency (LTCEE) of 4.65 % with a moderate light intensity. We propose that a light-induced metal-to-metal charge transfer plays a crucial role in the DRM reaction, which induces a redox looping between Ce to W species to lower the activation energy. Quantum mechanical studies reveal that a high oxygen mobility of Cex WO3 , accompanied with the formation of oxo-bridge species, results in a substantial elimination of deposited C species during the reaction. Our catalyst design strategy could offer a promising energy-efficient industrial process for DRM.

Metallization of Epitaxial VO2 Films by Ionic Liquid Gating through Initially Insulating TiO2 Layers.

Ionic liquid gating has been shown to metallize initially insulating layers formed from several different oxide materials. Of these vanadium dioxide (VO2) is of especial interest because it itself is metallic at temperatures above its metal-insulator transition. Recent studies have shown that the mechanism of ionic liquid gated induced metallization is entirely distinct from that of the thermally driven metal-insulator transition and is derived from oxygen migration through volume channels along the (001) direction of the rutile structure of VO2. Here we show that it is possible to metallize the entire volume of 10 nm thick layers of VO2 buried under layers of rutile titanium dioxide (TiO2) up to 10 nm thick. Key to this process is the alignment of volume channels in the respective oxide layers, which have the same rutile structure with clamped in-plane lattice constants. The metallization of the VO2 layers is accompanied by large structural expansions of up to ∼6.5% in the out-of-plane direction, but the structure of the TiO2 layer is hardly affected by gating. The TiO2 layers become weakly conducting during the gating process, but in contrast to the VO2 layers, the conductivity disappears on exposure to air. Indeed, even after air exposure, X-ray photoelectron spectroscopy studies show that the VO2 films have a reduced oxygen content after metallization. Ionic liquid gating of the VO2 films through initially insulating TiO2 layers is not consistent with conventional models that have assumed the gate induced carriers are of electrostatic origin.

Deterministic Orientation Control of Ferroelectric HfO2 Thin Film Growth by a Topotactic Phase Transition of an Oxide Electrode.

The scale-free ferroelectricity with superior Si compatibility of HfO2 has reawakened the feasibility of scaled-down nonvolatile devices and beyond the complementary metal-oxide-semiconductor (CMOS) architecture based on ferroelectric materials. However, despite the rapid development, fundamental understanding, and control of the metastable ferroelectric phase in terms of oxygen ion movement of HfO2 remain ambiguous. In this study, we have deterministically controlled the orientation of a single-crystalline ferroelectric phase HfO2 thin film via oxygen ion movement. We induced a topotactic phase transition of the metal electrode accompanied by the stabilization of the differently oriented ferroelectric phase HfO2 through the migration of oxygen ions between the oxygen-reactive metal electrode and the HfO2 layer. By stabilizing different polarization directions of HfO2 through oxygen ion migration, we can gain a profound understanding of the oxygen ion-relevant unclear phenomena of ferroelectric HfO2.

Comparative Study of α- and ß-MnO2 on Methyl Mercaptan Decomposition: The Role of Oxygen Vacancies.

As a representative sulfur-containing volatile organic compounds (S-VOCs), CH3SH has attracted widespread attention due to its adverse environmental and health risks. The performance of Mn-based catalysts and the effect of their crystal structure on the CH3SH catalytic reaction have yet to be systematically investigated. In this paper, two different crystalline phases of tunneled MnO2 (α-MnO2 and ß-MnO2) with the similar nanorod morphology were used to remove CH3SH, and their physicochemical properties were comprehensively studied using high-resolution transmission electron microscope (HRTEM) and electron paramagnetic resonance (EPR), H2-TPR, O2-TPD, Raman, and X-ray photoelectron spectroscopy (XPS) analysis. For the first time, we report that the specific reaction rate for α-MnO2 (0.029 mol g-1 h-1) was approximately 4.1 times higher than that of ß-MnO2 (0.007 mol g-1 h-1). The as-synthesized α-MnO2 exhibited higher CH3SH catalytic activity towards CH3SH than that of ß-MnO2, which can be ascribed to the additional oxygen vacancies, stronger surface oxygen migration ability, and better redox properties from α-MnO2. The oxygen vacancies on the catalyst surface provided the main active sites for the chemisorption of CH3SH, and the subsequent electron transfer led to the decomposition of CH3SH. The lattice oxygen on catalysts could be released during the reaction and thus participated in the further oxidation of sulfur-containing species. CH3SSCH3, S0, SO32-, and SO42- were identified as the main products of CH3SH conversion. This work offers a new understanding of the interface interaction mechanism between Mn-based catalysts and S-VOCs.

