Trimetallic Mn‐Fe‐Ni Oxide Nanoparticles Supported on Multi‐Walled Carbon Nanotubes as High‐Performance Bifunctional ORR/OER Electrocatalyst in Alkaline Media

Discovering precious metal‐free electrocatalysts exhibiting high activity and stability toward both the oxygen reduction (ORR) and the oxygen evolution (OER) reactions remains one of the main challenges for the development of reversible oxygen electrodes in rechargeable metal–air batteries and reversible electrolyzer/fuel cell systems. Herein, a highly active OER catalyst, Fe_0.3Ni_0.7O_X supported on oxygen‐functionalized multi‐walled carbon nanotubes, is substantially activated into a bifunctional ORR/OER catalyst by means of additional incorporation of MnO_X. The carbon nanotube‐supported trimetallic (Mn‐Ni‐Fe) oxide catalyst achieves remarkably low ORR and OER overpotentials with a low reversible ORR/OER overvoltage of only 0.73 V, as well as selective reduction of O₂ predominantly to OH^?. It is shown by means of rotating disk electrode and rotating ring disk electrode voltammetry that the combination of earth‐abundant transition metal oxides leads to strong synergistic interactions modulating catalytic activity. The applicability of the prepared catalyst for reversible ORR/OER electrocatalysis is evaluated by means of a four‐electrode configuration cell assembly comprising an integrated two‐layer bifunctional ORR/OER electrode system with the individual layers dedicated for the ORR and the OER to prevent deactivation of the ORR activity as commonly observed in single‐layer bifunctional ORR/OER electrodes after OER polarization.     

Efficient Optimization of Electron/Oxygen Pathway by Constructing Ceria/Hydroxide Interface for Highly Active Oxygen Evolution Reaction

Owing to the unique electronic properties, rare‐earth modulations in noble‐metal electrocatalysts emerge as a critical strategy for a broad range of renewable energy solutions such as water‐splitting and metal–air batteries. Beyond the typical doping strategy that suffers from synthesis difficulties and concentration limitations, the innovative introduction of rare‐earth is highly desired. Herein, a novel synthesis strategy is presented by introducing CeO₂ support for the nickel–iron–chromium hydroxide (NFC) to boost the oxygen evolution reaction (OER) performance, which achieves an ultralow overpotential at 10 mA cm^?2 of 230.8 mV, the Tafel slope of 32.7 mV dec^?1, as well as the excellent durability in alkaline solution. Density functional theory calculations prove the established d–f electronic ladders, by the interaction between NFC and CeO₂, evidently boosts the high‐speed electron transfer. Meanwhile, the stable valence state in CeO₂ preserves the high electronic reactivity for OER. This work demonstrates a promising approach in fabricating a nonprecious OER electrocatalyst with the facilitation of rare‐earth oxides to reach both excellent activity and high stability.     

An Easily Sintered,Chemically Stable,Barium Zirconate‐Based Proton Conductor for High‐Performance Proton‐Conducting Solid Oxide Fuel Cells

Yttrium and indium co‐doped barium zirconate is investigated to develop a chemically stable and sintering active proton conductor for solid oxide fuel cells (SOFCs). BaZr_0.8Y_0.2‐xIn_xO_{3‐ δ} possesses a pure cubic perovskite structure. The sintering activity of BaZr_0.8Y_0.2‐xIn_xO_{3‐ δ} increases significantly with In concentration. BaZr_0.8Y_0.15In_0.05O_{3‐ δ} (BZYI5) exhibits the highest total electrical conductivity among the sintered oxides. BZYI5 also retains high chemical stability against CO₂, vapor, and reduction of H₂. The good sintering activity, high conductivity, and chemical stability of BZYI5 facilitate the fabrication of durable SOFCs based on a highly conductive BZYI5 electrolyte film by cost‐effective ceramic processes. Fully dense BZYI5 electrolyte film is successfully prepared on the anode substrate by a facile drop‐coating technique followed by co‐firing at 1400 °C for 5 h in air. The BZYI5 film exhibits one of the highest conductivity among the BaZrO₃‐based electrolyte films with various sintering aids. BZYI5‐based single cells output very encouraging and by far the highest peak power density for BaZrO₃‐based proton‐conducting SOFCs, reaching as high as 379 mW cm^?2 at 700 °C. The results demonstrate that Y and In co‐doping is an effective strategy for exploring sintering active and chemically stable BaZrO₃‐based proton conductors for high performance proton‐conducting SOFCs.     

