Reaction Mechanism Research Articles

Operando Spectroscopic Monitoring of Metal Chalcogenides for Overall Water Splitting: New Views of Active Species and Sites

AbstractMetal‐based chalcogenides exhibit great promise for overall water splitting, yet their intrinsic catalytic reaction mechanisms remain to be fully understood. In this work, we employed operando X‐ray absorption (XAS) and in situ Raman spectroscopy to elucidate the structure–activity relationships of low‐crystalline cobalt sulfide (L−CoS) catalysts toward overall water splitting. The operando results for L−CoS catalyzing the alkaline hydrogen evolution reaction (HER) demonstrate that the cobalt centers in the bulk are predominantly coordinated by sulfur atoms, which undergo a kinetic structural rearrangement to generate metallic cobalt in S−Co−Co−S moieties as the true catalytically active species. In comparison, during the acidic HER, L−CoS undergoes local structural optimization of Co centers, and H2 production proceeds with adsorption/desorption of key intermediates atop the Co−S−Co configurations. Further operando characterizations highlight the crucial formation of high‐valent Co4+ species in L−CoS for the alkaline oxygen evolution reaction (OER), and the formation of such active species was found to be far more facile than in crystalline Co3O4 and Co‐LDH references. These insights offer a clear picture of the complexity of active species and site formation in different media, and demonstrate how their restructuring influences the catalytic activity.

Operando Spectroscopic Monitoring of Metal Chalcogenides for Overall Water Splitting: New Views of Active Species and Sites.

Metal-based chalcogenides exhibit great promise for overall water splitting, yet their intrinsic catalytic reaction mechanisms remain to be fully understood. In this work, we employed operando X-ray absorption (XAS) and in situ Raman spectroscopy to elucidate the structure-activity relationships of low-crystalline cobalt sulfide (L-CoS) catalysts toward overall water splitting. The operando results for L-CoS catalyzing the alkaline hydrogen evolution reaction (HER) demonstrate that the cobalt centers in the bulk are predominantly coordinated by sulfur atoms, which undergo a kinetic structural rearrangement to generate metallic cobalt in S-Co-Co-S moieties as the true catalytically active species. In comparison, during the acidic HER, L-CoS undergoes local structural optimization of Co centers, and H2 production proceeds with adsorption/desorption of key intermediates atop the Co-S-Co configurations. Further operando characterizations highlight the crucial formation of high-valent Co4+ species in L-CoS for the alkaline oxygen evolution reaction (OER), and the formation of such active species was found to be far more facile than in crystalline Co3O4 and Co-LDH references. These insights offer a clear picture of the complexity of active species and site formation in different media, and demonstrate how their restructuring influences the catalytic activity.

KINETICS AND THERMODYNAMIC ASSESSMENT OF RICE HUSK IN AN INERT ATMOSPHERE AS A FEEDSTOCK FOR ALTERNATIVE FUEL PRODUCTION

The utilisation of rice husk as a feedstock for alternative fuel production is an area of growing interest due to its abundance and potential as a renewable energy source. This study reports investigation of kinetics and thermodynamics of rice husk pyrolysis in an inert atmosphere. Experimental analysis, including proximate, ultimate, structural composition and thermogravimetric analyses (TGA), were conducted to determine the proxanal, ultanal, chemical composition and pyrolysis characteristics of rice husk under inert conditions. Kinetics of the pyrolysis process was evaluated using distributed activation energy model (DAEM) while thermodynamic parameters such as activation energy (E A), changes in enthalpy (ΔH), entropy (ΔS),and Gibbs free energy (ΔG) were computed to provide insights into the reaction mechanisms. The feedstock exhibited ash content, fixed carbon, volatile matter, and higher heating value on dry basis of 13.56wt%, 16.37wt%, 70.07wt% and 15.22MJ/kg respectively while the result of ultimate analysis showed carbon, hydrogen, nitrogen, sulphur and oxygen content of 40.95, 5.67, 0.22, 0.09 and 52.17wt%. The chemical composition result (water extractives-free) indicated cellulose, hemicellulos and lignin content of 39.12, 17.56 and 22.43 wt%. The kinetics analysis revealed that the pyrolysis process followed a single-order reaction mechanism and irreversible, suggesting that the pyrolysis reactions proceed in a direction that favors the formation of products. The average E A, ΔH, ΔS and ΔG required for the pyrolysis reactions was established to be 140.56 kJ/mol, 137.00 kJ/mol, -135.25 J/mol and 222.38 kJ/mol respectively. The comprehensive assessment of the feedstock affirms its suitability for alternative fuel production towards a greener energy landscape.

