Surface Protonation Research Articles

Study on AuNPs size regulation and AuNPs/BP photocatalytic performance

As a new two-dimensional material, black phosphorus (BP) has many advantages, like layer-dependent direct band gap, wide spectral response, high carrier mobility and abundant active sites. It is widely used in photocatalysis, solar energy conversion and other fields. However, the rapid recombination of photo-generated carriers and poor chemical stability limit the development of BP in the field of photocatalysis. In this study, a composite photocatalyst was configurated by loading Au nanoparticles (AuNPs) on the surface of the BP, namely AuNPs/BP. By adjusting the conditions such as reducing agent, protective agent, temperature, gold source in the reaction system, the mechanism and influencing factors of AuNPs particle size were explored. The composite catalyst was characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet–visible spectrometry (UV–vis), X-ray photoelectron energy spectrometry (XPS), and photochemical test platforms. Next, the catalytic performance of AuNPs/BP was evaluated by photocatalytic degradation of methyl orange (MO). The results showed that the degradation performance of AuNPs/BP on MO is significantly better than that of pure BP, and the degradation rate increased from 49.7% to 67.7%. The apparent rate constant increased from 5.726 × 10−3min−1 to 9.418 × 10−3min−1. Due to the surface proton resonance effect of AuNPs, BP with AuNPs evenly loaded on the surface showed strong absorption of visible light, high carrier separation efficiency, and widened the band gap of BP.

Highly Active and Durable Air Electrodes for Reversible Protonic Ceramic Electrochemical Cells Enabled by an Efficient Bifunctional Catalyst

AbstractThe commercialization of reversible protonic ceramic electrochemical cells is hindered by the lack of highly active and durable air electrodes exposed to high concentration of steam under operating conditions. Here, findings that dramatically enhance the electrocatalytic activity and stability of a conventional (La0.6Sr0.4)0.95Co0.2Fe0.8O3−δ (LSCF) air electrode by a multiphase catalyst coating composed of a conformal Pr1−xBaxCoO3−δ thin film and exsolved BaCoO3−δ nanoparticles, are reported. At 600 °C, the catalyst coating decreases the polarization resistance of the LSCF air electrode by a factor of 25 (from 1.09 to 0.043 Ω cm2) in air and the degradation rate by two orders of magnitude (from 1.0 × 10−2 to 1.8 × 10−4 Ω cm2 h−1 in humidified air with 30 vol% H2O). Further, a single cell with the catalyst‐coated LSCF air electrode at 600 °C demonstrates a high peak power density of 1.04 W cm−2 in the fuel cell mode and a high current density of 1.82 A cm−2 at 1.3 V in the electrolysis mode. The significantly enhanced performance of the LSCF air electrode is attributed mainly to the high rate of surface oxygen exchange, fast surface proton diffusion, and the rapid H2O and O2 dissociation on the catalysts.

Quantitative investigation of CeO2 surface proton conduction in H2 atmosphere.

This report is the first describing a study quantitatively analysing aspects of oxide surface protonics in a dry H2 atmosphere. Elucidating surface protonics is important for electrochemical and catalytic applications. In this study, AC impedance spectroscopy was used to investigate surface conduction properties of porous CeO2 at low temperatures (423-573 K) and in a dry H2 atmosphere. Results demonstrated that the conductivity increased by several orders of magnitude when H2 was supplied. Dissociative adsorption of H2 contributes to conduction by forming proton-electron pairs. Also, H/D isotope exchange studies confirmed protons as the dominant conduction carriers. Furthermore, H2 adsorption equilibrium modelling based on the Langmuir mechanism was applied to explain the H2 partial pressure dependence of conductivity. For the first time, the obtained model explains the experimentally obtained results both qualitatively and quantitatively. These findings represent new insights into surface protonics in H2 atmosphere.

