Atomic Rearrangement Research Articles

Atomically Resolved Surface Reconstruction of WO3 (002).

The rearrangement of surface atoms in oxide nanocrystals, namely surface reconstruction, plays an important role in improving the physical and chemical properties of metal oxides. However, structural information pertaining to reconstructed surfaces is scarce due to the challenges associated with directly imaging surface and sub-surface atoms under reconstruction conditions. Herein, the reconstruction of the nanocrystalline tungsten trioxide (002) surface is directly investigated via scanning transmission electron microscope (STEM). The results reveal that the atoms on the reconstructed WO3 (002) surface are rearranged into a (1 × 2) structure, and the structural model is determined by density functional theory (DFT) calculation. In addition, after surface reconstruction, the Fermi level shifted toward the conduction band compared to the initial surface, achieving an effect similar to n-type doping. Surprisingly, analogous atomic rearrangements are also observed in cracks, indicating that sub-nanometer fractures in tungsten trioxide can be remedied through surface reconstruction, thus proposing an unconventional mechanism for crack healing. Furthermore, DFT calculations are used to analyze the models and electronic properties of the reconstruction structures. These findings provide insights into the surface reconstruction of WO3 (002) and the healing of nanoscale cracks in tungsten trioxide.

Infinitely rugged intra-cage potential energy landscape in metallic glasses caused by many-body interaction

The absence of translational symmetry in glassy materials poses a significant challenge in establishing effective structure-property relationships in real space. Consequently, the potential energy landscape (PEL) in phase space is widely utilized to comprehend the complex phenomena in glasses. The classical PEL features a two-scale profile comprising mega-basins and sub-basins, corresponding to α-relaxations (e.g. glass transition) and β-relaxations (e.g. local cage-breaking atomic rearrangements), respectively. Recent studies, however, reveal that sub-basins are not smooth and contain finer structures, the origins of which remain elusive. Here we probe the smoothness of sub-basin bottoms in glasses' PEL by introducing small intra-cage cyclic loading and then measuring the net changes in atomic-level stresses. Compared to glasses with pair interaction, glasses with many-body interaction exhibit orders-of-magnitude larger and loading-dependent stress changes even before the first cage-breaking event takes place, which reflect much more feature-rich sub-basins. We further demonstrate this stark contrast stems from the spatial distribution of individual atom's constraining force field. Specifically, at vanishing perturbations, many-body interactions disrupt the positive-definite synchrony in energy variations of the perturbed atom and the whole system, causing inherently less confined atomic responses and infinitely rugged sub-basins. The implications of these findings for the selective addition or removal of fine structures in the PEL and the subsequent tuning of glassy materials' responses to external stimuli are also explored.

In situ synthesis and structural morphology analysis of 3D porous hierarchical V2O5 films for transmissive-to-black all-solid-state electrochromic devices

3D, porous, low-dimensional, and nanostructured V2O5 films have significant potential for application in ECDs, but their development is still in its nascency. This paper reports a facile strategy of using PEG as a structure-directing agent and short-time heat treatments to obtain 3D, porous, and hierarchical V2O5 films comprising interpenetrating stacked ultra-long nanowire surfaces and nanorod/nanosheet mixed interiors deposited on ITO-glass substrates. The mechanism of morphological transformation was studied in detail, and the analysis shows that the formation of such special structured films is a synergetic result of the guided intercalation of PEG, atomic rearrangement, Ostwald ripening, anisotropy of crystal growth, and orientation attachment mechanism. Among them, the preferred PEG addition amount of 25 % for the 350-3-V2O5 film was applied in two types of all-solid-state ECDs: one using a gel quasi-solid electrolyte and the other using a solid-film electrolyte. The 350-3-V2O5 film served as an ion storage coating and WO3 was the electrochromic layer. These devices achieved ideal reversible switching of transmissive-to-black electrochromic characteristics. Notably, the ‘Integrated-Type’ ECD, composed of inorganic all-solid-state films, has a large optical modulation range ΔT = 72.0 %, rapid switching responses (colouration 25.4 s and bleaching 20.8 s), and sustained electrochromic performance.

