Interfacial Species Research Articles

Selective hydrogenation of furfuryl alcohol to 1,2-pentanediol over Pt/Mg2AlO catalysts with different synthesis methods

Selective cleavage of C–O bond in biomass-derived furfuryl alcohol (FFA), with complex chemical functional groups, poses a great challenge to biomass upgrading. In this work, Pt/Mg2AlO catalysts were prepared by urea hydrolysis (Pt-HT), coprecipitation (Pt-CP) and sol-gel (Pt-SG) methods to study the interfacial property caused by support synthesis methods during selective hydrogenation of FFA to 1,2-pentanediol (1,2-PeD). The results clearly showed that 1,2-PeD yield on Pt-HT was 60.3 %, better than those on Pt-CP and Pt-SG catalysts. The superior catalytic activity of Pt-HT is ascribed to effective adsorption and split of C–O bonds, facilitated by plentiful interfacial oxygen vacancies and Pt0 species. Furthermore, the superior selectivity of 1,2-PeD is related to the deforming non-parallel adsorption mode of FFA rings on Pt-HT resulting from their interaction with interfacial oxygen vacancies.

Extreme Environment-Adaptable and Ultralong-Life Energy Storage Enabled by Synergistic Manipulation of Interfacial Environment and Hydrogen Bonding

The broad applications of energy storage systems have brought improving demands for stable electrodes with robust tolerance to extreme environmental challenges. MXenes show promising pseudocapacitive behaviors, however, the poor thermodynamical and mechanical stability makes them unfavorable for applications under complex and harsh environments. Herein, we break these limitations by aramid nanofibers (ANF)-driven interfacial nanofilling and hydrogen-bonds effects in MXenes. Theoretical and experimental results unveil that ANF with unique polarity preferentially interacts with H2O molecules and forms hydrogen bonding networks to restrain oxidative and mechanical attack toward MXene, at the same time, the nanofilling enables interfacial mass transport intensification for increment in redox dynamics. As such, the synergistically coupled ANF-MXene microstructure (AM) unlocks superior mechanical properties for facing hash forces, i.e., tensile strength of 115.2 MPa and toughness of 1.8 MJ m-3, and an ultra-long cycling life with a capacitance retention of 90.7% after 40,000 cycles. Besides, the effective IR thermal camouflage performance (IR-emissivity: 20.9%) further renders the power supply working invisibly after fast charge/discharge-driven heat generation. Moreover, the performances can be well maintained when subjected to strong acid/alkali, high-temperature (200°C), and cryogenic (-196°C) treatments. These results highlight the key role of interfacial species synergy in accelerating versatile and robust energy applications.

Quantitative Analysis on Interfacial Charges and Ions’ Speciation, and Identification of Interfacial Species Through Interfacial Waters’ Structure Revealed by Interface-specific Spectroscopy

Quantitative Analysis on Interfacial Charges and Ions’ Speciation, and Identification of Interfacial Species Through Interfacial Waters’ Structure Revealed by Interface-specific Spectroscopy

Super SEI-Forming Anion for Enhanced Interfacial Stability in Solid-State Lithium Metal Batteries.

The extremely high chemical reactivity of lithium metal (Li°) electrodes and its enormous volume change during repetitive cycles cause continuous interfacial degradations in prevailing organic electrolytes, thus deteriorating the cycling performances of rechargeable lithium metal batteries (LMBs). Herein, departing from traditional wisdom on the design of electrolyte components, a super SEI-forming anion (SSA), as an efficient percussor for building stable interphases on Li° electrode, is proposed. Comprehensive investigations related to the unique anion chemistry of SSA reveal that the sulfonate and polyfluoroalkyl functionalities synergistically contribute to uniform spatial distributions of designer interfacial species, greatly improving the surface coverage property and conformal ability of the resulting interphases. Consequently, the incorporation of SSA leads to significant improvements in the cyclability of Li° electrode (exceeding 575 mAh cm-2 before failure) and the corresponding rechargeable Li°||LiFePO4 cells [a five-time increase in lifespan as compared to the benchmark cell with the popular SEI-forming anion bis(fluorosulfonyl)imide (FSI)]. The present work offers a paradigm shift to tame the notorious interfacial issues via upgraded anion chemistry, which can promote the practical development of rechargeable LMBs and other kinds of metal batteries.