Realizing Metastable Cobaltite Perovskite via Proton-Induced Filling of Oxygen Vacancy Channels.

The interaction between transition-metal oxides (TMOs) and protons has become a key issue in magneto-ionics and proton-conducting fuel cells. Until now, most investigations on oxide-proton reactions rely on electrochemical tools, while the direct interplay between protons and oxides remains basically at simple dissolution of metal oxides by an acidic solution. In this work, we find classical TMO brownmillerite SrCoO2.5 (B-SCO) films with ordered oxygen vacancy channels experiencing an interesting transition to a metastable perovskite phase (M-SCO) in a weak acidic solution. M-SCO exhibits a strong ferromagnetism (1.01 µB/Co, Tc > 200 K) and a greatly elevated electrical conductivity (∼104 of pristine SrCoO2.5), which is similar to the prototypical perovskite SrCoO3. Besides, such M-SCO tends to transform back to B-SCO in a vacuum environment or heating at a relatively low temperature. Two possible mechanisms (H2O addition/active oxygen filling) have been proposed to explain the phenomenon, and the control experiments demonstrate that the latter mechanism is the dominant process. Our work finds a new way to realize cobaltite perovskite with enhanced magnetoelectric properties and may deepen the understanding of oxide-proton interaction in an aqueous solution.

Highly Efficient Solar-Driven Dry Reforming of Methane on a Rh/LaNiO3 Catalyst through a Light-induced Metal-To-Metal Charge Transfer Process.

As an energy-saving and green method, solar-driven dry reforming of methane (DRM) is expected to introduce new activation processes and prevent sintering and coking of the catalysts. However, it still lacks an efficient way to coordinate the regulation of activation of reactants and lattice oxygen migration. In this study, Rh/LaNiO3 is designed as a highly efficient photothermal catalyst for solar-driven DRM, which performs production rates of 452.3 mmol h-1  gRh -1 for H2 and 527.6 mmol h-1  gRh -1 for CO2 under a light intensity of 1.5 W cm-2 , with an excellent stability. Moreover, a remarkable light-to-chemical energy efficiency (LTCEE) of 10.72% is achieved under a light intensity of 3.5 W cm-2 . The characterizations of surface electronic and chemical properties and theoretical analysis demonstrate that strong adsorption for CH4 and CO2 , light-induced metal-to-metal charge transfer (MMCT) process and high oxygen mobility together bring Rh/LaNiO3 excellent performance for solar-driven DRM.

Pt/MnOx for toluene mineralization via ozonation catalysis at low temperature: SMSI optimization of surface oxygen species.

The problem of deep oxidation of low concentrations of VOCs in industrial tail gas is exceptionally urgent. The preparation of VOCs ozonation catalyst with a high mineralization rate is still a challenge. In this paper, manganese oxide carriers with different morphologies were synthesized by simple methods and used to catalyze ozone mineralization of toluene after loading Pt nanoparticles efficiently. The conversion of toluene over Pt/MnOx-T catalyst was more than 98 % at ambient temperature, and the mineralization rate of toluene was close to 100 % at 70 °C. Through a variety of characterization methods, the strong metal-support interaction (SMSI) between Pt nanoparticles and carriers was successfully constructed. It was found that SMSI successfully optimized the surface oxygen species and oxygen migration ability of the catalyst, and then realized the high degree of mineralization of toluene at low temperature. This paper guides the subsequent development of Pt-Mn catalysts for catalytic organic pollutants ozonation with high activity.

Compressive-Strain-Facilitated Fast Oxygen Migration with Reversible Topotactic Transformation in La0.5Sr0.5CoOx via All-Solid-State Electrolyte Gating.