Unraveling defect chemistry in doped-ceria catalyst for oxidative coupling of lignin-based aniline and benzyl alcohol

The defect chemistry of doped-ceria is vital but tangled for sustainable conversion of biomass resources. In this work, a group of Zr-doped CeO2 solid solutions were prepared and the defect chemistry in CeZrxOy (0.02 ≤ x ≤ 5) catalyst was elucidated over the oxidative coupling of lignin-based aniline and benzyl alcohol. Varying the Zr molar fraction enabled to successfully adjust the defect sites of catalysts and further influence their catalytic performances. In addition, the optimal CeZr1Oy catalyst exhibited a flexible temperature adaptability, wide substrate scope and superior reusability. Various characterizations, kinetic investigations, controlled experiments, DFT calculations and in situ DRIFT-IR technique were used to unravel the roles of Ce3+ and oxygen defects and the reaction mechanism. It was disclosed that Zr-doped defects can obviously increase surface Ce3+ cations, oxygen species (peroxide and superoxide anions) and oxygen vacancies. These coordinatively unsaturated sites were shown to play critical roles in absorbing and activating substrates hence can accelerate the formation rate of bio-based imines.

Chemical insight into thermal degradation, chemical kinetics, and thermodynamics behavior of sewage sludge through thermogravimetry and Fourier transform infrared analysis

Pyrolysis emerges as a promising path for sewage sludge (SS) management and value creation by producing compounds with enhanced utility. This study focuses on a comprehensive analysis of the thermal decomposition of SS using thermogravimetric analysis (TGA) and Fourier transform infrared spectrometry (FTIR). The TGA and FTIR were employed to evaluate the pyrolysis behavior, kinetics, and characteristics during pyrolysis of SS. The process revealed three distinct stages: 1st stage ranged between 30–185 °C with the removal of moisture, 2nd stage saw devolatilization of SS in the range of 185–595 °C, and the 3rd stage was mainly the formation of char in the temperature range of 595–900 °C. Pyrolysis kinetics, reaction mechanisms, and thermodynamic properties were extensively investigated at three different heating rates of 10, 20, and 30 °C /min. It was observed that with the temperature rise, the decomposition rate also increased rapidly, notably for the heating rate of 30 °C/min. Using Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, Starink, and Tang methods, activation energies for SS pyrolysis were estimated for α in the range of 0.2–0.85, and the average value for that range was found to be 84.72, 92.29, 91.99, and 91.76 kJ/mol, respectively for different iso-conversional methods. The chemical kinetics analysis through Coats-Redfern methods identified that 3-D diffusion-reaction mechanisms have the highest coefficient of determination among the other models. Criado z-master plot emphasizes the prevalence of Avrami-Erofeev (A4) as the bestsuited reaction model in combination with α, providing a detailed examination that illuminates the complex processes and mechanisms inherent in the pyrolysis of sewage sludge.

Poly-3,4-dihydroxybenzylidenhydrazine, a different analogue of polydopamine

Abstract In this article, 3,4-dihydroybenzylidenehydrazine is synthesized for the first time, and its properties as a dopamine analogue for polymerization are investigated. Using an oxidative polymerization reaction, the reaction mechanism as well as the coating ability of the new polymer is determined and compared to that of polydopamine. The polymerization reactions were performed in a mixture of methanol–water with NaIO4 as an oxidation reagent. The polymer was used as a coating on both glass surfaces with a thickness of ∼5 nm as determined by AFM, as well as on TiO2 nanoparticles. For the latter, SEM/TEM and the pH-dependent variation of zeta potential were measured. As a free polymer, poly-3,4-dihydroxybenzylidenhydrazine was investigated by UV-Vis, ss-NMR, and FTIR, and a variety of monomeric units were found in the polymer matrix. The solubility in methanol or DMSO of the monomer and the slight solubility of the polymer allowed us to study the fluorescence and cyclic voltammetry properties for both the monomer and polymer.

