Kinetics Of Oxidation Reaction Research Articles

Atomically dispersed chromium coordinated with hydroxyl clusters enabling efficient hydrogen oxidation on ruthenium

Overcoming the sluggish kinetics of alkaline hydrogen oxidation reaction (HOR) is challenging but is of critical importance for practical anion exchange membrane fuel cells. Herein, abundant and efficient interfacial active sites are created on ruthenium (Ru) nanoparticles by anchoring atomically isolated chromium coordinated with hydroxyl clusters (Cr1(OH)x) for accelerated alkaline HOR. This catalyst system delivers 50-fold enhanced HOR activity with excellent durability and CO anti-poisoning ability via switching the active sites from Ru surface to Cr1(OH)x-Ru interface. Fundamentally different from the conventional mechanism merely focusing on surface metal sites, the isolated Cr1(OH)x could provide unique oxygen species for accelerating hydrogen or CO spillover from Ru to Cr1(OH)x. Furthermore, the original oxygen species from Cr1(OH)x are confirmed to participate in hydrogen oxidation and H2O formation. The incorporation of such atomically isolated metal hydroxide clusters in heterostructured catalysts opens up new opportunities for rationally designing advanced electrocatalysts for HOR and other complex electrochemical reactions. This work also highlights the importance of size effect of co-catalysts, which should also be paid substantial attention to in the catalysis field.

Electrochemically embedded nickel oxide in a highly porous manganese oxide film with enhanced catalytic kinetics of the urea oxidation reaction

The use of well-dispersed nickel catalysts with atomic-scale sizes is an effective approach for maximizing catalytic activity and selectivity for the urea oxidation reaction (UOR). Herein, a porous ultrathin film of Birnessite-type manganese oxide is anodically deposited on a nickel substrate as a catalyst support. Some of the intercalated sodium ions are replaced by the dissolved nickel ions from the nickel substrate in the anodic process, forming manganese oxide with partially intercalated nickel ions (denoted MnO2). The amount of nickel species can be easily increased by cyclic voltammetry in the nickel sulfate electrolyte (denoted MnO2-Ni), without the relatively time-consuming process of conventional ion exchange. Most of the embedded nickel species are catalytic Ni3+ ions, rendering MnO2-Ni a favorable catalyst to boost the UOR. The cyclic voltammetry results reveal that Ni3+ catalysts, when inserted into the layer-structured manganese oxide, can increase the electroactive surface area for the adsorption of urea and increase the charge-transfer rate constant for the Ni3+/Ni2+ redox couple, leading to an improved catalytic rate constant of the UOR. A highly porous manganese oxide matrix provides many transport pathways for facilitating UOR kinetics. Electrochemical impedance spectroscopy shows that MnO2-Ni has lower direct and indirect UOR impedances than MnO2 and bare Ni electrodes, leading to a greater oxidation current and lower onset potential.

Design of a Metal/Oxide/Carbon Interface for Highly Active and Selective Electrocatalysis.

Sustainable energy-conversion and chemical-production require catalysts with high activity, durability, and product-selectivity. Metal/oxide hybrid structure has been intensively investigated to achieve promising catalytic performance, especially in neutral or alkaline electrocatalysis where water dissociation is promoted near the oxide surface for (de)protonation of intermediates. Although catalytic promise of the hybrid structure is demonstrated, it is still challenging to precisely modulate metal/oxide interfacial interactions on the nanoscale. Herein, we report an effective strategy to construct rich metal/oxide nano-interfaces on conductive carbon supports in a surfactant-free and self-terminated way. When compared to the physically mixed Pd/CeO2 system, a much higher degree of interface formation was identified with largely improved hydrogen oxidation reaction (HOR) kinetics. The benefits of the rich metal-CeO2 interface were further generalized to Pd alloys for optimized adsorption energy, where the Pd3Ni/CeO2/C catalyst shows superior performance with HOR selectivity against CO poisoning and shows long-term stability. We believe this work highlights the importance of controlling the interfacial junctions of the electrocatalyst in simultaneously achieving enhanced activity, selectivity, and stability.