Silicate impedes arsenic release and oxidation from ferrihydrite

Silicate fertilization is a common farming practice and an effective method to mitigate arsenic (As) pollution in paddy. Investigating the interaction between silicate and ferrihydrite on As retention is key to comprehensively understand the mechanism of As sequestration by silicate fertilization. Our results indicated that the transformation of ferrihydrite into goethite and hematite was inversely proportional to Si/Fe ratios. The added silicate impeded the decrease of solution pH from neutral to acidity, and imposed strong inhibitory effect on goethite formation. The aqueous As in silicate-free system was 3.43 times higher than that with Si/Fe ratio at 0.33, but similar results were not observed in those with high-level As pollution due to the inhibitory effect of As on ferrihydrite transformation. Solid characterization showed that silicate was monomerically adsorbed to ferrihydrite through Si-O-Fe bond, which impeded the reductive dissolution, Fe atom exchange, internal atomic rearrangement and dehydration of ferrihydrite. As(III) oxidation weakened in silicate-coprecipitated ferrihydrite due to the lack of Fe(II) catalysis stem from ferrihydrite dissolution. This work demonstrated that As release could be effectively impeded through the inhibitory effect of silicate on ferrihydrite transformation, thereby providing new insights into the understanding of As accumulation reduction in rice by silicate fertilization.

Engineering medium-entropy alloy nanoparticle nanotubes for efficient oxygen reduction

Fuel cells, as promising energy conversion devices, realize the direct conversion of hydrogen fuel chemical energy into electrical energy. The kinetics of cathodic oxygen reduction reaction (ORR) is slow and plays a decisive role in the output efficiency of fuel cells. Platinum catalysts have been commercialized, but their high cost, relatively low catalytic activity and poor cycling durability limit the development of fuel cells. The introduction of non-platinum components is an effective strategy to minimize the cost and maximize the activity. In this study, PtPdCu medium entropy alloy nanoparticle nanotubes (PtPdCu MEANPTs) that demonstrate high catalytic activity and long durability are presented. Combined with density functional theory calculations, the introduction of Pd and Cu modulates surface electronic structure and optimizes the oxygen adsorption energy, thus enhancing the catalytic activity. The 0D/1D hybrid structure exposes more surface sites and inhibits particle maturation. The atomic migration and rearrangement are emerged during the initial stage of potential cycling process, induing a palladium-rich outer layer and preventing the oxidation of platinum atoms. The best-performing Pt24Pd28Cu48 MEANPTs deliver the impressive ORR activity (1.42 A/mgPt at 0.9 V vs. RHE, which is 6.17 times that of commercial Pt/C) and durability (retaining 2.87 times the initial activity of benchmark catalyst after 30,000 potential cycles). Theoretical calculations have confirmed the regulation of alloying on the surface oxygen affinity and revealed the true active sites on the catalyst surface. This work explores the research direction of platinum-based multi-element catalysts with low platinum content and high catalytic activity.

Enhancing damping properties of Mg–Sn–Y alloys: The role of metastable clustering

The damping properties of Mg–Sn–Y alloys with varied Sn/Y atomic ratios and heat-treatment processes have been studied. In the as-cast state, the alloy with a Sn/Y ratio of 3:1 exhibits the highest damping property in the low strain region due to the low Y solid solution and small lattice distortion. After heat treatment with 480 °C and 24 h, the lattice distortion of the alloy with a Sn/Y atomic ratio of 1:1 is significantly reduced compared to the cast alloy, resulting in an ultra-high damping property in the low strain region (ε = 10−4, Q−1 = 0.023). This change in damping property is attributed to the presence of metastable clusters, which consume energy through atomic rearrangement, separation, and redissolution, thereby enhancing the damping property. However, excessively long heat treatment times or high temperatures are detrimental to the formation of these metastable clusters, leading to a decreased damping property.

