Surface Hydrogen Research Articles

Quantification of Hydrogen Flux from Atmospheric Corrosion of Steel Using the Scanning Kelvin Probe Technique

The atmospheric corrosion of high-strength steels can lead to hydrogen absorption directly linked to hydrogen embrittlement or delayed fracture phenomena. A scanning Kelvin probe (SKP) and electrochemical permeation technique (EPT) were applied to correlate the potential of an oxidized surface with the flux of hydrogen across a thin steel membrane. The side of the membrane opposite the corroding or electrochemically charged area was analyzed. The potential drop in the oxide was calibrated in terms of surface hydrogen activity, and SKP can be applied in situ for the mapping of hydrogen distribution in the corroding metal. A very low flux of hydrogen can be characterized and quantified by SKP, which is typically observed under atmospheric corrosion conditions. Therefore, hydrogen localization that drives steel durability under atmospheric corrosion conditions can be evaluated.

Toward more accurate surface properties of ceria using many-body perturbation theory.

Despite the wide applications, the abinitio modeling of the ceria based catalyst is challenging. The partial occupation in the 4f orbitals creates a fundamental challenge for commonly used density functional theory (DFT) methods, including semilocal functionals with Hubbard U correction to force localization and hybrid functionals. In this work, we benchmark the random phase approximation (RPA) for ceria surface properties, including surface energy and hydrogenation energy, compared to the results utilizing the DFT + U approach or hybrid functionals. We show that, for the latter approaches, different surface properties require opposite directions of parameter tuning. This forms a dilemma for the parameter based DFT methods, as the improvement of a certain property by tuning parameters will inevitably lead to the worsening of other properties. Our results suggest that the parameter-free many-body perturbation theory methods exemplified by RPA are a promising strategy to escape the dilemma and provide highly accurate descriptions, which will allow us to better understand the catalytic reactions in ceria related systems.

The abiotic removal of organic micropollutants with iron and manganese oxides in rapid sand filters for groundwater treatment.

Rapid sand filters (RSFs) have shown potential for removing organic micropollutants (OMPs) from groundwater. However, the abiotic removal mechanisms are not well understood. In this study, we collect sand from two field RSFs that are operated in series. The sand from the primary filter abiotically removes 87.5% of salicylic acid, 81.4% of paracetamol, and 80.2% of benzotriazole, while the sand from the secondary filter only removes paracetamol (84.6%). The field collected sand is coated by a blend of iron oxides (FeOx) and manganese oxides (MnOx) combined with organic matter, phosphate, and calcium. FeOx adsorbs salicylic acid via bonding of carboxyl group with FeOx. The desorption of salicylic acid from field sand indicates that salicylic acid is not oxidized by FeOx. MnOx adsorbs paracetamol through electrostatic interactions, and further transforms it into p-benzoquinone imine through hydrolysis-oxidation. FeOx significantly adsorbs organic matter, calcium, and phosphate, which in turn influences OMP removal. Organic matter on field sand surfaces limits OMP removal by blocking sorption sites on the oxides. However, calcium and phosphate on field sand support benzotriazole removal via surface complexation and hydrogen bonding. This paper provides further insight into the abiotic removal mechanisms of OMPs in field RSFs.

Friction reactions induced by selective hydrogenation of textured surface under lubricant conditions

The passivation of hydrogen atoms and the conformation of textured surfaces under oil-lubricated conditions are effective strategies to obtain amorphous carbon (a-C) films with extremely low friction. It is critical to understanding the influence mechanism of selective surface hydrogenation on the tribological behaviors of textured a-C film under oil-lubricated conditions. In particular, the interactions of hydrogen atoms and lubricants are confusing, which is enslaved to the in situ characterization technique. The reactive molecular dynamics (RMD) simulations were conducted to analyze the friction response of textured a-C films with selective hydrogenation surfaces under oil-lubricated conditions. The results indicate that the existence of hydrogen atoms on specific bump sites significantly decreases the friction coefficient (μ) of textured a-C film, which is highly dependent on the surface hydrogen content. The repulsion between hydrogen atoms and lubricant molecules prompts the formation of a dense lubricant film on the surface of the mating material. Interestingly, with the enhancement of the surface hydrogen content, the passivation of the friction interface and the repulsion between hydrogen atoms and lubricants play dominant roles in reducing the friction coefficient instead of hydrodynamic lubrication.