Surface strain and co-doping effect on Sm and Y co-doped BaCeO3 in proton conducting solid oxide fuel cells

Although promising, regulating the surface strain is still immature for enhance the performance of proton-conducting materials and no clear law has been found. In this work, surface strain and co-doping effect on dopant segregation, hydration reaction and proton transport of Sm and Y co-doped BaCeO3 (BCYS) in proton-conducting solid oxide fuel cells (P-SOFC) was investigated. We found that although the dopant segregation trend is reduced as the surface strain increase from −2% to 2%, which means that a large tensile strain is beneficial to enhance structural stability, oxygen vacancy formation energy and proton binding energy near the BCYS surface do not change monotonously with the surface strain. We found that the fewer electrons around the oxygen atoms before hydrogen adsorption, the more stable the proton. It is worth noting that 1% tensile strain is most favorable for enhancing the degree of surface hydration and proton transport in our calculation results, which helps to weaken the negative effects of the space charge layer formed by the accumulation of positive charges on the surface. The collocation of Sm and Y has a synergistic effect, which means Sm facilitates oxygen vacancy formation, while Y promotes hydration reaction. Moreover, the introduction of Sm and Y can hardly change the electronic conductivity of BCYS, which is conducive to the open circuit voltage of P-SOFC.

Nonlinear regression for analysis of the uptake of KMnO4 from aqueous solutions onto natural marl

The present work aims to evaluate the performance of raw marl collected from the region of Oum El Bouaghi on the elimination of KMnO4 from aqueous solution. The adsorption capacities were studied using the batch technique as a function of pH, initial concentration and temperature. The maximum adsorption for KMnO4 was found to be 83.517% at pH 3.0. When the pH is low (pH<3.0), the uptake of KMnO4 occurs with an electrostatic attraction between the MnO4-ions and the surface proton groups, while at pH ≥3.0-8.0, the formation of complexes with the surface functional groups during the adsorption process and/or cation exchange are responsible for retention of Mn(II) ions onto marl. Experimental adsorption data were modeled with different nonlinear isotherms and kinetic models. Furthermore, statistical errors (SSE, SD, ARE, χ 2, R2 and R2 adj) were calculated to choose the suitable model. Langmuir isotherm was found to be best for fitting the experimental data. The calculated thermodynamic parameters indicated that adsorption process was physical, spontaneous and endothermic in nature. From this work, it was concluded that the natural marl can be used for effective elimination of KMnO4 from aqueous solution and wastewater.

Surface architecture and proton conduction in SPVDF-co-HFP based nanocomposite membrane for fuel cell applications: Influence of aprotic solvent mixture

In the present study, the prime focus is to study the effect of a new solvent mixture on the formation of PVDF-co-HFP based nanocomposite membrane by solution casting method and their applicability to perform as a proton conducting membrane for fuel cell applications. A definite proportion two dipolar aprotic solvent mixture N-Methyl-2-pyrrolidone (NMP) and Acetonitrile (ACN) was used as the solvent mixture and it has been observed that the use of these solvents results in a porous structure with smaller micro domains within it, as evidenced from the FESEM micrographs. The mechanical resistance of the membranes also significantly improved with the change of solvent resulting in the formation of a ductile membrane. Incorporation of in-situ synthesized silanized silica nanoparticles into the polymer backbone following the sulfonation of the membranes using chlorosulfonic acid, also contributed in the improved physicochemical and the electrochemical properties with respect to higher water retention, better ion exchange capability (0.98 meq. g−1) and proton conductivities. Additionally, the silanized silica nanoparticles showed improved dispersibility within the polymer membrane thereby resulting in absorption of more sulfonic acid groups and shortened interchain separation distance which has been confirmed from XRD analysis. Thus, an interconnected proton conduction pathway which was formed, enhanced the proton conductivity to 0.113 S cm−1. Further, the barrier properties of the silica nanoparticles additionally suppressed the methanol crossover as compared with Nafion, while improving the membrane selectivity (3.65 × 104 S.scm−3).