Regulating the evolution of interfacial species via B, N-codoped Pt sites for oxygen reduction electrocatalysis

The sluggish kinetics of the oxygen reduction reaction (ORR) poses significant limitations to the widespread application of the ORR in advanced energy systems. Here, we present a composite catalyst consisting of Pt nanoparticles immobilized on 3D B, N-doped graphene oxide (Pt/GO-BCN). Through X-ray absorption fine structure spectroscopy and synchrotron radiation infrared spectroscopy analyses, we discovered that the codoping of B and N significantly regulates the electronic structure of graphene and enhances the interaction between Pt nanoparticles and the supports. The electronic state-optimized 3D support promotes the uniform distribution of Pt nanoparticles with small size, forming a low-resistance interfacial environment to accelerate the cleavage of the *OOH species during the reaction process. The ORR activity and selectivity of Pt/GO-BCN significantly surpass those of commercial Pt/C catalysts, and excellent durability under long-term operation is achieved. These results provide a new avenue for the design of advanced Pt-based catalysts.

Unveiling the Interfacial Species Synergy in Promoting CO2 Tandem Electrocatalysis in Near-Neutral Electrolyte.

The interfacial species-built local environments on Cu surfaces impact the CO2 electroreduction process significantly in producing value-added multicarbon (C2+) products. However, intricate interfacial dynamics leads to a challenge in understanding how these species affect the process. Herein, with ab initio molecular dynamics (AIMD) and finite element method (FEM) simulations, we reveal that the highly concentrated interfacial species, including the *CO, hydroxide, and K+, could synergistically promote the C-C coupling on the one-dimensional (1D) porous hollow structure regulated interfacial environment. The Cu-Ag tandem catalyst was then synthesized with the as-designed structure, exhibiting a high C2+ Faradaic efficiency of 76.0% with a partial current density of 380.0 mA cm-2 in near-neutral electrolytes. Furthermore, in situ Raman spectra validate that the 1D porous structure regulates the concentration of interfacial CO intermediates and ions to increase *CO coverage, local pH value, and ionic field, promoting the CO2-to-C2+ activity. These results provide insights into the design of practical ECR electrocatalysts by regulating interfacial species-induced local environments.

Cryogenic Atom Probe Tomograph to Resolve Confined Electrochemical Interfaces

Atom Probe Tomography (APT) is an analysis technique capable of providing a 3-dimensional, element-sensitive map of needle-shaped samples (where the tip radius is about 50 nm) with sub-nanometre resolution [1]. APT analysis is carried out at temperatures in the range of 25-75 K to limit the thermal motion of surface atoms which improves the spatial and mass resolution. As a result, this enables the analysis of frozen liquids, and by extension solid-liquid interfaces, by so-called “cryo-APT”. While this was historically challenging, recent advancements in UHV-cryogenic transfer and sample preparation methods now make it possible for the atomic scale analysis of interfacial species in electrochemical systems [2-4].In this study, we will attempt to explore the effect of nanoscale geometrical confinement on the distribution of interfacial ions for the first time and to resolve the electric double layer, using cryo-APT. We will describe the workflow for cryo-APT sample preparation to study confined solid-liquid interfaces, using nanoporous gold as a template material with a frozen sodium iodide solution inside its pores. APT reconstructions will allow 3-dimensional mapping of aqueous interfacial species, helping to develop our understanding of the structure of the electric double layer under nanoscale geometrical confinement. The attached Figure shows an SEM image of the later stages of cryo-FIB milling of an APT tip of frozen deionised water and 50 mM sodium iodide and a segment of the related APT atom map reconstruction.