Investigation of water effects on hydrogen dissolution, diffusion, and reaction in high temperature proton exchange membrane fuel cell

High-temperature proton exchange membrane fuel cell with phosphoric acid-doped polybenzimidazole membrane is typically utilized with a methanol steam reformer due to its high CO tolerance. However, methanol reformate commonly contains 20 % water, and its effect on the high temperature fuel cell is unclear. A comprehensive 3D multiphase non-isothermal model with an enhanced electrochemical kinetics model considering the water influence mechanism is developed. The water influence mechanism includes the proton conductivity, hydrogen dissolution on the pore-ionomer interface, hydrogen diffusion inside the ionomer, and hydrogen surface reaction on the platinum. The sensitivity analysis found that hydrogen dissolution on the pore-ionomer and hydrogen surface reaction on the platinum significantly affect cell performance. The influences of water on ionomer hydrogen concentration, platinum surface hydrogen concentration, and surface reaction rates are investigated under the voltage range of 0.9–0.4 V. The increase of water content can improve the net adsorption rate and benefit electrochemical reaction. Besides, the anode water is better for the uniformity of surface reaction rate distributions while not affecting the hydrogen distributions inside the ionomer and on the platinum surface. Additionally, the positive influence of water on CO poisoning is investigated in terms of surface reaction. The water's beneficial effect on decreasing platinum loading is also discussed. The results show that 20 % water can reduce the platinum loading by 20 %.

Deciphering the role of fucoidan from brown macroalgae in inhibiting SARS-CoV-2 by targeting its main protease and receptor binding domain: Invitro and insilico approach

The current study investigated the role of fucoidan from Padina tetrastromatica and Turbinaria conoides against 3-chymotrypsin like protease (3CLpro) and receptor binding domain (RBD) spike protein of SARS-CoV-2 using an invitro and computational approach. The 3CLpro and RBD genes were successfully cloned in pET28a vector, expressed in BL-21DE3 E. coli rosetta cells and purified by ion exchange affinity and size exclusion chromatography. Fucoidan extracted from both biomass using green approach, subcritical water, was found to inhibit 3CLpro of SARS-CoV-2 with an IC50 value of up to 0.35 mg mL−1. However, fucoidan was found to be inactive against the RBD protein. Molecular docking studies demonstrated that fucoidan binds to the active sites of 3CLpro with an affinity of −5.0 kcal mol−1. In addition, molecular dynamic simulations recorded stabilized interactions of protein-ligand complexes in terms of root mean square deviation, root mean square fluctuation, the radius of gyration, solvent accessible surface area and hydrogen bond interaction. The binding energy of fucoidan with 3CLpro was determined to be −101.821 ± 12.966 kJ mol−1 using Molecular Mechanic/Poisson-Bolt-Boltzmann Surface Area analysis. Fucoidan satisfies the Absorption, Distribution, Metabolism, and Excretion (ADME) properties, including Lipinski's rule of five, which play an essential role in drug design. According to the toxicity parameters, fucoidan does not exhibit skin sensitivity, hepatotoxicity, or AMES toxicity. Therefore, this work reveals that fucoidan from brown macroalgae could act as possible inhibitors in regulating the function of the 3CLpro protein, hence inhibiting viral replication and being effective against COVID-19.