Impact of Carbon Support Meso‐Porosity on Mass Transport and Performance of PEMFC Cathode Catalyst Layers

AbstractThe analysis of the impact of the cathode catalyst layer pore structure on the membrane electrode assembly (MEA) cell performance of a PEMFC is presented. In this study, a pristine CMK‐3 catalyst carbon support material with well‐defined pore structure in the 3–6 nm range together with two nitrogen‐doped variants is analyzed against a commercial carbon black to achieve a better understanding of catalyst layer porosity‐performance relations. We used chemically N‐doped CMK‐3 catalyst to learn more about the effect of N‐doped porous catalyst supports on the concomitant transport properties and PEMFC cell performance. Chemical treatment using cyanamide was conducted to introduce a variety of N‐functionalities. A detailed in‐situ electrochemical investigation was combined with N2‐physisorption analysis. Based on their structural properties, the mesopore fractions and pore openings display a major role for reducing oxygen transport resistance and enhance Pt accessibility. We find that hierarchically ordered mesoporosity is superior to disordered porosity with prevalent micropore character: Analysis including adsorption electrochemical active surface area (ECSA), Pt‐accessibility, ionomer coverage, pore geometry, proton resistivity and transport loss we conclude the importance of a well‐defined mesoporous structure for its cell performance.

Alizarin-graphene nanocomposite for calibration-free and online pH monitoring of microbial fuel cell

Microbial fuel cells (MFCs) are sensitive to acidity variations in both bioelectricity generation and biochemical digestion aspects, therefore online pH monitoring is of necessity to guarantee optimal function of MFCs. Present pH meters hardly fulfill this special need. In this work, we designed a novel voltammetric pH sensor based on electrochemically reduced graphene oxide (rGO) modified screen printed electrode. By surface doping of alizarin, good linearity of pH sensing over the range of 4.0–9.0 can be realized. Fast readout can be acquired within 15 s for each test. pH monitoring for artificial wastewater with inoculum of granular activated sludge in a MFC was successfully illustrated. Specially, it was verified that the performance was improved with alizarin doping due to the enhanced rGO surface proton diffusion. This approach provides an online, calibration-free and long stable pH monitoring method for the future MFC development.

Fabrication and Characterization of Chitosan/N-Phthaloyl Composite Membrane for DMFC Application

Modified chitosan membrane is one of the promising membranes for polymer electrolyte membrane. Chitosan/N-phthaloyl chitosan composite membranes were fabricated to obtain high proton conductivity and low methanol permeability. Membranes were fabricated by casting method and solvent evaporation. Surface morphology, mechanical analysis, methanol permeability, and proton conductivity were used to characterize the overall properties. FT-IR spectra exhibited the presence of interaction of chitosan and n-phthaloyl/chitosan. SEM analysis showed that the surface roughness of composite membrane increases as the n-phthaloyl loading increases. The highest proton conductivity of synthesized membrane is at 2.4 mS.cm-1 and is higher than pristine chitosan membrane at 1.6 mS.cm-1. Moreover, with n-phthaloyl/chitosan addition, the methanol permeability was also improved. The correlation between proton conductivity and methanol permeability in composite membranes suggests that the blend has its potential in DMFC application.

Electroassisted Propane Dehydrogenation at Low Temperatures: Far beyond the Equilibrium Limitation.

Propylene production by propane dehydrogenation (PDH) generally requires high temperatures due to thermodynamic equilibrium limitations. This study developed a novel type of catalytic system for low-temperature PDH by combining a surface protonics methodology with intermetallic active sites. By application of an electric current, the intermetallic Pt–In/TiO2 catalyst gave a propylene yield of 10.2% with high selectivity, even at 250 °C, where the thermodynamic equilibrium yield was only 0.15%. Electroassisted proton collisions with propane allowed an unusual reaction pathway for low-temperature PDH. Alloying of Pt with In drastically enhanced the activity and selectivity due to the increased electron density of Pt.

Influence of calcination temperature of acidic ammonium salts of phosphotungstic acid on their composition and properties

The effect of the calcination temperature on the structure and properties of acidic ammonium salt (NH4)2HPW12O40 was studied. The absence of the influence of the calcination temperature of the samples on their particle size distribution, thermal stability and water content was shown. In the investigated range from 300 to 450 ​°C, a nonmonotonic change in the specific surface area and proton-conducting properties is observed depending on the calcination temperature. Calcination at a temperature other than optimal leads to a decrease in the specific surface area and proton conducting properties. A lower temperature is probably not enough for a complete redistribution of protons and ammonium ions; and an increase in the calcination temperature above optimal one entails the compaction of the salt crystallites.