(Invited) Analysis of Interfacial Species at Finite Bias - Calcium Borohydride in Tetrahydrofuran

To understand the operation of complex electrolytes we must determine which species are present and active at the interface with the electrode. We combine molecular dynamics sampling with continuum modeling to determine the speciation of Ca(BH4)2 in THF next to a model electrode (graphite). Mulitvalent ions in organic solvents with poor dielectric screening may exist in multiple coordinated states. We explore the free energy landscape associated with the interconversion of species in the bulk electrolyte using metadynamics simulations. We find that the chemical equilibrium between neutral and charged species is dominated by disproportionation following dimer formation - consistent with experimental findings. We also make use of clustering analysis to reveal distinct molecular conformations within constrained coordination states. To assess how the chemical equilibrium may be modified by the potential difference at the electrode, we develop a continuum model based on the modified Poisson-Boltzmann equation, with volume exclusion. This model also incorporates molecular-scale details through sampled free energy profiles of each relevant species within the solvent as a function of distance from the electrode. We find that a narrow (approximately 1 nm) region near the electrode, with highly variable speciation driven by potential difference, dominates the electrochemical activity of this electrolyte.

Understanding Electrode-Electrolyte Interfaces in Gel Polymer Electrolytes Using in-Operando Raman Spectroscopy

Gel polymer electrolytes hold enormous potential for advancing battery performance and technology, promising high energy densities and safe, rechargeable quasi solid-state batteries. GPEs offer higher ionic conductivities than solid electrolytes and enhanced safety in comparison to liquid electrolytes. A particular advantage of these electrolytes has been their ability to create robust electrode electrolyte interfaces that guide uniform deposition and stripping of lithium via their mechanical strength from the polymer and interface species that form during initial cycling.Herein we report that 1:1 dimethoxyethane (DME) and dioxolane (DOL) with lithium bistrifluoromethanosulfonyl imide (LiTFSI) and lithium nitrate entrapped in Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) gel polymer electrolytes have shown stability for up to 500 hours in lithium metal symmetric cells at 1 mAh/cm2 and performs at 5mAh/cm2 in dynamic symmetric cell cycling. To understand the fundamental interfacial phenomenon governing lithium deposition and growth in this system in-operando Raman was conducted on an anodeless Cu|PVDF-HFP|Li cell. Copper was sputtered onto the polymer electrolyte before assembly with a thickness of 20nm, providing an optically transparent electrode through which the Raman laser could pass through to detect interfacial species. We observe that PVDF-HFP acted as a chemically stable polymer electrolyte while Raman shifts associated with TFSI anions disappear near the electrode surface. The spectral and electrochemical data allow us to build a model for the growth and evolution of interfaces in an anodeless lithium metal battery cell with a GPE.Acknowledgement: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists, Office of Science Graduate Student Research (SCGSR) program. The SCGSR program is administered by the Oak Ridge Institute for Science and Education for the DOE under contract number DE‐SC0014664. Figure 1

Quantifying Chemical Reactions and Interfacial Properties at Buried Polymer/Polymer Interfaces.

Maleic anhydride (MAH)-modified polymers are used as tie layers for binding dissimilar polymers in multilayer polymer films. The MAH chemistry which promotes adhesion is well characterized in the bulk; however, only recently has the interfacial chemistry been studied. Sum frequency generation vibrational spectroscopy (SFG) is an interfacial spectroscopy technique which provides detailed information on interfacial chemical reactions, species, and molecular orientations and has been essential for characterizing the MAH chemistry in both nylon and ethyl vinyl alcohol copolymer (EVOH) model systems and coextruded multilayer films. Here, we further characterize the interfacial chemistry between MAH-modified polyethylene tie layers and both EVOH and nylon by investigating the model systems over a range of MAH concentrations. We can detect the interfacial chemical reaction products between MAH and the barrier layer at MAH concentrations of ≥0.022 wt % for nylon and ≥0.077 wt % for EVOH. Additionally, from the concentration-dependent reaction reactant/product SFG peak positions and the product imide or ester/acid C═O group tilt angles extracted from the polarization-dependent SFG spectra, we quantitatively observe concentration-dependent changes to both the interfacial chemistry and interfacial structure. The interfacial chemistry and molecular orientation as a function of MAH concentration are well correlated with the adhesion strength, providing important quantitative information for the future design of MAH-modified tie layers for a variety of important applications.

