Electrocatalytic reactions involve interfacial interactions between the surfaces of electrodes and reactive species at an electrolyte interface. There are presently no universal or unambiguous methods to directly assay the active top atomic layer composition that influences the reactivity of these electrodes under relevant operating conditions. Low-energy ion scattering (LEIS) spectroscopy is a surface characterization technique that yields compositional analysis of the outermost atomic layer of a material, but it must be performed in ultrahigh vacuum (UHV). Application of LEIS measurements to electrochemical materials that are removed from ambient liquid-phase environments thus leaves an open question as to whether the surface that is transferred to UHV is truly the surface that manifested during the electrochemical reaction. Toward the goal of preserving the active surface state, we developed a sample transfer workflow for LEIS enabling air-free removal and drying of an electrode from an electrochemical cell while maintaining control of the potential using an auxiliary electrode. The potential-controlled emersion method was demonstrated to give distinct potential-dependent surface compositions for a Cu-Pd alloy relative to removal after uncontrolled return to open-circuit potential. A Cu-enriched surface was found at anodic potential and a Pd-enriched surface at cathodic potential, suggesting that the approach can be used to retain representative atomic configurations during transfer. Since adsorbates will often persist from the reaction environment, conventional sample pretreatment methods for removal, including atomic O and atomic H exposure, were also contrasted. Both methods were found to differ with results from incidental low-dose depth profiling by the LEIS primary ion source, which removes adventitious species and surface atoms during the course of repeated measurements. These depth profiles were found to be sensitive to sample history and thus qualitatively informative, despite the possible changes induced by ion damage. The results exhibit (i) the need for complete control over the polarization state of the sample at all times (no excursions to open circuit during transfer) and (ii) the utility of low-dose depth profiling to capture changes in the near-surface composition.
Ferroelectric oxides from the perovskite-type (Ba,Ca)-(Zr,Ti)-O3 system are emerging as one of the upcoming lead-free piezoelectrics for future sensing and actuating applications. Improving their functionality requires a precise adjustment of precursor choice, pretreatment, as well as reaction and sintering times and temperatures to optimize the defect chemistry and microstructure of the material. In this respect, understanding the reaction pathways of the precursors has a crucial impact on the final functional properties. In this article, we show that the high-temperature modification of the BaCO3 precursor can strongly influence the reaction by facilitating a topochemical reaction pathway via the formation of an intermediate oxycarbonate phase of BaTiO3-x (CO3) x (x ≈ 1/3). This results from the diffusion of Ti4+ and 2 O2- into the material in combination with CO2 outgassing, distinguishing this reaction path from the previously reported diffusion mechanism via an intermediate phase of Ba2TiO4, which happens in parallel. We used high-temperature in situ X-ray diffraction and automated diffraction tomography to derive a structural model of this previously unknown intermediate oxycarbonate phase, which can be understood as a trigonal distortion variant of the cubic perovskite structure, where the trigonal distortion originates from the planar nature of the carbonate anion. This mechanism might have implications on how the BaCO3 precursor and its decomposition behavior could decisively influence particle morphology and composition obtained prior to sintering of (Ba,Ca)-(Zr,Ti)-O3 ferroelectric oxides.
Chalcohalide semiconductors are rapidly gaining traction as stable, biocompatible materials for energy conversion applications. While the solid-state synthesis of bulk chalcohalides is relatively well-developed, the colloidal chemistry of these materials is still in its early stages. Colloidal semiconductors are often advantageous in device fabrication due to the cost effectiveness of solution processing. Thus, we aim to increase the utility of chalcohalides in device fabrication by establishing solution phase chemistry of promising compositions. We show that silyl hot-injection is a versatile and effective method of making colloidal PnChI (Pn = Sb, Bi; Ch = S, Se) and Sn2PnS2I3 (Pn = Sb, Bi) chalcohalides of tunable sizes and compositions. Furthermore, we demonstrate the preparation of mixed-pnictide chalcohalides through direct hot-injection and/or postsynthetic cation exchange, the latter being one of the few reported instances in chalcohalides. Additionally, we use the thiocyanate heat-up approach in combination with density functional theory to study halide mixing in quaternary tin chalcohalides. By pushing the limits of each synthetic technique, we have designed more soluble chalcohalides with tunable compositions while also gaining a better understanding of the efficacy of each procedure in respect to thin film and subsequent device fabrication. In addition to size and composition tuning, silyl hot-injection can help facilitate the future development and wide-scale application of chalcohalide-based devices by expanding the selection of solution-processable chalcohalides.