The dynamic interplay between water and oxygen vacancy at the near-surface of ceria

Water, even at trace concentrations, strongly increases the CO oxidation activities of the reducible metal oxide supported noble-metal catalysts, where the transfer of proton plays a key role. In this paper, we performed a thorough investigation of the interplay between water molecules and the reduced CeO2(111) surface. It was found that water molecules can induce the migration of oxygen vacancies which in turn results in the formation of surface protons. The proton then entangles with the near-surface polaron to form polaron–proton pair due to their mutual attractive interactions. The hopping of the polaron can easily trigger the long-range or short-range diffusion of protons mediated by water molecules at the CeO2(111) surface. These findings provide new insights into the key roles of oxygen vacancies and polarons in reducible oxide based heterogeneous catalysis, which is beneficial for the understanding of the increased activity of reducible oxide supported metal nanoparticles in the presence of water.

Oxygen vacancy-rich WO3 heterophase structure: A trade-off between surface-limited pseudocapacitance and intercalation-limited behaviour

Intercalation-pseudocapacitance materials are attracting increasing interest as promising electrodes for use in high-capacitance supercapacitors. However, these materials typically exhibit unsatisfactory rate performances due to their relatively slow cation-insertion process. Under high mass loading, their rate performances are even further degraded. Herein is presented our fabrication of an oxygen vacancy-rich h-WO3/ort-WO3·0.33H2O heterophase structure (HOHS) by a facile hydrothermal synthesis. The HOHS has a split-level nanotubes-on-nanoplates morphology and its formation and energy-storage mechanisms are discussed in detail. The HOHS exhibits a collaborative charge-storage mechanism involving surface redox and proton intercalation, and the capacitance contribution associated with the proton intercalation can be regulated over a wide range. By achieving a trade-off between the surface-limited pseudocapacitance and intercalation-limited behaviours and regulating its morphology, the HOHS electrode with an ultra-high mass loading of 10.8 mg cm−2 delivers a high areal capacitance of 2552 mF cm−2 at 1 mA cm−2 and excellent long-term stability. More importantly, the rate performance of the HOHS (78% capacitance retention at 20 mA cm−2 in comparison to 1 mA cm−2) is better than those reported for WO3-based materials. This strategy opens avenues for the fundamental study of the regulation of the energy storage mechanism and the achievement of a trade-off between the capacitance and rate capability in high-mass-loading electrodes.

Direct Electrochemical Protonation of Metal Oxide Particles.

Metal oxides with surface protonation exhibit versatile physical and chemical properties suitable for use in many fields. Here, we develop an electrochemical route to directly protonize the physically assembled oxide particles, such as TiO2, Nb2O5, and WO3, in a Na2SO4 neutral electrolyte, which is a result of electrochemically induced oxygen vacancies reacting with water molecules. With no need of electric connection among particles or between particles and conductive substrate, the electrochemical protonation follows a bottom-up particle-by-particle surface protonation mechanism due to the fact that the protonation inducing high surface conductivity creates an efficient electron transfer pathway among particles. Our results show that electrochemical protonation of particles provides a chance to finely functionalize the surface of a single particle by only adjusting electrode potentials. Such a facile, cost-efficient, and green route is easy to run for a large-scale production and unlocks the potential of semiconductor oxides for various applications.

