High Overpotentials Research Articles

Facile Synthesis of CuxS Electrocatalysts for CO2 Conversion into Formate and Study of Relations Between Cu and S with the Selectivity

AbstractThe conversion of CO2 into formate (HCOO−), a techno‐economically feasible product, can be achieved using earth‐abundant CuxS electrocatalysts, but questions remain regarding how catalyst structure, composition, and reaction environment influence product selectivity. A novel synthesis method based on electrodeposition of Cu foam and its subsequent sulfidation via immersion in sulfur saturated toluene solution resulted in CuxS foams. Catalytic activity studies found that HCOO− selectivity is dependent on electrochemical activation at higher overpotentials. To understand the effects of activation, determine the active forms of the catalysts, and identify the role of sulfur, the electrodes are carefully characterized as well as gaseous and sulfur dissolved in electrolyte. This included study of the effects of intentional addition of solution sulfur species, identification of the sulfur loss, determination of the electrode composition and relating sulfur speciation to observed product selectivity. It is found that residual sulfur stabilizes Cu+ during electrolysis at potentials favoring HCOO− production, in contrast to pristine Cu that undergoes complete reduction and shows poor HCOO− selectivity. Sulfur in both the catalyst and dissolved in electrolyte are of dynamic nature, and surface residues of SO42− species are identified in all activated catalysts which correspond with enhanced HCOO− production.

Mechanistic insights into multimetal synergistic and electronic effects in a hexanuclear iron catalyst with a [Fe3(μ3-O)(μ2-OH)]2 core for enhanced water oxidation.

Multinuclear molecular catalysts mimicking natural photosynthesis have been shown to facilitate water oxidation; however, such catalysts typically operate in organic solutions, require high overpotentials and have unclear catalytic mechanisms. Herein, a bio-inspired hexanuclear iron(III) complex I, Fe6(μ3-O)2(μ2-OH)2(bipyalk)2(OAc)8 (H2bipyalk = 2,2'-([2,2'-bipyridine]-6,6'-diyl)bis(propan-2-ol); OAc = acetate) with desirable water solubility and stability was designed and used for water oxidation. Our results showed that I has high efficiency for water oxidation via the water nucleophilic attack (WNA) pathway with an overpotential of only ca. 290 mV in a phosphate buffer of pH 2. Importantly, key high-oxidation-state metal-oxo intermediates formed during water oxidation were identified by in situ spectroelectrochemistry and oxygen atom transfer reactions. Theoretical calculations further supported the above identification. Reversible proton transfer and charge redistribution during water oxidation enhanced the electron and proton transfer ability and improved the reactivity of I. Here, we have shown the multimetal synergistic and electronic effects of catalysts in water oxidation reactions, which may contribute to the understanding and design of more advanced molecular catalysts.

Li2MoO4 tailored Anion‐enhanced Solvation Sheath Layer Promotes Solution‐phase Mediated Li‐O2 Batteries

The high overpotential of Li‐O2 batteries (LOBs) is primarily triggered by sluggish charge transfer kinetics at the reaction interfaces. A typical LiBr redox mediator (RM) catalyst can effectively reduce the battery’s overpotential. However, it is prone to shuttling and corroding the Li anode, leading to RM loss and reduced energy efficiency. To address these challenges, we introduced Li2MoO4 into the LiBr‐containing electrolyte to promote the solution‐phase mediated LOBs. This addition tailors the anion‐enhanced Li+ solvation sheath layer and forms a robust anion‐derived solid electrolyte interphases (SEI) on the Li anode. The robust SEI effectively mitigates the corrosion of soluble Br3‐/Br2 and attacks by highly reactive oxygen species. Additionally, the dispersed and high‐density Li2MoO4 exhibits strong adsorption capabilities for O2/LiO2 and Br‐related species during the discharge/charge process, thereby promoting the growth and decomposition of Li2O2 in the solution phase and inhibiting the shuttle effect of Br‐related species in LOBs. Consequently, the LOBs demonstrate exceptional cycling stability (415 cycles) and high energy efficiency (86.2%), paving the way for the sustainable development and practical application of these battery systems.

