Rate-limiting Step Of Reaction Research Articles

Electrochemical performance of Sn-doped Bi0.5Sr0.5FeO3- perovskite as cathode electrocatalyst for solid oxide fuel cells

Abstract The Sn-doped Bi0.5Sr0.5FeO3-δ (BSF)-based perovskite oxide is evaluated as novel cathode electrocatalyst for intermediate-temperature solid oxide fuel cells (IT-SOFCs). In particular, the effects of 10 mol% Sn substitution on phase evolution, thermal expansion behavior and electrochemical performance of Bi0.5Sr0.5Fe0.9Sn0.1O3-δ (BSFSn) material are systematically investigated. BSFSn crystallizes in cubic perovskite structure with space group Pm-3m. Sn doping is found to decrease the average thermal expansion coefficient (TEC) from 14.7 × 10−6 K−1 (BSF) to 12.9 × 10−6 K−1 (BSFSn) within a temperature range of 50–800 °C, due to the enlarged metal-oxygen (Sn-O) bond energy in BSFSn. The X-ray photoelectron spectroscopy (XPS) result proves that Sn doping promotes the oxygen adsorption ability on BSFSn surface. Consequently, the ORR activity of BSFSn is improved as expected. The polarization resistance (Rp) value of BSFSn cathode is 0.09 Ω cm2 at 700 °C in air, which is lower than BSF. The cathode overpotential is 35.6 mV at a current density of 140.8 mA cm−2 at 700 °C in air. The peak power density of the anode-supported cell reaches 960 mW cm−2 at 700 °C. Furthermore, the relationship between oxygen partial pressure and Rp demonstrates that oxygen surface adsorption-desorption is a major rate-limiting step for oxygen reduction reaction (ORR) process on BSFSn cathode. These attractive electrochemical properties suggest that BSFSn oxide is a promising potential cathode electrocatalyst for SOFCs.

Mechanism of CO oxidation by oxygen in the presence of palladium(ii) bromide complexes: a quantum chemical modeling

Mechanisms of CO oxidation by oxygen in the PdBr2-LiBr-MeCN-H2O system in the absence and in the presence of iron(ii) phthalocyaninate (PcFe) as co-catalyst were studied within the framework of the density functional theory with the PBE functional. According to calculations, palladium(ii) bromide complexes most likely occur as Pd(AN)(CO)Br2 (AN is acetonitrile), Pd(CO)2Br2, and [Pd(CO)Br3]−. From the results of calculations it follows that neutral complexes Pd(AN)(CO)Br2 and Pd(CO)2Br2 can be highly catalytically active in the CO oxidation. Insertion of O2 into the Pd-H bond in the hydride complexes is the rate-limiting step of the CO oxidation reaction proceeding in the absence of PcFe as co-catalyst. Iron(ii) phthalocyaninate present in the reaction system causes a noticeable decrease in the activation energy of regeneration of the PdII complexes due to more efficient activation of O2. The oxidation of palladium hydride complexes by iron superoxophthalocyaninate can follow two routes that differ in the fashion of hydride transfer.

Kohn-Sham Density Functional Calculations Reveal Proton Wires in the Enolization and Carboxylase Reactions Catalyzed by Rubisco.

Ribulose 1,5-bisphosphate (RuBP) carboxylase-oxygenase (Rubisco) plays a fundamental role in the carbon cycle by fixing the atmospheric CO2 used in photosynthesis. Rubisco is all the more remarkable because it must catalyze some difficult multistep reaction chemistry involving proton transfers within the one active site. In the present study, we have used Kohn-Sham density functional theory at the B3LYP/6-31G* level with basis set superposition error and dispersion corrections (B3LYP-gCP-D3) to examine the possibility that the proton transfers can take place through molecular wires (including active-site water molecules) via the classical Grotthuss proton-shuttle mechanism. The results support an essential role for water molecules found in the crystal structures of Rubisco complexes as facilitators of proton transport in all the rate-limiting (catalytic) reaction steps through a network of short proton wires within the Rubisco active site. We suggest that completion of the initial product turnover (cycle) requires two excess protons produced in the initial carbamylation that is required for Rubisco activation. By use of proton wires, a large number of reaction steps may be accommodated within a single active site without necessitating the input of excessive conformational strain energy arising from the movement of residue side chains into positions where direct protonation of substrates can occur. The involvement of the identified types of proton wires in the kinetic mechanism is capable of providing a unique explanation for various experimental observations, including deuterium isotope effects and the results of site-directed mutagenesis experiments, and may thus provide a realistic solution to the problem of Rubisco's challenging chemistry.