Mechanistic Insights into the Excited-State Intramolecular Proton Transfer (ESIPT) Process of 2-(2-Aminophenyl)naphthalene.

The 2-(2-aminophenyl)naphthalene molecule attracted much attention due to excited-state intramolecular proton transfer (ESIPT) from an amino NH2 group to a carbon atom of an adjacent aromatic ring. The ESIPT mechanisms of 2-(2-aminophenyl)naphthalene are still unclear. Herein, the decay pathways of this molecule in vacuum were investigated by combining static electronic structure calculations and nonadiabatic dynamics simulations. The calculations indicated the existence of two stable structures (S0-1 and S0-2) in the S0 and S1 states. For the S0-1 isomer, upon excitation to the Franck-Condon point, the system relaxed to the S1 minimum quickly, and then there exist four decay pathways (two ESIPT ones and two decay channels with C atom pyramidalization). In the ESIPT decay pathways, the system encounters the S1S0-PT-1 or S1S0-PT-2 conical intersection, which funnels the system rapidly to the S0 state. In the other two pathways, the system de-excited from the S1 to the S0 state via the S1S0-1 or S1S0-2 conical intersection. For the S0-2 structure, the decay pathways were similar to those of S0-1. The dynamics simulations showed that 75 and 69% of trajectories experienced the two ESIPT conical intersections for the S0-1 and S0-2 structures, respectively. Our simulations showed that the lifetime of the S1 state of S0-1 (S0-2) is estimated to be 358 (400) fs. Notably, we not only found the detailed reaction mechanism of the system but also found that the different ground-state configurations of this system have little effect on the reaction mechanism in vacuum.

Microcosmic insights into Hg0-SO2 interaction on CuFe2O4 catalyst

CuFe2O4 is considered as a very promising kind of catalysts for Hg0 oxidation in the industrial flue gas. The flue gas produced by solid-fuel combustion usually contains acid gas component SO2, which can exhibit the versatile effects on Hg0 oxidation. However, the effects of SO2 on Hg0 oxidation catalyzed by CuFe2O4 catalyst and its reaction mechanism remain elusive. Herein, the reaction mechanism governing the effects of SO2 on Hg0 oxidation was investigated via the Hg0 oxidation experiments and density functional theory (DFT) calculations. The experimental results show that the temperature change and SO2 presence can affect the Hg0 removal efficiency of CuFe2O4 catalyst. SO2 has a certain degree of inhibition effect on the Hg0 oxidation of CuFe2O4 catalyst. The inhibition effect of SO2 is relatively weak in the low temperature range of 50–150 °C, which is closely associated with the competitive adsorption between SO2 and Hg0. SO2 exhibits a relatively strong inhibition effect on Hg0 oxidation in the high temperature range of 200–350 °C, which is related to the high-temperature sulfation of CuFe2O4 catalyst surface. Mercury species on the CuFe2O4 catalyst surface mainly exists in the forms of HgSO4 and HgO in the presence of SO2. The DFT-calculation results indicate that the conversion process of SO2 to SO3 includes two steps: SO2 adsorption and SO2 oxidation. The activation energy barrier of SO2 oxidation reaction is 216.42 kJ/mol. The oxidation of Hg0 on the surface of CuFe2O4 catalyst includes four steps: Hg0 adsorption, Hg* oxidation into HgO*, HgO*-to-HgSO4* conversion and HgSO4 desorption. HgSO4 is formed by the bimolecular reaction of HgO* and SO3* on CuFe2O4 catalyst. Hg* oxidation into HgO* is found to be the rate-determining step of HgSO4 formation.

