Surface Reconstruction of Perovskites for Water Oxidation: The Role of Initial Oxides’ Bulk Chemistry

Quantifying Dynamic Changes of Oxygen Nonstoichiometry and Formation of Surface Phases of SrCoOx Electrocatalysts by Operando Characterizations

Perovskite electrocatalysts like strontium cobaltite (SrCoOx, denoted as SCO) experience dynamic changes in both surface and bulk during the oxygen evolution reaction (OER), rather than remaining static. This dynamic, electrochemically driven evolution in composition, structure, and ionic defects (e.g., oxygen vacancies) can strongly impact the OER activity and stability. Yet, the current lack of quantitative information on these processes impedes a precise and predictive evaluation of the individual and combined effect of both bulk and surface transformations. Here, using epitaxial SCO thin films as a model system, we demonstrate that SCO is a bulk and surface redox-active OER electrocatalyst that undergoes a bulk phase transition via electrochemically induced oxygen intercalation, as well as a surface phase transition toward Co (oxy-)hydroxide. Specifically, applying a suite of operando and ex situ characterization we established a reliable relationship between oxygen nonstoichiometry, optical density, and conductivity as a function of applied potentials. We further accurately quantify the evolution of oxygen stoichiometry in the SCO bulk and the thickness of the formed surface secondary phase. Our work provides a reliable and generalizable workflow and operando characterization toolbox for quantitative assessment of surface and bulk transformations in oxygen-deficient perovskite electrocatalysts.

Perovskite Type ABO3 Oxides in Photocatalysis, Electrocatalysis, and Solid Oxide Fuel Cells: State of the Art and Future Prospects

Since photocatalytic and electrocatalytic technologies are crucial for tackling the energy and environmental challenges, significant efforts have been put into exploring advanced catalysts. Among them, perovskite type ABO3 oxides show great promising catalytic activities because of their flexible physical and chemical properties. In this review, the fundamentals and recent progress in the synthesis of perovskite type ABO3 oxides are considered. We describe the mechanisms for electrocatalytic oxygen evolution reactions (OER), oxygen reduction reactions (ORR), hydrogen evolution reactions (HER), nitrogen reduction reactions (NRR), carbon dioxide reduction reactions (CO2RR), and metal-air batteries in details. Furthermore, the photocatalytic water splitting, CO2 conversion, pollutant degradation, and nitrogen fixation are reviewed as well. We also stress the applications of perovskite type ABO3 oxides in solid oxide fuel cells (SOFs). Finally, the optimization of perovskite type ABO3 oxides for applications in various fields and an outlook on the current and future challenges are depicted. The aim of this review is to present a broad overview of the recent advancements in the development of perovskite type ABO3 oxides-based catalysts and their applications in energy conversion and environmental remediation, as well as to present a roadmap for future development in these hot research areas.

Vector substrate design for grain boundary engineering: boosting oxygen evolution reaction performance in LaNiO3

The realization and subsequent control of emerging structural and electronic phases in solid materials has significantly enhanced their functionalities, thereby benefiting both fundamental research and practical applications. The grain boundary (GB), as a transitional region within the crystal lattice, exhibits atomic shifts and distinct energy profiles. These unique characteristics offer a promising avenue for the discovery of advanced active catalytic phases for carbon, oxygen, hydrogen, and nitrogen evolution/reduction reactions. However, the challenge lies in isolating and controlling the quantity of grain boundaries in conventional catalysts, which hinders the identification of their functional attributes. In this study, we successfully engineered the (001)/(110), (001)/(111), and (110)/(111) GBs in LaNiO3 (LNO) using a vector substrate design approach. Subsequent evaluation of these GBs in the oxygen evolution reaction (OER) revealed that LNO (110)/(111) exhibited the fastest surface reconstruction into Ni oxyhydroxide and the most superior OER performance, achieving 2.36 mA cm-2 at η = 400 mV. This outstanding performance is attributed to its strongest Ni-O covalency and the proximity of the O 2p-band center to the Fermi level. This research aims to address the challenges associated with isolating and controlling GBs for optimized OER performance, while also providing comprehensive insights into the relationship between GBs and surface reconstruction behaviors.