Li2MoO4 tailored Anion-enhancedSolvation Sheath Layer Promotes Solution-phase Mediated Li-O2 Batteries.

The high overpotential of Li-O2 batteries (LOBs) is primarily triggered by sluggish charge transfer kinetics at the reaction interfaces. A typical LiBr redox mediator (RM) catalyst can effectively reduce the battery's overpotential. However, it is prone to shuttling and corroding the Li anode, leading to RM loss and reduced energy efficiency. To address these challenges, we introduced Li2MoO4 into the LiBr-containing electrolyte to promote the solution-phase mediated LOBs. This addition tailors the anion-enhanced Li+ solvation sheath layer and forms a robust anion-derived solid electrolyte interphases (SEI) on the Li anode. The robust SEI effectively mitigates the corrosion of soluble Br3-/Br2 and attacks by highly reactive oxygen species. Additionally, the dispersed and high-density Li2MoO4 exhibits strong adsorption capabilities for O2/LiO2 and Br-related species during the discharge/charge process, thereby promoting the growth and decomposition of Li2O2 in the solution phase and inhibiting the shuttle effect of Br-related species in LOBs. Consequently, the LOBs demonstrate exceptional cycling stability (415 cycles) and high energy efficiency (86.2%), paving the way for the sustainable development and practical application of these battery systems.

Coupled Lattice‐Expanded Ni and MoO2 Array for Efficient Alkaline Hydrogen Evolution

AbstractTransition metal oxides have attracted much attention due to their good electrical conductivity, high chemical stability, and easy electronic structure modulation. However, it is still a great challenge to solve the problems of sluggish reaction kinetics and high overpotential in the alkaline hydrogen evolution reaction (HER) due to their poor intrinsic activity. Herein, a lattice‐expanded Ni‐decorated MoO2 array (Ni‐MoO2‐700) catalyst is prepared for the alkaline HER. Unlike most of the reported literature, the decoration of metal heteroatoms may lead to lattice expansion of the carrier catalyst. In contrast, lattice expansion of Ni is also achieved by adjusting the annealing temperature in this work. The Ni‐induced lattice‐expanding effect can not only modulate the electronic structure of the catalyst but also accelerate electron transfer during the reaction, thus increasing its intrinsic activity for the HER. As a result, Ni‐MoO2‐700 exhibits significantly enhanced catalytic activity with an overpotential of 74.9 mV at 10 mA cm−2 in 1.0 m KOH, which is far superior to that of most of the reported advanced Ni‐ and Mo‐based materials. This work provides deep intrinsic insight and a great opportunity to design efficient transition metal oxide catalysts for the alkaline HER.

Probing the effect of Se doping in S cathode for high performance Mg-S batteries

Magnesium-sulfur (Mg-S) batteries present an attractive option as a new type of energy storage device given their high energy density, safety and the use of low-cost original materials. However, magnesium polysulfide (MgPS) is susceptible to dissolution and shuttling, and the insulating nature of sulfur and MgS leads to high overpotentials and low columbic efficiencies. The selenium-sulfur system is noted to offer enhanced electronic conductivity and improved sulfur utilization. In this study, S K-edge X-ray absorption near-edge structure (XANES) spectra demonstrate that Se doping mitigates irreversibility in Mg-S batteries. Mg-K spectra demonstrate that Se dopants induce local negative charges on S, strengthening the Mg-S bond compared to that of pure sulfur, thereby promoting Mg/Mg2+ redox reactions. Operando Raman spectroscopy was also used to reveal Mg-S0.9Se0.1/C battery redox mechanisms. Hence, kinetically favored S0.9Se0.1/C cathodes deliver an initial capacity of ∼1350 mAh·g−1 at 0.2C. Furthermore, separators modified with layered MoS2 entrap polysulfides, thereby postponing cell death. Thus, Mg-S battery with a S0.9Se0.1/C cathode and a MoS2@polypropylene (PP) separator exhibit a reversible capacity of ∼200 mAh·g−1 at 0.2C after 250 cycles, with a low fade rate of 4 mAh·g−1/cycle. This study delineates the overall impact of Se doped cathodes on Mg-S batteries. Moreover, the MoS2 modified separator provides a route to chemically immobilize MgPS and accelerate sulfur redox reactions, consequently enabling high capacities and sustained cycling.