Improving the Activity for Oxygen Evolution Reaction by Tailoring Oxygen Defects in Double Perovskite Oxides

Developing low‐cost, high‐performance electro‐catalysts is essential for large‐scale application of electrochemical energy devices. In this article, reported are the findings in understanding and controlling oxygen defects in PrBa_0.5Sr_0.5Co_1.5Fe_0.5O_{5+ δ} (PBSCF) for significantly enhancing the rate of oxygen evolution reaction (OER) are reported. Utilizing surface‐sensitive characterization techniques and first‐principle calculations, it is found that excessive oxygen vacancies promote OH^? affiliation and lower the theoretical energy for the formation of O* on the surface, thus greatly facilitating the OER kinetics. On the other hand, however, oxygen vacancies also increase the energy band gap and lower the O 2p band center of PBSCF, which may hinder OER kinetics. Still, careful tuning of these competing effects has resulted in enhanced OER activity for PBSCF with oxygen defects. This work also demonstrates that oxygen defects generated by different techniques have very different characteristics, resulting in different impacts on the activity of electrodes. In particular, PBSCF nanotubes after electrochemical reduction exhibit outstanding OER activity compared with the recently reported perovskite‐based catalysts.     

Enhanced Electrocatalytic Oxygen Evolution Activity by Tuning Both the Oxygen Vacancy and Orbital Occupancy of B‐Site Metal Cation in NdNiO3

Perovskite oxides have been explored as promising electrocatalysts for the oxygen evolution reaction (OER), while a lack of understanding of key factors impacting the catalytic activity restricts their further design and development. Here, for the first time, the contributions of oxygen vacancy (V_O) and orbital occupancy of B‐site cations to the catalytic activity of NdNiO₃ films are systematically investigated. It is found that OER activity follows a typical volcano‐shaped dependence on the oxygen pressure. In the range of 0.2–10 Pa, proper concentration of V_O can provide a moderate bonding strength with intermediate hydroxyl OH* and the increased ratio of Ni³⁺/Ni²⁺ provides a more favorable occupancy of e_g orbital for the catalytic activity; while in the range of 10–60 Pa, insufficient concentration of V_O leads to an enhanced strength of hybridization between Ni 3d and O 2p band and thus deteriorated catalytic activity. The superior OER catalytic performance can be only achieved with both appropriate concentration of V_O and the ratio of B‐site metal cations with different valences.     

Mixed‐Conducting Perovskites as Cathode Materials for Protonic Ceramic Fuel Cells: Understanding the Trends in Proton Uptake

The proton uptake of 18 compositions in the perovskite family (Ba,Sr,La)(Fe,Co,Zn,Y)O_3‐δ, perovskites, which are potential cathode materials for protonic ceramic fuel cells (PCFCs), is investigated by thermogravimetry. Hydration enthalpies and entropies are derived, and the doping trends are explored. The uptake is found to be largely determined by the basicity of the oxide ions. Partial substitution of Zn on the B‐site strongly enhances proton uptake, while Co substitution has the opposite effect. The proton concentration in Ba_0.95La_0.05Fe_0.8Zn_0.2O_3‐δ is found to be 10% per formula unit at 250 °C, 5.5% at 400 °C, and 2.3% at 500 °C, which are the highest values reported so far for a mixed‐conducting perovskite exhibiting hole, proton, and oxygen vacancy transport. A comprehensive set of thermodynamic data for proton uptake in (Ba,Sr,La)(Fe,Co,Zn,Y)O_3‐δ is determined. Defect interactions between protons and holes partially delocalized from the B‐site transition metal to the adjacent oxide ions decrease the proton uptake. From these results, guidelines for the optimization of PCFC cathode materials are derived.     

Controlled Fabrication of Hierarchically Structured Nitrogen‐Doped Carbon Nanotubes as a Highly Active Bifunctional Oxygen Electrocatalyst