Anomerisation of Fluorinated Sugars by Mutarotase Studied Using 19F NMR Two-Dimensional Exchange Spectroscopy

Five 19F-substituted glucose analogues were used to probe the activity and mechanism of the enzyme mutarotase by using magnetisation-exchange NMR spectroscopy. The sugars (2-fluoro-2-deoxy-d-glucose, FDG2; 3-fluoro-3-deoxy-d-glucose, FDG3; 4-fluoro-4-deoxy-d-glucose, FDG4; 2,3-difluoro-2,3-dideoxy-d-glucose, FDG23; and 2,2,3,3-tetrafluoro-2,3-dideoxy-d-glucose (2,3-dideoxy-2,2,3,3-tetrafluoro-d-erythro-hexopyranose), FDG2233) showed separate 19F NMR spectroscopic resonances from their respective α- and β-anomers, thus allowing two-dimensional exchange spectroscopy measurements of the anomeric interconversion at equilibrium, on the time scale of a few seconds. Mutarotase catalysed the rapid exchange between the anomers of FDG4, but not the other four sugars. This finding, combined with previous work identifying the mechanism of the anomerisation by mutarotase, suggests that the rotation around the C1–C2 bond of the pyranose ring is the rate-limiting reaction step. In addition to d-glucose itself, it was shown that all other fluorinated sugars inhibited the FDG4 anomerisation, with the tetrafluorinated FDG2233 being the most potent inhibitor. Inhibition of mutarotase by F-sugars paves the way for the development of novel fluorinated compounds that are able to affect the activity of this enzyme invitro and invivo.

Probing the efficiency of platinum nanotubes for the H2 production by water gas shift reaction: A DFT study

The water gas shift (WGS) reaction is an important step in many industrial processes and has thus stimulated various investigations focusing on optimising its catalysts. Previous studies comparing the reactivity of pure and doped-metallic nanotubes towards the catalysis of water dissociation, the key rate-limiting step for the WGS reaction on copper surfaces, suggest that platinum nanotubes stand up as being probably the most active catalysts for the water gas shift reaction. Therefore, we present here a detailed analysis of the performance of platinum nanotubes in the catalysis of the WGS reaction, by employing the Pt(5,3) nanotube as catalyst model and periodic density functional theory calculations. To do so, several reaction pathways were considered on the faces of the Pt(5,3) nanotube and then, energetic balances for the elementary steps on each pathway were determined. This allowed us to conclude that the most feasible reaction route for the WGS reaction on this nanotube follows an associative mechanism through the carboxyl intermediary. The results of this study revealed also that the Pt(5,3) nanotube is an adequate system for the catalysis of the WGS reaction, apart from avoiding the sintering problem intrinsic to catalysts based on nanoparticles dispersed on a support.

Toward Atomistic Modeling of Irreversible Covalent Inhibitor Binding Kinetics.