Enhanced CO2 Hydrogenation Performance of CoCrNiFeMn High Entropy Alloys

CO2 hydrogenation is a promising process for removing anthropogenic CO2 emissions and yielding C1 chemicals that can be utilized as fuels and valuable precursors for chemical synthesis. Commercial high-entropy alloys (HEAs) have widespread application in various fields owing to their exceptional thermal stability and tunable microstructure. However, their potential application as catalysts is often limited by the low exposure of active sites. In this study, the commercial CoCrNiFeMn powder was applied for atmospheric pressure CO2 hydrogenation and enhanced its catalytic performance by a combined treatment of ball milling and high-temperature H2 reduction. The high-energy ball milling results in a morphological transition in CoCrNiFeMn HEAs from spherical to irregular. This transformation leads to a significant decrease in particle size and more surface reactive sites. The high-temperature H2 reduction promoted the atomic rearrangement on the CoCrNiFeMn surface, thereby improving its alloy structural homogeneity. These modifications greatly improve the performance of CoCrNiFeMn for CO2 hydrogenation. This work introduces a facile modification approach to facilitate the catalytic efficiency of commercial HEAs in CO2 hydrogenation with high selectivity.

High-value multilayer graphene oxide prepared by catalytic pyrolysis of petroleum tar and applications: Trash to treasure

Petroleum tar (PT), a by-product of heavy oil refining, poses significant environmental challenges due to its high production volume and associated pollution risks. This study presents an innovative approach for the catalytic conversion of PT into multilayer graphene oxide using nickel foam (NiF) as a catalyst at reaction temperatures of 500 °C and 700 °C (GT/Ni500 and GT/Ni700). The process effectively decomposes PT and facilitates the structured rearrangement of carbon atoms into graphene layers. Comprehensive characterization techniques, including SEM-EDS, HRTEM, BET, XRD, XPS, and Raman spectroscopy, confirm the formation of high-quality graphene oxide. The synthesized GT/Ni700 material exhibits remarkable electrochemical performance with a specific capacitance of 3.34F/g. GT/Ni500 shows adsorption capacities of 59.86 mg/g for Pb2+ and 56.84 mg/g for Cu2+. Life Cycle Assessment reveals a substantial reduction in the carbon footprint, with CO2 equivalents for GT/Ni500 and GT/Ni700significantly lower than traditional methods, at 17.64 kg/CO2eq and 14.03 kg/CO2eq, respectively, representing a reduction of over 50 %. This study not only offers a sustainable pathway for PT utilization but also provides advanced materials with dual utility in electrochemical applications and heavy metal adsorption, contributing to environmental remediation and reducing reliance on non-renewable resources.

Tailoring closed pore structure in phenolic resin derived hard carbon enables excellent sodium ion storage

The existed plenty of oxygen-containing species in phenolic resin easily inhibit the migration and rearrangement of carbon atoms during pyrolysis, which disfavors the formation of pseudo-graphite structure with larger lateral length (La) and hence leads to poor closed pores, accounting for a low capacity and initial Coulombic efficiency (ICE). Herein, hard carbon with rich closed pores and the most suitable pore size and volume is constructed via a two-step carbonization strategy. It is found that the pre-annealing step can effectively decrease oxygen content by changing the interconnection form of molecule chains, which promotes the growth of La during post-carbonization process, accelerating the formation of closed pores. Besides, with decreasing oxygen content, closed pore size gradually increases, while closed pore number and volume both first increase and then decrease, unveiling that an excessive high and too low oxygen content are unfavorable for the formation of ideal closed pores, resulting from an unsuitable La size. Therefore, the resulting sample, featured by the optimal balance between closed pore number, size (2.52 nm), and volume (0.215 cm3 g−1), delivers a high capacity of 351 mAh g−1 along with an excellent ICE of 83 %.