Hierarchically structured nitrogen‐doped carbon nanotube (NCNT) composites, with copper (Cu) nanoparticles embedded uniformly within the nanotube walls and cobalt oxide (Co_xO_y) nanoparticles decorated on the nanotube surfaces, are fabricated via a combinational process. This process involves the growth of Cu embedded CNTs by low‐ and high‐temperature chemical vapor deposition, post‐treatment with ammonia for nitrogen doping of these CNTs, precipitation‐assisted separation of NCNTs from cobalt nitrate aqueous solution, and finally thermal annealing for Co_xO_y decoration. Theoretical calculations show that interaction of Cu nanoparticles with CNT walls can effectively decrease the work function of CNT surfaces and improve adsorption of hydroxyl ions onto the CNT surfaces. Thus, the activities of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are significantly enhanced. Because of this benefit, further nitrogen doping, and synergistic coupling between Co_xO_y and NCNTs, Cu@NCNT/Co_xO_y composites exhibit ORR activity comparable to that of commercial Pt/C catalysts and high OER activity (outperforming that of IrO₂ catalysts). More importantly, the composites display superior long‐term stability for both ORR and OER. This simple but general synthesis protocol can be extended to design and synthesis of other metal/metal oxide systems for fabrication of high‐performance carbon‐based electrocatalysts with multifunctional catalytic activities.     

Unlocking the Potential of Mechanochemical Coupling: Boosting the Oxygen Evolution Reaction by Mating Proton Acceptors with Electron Donors

The oxygen evolution reaction (OER) is the bottleneck of many sustainable energy conversion systems, including water splitting technologies. The kinetics of the OER is generally sluggish unless precious metal-based catalysts are used. Perovskite oxides have shown promise as alternatives to these expensive materials. However, for several perovskites, including SrCoO_3−δ, the rate-limiting step is proton-transfer. In this study, it is shown that such a kinetic limitation can be overcome by coupling those perovskites with MoS₂ mechanochemically. By studying composites of SrMO_3−δ (M = Co, Fe, Ti) and MoS₂, the role that the formed heterointerfaces play in enhancing the activity is investigated. Mechanochemically mating SrCoO_3−δ and MoS₂ increases the mass activity toward OER by a factor of ten and led to a Tafel slope of only 37 mV dec⁻¹. In contrast, combining MoS₂ with SrFeO_3−δ or SrTiO_3−δ, two materials whose OER is not limited by proton-transfer, does not result in an improvement of the performance. The experimental measurements and first-principle calculations reveal that the MoS₂ at the MoS₂@SrCoO_3−δ heterointerfaces is both an electron and a proton acceptor, thereby facilitating deprotonation of the perovskite and resulting in faster OER kinetics.     

A High‐Performance Binary Ni–Co Hydroxide‐based Water Oxidation Electrode with Three‐Dimensional Coaxial Nanotube Array Structure

Developing nanostructured Ni and Co oxides with a small overpotential and fast kinetics of the oxygen evolution reaction (OER) have drawn considerable attention recently because their theoretically high efficiency, high abundance, low cost, and environmental benignity in comparison with precious metal oxides, such as RuO₂ and IrO₂. However, how to increase the specific activity area and improve their poor intrinsic conductivity is still challenging, which significantly limits the overall OER rate and largely prevent their utilization. Thus, developing effective OER electrocatalysts with abundant active sites and high electrical conductivity still remains urgent. In this work, a scrupulous design of OER electrode with a unique sandwich‐like coaxial structure of the three‐dimensional Ni@[Ni^(2+/3+)Co₂(OH)_6–7]_x nanotube arrays (3D NNCNTAs) is reported. A Ni nanotube array with open end is homogeneous coated with Ni and Co co‐hydroxide nanosheets ([Ni^(2+/3+)Co₂(OH)_6–7]_x) and is employed as multifunctional interlayer to provide a large surface area and fast electron transport and support the outermost [Ni^(2+/3+)Co₂(OH)_6–7]_x layer. The remarkable features of high surface area, enhanced electron transport, and synergistic effects have greatly assured excellent OER activity with a small overpotential of 0.46 V at the current density of 10 mA cm^?2 and high stability.     

Advances in Manganese‐Based Oxides Cathodic Electrocatalysts for Li–Air Batteries

Li–air batteries, characteristic of superhigh theoretical specific energy density, cost‐efficiency, and environment‐friendly merits, have aroused ever‐increasing attention. Nevertheless, relatively low Coulomb efficiency, severe potential hysteresis, and poor rate capability, which mainly result from sluggish oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) kinetics, as well as pitiful cycle stability caused by parasitic reactions, extremely limit their practical applications. Manganese (Mn)‐based oxides and their composites can exhibit high ORR and OER activities, reduce charge/discharge overpotential, and improve the cycling stability when used as cathodic catalyst materials. Herein, energy storage mechanisms for Li–air batteries are summarized, followed by a systematic overview of the progress of manganese‐based oxides (MnO₂ with different crystal structures, MnO, MnOOH, Mn₂O₃, Mn₃O₄, MnOx, perovskite‐type and spinel‐type manganese oxides, etc.) cathodic materials for Li–air batteries in the recent years. The focus lies on the effects of crystal structure, design strategy, chemical composition, and microscopic physical parameters on ORR and OER activities of various Mn‐based oxides, and even the overall performance of Li–air batteries. Finally, a prospect of the research for Mn‐based oxides cathodic catalysts in the future is made, and some new insights for more reasonable design of Mn‐based oxides electrocatalysts with higher catalytic efficiency are provided.     