Rational design of precatalysts and controlled evolution of catalyst-electrolyte interface for efficient hydrogen production

The concept of precatalyst is widely accepted in electrochemical water splitting, but the role of precatalyst activation and the resulted changes of electrolyte composition is often overlooked. Here, we elucidate the impact of potential-dependent changes for both precatalyst and electrolyte using Co2Mo3O8 as a model system. Potential-dependent reconstruction of Co2Mo3O8 precatalyst results in an electrochemically stable Co(OH)2@Co2Mo3O8 catalyst and additional Mo dissolved as MoO42- into electrolyte. The Co(OH)2/Co2Mo3O8 interface accelerates the Volmer reaction and negative potentials induced Mo2O72- (from MoO42-) further enhances proton adsorption and H2 desorption. Leveraging these insights, the well-designed MoO42-/Mo2O72- modified Co(OH)2@Co2Mo3O8 catalyst achieves a Faradaic efficiency of 99.9% and a yield of 1.85 mol h-1 at -0.4 V versus reversible hydrogen electrode (RHE) for hydrogen generation. Moreover, it maintains stable over one month at approximately 100 mA cm-2, highlighting its industrial suitability. This work underscores the significance of understanding on precatalyst reconstruction and electrolyte evolution in catalyst design.

Leveraging Iron in the Electrolyte to Improve Oxygen Evolution Reaction Performance: Fundamentals, Strategies, and Perspectives

Electrochemical water splitting is a pivotal technology for storing intermittent electricity from renewable sources into hydrogen fuel. However, its overall energy efficiency is impeded by the sluggish oxygen evolution reaction (OER) at the anode. In the quest to design high-performance anode catalysts for driving the OER under non-acidic conditions, iron (Fe) has emerged as a crucial element. Although the profound impact of adventitious electrolyte Fen+ species on OER catalysis had been reported forty years ago, recent interest in tailoring the electrode-electrolyte interface has spurred studies on the controlled introduction of Fe ions into the electrolyte to improve OER performance. During the catalytic process, scenarios where the rate of Fen+ deposition on a specific host material outruns that of dissolution pave the way for establishing highly efficient and dynamically stable electrochemical interfaces for long-term steady operation. This review systematically summarizes recent endeavors devoted to elucidating the behaviors of in situ Fe(aq.) incorporation, the role of incorporated Fe sites in the OER, and critical factors influencing the interplay between the electrode surface and Fe ions in the electrolyte environment. Finally, unexplored issues related to comprehensively understanding and leveraging the dynamic exchange of Fen+ at the interface for improved OER catalysis are summarized.

Decorated and reconstructed perovskite-oxide electrodes for oxygen electrocatalysis and Zn-air batteries

Although decorated nanoparticles offer a great potential to generate extra active sites, their preparation usually requires time- and energy-consuming approaches. We report the remarkable activity and durability augmentation for the oxygen evolution reaction (OER) via effective and facile on-site electrochemical manipulation, using LaNiO3 as a model catalyst. When compared to the pristine LaNiO3, the electrochemically manipulated LaNiO3 cycled in Fe3+-containing 0.1 M KOH (i.e., E-LNO+Fe) exhibits an almost three-fold improvement in current density at 1.65 V. It is experimentally and theoretically shown that the electrochemical manipulation leads to the creation of defective LaNiO3-δ and NiO on the surfaces, which accelerate phase transformation to (oxy)hydroxides and hence the OER. Furthermore, a Zn-air battery assembled with E-LNO+Fe has demonstrated superior activity by presenting 171 mW cm-2. Thus, our work demonstrates that substantial performance increases may be achieved by decorating and reconstructing perovskite-oxide electrodes via on-site electrochemical modification.