Heavy metals are a persistent environmental problem due to their high toxicity, even at very low concentrations (parts per billion, ppb). The removal of such diluted heavy metals is challenging because of the competition the counterions (Ca2+, Na+, Mg2+, etc.) present in natural water bodies. The design of sorbents capable of removing ions below the action limit (15 ppb for Pb2+) requires a strong driving force for selective uptake and rapid removal. In this work, we report the synthesis of porous CaS aerogels (surface area = 143.6 m2/g) by oxidative assembly of CaS nanoparticles and describe their use in selective Pb2+ ion remediation from water. Despite the presence of amorphous CaCO3 (up to 50 wt %) in the gel network, the gels demonstrated a capacity of 17.1 mmol Pb/g aerogel (3543 mg/g), and this could be augmented to 22.5 mmol Pb/g aerogel (4593 mg/g) by modifying the synthesis to reduce CaCO3 content to ca. 15 wt %. Moreover, the selectivity of CaS aerogels toward Pb2+ ions is high, as evidenced by little-to-no change in the distribution constant (K d ∼ 104) in the presence of competing ions (1 M) such as Na+, Mg2+, and Ca2+. During remediation with low concentrations (100 ppb) of Pb2+ with CaS aerogels, the level of Pb2+ dropped to 5.4 ppb (below the 15 ppb EPA limit) within 1 h with a 95.4% removal efficiency. In contrast to the CO2 supercritically dried aerogels, lower surface area ambient dried gels (xerogels) only remove 40% of the lead ions from a 100 ppb solution, saturating within 1 h. The efficiency and rapidity of selective Pb2+ uptake using CdS aerogels arise from a combination of a strong thermodynamic driving force for cation exchange (K eq = 2.5 × 1027) and chemisorption along with favorable kinetics associated with the high surface area porous architecture. These results show that formation of high surface area metal chalcogenide aerogels by oxidative assembly to form nanocrystalline architectures, as previously demonstrated for II-VI and IV-VI semiconductors, can be extended to the more highly ionic alkaline earth sulfides.
We present the discovery of Mo4FeGa17.25-x Ge x (x ∼ 2.1(4), based on determination of Ge content), a complex gallide featuring a variety of point substitution phenomena. Its crystal structure is derived from the Ti2Ni type, in which a diamond network of face-sharing octahedra is interpenetrated by a second diamond network of vertex-sharing stella quadrangula. However, while in the ideal Ti2Ni type these two frameworks run uninterrupted through the crystal, Mo4FeGa17.25-x Ge x shows three variations. First, the inner tetrahedron of every other stella quadrangula is replaced with a main group atom, creating tetrahedra reminiscent of the Zintl phase NaTl. Next, a selection of Ga6 octahedra are filled with Fe atoms, in a manner analogous to the stuffed AuCu3-type phases. Finally, the refined crystal structure shows that in each unit cell a single Ga2 atom in the octahedral network is substituted with a dumbbell of Ga/Ge atoms. Electronic structure calculations on ordered models of Mo4FeGa17.25-x Ge x reveal a narrow band near the Fermi energy, which is explained in terms of the 18-n and octet bonding schemes using reversed approximation Molecular Orbital analysis. A DFT-chemical pressure analysis connects the tetrahedron/atom and atom/dumbbell substitutions to the relief of atomic packing tensions and highlights soft atomic motions within the octahedral framework and driving forces for atom/dumbbell substitution. The combination of soft vibrational modes, disorder, and a narrow band gap could make this phase of interest for potential thermoelectric properties.
