Exploring the Mechanisms of LiNiO 2 Cathode Degradation by the Electrolyte Interfacial Deprotonation Reaction
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25 ENERGY STORAGE↗
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Exploring the Structure–Function Relationship in Iridium–Cobalt Oxide Catalyst for Oxygen Evolution Reaction across Different Electrolyte Media
Renewable hydrogen generation from water electrolysis offers a viable path to decarbonization if the costs can be reduced. The iridium-based anode catalyst is one of the most expensive components in electrolyzers. We propose reducing iridium usage by substituting Ir with Co, a more affordable metal, in the mixed oxide phase to enhance the catalytic activity while minimizing Ir consumption. A modified surfactant-assisted Adams fusion synthesis technique was developed as a scalable method for producing IrCo oxide nanoparticles. The synthesized material outperforms the commercial baseline, iridium oxide with carbon (IrOx_C), in both acidic and alkaline media. Acid etching (IrCo_ae) further enhances activity by selectively removing Co to expose more active sites. IrCo_ae achieved a significantly lower overpotential at 10 mA/cm 2 compared to IrOx_C, with reductions of approximately 18% under acidic conditions and 14% under alkaline conditions. This work demonstrates that the proposed synthesis method enables efficient Ir utilization and can be adapted to enhance catalyst stability for renewable hydrogen production.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Improving protonic ceramic electrochemical cell performance via a dual-phase reaction-sintered bilayer electrolyte
Protonic ceramic electrochemical cells (PCCs) are promising energy conversion devices, but their fabrication remains challenging. In particular, the typical electrolytes for PCCs such as BaCe 0.7 Zr 0.1 Y 0.1 Yb 0.1 O 3−δ (7111) and BaCe 0.4 Zr 0.4 Y 0.1 Yb 0.1 O 3−δ (4411) suffer from intrinsic barium evaporation issues during high-temperature sintering. This tendency towards barium loss, combined with their highly refractory nature, leads to a tradeoff between sinterability and chemical stability. To address this tradeoff, we propose a bilayer electrolyte combining layers of 4411 and 7111 materials that is designed to enhance sinterability and conductivity through dual-phase reactive sintering. Our findings demonstrate that the bilayer structure exhibits shrinkage behavior closely matched to that of the fuel electrode substrate, with a higher shrinkage compared to a single-layer 4411 electrolyte. Utilizing this bilayer electrolyte structure, our PCCs achieve a peak power density of 637 mW∙cm −2 in fuel-cell mode and a current density of 1060 mA∙cm −2 at 1.3 V in electrolysis mode at 600 °C. Our PCCs demonstrate high Faradaic efficiency of 83% at 1.3 V and 500 °C. Hybrid distribution of relaxation times (DRT) polarization mapping further reveals that the bilayer structure reduces Ohmic and polarization resistance in both fuel-cell and electrolysis modes.
ceramic processing↗
Role of electron pathway in dimensionally increasing water splitting reaction sites in liquid electrolytes
Hydrogen from water splitting is one of the most promising alternatives for fossil fuels in solving the global energy crisis, while its electrochemical reaction mechanism, especially in liquid electrolytes, remains unclear. Herein, how the electrode conductivity affects the reaction sites of oxygen evolution reactions (OERs) in acidic and alkaline solutions was investigated by employing visualization system and electrochemical testing. Inserting Au nanolayers greatly increased electrode conductivities, improved OER kinetics and reduced cell ohmic resistance, leading to excellent water splitting performances in both acidic and alkaline electrolytes. Furthermore, the in-situ visualization results showed more reaction sites and higher catalyst utilizations were achieved by augmenting the electrode conductivity, and reaction sites increased from 1-dimension to 2-dimension. Additionally, it was discovered that electrical conductivities of acidic and alkaline solutions are insufficient to overcome the sharp drop of potential in the electrical double layer for activating OER uniformly on low-conductivity catalysts, indicating the importance of electrical conductivity of the electrode in acidic and alkaline water electrolyzers. This study provided a guidance on how to develop efficient and compact electrodes for acidic and alkaline water electrolyzer stacks and other electrochemical devices, such as fuel cell, N2 reduction, CO 2 conversion, etc.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Mixed-Metal Nickel–Iron Oxide Aerogels for Oxygen Evolution Reaction
Alkaline electrolyte membrane electrolyzers are a promising technology to efficiently produce clean hydrogen without the use of critical raw materials. At the heart of these electrolyzers are the electrocatalysts, which facilitate the cathodic and anodic reactions, with the latter oxygen evolution reaction (OER) being the most sluggish. In recent years, aerogels have become a very well-studied class of materials due to their unique properties, including very high surface area. Until now, aerogels have not been used to catalyze the OER by themselves but were mainly considered catalyst supports. Here, mixed-metal nickel–iron oxide aerogels were synthesized with a modified epoxide route synthesis and tested as OER catalysts. Depending on the Ni/Fe ratio, they show very high catalytic activity and low overpotential to reach 10 mA cm –2 (at η = 380 mV). This activity is beyond that of the existing state-of-the-art platinum group metal-free OER catalysts.