Metal-organic Frameworks (MOFs) on Hydrogen Storage and Purification

As a clean energy source, hydrogen shows promise as a potential substitute for non-renewable fossil fuels. However, the challenges with hydrogen include the difficulties in storing it feasibly and separating it from other gases mixed during industrial production. Metal-organic frameworks (MOFs) refer to crystalline substances that possess a significant porosity and expansive surface area, enabling them to effectively adsorb hydrogen via the van der Waals force. MOFs have been studied for ways to improve their surface area and hydrogen uptake capacities by various modification methods. This review discusses the key strategies for enhancing the hydrogen storage properties of MOFs to achieve the necessary increase in energy supply and the mechanisms behind the purification of hydrogen in practical use. Detailed discussions take place regarding synthesis methods, experimental testing results, and the mechanism behind the enhancement of hydrogen storage for each modification of MOF material discovered. Also, other parameters that may influence MOFs’ hydrogen storage properties are demonstrated, together with the separating mechanism of purifying hydrogen from other gases and isotopes.

Assessment of the Push-Out Bond Strength for Glass Fiber Posts After Different Surface Treatments: An In Vitro Study.

The goal of the study was to assessthe push-out bond strength of the glass fibre post after different surface treatments. For the purpose of the investigation, 40 mandibular premolars were chosen. After gaining access, the biomechanical preparation was completed using the step-back approach up to a size 40K file, and the canals were sealed using gutta-percha cones and the lateral condensation procedure with AH Plus sealer (epoxide-amine resin pulp canal sealer). Peeso reamers were used to remove the canal fillings, leaving 5mm of gutta-percha apically. Drills included in the package were used to prepare the post spaces so that the posts would fit in their respective post slots. These were attached to self-curing acrylic resin blocks. Fibre posts were split into four groupings of n = 10 each for surface treatment, i.e., control, hydrogen fluoride, sandblasting, and hydrogen peroxide. The cementation of posts was done by utilising dual-cure resin cement. Two millimetres of the anatomical crown were removed from each sample. Each sample's 1-mm cervical segment was taken utilising the isotope from the remaining coronal area. To perform a push-out test, at the rate of 0.5mm/min of the crosshead, every sample was inserted into a universal testing device. Each post's dislodge force from the pre-set post spacing was measured. Statistics were utilised to analyse the data. Strongest bonds were made by silanization, followed by sandblasting (p value=0.002). The weakest bonds were made by the control group. The ultimate deduction was that when glass fibre posts underwent various types of surface treatments followed by silanization, it had a significant impact on increasing their strength.

Adsorption properties and mechanisms of methylene blue and tetracycline by nano-silica biochar composites activated by KOH

Dyestuff wastewater and pharmaceutical wastewater have become typical representatives of water pollution. In this study, a novel nano-silica-biochar composite (NSBC) was synthesized based on corn straw as raw material, by a combination of ball milling, pyrolysis and KOH activation. The modified biochar with rough surface had higher specific surface area (117.67–132.82 m2/g), developed pore structure (0.12–0.15 cm3/g) and abundant surface functional groups (-OH, –COOH, Si–O and aromatic CC were dominated). These provided abundant active sites for the adsorption of pollutants. The adsorption capacities of NSBC for Methylene Blue (MB) and Tetracycline (TC) were both higher than that of other similar products, the maximum adsorption capacity of Langmuir were 247.22 and 86.95 mg/g, respectively. After five adsorption-desorption cycle experiments, the adsorption capacities of NSBC for both were still excellent, reaching 99.30 and 19.87 mg/g, respectively. Due to the different structure and molecular size of MB and TC, the adsorption capacities of NSBC were significantly different, especially the influence of solution pH value. The adsorption mechanisms were comprehensively discussed by FTIR and XPS of the samples before and after adsorption, and combining experimental results of BET and simultaneously, which were manifested as monolayer chemisorption, specifically surface complexation, hydrogen bonding, n-π/π-π conjugation, electrostatic interaction and pore filling.