Exploring the graphitization transformation mechanism of deposited carbon in molten salt electrolysis: A novel insight from molecular structure models

Molten salt electrolysis graphitization is a novel method for the electrochemical graphitization, offering significant technological advantages. Researchers have shown keen interest in preparing graphite materials through molten salt strategies. However, there is still a lack of comprehensive research methodologies at the molecular scale for the removal of heteroatoms and rearrangement of carbon atoms in different amorphous carbon conversion systems. To address the above issue, the deposited carbon (DC, a coking byproduct) was converted into graphitized material (electrolysis products, EP) through the electrochemical method in this study. By processing Transmission Electron Microscope images with Python programming, aromatic skeleton structure information was quantitatively extracted. The evolution of the structure of DC was studied using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Based on information about elemental content, aromatic skeletal structure, and heteroatom functional groups, average chemical structure models were constructed for DC and EP, and relevant chemical bond parameters were statistically analyzed. Then, the influence of the electric field on the structural transformation of amorphous carbon in molten salts was investigated. The research results show that the electric field significantly affects the graphitization transformation process of amorphous carbon in molten salts, enhancing the interaction between calcium ions and DC molecules, increasing the diffusion coefficient of particles in the system, and promoting the formation of more sp2-hybridized carbon atoms, thus forming a more compact aromatic ring network. This study provides a new research method and molecular/atomic-level insights for a deeper understanding of the mechanism of graphitization transformation of amorphous carbon.

Efficient electron transport at the perovskite nanodots interface facilitates CO2 photoreduction

How to achieve controllable preparation of heterostructure and in-situ optimize the interface and internal electron transfer by a fast and economic synthesis method has become a big challenge in the practical application of photocatalysis. Herein, an island-shaped SrTiO3 (STO) perovskite nanodots and TiO2 (T) compounded S-scheme SrTiO3/TiO2 (ST) heterostructure was successfully developed. During the millisecond reaction process, the decomposed Sr2+ penetrated into the TiO2 lattice causing the lattice expansion and inducing local atomic rearrangements, resulting in the generation of STO phase. Owing to the synergy of the efficient electron transport at the perovskite nanodots interface and the stronger reduction capacity, the performance of the optimized ST1 sample is greatly improved to 86.90 μmol g−1 for CO2-to-CO and 21.31 μmol g−1 for CO2-to-CH4. The utilization of electrons reached up to 119.74 μmol g−1 h−1, which was 3.13 times higher than that of T. Detailed characterizations and density functional theory (DFT) calculations proof that the formation of intermediates HCOO− and CO32− is the key to the performance improvement critically. Overall, this work originally reports a feasible strategy for flame synthesis of S-scheme heterostructure photocatalyst.

Chemical short-range ordering accompanies shear band initiation in CrCoNi medium entropy alloy

Extended X-ray absorption fine structure (EXAFS), high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction have been used to monitor the structural development, on atomic-to-nanometer scale, prior to and along with shear band initiation in a face-centered-cubic CrCoNi medium-entropy alloy (MEA) under impact punch shear loads. Our findings provide clear evidence of chemical ordering with accompanying compositional inhomogeneity, on the length scale of one nanometer at the beginning of shear banding initiation. This chemical short-range atomic rearrangement of the three constituent elemental species is a result of atomic diffusion during high-strain-rate straining. The increasing chemical/structural inhomogeneity is likely to exert perturbations to cause uneven energy dissipation and encourage dislocation slip plane softening, both promoting strain localization that may have helped to instigate shear banding. Dynamic recrystallization is observed in later mature shear bands.