Covalent inhibitors have emerged as an important drug class in recent years, largely due to their many unique advantages as compared to noncovalent inhibitors, including longer duration of action, lower prolonged systemic exposure, higher potency, and selectivity. However, the potential off-target toxicity of covalent inhibitors, particularly of irreversible covalent inhibitors, represents a great challenge in covalent drug development. Therefore, accurate calculation of protein covalent inhibitor reaction kinetics to guide the design of selective inhibitors would greatly benefit covalent drug discovery efforts. In the present paper, we present a computational method to calculate the relative reaction kinetics between congeneric irreversible covalent inhibitors and their protein receptors. The method combines density functional theory calculations of the transition state barrier height of the rate-limiting step for reaction between the warhead of the inhibitor and a single protein residue, and molecular-mechanics-based free energy calculations to account for the interactions between the ligand in the transition state and the protein environment. The method was tested on four pharmaceutically interesting irreversible covalent binding systems involving 28 ligands; the mean unsigned error (MUE) of the relative reaction rate for all pairs of ligands between the predictions and experimental results for these tested systems is 0.79 log unit. This is to our knowledge the first time where the reaction kinetics of protein irreversible covalent inhibition have been directly calculated with physics-based free energy calculation methods and transition state theory. We anticipate the outstanding accuracy demonstrated here across a broad range of target classes will have a strong impact on the design of selective covalent inhibitors.

Mechanism of rhodium catalyzed desymmetrization by hydroacylation: a DFT study

<p indent="0mm">Density functional theory (DFT) calculations were employed to investigate the mechanism and the chemoselectivity of Rh(I)-catalyzed desymmetrization of prochiral by hydroacylation. Detailed calculations show that the hydroacylation reaction occurs through C–H bond activation, allyl migratory insertion, β-H elimination, another allyl migratory insertion into Rh–H bond and reductive elimination. Theoretical calculations indicated that the rate-limiting step of the hydroacylation reaction is the final reductive elimination, while the enantioselectivity of this reaction is determined by the first allyl migratory insertion step. The mechanism of the carboacylation, which is the side reaction for the hydroacylation reaction, was also calculated. The theoretical investigations indicated that the hydroacylation is more favorable than carboacylation, which is agreement with the experimental results. The NCI analysis was introduced to study the chemoselectivity of this hydroacylation reaction. The calculated results suggested that the large steric repulsion between (<italic>R</italic>)-DTBM-MeOBIPHEP ligand and substrate make the carboacylation difficult to occur, while the carboacylation becomes favorable with BzDPPB as ligand. It can be concluded that the chemoselectivity of this desymmetrization and hydroacylation reaction is controlled by the steric repulsion between the ligand and the substrate.

Red Light Triggered Fluorogenic Reaction with Picomolar Sensitivity Toward Nucleic Acids.

We have previously reported on a red light triggered, singlet oxygen-mediated fluorogenic reaction that is templated in a highly sequence specific fashion by nucleic acids (S. Dutta, A. Fulop, A. Mokhir, Bioconjgate Chem. 2013, 24 (9), 1533-1542). Up to the present date, it has remained a single templated reaction responsive to nontoxic >650 nm light. However, it is operative only in the presence of relatively high (>2 nM) concentrations of templates that dramatically limit its applicability in nucleic acid detection. In the current work, we established that an inefficient intermolecular electron transfer involved in reduction of the 1,4-endoperoxide intermediate, formed in the rate-limiting reaction step, is responsible for inhibition of the reaction at low reagent concentrations. We suggested the solution of the problem which includes a combination of a cleavable (9-alkoxyanthracene) moiety with a two-electron donating fragment in one molecule. This approach enables the efficient intramolecular electron transfer to the endoperoxide intermediate in the critical reaction step. Due to the intramolecular character of the latter process, it is practically independent of concentration of the reagents. The reaction based on the improved cleavable moiety was found to be >200-fold more sensitive than the previously reported one. It is fast, sequence specific, and compatible with live cells. Accounting for short reactions times (<30 min), nontoxic trigger (red light), excellent sensitivity, and sequence specificity, this is presently the best reported photochemical templated reaction compatible with live cells.