Modifying the crystal structure and corresponding functional properties of complex oxides by regulating their oxygen content has promising applications in energy conversion and chemical looping, where controlling oxygen migration plays an important role. Therefore, finding an efficacious and feasible method to facilitate oxygen migration has become a critical requirement for practical applications. Here, we report a compressive-strain-facilitated oxygen migration with reversible topotactic phase transformation (RTPT) in La0.5Sr0.5CoOx films based on all-solid-state electrolyte gating modulation. With the lattice strain changing from tensile to compressive strain, significant reductions in modulation duration (∼72%) and threshold voltage (∼70%) for the RTPT were observed, indicating great promotion of RTPT by compressive strain. Density functional theory calculations verify that such compressive-strain-facilitated efficient RTPT comes from significant reduction of the oxygen migration barrier in compressive-strained films. Further, ac-STEM, EELS, and sXAS investigations reveal that varying strain from tensile to compressive enhances the Co 3d band filling, thereby suppressing the Co-O hybrid bond in oxygen vacancy channels, elucidating the micro-origin of such compressive-strain-facilitated oxygen migration. Our work suggests that controlling electronic orbital occupation of Co ions in oxygen vacancy channels may help facilitate oxygen migration, providing valuable insights and practical guidance for achieving highly efficient oxygen-migration-related chemical looping and energy conversion with complex oxides.

Design method of a modified layered aerobic waste landfill divided by coarse material.

To overcome the weaknesses of traditional landfills, a modified aerobic landfill concept with intermediate covers of coarse material between waste layers functioning as facilities of drainage and aeration has been proposed recently. In this study, a one-dimensional coupled model, including aerobic biodegradation, oxygen diffusion, and advection, is proposed to describe oxygen distribution in this new type of landfill. Homotopy analysis method and perturbation method are applied to solve this model at passive aeration and active aeration, respectively. The model has six input variables, that is, oxygen diffusion coefficient, gas permeability, maximum oxygen consumption rate, layer thickness of waste, and injection pressure and extraction pressure. A combination of their typical values gives rise to over 700,000 scenarios which can be calculated by the proposed solution. The coupled effect of the above variables on oxygen migration is quantitatively investigated, followed by an estimation formula of the minimum oxygen concentration in waste layer. The maximum waste layer thickness is defined as a function of other variables for a given aeration target of oxygen volume concentration larger than 5%. A generalized design method of waste layer thickness, injection pressure, and extraction pressure is then developed for the newly proposed modified layered aerobic landfill, which can promote its popularization and application.

Temporal Evolution of Microscopic Structure and Functionality during Crystallization of Amorphous Indium-Based Oxide Films.

Understanding the crystallization mechanism of amorphous metal-oxide thin films remains of importance to avoid the deterioration of multifunctional flexible electronics. We derived the crystallization mechanism of indium-based functional amorphous oxide films by using in situ X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. Crystallization begins with surface nucleation, especially at low annealing temperatures, and proceeds simultaneous nucleation and growth in the bulk. Three-dimensional crystal growth in the film was observed when the crystallite size was sufficiently smaller than the film thickness. When the growing crystallites reached the film surface, the crystallization was dominated by two- or lower-dimensional growth. Such crystallization can be explained within the framework of the modified Avrami theory and can be varied for tailoring the electrical properties of the amorphous In2O3 film. After tailoring the film crystallinity and crystallite size, the carrier mobility was improved to >100 cm2/V·s in 30 min. Our results show that a carrier mobility of >90 cm2/V·s can be implemented for the In2O3 film with a crystallinity of >40% and a crystallite size of >70 nm by an optimized annealing process. The incorporation of Ga element into amorphous In2O3 films obviously increases the activation energy of nucleation and migration. In contrast, Sn dopants can promote the crystal growth. This is attributed to two kinds of migration mechanisms during the annealing in air, one of which is the dominant migration mechanism of oxygen interstitials in crystallized indium-tin oxide (ITO) films and the other dominated by oxygen vacancies in In2O3 and IGO films. Combining the modified Avrami theory with TEM observations, we predicted the structural evolution kinetics for indium-based amorphous oxide films and gained new insights for understanding the temporal structure-functionality relationship during crystallization.

Enhanced moisture resistance of Cu/Ce catalysts for CO oxidation via Plasma-Catalyst interactions.