Dynamic Self-Healing of the Reconstructed Phase in Perovskite Oxides for Efficient and Stable Electrocatalytic OER

Neither electrocatalytic activity nor structural stability is inconsequential in water electrolysis. Unfortunately, they have to be compromised in practice, especially in the anodic redox chemistry of lattice oxygen. Herein, the discovery of a La1- xCexFeO3 perovskite is presented which shows both good stability and high catalytic activity. Using advanced operando characterizations, it is identified that the self-healing evolution of the La1- xCexFeO3 perovskite plays a key role during water oxidation in the lattice oxygen-mediated mechanism (LOM) pathway. Unlike irreversible reconstruction, the formation of reconstructed active-phase α-FeOOH is reversed by re-crystallization of surface La1- xCexFeO3 upon return to noncatalytic conditions. The self-healing transformation of the α-FeOOH termination layer on the stable La1- xCexFeO3 core imparts remarkable long-term stability as well as excellent electrocatalytic performance. As a result, a composition La0.9Ce0.1FeO3@FeOOH is designed that exhibits ultralow overpotentials of 257 and 312 mV to achieve 10 and 100 mA cm-2, respectively. The findings provide insight into self-healing behavior toward engineering perovskite oxides for efficient and stable oxygen electrocatalysis.

Vacancy-Activated Surface Reconstruction of Perovskite Nanofibers for Efficient Lattice Oxygen Evolution

Inducing the surface reconstruction of perovskites to promote the oxygen evolution reaction (OER) has garnered increasing attention due to the enhanced catalytic activities caused by the self-reconstructed electroactive species. However, the high reconstruction potential, limited electrolyte penetration, and accessibility to the perovskite surface greatly hindered the formation of self-reconstructed electroactive species. Herein, trace Ce-doped La0.95Ce0.05Ni0.8Fe0.2O3-δ nanofibers (LCNF-NFs) were synthesized via electrospinning and postcalcination to boost surface reconstruction. The upshift of the O 2p band center induced by the rich oxygen vacancies lowered the reconstruction potential, and the specific one-dimensional nanostructure effectively enabled enhanced electrolyte accessibility and permeation to the LCNF-NFs. These collectively caused massive in situ generation of self-reconstructed electroactive Ni/FeO(OH) species on the surface. As a result, the surface-reconstructed LCNF-NFs exhibited accelerated lattice kinetics with a comparatively lower Tafel slope of 50.12 mV dec-1, together with an overpotential of only 342.3 mV to afford a current density of 10 mA cm-2 in 0.1 M KOH, which is superior to that of pristine LaNi0.8Fe0.2O3-δ nanoparticles (NPs) and the same stoichiometric La0.95Ce0.05Ni0.8Fe0.2O3-δ NPs, commercial IrO2, and most of the state-of-the-art OER electrocatalysts. This study provided deep insights into the surface reconstruction behaviors induced by oxygen defects and an intellectual approach for constructing electroactive species in situ on perovskites for various energy storage and conversion devices.

Deciphering Water Oxidation Catalysts: The Dominant Role of Surface Chemistry over Reconstruction Degree in Activity Promotion

Water splitting hinges crucially on the availability of electrocatalysts for the oxygen evolution reaction. The surface reconstruction has been widely observed in perovskite catalysts, and the reconstruction degree has been often correlated with the activity enhancement. Here, a systematic study on the roles of Fe substitution in activation of perovskite LaNiO3 is reported. The substituting Fe content influences both current change tendency and surface reconstruction degree. LaNi0.9Fe0.1O3 is found exhibiting a volcano-peak intrinsic activity in both pristine and reconstructed among all substituted perovskites in the LaNi1-xFexO3 (x = 0.00, 0.10, 0.25, 0.50, 0.75, 1.00) series. The reconstructed LaNi0.9Fe0.1O3 shows a higher intrinsic activity than most reported NiFe-based catalysts. Besides, density functional theory calculations reveal that Fe substitution can lower the O 2p level, which thus stabilize lattice oxygen in LaNi0.9Fe0.1O3 and ensure its long-term stability. Furthermore, it is vital interesting that activity of the reconstructed catalysts relied more on the surface chemistry rather than the reconstruction degree. The effect of Fe on the degree of surface reconstruction of the perovskite is decoupled from that on its activity enhancement after surface reconstruction. This finding showcases the importance to customize the surface chemistry of reconstructed catalysts for water oxidation.