Structure and physicochemical properties of MgB2 nanosheets obtained via sonochemical liquid phase exfoliation

We have performed ultrasonic liquid phase exfoliation (LPE) of MgB2 in ethanol and investigated the resulting nano-assemblies as a function of the ultrasound processing time. TEM morphological and structural analysis, along with STM topographic characterization, showed that for short sonication times the exfoliated grains preserve the MgB2 crystal structure, have a 2D character and produce Moiré patterns corresponding to stacked layers with rotational misalignment. On the other hand, the longest process times result in spheroidal nanoparticles with diameters of the order of 10 nm, which can also coalesce into larger agglomerates. Optical absorbance spectra confirmed that the exfoliated material preserves a metallic nature with a predominant 2D character corresponding to the ab-plane, whereas Raman spectra showed the presence of extra-modes induced by 3D symmetry breaking in the exfoliated products, along with indications of some B-H stretching modes. The detection of a positive zeta potential confirms that an active surface hydrogenation process has taken place during sonication. The mechanochemistry of the exfoliation mechanism has been attributed to particle–particle collisions and particle-shockwave interactions originating from the implosive bubble-collapse. The present study provides important information useful for implementing the LPE process in different contexts for MgB2, like few-layer superconductivity, antibacterial coating and nano-drug preparation.

Relativistic Corrections in White Dwarf Asteroseismology

Abstract With the precision now afforded by modern space-based photometric observations from the retired K2 and current TESS missions, the effects of general relativity (GR) may be detectable in the light curves of pulsating white dwarfs (WDs). Almost all WD models are calculated using a Newtonian description of gravity and hydrodynamics. To determine if the inclusion of GR leads to observable effects, we used idealized models of compact stars and made side-by-side comparisons of mode periods computed using a: (i) Newtonian and (ii) GR description of the equilibrium structure and nonradial pulsations. For application to WDs, it is only necessary to include the first post-Newtonian (1pn) approximation to GR. The mathematical nature of the linear nonradial pulsation problem is then qualitatively unchanged and the GR corrections can be written as extensions of the classic Dziembowski equations. As such, GR effects might easily be included in existing asteroseismology codes. The idealized stellar models are (i) 1pn relativistic polytropes and (ii) stars with a cold degenerate electron equation of state featuring a near-surface chemical transition from μ e = 2 to μ e = 1, simulating a surface hydrogen layer. A comparison of Newtonian and 1pn normal mode periods reveals fractional differences in the order of the surface gravitational redshift z. For a typical WD, this fractional difference is ∼10−4 and is greater than the period uncertainty σ Π/Π of many WD pulsation modes observed by TESS. Consistent theoretical modeling of periods observed in these stars should, in principle, include GR effects to 1pn order.

Theoretical assessments of CO2 activation and hydrogenation pathways on transition-metal surfaces

Carbon dioxide (CO2) hydrogenation on transition-metal active sites offers a promising carbon utilization route toward mitigating greenhouse gas emissions. C1 products are often formed in parallel during CO2 hydrogenation, prompting investigations into the intrinsic properties of transition metals that drive activity and product selectivity. In this work, close-packed surfaces of a selection of transition-metal catalysts (Ni, Co, Rh, Ru, Pd, and Pt) were studied with density functional theory (DFT) calculations to understand their fundamental reactivities for CO2 transformation reactions. Results indicate that CO2 conversion proceeds through CO* formation and hydrogenation to form C1 products (* denotes an adsorbed species). Ni, Co, Rh, and Ru favor CO/CH4 formation, while Pd and Pt favor CO/CH3OH formation. The ability of a metal to dissociate C-O bonds drives selectivity between CH4 and CH3OH, while competition between CO* desorption and surface hydrogenation describes CO selectivities. The C-O bond dissociation steps often impose the highest barrier along CH4 formation reaction profiles, suggesting their kinetic relevance for CH4 formation rates. The provided DFT-derived data sets detail a comprehensive reaction network of elementary steps relevant to C1 chemistries, ultimately offering a benchmark for insights into design strategies for materials that exploit transition-metal active sites in carbon capture or utilization processes.