Copper/cerium bimetallic catalyst is an efficient material for the removal of carbon monoxide, while the rapid deactivation under moisture-rich conditions in the conventional thermal-catalysis limited its wide application. Here, we investigated the plasma-assisted catalytic oxidation of CO over Cu/Ce oxides supported on γ-Alumina in comparison with the conventional thermal catalytic oxidation. The TOF values of the Cu/Ce catalysts showed that the plasma catalysis was the better catalytic system for CO oxidation (2.96 s-1 for thermal catalysis, 5.13 s-1 for plasma catalysis). Importantly, the energy barriers for plasma catalysis were much lower than that for thermal catalysis, especially under moisture-rich conditions (e.g. 130.3 kJ/mol versus 246.1 kJ/mol under 9.8 vol% water vapor). The loss of activity caused by water was reversible for the plasma process, but not for the thermal process. The Cu/Ce catalyst remained good stability within 60 h in the presence of 6.1% water for plasma oxidation, while the thermal catalytic activity declines gradually. Also, water could inhibit the formation of gas byproducts (O3 and NOx). The promoting role of plasma could be mainly ascribed to the enhanced strength of oxygen mobility and plasma-assisted decomposition of surface carbonate in the presence of water, as revealed by the in-situ NTP-TPR, XPS, and the ex-situ DRIFTS analyses.

Atomic Origin of Interface-Dependent Oxygen Migration by Electrochemical Gating at the LaAlO3-SrTiO3 Heterointerface.

Electrical control of material properties based on ionic liquids (IL) has seen great development and emerging applications in the field of functional oxides, mainly understood by the electrostatic and electrochemical gating mechanisms. Compared to the fast, flexible, and reproducible electrostatic gating, electrochemical gating is less controllable owing to the complex behaviors of ion migration. Here, the interface-dependent oxygen migration by electrochemical gating is resolved at the atomic scale in the LaAlO3-SrTiO3 system through ex situ IL gating experiments and on-site atomic-resolution characterization. The difference between interface structures leads to the controllable electrochemical oxygen migration by filling oxygen vacancies. The findings not only provide an atomic-scale insight into the origin of interface-dependent electrochemical gating but also demonstrate an effective way of engineering interface structure to control the electrochemical gating.

∑3 Twin Boundaries in Gd2Ti2O7 Pyrochlore: Pathways for Oxygen Migration.

Understanding the chemistry at twin boundaries (TB) is a well-recognized challenge, which could enable the capabilities to manipulate the functional properties in complex oxides. The study of this atomic imperfection becomes even more important, as the presence of twin boundaries has been widely observed in materials, regardless of the dimensionalities, due to the complexities in growth methods. In the present study, we provide atomic-scale insights into a ∑3(111̅) ⟨11̅0⟩ twin boundary present in pyrochlore-structured Gd2Ti2O7 using atomic-resolution electron microscopy and atomistic modeling. The formation of the observed TB occurs along (111̅) with a 71° angle between two symmetrically arranged crystals. We observe distortions (∼3 to 5% strain) in the atomic structure at the TB with an increase in Gd-Gd (0.66 ± 0.03 nm) and Ti-Ti (0.65 ± 0.02 nm) bond lengths in the (11̅0) plane, as compared to 0.63 nm in the ordered structure. Using atomistic modeling, we further calculate the oxygen migration barrier for vacancy hopping at 48f-48f sites in the pyrochlore structure, which is the primary diffusion pathway for fast oxygen transport. The mean migration barrier is lowered by ∼25% to 0.9 eV at the TB as compared to 1.23 eV in the bulk, suggesting the ease in oxygen transport through the ∑3 twin boundaries. Overall, these results offer a critical understanding of the atomic arrangement at the twin boundaries in pyrochlores, leading to control of the interplay between defects and properties.

A Surface Se-Substituted LiCo[O2- δ Seδ ] Cathode with Ultrastable High-Voltage Cycling in Pouch Full-Cells.