Insights into the synergetic mechanism of basic active site and oxygen vacancy on thermally activated MOFs for the colophony esterification: Experiments and DFT calculations

Investigating an feasible catalytic mechanism on Zn-MOF and its derivative amphoteric oxides is of great importance for esterification. Herein, activated Fe3O4-functionalized IRMOF-1 that was well retained the porosity was fabricated by encapsulating magnetic Fe3O4 in IRMOF-1 and activating thermally at 298−1273 K, which was evaluated for the esterification of colophony with glycerol. Results demonstrate that the catalytic performance of catalysts could be effectively enhance by thermal activation due to the additional basic sites and oxygen vacancies created. FT-IR and several thermal analyses reveal the unique adsorption of glycerol instead of the traditional carboxylic acids. Density functional theory (DFT) calculations suggest that the basic sites of catalysts are the crucial active sites for the glycerol hydroxyl dissociation and the formation of nucleophilic glyceroxide, and the presence of oxygen vacancy could significantly destabilize the surface proton and glyceroxide anions. A synergetic esterification mechanism of basic active site and oxygen vacancy was proposed.

Clinoptilolite and iron sorption/desorption under multiple pH conditions: Testing a substrate for passive treatment of acidic, iron-rich solutions.

Equilibrium sorption and desorption experiments were conducted with clinoptilolite to evaluate the potential sorption/desorption of iron during different pH conditions. Sorption experiments indicated a partitioning of 0% to 17% of the iron in solution given pH of 2 to 4. The pH 2 solution was able to desorb 70% of the iron that was captured from a pH 3 solution. The largest desorption and sorption of iron and corresponding pH represent the end points of iron capture primarily by sorption/exchange. These endpoints are the estimated pHpzc of 2.5 and the initial precipitation point of iron(II) at pH ~3.5. This acidity range is where clinoptilolite is able to capture iron without precipitation or the occurrence of full surface protonation. The inability of the highest acidity to remove all sorbed iron represents the greater bound iron that will not readily desorb with a change in pH. This retained iron creates a metastable state of the clinoptilolite that has a lower sorption capacity but reflects the ability of clinoptilolite to retain a sorbed transition metal with changes in pH. As pH varies, clinoptilolite may evolve in a sequence of metastable states reflective of its ability to capture or retain metals. PRACTITIONER POINTS: Clinoptilolite is a capable reactive substrate, but its sorption/exchange effectiveness at low and variable pH and ability to retain captured metals was unknown. Clinoptilolite retains its metal capture properties to a pH of 2.5 where surface protonation and mineral degradation likely occurs. The ability of clinoptilolite to retain captured iron under greater acidity reflects an evolution of its sorption/retention capacity.

Removal of chromate ions from leachate-contaminated groundwater samples of Khan Chandpur, India, using chitin modified iron-enriched hydroxyapatite nanocomposite.

Chromite ore processing residues (COPR) are real environmental threats, leading to CrO42-, i.e., Cr (VI) leaching into groundwater. It is of serious concern as Cr (VI) is proven to be carcinogenic. Here we emphasize the application of novel and eco-friendly chitin functionalized iron-enriched hydroxyapatite nanocomposite (HAP-Fe0-Ct) in the remediation of Cr (VI)-contaminated groundwater samples collected from Khan Chandpur, India, where the level of Cr (VI) is found to be 11.7 mg/L in a complex aqueous matrix having 793 mg/L of total dissolved solids. Chitin functionality in the composite has resulted in positive zeta potential at circum-neutral pH, favoring electrostatic attraction of chromate ions and resulting in its bulk surface transport. The HAP-Fe0-Ct showed faster kinetics of removal with efficiency (qm = 13.9 ± 0.46 mg/g) for Cr (VI). The composite has shown sorption equilibrium and 100% removal of Cr (VI) within 3 h of interaction time in groundwater samples. No Cr (VI) leaching in the acid wash process at pH 3.5 also suggests chromium's strong chemisorption onto nanocomposite. During the interaction in aqueous solutions, thereduced iron (Fe0) on the nanocomposite becomes oxidized, suggesting the probable simultaneous reduction of Cr (VI) and its co-precipitation. Continuous column extraction of chromate ions was also efficient in both spiked solutions (39.7 ± 0.04 mg/g) and COPR contaminated water (13.2 ± 0.09 mg/g). Reusability up to three cycles with almost complete Cr (VI) removal may be attributed to surface protonation, new binding sites generation, and electron transfer from Fe0 core through defects. The study concludes that HAP-Fe0-Ct could be utilized for continuous Cr (VI) removal from COPR contaminated complex groundwater matrices.