Effect of additive manufacturing and subsequent heat and/or surface treatment on the hydrogen embrittlement sensitivity of 316L austenitic stainless steel

Austenitic stainless steels (ASS) offer attractive characteristics for use in hydrogen service, such as low hydrogen diffusivity and high solubility. The role of the production process is, however, still unclear. Especially the effect of additive manufacturing (AM) on the hydrogen interaction is not extensively researched yet. The present work compares the hydrogen embrittlement sensitivity of conventional (cold rolled and annealed) and additive manufactured 316L ASS and evaluates the possible advantage of performing a heat treatment and/or reducing the surface roughness post printing. AM increases the hydrogen solubility but the hydrogen diffusivity was only slightly reduced. The heat treatment reduced the hydrogen solubility of the AM materials and significantly increased the hydrogen diffusivity. Despite these observations, the conventional 316L ASS shows a higher hydrogen embrittlement (HE) sensitivity compared to AM316L. This is linked to the increased hydrogen-assisted cracking sensitivity of conventional 316L ASS. The heat treated microstructure behaves similarly as the as-built material in terms of HE sensitivity, while a major improvement is observed when the surface oxide layer formed during the heat treatment is maintained since this reduces hydrogen absorption. Surface polishing intensifies the HE sensitivity which is linked to a higher surface hydrogen concentration leading to more crack initiation.

Designed Nanomaterials for Electrocatalytic Organic Hydrogenation Using Water as the Hydrogen Source.

ConspectusThe hydrogenation reaction is one of the most frequently used transformations in organic synthesis. Electrocatalytic hydrogenation by using water (H2O) as the hydrogen source offers an efficient and sustainable approach to synthesize hydrogenated products under ambient conditions. Such a technique can avoid the use of high-pressure and flammable hydrogen gas or other toxic/expensive hydrogen donors, which usually cause environmental, safety, and cost concerns. Interestingly, utilizing easily available heavy water (D2O) for deuterated syntheses is also attractive due to the widespread applications of deuterated molecules in organic synthesis and the pharmaceutical industry. Despite impressive achievements, electrode selection mainly relies on trial-and-error modes, and how electrodes dictate reaction outcomes remains elusive. Therefore, the rational design of nanostructured electrodes for driving the electrocatalytic hydrogenation of a series of organics via H2O electrolysis is developed.In this Account, we review recent advances in the electrocatalytic hydrogenation of different types of organic functional groups, including C≡C, C≡N, C═C, C═O, and C-Br/I bonds, -NO2, and N-heterocycles, with H2O over nanostructured cathodes. First, the general reaction steps (reactant/intermediate adsorption, active atomic hydrogen (H*) formation, surface hydrogenation reaction, product desorption) are analyzed, and key factors are proposed to optimize hydrogenation performance (e.g., selectivity, activity, Faradaic efficiency (FE), reaction rate, and productivity) and inhibit side reactions. Then, ex situ and in situ spectroscopic tools to study key intermediates and interpret mechanisms are introduced. Third, based on the knowledge of key reaction steps and mechanisms, we introduce catalyst design principles in detail on how to optimize the adoption of reactants and key intermediates, promote the formation of H* from water electrolysis, inhibit hydrogen evolution and side reactions, and improve the selectivity, reaction rate, FEs, and space-time productivity of products. We then introduce some typical examples. (i) P- and S-modified Pd can decrease C═C adsorption and promote H* formation, enabling semihydrogenation of alkynes with high selectivity and FEs at lower potentials. Then, creating high-curvature nanotips to concentrate the substrates further speeds up the hydrogenation process. (ii) By introducing low-coordination sites into Fe and combining low-coordination sites and surface fluorine to modify Co to optimize the adsorption of intermediates and facilitate H* formation, hydrogenation of nitriles and N-heterocycles with high activity and selectivity is obtained. (iii) By forming isolated Pd sites to induce a specific σ-alkynyl adsorption of alkynes and steering S vacancies of Co3S4-x to preferentially adsorb -NO2, hydrogenation of easily reduced group-decorated alkynes and nitroarenes with high chemoselectivity is realized. (iv) For gas reactant participated reactions, by designing hydrophobic gas diffusion layer-supported ultrasmall Cu nanoparticles to enhance mass transfer, improve H2O activation, inhibit H2 formation, and decrease ethylene adsorption, ampere-level ethylene production with a 97.7% FE is accomplished. Finally, we provide an outlook on the current challenges and promising opportunities in this area. We believe that the electrode selection principles summarized here provide a paradigm for designing highly active and selective nanomaterials to achieve electrocatalytic hydrogenation and other organic transformations with fascinating performances.