A synthesis of styrene-grafted starch accompanied with reaction condition optimization and microstructural and macroscopic property analysis

Styrene grafting is efficient to alter starch macroscopic property. Nevertheless, reaction mechanism, condition and products structure and properties are blurry. A deep exploration is necessary. Herein, K2S2O8 and styrene were chosen for corn starch modification. Reaction conditions involving K2S2O8 and styrene amounts, temperature and period were explored. Concurrently, microstructural and macroscopic properties of modified starches were explored via FT-IR, XPS, 13C NMR, GPC, XRD, SEM, TGA, DSC, CA and water dispersibility analysis. Main results reveal that K2S2O8 and styrene amounts, temperature and period as 3 and 200 wt%, 50 °C and 3 h is an optimized condition for starch grafting styrene, achieving a grafting yield (GY) as 45.8 wt%. GPC, XPS and 13C NMR analysis certified successful grafting and grafting mainly occurred at C-3 site OH within glucose unit. This variation converted starch crystalline shape transformation from A-typed to V-typed accompanied with crystallinity, thermal-stability and swelling characteristic decrease and surface hydrophobicity elevation. With GY increased from 0 to 45.8 wt% crystallinity decreased from 38.7 to 15.1%, thermal-decomposition temperature decreased by 10 °C, gelatinization temperature and CA increased by 50 °C and 70°, respectively. It seems a small amount styrene grafting can alter starch macroscopic property such as hydrophilicity efficiently, readily to manufacture hydrophobic starch. This hydrophobic starch might have a potential use in plastic industry, enlarging starch use application, meaningful.

Quantitative investigation on microwave-accelerated fructose conversion via fluorescent thermometry

The use of microwave (MW) is promising for resolving energy-intensive problems that occur in carbohydrate bioconversion. To quantitatively investigate the mechanism of MW-accelerated reactions, the present study designs three carbon-based catalysts with distinct dielectric loss values (namely, SCS-SO3H, SCS-800-SO3H, MHCS-800-SO3H) for fructose hydrolysis. A fluorescence thermometer (Eu/Tb metal organic complex) was loaded on catalysts for in situ measurement of their localized temperature during MW heating. The combination of fluorescence experiments and theoretical modelling predicts that the temperature gradient between SCS-800-SO3H particles and bulk solvents reaches 26.10°C, which causes an 8.13-fold increase in reaction rate constants. Surprisingly, this speedup value is increased to 28.57 because of the thermal gradient up to 62.10°C when using MHCS-800-SO3H. In contrast, the MW-transparent SCS-SO3H exhibits no significant increase in the reaction rate. The quantitative elucidation of dominant roles of hot spots is promising for guiding the development of high-efficiency catalysts for MW-assisted heterogeneous reactions.

Unveiling the Mechanistic Role of Chiral Palladacycles in Pd(II)-Catalyzed Enantioselective C(sp3)-H Functionalization.

Palladium-catalyzed enantioselective C(sp3)-H functionalization reactions has attracted considerable attention due to its ability for the synthesis of enantiomerically enriched molecules and stimulation of novel retrosynthetic disconnections. Understanding the reaction mechanism, especially the stereochemical process of the reaction, is crucial for the rational design of more efficient catalytic systems. Previously, we developed a Pd(II)/sulfoxide-2-hydroxypridine (SOHP) catalytic system for asymmetric C(sp3)-H functionalization reactions. In this study, we focused on unraveling the chemistry of chiral palladacycles involved in the Pd(II)-catalyzed enantioselective C(sp3)-H functionalization. We have isolated key palladacycle intermediates involved in the enantioselective β-C(sp3)-H arylation of carboxylic acids catalyzed by the Pd(II)/SOHP system. These palladacycles, exhibiting ligand-induced chirality, provided a significant opportunity to investigate the stereochemical process and the ligand effect in this asymmetric C-H functionalization. Our investigation provided direct evidence for the C-H palladation step as the enantioselectivity-determining step, which forms diastereomeric palladacycles that exhibited preservation of chirality in the functionalization step. DFT calculations provided insights into the chiral induction in palladacycle formation. This work highlights the value of chiral palladacycle chemistry in offering mechanistic insights into the Pd(II)-catalyzed asymmetric C(sp3)-H functionalization reactions.