In situ revealing the dehydration and atomic structure evolution of protonated titanate nanotubes via environmental transmission electron microscopy

The precise control of nanomaterial microstructure at the atomic level relies on the comprehensive understanding of atomic structural transition during the fabrication process at the atomic level. The phase transition from protonated titanate to TiO2 is a prevalent route to synthesize low dimensional TiO2-based nanomaterials, which exhibit excellent photocatalytic, lithium-ion battery performances, while the detailed phase transition mechanism remains to be clarified due to lack of atomic-level in situ information. Herein, the atomic structural transitions from one-dimensional H2Ti3O7 (HT) to TiO2(B) and anatase TiO2 (TB and TA) nanocrystals were revealed through in situ environmental transmission electron microscopy, which exhibited a two-step phase transition at 200–600 °C. (I) H2Ti3O7 to TiO2(B) transition began via an indirect pathway at ∼200 °C: The HT (200) interlayer dehydration occurred firstly with lattice shrinkage; Then TB discretely nucleated at the dehydrated H2Ti3O7 nanotube wall with a crystallographic relationship of (200)HT∥(200)TB {[001]HT∥[001]TB}; At higher temperature, the separated nuclei grew up with defects and distorted crystal lattice among them, which then connected and jointed to a single crystalline TB nanotube by atomic rearrangement. (II) The further transition of TiO2(B) to anatase TiO2 occurred via a direct pathway above 400 °C: Scarce nucleation event of TA phase was observed, which generated within TB nanocrystal with a crystallographic relationship of (200)TB∥(002)TA {[001]TB∥[010]TA}. Once a TA nucleus formed, it grew up to a large crystal by consuming the neighbor TB nanocrystals. These findings may contribute to comprehensively understanding phase transition and precisely manipulating the atomic structure of one-dimensional TiO2 nanocrystals.

Insulator-Transition-Induced Degradation of Pyrochlore Ruthenates in Electrocatalytic Oxygen Evolution and Stabilization through Doping.

Ru-based pyrochlores (e.g., Y2Ru2O7-δ) are promised to replace IrO2 in polymer electrolyte membrane (PEM) electrolyzers. It is significant to reveal the cliff attenuation on the oxygen evolution reaction (OER) performance of these pyrochlores. In this work, we monitor the structure changes and electrochemical behavior of Y2Ru2O7-δ over the OER process, and it is found that the reason of decisive OER inactivation is derived from an insulator transition occurred within Y2Ru2O7-δ due to its inner "perfecting" lattice induced by continuous atom rearrangement. Therefore, a stabilization strategy of the Ir-substituted Y2Ru2O7-δ is proposed to alleviate this undesirable behavior. The double-exchange interaction between Ru and Ir in [RuO6] and [IrO6] octahedra leads the charge redistribution with simultaneous spin configuration adjustment. The electronic state in newly formed octahedrons centered with Ru 4d3 (with the state of eg'↑↑a1g ↑ eg 0) and Ir 5d6 (eg'↑↓↑↓a1g ↑↓ eg 0) relieves the uneven electron distributions in [RuO6] orbital. The attenuated Jahn-Teller effect alleviates atom rearrangement, represented as the mitigation of insulator transition, surface reconstruction, and metal dissolution. As results, the Ir-substituted Y2Ru2O7-δ presents the greatly improved OER stability and PEM durability. This study unveils the OER degradation mechanism and stabilization strategy for material design of Ru-based OER catalysts for electrochemical applications.

Understanding of the irradiation response of Cr-based ATF coatings using in-situ TEM

Although CrNb coated zirconium alloy materials are considered as ATF candidates with excellent oxidation resistance and mechanical properties, the irradiation response behavior under harsh and complex service conditions is still unrevealed. Here, we report the evolution of the microstructure of pure Cr and CrNb coatings with different Nb contents under simultaneous irradiation with Cr+-He+-H2+ triple ion beams at 633 K by using an advanced in-situ transmission electron microscope (TEM). The results show that CrNb coatings with high Nb content have better irradiation stability. Under high-temperature irradiation conditions, irradiation-induced oxidation and grain growth or crystallization are observed for both Cr-8 Nb with a nanocrystalline structure and Cr-18 Nb coatings with an almost amorphous structure, whereas Cr-37 Nb coatings maintains relatively intact in the amorphous phase after irradiation at a dose of 10 dpa. Based on the in-situ tracking of the microstructural evolution, it is revealed that the mechanism of irradiation-accelerated oxidation and crystallization of coatings originates from displacement cascades enhancing local atomic diffusion and rearrangement.

