Differences In Adsorption Energies Research Articles

Aluminum-induced electron structure on nickel phosphide for effective hydrazine‑assisted water splitting at large current density

Hydrazine-assisted water electrolysis emerges as a promising strategy to replace conventional device for effective hydrogen generation. Limited to the great difference of intermediate adsorption energy for hydrogen evolution reaction (HER) and hydrazine oxidation reaction (HzOR), the design and fabrication of bifunctional catalysts is still a knotty challenge in industrial conditions. Herein, Al-doped Ni2P nanoflower architecture grown in-situ on nickel foam (Al-Ni2P/NF) is fabricated through the combination of hydrothermal process and subsequent phosphorization treatment. Ascribed to the redistribution of electron state and optimization of reaction intermediate energy induced by Al, Al-Ni2P/NF expresses distinguished bifunctional catalytic performance with ultralow potentials of −205 and 300 mV at 500 mA cm−2 for HER and HzOR, respectively. When integrated into hydrazine-assisted water splitting as both the anode and cathode, only 0.717 V is required to reach a large current density of 500 mA cm−2. Specially, a novel integrated system driven entirely by sustainable solar energy is proposed, generating energy-saving hydrogen and purify hydrazine-containing sewage simultaneously. This work provides an attracting and practical path for accelerating the development of hydrogen economy.

Screening Efficient C-N Coupling Catalysts for Electrosynthesis of Acetamide and Output Ammonia through a Cascade Strategy of Electrochemical CO2 and N2 Reduction Using Cu-Based Nitrogen-Carbon Nanosheets.

Due to the limitation of the high-value-added products obtained from electrocatalytic CO2 reduction within an acid environment, introducing additional elements can expand the diversity of the products obtained during the CO2 reduction reaction (CO2RR) and nitrogen reduction reaction (NRR). Thus, coelectroreduction of CO2 and N2 is a new strategy for producing acetamide (CH3CONH2) via both C-C and C-N bond coupling using Cu-based nitrogen-carbon nanosheets. CO2 can reduce to CO, and a key ketene (*C═C═O) can be generated from *CO*CO dimerization; this ketene is postulated as an intermediate in the formation of acetamide. However, most studies focus on promoting the C-C bond formation. Here, we propose that C-N bond coupling can form acetamide through the interaction of *C═C═O with NH3. The acetamide is formed via a nucleophilic attack between *NH3 and the *C═C═O intermediate. The C-N coupling mechanism was successfully applied to expand the variety of nitrogen-containing products obtained from CO2 and N2 coreduction. Thus, we successfully screened Cu2-based graphite and Cu-based C3N4 as catalysts that can produce C2+ compounds by integrating CO dimerization with acetamide synthesis. In addition, we observed that Cu2-based C2N and Cu-based C3N4 catalysts are suitable for the NRR. Cu-based C3N4 showed high CO2RR and NRR activities with small negative limiting potential (UL) values of -0.83 and -0.58 V compared to those of other candidates, respectively. The formation of *COHCOH from *COHCO was considered the rate-determining step (RDS) during acetamide electrosynthesis. The limiting potential value of Cu2-based C2N was only -0.46 V for NH3 synthesis, and the formation of *NNH was via the RDS via an alternating path. The adsorption energy difference analysis both CO2 and N2 compare with the hydrogen evolution reaction (HER), suggesting that Cu2-based C2N exhibited the highest CO2RR and NRR selectivity among the 13 analyzed catalysts. The results of this study provide innovative insights into the design principle of Cu-based nitrogen-carbon electrocatalysts for generating highly efficient C-N coupling products.

Novel chiral composite membranes coated by microporous hyper-crosslinked polymer for efficiently enantioselective separation