Thermochemical Properties of High Entropy Oxides Used as Redox-Active Materials in Two-Step Solar Fuel Production Cycles

The main challenges and obstacles to the development of hydrogen/carbon monoxide production from the splitting of water/carbon dioxide through two-step solar thermochemical cycles are strongly related to material concerns. Ineed, ceria is the main benchmark redox material used in such processes because it provides very good oxidation reaction kinetics, reactions reversibility and thermal cycling stability. This is at the expense of a low reduction yield (non-stoichiometry δ in CeO2-δ) at relatively high temperatures (≥1400 °C), which requires operation at low oxygen partial pressures during the reduction step. Hence, the specific fuel output per mass of redox material, i.e., the amount of H2/CO produced per cycle, remains low, thereby limiting the overall solar-to-fuel conversion efficiency. Perovskites offer larger amounts of fuel produced per cycle but the reaction kinetics are slow. This study addresses the thermochemical investigation of a new class of metal oxides, namely high entropy oxides (HEOs), with the aim of improving the specific amount of fuel generated per cycle with good kinetic rates. Different formulations of high entropy oxides were investigated and compared using thermogravimetric analysis to evaluate their redox activity and ability to split CO2 during thermochemical cycles. Among the different formulations tested, five HEOs yielded CO with a maximum specific fuel output of 154 µmol/g per cycle. These materials’ performances exceeded the production yields of ceria under similar conditions but are still far from the production yields reached with lanthanum–manganese perovskites. This new class of materials, however, opens a wide path for research into new formulations of redox-active catalysts comparing favorably with the ceria redox performance for solar thermochemical synthetic fuel production.

Ethanol Electro-Oxidation on Catalysts with S-ZrO2-Decorated Graphene as Support in Fuel Cell Applications.

Direct ethanol fuel cells (DEFCs) are considered the most suitable direct alcohol fuel cell (DAFC) in terms of safety and current density. The obstacle to DEFC commercialization is the low reaction kinetics of ethanol (C2H5OH) oxidation because of the poor performance of the electrocatalyst. In this study, for the first time, graphene nanoplates (GNPs) were coated with sulfated zirconium dioxide (ZrO2) as adequate support for platinum (Pt) catalysts in DEFCs. A Pt/S-ZrO2-GNP electrocatalyst was prepared by a new process, polyol synthesis, using microwave heating. Field emission scanning electron microscope (FESEM) imaging revealed well-dispersed platinum nanoparticles supported on the S-ZrO2-GNP powder. Analysis of the Fourier transform infrared (FTIR) spectrometry confirmed that sulfate modified the surfaces of the sample. In X-ray diffraction (XRD), no effect of S-ZrO2 on the crystallinity net in Pt was found. Pt/S-ZrO2-GNP electrode outperformed those with unsulfated counterparts, primarily for the higher access with electron and proton, confirming sulfonating as a practical approach for increasing the performance, electrocatalytic activity, and carbon monoxide (CO) tolerance in an electrocatalyst. A considerable decrease in the voltage of the CO electrooxidation peak from 0.93 V for Pt/C to 0.76 V for the Pt/S-ZrO2-GNP electrode demonstrates that the new material increases activity for CO electrooxidation. Moreover, the as-prepared Pt/S-ZrO2-GNPs electrocatalyst exhibits high catalytic activity for the EOR in terms of electrochemical surface area with respect to Pt/ZrO2-GNPs and Pt/C (199.1 vs. 95 and 67.2 cm2.mg−1 Pt), which may be attributed to structural changes caused by the high specific surface area of graphene nanoplates catalyst support and sulfonating effect as mentioned above. Moreover, EIS results showed that the Pt/S-ZrO2-GNPs electrocatalyst has a lower charge transfer resistance than Pt/ ZrO2-GNPs and Pt/C in the presence of ethanol demonstrating an increased ethanol oxidation activity and reaction kinetics by Pt/S-ZrO2-GNPs.