Highly selective photocatalytic oxidation of CH4 to CH3OH: A theoretical study

Photooxidation of methane (CH4) in aqueous solution to generate high-value organic compounds is an effective way to replace traditional industrial methods. It is crucial to select catalysts that can avoid competitive reactions and achieve high selectivity. Using first principles calculations, a novel one-dimensional (1D) Ti3C2O2 nanoribbon (NR)/two-dimensional (2D) monolayer MoS2 (MS) heterojunction photocatalyst was ingenious designed in this work, which can achieve the oxidation of CH4 molecules and suppress the execution of competitive reactions. The results indicate that the constructed 1D NR exhibits semiconductor properties and its energy level position meet the requirements of photocatalytic oxidation for CH4. The heterojunction structure composed of NR and MS forms an efficient S-Scheme electron transfer mechanism under illumination, which not only provides sufficient internal driving force for CH4 oxidation, but also effectively avoids the competitive reaction between water molecules and photo-generated holes. Specifically, the photocatalysts exhibits high selectivity and low reaction overpotential for the generation of methanol (CH3OH). This study provides a new perspective for photocatalytic CH4 oxidation and demonstrates the potential application value of 1D MXene in the future field of photocatalysis.

Introducing a new model for solid-state batteries: Parameter estimation and sensitivity analysis on diffusion, concentration, and electrochemical kinetics

Despite their potential, solid-state batteries (SSBs) are challenging to optimize due to the complexity of their materials and the early stage of their modeling, especially compared to liquid-electrolyte technologies. Many existing models rely on empirical equations that cannot represent internal mass-transport and kinetic phenomena. Even studies based on mechanistic models often focus on theoretical explanations of experimental phenomena or generating hard-to-obtain experimental data. In this work, a simple yet versatile mechanistic model – able to simulate any battery composed of a metallic anode, solid electrolyte and intercalation cathode – is proposed and used in a parameter estimation routine to identify the material properties of a Li/LiPON/LiCoO2 battery. After validation, a parametric study is made to address how each material property impacts concentration profiles, discharge curves, overpotentials, and core key-performance indexes (KPIs) related to energy efficiency and battery capacity. Findings reveal that cathode diffusion is critical to enhancing Extraction Efficiency, in some cases reaching 98.9% of the theoretical capacity without enhancing any other parameter. In the case of Energy Efficiency being a priority over capacity, electrolyte diffusion and concentration showed a pivotal role, in the range of parameters studied, to increase Voltaic Efficiency up to 97.8%. Despite not directly affecting the Extraction Efficiency, it is discussed how high overpotentials caused by Electrolyte Concentration and Kinetic Constants still can harm battery capacity, for charge–discharge cycles limited by boundaries in electrical potential. Finally, studies simultaneously varying two or more parameters show that, despite extreme property enhancements (up to ca 500x higher than the standard case) indeed lead to exceptional results (up to 96.4% for Voltaic Efficiency and 98.9% for Extraction Efficiency), to use such materials at its full potential will result in other zones of the device usually neglected – such as the overpotentials from the metal anode or even the current collector – may become the new stumbling block, underscoring the significance of considering the battery as a holistic system that will inherently exhibit bottlenecks. This also implies, however, in the perpetual potential for enhancement across its components.