Cycling LiCoO2 to above 4.5 V for higher capacity is enticing; however, hybrid O anion- and Co cation-redox (HACR) at high voltages facilitates intrinsic Oα - (α < 2) migration, causing oxygen loss, phase collapse, and electrolyte decomposition that severely degrade the battery cyclability. Hereby, commercial LiCoO2 particles are operando treated with selenium, a well-known anti-aging element to capture oxygen-radicals in the human body, showing an "anti-aging" effect in high-voltage battery cycling and successfully stopping the escape of oxygen from LiCoO2 even when the cathode is cycled to 4.62 V. Ab initio calculation and soft X-ray absorption spectroscopy analysis suggest that during deep charging, the precoated Se will initially substitute some mobile Oα - at the charged LiCoO2 surface, transplanting the pumped charges from Oα - and reducing it back to O2- to stabilize the oxygen lattice in prolonged cycling. As a result, the material retains 80% and 77% of its capacity after 450 and 550 cycles under 100 mA g-1 in 4.57 V pouch full-cells matched with a graphite anode and an ultralean electrolyte (2 g Ah-1 ).

Electric Field Control of Magnetism in Iron Oxide Nanoporous Thin Films.

Voltage control of the magnetic properties of oxide thin films is highly appealing to enhance energy efficiency in miniaturized spintronic and magnetoelectric devices. Herein, magnetoelectric effects in electrolyte-gated nanoporous iron oxide films are investigated. Highly porous films were prepared by the evaporation-induced self-assembly of sol-gel precursors with a sacrificial block-copolymer template. For comparison, films with less porosity but analogous crystallographic structure were also prepared using an identical procedure except without the polymer template. The films were found to be 70-85 nm in thickness as measured by scanning electron microscopy and primarily hematite as determined by Raman spectroscopy. The templated (highly porous) films showed a very large magnetoelectric response with a maximum increase in magnetic moment at saturation of a factor of 13 and a noticeable (2-fold) increase of coercivity (after applying -50 V). The nontemplated films also exhibited a pronounced increase of magnetic moment at saturation of a factor of 4, although the coercivity remained unaffected over the same voltage range. Magnetoelectric effects in these latter films were found to be fully reversible in the voltage window ±10 V. The observed changes in magnetic properties are concluded to be magneto-ionically driven with oxygen ion exchange between the iron oxide and the liquid electrolyte, as evidenced from Raman and X-ray photoelectron spectroscopy experiments.

In Situ TEM Study of the Amorphous-to-Crystalline Transition during Dielectric Breakdown in TiO2 Film.

Dielectric breakdown of oxides is a main limiting factor for improvement of the performance of electronic devices. Present understanding suggests that defects produced by intense voltage accumulate in the oxide to form a percolation path connecting the two electrodes and trigger the dielectric breakdown. However, reports on directly visualizing the process at nanoscale are very limited. Here, we apply in situ transmission electron microscopy to characterize the structural and compositional changes of amorphous TiO2 under extreme electric field (∼100 kV/mm) in a Si/TiO2/W system. Upon applying voltage pulses, the amorphous TiO2 gradually transformed into crystalline substoichiometric rutile TiO2-x and the Magnéli phase Ti3O5. The transitions started from the anode/oxide interface under both field polarities. Preferred growth orientation of rutile TiO2-x with respect to the Si substrate was observed when Si was the anode, while oxidation and melting of the W probe occurred when W was the anode. We associate the TiO2 crystallization process with the electrochemical reduction of TiO2, polarity-dependent oxygen migration, and Joule heating. The experimental results are supported by our phase-field modeling. These findings provide direct details of the defect formation process during dielectric breakdown in amorphous oxides and will help the design of electronic devices with higher efficiency and reliability.

Surface-Functionalized Coating for Lithium-Rich Cathode Material To Achieve Ultra-High Rate and Excellent Cycle Performance.

Although the lithium-rich cathode material Li1.2Mn0.54Ni0.13Co0.13O2, as a promising cathode material, has a high specific capacity, it suffers from capacity decay and discharge voltage decay during cycling. In this work, the specific capacity and discharge voltage of Li1.2Mn0.54Ni0.13Co0.13O2 are stabilized by surface-functionalized LiCeO2 coating. We have conducted LiCeO2 coating via a mild synchronous lithium strategy to protect the electrode surface from electrolyte attack. This optimized LiCeO2 coating has high Li+ conductivity and abundant oxygen vacancies. The results demonstrate that 3% LiCeO2-coated Li1.2Mn0.54Ni0.13Co0.13O2 exhibits the highest capacity retention rate at 1, 2, and 5 C after 200 cycles, which were 84.3%, 85.4%, and 86.3%, respectively. The discharge specific capacity was almost 1.3, 1.4, and 1.4 times that of the pristine electrode. In addition, the 3% LiCeO2 electrode exhibited the least voltage decay of 0.409, 0.497, and 0.494 V at 1, 2, and 5 C, which was only about half of the pristine electrode. It should not be overlooked that the 3% LiCeO2 electrode still exhibits a high capacity at high current densities of 1250 mA g-1 (5 C) and 2500 mA g-1 (10 C), and its specific discharge capacities are 190.5 and 160.6 mAh g-1, respectively. These outstanding electrochemical properties benefit from surface-functionalized LiCeO2 coatings. To better understand the mechanism of oxygen loss of lithium-rich materials, we propose the lattice oxygen migration path of the LiCeO2-coated electrodes during the cycle. Our research provides a possible solution to the poor rate capability and cycle performance of cathode materials through surface-functionalized coatings.