Tuning Bifunctional Oxygen Electrocatalysts by Changing the A‐Site Rare‐Earth Element in Perovskite Nickelates

Perovskite‐structured (ABO₃) transition metal oxides are promising bifunctional electrocatalysts for efficient oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). In this paper, a set of epitaxial rare‐earth nickelates (RNiO₃) thin films is investigated with controlled A‐site isovalent substitution to correlate their structure and physical properties with ORR/OER activities, examined by using a three‐electrode system in O₂‐saturated 0.1 m KOH electrolyte. The ORR activity decreases monotonically with decreasing the A‐site element ionic radius which lowers the conductivity of RNiO₃ (R = La, La_0.5Nd_0.5, La_0.2Nd_0.8, Nd, Nd_0.5Sm_0.5, Sm, and Gd) films, with LaNiO₃ being the most conductive and active. On the other hand, the OER activity initially increases upon substituting La with Nd and is maximal at La_0.2Nd_0.8NiO₃. Moreover, the OER activity remains comparable within error through Sm‐doped NdNiO₃. Beyond that, the activity cannot be measured due to the potential voltage drop across the film. The improved OER activity is ascribed to the partial reduction of Ni³⁺ to Ni²⁺ as a result of oxygen vacancies, which increases the average occupancy of the e_g antibonding orbital to more than one. The work highlights the importance of tuning A‐site elements as an effective strategy for balancing ORR and OER activities of bifunctional electrocatalysts.     

Non‐stoichiometry in Oxide Thin Films: A Chemical Capacitance Study of the Praseodymium‐Cerium Oxide System

While the properties of functional oxide thin films often depend strongly on their oxygen stoichiometry, there have been few ways to extract this information reliably and in situ. In this work, the derivation of the oxygen non‐stoichiometry of dense Pr_0.1Ce_0.9O_2?δ thin films from an analysis of chemical capacitance obtained by impedance spectroscopy is described. Measurements are performed on electrochemical cells of the form Pr_0.1Ce_0.9O_2?δ/Y_0.16Zr_0.84O_1.92/Pr_0.1Ce_0.9O_2?δ over the temperature range of 450 to 800 °C and oxygen partial pressure range of 10^?5 to 1 atm O₂. With the aid of a defect equilibria model, approximations relate chemical capacitance directly to non‐stoichiometry, without need for fitting parameters. The calculated non‐stoichiometry allows extraction of the thermodynamic constants defining defect generation. General agreement of these constants with bulk values derived by thermogravimetric analysis is found, thereby confirming the suitability of this technique for measuring oxygen non‐stoichiometry of thin oxide films. Potential sources of error observed in earlier chemical capacitance studies on perovskite structured oxide films are also discussed.     

Superaerophobic Electrode with Metal@Metal‐Oxide Powder Catalyst for Oxygen Evolution Reaction

A stable and highly active oxygen evolution reaction (OER) electrode is the key for fast and robust O₂ production, which is one of the essential points for various kinds of energy conversion systems, such as water splitting, lithium‐O₂ battery and artificial photosynthesis. Here, superaerophobic electrodes with metal@metal‐oxide powder catalysts are shown, which demonstrate high and stable OER activity. The active‐site‐density of metal@metal‐oxide catalysts is increased over one order of magnitude than those of pure metal oxides due to the large enhancement of electrical conductivity, revealing the substantial enhancement of electrochemical OER kinetics. Furthermore, the superaerophobic property of electrodes is favorable for fast O₂ desorption, which improves electrochemical active surface area (EASA) during OER. The superaerophobic electrode with metal@metal‐oxide powder catalysts provides the new insight for increase of active‐site‐density and EASA simultaneously, which are the key factors to determine the activity of OER electrode.     