Fast uranium electro-extraction through synergistic hydrophilic channel and modulating local interfacial species

Capturing uranium from seawater and spent fuel storage phase identification for nuclear energy sustainable development represents the effective solution to carbon neutral. Here, we demonstrated boosting electrocatalytic uranium extraction on electrode consisted of 3D ethoxy substituted Ni oxalate (Ni-C2O4) nanowire spongs with the interlayer spacing and hydrophilic surface which are favourable for uranyl-specific liquid mass and fluid transfer. Thermodynamically stable U(VI or IV) phases were selected formation at 1.0 V and 2.5 V, respectively by alternation of the local spatial species including [UO2Cl]+, OH– or OH radical. Since the chemical reaction between UO22+ and in-situ generated OH–, insoluble Clarkeite NaUO2(OH)2 U(VI) phase formed with removal efficiency of 99 % after 30 min at a low cell voltage of 1.0 V. In comparison, at 2.5 V, it is found that yellow Studtite appeared as intermediate involved electro-generated OH radical species. Stable black UO2 is final reductive products, which is well understanding for uranium stockpile stewardship and waste processing.

Spontaneous Degradation of the "Forever Chemicals" Perfluoroalkyl and Polyfluoroalkyl Substances (PFASs) on Water Droplet Surfaces.

Because of their innate chemical stability, the ubiquitous perfluoroalkyl and polyfluoroalkyl substances (PFASs) have been dubbed "forever chemicals" and have attracted considerable attention. However, their stability under environmental conditions has not been widely verified. Herein, perfluorooctanoic acid (PFOA), a widely used and detected PFAS, was found to be spontaneously degraded in aqueous microdroplets under room temperature and atmospheric pressure conditions. This unexpected fast degradation occurred via a unique multicycle redox reaction of PFOA with interfacial reactive species on the droplet surface. Similar degradation was observed for other PFASs. This study extends the current understanding of the environmental fate and chemistry of PFASs and provides insight into aid in the development of effective methods for removing PFASs.

Spectroscopic visualization of reversible hydrogen spillover between palladium and metal–organic frameworks toward catalytic semihydrogenation

Hydrogen spillover widely occurs in a variety of hydrogen-involved chemical and physical processes. Recently, metal–organic frameworks have been extensively explored for their integration with noble metals toward various hydrogen-related applications, however, the hydrogen spillover in metal/MOF composite structures remains largely elusive given the challenges of collecting direct evidence due to system complexity. Here we show an elaborate strategy of modular signal amplification to decouple the behavior of hydrogen spillover in each functional regime, enabling spectroscopic visualization for interfacial dynamic processes. Remarkably, we successfully depict a full picture for dynamic replenishment of surface hydrogen atoms under interfacial hydrogen spillover by quick-scanning extended X-ray absorption fine structure, in situ surface-enhanced Raman spectroscopy and ab initio molecular dynamics calculation. With interfacial hydrogen spillover, Pd/ZIF-8 catalyst shows unique alkyne semihydrogenation activity and selectivity for alkynes molecules. The methodology demonstrated in this study also provides a basis for further exploration of interfacial species migration.

Nanoparticle-Assisted Liquid Crystal Droplet Sensors Enable Analysis of Low-Concentration Species in Aqueous Medium.