Ternary spinel oxides of formula MB2O4 are attractive materials for optoelectronic and photocatalytic applications due to their chemical stability and compositional flexibility. Understanding how the compositions of these materials influence their optical properties is crucial for their further development as photoactive materials. Here, we present a quantitative comparison of the absorption spectra of two families of colloidal ternary spinel oxide nanocrystals:metal ferrites (MFe2O4) and metal gallates (MGa2O4). We found that, despite the similar crystal structure, shape, and surface ligands of the ternary spinel ferrites and gallates, the optical properties of these materials are significantly different. The ferrites exhibit strong absorption throughout the visible region, with spectra and per iron extinction coefficients that do not change significantly upon changing the identity of the M metal. In contrast, the gallates exhibit significantly larger band gaps and much lower extinction coefficients, with spectra that do depend on the identity of the M metal. We assign the visible absorption observed in ferrites to O 2p → Fe 3d charge transfer transitions, whereas the visible range transitions observed in some of the gallates arise from intra-atomic d-d transitions associated with the M2+ cations. We corroborate our findings with band structures calculated by using Hubbard- and Hund-corrected density functional theory computations (DFT+U+J).
Effective design of cell-delivery scaffolds is of key importance for regenerative medicine technologies to meet their full potential, especially when considering cell delivery to wounds of complex architecture or directly into the biological environment. Few studies, however, focus on a systematic approach to understanding the cell, polymer scaffold, and final biomaterial properties of this composite material. In this work, we report on the systematic analysis of a supramolecular hydrogel composed of ionically cross-linked peptide amphiphile (PA) nanofibers, optimized for high-shear delivery of therapeutic cells, and compare the performance of this biomaterial to a covalent polymer hydrogel of ionically cross-linked alginate. Using a full factorial design of experiments (DoE), we investigated the interplay between polymer concentration and cell loading to determine the impact on mechanical properties, structural integrity, substrate adhesion, and sprayability of the hydrogel. The shear-thinning and thixotropic nature of the supramolecular hydrogels enabled effective deposition through a spray nozzle, not possible with the alginate hydrogel, while preserving cell viability and hydrogel mechanical properties. The supramolecular backbone of the PA nanofibers enabled remarkable mechanical resilience and full recovery post-spray, even at cell loadings as high as 2 million cells/mL, while significant loss of gel integrity was observed with the alginate hydrogel at equivalent cell loadings. Our findings establish a robust structure-property relationship framework for the formulation of cell-laden supramolecular hydrogels capable of high-shear delivery, highlighting their potential as customizable platforms for regenerative medicine, advanced wound care, and 3D printing applications.
The exploration of higher-dimensional chemical phase spaces and the synthesis of novel compounds can be achieved by applying a multiple-anion approach to materials discovery. The ability to combine and tune the stoichiometry of anions in a material can enable enhanced control of both the physical and electronic structures, providing a strategy for the modification of the properties of new materials being developed for a variety of applications, including solar absorbers and thermoelectrics. Here, we report the synthesis of Cu7.62Bi6Se12Cl6I, a quadruple-anion (Se2-, (Se2)2-, Cl-, I-) material within the Cu-Bi-Se-Cl-I phase space. Crystal growth reactions yield black, needle-like crystals, which exhibit a highly anisotropic and complex structure containing the four distinct anion types, solved from single-crystal X-ray diffraction data. Compositional analysis confirms the complex material stoichiometry, and a low band gap of 0.94(5) eV is measured to understand the potential for solar-absorbing applications. Cu7.62Bi6Se12Cl6I has a low thermal conductivity of 0.25(2) W K-1 m-1, which is attributed to multiple structural features via analysis of experimental heat capacity data and is achieved through the diversity in bonding that is accessed through the combination of four different types of anion.
NU-1000, a pyrene-containing benchmark metal-organic framework (MOF), is well-known for its utility and potential across a wide range of applications. Although the extended π-systems in NU-1000 confer favorable properties for diverse photochemical applications, they also increase the susceptibility of the MOF to photodegradation. However, the photostability of NU-1000 has yet to be systematically studied and remains poorly understood. Herein, we report that in the presence of oxygen, water, and light of appropriate energy, extensive oxidation of the pyrene linkers of NU-1000 can occur to yield terephthalic acid as the major decomposition product. Through extensive mechanistic studies, we show that the open framework structure of NU-1000 greatly facilitates linker oxidation, with more than 25-fold greater linker decomposition from the MOF within 3 h of photoirradiation compared to a homogeneous solution of the linker, brought about by rapid generation of pyrene-centred holes. By determining the specific conditions under which the MOF remains stable, our findings offer not just valuable strategies for preserving the integrity of NU-1000 for controlled applications but also reveal its ability to decompose into benign products under ambient light and oxygen, which could provide an eco-friendly route for avoiding environmental accumulation of MOF materials for various applications.
