59 Search Results

Transition-metal oxyhydroxides such as CoOOH are promising low-cost electrocatalysts for the selective electrooxidation of organic molecules, yet the influence of ubiquitous transition-metal impurities on their performance and durability remains poorly understood. Here, we experimentally probed the individual and synergistic electrochemical and structural effects of Ni and Mn incorporations into model CoOOH electrocatalysts toward an efficient benzyl alcohol oxidation reaction (BAOR). Comprehensive electrochemical, microscopic, and spectroscopic analyses reveal that Ni incorporation enhances charge-transfer kinetics and overall activity through the formation of catalytically active Ni³⁺ sites, whereas Mn exhibited a more complex but interesting role. At the early stages of operation, Mn⁴⁺more » acts as a stabilizing surface layer that mitigates catalyst degradation but partially blocks Co sites before they undergo gradual leaching. The concurrent incorporation of both Ni and Mn yields a trimetallic 2NMC@NF electrocatalyst that integrates the activity benefits of Ni with the stability conferred by Mn, achieving 92.9% benzyl alcohol conversion and 91.4% Faradaic efficiency after 24 h at 1.5 V vs RHE. These findings elucidate how trace Ni and Mn impurities, often introduced from electrolytes or external sources, can modulate the lattice and electronic structure of CoOOH, offering a design strategy for enhancing both activity and long-term stability in electrocatalytic organic oxidation.« 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

A series of three symmetric, hollow spherical, and shape-persistent molecular organic cages analogous to C₂₀ and C₆₀ were examined by computational modeling, analyzing structural elements, strain indicators, and physical properties relevant for potential applications. The compounds are covalent aromatic cages based on 1,3,5-substituted benzene nodes linked by paraphenylene or para-pyrenylene-connectors, with diameters varying from 2.3 to 4.2 nm. The apertures in the cage interior are varied by virtue of the cage type (C₂₀- or C₆₀-type cage) and the linear connectors placed between the C₆H₃-units. NBO and MESP analyses indicate the presence of electrophilic and nucleophilic sites in the molecular skeleton.more » In the cages with the phenylene-connectors, the HOMO−LUMO gaps are close to 4.0 eV. In the cage coated with an enlarged polyaromatic spacer (pyrene-unit), the gap is reduced by approximately 0.4 eV.« less

Water electrolysis, including seawater splitting to produce hydrogen and oxygen, stands as a promising approach for the efficient storage of intermittent energy. However, the half-reactions of water splitting, the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), are known to be very sensitive toward the quality of water employed and are susceptible to contaminants originating from various sources, including the electrolyte or the electrodes. Those contaminants have a profound impact on the activity of these reactions of water splitting by modifying the electronic and physical structures of electrocatalysts as well as electrode–electrolyte interfaces. For seawater electrolysis, the unintentional presencemore » of impurities, such as anions, cations, and organic compounds, affects the catalyst stability, selectivity, and activity. Despite the existence of numerous comprehensive reviews that delve into various aspects of catalysts and their structure–property relationships for several electrocatalytic reactions, the impact of contaminants has often been ignored. This critical review endeavors to address this issue by providing an overview of the diverse sources of contaminants influencing electrocatalytic water splitting and seawater splitting reactions, delineating the trends in electrochemical parameters and detailing different characterization methods for elucidating the physical and electronic changes of the electrode and electrolyte.« less

Spherical and hollow molecular cages based on planar triazine (C₃N₃) hubs and aromatic phenylene connectors have been developed. The cages exhibit topologies akin to C₂₀, C₆₀, and C₇₀ fullerenes with diameters that range from 2.3 to 4.9 nm. Apertures into the cage interiors are tuned by varying the aromatic connectors situated between the C₃N₃-units. The stabilities of the C₃N₃ cages increase with size owing to reduced bending strain of planar nodes and connectors that make up the spherical aromatic networks. Doping of the cages with Li⁺ reveals the capacity of the cages for significant adsorption of gaseous H₂ and CO₂.more » The design of graphene-like spherical cages is also discussed.« less

X-ray Photoelectron Spectroscopy spectra peak models, designed to partition photoemission signals emanating from different elements or chemical states within an atom, are fitted to data limited to an energy interval over which inelastically scattered photoemission signal can be estimated. While the choice of background approximation and line shapes of components to the peak model requires careful consideration, the energy interval used to define the data to which the peak model is optimized has a significant impact on the final peak model. The relationship between the background intensity and data intensity at the start and end of the energy interval dictatesmore » the line shapes used in the peak model. In this work, we devise a method to peak fit a complex overlapping Cu 3p and Pt 4f XPS peak structure to perform the elemental quantification. We first use an Al 2s peak to illustrate how background curves approach data at the limits of the energy interval over which the background is defined, influencing the analysis of XPS spectra. Next, we demonstrate the nature of interactions between specific line shapes (Voigt and pseudo-Voigt profiles) suitable for photoemission peaks and a specific background curve (Shirley) and a peak model is presented that includes components to the peak model that accommodates background intensity during fitting of the peak model to data. The peak model allowed for quantification of the contributions of Pt 4f peaks emanating from the substrate that exhibits strong asymmetry in the presence of the inhomogeneously distributed Cu species, mostly of Lorentzian character.« less