Constructing defect-related subband in silver indium sulfide QDs via pH-dependent oriented aggregation for boosting photocatalytic hydrogen evolution

Surface engineering of quantum dots (QDs) plays critical roles in tailoring carriers’ dynamics of I-III-VI QDs via the interplay of QDs in aggregates or assembly, thus influencing their photocatalytic activities. In this work, an aqueous synthesis and the followed pH tuned oriented assembly method are developed to prepare network-like aggregates, dispersion, or sheet-like assembly of GSH-capped Silver Indium Sulfide (AIS). FTIR, DLS, and HRTEM investigation revealed that surface protonation or deprotonation of QDs occurred at pH < 6 or pH > 12 favors the formation of network-like aggregates with various defects or sheet-like assembly with perfect crystal lattice, respectively, via the surface charge induced interaction among AIS QDs. Further UV–vis, steady and transient PL investigation confirm the narrowed band gaps and the prolonged PL lifetime of the acidic network-like aggregates. As a result, the optimized network-like aggregates (3.0-AIS) exhibits superior photocatalytic H2 evolution (PHE) rates (5.2 mmol·g−1·h−1), about 113 times that of alkaline sheet-like assembly (13.0-AIS) or 2.7 times higher than that of dispersed AIS QDs (AIS-8.0). The formation of defects and their roles in PHE mechanisms are discussed. This work is expected to give some new insight for designing efficient non-cadmium/non-novel metal I-III-VI photocatalysts for boosting PHE.

Understanding the Role of Concentrated Phosphoric Acid Solutions as High-Temperature Silicon Nitride Etchants

The ongoing demands for increased storage capacity flash memory in 2D-NAND structures resulted in their replacement by more advanced 3D-NAND structures, with the memory cells made of multiple, vertically stacked silicon oxide/silicon nitride layers. A critical step is selectively etching the silicon nitride films involving a wet etch technique using concentrated phosphoric acid at high temperatures. Concentrated phosphoric acid solutions demonstrate unique behaviors and have particularly high electrical conductivity, but the etching mechanism remains poorly understood. This study investigates the fundamental role of phosphoric acid in the silicon nitride etching and proposes complex active species for the silicon nitride surface protonation and hydroxylation. Characterization methods include 31P-NMR, XPS, FTIR, conductometry, viscometry and ellipsometry. We conclude that the unique performance of concentrated phosphoric acid as silicon nitride etchant results from an anomalously fast proton transport via the Grotthuss diffusion mechanism based on an intramolecular proton transfer driven by easily polarizable, hydrogen bond rearrangements between dissociated molecules as dimers, trimers and triple ions. By contrast, dilute phosphoric acid solutions and other strong protic acids (methanesulfonic acid, sulfuric acid, nitric acid), at both high and low concentrations exhibit protonic conductivity based on molecular diffusion of the H3O+/H2O/anions as separate entities (classical vehicle mechanism).

Revisiting paramagnetic relaxation enhancements in slowly rotating systems: how long is the long range?

Cross-relaxation terms in paramagnetic systems that reorient rigidly with slow tumbling times can increase the effective longitudinal relaxation rates of protons of more than 1 order of magnitude. This is evaluated by simulating the time evolution of the nuclear magnetization using a complete relaxation rate-matrix approach. The calculations show that the Solomon dependence of the paramagnetic relaxation rates on the metal-proton distance (as ) can be incorrect for protons farther than 15 Å from the metal and thus can cause sizable errors in -derived distance restraints used, for instance, for protein structure determination. Furthermore, the chemical exchange of these protons with bulk water protons can enhance the relaxation rate of the solvent protons by far more than expected from the paramagnetic Solomon equation. Therefore, it may contribute significantly to the water proton relaxation rates measured at magnetic resonance imaging (MRI) magnetic fields in the presence of slow-rotating nanoparticles containing paramagnetic ions and a large number of exchangeable surface protons.