With the rapid development of the pharmaceutical industry, efficient enantiomeric resolution is of great significance for the preparation of single enantiomer drugs. Herein, several kinds of chiral hyper-crosslinked polymer composite membranes (CHCPs/PSS) were fabricated by surface-initiated Friedel-crafts alkylation reaction on the porous SiO2 substrate for enantioseparation. The membrane fabrication conditions were optimized by changing various monomer concentrations, polymerization times and substrate pore sizes using phenylalanine as separated substance and the percent enantiomeric excess (ee%) reached 91.2 % with a permeability up to 6.31 × 10−2 m2/h which was 1012 folders higher than the traditional chiral polymer membranes. Besides, the enantioseparation of disparate enantiomers including clinical drug were also evaluated using CHCPs/PSS membranes to expand its application scope. The ee% and permeability reached 9.48 % and 5.13 × 10−1 m2/h for tryptophan and 24.4 % and 1.56 m2/h for ibuprofen, respectively. Static adsorption and quantum chemical computation were utilized to analyze the separation mechanism and the results indicated that the adsorption energy difference which resulted from the multiple interactions contributed to the effective separation of enantiomers. Consequently, this work will provide a new method for the application of chiral hyper-crosslinked polymer membranes in enantiomeric separation.

Enhancement of gas adsorption on transition metal ion-modified graphene using DFT calculations.

Graphene-based nanomaterial was widely used in gas sensors, detection, and separation. However, weak adsorption and low selectivity of the pristine graphene used for gas sensors are major problems. Here, using density functional theory (DFT) calculations, we reported the significant increase of four gas molecules (N2, CO2, C2H2, and C2H4) adsorption on the transition metal ion (Fe3+, Co2+, Ni2+)-modified graphene complex (Fe3+/Co2+/Ni2+-G) comparing to be absorbed on the pristine graphene (G). Moreover, the Co2+-G is suitable for the selective separation of C2H4/C2H2 due to the larger adsorption energy difference (8.5kcal/mol) between them. The addition of transition metal ions also decreased the HOMO-LUMO gap of the systems, which benefits the enhancement of electrical conductivity. This suggests that the transition metal ion-modified graphene can be used to distinguish the different gas molecule's adsorption, facilitating the design of graphene-based gas sensors and selective separation. All the density functional theory (DFT) calculations were performed by B3LYP with the GD3 dispersion method using Gaussian 16 software. The basis set 6-31G(d) was used for C, H, O, and N atoms, and Lanl2DZ was used for transition metal ions (Fe3+, Co2+, Ni2+). The DOS analysis and energy decomposition analysis were performed using the Multiwfn program.

Adsorption mechanism and compatibility of environmentally friendly insulating gas CF3I and its main decomposition products with Al and Cu(1 1 1) surfaces

Good environmental compatibility and excellent insulation performance make trifluoroiodomethane (CF3I) have the potential to replace SF6 in gas-insulated equipment. The gas–solid compatibility of CF3I, its main decomposed products (I2, C2F6, C3F8, C2F4, HF, CF3H, COF2), and environmental molecule H2O with the Al and Cu(111) surfaces is investigated based on first-principles calculations. The most stable adsorption configurations of Al and Cu(111) surfaces adsorbed by all gas molecules are constructed, and the interaction types between gas molecules and two metal surfaces are determined by adsorption energy (E ad), charge transfer, and charge density difference. The absolute E ad of CF3I and I2 adsorbed on Al(111) surfaces are 4.09 and 3.76 eV, respectively. In contrast, the absolute E ad of other gases adsorbed on Al(111) surfaces do not exceed 0.99 eV, indicating that CF3I and I2 have strong chemical interactions and poor gas–solid compatibility with Al(111) surfaces, while other gases exhibit good gas–solid compatibility with the Al surface. The absolute E ad of I2 (1.15 eV) adsorbed on Cu(111) surface is significantly larger than that of other gases-adsorbed systems (not exceeding 0.99 eV) including CF3I-adsorbed system, proving that the gas–solid compatibility of I2 with Cu(111) surfaces is worse than that of other gases. In addition, the reasons for the different compatibility of CF3I with Al and Cu(111) surfaces are analyzed in depth through the density of states.

