209 Search Results

Plastic waste accumulation necessitates innovative recycling approaches to achieve sustainability goals. Mechanochemical depolymerization offers a solvent-free, energy-efficient route to convert polymers into valuable monomers. In addition to their chemical properties, the way that polymers absorb kinetic energy is a key parameter of any mechanochemical process. This perspective explores the principles underpinning mechanochemical recycling, emphasizing how deformation and localized transient heating mediate energy transfer between impacts and localized excitations. Key factors such as polymer crystallinity, molecular weight, viscoelasticity, and thermal effects are analyzed to elucidate their role in energy transfer mechanisms during ball milling. This work establishes a foundational framework formore » the design and optimization of mechanochemical recycling by connecting polymer response to mechanical energy with the intention to improve depolymerization efficiency. Future research opportunities are outlined to advance the integration of polymer science and mechanochemistry for scalable, sustainable plastic upcycling.« less

Electrochemical transformations of stable molecules and water into fuels and value-added chemicals require efficient catalyst surfaces. Introducing controlled defects at atomic scales can offer promising routes to enhance catalyst performance. In this study, we found novel dual copper site (-Cu-Cu-) defects within a copper sulfide (Cu-S) layer supported on Cu(111). Using scanning tunneling microscopy (STM) and density functional theory (DFT), we found these dual copper sites enhance molecular adsorption strength, specifically for water molecules, compared to intact Cu-S layer or pristine copper surfaces. This discovery highlights the potential of engineered dual-site copper defects to advance electrochemical catalytic materials, particularly formore » reactions involving water activation.« less

The commercial viability of anion exchange membrane (AEM) electrolysis requires optimization of various stack components, with specific catalyst-ionomer combinations often yielding higher current densities, lowered Tafel slopes, and improved mass activity. In this joint theoretical-experimental study, theoretical calculations detail the impact of Versogen's piperidinium functional group on the complex, kinetically limiting oxygen evolution reaction, finding that the functional group can act as a promoter of specific steps (O*/O2* formation; H2O/O2 desorption with reaction enthalpies ranging between 0.2-0.6 eV at higher coverages of OxHy intermediates) on NiO and NiFeOx catalysts. In particular, Fe sites on the NiFeOx catalyst facilitate concerted mechanismsmore » of O*/O2* formation and H2O desorption with a low enthalpy of 0.5 eV; O2 desorption alone requires only 0.3 eV. In contrast, Versogen-IrO2 results in stronger Ir-O bonds, where the enthalpies for bond breaking (Ir-OH2 and Ir-O2) are considerably higher (1.4 eV and 1.6 eV, respectively). Rotating disk electrode studies utilized commercially available NiO and IrO2 and synthesized 7.5 wt % Fe in NiFeOx catalysts in combination with Versogen, a common AEM ionomer, and Nafion, an alternative binder. Electrochemical testing validated the impact of these mechanistic changes on ionomer-catalyst combinations, finding that Versogen particularly activates NiO and NiFeOx compared to IrO2. Following a 13.5 h hold at 1.8 V, mass activities and Tafel slopes improved to 34 +- 13 A g-1 and 79 +- 2 mV dec-1 (NiO) and 82 +- 4.9 A g-1 and 72 +- 2 mV dec-1 (NiFeOx). In contrast, Versogen-IrO2 only reached 17 +- 2.9 A g-1 and 81 +- 3 mV dec-1. Optimization of the ionomer-catalyst can yield significant increases in performance from initial activity and after an electrochemical conditioning procedure: this enhancement to the mass activity resulted in a 200.9 +- 106.1% improvement for Versogen-NiFeOx and 1284.2 +- 260.5% for Versogen-NiO. In contrast, Nafion-NiFeOx and -NiO offered moderate improvements of 39.1 +- 30.5% and 120.9 +- 59.1%, respectively.« less