Force-Free Identification of Minimum-Energy Pathways and Transition States for Stochastic Electronic Structure Theories.

The accurate mapping of potential energy surfaces (PESs) is crucial to our understanding of the numerous physical and chemical processes mediated by atomic rearrangements, such as conformational changes and chemical reactions, and the thermodynamic and kinetic feasibility of these processes. Stochastic electronic structure theories, e.g., Quantum Monte Carlo (QMC) methods, enable highly accurate total energy calculations that in principle can be used to construct the PES. However, their stochastic nature poses a challenge to the computation and use of forces and Hessians, which are typically required in algorithms for minimum-energy pathway (MEP) and transition state (TS) identification, such as the nudged elastic band (NEB) algorithm and its climbing image formulation. Here, we present strategies that utilize the surrogate Hessian line-search method, previously developed for QMC structural optimization, to efficiently identify MEP and TS structures without requiring force calculations at the level of the stochastic electronic structure theory. By modifying the surrogate Hessian algorithm to operate in path-orthogonal subspaces and at saddle points, we show that it is possible to identify MEPs and TSs by using a force-free QMC approach. We demonstrate these strategies via two examples, the inversion of the ammonia (NH3) molecule and the nucleophilic substitution (SN2) reaction F- + CH3F → FCH3 + F-. We validate our results using Density Functional Theory (DFT)- and Coupled Cluster (CCSD, CCSD(T))-based NEB calculations. We then introduce a hybrid DFT-QMC approach to compute thermodynamic and kinetic quantities, free energy differences, rate constants, and equilibrium constants that incorporates stochastically optimized structures and their energies, and show that this scheme improves upon DFT accuracy. Our methods generalize straightforwardly to other systems and other high-accuracy theories that similarly face challenges computing energy gradients, paving the way for highly accurate PES mapping, transition state determination, and thermodynamic and kinetic calculations at significantly reduced computational expense.

Manganese-doped Zinc Oxide recycled from spent alkaline batteries for photocatalysis and supercapacitor applications

In a sustainable future, recycling e-waste will offer an adequate solution to control the raw materials and energy crisis. Our study aims to obtain ZnO-based materials by recycling the alkaline batteries using mild and cost-effective methods. Manganese-doped ZnO materials were obtained through anodic paste annealing at different temperatures. In terms of morphology and structure, particles with rod shape, high crystallinity, and hexagonal symmetry were obtained. The annealing provides an atomic rearrangement ensuring the presence of isolated Mn2+ ions in the ZnO lattice, as evidenced by EPR spectroscopy. The sample defect evolution with the annealing temperature was highlighted by photoluminescence spectroscopy. The photocatalytic and energy storage applications of the obtained sample were investigated. The photocatalytic activity was tested on Rhodamine B and Oxytetracycline under visible light irradiation. The highest photocatalytic efficiency was obtained for Mn-doped ZnO annealed at 700 °C, and the proposed mechanism was based on reactive oxygen species generation correlated with scavengers’ tests, defect’s structure, and pores diameter. Additionally, the samples were used to design symmetric supercapacitors and tested using different electrochemical techniques to prove their energy storage features. As a result, the Mn-doped ZnO particles annealed at 800 °C showed increased specific capacitance of 182 F/g, energy density of 25.2 Wh/kg, and power density of 38.7 kW/Kg without the use of booster materials.

Origins of Severe Structural Changes during Alloying-Dealloying Reactions in Black Phosphorus.