Structural Determination and Imaging of Charge Ordering and Oxygen Vacancies of the Multifunctional Oxides REBaMn2O6‐χ (RE = Gd,Tb)

Charge ordering and oxygen vacancy ordering are revealed in REBaMn₂O_6‐δ (RE = Gd, Tb) oxides with perovskite‐related structures. Electron diffraction and transmission electron microscopy results indicate a modulation of the crystal structure. The average oxidation state of Mn and the oxygen stoichiometry are determined by means of electron energy‐loss spectroscopy, giving a REBaMn₂O_5.75 general formula. A 1:3 Mn⁴⁺:Mn³⁺ charge ordering model is confirmed by neutron powder diffraction, and oxygen vacancies‐Mn³⁺ association is suggested by pair distribution function analysis. Direct imaging of the oxygen sublattice is obtained by phase image reconstruction. Location of the oxygen vacancies in the anion sublattice is achieved by analysis of the intensity of the averaged phase image. Both ionic conduction and multiferroic behavior are predicted from the crystal structures of these oxides.     

Defect‐Rich Nitrogen Doped Co3O4/C Porous Nanocubes Enable High‐Efficiency Bifunctional Oxygen Electrocatalysis

Heteroatom doping plays a significant role in optimizing the catalytic performance of electrocatalysts. However, research on heteroatom doped electrocatalysts with abundant defects and well‐defined morphology remain a great challenge. Herein, a class of defect‐engineered nitrogen‐doped Co₃O₄ nanoparticles/nitrogen‐doped carbon framework (N‐Co₃O₄@NC) strongly coupled porous nanocubes, made using a zeolitic imidazolate framework‐67 via a controllable N‐doping strategy, is demonstrated for achieving remarkable oxygen evolution reaction (OER) catalysis. X‐ray photoelectron spectroscopy, X‐ray absorption fine structure, and electron spin resonance results clearly reveal the formation of a considerable amount of nitrogen dopants and oxygen vacancies in N‐Co₃O₄@NC. The defect engineering of N‐Co₃O₄@NC makes it exhibit an overpotential of only 266 mV to reach 10 mA cm^?2, a low Tafel slope of 54.9 mV dec^?1 and superior catalytic stability for OER, which is comparable to that of commercial RuO₂. Density functional theory calculations indicate N‐doping could promote catalytic activity via improving electronic conductivity, accelerating reaction kinetics, and optimizing the adsorption energy for intermediates of OER. Interestingly, N‐Co₃O₄@NC also shows a superior oxygen reduction reaction activity, making it a bifunctional electrocatalyst for zinc–air batteries. The zinc–air battery with the N‐Co₃O₄@NC cathode demonstrates superior efficiency and durability, showing the feasibility of N‐Co₃O₄/NC in electrochemical energy devices.     

Searching General Sufficient‐and‐Necessary Conditions for Ultrafast Hydrogen‐Evolving Electrocatalysis

The development of cost‐effective and high‐performance electrocatalysts for the hydrogen evolution reaction (HER) is one critical step toward successful transition into a sustainable green energy era. Different from previous design strategies based on single parameter, here the necessary and sufficient conditions are proposed to develop bulk non‐noble metal oxides which are generally considered inactive toward HER in alkaline solutions: i) multiple active sites for different reaction intermediates and ii) a short reaction path created by ordered distribution and appropriate numbers of these active sites. Computational studies predict that a synergistic interplay between the ordered oxygen vacancies (at pyramidal high‐spin Co³⁺ sites) and the O 2p ligand holes (OLH; at metallic octahedral intermediate‐spin Co⁴⁺ sites) in RBaCo₂O_5.5+δ (δ = 1/4; R = lanthanides) can produce a near‐ideal HER reaction path to adsorb H₂O and release H₂, respectively. Experimentally, the as‐synthesized (Gd_0.5La_0.5)BaCo₂O_5.75 outperforms the state‐of‐the‐art Pt/C catalyst in many aspects. The proof‐of‐concept results reveal that the simultaneous possession of ordered oxygen vacancies and an appropriate number of OLH can realize a near‐optimal synergistic catalytic effect, which is pivotal for rational design of oxygen‐containing materials.     

Pt Dopant: Controlling the Ir Oxidation States toward Efficient and Durable Oxygen Evolution Reaction in Acidic Media

Dissolution of Ir oxides in Ir‐based catalysts, which is closely linked to the catalyst activity and stability toward the oxygen evolution reaction (OER) in acidic media, is a critical unresolved problem in the commercialization of water electrolysis. Doping foreign elements into the Ir oxides can accomplish an optimal combination of Ir oxidation states that is conducive to the leaching‐resistance of active catalytic sites. Here, it is reported that Pt doping into IrO_x‐based nanoframe is beneficial in both terms of activity and stability. The Pt‐doped IrO_x‐based nanoframe achieves the mass activity of 0.644 A mg^?1_Ir+Pt at 1.53 V_RHE, which is 15‐fold higher than that of the commercial IrO₂. During the accelerated durability test, the Ir^IV‐to‐Ir^III ratio of 5 is maintained in the presence of Pt dopant to effectively mitigate the degradation of Ir catalyst, leading to the superb catalyst durability in acidic media.     