Evaluation of the Cr(VI) Adsorption Performance of Xanthate Polysaccharides Supported onto Agave Fiber-LDPE Foamed Composites

In this work, hexavalent chromium adsorption onto LDPE and agave fiber composites coated with chitosan or cellulose was studied in batch experiments. Chemical modifications consisting in cross-linked chitosan, cross-linked chitosan xanthate, and cellulose xanthate were applied to the polysaccharide-coated sorbents in order to increase their stability and adsorption capacity. The sorbents were characterized in terms of morphology by scanning electron microscopy and their chemical composition was evaluated by infrared and nuclear magnetic resonance spectroscopies. The results showed that the adsorption kinetics followed the pseudo-second-order model in all cases (i.e., chemisorption as the rate-limiting step of the adsorption reaction). Moreover, the isotherms evidenced a monolayer adsorption on homogeneous sites described by the Langmuir model. The maximum adsorption capacity of 284.7 mg Cr(VI)/g was obtained for the cross-linked chitosan xanthate sorbent at pH 4 which represents an increase of 43% against the chitosan-coated sorbent (199.1 mg Cr(VI)/g). Besides, functionalized cellulose sorbent also increased its capacity from 84.5 to 106.0 mg Cr(VI)/g cellulose due to the xanthate group. Up to six adsorption-desorption cycles were completed for the case of functionalized chitosan sorbent, confirming that the stability was increased with the cross-linking and the material could be reused several times without losing its adsorption capacity. In the case of cellulose xanthate, only three adsorption cycles were completed. However, improvements were observed in the desorption capacity considering that it decreased below 20% after two cycles in the cellulose-coated sorbent.

Understanding the conversion of ethanol to propene on In2O3 from first principles

Abstract It is highly desirable to convert bioethanol to value-added chemicals. As such, conversion of ethanol to propene (ETP) is attractive because propene is an important raw material for the production of plastics. In2O3 has shown promising catalytic performance for ETP conversion. However, the underlying mechanisms remain elusive. In this work, we use density functional theory (DFT) to investigate ETP reaction pathways on the In2O3 (110) surface. We find that the ETP reactions proceed through three major stages: ethanol to acetaldehyde, acetaldehyde to acetone, and acetone to propene. The ethanol-to-acetaldehyde step is kinetically facile. Comparing the two pathways from acetaldehyde to acetone, we show that the aldol reaction pathway via direct coupling of two acetaldehyde is more favorable than the acetate-ketonization pathway. The acetone-to-propene process is found to be the rate-limiting step of the overall reaction. This work provides a detailed mechanistic view of the ETP chemistry on In2O3(110) that paves the way for further exploration of effects such as surface termination, surface doping, and co-feeding of H2 and H2O on selectivity and catalyst stability.

Elemental behaviors of InGaAs surface after treatment in aqueous solutions

Indium gallium arsenide (InGaAs) is one of the candidates as a channel material for the high-performance complementary metal-oxide-semiconductor (CMOS) devices superior to silicon-based CMOS devices because of its higher electron mobility. In order to introduce InGaAs as a new channel material for high-performance CMOS devices, it is important to prepare its surface to suppress material loss and surface oxide formation in the InGaAs layer. In this study, the behavior of each element of the In0.53Ga0.47As surface in chemical solutions such as HCl, NH4OH, HPM (HCl/H2O2/H2O) and APM (NH4OH/H2O2/H2O) was investigated from the viewpoint of thermodynamics and reaction kinetics. In the acidic HCl solution, the dissolution of the InGaAs surface was the dominant reaction, whereas a sub-oxide formed on the InGaAs surface in the basic NH4OH solution. The formation of the oxide on the surface was considered the rate-limiting step of the overall etching reaction of InGaAs in the acidic solution; therefore, the surface oxidation and overall etching (dissolution) of the InGaAs layer were determined using different amounts of H2O2 in the solution. In particular, the overall etching of the InGaAs surface in the HPM solution was more aggressive than that in the APM solution. The behavior of InGaAs in the surface preparation process sequences with APM, HPM, and HF was also investigated, and it was observed that the material loss and surface roughening of the InGaAs layer were mostly determined in the HPM process. Finally, it was possible to suppress the surface oxidation, material loss, and surface roughening of the InGaAs layer by reducing the concentration of H2O2 in the HPM solution.