PGM free catalysts↗
Size-Dependent Chemomechanical Failure of Sulfide Solid Electrolyte Particles during Electrochemical Reaction with Lithium
The very high ionic conductivity of Li 10 GeP 2 S 12 (LGPS) solid electrolyte (SE) makes it a promising candidate SE for solid-state batteries in electrical vehicles. However, chemomechanical failure, whose mechanism remains unclear, has plagued its widespread applications. Here, we report in situ imaging lithiation-induced failure of LGPS SE. In this work, we revealed a strong size effect in the chemomechanical failure of LGPS particles: namely, when the particle size is greater than 3 μm, fracture/pulverization occurred; when the particle size is between 1 and 3 μm, microcracks emerged; when the particle size is less than 1 μm, no chemomechanical failure was observed. This strong size effect is interpreted by the interplay between elastic energy storage and dissipation. Our finding has important implications for the design of high-performance LGPS SE, for example, by reducing the particle size to less than 1 μm the chemomechanical failure of LGPS SE can be mitigated.
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Electrolyte Organization Leads to Potential-Dependence in Thermochemical Catalysis of Nonpolar Reactions
Electrochemical polarization is now known to play a key role in thermochemical catalysis at solid–liquid interfaces. However, existing frameworks cannot account for why even nonpolar, nonfaradaic reactions are sensitive to interfacial polarization. In order to uncover the molecular basis of this phenomenon, we herein study the potential-dependent reaction kinetics of ethylene and trans-2-butene hydrogenation at Pt–liquid interfaces. Measurements were performed in aqueous and ortho-difluorobenzene (o-DFB) solutions, spontaneously polarizing the Pt–liquid interfaces by, respectively, varying the pH or dissolving distinct metallocene redox buffers into solution. Here, we find that at comparable mechanistic regimes, the rates of both ethylene and trans-2-butene hydrogenation are maximized near the same electrochemical potential, E. Moreover, the potential-dependence, defined as $\frac{∂ln 𝑟}{∂𝐸}$, of trans-2-butene hydrogenation is approximately 2.2× greater than that of ethylene hydrogenation across the full potential range studied. These observations are all consistent with a model in which polarization of the Pt surface away from the local potential of zero free charge (E PZFC ) induces electrostatic organization of the polar solvent and charged ions near the interface, which impedes olefin adsorption and surface reaction because these surface reactions induce electrolyte displacement. Accordingly, interfacial polarization alters the free energy landscape and thus the rate of nonpolar heterogeneous catalysis by controlling the degree of electrostatic organization of polar and charged spectators at the interface, which do not in general need to be specifically chemisorbed onto the surface but could simply be close enough to the surface to be perturbed by the olefin adsorption. These results point toward electrochemical design handles, namely, the electrolyte, catalyst potential, and local E PZFC of the catalyst, with which to tune interfacial catalysis of thermochemical organic transformations.