Polysulfides are poorly retained within porous cathodes and readily diffuse into the electrolyte over time, leading to the well-known shuttle effect that undermines the reversibility of Li-S batteries. Here, in this study, we demonstrate that catalytic disproportionation of polysulfides provides an effective pathway to suppress this process by rapidly converting dissolved species into solid sulfur and sulfides, thereby preventing their migration into the electrolyte. Fundamentally, the sluggish kinetics of sulfur redox reactions are responsible for the accumulation and redistribution of soluble polysulfides in the bulk electrolyte. By accelerating these kinetics, catalyzed disproportionation not only confines sulfur within the conductive cathodemore » matrix but also promotes the homogeneous precipitation of Li₂S₂/Li₂S, which enhances electrochemical reversibility and cycling stability. Using nitrogen-doped carbon (NC800) as a model catalyst, we reveal its ability to drive a pseudo-16-electron reduction pathway, leading to a single dominant Li₂S product and uniform deposition within the porous framework. In contrast, a non-catalytic carbon (KB) yields multiple polysulfide intermediates and heterogeneous deposition. The mechanistic insights provided here highlight the pivotal role of catalytic disproportionation in reshaping sulfur redox pathways and offer a rational strategy for mitigating polysulfide shuttling in practical Li-S pouch cells.« less

Reaction kinetics experiments coupled with phenomenological kinetic modeling and parameter estimation are used to elicit insights into the mechanism and active sites for the plasma-catalytic dissociation of CO₂ on TiO₂. Experimental and model insights showed that gas-phase reactions contribute at least two-thirds of the overall product formation at explored conditions; weak temperature dependence, strong sensitivity to specific energy input (SEI), apparent first order in CO₂, and positive influence of cofed argon (Ar) and oxygen (O₂) for the gas-phase contributions all suggest that expected plasma reaction steps such as electron-impact and high-energy collisions are the dominant modes for CO₂ dissociation. Themore » Arrhenius-like expression for gas contributions resulted in a preexponential of 4.40 × 10^–3 s^–1, an E_SEI,g of 7.90 × 10^–4 mol/kJ, and an E_a,g of 1.00 × 10^–3 J/mol. For surface contributions, the small apparent barrier of 16.3 kJ/mol, relatively weaker dependence on SEI, first-order dependence on CO₂, and insensitivity to cofed Ar and O₂ all point to CO₂ dissociation on TiO₂ surface facets without vacancies and aided by plasma (leading to vibrationally excited CO₂ and/or a reactive surface with significant surface charge accumulation). The Arrhenius-like expression resulted in a preexponential of 7.81 × 10^–2 s^–1, an E_SEI,s of 1.90 × 10^–3 mol/kJ, and an E_a,s of 1.63 × 10⁴ J/mol. The derived kinetic model further enabled a systematic evaluation of the effect of inputs (plasma power, flow rate, CO₂ inlet concentration, and temperature) to identify process trends and optimal operating conditions.« less

The development of advanced heat pump technologies is critical for reducing global energy consumption in the building sector, where space heating and cooling account for nearly 50% of energy use. Electrochemical heat pumps (EHPs) offer a promising alternative to vapor compression systems by enabling direct electrochemical-to-thermal energy conversion, often with environmentally benign working fluids that exhibit low or zero global warming potential (GWP). Prior literature has predominantly focused on chemically reactive heat pumps, while comprehensive assessments of electrochemical mechanisms remain limited. Here, this review addresses this gap by systematically evaluating the underlying principles, architectures, and performance metrics of EHP systems.more » Compared to conventional vapor compression systems, EHPs can achieve 10%-30% higher energy efficiency, with reported cooling coefficients of performance (COP_c) ranging from 3.5 to 14.3 under standard operating conditions. Despite these advantages, widespread adoption is hindered by challenges including membrane degradation, electrode fouling, sluggish redox kinetics, and elevated system-level capital costs. To address these limitations, the review outlines three research priorities: (i) the development of advanced membranes, catalysts, and electrode materials with enhanced chemical and mechanical stability; (ii) the application of molecular-level simulations for the rational design of high-performance redox-active working fluids; and (iii) the integration of advanced diagnostic techniques for real-time monitoring and sustained operation of EHPs. By consolidating recent advances and explicitly identifying technological and scientific gaps, this work uniquely contributes a comprehensive framework for guiding future electrochemical heat pump research and facilitating the transition to sustainable thermal management technologies.« less