Hierarchical core-shell structure of ZIF-8 derived porous carbon supported PdZn nanoalloys within mesoporous silica shells as efficient methanol oxidation electrocatalysts

The anodic precious metal catalyst of direct methanol fuel cell (DMFC) is poisoned due to CO adsorption, which makes the methanol oxidation reaction (MOR) kinetics tardily. In this study, a series of hierarchical core–shell structure catalysts PdZn/ZDC@SiO2 were synthesized by loading PdZn nanoparticles (NPs) on ZIF-8 derived porous carbon (ZDC) and protecting by the mesoporous silica (SiO2) are reported. A hierarchical core–shell structure informed in PdZn/ZDC@SiO2(20) caused by mesoporous silica shell leads to well-dispersed and uniform of PdZn NPs (10 nm). Compared with commercial palladium carbon (Pd/C), the optimized catalyst PdZn/ZDC@SiO2(20) has higher current density (765.2 mA/mg) and stronger CO toxicity tolerance (If/Ib = 3.30). And the onset potential and the peak potential of PdZn/ZDC@SiO2(20) (−0.294 V, −0.203 V) are more negative in CO stripping experiment. Silica is an inorganic oxide that can provide oxygen-containing species to the adjoining precious metal sites and promote CO oxidation. In addition, PdZn NPs can accelerated electron transport and then improve methanol oxidation performance due to the changing electronic structure of Pd and the modifying the surface adsorption of the catalyst. PdZn/ZDC@SiO2(20) is a potential substitute material for noble metal catalyst that can be used for direct methanol fuel cells.

Combustion of the banana Pseudo-stem hydrochar by the High-Pressure CO2-Hydrothermolysis: Thermal conversion, kinetic, and emission analyses

Due to slow degradation and potentially carrying fungus of banana pseudo-stem, the irresponsibly disposed (such as optionally dumping and burning on the spot) of banana pseudo-stem caused severe environmental problems and fungus disease. However, the combustion efficiency of the banana pseudo-stem was limited by the higher moisture and lower heating value. The high-pressure CO2-hydrothermolysis provides an efficient strategy for upgrading the fuel quality and combustion characteristics. In this study, the combustion characteristics and emission analyses of the sample after and before treatment were investigated by TG–FTIR. Meanwhile, the oxidation reaction kinetics of the sample was established using the Friedman method. The results showed that the “coal-like” fuel, higher heating value (HHV) between 13.64 and 25.76 MJ/kg, was produced from banana pseudo-stem by the high-pressure CO2-hydrothermolysis. The ignition temperature of the sample after treatment is higher than that of the banana pseudo-stem. However, the combustion character index of the sample after treatment at 160 °C (BP-160) is the best among all samples, but that of the sample after treatment at 280 °C (BP-280) is the lowest. The sample after treatment has the higher combustion reactivity except for BP-280. The averaged activation energy values of the sample after treatment decrease with the increased temperature and are higher than that of BP, except for BP-280. The carbon emission (CO2 + CO), SO2 and N species emission (NO + N2O) was reduced during sample combustion after treatment. Overall, the high-pressure CO2-hydrothermolysis is a promising treatment technology for minimizing and energy utilization of banana waste.

Synthesis of keto-biomacromolecule derivatives by oxidation of carboxymethyl cellulose using alkaline hexacyanoferrate (III) for alternative applications in biotechnology

The oxidation kinetics of polysaccharides involving carboxymethyl cellulose (CMC) by several oxidizing agent have been investigated in more detail with shedding some light on the synthesis of their respective keto-derivatives as oxidation precursor products. However, the literature survey indicated that no reports have appeared on the oxidation kinetics of CMC or the synthesis of keto-CMC using hexacyanoferrate (III) ion. Therefore, a lack of information on the transfer of electron process in the rate-determining stage as well as the nature of such keto-derivatives obtained as a result of polysaccharides oxidation using various oxidants in aqueous solutions.Accordingly, the present study presents synthesis of diketo CMC as a biomacromolecule derivative using potassium ferricyanide in alkaline media. The experimental results revealed the formation of either monoketo or diketo-derivatives of CMC based on initial molar ratio between the two reactants. The formation of such keto derivatives was confirmed by the reaction of the oxidation products with both 2,4-dinitrophenyl hydrazine and hydroxyl amine as well as FTIR spectra. The reaction kinetics of oxidation showed unity order in [Fe(CN)63−] and fractional first-orders with respect to both [CMC] and [OH−].The obedience of the reaction behavior to the Michael-Menten kinetics was indicative to the formation of 1:1 intermediate complex prior to the rate-determining step as a pathway route for oxidation.