Citrate ions-modified NiFe layered double hydroxide for durable alkaline seawater oxidation

Seawater electrolysis taking advantage of coastal/offshore areas is acknowledged as a potential way of large-scale producing H2 to substitute traditional technology. However, anodic catalysts with high overpotentials and limited lifespans (caused by chloride-induced competitive chemical reactions) hinder the system of seawater electrolysis for H2 production. Herein, we present a citrate anion (CA) modified NiFe layered double hydroxide nanosheet array on nickel foam (NiFe LDH@NiFe-CA/NF), which serves as an efficient and stable electrocatalyst towards long-term alkaline seawater oxidation. It requires only a low overpotential of 387 mV to achieve a current density of 1000 mA cm−2, outperforming NiFe LDH/NF (414 mV). Moreover, NiFe LDH@NiFe-CA/NF exhibits continuous oxygen evolution testing for 300h at 1000 mA cm−2 due to its anti-corrosion characterization. Additionally, the fabricated cell can stably operate at 300 mA cm−2 (60 °C, 6 M KOH + seawater) and only require 1.69 V, achieving low energy consumption of seawater splitting.

Computational Insight into Transition Metal Atoms Anchored on B2C3P as Single‐Atom Electrocatalysts for Nitrogen Reduction Reaction

AbstractNH3 is not only an important chemical raw material but also a high‐energy storage chemical with zero carbon. Electrocatalytic nitrogen reduction reaction (NRR), which can be driven by clean electric energy under ambient conditions, has become a promising technology for NH3 synthesis due to its environmentally friendly properties. Because of the limitations of low yield and high overpotential, efficient catalysts are urgently needed to solve this problem. In this study, based on density functional theory method and high throughput screening strategy, the NRR was investigated on transition metal single atom anchored to 2D B2C3P surface (TM@B2C3P) as single‐atom catalysts (SACs). The results showed that V@B2C3P and Ti@B2C3P have good catalytic properties, and the limiting potentials were −0.10 and −0.24 V, respectively. Furthermore, the charge density difference and crystal orbital Hamilton population calculations demonstrated that the high catalytic activity can be attributed to the obvious charge transfer between TM@B2C3P and the adsorption intermediates. It is hoped that this work can play a certain role in exploring the application of SACs in NRR.

Boosting synergistic effects between PtGe nanoalloys and 2D materials for PEMFC applications

In the present work we have investigated the stability, CO poisoning tendency and HOR and ORR activities of small-sized monometallic Pt and bimetallic PtGe nanoclusters deposited on a series of 2D materials. By means of global minima search and mechanistic studies at the density functional theory (DFT) level with continuum implicit solvent, a screening of size, composition and support material has been carried out to obtain the optimal catalyst compositions that may boost the catalytic performance. Alloying and support effects work in two directions. On the one hand, the support increases the stability and modifies the electronic structure of the cluster via metal-support interaction. On the other hand, the cluster can change the electronic properties and catalytic activity of the support, which can be modulated with its size and composition. In addition, the 2D support assists pure Pt clusters in reducing the propensity to undergo CO poisoning, which can be further reduced by Ge alloying. This effect can be exploited to the point that the interaction with CO is not even favorable, as in Pt5Ge5/germanene, thus completely inhibiting the CO poisoning on the catalyst. Regarding the catalytic activities, all the catalysts studied in this work yield too high overpotentials for the ORR in acidic conditions, due to the presence of too oxophilic active sites which results in the overbinding of oxygenated species. However, the combination of Ge alloying and 2D support yield remarkable results in the HOR performance. The simultaneous tailoring of catalyst composition and support is demonstrated to be an effective strategy to successfully adjust the catalytic properties.

Concurrent oxygen evolution reaction pathways revealed by high-speed compressive Raman imaging.