Electrolysis of impure water (such as seawater) has recently garnered research interest as it may enable hydrogen production at reduced costs. However, the tendency of impurity ions and other species to degrade electrocatalysts and membranes within an electrolyzer is a serious challenge. Here, we investigate the effects of copper impurities of varying concentrations on the hydrogen evolution reaction (HER) using platinum electrocatalysts. A decrease of current density is observed with an increasing copper concentration. By comparing the effect of ionic impurities on current density at different concentrations, we gain insight into how impurities can interfere with the HER at differentmore » potentials. Surface characterization of the electrodes reveals differences in the morphology and extent of copper deposition on HER-active platinum vs inactive gold electrodes. This enables an improved understanding of how copper nucleates and grows on the two types of electrodes under different electrochemical conditions while also confirming deposition in low-concentration cases, as present in seawater. The results indicate that copper electrodeposition competes with the HER, and the nature of copper electrodeposition varies depending on the electrocatalytic activity of the electrode. This study provides insight toward catalyst design that can withstand the effects of impurity-induced degradation over extended use.« less

Palm oil, one of the most widely used vegetable oils, offers significant potential as a sustainable feedstock for biofuel production. This study explores the deoxygenation of palm oil using glycerol as a hydrogen donor, with nickel-molybdenum (NiMo) catalysts supported on commercial alumina (Al₂O₃), and zeolite (HZSM-5) comparing with self-prepared zirconia (ZrO₂). The catalysts were synthesized via incipient wetness impregnation and evaluated for their performance in biofuel production. NiMo/Al₂O₃ exhibited the lowest oxygen removal efficiency (68.5 %), while NiMo/HZSM-5 achieved a higher oxygen removal (74.3 %) but also demonstrated the highest coke formation. The type of support material influenced the resultingmore » biofuel range, with NiMo/HZSM-5 and NiMo/ZrO₂ favoring jet fuel production, whereas NiMo/Al₂O₃ was more suitable for diesel production. Notably, NiMo/ZrO₂ exhibited the highest performance in palm oil deoxygenation while minimizing coke formation. These findings highlight NiMo/ZrO₂ as a promising catalyst for efficient and stable biofuel production, with the support material significantly influencing product yield and fuel quality.« less

Biofuels offer a promising solution in the fight against climate change. With a global increase in waste cooking oil, this research investigated the production of bio-hydrogenated diesel (BHD) from waste cooking oil, using ethanol as a hydrogen donor in the deoxygenation process. A hydrolyzed waste cooking oil model compound served as the feedstock, and the deoxygenation was performed at 300–400 °C. The catalysts used in the experiments were 2.6 wt% Ni and 7.8 wt% Mo (2.6Ni-7.8Mo) and 10 wt% Ni and 5 wt% Mo (10Ni-5Mo) on γ-Al₂O₃. The results showed that ethanol is an effective hydrogen donor for biofuel productionmore » without the need for external hydrogen at an elevated pressure. The increasing temperature enhanced the free fatty acid (FFA) conversion and n-alkane selectivity in the oil product, with the highest FFA conversion and alkane selectivity of 100 % and 46 %, respectively, observed at 400 °C for the sulfided 10Ni-5Mo catalyst. On the other hand, 2.6Ni-7.8Mo offers 100 % FFA conversion with a lower n-alkane selectivity of 35 % at identical temperatures. The total acid number (TAN) of the oil products decreased from 174.03 mg KOH/g of feedstock to 9.43 and 8.67 mg KOH/g with the sulfided 2.6Ni-7.8Mo and 10Ni-5Mo catalysts, respectively. Both the catalysts achieved similar heating values (~43 MJ/kg) at 400 °C. This is a significant improvement to the HHV of the feedstock, which was 36.02 MJ/kg. Additionally, aromatic compounds, mainly BTXE (benzene, toluene, xylene, and ethylbenzene), were also produced. Compared to glycerol as a hydrogen donor, ethanol more effectively increased n-alkane selectivity due to its higher effective hydrogen-to-carbon ratio (H/C_eff). Conversely, glycerol was more advantageous for achieving greater selectivity towards BTXE compounds due to its lower H/C_eff, which potentially leads to coke formation. Since aromatic compounds are intermediates in coke production, glycerol provides higher aromatic selectivity than ethanol. Finally, this study presents an alternative pathway for producing diesel fuel from waste cooking oil using ethanol as a hydrogen donor.« less

Ni-doped LaFeO₃ perovskite oxide is a promising cathode material for solid oxide electrolysis cells (SOECs) designed for CO₂/H₂O coelectrolysis. Here, the performance of LaFe_0.9Ni_0.1O₃ is being investigated under real-world conditions that include exposure to acid gases, such as SO₂, relevant to SOEC operation. Experiments show that LaFe_0.9Ni_0.1O₃ exsolves NiFe nanoparticles, along with the formation of surface SO₄^2– and SO₃^2– after being exposed to 200 ppm of SO₂. This suggests that the ionic diffusion of Ni³⁺ and Fe³⁺ between the bulk and the surface remains unaffected throughout the exsolution–dissolution–exsolution cycle. Thermochemical water splitting has been employed as a probe reaction tomore » evaluate the catalytic properties of the exsolved NiFe nanoparticles. These nanoparticles demonstrated improved hydrogen production compared to bare perovskite oxide substrates. However, after exposure to SO₂, the formation of Fe-rich NiFe nanoparticles led to poor thermocatalytic performance and rapid deactivation of the perovskite at elevated temperatures. Density functional theory (DFT) analysis was utilized to validate the experimental findings, indicating a significantly negative reaction energy for water splitting over exsolved Fe, as well as stronger binding of SO₂ to Fe than to Ni. Computational analysis further suggests that the presence of surface sulfate promotes the formation of Fe-rich NiFe nanoparticles, aligning with the experimental results. Overall, this study clarifies how SO₂ affects the structure of SOEC perovskite oxide candidate materials. Future engineering efforts should focus on enhancing nanoparticle exsolution and sulfur resistance, which is crucial for improving the hydrogen production capacity of La-based perovskite oxides for electro- and thermocatalytic water splitting in real environments containing acid gases.« less