Long-term leaching kinetics and solution chemistry of aqueous BaTiO3 powder suspensions: a numerical model supported experiment

The advent of lead-free perovskite materials with favorable toxicity profiles has made them candidates for in vivo and environmental applications. However, their tendency to leach A-site cations raises concerns about toxicity, catalytic efficiency, and slurry properties. The present study investigates the long-term leaching kinetics of BaTiO3 powders over 31 days in aqueous solutions of varying pH levels. Using ICP-MS analysis and a numerical model based on the Unreacted Shrinking Core (USC) principle. The study extends the understanding of BaTiO3 stability beyond previously reported timeframes. The findings highlight the material's long-term stability, with implications for biomedical and environmental applications.

Local hydroxide ion enrichment at the inner surface of lacunaris perovskite nanotubes facilitates the oxygen evolution reaction

Numerous strategies have been devised to optimize the intrinsic activity of perovskite oxides for the oxygen evolution reaction (OER). However, conventional synthetic routes typically yield limited numbers of active sites and low mass activities. More critically, the sluggish mass transfer poses a huge challenge, particularly under high polarization conditions, which impedes the overall reaction kinetics. Herein, lacunaris La0.5Pr0.25Ba0.25Co0.8Ni0.2O3-δ nanotubes (LPBCN-NTs) were prepared via electrospinning and post-annealing, which exhibited a small overpotential of 358.8 mV at 10 mA cm-2 and a lower Tafel slope of 71.46 mV dec-1, superior to the values for the same stoichiometric LPBCN nanoparticles and solid nanofibers, state-of-the-art counterparts and commercial IrO2. Density functional theory calculations revealed that the surface oxygen vacancies in LPBCN-NTs significantly lowered the OH- adsorption energy, while finite element analysis indicated that the precisely constructed lacunaris NT structure enriched the OH- concentration at its inner surface by an order of magnitude, both of which collectively resulted in accelerated OER kinetics. This study clarifies the underlying mechanism of how the lacunaris nanotubular architecture and the surface oxygen vacancies of perovskite oxides affect heterocatalysis, which undoubtedly paves the way to handling the long-standing issues of sluggish mass transfer rates and poor intrinsic catalytic activity.

Elevated Water Oxidation by Cation Leaching Enabled Tunable Surface Reconstruction

Water electrolysis is one promising and eco-friendly technique for energy storage, yet its overall efficiency is hindered by the sluggish kinetics of oxygen evolution reaction (OER). Therefore, developing strategies to boost OER catalyst performance is crucial. With the advances in characterization techniques, an extensive phenomenon of surface structure evolution into an active amorphous layer was uncovered. Surface reconstruction in a controlled fashion was then proposed as an emerging strategy to elevate water oxidation efficiency. In this work, Cr substitution induces the reconstruction of NiFexCr2-xO4 during cyclic voltammetry (CV) conditioning by Cr leaching, which leads to a superior OER performance. The best-performed NiFe0.25Cr1.75O4 shows a ~1500 % current density promotion at overpotential η=300 mV, which outperforms many advanced NiFe-based OER catalysts. It is also found that their OER activities are mainly determined by Ni : Fe ratio rather than considering the contribution of Cr. Meanwhile, the turnover frequency (TOF) values based on redox peak and total mass were obtained and analysed, and their possible limitations in the case of NiFexCr2-xO4 are discussed. Additionally, the high activity and durability were further verified in a membrane electrode assembly (MEA) cell, highlighting its potential for practical large-scale and sustainable hydrogen gas generation.