Unraveling Pathways of Photocatalytic Oxygen Evolution on Fluorinated Anatase TiO2

Recent experiments reported that the efficiency of the oxygen evolution reaction (OER) was greatly improved in fluorinated TiO2 by forming the surface hydrogen bonds, but the mechanism remains ambiguous. Herein, we systematically investigated dual OER pathways on the fluorinated anatase TiO2(101) surface by using the first-principles calculations. The dual H-bonding water is significantly activated by trapping a first hole in the system and facilitates its proton transfer in pathway I. The inactive Ti-coordinated water also transfers a proton to a bridge O2– ion with a similar barrier and simultaneously traps the first hole in pathway II. Both ·OH radicals separately transfer a proton to the F– ion and bridge O2– ion very quickly and trap the second hole to produce the ·O radical. Consequently, the ·O radical directly couples with the bridge O2– ions with a high barrier of about 0.72 eV to produce the flat peroxo dimer (O22–) in pathway I. The Ti-coordinated ·O radical undergoes two steps of the proton transfer and O–O coupling with both high barriers of about 0.75 eV to produce the oblique O22– species in pathway II. Finally, the O22– spontaneously and successively traps the third and fourth holes to quickly form the oxygen molecule. Additionally, the fluorine atoms are further demonstrated to accelerate the proton transfer and the O–O coupling steps by comparing the pathways on the fluorinated and pure TiO2 surfaces. These results may provide new insights into the OER mechanism in fluorinated TiO2 and roles of the dopant in improving OER efficiency of the TiO2 photocatalysts.

Construction of CuBi2O4/CdO p-n buried junction for boosted photoelectrochemical water splitting

The rational design and construction of interface heterostructures, which can simultaneously accelerate the photoinduced carrier separation and enhance the surface hydrogen evolution kinetics, is of great necessity for photoelectrochemical (PEC) water splitting. Here we construct a CuBi2O4/CdO p-n buried junction for boosting the PEC hydrogen evolution. Compared to the bare CuBi2O4 photocathode, the CuBi2O4/CdO heterojunction reveals an anodic shift of 170 mV for the onset potential and achieves a cathodic photocurrent density of 0.32 mA cm−2 at 0.4 V vs. RHE, as well as improved long-term stability under AM 1.5 G illumination without sacrificial reagent. The experimental characterizations and theoretical calculations confirm the significance of the CuBi2O4/CdO p-n junction in increasing the photoinduced charge separation efficiency and reducing the activation energy of hydrogen evolution reaction (HER), which accounts for enhanced PEC performance. Meanwhile, the change of photoexcited charge-transition route evidenced by DFT calculation in CuBi2O4/CdO provides the fundamental explanation for spatial charge separation, which is responsible for the improved PEC hydrogen evolution stability. The present work highlights the importance of constructing heterojunctions to boost the PEC performance and elucidates the probable intrinsic mechanism involved in the interface.