MINI REVIEW ON RECENT ADVANCES OF THE ADSORPTION MECHANISM BETWEEN MICROPLASTICS AND EMERGING CONTAMINANTS FOR CONSERVATION OF WATER

Pharmaceuticals and microplastics have long been identified as water pollutants. Pollutants, including pharmaceutical compounds, have been shown to be transported by microplastics (MPs). In this mini-review, adsorption mechanism between microplastics and emerging contaminants were highlighted. Polyethylene is a non-polar, semi-cystalline microplastic with a density of 240 to 244 kg/m3. Besides, Ibuprofen adsorption onto microplastics is pH dependent. Non-polar or neutral compounds that are homogeneous and extremely hydrophobic in nature interact with non-polar and weakly polar plastics such as Polypropylene and Polyethylene. Furthermore, Molecular dynamic (MD) simulation can be employed to study the mechanism of interaction between MPs and contaminants. As a result, some studies show a complex interaction between polyethylene (PE) and certain contaminants, with no significant differences in adsorption energies, but sulfamethazine molecules effectively adsorbed on the MPs surface. In summary, this mini review shed lights on the insights of adsorption mechanism between these compounds.

π-Sticked Metal‒Organic Monolayers for Single-Metal-Site Dependent CO2 Photoreduction and Hydrogen Evolution Reaction.

Hierarchical self-assembly of 2D metal‒organic layers (MOLs) for the construction of advanced functional materials have witnessed considerable interest, due to the increasing atomic utilizations and well-defined atom‒property relationship. However, the construction of atomically precise MOLs with mono-/few-layered thickness through hierarchical self-assembly process remains a challenge, mostly because the elaborate long-range order is difficult to control via conventional noncovalent interaction. Herein, a quadruple π-sticked metal‒organic layer (πMOL) is reported with checkerboard-like lattice in ≈1.0 nanometre thickness, on which the catalytic selectivity can be manipulated for highly efficient CO2 reduction reaction (CO2RR) and hydrogen evolution reaction (HER) over a single metal site. In saturated CO2 aqueous acetonitrile, Fe-πMOL achieves a highly effective CO2RR with the yield of ≈3.98mmolg‒1h‒1 and 91.7% selectivity. In contrast, the isostructural Co-πMOL as well as mixed metallic FeCo-πMOL exhibits a high activity toward HER under similar conditions. DFT calculations reveal that single metal site exhibits the significant difference in CO2 adsorption energy and activation barrier, which triggers highly selective CO2RR for Fe site and HER for Co site, respectively. This work highlights the potential of supramolecular π…π interaction for constructing monolayer MOL materials to uniformly distribute the single metal sites for artificial photosynthesis.

DFT Calculations of Silver Atom Modified Tungsten Disulfide Monolayer as Promising Sensing Materials for Small Molecular Toxic Gases

In the contemporary context, the significance of detecting harmful gases cannot be overstated, as it profoundly affects both environmental integrity and human welfare. In this study, theoretically, density functional theory was employed to explore the adsorption behavior of three prevalent hazardous gases, namely CO, NO2, and SO2, on silver-atom-modified tungsten disulfide (WS2) monolayer. The multifaceted analysis encompasses an array of critical aspects, including the adsorption structure, adsorption energy, electron transfer, and charge density difference to unravel the adsorption behavior. Further exploration of electronic properties encompassing band structure, density of states (DOS), and work function was conducted. The ambit of our exploration extends to the desorption properties based on adsorption-free energies. Among these gas molecules, NO2 stands out with the highest adsorption energy and the most substantial electron transfer. Notably, each of these adsorption processes triggers a redistribution of electron density, with NO2 exhibiting the most pronounced effect. Furthermore, the adsorptions of CO, NO2, and SO2 induce a noteworthy reduction in the band gap, prompting the reconfiguration of molecular orbitals. Additionally, the adsorption of these gases also leads to an increase in the work function of Ag-WS2 to a different extent. Our investigation of desorption properties uncovers that Ag-WS2 can adeptly function at ambient temperatures to detect CO and SO2. However, for NO2 detection, higher temperatures become imperative due to the necessity for poison removal. The implications of our findings underscore the tremendous potential of Ag-WS2 as a sensing material for detecting these hazardous gases. Our research extends to the broader realm of surface modification of transition metal dichalcogenides and their promising applications in the domain of gas sensing.