Reaction kinetics of OH radicals with 1,3,5-trimethyl benzene: An experimental and theoretical study

Alkylated aromatics are ubiquitous in transportation fuels. 1,3,5-Trimethyl benzene (135TMB) is a popular surrogate for the aromatic content of distillate fuels due to its symmetry (point group, C3h), which facilitates the construction of an accurate chemical kinetic model. The reaction of OH radicals with 135TMB plays a crucial role in the oxidation kinetics of 135TMB. In this work, the reaction kinetics of OH-initiated oxidation of 135TMB were investigated behind reflected shock waves over 975–1318 K and atmospheric pressure. The reaction was followed by monitoring OH radicals near 307 nm. The rate coefficients were extracted from detailed chemical kinetic modeling of OH concentration-time profiles. Our measured data clearly showed a positive temperature dependence, in contrast to the negative temperature dependence of the literature low-temperature data. At 1000 K, our measured rate coefficient is 1.3 × 10−11 cm3 molecule−1 s−1, which is roughly a factor of 5 lower than the room-temperature data reported in the literature. This observation reflects the complex nature of the OH + 135TMB reaction, similar to that observed for various aromatics + OH chemical systems. Our measurements did not show any discernible pressure dependence over the narrow pressure range of 870 – 1148 Torr. The title reaction has several possible channels in the reactive potential energy surface. The importance of each channel was characterized using ab initio/RRKM-ME calculations over T = 200–2000 K and P = 0.76 -7600 Torr. Our analyses revealed that addition channels and hydrogen abstraction from the methyl site have negative energy barriers. The reaction was found to undergo almost exclusively (∼93%) via the addition channel under ambient conditions. However, beyond 600 K, the abstraction channels take the lead, yielding the positive T-dependence of the overall rate coefficient. Although addition channels display a sharp fall-off behavior beyond 500 K, the general rate coefficients are pressure-independent. The title reaction shows a complex kinetic behavior due to competing channels whose contribution changes significantly with temperature. Our theoretical calculations nicely reproduced the complex T-dependence of the reaction. After adjusting the barrier height, our theory remarkably captured the positive T-dependence of our high-T kinetic data and the negative T-dependence of the low-T literature data. To our knowledge, this is the first detailed study on the reaction kinetics of 135TMB with OH radicals. The reported rate data will be helpful for the combustion modeling of alkylated aromatic species.

Accelerated kinetics of hydrogen oxidation reaction on the Ni anode coupled with BaZr0.9Y0.1O3-δ proton-conducting ceramic electrolyte via tuning the electrolyte surface chemistry

Owing to the promise of proton mobility in solids, proton ceramic fuel cells (PCFCs) have demonstrated their great potential for operating at the low temperature range of 400-600˚C. For speeding up electrode reactions in PCFCs, the kinetics of the hydrogen oxidation reaction (HOR) on the Ni anode coupled with BaZr0.9Y0.1O3-δ (BZY10) proton-conducting ceramic electrolyte (abbreviated as Ni/BZY10) was investigated in correlation to the electrolyte surface chemistry. It was found that thermal annealing treatments are an effective approach to tune the surface chemistry of BZY10 (ABO3 perovskite structure) electrolytes, resulting in progressively Ba segregation toward the outer surface and enriched Y cations in B-site at subsurface. As the post-annealing temperature of BZY10 electrolytes increase from 600˚C to 1500˚C, the polarization resistance for the corresponding BZY10-based half cells decreases by a factor of 3 and 6 at the testing condition of open circuit potential and anodic overpotential, respectively. Considering a core-space-charge layer model at the Ni/BZY10 interface, the segregation of net charged Y cations (YZr') at the subsurface can partially counterbalance the positive electric potential induced by accumulation of protons in the outer surface, led to a reduced electrical potential and thus the accelerated HOR kinetics on the Ni/BZY10.