adsorption↗
Mechanistic Insights into Oxygen Reduction Reaction on Metal Cathode Over BaZrO 3 -Based Electrolyte under Moist Atmosphere: Interfacial Interactions and Reaction Pathways
The oxygen reduction reaction (ORR) is a critical process that often governs the overall performance of electrochemical systems such as proton conducting solid oxide fuel cells. Despite its significance, the current understanding about the ORR, especially when it involves H 2 O is still limited. In this study, the proton involved ORR (PI-ORR) on metal cathode (e.g., Pt) over BaZrO 3 (BZO) electrolyte is investigated using density functional theory (DFT) under moist atmosphere. Two scenarios are considered: one at relatively high temperature (900 K) in the presence of oxygen vacancy in BZO substrate and one at relatively low temperature (700 K) without oxygen vacancy. We systematically explored oxygen vacancy effects on adsorption sites and proton transfer pathways, calculated energy profiles and Gibbs free energies for elementary steps along the O 2 dissociated and the O 2 concerted reaction pathways. We also evaluated H 2 O impacts on intermediate oxygen species (*O and *OH) through Ab Initio molecular dynamics. These analyses revealed pathway-dependent reaction mechanisms and hydration effects at triple-phase boundary, advancing fundamental understanding of PI-ORR in metal cathode/Ba-based electrolyte systems for energy applications.
08 - HYDROGEN↗
Electrode material–ionic liquid coupling for electrochemical energy storage
The development of new electrolyte and electrode designs and compositions has led to advances in electrochemical energy-storage (EES) devices over the past decade. However, focusing on either the electrode or electrolyte separately is insufficient for developing safer and more efficient EES devices in various working environments, as the energy-storage ability is determined by the ion arrangement and charge and/or electron transfer at the electrode–electrolyte interface. Here, we assess the fundamental physicochemical and electrochemical properties at the electrode–electrolyte interfaces in Li-ion batteries and supercapacitors using safe and electrochemically stable ionic-liquid electrolytes. Key reactions and interactions at the electrode–electrolyte interface, as well as geometric constraints and temperature effects, are highlighted. Building on the fundamental understanding of interfacial processes, we suggest potential strategies for designing stable and efficient ionic-liquid-based EES devices with emerging electrode materials.
36 MATERIALS SCIENCE↗
Electrocatalysis of Oxygen Reduction Reaction in a Polymer Electrolyte Fuel Cell with a Covalent Framework of Iron Phthalocyanine Aerogel
Carbon aerogels have been studied in the context of fuel cell electrodes mainly as catalyst support materials due to their high surface area, porosity, and electrical conductivity. Recently, aerogels composed solely of inorganic molecular complexes have shown to be promising materials for the electrocatalysis of oxygen reduction reaction (ORR). These aerogels consist of atomically dispersed catalytic sites. Herein, we report on the synthesis and characterization of an aerogel-based catalyst: iron phthalocyanine aerogel. It was synthesized by coupling of ethynyl-terminated phthalocyanine monomers and then heat-treated at 800 °C to increase its electrical conductivity and catalytic activity. Further, the aerogels reported here were tested as catalysts for ORR in acidic conditions for the first time and found to have a ultra-high number of atomically dispersed catalytic sites (7.11 × 10 20 sites g –1 ) and very good catalytic activity (E onset = 0.9 V vs RHE and TOF = 9.2 × 10 –3 e – s –1 site –1 at 0.8 V vs RHE). The iron phthalocyanine aerogel was also studied in a proton exchange membrane fuel cell, reaching a peak power density of 292 mW cm –2 and an open circuit voltage of 0.83 V.