Li-alloying reactions facilitate the incorporation of a large number of Li atoms into the crystalline structures of electrodes, such as black phosphorus (BP). However, the reactions inevitably induce multistep phase transitions characterized by drastic atomic rearrangements and lattice collapse. Despite many theoretical and experimental studies on alloying mechanisms, long-term debates persist regarding the structures of the intermediate phases, the accurate pathways of phase transitions, the formation of specific configurations, and alloying/dealloying reversibility. Here, through a combination of operando electron diffraction measurements and ab initio simulations at the atomic and electronic scales, we identify key factors that govern the severe structural changes during alloying-dealloying reactions in BP. P-P bonds of three-bond P atoms are continuously broken during lithiation, generating two-bond P atoms with a high ability to accept inserted electrons and Li ions. Consequently, the pristine layered structure in BP is transformed to P7 cages in Li3P7, which then evolve to chain configurations in LiP and finally to isolated P atoms in Li3P. Specifically, the preferential formation of the P7 cage results from its lowest binding energy with three Li ions compared to other cage isomers. Furthermore, only LiP can be reversibly transformed to the crystalline structure of Li3P7 during charge, but it is thermodynamically favorable for Li3P7 and Li3P intermediates to be delithiated to amorphous structures. Our findings offer unique insights into the alloying mechanisms and deepen the fundamental understanding of alloying anode systems.

High-Performance Low-Iridium Catalyst for Water Oxidation: Breaking Long-Ranged Order of IrO2 by Neodymium Doping.

Exploring efficacious low-Irelectrocatalysts for oxygen evolution reaction (OER) is crucial for large-scale application of proton exchange membrane water electrolysis (PEMWE). Herein, an efficient non-precious lanthanide-metal-doped IrO2 electrocatalyst is presented for OER catalysis by doping large-ionic-radius Nd into IrO2 crystal. The doped Nd breaks the long-ranged order structure by triggering the strain effect and thus inducing an atomic rearrangement of Nd─IrO2 involving the forming of Nd─O─Ir bonds along with an increased amount of oxygen vacancies (Ov), giving rise of a long-ranged disorder but a short-ranged order structure. The formed Nd─O─Ir bonds tailor the electronic structure of Ir, leading to a lowered d-band center that weakens intermediates absorption on Ir sites. Moreover, doping Nd triggers Nd─IrO2 to catalyze OER mainly through lattice oxygen mechanism (LOM) by activating lattice oxygen owing to abundant Ov. The optimal catalyst only requires a relatively low overpotential of 263 mV@10mA cm-2 with a high mass activity of 216.98 A gIr -1 (at 1.53V) (eightfold of commercial IrO2), and also shows a superior durability at 50mA cm-2 (20h) than commercial IrO2 (3h) due to the oxidation-suppressing effect induced by Nd doping. This work offers insights into designing high-performance low-Ir electrocatalysts for PEMWE application.

Molecular O2 Dimers and Lattice Instability in a Perovskite Electrocatalyst.

Structural degradation of oxide electrodes during the electrocatalytic oxygen evolution reaction (OER) is a major challenge in water electrolysis. Although the OER is known to induce changes in the surface layer, little is known about its effect on the bulk of the electrocatalyst and its overall phase stability. Here, we show that under OER conditions, a highly active SrCoO3-x electrocatalyst develops bulk lattice instability, which results in the formation of molecular O2 dimers inside the bulk and nanoscale amorphization induced via chemo-mechanical coupling. Using high-resolution resonant inelastic X-ray scattering and first-principles calculations, we unveil the potential-dependent evolution of lattice oxygen inside the perovskite and demonstrate that O2 dimers are stable in a densely packed crystal lattice, thus challenging the assumption that O2 dimers require sufficient interatomic spacing. We also show that the energy cost of local atomic rearrangements in SrCoO3-x becomes very low under the OER conditions, leading to an unusual amorphization under intercalation-induced stress. As a result, we propose that the amorphization energy can be calculated from the first principles and can be used to assess the stability of electrocatalysts. Our study demonstrates that extreme oxidation of electrocatalysts under OER can intrinsically destabilize the lattice and result in bulk anion redox and disorder, suggesting why some oxide materials are unstable and develop a thick amorphous layer under water electrolysis conditions.