We introduce nanoparticle-assisted liquid crystal (LC) droplet-based sensors that allow determination of low-level concentrations of aqueous soluble species. The silica nanoparticles functionalized with mixed monolayers composed of two distinct groups, hydrophobic alkane tail- and charged group-terminated silanes, facilitated ternary physical interactions between the model analytes (methylene blue (MB) or methyl orange (MO)) and the nematic mesogens 5CB (4-cyano-4'-pentylbiphenyl), and the interfacial species of the nanoparticle. The response of the LC droplets was measured upon nanoparticle adsorption as a function of analyte concentration, which was characterized by the optical determination of the configuration distributions of the LC droplets. We highlight the importance of the charging and the composition of the nanoparticle interfaces for analytical purposes that allow accurate determination of the concentration of the analytes on the order of 0.01 ppb. Such a low concentration corresponds to a low interfacial coverage of nanoparticles, indicating the promisingly high sensitivity of the sensor platform to target analytes. Distinct from the past examples of the LC-based sensors, the nanoparticle-assisted LC sensors allow detection of the species that do not directly cause an ordering transition at the LC-water interfaces, which allow a broader range of analytical targets. The sensor platform that we report herein can be easily tunable for a range of target molecules and will find use in the determination of a wide range of micropollutants in aqueous environments.

The nature of crystal facet effect of TiO2-supported Pd/Pt catalysts on selective hydrogenation of cinnamaldehyde: electron transfer process promoted by interfacial oxygen species.

Supported noble metal nanocatalysts typically exhibit strong crystal plane dependent catalytic behavior, but their working mechanism is still unclear. Herein, using anatase TiO2 with well-exposed crystal facets of {101}, {100} and {001} as a prototype support, Pd- and Pt-based supported TiO2 nanocatalysts (TiO2-Pd and TiO2-Pt) were prepared by chemical reduction with NaBH4 as reducer, and they showed a distinct metal-dependent crystal facet effect in the selective hydrogenation of cinamaldehyde (CAL). For Pd-based nanocatalysts, most Pd species on the {100} plane of TiO2 are present in the oxidized form with positive charges and unexpectedly show higher reactivity than the Pd species in the zero-valence state on the {101} and {001} planes. On the contrary, Pt species on all three crystal planes of TiO2 show zero-valence state, with relatively low conversion, but much better selectivity for hydrogenation of a CO bond than Pd-based catalysts. Well-designed experiments manipulating the stability and type of surface oxygen species confirmed that the essence of the crystal facet effect of the catalyst support actually creates a unique nanoconfined interface at the molecular level to construct a surface p-band intermediate state (PBIS), which provides a new alternative channel for surface electron transfer and consequently accelerates the reaction kinetics.

Boosting propane combustion over Pt/WO3 catalyst by activating interface oxygen species

Surface active oxygen species in heterogeneous catalyst material is very vital for driving catalytic volatile organic compounds (VOCs) oxidation, but it still remains challenging to effectively modulate such active oxygen species. Herein, the interfacial oxygen species in Pt/WO3 catalyst is conveniently activated by a heating treatment under nitrogen flow. The obtain Pt/WO3-N2-T (T = 200, 400, 600, represents the calcination temperature) shows much superior catalytic activity than the bare Pt/WO3 catalyst, particularly for the Pt/WO3-N2-400 catalyst with T95 of only 250 °C (T95 of Pt/WO3 = 350 °C). The changes of catalyst structure during heating treatment in nitrogen flow contributes to the improved activity, including re-dispersed WO3 support and Pt nanoparticles. More importantly, the surface oxygen species in the Pt/WO3-N2-400 catalyst is more active than that of the bare Pt/WO3 catalyst, which is generated by removing hydroxyl groups and its residual oxygen species activated by nearby Pt species. These novel findings provide the strategy to rationally activate surface oxygen in the heterogeneous catalyst materials for catalytic oxidation reaction.