Engineering an Earth‐Abundant Element‐Based Bifunctional Electrocatalyst for Highly Efficient and Durable Overall Water Splitting

The simultaneous and efficient evolution of hydrogen and oxygen with earth‐abundant, highly active, and robust bifunctional electrocatalysts is a significant concern in water splitting. Herein, non‐noble metal‐based Ni–Co–S bifunctional catalysts with tunable stoichiometry and morphology are realized. The engineering of electronic structure and subsequent morphological design synergistically contributes to significantly elevated electrocatalytic performance. Stable overpotentials (η₁₀) of 243 mV (vs reversible hydrogen electrode) for oxygen evolution reaction (OER) and 80 mV for hydrogen evolution reaction (HER), as well as Tafel slopes of 54.9 mV dec^?1 for OER and 58.5 mV dec^?1 for HER, are demonstrated. In addition, density functional theory calculations are performed to determine the optimal electronic structure via the electron density differences to verify the enhanced OER activity is related to the Co top site on the (110) surface. Moreover, the tandem bifunctional NiCo₂S₄ exhibit a required voltage of 1.58 V (J = 10 mA cm^?2) for simultaneous OER and HER, and no obvious performance decay is observed after 72 h. When integrated with a GaAs solar cell, the resulting photoassisted water splitting electrolyzer shows a certified solar‐to‐hydrogen efficiency of up to 18.01%, further demonstrating the feasibility of engineering protocols and the promising potential of bifunctional NiCo₂S₄ for large‐scale overall water splitting.     

Uniform,Assembled 4 nm Mn3O4 Nanoparticles as Efficient Water Oxidation Electrocatalysts at Neutral pH

Electrochemical water splitting is one of the ways to produce environmentally‐friendly hydrogen energy. Transition‐metal (TM)‐based catalysts have been attracting attention due to their low cost and abundance, but their insufficient activity still remains a challenge. Here, 4 nm Mn₃O₄ nanoparticles (NPs) are successfully synthesized and their electrochemical behavior is investigated. Using electrokinetic analyses, an identical water oxidizing mechanism is demonstrated between the 4 and 8 nm Mn₃O₄ NPs. In addition, it is confirmed that the overall increase in the active surface area is strongly correlated with the superb catalytic activity of the 4 nm Mn₃O₄ NPs. To further enhance the oxygen evolution reaction (OER) performance, Ni foam substrate is introduced to maximize the entire number of the NPs participating in OER. The 4 nm Mn₃O₄/Ni foam electrode exhibits outstanding electrocatalytic activity for OER with overpotential of 395 mV at a current density of 10 mA cm^?2 under neutral conditions (0.5 m PBS, pH 7).     

Nanoscale Resistive Switching in Amorphous Perovskite Oxide (a‐SrTiO3) Memristors

Memristive devices are the precursors to high density nanoscale memories and the building blocks for neuromorphic computing. In this work, a unique room temperature synthesized perovskite oxide (amorphous SrTiO₃: a‐STO) thin film platform with engineered oxygen deficiencies is shown to realize high performance and scalable metal‐oxide‐metal (MIM) memristive arrays demonstrating excellent uniformity of the key resistive switching parameters. a‐STO memristors exhibit nonvolatile bipolar resistive switching with significantly high (10³–10⁴) switching ratios, good endurance (>10⁶I–V sweep cycles), and retention with less than 1% change in resistance over repeated 10⁵ s long READ cycles. Nano‐contact studies utilizing in situ electrical nanoindentation technique reveal nanoionics driven switching processes that rely on isolatedly controllable nano‐switches uniformly distributed over the device area. Furthermore, in situ electrical nanoindentation studies on ultrathin a‐STO/metal stacks highlight the impact of mechanical stress on the modulation of non‐linear ionic transport mechanisms in perovskite oxides while confirming the ultimate scalability of these devices. These results highlight the promise of amorphous perovskite memristors for high performance CMOS/CMOL compatible memristive systems.