Boosting Water Dissociation Kinetics on Pt-Ni Nanowires by N-Induced Orbital Tuning.

Although it is commonly believed that the water-dissociation-related Volmer process is the rate-limiting step for alkaline hydrogen evolution reaction (HER) on Pt-based catalysts, the underlying essence, particularly on the atomic scale, still remains unclear. Herein, it is revealed that the sluggish water-dissociation behavior probably stems from unfavorable orbital orientation and the kinetic issue is successfully resolved via N-induced orbital tuning. Impressively, N modified Pt-Ni nanowires deliver an ultralow overpotential of 13 mV at 10 mA cm-2 , which represents a new benchmark for alkaline HER catalysis. Fine-structural characterization and density functional theory analysis illustrate that the introduced nitrogen can uniquely modulate the electron densities around the Ni sites, and further create empty dz 2 orbitals with superior orientation for water adsorption and activation. More importantly, it is demonstrated that N-induced orbital modulation can generally boost the alkaline HER activities of Pt-Co, Pt-Ni, and Pt-Cu, offering a new perspective for the design of HER catalysts and beyond.

Amorphous silica-alumina composite with regulated acidity for efficient production of hydrogen via steam reforming of dimethyl ether

Abstract In this work, we demonstrate that the amorphous silica-alumina composite (ASA) is an efficient solid acid for the steam reforming of dimethyl ether (SRD). Thus, a series of ASA with different Si/Al molar ratios was synthesized via the modified hydrolytic method by using Al(NO3)3·9H2O and/or NaAlO2 as Al precursor and tetraethoxysilane as Si precursor, respectively. Irrespective of the synthesis conditions, all of ASA composites were in an amorphous nature. However, both the acidity and the surface area were significantly affected by the synthesis conditions, the extent of which depends on the specific precursor and Si/Al molar ratios. The ASA physically mixed with a commercial Cu/ZnO/Al2O3 was investigated as a bifunctional catalyst for SRD under the conditions of P=0.1 MPa and gas hourly space velocity of 4000 h−1. Results indicate that both the conversion of dimethyl ether (DME) and the hydrogen yield were strongly dependent on the acidic property of ASA and the ASA to Cu/ZnO/Al2O3 ratios. Following the two-step consecutive mechanism of SRD, the catalytic results were well explained based on the acidic property of ASA, and the synergetic effect between the two catalytic functions was found to play a crucial role in determining the activity and stability of the bifunctional catalyst. Moreover, the DME hydrolysis was revealed to be the rate-limiting step for SRD reactions in the case of ASA as an acidic catalyst. By optimizing the synthesis conditions of ASA and the composition of the bifunctional catalyst, greater than 99% of DME conversion and hydrogen yield was achieved, and was kept for a time on stream of 66 h without an observable decrease. Thus, ASA is a very efficient solid acid for SRD.

Electrochemical performance and effect of moisture on Ba0.5Sr0.5Sc0.175Nb0.025Co0.8O3-δ oxide as a promising electrode for proton-conducting solid oxide fuel cells

Proton conducting solid oxide fuel cells are solid state electrochemical devices for power generation at a conversion efficiency (>60%) higher than conventional thermal power plants (∼40%). The cathode is the key component of proton conducting solid oxide fuel cells as it contributes to more than 50% of the total overpotential loss of an H+-SOFC with thin film electrolyte. This work aims to develop high performance and durable cathode for proton conducting solid oxide fuel cells by doping Ba2+ into the Sr-site of the SrSc0.175Nb0.025Co0.8O3-δ perovskite oxide. The influence of moisture on the catalytic activity of Ba0.5Sr0.5Sc0.175Nb0.025Co0.8O3-δ cathode was investigated using electrochemical impedance spectroscopy of symmetric cell at 600 °C. The resistance in the low-frequency range was found to be the rate-limiting step of the oxygen reduction reaction in the dry air, while the resistance in the medium-frequency range became the rate-limiting step in the moist air. With a Ba0.5Sr0.5Sc0.175Nb0.025Co0.8O3-δ cathode, a proton conducting single cell achieved good performance at a temperature of 700 °C with a power density of 633 mW cm−2. However, the performance of single cell decreased with time, probably due to the agglomeration of cathode particles and the coverage of produced water on the active surface. To improve the durability of the proton conducting solid oxide fuel cell, it is critical to minimize the cathode particle agglomeration and remove the produced water effectively. The research results contribute to the development of high-performance fuel cell for efficient energy conversion.