Unveiling the Mechanistic Role of Chiral Palladacycles in Pd(II)‐Catalyzed Enantioselective C(sp3)‐H Functionalization

Palladium‐catalyzed enantioselective C(sp3)‐H functionalization reactions has attracted considerable attention due to its ability for the synthesis of enantiomerically enriched molecules and stimulation of novel retrosynthetic disconnections. Understanding the reaction mechanism, especially the stereochemical process of the reaction, is crucial for the rational design of more efficient catalytic systems. Previously, we developed a Pd(II)/sulfoxide‐2‐hydroxypridine (SOHP) catalytic system for asymmetric C(sp3)‐H functionalization reactions. In this study, we focused on unraveling the chemistry of chiral palladacycles involved in the Pd(II)‐catalyzed enantioselective C(sp3)‐H functionalization. We have isolated key palladacycle intermediates involved in the enantioselective β‐C(sp3)‐H arylation of carboxylic acids catalyzed by the Pd(II)/SOHP system. These palladacycles, exhibiting ligand‐induced chirality, provided a significant opportunity to investigate the stereochemical process and the ligand effect in this asymmetric C‐H functionalization. Our investigation provided direct evidence for the C‐H palladation step as the enantioselectivity‐determining step, which forms diastereomeric palladacycles that exhibited preservation of chirality in the functionalization step. DFT calculations provided insights into the chiral induction in palladacycle formation. This work highlights the value of chiral palladacycle chemistry in offering mechanistic insights into the Pd(II)‐catalyzed asymmetric C(sp3)‐H functionalization reactions.

A mitochondrial targeted dual ratiometric near-infrared fluorescent probe based on ICT effect for the detection of SO2 derivative and its bioimaging

SO2 derivatives play an important role in many metabolic processes, excessive ingestion of them can lead to serious complications of various diseases. In this work, a novel dual ratiometric NIR fluorescent probe XT-CHO based on ICT effect was synthesized for detecting SO2 derivative. In the design of the probe, the α, β-unsaturated bond formed between benzopyran and coumarin was used as the reaction site for SO2, meanwhile, the extended π-conjugate system promoted maximum emission wavelength of the probe up to 708 nm. Notably, the probe exhibited high selectivity and sensitivity for detecting SO2, the limit of detection reached 2.13 nM and 58.5 nM in fluorescence spectra and UV–Vis absorption spectra, respectively. The reaction mechanism of SO2 and XT-CHO had been verified by 1H NMR, ESI-MS spectra and DFT calculation. Moreover, the probe was successfully applied in detecting endogenous and exogenous SO2 in living cells and proved possessed the mitochondrial targeted ability.

Facet‐Junction Induced Strong Metal Support Interaction for Enhanced Alkaline Hydrogen Evolution Reaction

AbstractStrong metal‐support interaction (SMSI) plays a critical role in enhancing the catalytic performance of electrocatalysts. Currently, effective approaches to enhance the SMSI effect in supported electrocatalysts still need to be developed, and a comprehensive atomic‐level understanding of the underlying reaction mechanisms remains unclear. In this study, a novel facet‐junction strategy is proposed to enhance the SMSI between the loaded Ru atoms and the Co3O4 support. By modulating the ratio of exposed facet for (111)/(100) crystal plane in Co3O4, the hydrogen evolution reaction (HER) performance can be dramatically enhanced by 560% and can achieve a Pt‐like HER activity with the overpotential of 45 mV. Detailed analysis with atomic‐resolution integrated differential phase contrast (iDPC)‐scanning transmission electron microscopy (STEM), atomic‐resolution high angle annular dark field (HADDF)‐STEM, and electron energy loss spectroscopy (EELS) further proved that with proper (111)/(100) crystal plane ratio, the intensified charge distribution near the facet‐junction region would modify the electronic structure around the active sites. This work provides new insights to enhance the SMSI and will contribute to the rational design of highly efficient electrocatalysts for water splitting.