Selective deep desulfurization of liquefied petroleum gas on Ni/ZnO-based catalyst

Process of selective deep desulfurization of liquefied petroleum gas (LPG) was developed using a Ni/ZnO-based catalyst. Ethyl mercaptan, dimethyl disulfide and methyl disulfide were used as model compounds in LPG to investigate sulfides conversion over different catalysts. All three model sulfides were totally removed over the composite catalyst at above 300 °C in hydrogen atmosphere. Desulfurization of LPG from FCC unit were studied in a micro-fixed bed reactor, and scaled up in a fixed-fluidized bed reactor. Results showed that highly selective desulfurization of LPG could be achieved using the composite catalyst when the sulfur loading of catalyst was in a particular range. The sulfur content of LPG could be decreased to lower than 2.0 μg·g−1 with an olefin loss ratio of less than 1.5 %. X-ray photoelectron spectroscopy (XPS) characterization indicated that the interaction of Ni with S strengthened with the increasing of sulfur loading. Density functional theory calculations showed that the pre-coated S on Ni (111) surface increased the adsorption energy difference between propylene and sulfides which was helpful for the retention of propylene during desulfurization on Ni/ZnO-based catalyst.

Amorphization Engineering of Bimetallic Metal‐Organic Frameworks to Identify Volcano‐Type Trend toward Oxygen Evolution Reaction

AbstractAmorphous metal‐organic frameworks (MOFs) with aperiodic atomic arrangements, featuring high intrinsic activity and rich active sites, have emerged as promising oxygen evolution reaction (OER) catalysts. However, the quantitative structure‐activity relationships (SARs) that determine the OER activity, the key to a rational catalyst design, remain unresolved. Inspired by controllable amorphization engineering, the amorphous MOF structures are rationally constructed as an ideal platform to explore the SAR in catalyzing OER. The mechanistic studies show that the OER activity could be volcano‐shape correlated with either constant adsorption energy difference between OOH* and O* (ΔGOOH* − ΔGO*) or the position of the d band center. The amorphous MOF (Ni8Co2‐BDC), situated close to the volcano summit, possesses an appropriate Ed energy level, which exhibits the balanced intermediates adsorption/desorption ability and consequently results in the boosted catalytic activity and long‐term stability. This work supplies new perspectives to investigate the SAR in amorphous MOF structures, thereby guiding the rational design of advanced OER catalysts.

I-V characteristics and adsorption properties of ZnO/rGO/ZnO for gas sensing detection

The heterostructure consisting of zinc oxide and reduced graphene oxide (ZnO/rGO/ZnO) is prepared on cotton fabric by repeated immersion and magnetron sputtering. In addition, the gas selectivity of the sample is analyzed based on I-V characteristics under different gas atmospheres (air, methanal, ethanol, acetone and toluene). Compare with that in air atmosphere, the I-V characteristic curve under toluene gas atmosphere changes significantly, and the current decreased significantly. The experimental results show that the samples exhibit high selectivity. In order to study the intrinsic physical characteristics of the heterostructure after gas adsorption, the band structures, density of states (DOS), adsorption energy (Ead) and charge density difference (CDD) are calculated based on density function theory (DFT). The existence of rGO results in a high electrical conductivity, which is consistent with the experimental results. Meanwhile, toluene has the highest Ead (-0.85 eV) and charge transfer (0.67 e). The charge transfer results prove that a large number of electrons are transferred from the surface of the heterostructure to the vicinity of toluene molecules, which leads to a change in the electrical conductivity of the heterostructure. Based on the excellent gas selectivity, the application of cotton-based ZnO/rGO/ZnO structure in gas sensing field is promoted.

DFT investigation and Polypyrrole sensitization mechanism of a selective NO2 sensor for room temperature application based on MXene@PPy heterojunction

Assembling a heterojunction-based composite nanomaterial to simultaneously achieve higher response and superior selectivity towards NO2 under room-temperature conditions remains a great challenge. In this work, the MXene@Polypyrrole heterojunction was synthesized via a facile in-suit chemical polymerization approach. The distribution of sphere-like PPy nanoparticles was confirmed via various characterization techniques. The response value of the 0.5MXP sensor toward 50 ppm NO2 is significantly higher than that of the pristine MXene based sensor, entailing greater response (6.5-fold). Nearly 98.11% recovery to the base resistance was observed in each sensing cycle. Noteworthy, the Schottky barriers formed between MXene and PPy contact surface, leading to the ideal selectivity and a lower limit of detection. Additionally, the sensor was tested for a 31-days-period with minimal deviation, predicting outstanding reproducibility and durability. The detailed polypyrrole sensitization mechanism containing selectivity mechanism, underlying heterojunction mechanism as well as the Density Function Theory (DFT) calculation were also revealed, offering new ideas for the development of room-temperature nitrogen dioxide sensors. Simultaneously, DFT calculation (21 models, 42 images) revealed the adsorption energy, electron transfer, and charge density differences between the NO2 molecules and the substrate (MXene, PPy and MXene@PPy). In summary, the outstanding MXene surface functionalization has been exploited by decorating with polypyrrole (PPy) nanoparticles.