Surface defects engineering of BiFeO3 films for improved photoelectrochemical water oxidation

As a promising material for photoelectrochemical (PEC) water oxidation, the fast recombination rate and sluggish surface reaction for BiFeO3 (BFO) still hinder its practical application. In this work, nitrogen plasma was first used to engineer surface defects of the pulsed laser deposition (PLD)-fabricated BFO films to suppress the surface charge recombination and improve the surface water oxidation activity, as well as enhance the stability. A remarkable photocatalytic activity enhancement was observed after the surface modification. Specifically, the photocurrent density is 95 μA/cm2 at 0.6 V (vs. Ag/AgCl, pH=12.8) for BFO–N (after nitrogen plasma treatment), which is about 8 times higher than as-grown BFO (12 μA/cm2) at the same potential. Meanwhile, the onset potential of BFO–N shifts toward the negative value by 120 mV compared to BFO. Also, the BFO–N reveals superior stability to BFO, which shows nearly no decay after the 1-h test. Complete experimental characterization and deep mechanistic analysis indicate that the enhanced performance could be due to the newly-formed Fe-enriched oxynitride layer on the surface after nitrogen plasma treatment, which suppresses the fast recombination, improves the water oxidation reaction kinetics, and protects the photoanode against photocorrosion. Our work offers a simple, but effective way to improve the PEC performance of BFO, which is instructive for fabricating similar high-performance photoelectrodes for PEC applications.

Improving Alkaline Hydrogen Oxidation Activity of Palladium through Interactions with Transition-Metal Oxides

Anion-exchange membrane fuel cells (AEMFCs) are a promising electrochemical power generation technology that will most likely find applications in stationary power supply and mobile applications such as electric vehicles in the future. One of the main technological challenges with AEMFCs is developing catalysts with improved activities to reduce the current overpotential losses in the cell. A historically underappreciated challenge for AEMFC catalyst development is the sluggish hydrogen oxidation reaction (HOR) kinetics at the anode that still requires high loadings of platinum group metals. Here, we demonstrate that the alkaline HOR activity of palladium nanoparticles is enhanced through strong interactions with transition-metal oxides. A series of transition-metal oxides in the IV oxidation state (ZrO2, CeO2, SnO2, and RuO2) were deposited onto Vulcan XC-72 carbon. Pd nanoparticles (20 wt %) were then grown on each support. This series of catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The alkaline HOR activity was investigated using cyclic voltammetry and linear sweep voltammetry. Of the several systems that were considered, Pd–RuO2/C displayed the highest HOR surface-specific activity (49 μA cmPd–2). It had an onset for CO electro-oxidation at around 200 mV, which is lower than the other materials analyzed herein. The results were explained using first-principles calculations by investigating Tafel and Volmer reactions. These results suggested that increased HOR activity is favored by the population of the Pd surface with OH– groups at lower overpotentials. These insights are valuable for the future design of next-generation catalysts with high activity toward alkaline HOR required by future high-performance AEMFCs.

The Role of Hydroxide Binding Energy in Alkaline Hydrogen Oxidation Reaction Kinetics on RuCr Nanosheet†

Comprehensive SummaryUnveiling the role of adsorbed hydroxide involved in the hydrogen oxidation reaction (HOR) under alkaline electrolyte is crucial for the development of advanced HOR electrocatalysts for the alkaline polymer electrolyte fuel cells (APEFCs). Herein, we report the synthesis of amorphous RuCr nanosheets with different molar ratios and their HOR performances under alkaline media. We find a volcano correlation between the Cr content in RuCr nanosheets and their alkaline HOR performance. Experimental results and density functional theory (DFT) calculation reveals that the optimized Cr content in RuCr nanosheets could lead to the optimum hydroxide binding energy (OHBE), contributes to their remarkable alkaline HOR performance with mass activity of 568.1 A·gPGM–1 at 50 mV, 13‐fold higher than that of Ru catalyst. When RuCr nanosheet is further used as the anodic electrocatalyst, a peak power density of 1.04 W·cm–2 can be achieved in an APEFC.

Prussian Blue Type Cocatalysts for Enhancing the Photocatalytic Water Oxidation Performance of BiVO4.

The efficiency of photocatalytic overall water splitting reactions is usually limited by the high energy barrier and complex multiple electron-transfer processes of the oxygen evolution reaction (OER). Although bismuth vanadate (BiVO4 ) as the photocatalyst has been developed for enhancing the kinetics of the water oxidation reaction, it still suffers from challenges of fast recombination of photogenerated electron-hole pairs and poor photocatalytic activity. Herein, six MII -CoIII Prussian blue analogues (PBAs) (M=Mn, Fe, Co, Ni, Cu and Zn) cocatalysts are synthesized and deposited on the surface of BiVO4 for boosting the surface catalytic efficiency and enhancing photogenerated carries separation efficiency of BiVO4 . Six MII -CoIII PBAs@BiVO4 photocatalysts all demonstrate increased photocatalytic water oxidation performance compared to that of BiVO4 alone. Among them, the Co-Co PBA@BiVO4 photocatalyst is employed as a representative research object and is thoroughly characterized by electrochemistry, electronic microscope as well as multiple spectroscopic analyses. Notably, BiVO4 coupling with Co-Co PBA cocatalyst could capture more photons than that of pure BiVO4 , facilitating the transfer of photogenerated charge carriers between BiVO4 and Co-Co PBA as well as the surface catalytic efficiency of BiVO4 . Overall, this work would promote the synthesis strategy development for exploring new types of composite photocatalysts for water oxidation.