Interpenetrating network based on soybean protein isolate and carboxymethyl chitosan: Investigation of intermolecular reaction mechanism, physicochemical stability and in vitro release properties of the hydrogel

In this study, interpenetrating network (IPN) hydrogels were constructed from soybean protein isolate (SPI) and carboxymethyl chitosan (CMCS) using TGase and genipin (GP) as cross-linking agents. And the influence of IPN formation on the physicochemical properties of hydrogels was illuminated. Multispectral analyses showed that there was a strong interaction between SPI and CMCS, which also promoted the increase of disulfide bonds and hydrophobic interactions in the hydrogels. The IPN was the densest when the addtion of SPI and CMCS were 10% and 3%, respectively. Meanwhile, this structure endowed the hydrogels with good mechanical properties and allowed them to exhibit thixotropy in rheological tests. The LF-NMR results showed that the IPN had a strong binding ability with water molecules and could effectively maintain the water in the hydrogel after freeze-thaw. Moreover, SPI-CMCS IPN hydrogels were pH responsive. This enabled it to adjust its own structure when pH changed, and to achieve controlled release of bioactives during simulated in vitro digestion. Overall, the results of this study showed that the IPN network formed by SPI and CMCS can effectively improve the performance of hydrogel. These results demonstrated the potential of SPI and CMCS as hydrogel synthesizers and provided a theoretical basis for the application of SPI-CMCS IPN hydrogel.

Active site remodeling in tumor-relevant IDH1 mutants drives distinct kinetic features and potential resistance mechanisms

Mutations in human isocitrate dehydrogenase 1 (IDH1) drive tumor formation in a variety of cancers by replacing its conventional activity with a neomorphic activity that generates an oncometabolite. Little is understood of the mechanistic differences among tumor-driving IDH1 mutants. We previously reported that the R132Q mutant unusually preserves conventional activity while catalyzing robust oncometabolite production, allowing an opportunity to compare these reaction mechanisms within a single active site. Here, we employ static and dynamic structural methods and observe that, compared to R132H, the R132Q active site adopts a conformation primed for catalysis with optimized substrate binding and hydride transfer to drive improved conventional and neomorphic activity over R132H. This active site remodeling reveals a possible mechanism of resistance to selective mutant IDH1 therapeutic inhibitors. This work enhances our understanding of fundamental IDH1 mechanisms while pinpointing regions for improving inhibitor selectivity.

Theoretical insights into the formation of oxygen activation sites with the affection of protein microenvironment in Flavin-Dependent monooxygenases MsuD

Flavin-dependent monooxygenases are very famous for their capability to catalyze the oxidation of various substrates using oxygen and reduced flavin mononucleotide (FMNH-) or reduced flavin adenine dinucleotide (FADH-). When investigating the catalytic mechanism of flavin-dependent monooxygenase systems, a fundamental problem remains unsolved is that the O2 binding scheme within the reaction cavity is unclear. By applying molecular dynamics simulations, MDpocket simulations, residue mutation molecular dynamics simulation and energy decomposition analyses, this work identified the O2 binding pockets and discovered a possible oxygen migration channel within MsuD enzyme. Molecular dynamics simulations after residue mutation proved that residues Asn104 plays an important role in maintaining the O2 position within the reaction cavity. By analyzing the interaction between O2 and the surrounding protein microenvironment, we demonstrated that N5 is a more favored reaction site and speculated a reasonable O2 activation process. This work recovers the formation of oxygen activation sites in MsuD enzyme, which is of great significance to further investigations of the catalytic reaction mechanism. This work provides a feasible method to study the O2 binding in proteins and the role of the protein microenvironment around the reaction cavity.

Progress and Opportunities in Photocatalytic, Electrocatalytic, and Photoelectrocatalytic Production of Hydrogen Peroxide Coupled with Biomass Valorization.