Tracking the atomic structure evolution of ZnO[formula omitted] polar surface via carbon dioxide infrared probe

So far, the clear periodic structures of ZnO polar surfaces and their depolarization stabilization mechanism have not yet been clarified because of the structural complexity and inferior conductivity of these surfaces. Here, we combined microchannel plate low-energy electron diffraction (MCP-LEED), CO2 molecule probe based on polarization-resolved infrared reflection adsorption spectra (PR-IRRAS) and first-principles calculations to systematically study the ZnO(0001¯) polar surface. Five clear periodic surface structures including 3×3R30°, (1×1), (1×2), (43×43)R30° and (3×3) were achieved depending on hydrogen coverage. These surfaces appear in sequence with reducing hydrogen coverage, and vice versa. The CO2 infrared probe tracked these surface atomic configuration evolutions. First-principles calculations revealed that the role of surface hydrogens is to fully fill the partially filled O-2p band at surface while retaining the compensation of surface polarity. Our works reveal the stabilization mechanism of hydrogen covered ZnO(0001¯) polar surface, clarify the long-standing controversy on such surface, and also supply a novel approach for investigating some complex surfaces.

Understanding Potential Decay during OCV Hold via Dry Recovery Process

Nearly ∼100 mV of open circuit voltage (OCV) decay is observed in the first 24 h of a typical OCV hold test for assessing the chemical durability of a polymer electrolyte. Significant recovery of this OCV loss has been achieved by subjecting the cell to so-called wet recovery process by lowering the cell potential often under over-humidified conditions, thereby confounding the effect of potential reduction and catalyst/ionomer interfacial reorganization due to humidification. In this work by applying a dry recovery protocol (30% RH) comprising 30 min of lower potential hold in the H2/N2 environment followed by the H2/Air environment, OCV recovery of 82%, 73%, 62% and 58 was achieved by holding potentials at 0.13, 0.2, 0.6, and 0.8 V, respectively. Small changes in electrochemically active surface area and hydrogen cross-over rate observed 48 h cannot explain the nearly 100 mV OCV. The wet recovery process (low potential and 100% RH) resulted in 85% recovery of ∼100 mV of lost OCV implying oxide coverage increase as the dominant factor for sharp OCV decay. Further, it is shown that cross-over hydrogen is not fully oxidized at OCV-like conditions (>0.6 V), highlighting the need to quantify potential-dependent crossover current for OCV decay models.

Effects of activation temperature and time on porosity features of activated carbons derived from lemon peel and preliminary hydrogen adsorption tests

Lemon peels, a common biomass waste, have an interesting composition in terms of cellulose and mineral salts that makes them good precursors for activated carbon production processes. From a circular economy perspective, this work highlights the possibility of turning a waste material into a new resource. The resulting nanostructures show interesting performance in terms of specific surface area and total pore volume, with excellent grade of microporosity, that make them suitable for various applications ranging from supercapacitors, sensors, gases separation and storage, etc. The last, and in particular hydrogen storage, represents the most interesting one. In this study the development of activated carbon through pyrolysis method, consisting of carbonization in inert ambient and subsequent physical activation in oxidizing atmosphere is reported. Influence of synthesis parameters on the porosity formation was investigated with the aim of textural properties optimization. All produced samples were initially characterized both morphologically and crystallographycally. Then, textural and adsorption properties were evaluated through volumetric apparatus. The experimental results show improvement of both textural and adsorption properties as function of synthesis parameters, developing adsorbent materials with high fraction of micropores (≃84 %), specific surface area (≃500 m2/g) and hydrogen uptake of 0.93 wt% at 77 K and 1 bar.

Catalytic methane combustion at low temperatures over YSZ-supported metal oxides: Evidence for lattice oxygen participation via the use of C18O2

Catalytic methane combustion was carried out over YSZ, Pd/YSZ and Rh/YSZ between 200 and 700 °C. Despite similar light-off curves for Pd/YSZ and Rh/YSZ between 200 and 450 °C, isotopic exchange experiments using CD4 and 18O2 revealed different behaviour of both supported catalysts regarding the activation of reactant molecules. The use of C18O2 isotopic gas was shown to be more appropriate than 18O2 to evaluate the bulk oxygen mobility in YSZ at low temperatures. The exchange of gaseous CO2 with lattice YSZ oxygen atoms, which occurs via surface hydrogen carbonate intermediate species, allowed to demonstrate the contribution of bulk oxygen atoms of YSZ in Rh/YSZ at low temperatures.