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Electrolyte Assisted Hydrogen Storage Reactions (Final Technical Report)
The goal of this project is to address critical deficiencies of hydrogen storage systems design based on hydride materials, as originally identified by the DOE Hydrogen Storage Engineering Center of Excellence (HSECoE). Baseline hydrogen storage technology presently relies on compressed gas operating at ~700 bar pressure, which imposes huge demands on fuel delivery, fuel storage and system cost. For onboard storage applications, Type IV composite overwrapped pressure vessels and associated balance-of-plant components are necessary to ensure safe and effective fuel delivery. However, such compressed gas technology falls well-short of volumetric targets even at 700 bar, given the density of gaseous molecular hydrogen is only 40 g·H2/l at ambient temperatures. One alternative is to utilize hydride materials which accommodate hydrogen in atomic form. Certain hydrides can attain volumetric densities that exceed the density of liquid H2 (71 g·H2/l) while also offering advantageous thermodynamic properties. However, such material systems presently rely on solid-state diffusion for hydrogen release, which has a very high activation barrier for atom mobility and, thus, requires impractically-high temperatures for operation. The initial focus of our research effort is to employ and demonstrate an electrolyte system to mediate the diffusion of species at lower temperatures relevant to transportation applications, with the goal of establishing the critical factors necessary to obviate the need for high-temperature release of hydrogen. A parallel goal of this exploratory effort is to determine the effectiveness of modest electrochemical potentials in overcoming any endothermic requirements for hydrogen release in a similar electrolyte-promoted scenario.
08 HYDROGEN↗
Impacts of Solvent Washing on the Electrochemical Remediation of Commercial End-of-Life Cathodes
Changes to surface structure and chemistry occurring throughout the functional lifetime of lithium-ion batteries (LIBs) may impact the effectiveness of end-of-life rejuvenation methods. Solvent washing prior to electrochemical relithiation is shown to both increase relithiation efficacy and beneficially alter the interfacial chemistry of heavily degraded industrial cathode material. Four common solvents (acetone, diethyl carbonate, isopropyl alcohol, propylene carbonate) are employed to investigate the role of varying physicochemical solvent properties on the mechanism of capacity recovery. Electrochemical (dQ/dV, EIS), structural (XRD), and chemical (SPME-GC-MS) analysis techniques are employed to comprehensively analyze solvent-cathode interactions. Highly nucleophilic solvents (acetone, DEC) are found to reduce cathode charge-transfer impedance and enable stable impedance growth throughout subsequent cycling. The use of nucleophilic solvents under mechanically aggressive washing conditions may also enable the reintroduction of bulk lattice oxygen, thereby restoring anionic redox capacity. Further, the four solvents are found to selectively remove a subset of surface species from the aged cathode material, including residual electrolyte, additives, and electrolyte-additive reaction products, which are qualitatively analyzed. Surface species removal by each solvent is correlated with the electrochemical performance of the correspondingly washed cathode, highlighting the importance of an optimized washing protocol to effective remediation in the context of direct LIB recycling. For the material under study, the use of a simple acetone washing protocol prior to electrochemical relithiation enables up to 174% capacity recovery relative to unwashed/relithiated black mass.
ADVANCED PROPULSION SYSTEMS↗
A Micrometer‐Sized Silicon/Carbon Composite Anode Synthesized by Impregnation of Petroleum Pitch in Nanoporous Silicon
Porous silicon (Si)/carbon nanocomposites have been extensively explored as a promising anode material for high-energy lithium (Li)-ion batteries (LIBs). However, shrinking of the pores and sintering of Si in the nanoporous structure during fabrication often diminishes the full benefits of nanoporous Si. Herein, a scalable method is reported to preserve the porous Si nanostructure by impregnating petroleum pitch inside of porous Si before high-temperature treatment. The resulting micrometer-sized Si/C composite maintains a desired porosity to accommodate large volume change and high conductivity to facilitate charge transfer. It also forms a stable surface coating that limits the penetration of electrolyte into nanoporous Si and minimizes the side reaction between electrolyte and Si during cycling and storage. A Si-based anode with 80% of pitch-derived carbon/nanoporous Si enables very stable cycling of a Si||Li(Ni0.5Co0.2Mn0.3)O 2 (NMC532) battery (80% capacity retention after 450 cycles). It also leads to low swelling in both particle and electrode levels required for the next generation of high-energy LIBs. In conclusion, the process also can be used to preserve the porous structure of other nanoporous materials that need to be treated at high temperatures.