Insights into the selectivity of metallic oxides for arsenic and phosphate from EXAFS and DFT calculations

Phosphate is the biggest competitor for arsenic removal. Nanoscale metal oxides (NMOs) are commonly used to treat arsenic-contaminated water, yet their selective adsorption mechanisms for arsenic and phosphate are poorly understood. We quantified the selectivity of iron oxide (Fe2O3), zinc oxide (ZnO), and titanium dioxide (TiO2) nanosheets for arsenic in systems containing arsenic and phosphate, and determined the interaction of phosphate and arsenate/arsenite on metal oxide surfaces through batch experiments, spectroscopic techniques, and DFT calculations. We found that Fe2O3, TiO2, and ZnO nanosheets exhibit selectivity for arsenate/arsenite in the presence of phosphate, with Fe2O3 the most selective, followed by TiO2 and ZnO. The bonding mechanism on these metallic oxide surfaces dominates the selectivity. The more stable inner-sphere complexes of arsenate on the surfaces of Fe2O3 (bidentate binuclear), TiO2 (bidentate binuclear), and ZnO nanosheets (tridentate trinuclear) contribute to their preference for arsenate over phosphate. This difference in arsenate selectivity can be reflected in the difference in adsorption energy, net electron transfer number, and M − O bond length of the most stable inner sphere complexes. Overall, our study elucidated the selective adsorption mechanisms of arsenate/arsenite on Fe2O3, TiO2, and ZnO surfaces and highlighted the need to consider the competition between arsenate and phosphate during their removal from contaminated water.

Surface Ti vacancy passivation of Ti3C2O2 MXene via transition metal atoms as high-performance potassium-ion batteries anodes

MXene exhibits tunable interlayer spacing, excellent conductivity and high redox activity, appearing to be ideal intercalated anodes of potassium ion battery. However, defects formed in the preparation process of this material seriously decrease the initial Coulombic efficiency (ICE) and diffusion rate. Herein, transition metals (TMs) passivation is employed to solve this problem based on DFT calculations. TMs filled in Ti vacancy (vTi) is figured out to form strong bonds with surround C and O atoms, which strength is positively-related with the outer electron numbers at d + s orbits of TMs. It enlarged the K adsorption energy difference (ΔEa) between cubic closest packing (ccp)- and hexagonal closest packing (hcp)-site, suggesting larger capacity than Ti3C2O2. ΔEa is revealed negatively linear-correlated with d-band center difference between TM and Ti element, then Fe and Mn would be excellent elements of passivation due to the smallest distance of d-band center to Ti. More importantly, TMs passivation obviously decreases the interaction between vTi and K+, lowering K+ diffusion barrier. This work provides new possibility of surface engineering for MXene performance modification beyond PIBs anodes.

Highly Sensitive and Selective Detection of Pharmaceuticals on Au/MIL-101(Cr) by SERS.

The detection of pharmaceuticals has been a matter of concern among scientists and health researchers in the past few decades. However, it is still difficult to realize the sensitivity and selectivity detection of pharmaceuticals with similar structures. Herein, the pharmaceutical molecules of 2-mercaptobenzimidazole (MBI) and 2-mercaptobenzothiazole (MBT) with so similar structures can be selectively detected by surface-enhanced Raman spectroscopy (SERS) taking advantage of the fingerprint identification on Au/MIL-101(Cr), with sensitive detection limits of 0.5 ng·mL-1 for MBI and 1 ng·mL-1 for MBT. MBI is selectively enriched by Au/MIL-101(Cr) from the mixture solution and detected by SERS below 30 ng·mL-1. MBI can also be selectively detected in the serum samples with a detection limit of 10 ng·mL-1. Density functional theory calculations combined with the SERS experiments explained that the high sensitivity and selectivity are caused by the intrinsic differences in Raman intensity and different adsorption energies from the pharmaceutical molecules adsorbed on Au/MIL-101(Cr), respectively. This study provides an effective way to enrich and detect pharmaceutical molecules with similar structures.