Suppressing Electron Back‐Donation for a Highly CO‐tolerant Fuel Cell Anode Catalyst via Cobalt Modulation

AbstractPlatinum on carbon (Pt/C) catalyst is commercially adopted in fuel cells but it undergoes formidable active‐site poisoning by carbon monoxide (CO). In particular, given the sluggish kinetics of hydrogen oxidation reaction (HOR) in anion‐exchange membrane fuel cell (AEMFC), the issues of Pt poisoning and slow rate would combine mutually, notably worsening the device performances. Here we overcome these challenges through incorporating cobalt (Co) into molybdenum‐nickel alloy (MoNi4), termed Co‐MoNi4, which not only shows superior HOR activity over the Pt/C catalyst in alkali, but more intriguingly exhibits excellent CO tolerance with only small activity decay after 10 000 cycles in the presence of 500 parts per million (ppm) CO. When feeding with CO (250 ppm)/H2, the AEMFC assembled by this catalyst yields a peak power density of 394 mW cm−2, far exceeding the Pt/C catalyst. Experimental and computational studies reveal that weakened CO chemisorption originates from the electron‐deficient Ni sites after Co incorporation that suppresses d→CO 2π* back‐donation.

In situ construction of Fe3O4@FeOOH for efficient electrocatalytic urea oxidation

Substituting water oxidation half of water splitting with anodic oxidation of urea can reduce the cost of H2 production and provide an avenue for treating urea-rich wastewater. However, developing an efficient and stable electrocatalyst is necessary to overcome the indolent kinetics of the urea oxidation reaction (UOR). Accordingly, we have used the Schikorr reaction to deposit Fe3O4 particles on the nickel foam (Fe3O4/NF). Results from the various analysis indicated that under the operational conditions, Fe3O4 underwent surface reconstruction to produce a heterolayered structure wherein a catalytically active FeOOH layer encased a conducting Fe3O4. Fe3O4/NF outperformed RuO2 as a UOR catalyst and delivered a current density of 10 50 and 100 mA cm−2 at low applied potentials of 1.38 1.42 and 1.46 V, respectively, with a Tafel slope of 28 mV dec−1. At the applied potential of 1.4 V, Fe3O4/NF demonstrated a turnover frequency (TOF) of 2.8 × 10−3 s−1, highlighting its superior intrinsic activity. In addition, a symmetrical urea electrolyzer constructed using Fe3O4/NF produced the current density of 10 mA cm−2 at a cell voltage of 1.54 V.

Ternary PtRuTe alloy nanofibers as an efficient and durable electrocatalyst for hydrogen oxidation reaction in alkaline media

Sluggish kinetics of anodic hydrogen oxidation reaction (HOR) in alkaline media, which arises from the two orders of magnitude lower HOR activity in alkali than that in acid media for platinum group metals, hinders the commercial implementation of anion exchange membrane fuel cells (AEMFCs). Consequently, the development of platinum-based catalysts combined with high efficiency and durability is urgently required. Herein, we report a facile route for the synthesis of ternary PtRuTe alloy nanofibers with Pt atomic ratio of only 11% via a simple galvanic replacement reaction. We optimize the adsorption strength of platinum and ruthenium towards hydrogen and hydroxyl species by regulating the electron donation from tellurium to platinum and ruthenium. Hence, the obtained trimetallic alloy catalyst exhibits an impressive kinetic current density of 30.6 mA cm−2geo at 50 mV and an exchange current density of 0.426 mA cm−2metal, which shows 3.0- and 2.5-fold enhancement compared with the commercial Pt/C in alkaline electrolyte, respectively. Moreover, the catalyst also demonstrates excellent stability with merely 5% activity attenuation after 2000 potential cycles. This work offers new pathways to boost alkaline HOR by rationally designing multicomponent alloys.