We report an aqueous synthesis of Rhodium (Rh) nanodendrites and evaluation of their merit as a bifunctional electrocatalyst toward hydrazine-assisted water splitting. The formation of dendritic morphology can be attributed to the fast reduction kinetics responsible for burst nucleation and then attachment growth. Rapid reduction results in a high concentration of Rh atoms, which quickly nucleate and grow into ultrafine Rh nanocrystals, followed by their evolution into dendritic structures through attachment growth. Extending the reaction time naturally prolongs the number of branched arms while increasing the overall size of the particles. Aging the Rh-(III) precursor solution slows down the reduction kinetics, leading to the formation of fewer Rh nanoparticles for the generation of smaller dendrites. The reaction temperature influences the reduction kinetics during nucleation and then aggregation thermodynamics governing the attachment process. Together with a high specific surface area, the lattice defects arising from attachment growth induce tensile strain, resulting in more and better catalytic sites. When evaluated as a bifunctional electrocatalyst toward hydrazine oxidation and hydrogen evolution reactions, the Rh nanodendrites gave an enhanced mass activity of 162.0 A mg-1 at 0.20 V vs RHE for hydrazine oxidation and 8.6 A mg-1 at -0.07 V vs RHE for hydrogen evolution, approximately 1.5 times greater than that of 5 nm Rh nanocubes, highlighting their promise for applications such as hydrazine-assisted water splitting.
A hallmark of nanoparticle cation exchange reactions is their ability to deterministically place different materials at precise locations within the same nanoparticle. This synthetic control underpins a broad application space, with synergistic properties that emerge from the relative spatial arrangements of the materials. However, despite advances in our understanding of how and why certain arrangements of materials and interfaces are preferentially observed as products of cation exchange reactions, our knowledge of design guidelines and synthetic tuning knobs remains limited. Here, we correlate the placement of ZnS, CdS, Co9S8, and Cu1.8S segments within heterostructured nanorods with the superionic transition temperature of copper sulfide, which is the most common nanoparticle template used for cation exchange. For cation exchange reactions that occur below the superionic transition temperature of approximately 100 °C, the resulting materials appear at various locations with the nanorods, including at the tips and within the body region. However, at higher cation exchange temperatures, material placement at the nanorod tips is observed almost exclusively. Additionally, we observe thin regions of copper sulfide sandwiched between Co9S8 and both ZnS and CdS, which help to relieve interfacial lattice strain. Overall, many different heterostructured nanorod architectures can be accessed through simple temperature-controlled partial cation exchange reactions that leverage interrelated contributions from interfacial lattice strain and the superionic nature of copper sulfide.
Two-dimensional van der Waals (vdW) magnets are attracting significant attention, both as platforms for studying fundamental magnetic interactions and for the exciting possibility of utilizing them as building blocks in devices and heterostructures, which may lead to new physical phenomena and functionalities. Here, we provide a detailed study of the crystal structure and physical properties of the recently discovered vdW ferromagnet FePd2Te2. We find this compound has a relatively wide width of formation, and grow single crystals with compositions Fe x Pd y Te2 where x ranges from 0.9 to 1.1 and y from 1.8 to 2.5, respectively. Temperature-dependent X-ray diffraction and transport measurements reveal that a first-order structural transition occurs in the range of T = 360-420 K, where the critical temperature, modulation wave vector, and corresponding room-temperature crystal structures all depend on chemical composition. Above the transition, the compounds with Pd fraction y > 2 adopt a disordered derivative of the tetragonal FeTe structure, with the Fe layer showing mixed Fe/Pd occupancy and the extra Pd atoms partially occupying interstitial sites. Below 370 K, the structure is incommensurately modulated, likely associated with the complex ordering of Pd/Fe atoms in the metal layers or the interstitial Pd in the vdW gaps. For y < 2, the composition Fe1.1Pd1.8Te2 has monoclinic symmetry at room temperature that is consistent with the reported structure of FePd2Te2. This phase undergoes a structural transition at 420 K for which the high temperature structure is yet to be determined; however, based on the similarities with the y > 2 compounds, we speculate that its T > 420 K structure is also tetragonal. Importantly, the high temperature, symmetry-breaking structural transition observed here provides a likely explanation for the origin of the structural domains previously observed in FePd2Te2. All compounds investigated in the Fe x Pd y Te2 series show metallic behavior, with magnetic characterization indicating that they are easy-plane, hard, ferromagnets with T C spanning 98-180 K. Both the critical temperature for the structural transition and the Curie temperature are moderately suppressed with increasing Pd fraction y and corresponding decreasing Fe fraction x, indicating that synthetic control over x and y paves way for the further exploration of these compounds.