Simulating Hard Carbon for Sodium-Ion Batteries with the DFN Model

The development of Sodium-ion battery technologies and materials is moving rapidly forward, and several companies are on the verge of commercialising their products. An important question is what knowledge and synergies that can be drawn from Lithium-ion batteries. This work has investigated whether the Doyle-Fuller-Newman model (DFN model) [1] can be used for simulating the insertion and extraction of mobile sodium ion in hard carbon. Previous work indicates that this should be the case [2]–[4].It has been shown that the insertion process of sodium in hard carbon does not follow the same process as for lithium in hard carbon [5]. The sodium insertion in hard carbon is suggested to be a combination of capacitive adsorption, intercalation and nanopore filling [6]–[8]. Hence, the question is if capacitive adsorption and nanopore filling can be simulated as an intercalation process. In addition, the sodium-ion has a lower charge density than lithium-ion, leading to different properties for the electrolyte and the interfacial species [9], [10].One of the issues with the DFN model is to measure, calculate or estimate the material and electrode properties needed. As a first step in investigating the above assumption, an additional assumption made is that the needed parameters can be extracted using similar methods as for Li-ion batteries. With this starting point, a parameter sensitivity analysis is made for simulating mobile sodium in hard carbon with the DFN model.

Molecular Additives at the Catalyst Ionomer Interface

The growth and viability of deep decarbonization through the hydrogen economy is dependent upon scientific advances that will address the existing political, regulatory, and technological barriers that currently hinder electrochemical energy technologies. The strong correlation between device-level performance and catalytic electrode activity/durability highlights the criticality of identifying the limiting processes and developing strategies to address these limitations. The goal of our group is to use fundamental insight derived from the study of well-defined systems to develop unique mitigation strategies, aimed at improving device-level performance, that go beyond simply varying electrocatalyst material properties. The interface between catalyst and ionomer in polymer electrolyte membrane fuel cells (PEMFC) greatly limits device performance through detrimental impacts to local reactant transport and reaction kinetics. Optimization of the catalyst/ionomer interface to not only mitigate these detrimental impacts, but to also beyond existing performance is a challenging task. In this presentation we will present our work in developing molecular interfacial modifying species to optimize the interaction between catalyst and ionomer. Integrating molecular components such as ionic liquids or caffeine both enhances the kinetics of the electrode reactions and limits the detrimental impacts of ionomer on the catalyst surface. We will present our fundamental understanding of why these molecular additives improve catalyst activity and limit the impacts of ionomer. We will also present our integration of these molecular moieties into next generation ionomers and their performance in PEMFC membrane electrode assemblies (MEA).

CFD-based bioreactor model with proportional-integral-derivative controller functionality for dissolved oxygen and pH.

A physics-based model for predicting cell culture fluid properties inside a stirred tank bioreactor with embedded PID controller logic is presented. The model evokes a time-accurate solution to the fluid velocity field and overall volumetric mass transfer coefficient, as well as the ongoing effects of interfacial mass transfer, species mixing, and aqueous chemical reactions. The modeled system also includes a direct coupling between process variables and system control variables via embedded controller logic. Satisfactory agreement is realized between the model prediction and measured bioreactor data in terms of the steady-state operating conditions and the response to setpoint changes. Simulation runtimes are suitable for industrial research and design timescales.

Synergistic effect of platinum single atoms and nanoclusters for preferential oxidation of carbon monoxide in hydrogen-rich stream

Despite the maximum atom-utilization efficiency and remarkable activity of single-atom catalysts, further improvement of catalytic activity can be obtained by the synergistic effect of single atoms and nanoclusters in some catalytic systems. Herein, CeFeOx-supported Pt single atoms coupling with subnanometric clusters (Pt1-Ptn) structures are developed via a facile strategy. They are applied as the highly efficient catalysts for the preferential oxidation of CO in H2-rich stream (CO-PROX), which achieve complete elimination of CO at low temperature of 50 °C, with a wide operating temperature window and extraordinary stability for over 500 h without noticeable deactivation. The exceptional performance is attributed to the synergistic effect of distinctive Pt1-Ptn structures, which couple the benefits of Pt single atoms and subnanometric clusters in a remarkable way. The disadvantages of single Pt species catalysts, such as sensibility to strong adsorption of CO or reduced lattice oxygen reactivity due to excessive coordination, can be well mitigated. The results of detailed characterizations and density functional theory calculations confirm that the unique structures possess moderate adsorption strength for CO and create abundant active interfacial oxygen species, because of the absence of bulk metallic Pt0 and appropriate coordination to lattice oxygen, which synergistically facilitate the catalytic performance.