Sodium layered oxide cathodes are drawing interest globally as a potential alternative to lithium layered oxides, but they suffer from egregious capacity fade and have intrinsically lower capacity. P2-type Na_2/3Ni_1/3Mn_2/3O₂ is a particularly relevant cathode material as it demonstrates an energy density of up to 550 W h kg⁻¹ at high operating potentials, although this can only be maintained for a handful of cycles with industrial electrolytes. Here, a localized saturated electrolyte (LSE) is shown to significantly improve the cycle life of Na_2/3Ni_1/3Mn_2/3O₂ by suppressing the surface reactivity, despite large volume changes during cycling. The demonstrated influence of surface stabilitymore » on cycle life in this work challenges the prevailing notion of a popular capacity stabilization strategy with titanium/magnesium co-doping, which is primarily thought to improve cycle life via improved structural stability. Single crystals of Na_2/3Ni_1/3−xMg_xMn_2/3−2xTi_2xO₂ (x = 0, 1/48, 1/24, 1/12) materials are cycled with a traditional electrolyte and the LSE to demonstrate that despite eliminating the phase transition with dopants in Na_2/3Ni_1/4Mg_1/12Mn_1/2Ti_1/6O₂, the predominant role of the dopants is in reducing the parasitic oxygen reactivity at the cathode surface. The different roles these dopants play are systematically disambiguated, and this work can guide future research to focus on reducing the parasitic cathode/electrolyte reactivity further.« less

Li-ion battery performance is strongly influenced by the 3D microstructure of its cathode particles. Cracks within these particles develop during calendaring and cycling, reducing connectivity but increasing reactive surface, making their impact on battery performance complex. Understanding these contradictory effects requires a quantitative link between particle morphology and battery performance. However, informative 3D imaging techniques are time-consuming, costly and rarely available, such that analyses often have to rely on 2D image data. This paper presents a novel stereological approach for generating virtual 3D cathode particles exhibiting crack networks that are statistically equivalent to those observed in 2D sections of experimentallymore » measured particles. Consequently, 2D image data suffices for deriving a full 3D characterization of cracked cathodes particles. Such virtually generated 3D particles could serve as geometry input for spatially resolved electro-chemo-mechanical simulations to enhance our understanding of structure-property relationships of cathodes in Li-ion batteries.« less

Solid-state batteries can offer higher energy density and improved safety compared to lithium ion batteries, which use flammable liquid electrolytes. Increasing the ratio of cathode active materials in composite cathodes enhances the energy density and reduces manufacturing costs. Changes in the ratio of cathode active materials alter the microstructure and chemo-mechanical response of a cathode during operation. Understanding the relationship between composition, microstructure, and chemo-mechanical interactions is critical for optimizing solid-state cathodes. Here, in this study, we engineered composite cathodes with varying ratios of LiNi_0.8Co_0.1Mn_0.1O₂ and Li₆PS₅Cl to systematically investigate the role of microstructural evolution in long-term chemo-mechanical transformations. Chemo-mechanicalmore » stresses resulting from the volume changes of the cathode active materials led to degradation mechanisms, such as fracture and interfacial delamination. Active material fracture and delamination led to underutilization of active material and significant capacity decay during cycling. Coatings that suppress active material-active material interactions during cycling may aid in suppressing the generation of local stress hotspots.« less

Catalytic hydrodeoxygenation (HDO) following catalytic fast pyrolysis (CFP) offers an approach to convert the vapor-phase product of biomass pyrolysis to a stable bio-oil product by reducing the oxygen content. Fundamental insights into the HDO of carboxylic acids, which are a corrosive and acidic CFP product, on promising catalyst materials, such as Pt/TiO₂, are needed to inform the design of multifunctional HDO catalysts with improved carbon efficiency. In this contribution, density functional theory (DFT) calculations were used to assess the role of Pt-metal and Pt-TiO₂-interface sites on acetic acid HDO (AA-HDO), and to determine the effect of interfacial oxygen vacancies atmore » the Pt-TiO₂ interface, by calculating the reaction energetics for key AA-HDO surface intermediates and elementary steps on each site type. Pt-metal sites, modeled via Pt(111), preferred to form undesired decarboxylation products (CH₄ and CO₂), whereas Pt-TiO₂-interface sites, modeled via an anatase-supported Pt nanowire, favored the formation of desired deoxygenation products (acetaldehyde and ethane). Interfacial-vacancy sites lowered the activation energy barrier for the first C-O bond-scission step in AA-HDO, predicted to be the rate-limiting step for AA-HDO at the Pt-TiO₂ interface in the absence of a vacancy. These atomistic insights reveal the importance of metal-metal oxide interface sites in AA-HDO selectivity and can be used to inform the rational design of improved HDO catalysts.« less