Solvent effect on adsorption of benzylidene oxindole to C20 nanocage: A DFT approach

AbstractIn this paper, one of the selective and potent inhibitors named (E)‐3‐benzylidene‐indoline‐2‐one (I), as against different receptor tyrosine kinase in metastasis, angiogenesis, and tumor growth, is inspected in the gas phase and in solution, at B3LYP/6‐311++G** and B3LYP/AUG‐cc‐pVTZ level of theory. A stimulating issue for this biologically active species is the effect of different media on its stability, structure, and energy gap in intermolecular [4 + 2] adsorption of I (as diene) to C20 (as dienophile) to yield (E)‐3‐benzylidene‐indoline‐2‐one[20]fullerene: Ia complex. In going from gas phase to C6H6, C2H4Cl2, EtOH, MeNO2, DMSO, and H2O solvents, individually, the optimization of complex (Ia) leads to the following: (1) The thermodynamic stability; the adsorption energy difference between liquid and gas phase (∆El–g) and dipole moment (μ) seem proportional to the dielectric constant (ε) of the scrutinized media. (2) The kinetic stability; energy difference (∆EL–H) between the frontier molecular orbitals; FMO in different media is altered in the opposite direction of ε. (3) Despite of popular belief that the endo isomer emerges thermodynamically more stable than its corresponding exo isomer, we suggest formation of kinetically more stable exo isomer because of π–π stacking among the benzyl ring and C20 nanocage. (4) The possibility of hetero [4 + 2] cycloaddition is anticipated by the lowest energy barrier of 3.8 kcal/mol probed for exo transition state (TS) in gas phase, while the highest energy barrier of 7.9 kcal/mol corresponds to the endo TS in water. (5) Due to lack of the repulsion type interaction, the exo [4 + 2] cycloaddition of unstable C20 fullerene with the scrutinized oxindole can be carried out thermally at r.t. and currently hold responsible for the origin of stereoselectivity.

Building Up an “Elemental Property—Adsorption Energy Descriptor—Decomposition Barrier” Three‐Tier Model for Screening Biatom Catalysts in Sodium–Sulfur Batteries

AbstractDeveloping highly efficient catalysts for the Na2S redox process and sodium polysulfide anchoring is becoming increasingly important for high‐performance sodium–sulfur (Na–S) batteries. The recently emerged graphene‐supported biatom catalysts (G‐BACs) exhibit great potential for providing high activity in both discharging and charging processes. However, the fast screening of promising G‐BACs for Na–S batteries is hindered by the formidable computational cost for calculating Na2S decomposition barriers (Eb). Herein, this work develops an “elemental property—adsorption energy descriptor—decomposition barrier” three‐tier model to accelerate this process and elucidates the origin of catalytic activity. It is found that Eb during the charging process is linearly correlated with the adsorption energy difference between the initial and final states of Na2S decomposition (Ediff) for both homonuclear and heteronuclear transition metal G‐BACs. This work further correlates Ediff with intrinsic properties of metal elements by machine learning approaches and unravels the most significant elemental feature to be the outer electron number. This work not only accelerates the design of highly efficient G‐BACs in Na–S batteries based on the structure–activity relationship, but also provides a feasible strategy for the fast screening of catalysts for other electrochemical reactions for potential experimental design.

Exceptional Sorption of Heavy Metals from Natural Water by Halloysite Particles: A New Prospect of Highly Efficient Water Remediation.