Transition metal oxides are state-of-the-art materials for catalysing the oxygen evolution reaction (OER), whose slow kinetics currently limit the efficiency of water electrolysis. However, microscale physicochemical heterogeneity between particles, dynamic reactions both in the bulk and at the surface, and an interplay between particle reactivity and electrolyte makes probing the OER challenging. Here, we overcome these limitations by applying state-of-the-art compressive Raman imaging to uncover concurrent bias-dependent pathways for the OER in a dense, crystalline electrocatalyst, α-Li2IrO3. By spatially and temporally tracking changes in stretching modes we follow catalytic activation and charge accumulation following ion exchange under various electrolytes and cycling conditions, comparing our observations with other crystalline catalysts (IrO2, LiCoO2). We demonstrate that at low overpotentials the reaction between water and the oxidized catalyst surface is compensated by bulk ion exchange, as usually only found for amorphous, electrolyte permeable, catalysts. At high overpotentials the charge is compensated by surface redox active sites, as in other crystalline catalysts such as IrO2. Hence, our work reveals charge compensation can extend beyond the surface in crystalline catalysts. More generally, the results highlight the power of compressive Raman imaging for chemically specific tracking of microscale reaction dynamics in catalysts, battery materials, or memristors.

FeNi nanoparticle-modified reduced graphene oxide as a durable electrocatalyst for oxygen evolution

Clean energy transition and decarbonization through hydrogen technology hold a crucial role in revitalizing a sustainable world. The development of catalysts free of precious elements to facilitate the water splitting process in an electrolyser represents a key sustainable goal to lower the production cost of green hydrogen fuel, therefore improving its accessibility and affordability. Here we report a hybrid electrocatalyst for oxygen evolution reaction (OER) in alkaline media with high stability and low overpotential, free of precious metals and rare elements. The hybrid catalyst is composed of laser-generated Fe50Ni50 nanoparticles (FeNi NPs) dispersed on reduced graphene oxide (rGO) and deposited on FeNi layered double hydroxide (FeNi LDH) grown on Ni foam substrate. The prepared FeNi-rGO/FeNi/Ni foam hybrid catalyst requires an overpotential of only 234 mV at a current density of 10 mA/cm2, which is 37 mV lower than the tested commercial RuO2 catalyst on Ni foam substrate. Besides, the hybrid catalyst is extremely robust; it stands 10,000 cycles of accelerated deterioration and runs for more than 1,300 h at a current density of 10 mA/cm2 without performance decay.

Few-shot learning for screening 2D Ga2CoS4−x supported single-atom catalysts for hydrogen production

Hydrogen generation and related energy applications heavily rely on the hydrogen evolution reaction (HER), which faces challenges of slow kinetics and high overpotential. Efficient electrocatalysts, particularly single-atom catalysts (SACs) on two-dimensional (2D) materials, are essential. This study presents a few-shot machine learning (ML) assisted high-throughput screening of 2D septuple-atomic-layer Ga2CoS4−x supported SACs to predict HER catalytic activity. Initially, density functional theory (DFT) calculations showed that 2D Ga2CoS4 is inactive for HER. However, defective Ga2CoS4−x (x = 0–0.25) monolayers exhibit excellent HER activity due to surface sulfur vacancies (SVs), with predicted overpotentials (0–60 mV) comparable to or lower than commercial Pt/C, which typically exhibits an overpotential of around 50 mV in the acidic electrolyte, when the concentration of surface SV is lower than 8.3%. SVs generate spin-polarized states near the Fermi level, making them effective HER sites. We demonstrate ML-accelerated HER overpotential predictions for all transition metal SACs on 2D Ga2CoS4−x. Using DFT data from 18 SACs, an ML model with high prediction accuracy and reduced computation time was developed. An intrinsic descriptor linking SAC atomic properties to HER overpotential was identified. This study thus provides a framework for screening SACs on 2D materials, enhancing catalyst design.