Molecular doping of conjugated polymers (CPs) is a key strategy for improving the performance of organic electronics devices, particularly thermoelectrics. Doped donor-acceptor (D-A) conjugated polymers, characterized by a tunable energy gap between the Fermi level and the transport band, show great promise in achieving high electrical conductivity (σ) while preserving a favorable Seebeck coefficient (S). Despite the promising performance enhancement of chemically doped D-A polymers, their thermal stability remains largely underexplored, a crucial consideration for the long-term operation of organic thermoelectric devices. In this study, we investigated the dopant size-dependent thermal stability of a diketopyrrolopyrrole-thiophene (DPP-T) D-A copolymer, utilizing two p-dopants: 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) and Mo-(tfd-CO2Me)3. Temperature-dependent UV-vis-NIR spectroscopy revealed that DPP-T/F4TCNQ is more prone to dedoping under a high temperature thermal stress than DPP-T/Mo-(tfd-CO2Me)3. Although the F4TCNQ doped polymer shows higher initial in-plane conductivity than its Mo-(tfd-CO2Me)3 counterpart, it undergoes a conductivity loss of more than an order of magnitude after annealing at 120 °C for 30 min. In contrast, the in-plane conductivity of DPP-T/Mo-(tfd-CO2Me)3 remains stable under the same thermal conditions. Thermogravimetric analysis ruled out dopant sublimation as a primary contributor to dedoping, leading us to attribute the conductivity loss in F4TCNQ-doped DPP-T to dopant phase separation and migration. This observation was further confirmed by X-ray scattering studies and nanoscale infrared microscopy and spectroscopy studies. This work could provide further insights into the thermal stability of doped conjugated polymers and suggests that incorporating bulkier dopants is an effective strategy to enhance the thermal robustness of doped DPP-type systems.
The controlled synthesis of bimetallic alloy nanoparticles within confined environments remains a significant challenge due to aggregation, uncontrolled growth, and/or support instability, among others. Metal-organic frameworks (MOFs) offer an attractive platform to address these limitations by acting as active supports that spatially confine nanoparticle nucleation and growth. Herein, we report a galvanic replacement strategy for the formation of ultrasmall Au/Ag alloy nanoparticles (Au/AgNPs) confined within the nanometric microporous framework of MIL-125-NH2(Ti). This approach enables controlled incorporation of alloy nanoparticles both at the external surface and within the internal porosity of the MOF while preserving the crystalline structure and colloidal stability of the host framework. Comprehensive structural and compositional characterization confirms the successful formation of confined Au/Ag alloy nanostructures. The functional implications of alloy confinement are illustrated through irradiation experiments, which indicate an enhanced interaction with ionizing radiation compared to the pristine MOF. These results highlight the potential of MOF-confined bimetallic alloys as a versatile platform for applications requiring controlled nanoscale composition, stability, and interactions.