Halloysite particles, with their unique multilayer nanostructure, are demonstrated here as highly efficient and readily available sorbent of heavy metals that can be easily scaled up and used in large-scale water remediation facilities. The various methods of raw material purification were applied, and their effects were verified using techniques such as BET isotherm (determination of specific surface area and size of pores), XRF analysis (composition), and SEM imaging (determination of morphology). A series of adsorption experiments for aqueous solutions of metal ions (i.e., lead, cadmium) were carried out to quantify the sorption capacity of halloysite particles for selected heavy metals. The ability of adequately activated halloysite to efficiently remove heavy metal ions from water solutions was confirmed. The value of the zeta potential of raw and purified halloysite particles in water was determined. This enables us to understand its importance for the sorption of positively charged ions (metal, organics) at various pH values. The adsorption process conducted in the pH range of 6.0-6.5 showed significant improvement compared to the acidic conditions (pH value 3.0-3.5) and resulted in a high sorption capacity of lead ions-above 24.3 mg/g for the sulphuric acid-treated sample. The atomic scale ab initio calculations revealed a significant difference in adsorption energy between the external siloxane surface and cross-sectional interlayer surface, resulting in pronounced adsorption anisotropy. A low energy barrier was calculated for the interlayer migration of heavy metals into the halloysite interior, facilitating access to the active sites in these regions, thus significantly increasing the sorption capacity and kinetics. DFT (density functional theory) calculations supporting this study allowed for predicting the sorption potential of pure halloysite structure towards heavy metals. To confront it with experimental results, it was crucial to determine proper purification conditions to obtain such a developed structure from the mineral ore. The results show a massive increase in the BET area and confirm a high sorption potential of modified halloysite towards heavy metals.

Phosphoric acid resistance PtCu/C oxygen reduction reaction electrocatalyst for HT-PEMFCs: A theoretical and experimental study

In high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs), dissociative H3PO4 in cathode will block the active sites of Pt-based electrocatalyst, which thus failure to catalyze the oxygen reduction reaction (ORR). Therefore, the electrocatalysts for the ORR in HT-PEMFCs with high resistance to H3PO4 poisoning are significantly important. Due to the similar bonding structure between HxPO43-x/O2 and Pt (Pt-O), the design of catalysts which could selectively reduce the adsorption energy of the H3PO4 is urgently needed. In this work, we screen proper H3PO4 resistance electrocatalysts through theoretical calculation based on the adsorption energy difference between HxPO43-x and O2 as an evaluation criterion. Then, we prepared a series of PtxCu catalysts based on the theoretical calculation results and further studied the structure-performance relationship of phosphoric acid-resistant catalysts through combining physical property characterization and electrochemical tests including half-cell and single-cell. The mass activity of Pt2Cu/C is 0.51 A/mgPt, exceeding the DOE's 2020 target of 0.44 A/mgPt. After add 0.1 M H3PO4 into the HClO4 electrolyte, the half-wave potential (E1/2) of Pt2Cu/C is only negatively shifted by 47 mV, much lower than 90 mV of TKK Pt/C. Furthermore, the HT-PEMFC with Pt2Cu/C in the cathode shows a peak power density of 383.4 mW/cm2, which surpasses that of TKK Pt/C for 231.0 mW/cm2. Our strategy of screening catalysts based on the adsorption energy difference study and further verified by experimental methods provides a promising strategy for the design of practical electrocatalyst in the cathode of HT-PEMFCs.

Investigation on adsorption of sodium fluoro-aluminates on graphite by density functional theory

The carbonous materials have been widely used as electrodes in the current aluminum industry. Cathode wear has been an unavoidable problem and limits the lifetime of electrolysis cells in aluminum production, which is mainly due to the reaction between molten cryolite salts and the graphite surface, formation of an aluminum carbide layer on the surface of the cathode, sodium penetration, and abrasion of molten salts. However, the mechanism of cathode wear is still not fully understood, and not clarified at the atom level. In this paper, density functional theory based calculations were performed to investigate the reactivity properties between fluoro-aluminates and graphite surfaces. The adsorption energy and optimized structures of three typical fluoro-aluminates on various sites were obtained, indicating that chemical adsorption has occurred, and Na2AlF5 was easier than Na3AlF6 and NaAlF4 to adsorb on the graphite surface. The adsorption sites only cause a slight difference in adsorption energy since the size of fluoro-aluminates is larger than the distance between various sites. Moreover, the charge density differences, density of states, and partial charge density were calculated to illustrate the electron transfer between fluoro-aluminates and the graphite cathode. During the adsorption of fluoro-aluminates on the graphite surface, electrons would transfer from sodium to the graphite cathode. Meanwhile, the electrons of carbons are attracted by fluorine atoms. However, there is no electrons transfer directly between the aluminum atom and the graphite surface.