anode materials↗
A Garnet-Type Solid-Electrolyte-Based Molten Lithium–Molybdenum–Iron(II) Chloride Battery with Advanced Reaction Mechanism
Solid-electrolyte-based molten-metal batteries have attracted considerable attention for grid-scale energy storage. Although ZEBRA batteries are considered one of the promising candidates, they still have the potential concern of metal particle growth and ion exchange with the β”-Al 2 O 3 electrolyte. Herein, a Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 solid-electrolyte-based molten lithium–molybdenum–iron(II) chloride battery (denoted as Li–Mo–FeCl 2 ) operated at temperature of 250 °C, comprising a mixture of Fe and LiCl cathode materials, a Li anode, a garnet-type Li-ion ceramic electrolyte, and Mo additive, is designed to overcome these obstacles. Different from conventional battery reaction mechanisms, this battery revolutionarily synchronizes the reversible Fe–Mo alloying–dealloying reactions with the delithiation–lithiation processes, meaning that the porous Mo framework derived from Fe–Mo alloy simultaneously suppresses the growth of pure Fe particles. By adopting a Li anode and a Li-ion ceramic electrolyte, the corrosion problem between the cathode and the solid electrolyte is overcome. With similar battery cost ($12 kWh –1 ), the theoretical energy density of Li–Mo–FeCl 2 battery surpasses that of a Na–FeCl 2 ZEBRA battery over 25%, to 576 Wh kg –1 and 2216 Wh L –1 , respectively. Experimental results further prove this cell has excellent cycling performance (472 mAh g LiCl –1 after 300 cycles, 50 mg active material) and strong tolerance against the overcharge–overdischarge (3–1.6 V) and freezing–thawing (25–250 °C) incidents.
36 MATERIALS SCIENCE↗
Li–Mn–O Li-rich cation disordered rock-salt cathode materials do not undergo reversible oxygen redox during cycling
An in-depth study of “Li 4 Mn 2 O 5 ”, a nanocomposite of Li 2 O and Li 4-x Mn 2 O 5 with a disordered rock salt structure (LMO), was conducted to determine the origins of the observed anomalously high charge and discharge capacity in lithium cells, which can exceed 350 mA h g -1 . Using soft and hard X-ray absorption spectroscopy (XAS), mapping of resonant inelastic X-ray scattering (mRIXS), and X-ray Raman spectroscopy (XRS), it was determined that electrochemical decomposition of Li 2 O upon charge and reduction of Mn to below 3+ during discharge is responsible for the capacities that are observed, with no evidence of contributions from reversible oxygen redox. Here, the over-reduction is exacerbated when charging limits of 4.5–4.8 V are used due to side reactions between electrolytic solution and the highly oxidized active material. These side reactions result in dissolution of Mn at room temperature and release of oxygen and other gases during initial cycles, which, in turn, cause rapid capacity fading. This is accompanied by evolution of the voltage profile upon cycling towards one that resembles that of manganese oxide spinels. The cycling behavior can be improved somewhat by reducing the upper voltage limit, although this results in a diminishment of the discharge capacities below 200 mA h g -1 . By adding various amounts of spinel LiMn 2 O 4 during synthesis, it was possible to produce LMOs with rock salt structures having significantly improved cycling behavior but still having capacities in excess of 250 mA h g -1 . An optimized modified material also exhibits better rate capability and much less gas evolution during initial cycles than the unmodified LMO. Interestingly, as-made modified materials generally exhibited lower than expected average Mn oxidation states attributable to oxygen loss during the synthesis process, as well as higher capacities than expected based on their manganese contents. The oxygen loss during processing may reduce the activity of the remaining oxygen and account for the lower reactivity of the spinel-modified material.