Design and simulation for improved performance via pump‐less direct ethanol fuel cell for mobile application

The advancement of direct ethanol fuel cells (DEFCs) as portable power sources demonstrated a significant challenge since the power output is still far from the acceptable standards, mainly due to the slow kinetics of the ethanol oxidation reaction (EOR) via the passive mode. While the active system presented higher power output but ends up with a bulky system including all the external mechanical devices. Thus, this work proposed a pump-less DEFC to replace the conventional passive and active DEFC systems to achieve both power generation and device portability. The electrochemical results showed that pump-less DEFCs generated comparable power output with active-feed DEFCs. Computational fluid dynamic (CFD) simulations of the anode flow field for pump-less DEFCs were carried out using three types of flow field designs with different fuel outlet directions. The results indicated that a winding outlet (L-shaped) channel produced the lowest fuel discharge velocity as a result of a high static pressure drop along the channel.

Thermochemistry and Kinetics of the Atmospheric Oxidation Reactions of Propanesulfinyl Chloride Initiated by OH Radicals: A Computational Approach.

The thermochemistry and kinetics of the atmospheric oxidation mechanism for propanesulfinyl chloride (CH3-CH2-CH2-S(═O)Cl; PSICl) initiated by the hydroxyl (OH) radical were investigated with high level quantum chemistry calculations and the Master equation solver for multi-energy well reaction (Mesmer) kinetic code. The mechanism for the oxidation of PSICl in the presence of OH radical can proceed via H-abstraction and substitution pathways. The CCSD(T)/aug-cc-pV(T+d)Z//MP2/aug-cc-pV(T+d)Z level calculated energies revealed addition of the OH radical to the S-atom of the sulfinyl (-S(═O)) moiety, followed by cleavage of the Cl-S(═O) single bond, leading to formation of propanesulfinic acid (PSIA) and the Cl radical to be the major pathway when compared to all other possible channels. The transition state barrier height for this reaction was found to be -3.0 kcal mol-1 relative to the energy of the starting PSICl + OH radical reactants. The rate coefficients were calculated for all possible paths in the atmospherically relevant temperature range of 200-320 K and at 1 atm. The rate coefficient for the formation of the PSIA + Cl radical from the PSICl + OH radical reaction was found to be 8.2 × 10-12 cm3 molecule-1 s-1 at 298 K and a pressure of 1 atm. From branching ratio calculations, it was revealed that the reaction resulting in the formation of the PSIA + Cl radical contributed ∼52% to the total reaction. The overall rate coefficient for the PSICl + OH reaction was also calculated and found to be 1.6 × 10-11 cm3 molecule-1 s-1 at 298 K and a pressure of 1 atm. In the aggregate, the results indicate the atmospheric lifetime of PSICl to be ∼12-20 h in the temperature range between 200 and 320 K, which suggests that its contribution to global warming is negligible. However, the degradation products revealed to be formed in its interactions with the OH radical, which include that SO2, Cl radical, HO2 radical, and propylene have significant effects on the formation of acid rain, secondary organic aerosols, the ozone layer, and global warming.

Design of Ru-Ni diatomic sites for efficient alkaline hydrogen oxidation.

Anion exchange membrane fuel cells are limited by the slow kinetics of alkaline hydrogen oxidation reaction (HOR). Here, we establish HOR catalytic activities of single-atom and diatomic sites as a function of *H and *OH binding energies to screen the optimal active sites for the HOR. As a result, the Ru-Ni diatomic one is identified as the best active center. Guided by the theoretical finding, we subsequently synthesize a catalyst with Ru-Ni diatomic sites supported on N-doped porous carbon, which exhibits excellent catalytic activity, CO tolerance, and stability for alkaline HOR and is also superior to single-site counterparts. In situ scanning electrochemical microscopy study validates the HOR activity resulting from the Ru-Ni diatomic sites. Furthermore, in situ x-ray absorption spectroscopy and computational studies unveil a synergistic interaction between Ru and Ni to promote the molecular H2 dissociation and strengthen OH adsorption at the diatomic sites, and thus enhance the kinetics of HOR.