In-depth study of rice husk torrefaction: Characterization of solid, liquid and gaseous products, oxygen migration and energy yield.

Torrefaction is a promising method for biomass upgrading, and analysis of all products is the essential way to reveal torrefaction mechanism. In this study, torrefaction of rice husk was performed at 210-300 °C. Results showed that the fuel properties of solid products were greatly enhanced upon removal of oxygen. The gaseous products were mainly CO2 (52.9-73.8 vol%), followed by CO (26.3-39.2 vol%). The liquid product was mainly water and some tar, and the latter contained acids, furans, ketones, aldehydes, and phenols, among which the relative content of acids was the highest. Torrefaction temperature has obvious effects on the oxygen migration. Within the temperature range of 210-300 °C, 9.5-63.2% of oxygen in rice husk was migrated to the gaseous and liquid products. The H2O was the major contributor to deoxygenation, followed by CO2 and CO. Thus, formation of H2O, CO2, and CO during torrefaction is important as it achieves the purpose of intense deoxygenation.

Understanding Structure-Activity Relationships in Sr1- xY xCoO3-δ through in Situ Neutron Diffraction and Electrochemical Measurements.

In this work, we report a systematic study on temperature-dependent local structural evolution, oxygen stoichiometry, and electrochemical properties of an oxygen-deficient perovskite Sr0.7Y0.3CoO3-δ (SYC30) for oxygen electrocatalysis. The obtained results are then closely compared with its analogue Sr0.9Y0.1CoO3-δ (SYC10) of different crystal structures to establish structure-activity relationships. The comparison shows that both SYC30 and SYC10 consist of alternate layers of oxygen-deficient Co1-polyhedra and oxygen-saturated Co2-octahedra with Co1-polyhedra being responsible for Vo•• migration. It is also found that the distribution and concentration of oxygen vacancies within the Co1-layer are, respectively, less symmetrical and lower in SYC30 than those in SYC10, making the former unfavorable for oxygen transport. A molecular orbital energy analysis reveals that the energy gap between Fermi level and O 2p level in the active Co1-polyhedra is larger in SYC30 than that in SYC10, further suggesting that SYC10 is a better oxide-ion conductor and thus a better electrocatalyst for oxygen reduction reaction, which is unambiguously confirmed by the subsequent electrochemical measurements.

The Mechanism of Electrolyte Gating on High-Tc Cuprates: The Role of Oxygen Migration and Electrostatics.

Electrolyte gating is widely used to induce large carrier density modulation on solid surfaces to explore various properties. Most of past works have attributed the charge modulation to electrostatic field effect. However, some recent reports have argued that the electrolyte gating effect in VO2, TiO2, and SrTiO3 originated from field-induced oxygen vacancy formation. This gives rise to a controversy about the gating mechanism, and it is therefore vital to reveal the relationship between the role of electrolyte gating and the intrinsic properties of materials. Here, we report entirely different mechanisms of electrolyte gating on two high-Tc cuprates, NdBa2Cu3O7-δ (NBCO) and Pr2-xCexCuO4 (PCCO), with different crystal structures. We show that field-induced oxygen vacancy formation in CuO chains of NBCO plays the dominant role, while it is mainly an electrostatic field effect in the case of PCCO. The possible reason is that NBCO has mobile oxygen in CuO chains, while PCCO does not. Our study helps clarify the controversy relating to the mechanism of electrolyte gating, leading to a better understanding of the role of oxygen electro migration which is very material specific.