Hydrogen peroxide (H2O2) has been considered an energy carrier (fuel) and oxidizer for various chemical synthesis and environmental remediation processes. Biomass valorization can generate high-value-added products in a green and pollution-free way to solve the energy and environmental crisis. The biomass valorization coupled with H2O2 generation via photo-, electro-, and photoelectrocatalysis plays a positive role in sustainable targets, which can maximize energy utilization and realize the production of value-added products and fuel synthesis. Recently, catalyst design and mechanism studies in H2O2 generation coupled with biomass valorization are in the infancy stage. Herein, this review begins with a background on photo-, electro-, and photoelectrocatalytic techniques for H2O2 generation, biomass valorization, and the H2O2 generation couples with biomass valorization. Meanwhile, the progress and reaction mechanism are reviewed. Finally, the prospects and challenges of a synergistic coupled system of H2O2 synthesis and value-added biomass in achieving high conversion, selectivity, and reaction efficiency are envisioned.

Cross-dimensional multi-physics model and two-phase mass-transport enhancement for the hydrogen peroxide-based fuel cell

The direct liquid fuel cell utilizing hydrogen peroxide as an oxidant is considered to be the promising energy conversion technology, owing to its superior energy density and theoretical voltage. In the hydrogen peroxide-based fuel cells, the ever-changing two-phase mass transport and multi-component reaction processes resulting from the hydrogen peroxide self-decomposition exerts a pivotal influence on their performance. In this work, taken hydrogen peroxide self-decomposition into account, a cross-dimensional multi-physics model for the hydrogen peroxide-based fuel cell was proposed and developed to clarify the complex mechanisms of transports and reactions. In this ingeniously developed model, the multi-component reaction in the porous electrode is elucidated by a two-dimensional (2D) sub-model, the two-phase mass transport in the flow field is captured by a three-dimensional (3D) sub-model, and the one-dimensional (1D) correlation equation is served as a bridge between them. The uneven distribution of gas–liquid volume, velocity and current density and their relationships in fuel cell with serpentine flow field and dot matrix flow field were thus achieved. Furthermore, a novel gradient dot matrix flow field was developed to match the two-phase mass transport and multi-component reaction processes of hydrogen peroxide-based fuel cell. It is found that the continuously increasing pressure and velocity along flow path is balanced by the gradient-downsized ribs and the formation of large-volume oxygen bubbles is prevented by the gradient-densified ribs, achieving obviously uniformized current density distribution. Moreover, the gradient dot matrix flow field enables 54 % higher average hydrogen peroxide coverage contents (49 %) and 86 % lower average pressure drop (172 Pa) compared to the serpentine flow field, yielding 6.3 % higher peak power density (210 mW cm−2) and ultra-low extra pump power in fuel cell. This work will make contribution towards gaining profound insights into the intricate mechanisms underlying mass and charge transport, and offering invaluable guidance for the flow field design for the hydrogen peroxide-based fuel cells.

Interfacial Reactions between Sn-Based Solders and n-Type Bi2(Te,Se)3 Thermoelectric Material.

This study investigated the interfacial reactions between n-type Bi2(Te,Se)3 thermoelectric material, characterized by a highly-oriented (110) plane, and pure Sn and Sn-3.0Ag-0.5Cu (wt.%) solders, respectively. At 250 °C, the liquid-state Sn/Bi2(Te,Se)3 reactions resulted in the formation of both SnTe and BiTe phases, with Bi-rich particles dispersed within the SnTe phase. The growth of the SnTe phase exhibited diffusion-controlled parabolic behavior over time. In contrast, the growth rate was considerably slower compared to that observed with p-type (Bi,Sb)2Te3. Solid-state Sn/Bi2(Te,Se)3 reactions conducted between 160 °C and 200 °C exhibited similar interfacial microstructures. The SnTe phase remained the primary reaction product, embedded with tiny Bi-rich particles, revealing a diffusion-controlled growth. However, the BiTe layer had no significant growth. Further investigation into growth kinetics of intermetallic compounds and microstructural evolution was conducted to elucidate the reaction mechanism. The slower growth rates in Bi2(Te,Se)3, compared to the reactions with (Bi,Sb)2Te3, could be attributed to the strong suppression effect of Se on SnTe growth. Additionally, the interfacial reactions of Bi2(Te,Se)3 with Sn-3.0Ag-0.5Cu were also examined, showing similar growth behavior to those observed with Sn solder. Notably, compared with Ag, Cu tends to diffuse towards the interfacial reaction phases, resulting in a high Cu solubility within the SnTe phase.