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Improved Rate for the Oxygen Reduction Reaction in a Sulfuric Acid Electrolyte using a Pt(111) Surface Modified with Melamine
The feasible commercialization of alkaline, phosphoric acid and polymer electrolyte membrane fuel cells depends on the development of oxygen reduction reaction (ORR) electrocatalysts with improved activity, stability, and selectivity. The rational design of surfaces to ensure these improved ORR catalytic requirements relies on the so-called "descriptors" (e.g., the role of covalent and noncovalent interactions on platinum surface active sites for ORR). Here, we demonstrate that through the molecular adsorption of melamine onto the Pt(111) surface [Pt(111)-M ad ], the activity can be improved by a factor of 20 compared to bare Pt(111) for the ORR in a strongly adsorbing sulfuric acid solution. Additionally, the M ad moieties act as "surface-blocking bodies," selectively hindering the adsorption of (bi)sulfate anions (well-known poisoning spectator of the Pt(111) active sites) while the ORR is unhindered. This modified surface is further demonstrated to exhibit improved chemical stability relative to Pt(111) patterned with cyanide species (CN ad ), previously shown by our group to have a similar ORR activity increase compared to bare Pt(111) in a sulfuric acid electrolyte, with Pt(111)-M ad retaining a greater than ninefold higher ORR activity relative to bare Pt(111) after extensive potential cycling as compared to a greater than threefold higher activity retained on a CN ad -covered Pt(111) surface. We suggest that the higher stability of the Pt(111)-M ad interface stems from melamine's ability to form intermolecular hydrogen bonds, which effectively turns the melamine molecules into larger macromolecular entities with multiple anchoring sites and thus more difficult to remove.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Electro-carburization of mild steel through two-step reaction in molten-salt electrolyte
The rapid carburization of mild steel is demonstrated via the electrochemical deposition of solid carbon, followed by thermochemical iron-carbon (Fe-C) reaction using a molten lithium-potassium carbonate (LiKCO 3 ) salt electrolyte and carbon dioxide as the carbon source. Depth-dependent microstructural and compositional changes in the steel are shown to be controlled by the applied cell voltage and reaction temperatures. Reaction temperatures above the Fe-C eutectoid temperature promote faster carburization due to carbon dissolution into austenite. The carbon deposition rate is regulated by the applied cell voltage: At - 2.4 V, carbon deposition occurs much faster than its diffusion into the steel, resulting in the accumulation of a carbon-rich layer exceeding 1 mm, which does not diffuse into the steel. In contrast, at - 1.8 V, all deposited carbon effectively diffuses into the steel, leaving a minimal external deposit. In both cases, carbon ingress forms a carbide-rich surface layer and precipitates additional carbides along the grain boundaries within the steel electrode. This method offers a potential approach to increase the carbon content of mild or low-carbon steel feedstocks, such as scrap or direct reduced iron, for industrial applications.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
In Situ Ion‐Exchange Metathesis Induced Conformal LiF Surface Films on Cathode (NMC811) as a Cathode Electrolyte Interphase
High-capacity cathodes (LiNi 0.8 Mn 0.1 Co 0.1 O 2 , NMC811) are promising for vehicle electrification because of their high gravimetric energy density. However, their electrochemical performance still relies upon the stability of the cathode electrolyte interphase (CEI). A highly reactive cathode interface leads to parasitic side reactions with electrolytes, resulting in accelerated capacity fading. Well-developed LiF and LiF-like inorganic compounds are believed to be good CEI components for stabilizing such reactive electrode interfaces. However, it is challenging to form an optimal surface sub-nanolayer of LiF on the cathode surfaces because of the complexity of the electrochemical reaction during battery cycling. Herein, the formation of a conformal LiF layer on the NMC811 electrode surface via an in situ ion-exchange metathesis process is reported, demonstrating a promising electrochemical performance because of a LiF-stabilized CEI. In situ generated LiF-coated NMC811 electrodes exhibit ≈97% capacity retention up to 100 cycles at a 0.3 C rate with average coulombic efficiency of ≈99.9% and ≈80% capacity retention up to 200 cycles at a 1 C rate with average coulombic efficiency of >99.6%. This finding may pave the way for reengineering the CEI to enhance the electrochemical performances and cycling stability of the high-capacity cathodes.
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