Research progress on layered metal oxide electrocatalysts for an efficient oxygen evolution reaction

Hydrogen, highly valued for its pristine cleanliness and remarkable efficiency as an emerging energy source, is anticipated to ascend to a preeminent status within the forthcoming energy landscape. Electrocatalytic water splitting is considered a pivotal, eco-friendly, and sustainable strategy for hydrogen production. The substantial energy consumption stemming from oxygen evolution side reactions significantly impedes the commercial viability of water electrolysis. Consequently, the pursuit of a cost-effective and efficacious oxygen evolution reaction (OER) catalyst stands as an imperative strategy for realizing hydrogen production via water electrolysis. Layered metal oxides, owing to their robust anisotropic properties, versatile adjustability, and extensive surface area, have emerged as suitable candidates for OER catalysts. However, owing to the distinctive attributes of layered metal oxides, ongoing investigations into these materials are slightly fragmented, lacking universal consensus. This article comprehensively surveys the recent advancements in layered metal oxide-based OER catalysts, categorized into single metal oxides, alkali cobalt oxides, perovskites, and miscellaneous metal oxides. Initially, the main OER intermediate reaction steps of layered metal oxides are scrutinized. Subsequently, the design, mechanism, and application of several pivotal layered metal oxides in the OER are systematically delineated. Finally, a summary is provided, alongside the proposal of future research trajectories and challenges encountered by layered metal oxides, with the aspiration that this paper may serve as a valuable reference for scholars in the field.

Reversible Hydrogen Electrode (RHE) Scale Dependent Surface Pourbaix Diagram at Different pH

In the analysis of electrocatalysis mechanisms and the design of catalysts, the effect of electrochemistry-induced surface coverage is a critical consideration that should not be overlooked. The surface Pourbaix diagram emerges as a fundamental tool in this context, providing essential insights into the surface coverage of adsorbates generated via electrochemical potential-driven water activation. A classic surface Pourbaix diagram considers the pH effects by correcting the free energy of H+ ions by the concentration-dependent term: -kBT ln(10) × pH, which is independent of the reversible hydrogen electrode (RHE) scale. However, this is sometimes inconsistent with the experimentally observed potential-dependent surface coverage at an RHE scale, especially under high-pH conditions. Here, we derived the pH-dependent surface Pourbaix diagram at an RHE scale by considering the energetics computed by density functional theory with the Bayesian Error Estimation Functional with van der Waals corrections (BEEF-vdW), the electric field effects, the derived adsorption-induced dipole moment and polarizability, and the potential of zero-charge. Using Pt(111) as the typical example, we found that the surface coverage predicted by the proposed RHE-dependent surface Pourbaix diagram can significantly minimize the discrepancy between theory and experimental observations, especially under neutral-alkaline, moderate-potential conditions. This work provides a new methodology and establishes guidelines for the precise analysis of the surface coverage prior to the evaluation of the activity of an electrocatalyst.

The Promising Seesaw Relationship Between Activity and Stability of Ru-Based Electrocatalysts for Acid Oxygen Evolution and Proton Exchange Membrane Water Electrolysis

The development of electrocatalysts that are not reliant on iridium for efficient acid-oxygen evolution is a critical step towards the proton exchange membrane water electrolysis (PEMWE) and green hydrogen industry. Ruthenium-based electrocatalysts have garnered widespread attention due to their remarkable catalytic activity and lower commercial price. However, the challenge lies in balancing the seesaw relationship between activity and stability of these electrocatalysts during the acid-oxygen evolution reaction (OER). This review delves into the progress made in Ru-based electrocatalysts with regards to acid OER and PEMWE applications. It highlights the significance of customizing the acidic OER mechanism of Ru-based electrocatalysts through the coordination of adsorption evolution mechanism (AEM) and lattice oxygen oxidation mechanism (LOM) to attain the ideal activity and stability relationship. The promising tradeoffs between the activity and stability of different Ru-based electrocatalysts, including Ru metals and alloys, Ru single-atomic materials, Ru oxides, and derived complexes, and Ru-based heterojunctions, as well as their applicability to PEMWE systems, are discussed in detail. Furthermore, this paper offers insights on in situ control of Ru active sites, dynamic catalytic mechanism, and commercial application of PEMWE. Based on three-way relationship between cost, activity, and stability, the perspectives and development are provided.