Direct Benzyl Alcohol and Benzaldehyde Synthesis from Toluene over Keggin-Type Polyoxometalates Catalysts: Kinetic and Mechanistic Studies

The catalytic activity of various Keggin polyoxometalate catalysts has been investigated in the gas-phase partial oxidation of toluene to produce benzyl alcohol and benzaldehyde. The catalyst systems HPMo12O40, HPMo11VO40, FePMo12O40, and PMo11FeO39were prepared and characterized by FT-IR, UV-visible, SEM, XRD, TGA, and cyclic voltammetry. The acid/base properties were evaluated using the decomposition of isopropanol. Catalytic studies were carried under atmospheric pressure and over the temperature range 200°C–350°C, using carbon dioxide as a mild oxidant. Toluene conversion and product distribution depend mainly on the catalyst composition and operating conditions. In addition to benzaldehyde, benzyl alcohol is obtained with a high selectivity on the PMo11FeO39catalyst. The kinetic data show that the reoxidation of the reduced catalyst is the rate-limiting step for the partial oxidation reaction of toluene.

Bicarbonate Inhibition of Carbonic Anhydrase Mimics Hinders Catalytic Efficiency: Elucidating the Mechanism and Gaining Insight toward Improving Speed and Efficiency

Carbonic anhydrase (CA) mimics are often studied with a focus on the hydration of CO2 for atmospheric carbon capture. Consequently, the reverse reaction (dehydration of HCO3–) has received minimal attention, so much so that the rate-limiting step of the dehydration reaction in CA mimics is currently unknown. The rate-limiting step of the hydration reaction is reported to be the bicarbonate-bound intermediate step, and thus is susceptible to product inhibition. It is not, however, clear if this inhibition is a consequence of an increase in the rate of the competing dehydration reaction or resulting from the strong affinity of bicarbonate to the mimic. To address this, insight into the dehydration reaction kinetics is needed. We therefore report the most comprehensive study of a CA mimic to date. The dehydration profile of the fastest small-molecule CA mimic, ZnL1S, was characterized, and consequently evidence for the rate-limiting step for the dehydration reaction was seen to be the bicarbonate-bound inter...

Removal of Diclofenac from Aqueous Phase by Birnessite: Effects of pH and Common Ions

In this study, the removal of diclofenac (DCF) from aqueous phase by birnessite, a layered manganese oxide, was investigated by batch experiments. The results indicated that 90% of DCF was removed by birnessite within 4 h in different initial concentrations of DCF, and the kinetic experiment data were well fitted with pseudo-first-order kinetic model (R2 > 0.98). The removal of DCF by birnessite was pH-dependent, and low pH was beneficial to the reaction. The presence of Fe2+ and Mn2+ strongly inhibited the removal of DCF. However, Ca2+, Mg2+, Zn2+, Cu2+, and humic acid (HA) promoted the reaction and following the order: Cu2+ > Zn2+ > HA > Mg2+ ≈ Ca2+. In addition, some typical anions, such as NO3−, PO43−, and SO42−, had slight effects on the reaction. Electrochemical results demonstrated that the adsorption of DCF on birnessite was reaction rate-limiting step.