Performance and catalytic mechanism of CNTs/Ti3C2Tx MXene composite cathode for air-breathing hybrid lithium-air batteries

Hybrid lithium-air batteries (HLABs) have not been widely used due to high overpotential, low cycling, slow kinetic rate, and poor cathode catalytic performance. CNTs/Ti3C2Tx MXene composite material was first used as a cathode for HLABs. The cycling performance of batteries equipped with composite cathodes with different mass ratios is tested in an air environment. It is found that when the mass ratio is mCNTs:mTi3C2TxMXene=1:1, the cycling performance of the battery is the best, reaching 405 cycles, i.e., 1620 h of cyclic charging and discharging under fixed capacity. In deep discharge testing, when the mass ratio of the composite cathode is mCNTs:mTi3C2TxMXene=1:1, the battery exhibits extremely high specific capacity, with a maximum value of 22,092.91 mAh/g. The first principles calculate the catalytic mechanism of Ti3C2Tx MXene as the catalyst for HLABs, and the adsorption energy of oxygen on the surface of Ti3C2Tx MXene and ORR processes is calculated. The experiments and calculations confirm that Ti3C2Tx MXene is suitable as a cathode catalyst for HLABs.

Electrochemical Nitrate Reduction to Ammonia on AuCu Single-atom Alloy Aerogels under Wide Potential Window.

Electrocatalytic nitrate reduction to ammonia (NO3RR) is very attractive for nitrate removal and ammonia production in industrial processes. However, the nitrate reduction reaction is characterized by intense hydrogen competition at strong reduction potentials, which greatly limits the Faraday efficiency at strong reduction potentials. Herein, we reported an AuxCu single-atom alloy aerogels (AuxCu SAAs) with three-dimensional network structure with significant nitrate reduction performance of Faraday efficiency (FE) higher than 90% over a wide potential range (0 ~ -1 VRHE). The FE of the catalyst was close to 100% at a high reduction potential of -0.8 VRHE, accompanying with NH3 yield reaching 6.21 mmol h-1 cm-2. More importantly, the catalyst maintained a long-term operation over 400 h at 400 mA cm-2 for the NO3RR using a continuous flow system in a H-cell. Experimental and theoretical analysis demonstrate that the catalyst can lower the energy barrier for the hydrogenation reaction of *NO2, leading to a rapid consumption of the generated *H, facilitate the hydrogenation process of NO3RR, and inhibit the competitive HER at high overpotentials, which efficiently promotes the nitrate reduction reaction, especially in industrial applications.

Impact of Nickel on Iridium-Ruthenium Structure and Activity for the Oxygen Evolution Reaction under Acidic Conditions.

Proton exchange membrane water electrolysis (PEMWE) is a promising technology to produce hydrogen directly from renewable electricity sources due to its high power density and potential for dynamic operation. Widespread application of PEMWE is, however, currently limited due to high cost and low efficiency, for which high loading of expensive iridium catalyst and high OER overpotential, respectively, are important reasons. In this study, we synthesize highly dispersed IrRu nanoparticles (NPs) supported on antimony-doped tin oxide (ATO) to maximize catalyst utilization. Furthermore, we study the effect of adding various amounts of Ni to the synthesis, both in terms of catalyst structure and OER activity. Through characterization using various X-ray techniques, we determine that the presence of Ni during synthesis yields significant changes in the structure of the IrRu NPs. With no Ni present, metallic IrRu NPs were synthesized with Ir-like structure, while the presence of Ni leads to the formation of IrRu oxide particles with rutile/hollandite structure. There are also clear indications that the presence of Ni yields smaller particles, which can result in better catalyst dispersion. The effect of these differences on OER activity was also studied through rotating disc electrode measurements. The IrRu-supported catalyst synthesized with Ni exhibited OER activity of up to 360 mA mgPGM -1 at 1.5 V vs RHE. This is ∼7 times higher OER activity than the best-performing IrO x benchmark reported in the literature and more than twice the activity of IrRu-supported catalyst synthesized without Ni. Finally, density functional theory (DFT) calculations were performed to further elucidate the origin of the observed activity enhancement, showing no improvement in intrinsic OER activity for hollandite Ir and Ru compared to the rutile structures. We, therefore, hypothesize that the increased activity measured for the IrRu supported catalyst synthesized with Ni present is instead due to increased electrochemical surface area.