Enhanced OER Performance and Dynamic Transition of Surface Reconstruction in LaNiO3 Thin Films with Nanoparticles Decoration

In an electrocatalytic process, the cognition of the active phase in a catalyst has been regarded as one of the most vital issues, which not only boosts the fundamental understanding of the reaction procedure but also guides the engineering and design for further promising catalysts. Here, based on the oxygen evolution reaction (OER), the stepwise evolution of the dominant active phase is demonstrated in the LaNiO3 (LNO) catalyst once the single-crystal thin film is decorated by LNO nanoparticles. It is found that the OER performance can be dramatically improved by this decoration, and the catalytic current density at 1.65 V can be enhanced by ≈1000% via ≈109 cm-2 nanoparticle adhesion after extracting the contribution of surface enlargement. Most importantly, a transition of the active phase from LNO to NiOOH via surface reconstruction with the density of LNO nanoparticles is demonstrated. Several mechanisms in terms of this active phase transition are discussed involving lattice orientation-induced change of the surface energy profile, the lattice oxygen participation, and the A/B-site ions leaching during OER cycles. This study suggests that the active phases in transition metal-based OER catalysts can transform with morphology, which should be corresponding to distinct engineering strategies.

Ex Situ Reconstruction-Shaped Ir/CoO/Perovskite Heterojunction for Boosted Water Oxidation Reaction

The oxygen evolution reaction (OER) is the performance-limiting step in the process of water splitting. In situ electrochemical conditioning could induce surface reconstruction of various OER electrocatalysts, forming reactive sites dynamically but at the expense of fast cation leaching. Therefore, achieving simultaneous improvement in catalytic activity and stability remains a significant challenge. Herein, we used a scalable cation deficiency-driven exsolution approach to ex situ reconstruct a homogeneous-doped cobaltate precursor into an Ir/CoO/perovskite heterojunction (SCI-350), which served as an active and stable OER electrode. The SCI-350 catalyst exhibited a low overpotential of 240 mV at 10 mA cm^-2 in 1 M KOH and superior durability in practical electrolysis for over 150 h. The outstanding activity is preliminarily attributed to the exponentially enlarged electrochemical surface area for charge accumulation, increasing from 3.3 to 175.5 mF cm^-2. Moreover, density functional theory calculations combined with advanced spectroscopy and ¹⁸O isotope-labeling experiments evidenced the tripled oxygen exchange kinetics, strengthened metal-oxygen hybridization, and engaged lattice oxygen oxidation for O-O coupling on SCI-350. This work presents a promising and feasible strategy for constructing highly active oxide OER electrocatalysts without sacrificing durability.

In Situ Activation Endows Orthorhombic Fluorite-Type Samarium Iridium Oxide with Enhanced Acidic Water Oxidation

Developing electrochemical catalysts for acidic water oxidation with improved activity and stability has been the key to the further popularization of proton exchange membrane electrolyzers. In this work, an orthorhombic fluorite-type samarium iridium oxide (Sm3IrO7) catalyst is synthesized by a simple solid-state reaction. After in situ activation, the as-prepared Sm3IrO7 exhibits higher mass activity and durability than that of commercial IrO2. The in-depth analyses indicate the formation of amorphous IrOx species on the surface to evolve to a new heterostructure IrOx/Sm3IrO7, along with Sm leaching during the in situ activation process. More importantly, strong electronic interactions exist between newborn IrOx species and remaining Sm3IrO7, leading to the compressed Ir-O bonds in IrOx compared to commercial IrO2, thus reducing the energy barrier for oxygen evolution reaction (OER) intermediates to improve the OER process. Based on the above-mentioned analyses, it is speculated that the actual active species for enhanced acidic water oxidation should be IrOx/Sm3IrO7, rather than Sm3IrO7 itself. Theoretical calculations confirm that the optimal energy level path of IrOx/Sm3IrO7 follows the lattice oxygen mechanism, and the energy level of surface Ir 5d orbitals is lower than O 2p orbitals in IrOx/Sm3IrO7, enabling it a superior OER activity.