The reduction of tetravalent manganese (Mn-(IV)) to trivalent manganese (Mn-(III)) by HEPES Good's buffer is often used to modify the reactivity of δ-MnO2 and to distinguish between the Mn-(III) and Mn-(IV) oxidants in redox reactions. However, the structure of HEPES-reacted δ-MnO2 has remained elusive, hindering a detailed understanding of interfacial electron transfer between adsorbed species and structural Mn. Here, we characterized the structure of δ-MnO2 reacted with HEPES at pH 6 and 8 under low and high NaCl ionic strength, using chemical analysis, high-energy X-ray diffraction, pair distribution function (PDF), extended X-ray absorption fine structure (EXAFS) spectroscopy, and high-resolution transmission electron microscopy (HRTEM) coupled with selected area electron diffraction (SAED). The average Mn oxidation state (AMOS) decreases from 3.92-3.87 to 3.71-3.59 after HEPES addition, depending on pH and ionic strength. HEPES-reacted δ-MnO2 has a distinctly different structure at low and high ionic strength. At low ionic strength, the δ-MnO2 HE crystallites are 3-6 nm across, and the MnO2 layers have approximately 23% vacant sites capped with mainly Mn-(III) and some Mn-(II). At high ionic strength and pH 8, δ-MnO2 HE contains large crystals, several hundred nanometers across, made up of crystallographically oriented nanodomains. Most SAED patterns show streaks along the [100]* direction, indicating a high degree of disorder in the close packing of the anionic sheets, in the Na position within the interlayer, and in the Mn-(IV)-Mn-(III) distribution within the layer. Some nanodiffraction patterns show distinct superstructure reflections along the streaks with A* = 3a*, as seen in well-crystallized triclinic birnessite, and A* = 6a*. High-ionic-strength δ-MnO2 HE has no interlayer Mn-(III), and the Na-(I) ions, along with the layer Mn-(III) and Mn-(IV) cations, are semiordered at the short- to medium-range scales and essentially disordered over longer distances. Identifying the two distinct structures of HEPES-reacted δ-MnO2 clarifies structural ambiguities reported in the literature and provides a solid foundation for exploring its redox reactivity and electrochemical performance.
Passivation of surface defects of cesium lead halide (CsPbX3, X = Cl, Br, I) nanocrystals is crucial to improving the stability and photoluminescence of these materials for further optoelectronic applications. Many ligands have been examined for surface passivation; however, a ligand design principle for improved photoluminescence quantum yield (PLQY) is still not available. Here, we report a combined computational and experimental study to systematically investigate 27 commercially available ligands and develop foundational guidelines. Using first-principles density functional theory, we calculated the binding energy of the ligands on the CsPbBr3 nanocrystal. We find a volcano relationship between ligand binding energy and the experimental PLQY, which reveals the negative impact of overly strong binding energy. We further perform electronic structure analysis and time-resolved optical spectroscopy to reveal that these strong-binding ligands can withdraw more electrons from the surface and induce trap states within the bandgap. With this, we develop a design principle for the PLQY of CsPbBr3 nanocrystals, highlighting the importance of the ligand binding energy comparable to that of the native halide species. We further applied this design principle to quantum-confined CsPbCl3 and CsPbI3 nanocrystals, and our computational predictions have been successfully validated by experiments.
We present a method for preparing NiPt-alloy tips on CdSe-core/CdS-shell dot-in-rod nanoparticles (DRs). The formation of the NiPt tips is separated into a two-step synthesis, where first Ni tips are grown, which then serve as nucleation sites for Pt before an alloying process occurs. Thus, the NiPt tips are formed in a seed-mediated approach. We find that the reactivity of the Ni tips can be controlled by oxygen treatment, while the reactivity of the lateral surface of the DRs can be tuned by ligands. Monitoring the growth dynamics of the NiPt reveals that an oxide layer on the Ni tips delays the nucleation of Pt, but it does not inevitably prevent it if a combination of oleic acid and oleylamine initiates oxide-layer conversion due to oleate formation. Without conversion, the oxide layer can be utilized to inhibit the NiPt formation. The choice of ligands can be exploited to enable or prevent separate Pt particle growth on the lateral semiconductor rod surface. Especially the DRs with NiPt-alloy tips show superior activity toward HER in both electrocatalytic and photocatalytic experiments.
Cell-matrix interactions are a central topic in the field of biomimetic material mechanics. While the influence of matrix stiffness on cellular adhesion, spreading, and differentiation has been extensively investigated, the reciprocal impact of cells on the mechanical properties of biomimetic matrices remains less explored. In this work, we demonstrate that fibroblasts can remodel the mechanical properties of collagen-alginate hybrid hydrogel (CAH) matrices in a 2D culture. We found that, in the absence of cells, CAHs showed a progressive stiffness decline in the cell culture medium due to calcium ion release. In contrast, when fibroblasts were present, the stiffness of the hydrogels remained stable despite calcium ion release. This stabilization was collectively contributed by fibroblast activity and calcium deposition, with cells serving as mineral nucleation sites and reinforcing the local collagen network. Together, these results highlight the role of cells in reshaping the biomaterials' mechanical properties and advance our understanding of the dynamic, reciprocal nature of cell-extracellular matrix interactions.