Electrochemical and structural properties of binder-free iron-based bifunctional catalyst for aqueous Zinc-Oxygen batteries

Global warming necessitates efficient new batteries, with Zn-O2 batteries standing out due to their high theoretical energy density, safety, and long cycle life, making them ideal for large-scale use. However, their industrial application faces challenges such as rapid energy density decline after initial cycles, limited cathode efficiency, and high overpotential between discharge and charge. This study focuses on synthesizing and characterizing ceramic iron compounds as catalysts for the cathode of Zn-O2 aqueous batteries. The findings revealed that obtained catalysts presented surface active areas beyond 220 m2/g after calcination at 800 °C, which removed organic templates. Various thermal treatments have been analysed to measure their impact on the final product. XRD, FTIR, and Raman spectroscopy confirmed sample nitridation, while SEM showed macro–meso-porosity. The electrochemical evaluation demonstrated a significant enhancement in the material's catalytic properties for ORR/OER in alkaline Zn-O2 batteries, surpassing 140 h of satable cyling with catalytic activity for ORR and OER. This improvement, coupled with optimized electrode design, resulted in a substantial increase in the batteries' operational life, achieving stable cycling for over 120 h.

Beyond Catalysts: Exploring Discharge Product Growth and Intrinsic Overpotential in Lithium-Oxygen Batteries.

The lithium-oxygen (Li-O2) battery, renowned for its exceptionally high theoretical energy density, is poised to revolutionize next-generation energy storage systems. However, its practical application depends on overcoming several challenges, particularly the high cathode overpotential, which significantly diminishes the battery's energy efficiency and durability. This study delves into the interactions at the cathode surface during oxygen reduction and evolution reactions (ORR/OER), extending the analysis beyond the initial reaction stages to encompass the extensive charge-discharge process. We introduce and define the concepts of intrinsic equilibrium potential and intrinsic overpotential, demonstrating that these critical parameters are predominantly influenced by the growth of discharge products, rather than the catalysts, thereby underscoring the inherent properties of the battery. This shift in focus from merely enhancing cathode catalysts to understanding and leveraging the intrinsic characteristics of the battery discharge process opens new avenues for optimizing and enhancing the performance of large-scale Li-O2 batteries. Furthermore, our findings indicate potential broader applications to other metal-oxygen systems, paving the way for the design of high-capacity, high-efficiency energy storage technologies.

Chemical Epitaxy of Iridium Oxide on Tin Oxide Enhances Stability of Supported OER Catalyst.

Significantly reducing the iridium content in oxygen evolution reaction (OER) catalysts while maintaining high electrocatalytic activity and stability is a key priority in the development of large-scale proton exchange membrane (PEM) electrolyzers. In practical catalysts, this is usually achieved by depositing thin layers of iridium oxide on a dimensionally stable metal oxide support material that reduces the volumetric packing density of iridium in the electrode assembly. By comparing two support materials with different structure types, it is shown that the chemical nature of the metal oxide support can have a strong influence on the crystallization of the iridium oxide phase and the direction of crystal growth. Epitaxial growth of crystalline IrO2 is achieved on the isostructural support material SnO2, both of which have a rutile structure with very similar lattice constants. Crystallization of amorphous IrOx on an SnO2 substrate results in interconnected, ultrasmall IrO2 crystallites that grow along the surface and are firmly anchored to the substrate. Thereby, the IrO2 phase enables excellent conductivity and remarkable stability of the catalyst at higher overpotentials and current densities at a very low Ir content of only 14 at%. The chemical epitaxy described here opens new horizons for the optimization of conductivity, activity and stability of electrocatalysts and the development of other epitaxial materials systems.