Turning Electrocatalytic Activity Sites for the Oxygen Evolution Reaction on Brownmillerite to Oxyhydroxide

One of the major challenges that hinder the practical application of water electrolysis lies in the design of advanced electrocatalysts toward the anodic oxygen evolution reaction (OER). In this work, a pure Co-based precatalyst of CoOOH/brownmillerite derived from the surface activation of brownmillerite by a surface acid etching method exhibits high activity and stable electrical properties toward the OER. Different from oxyhydroxide derived from in situ surface reconstruction during the electrochemical process, the growth of highly crystalline CoOOH from the brownmillerite surface enables rational control over the surface/bulk structure as well as the concentration of active sites, and this structure can be well maintained and serve as highly active sites. The catalyst shows a low overpotential of 320 mV to obtain 10 mA cm^-2 and high stability in an alkaline electrolyte for the OER, which is comparable to the majority of Co-based electrocatalysts. Moreover, the appropriate interfacial interaction of the composite catalysts greatly contributes to the hydroxide insertion to improve water oxidation ability. This work proposes an effective strategy to develop high-performance metal oxide-based materials for the OER.

Dynamic Electrochemical Interfaces for Energy Conversion and Storage

Electrochemical energy conversion and storage are central to developing future renewable energy systems. For efficient energy utilization, both the performance and stability of electrochemical systems should be optimized in terms of the electrochemical interface. To achieve this goal, it is imperative to understand how a tailored electrode structure and electrolyte speciation can modify the electrochemical interface structure to improve its properties. However, most approaches describe the electrochemical interface in a static or frozen state. Although a simple static model has long been adopted to describe the electrochemical interface, atomic and molecular level pictures of the interface structure should be represented more dynamically to understand the key interactions. From this perspective, we highlight the importance of understanding the dynamics within an electrochemical interface in the process of designing highly functional and robust energy conversion and storage systems. For this purpose, we explore three unique classes of dynamic electrochemical interfaces: self-healing, active-site-hosted, and redox-mediated interfaces. These three cases of dynamic electrochemical interfaces focusing on active site regeneration collectively suggest that our understanding of electrochemical systems should not be limited to static models but instead expanded toward dynamic ones with close interactions between the electrode surface, dissolved active sites, soluble species, and reactants in the electrolyte. Only when we begin to comprehend the fundamentals of these dynamics through operando analyses can electrochemical conversion and storage systems be advanced to their full potential.

Electrochemistry in Magnetic Fields

Developing new strategies to advance the fundamental understanding of electrochemistry is crucial to mitigating multiple contemporary technological challenges. In this regard, magnetoelectrochemistry offers many strategic advantages in controlling and understanding electrochemical reactions that might be tricky to regulate in conventional electrochemical fields. However, the topic is highly interdisciplinary, combining concepts from electrochemistry, hydrodynamics, and magnetism with experimental outcomes that are sometimes unexpected. In this Review, we survey recent advances in using a magnetic field in different electrochemical applications organized by the effect of the generated forces on fundamental electrochemical principles and focus on how the magnetic field leads to the observed results. Finally, we discuss the challenges that remain to be addressed to establish robust applications capable of meeting present needs.

Size Effects of Electrocatalysts: More Than a Variation of Surface Area

The efficiency of electrocatalytic reactions has been continuously improved in recent years due to the great effort in the development of electrocatalysts. A popular strategy is engineering the size of electrocatalysts for better electrochemical performance and lower cost. Nanosized electrocatalysts with high specific surface area have been widely used in state-of-the-art electrochemical devices such as fuel cells. From an engineering aspect, nanosizing electrocatalysts increases the surface area of the electrode and improves the electrode/device performance. Beyond an engineering scope, this perspective highlights the size effects of certain scientific fundamentals in electrocatalytic reactions. The paper summarizes the representative examples in studying the size effects of electrocatalysts and sheds light on the change of intrinsic properties of electrocatalysts caused by the size variation. The size effects of electrocatalysts should be investigated in terms of both engineering and fundamental aspects; that is, the observed activity change is more than a result of surface area variation, and it is interesting to investigate the link between the intrinsic activity and the properties of the catalysts.