Development of efficient electrocatalyst materials for performing both the oxygen evolution reaction (OER) and the electrochemical oxidation of ethylene glycol (EGOR) is crucial for advancing energy-efficient electrolysis and valorization of plastic waste-derived chemicals. In this study, we present a comprehensive investigation of self-supported Ni-based catalysts grown on nickel foam and systematically tuned with Mn, Fe, Co, and Pd to achieve controllable bifunctional activity. Among these materials, Fe-NiO x H y exhibits superior OER performance in 1 M KOH, delivering an overpotential of 250 ± 7 mV at 100 mA cm-2 with a Tafel slope of 35 ± 2 mV/dec. Hierarchical architectures and their crystal structure, confirmed by scanning electron microscopy and X-ray diffraction, provide abundant active sites and enhance mass transport kinetics. Quasi in situ Raman spectroscopy and ex situ X-ray photoelectron spectroscopy reveal potential, reactant concentration and activation-dependent reconstruction of metal active sites, demonstrating how controlled tuning of metal oxidation states affects both OER activity and EGOR selectivity. Electrochemical activation enhances the valence of metal centers, enabling precise control over EGOR product selectivity. Pd incorporation stabilizes *C2 intermediates, favoring glycolate formation at low anodic potentials, while Mn-, Fe-, and Co-modified Ni promote a *C1 pathway leading to formate at relatively higher potentials, with Fe-NiO x H y achieving a Faradaic efficiency (FE) of up to 86.2% toward formate. In contrast, Pd-NiO x H y /NF delivers a glycolate FE of up to 92.5%. Optimized reaction conditions, including applied potential, EG concentration, and activation protocol, allow selective production of either glycolate or formate during EGOR. This work provides an active site and mechanistic understanding connecting catalyst composition, activation, and oxidation-state dynamics to selectivity, providing a detailed insight for integrating PET-derived EG valorization with energy-efficient hydrogen production.
Chemically preintercalated bilayered vanadium oxide (BVO) electrodes derived from V2CT x MXene exhibit superior Na-ion storage performance compared to compositionally similar BVO counterparts synthesized from α-V2O5 powder. Here, we report for the first time the precursor-dependent structural differences in Na-preintercalated BVO electrodes (δ-Na x V2O5·nH2O) synthesized from α-V2O5 powder (AD-NVO) and V2CT x MXene nanoflakes (MD-NVO) and show how these differences govern their electrochemical behavior in a nonaqueous Na-ion energy storage system. Our analyses show that AD-NVO and MD-NVO exhibit distinct compositions of δ-Na0.37V2O5·0.46H2O and δ-Na0.33V2O5·0.21H2O, respectively, along with pronounced differences in morphology, electronic structure, and interlayer chemistry. Scanning electron microscopy reveals the formation of 1D nanobelts for AD-NVO, whereas MD-NVO consists of 2D nanoflakes assembled into nanoflower-like agglomerates. X-ray photoelectron spectroscopy indicates that Na preintercalation led to different extents of V5+ to V4+ reduction in AD-NVO and MD-NVO, attributed to differences in the structural water content, which was further supported by the V4+ content quantification via electron paramagnetic resonance. Electrochemical measurements show fundamentally different charge storage behaviors: AD-NVO exhibits largely capacitive responses, while MD-NVO displays pronounced Na+ redox activity and delivers a higher specific capacity, improved rate capability, and superior cycling stability. Magic-angle spinning 23Na solid-state NMR identifies two distinct interlayer Na environments in MD-NVO, in contrast to a single Na site in AD-NVO. These sites play complementary roles, with one facilitating Na+ transport and the other acting as stabilizing pillars, as confirmed by ex situ X-ray diffraction. This study reveals how precursor-dependent structural evolution in chemically preintercalated layered oxides governs interlayer chemistry and electrochemical function, providing design principles for engineering layered metal oxides for advanced energy storage.