Effect of Surface-Specific Treatment by Infiltration into LaNi6Fe4O3- δ Cathodic Backbone for Solid Oxide Fuel Cells

In this study, the impact of various infiltrates on the kinetics and rate-limiting step of oxygen reduction reaction (ORR) is examined with LaNi0.6Fe0.4O3- δ (LNF) as the cathode backbone of a solid oxide fuel cells (SOFC). Five materials were infiltrated: LaNi1-xFexO3- δ, LaxSr1-xCoyFe1-yO3-δ (LSCF), La1-xSrxMnO3-δ (LSM), Gd1-xCexO2-δ (GDC) and Pr6O11. The dependence of electrode polarization resistance on the precursor concentration, temperature, oxygen partial pressure is presented with related discussions on ORR kinetics and rate-determining step for ORR. A one-step infiltration of all five materials resulted in a dramatic decrease in polarization resistance (Rp) and related activation energy (Ea), which is ascribed to a significant facilitation of surface processes such as dissociative adsorption with electron transfer and diffusion of oxygen intermediates. Finally, a short-term durability test in a Cr-containing environment indicated that the LSCF-infiltrated cell is susceptible to Cr poisoning unlike the GDC- or LNF-infiltrated cells as expected but advantageous in terms of morphological stability during operation.

A experimental study on the dehydrogenation performance of dodecahydro-N-ethylcarbazole on M/TiO2 catalysts

Liquid organic hydrogen carrier (LOHC) is considered as a promising candidate for large-scale hydrogen storage. In this work, we found that Pt/TiO2 catalysts exhibited better catalytic activity and selectivity compared to Pd/TiO2 and commercial Pd/Al2O3 catalysts in the dehydrogenation of dodecahydro-N-ethylcarbazole (12H-NECZ) at 453 K. The catalytic activity of the noble metal catalysts followed the trend of Pt/TiO2 > Pd/TiO2 > Rh/TiO2 > Au/TiO2 > Ru/TiO2. Compared with the commercial Pd/Al2O3, Pt/TiO2 greatly improved the selectivity and conversion rate, the reaction time was also shortened. In addition, kinetics calculation was carried out to obtain fundamental reaction parameters. It was found that the third step of 4H-NECZ dehydrogenation to NECZ was the rate-limiting step of the entire dehydrogenation reaction for all catalysts.

Enhanced oxygen reduction reaction through Ca and Co Co-doped YFeO3 as cathode for protonic ceramic fuel cells

Protonic ceramic fuel cells offer the potential for environmentally sustainable and cost-effective electric power generation. However, the power outputs of protonic ceramic fuel cells are far from the requirements due to the lack of active cathodes. In this work, porous thin sheets CaxY1-xFe0.5Co0.5O3-δ (x = 0.1, 0.3 and 0.5) are synthesized by a modified pechini method and investigated as cathode materials for protonic ceramic fuel cells. CaxY1-xFe0.5Co0.5O3-δ show high electrical conductivities and excellent chemical compatibility with Ba(Zr0.1Ce0.7Y0.2)O3 electrolyte. The maximum electrical conductivity of Ca0.3Y0.7Fe0.5Co0.5O3-δ reaches 202 S cm−1 in air at 750 °C. The detailed mechanism for oxygen reduction reaction reveals that the rate-limiting step of oxygen reduction reaction is transformed from charge transfer to O2 adsorption-dissociation with temperature rising or Ca doping. The composite cathode Ca0.3Y0.7Fe0.5Co0.5O3-δ-Ba(Zr0.1Ce0.7Y0.2)O3 presents a relatively low polarization resistance of 0.07 Ω cm2 at 750 °C in air. The power density of the anode-supported cell of NiO Ba(Zr0.1Ce0.7Y0.2)O3∣Ba(Zr0.1Ce0.7Y0.2)O3∣Ca0.3Y0.7Fe0.5Co0.5O3-δ-Ba(Zr0.1Ce0.7Y0.2)O3 is 798 mW cm−2 as the electrolyte thickness is about 150 μm. The prepared CaxY1-xFe0.5Co0.5O3-δ oxides are promising candidates as high-performance cathodes for protonic ceramic fuel cells.