Kinetics Of Oxidation Reaction Research Articles

In situ evolution of surface Co2CrO4 to CoOOH/CrOOH by electrochemical method: Toward boosting electrocatalytic water oxidation

Developing non-noble-metal electrocatalyst with efficient and durable activity is a urgent task for addressing the sluggish reaction kinetics of electrochemical water oxidation. Structural evolution of the electrocatalyst is an important strategy for achieving enhanced performance. Herein, in situ evolution of surface Co2CrO4 to CoOOH/CrOOH (CoOOH/CrOOH-Co2CrO4) by an electrochemical method under alkaline conditions was designed for enhancing the electrocatalytic performance of water oxidation. The experiments demonstrated that the synergy between CoOOH/CrOOH and Co2CrO4 resulted in a marked increase in the number of active sites and improved the rate of charge transfer, which enhanced the activity for water oxidation. At a geometrical current density of 20 mA cm−2, the overpotential of the oxygen evolution reaction was 244 mV and the turnover frequency was 0.536 s−1 in 1.0 M NaOH.

Boosting SO2-depolarized electrolysis with anodic HI for efficient and energy-saving hydrogen production

The SO2-depolarized electrolysis (SDE) is a promising method for SO2 capture and hydrogen production. But the SDE is limited by the high overpotential and slow kinetics of anodic SO2 oxidation reaction (SOR). Herein, to boost SDE process, we add hydroiodic acid (HI) to the anolyte and form HI-assisted SO2-depolarized electrolysis (HASDE). The mechanism of HI assisted SOR is explored, the existence of HI reduces the onset potential and impedance, but increases current density and reaction rate of SOR. HI is supposed to change the single-step SOR into three-step reactions, without changing the overall anodic reaction. A HI concentration of less than or equal to 0.02 mol/L and an operating temperature of 50 °C or less are recommendable. The comparison of SDE and HASDE processes indicates that HASDE delivers a lower cell voltage than SDE during continuous constant-current electrolysis, and has negligible effect on cathodic H2 evolution, while it achieves 27.03–48.65% reduction in electric energy consumption compared with SDE. The present work provides an innovative strategy for improving SDE and energy-saving production of value-added chemicals like H2SO4 and H2.

Unravelling CO oxidation reaction kinetics on single Pd nanoparticles in nanoconfinement using a nanofluidic reactor and DSMC simulations

Steady state catalytic oxidation of CO in nanofluidic channels decorated with Pd nano particles was studied using the Direct Simulation Monte Carlo (DSMC) method. Diffusion, collision, adsorption, desorption and reaction processes are simulated simultaneously. The influence of various adsorption (sticking coefficient, saturation coverage), desorption (activation energy, pre-exponential factor) and reaction (activation barrier) parameters on the final CO2 turnover are determined. These effects are considered to tune DSMC surface reaction model with respect to the experimental results. With DSMC, it was possible to get insights on reactivity of the individual Pd particles and the resulting varying reaction conditions along the channel due to local conversion effects. From the local coverages, the limit of CO:O2 inlet ratio to get maximum CO2 turnover without poisoning the catalyst with CO were determined. The approach paves the way to accurately represent micro- and nanoscale flows at the same system size as that of experiments.

Carbide-Supported PtRu Catalysts for Hydrogen Oxidation Reaction in Alkaline Electrolyte

Owing to the sluggish kinetics of the hydrogen oxidation reaction (HOR) in alkaline electrolyte, it is considered a limiting reaction for the development of anion-exchange membrane fuel cell (AEMFC...

Development of Wastewater Treatment Technique by Catalytic Oxidation in Superheated Steam

The purpose of this research was the development of a wastewater treatment technique using catalytic oxidation in superheated steam. The target substance was isopropyl alcohol (IPA). The experiment was carried out using a plug-flow reactor filled with MnO2 catalyst. The optimum decomposition condition was determined, and the kinetics of the catalytic oxidation reaction were analyzed. The experimental results were expressed as total organic carbon (TOC) removal. The dependences of the TOC removal on the reaction temperature and residence time were investigated. The TOC removal increased with the reaction temperature and residence time. It was 99.8% at 300°C, 0.9 MPa, 11 s, and oxidant ratio of 1.2. On the other hand, the TOC removal was constant for a long residence time at low reaction temperatures of 200 and 230°C. This was because acetone and acetic acid were produced via the oxidation of IPA, and they were detected as TOC. The reaction kinetics were examined using the pseudo-first-order reaction model; the TOC removal correlated well with this model. Based on the results of the kinetics, the activation energy (Ea) for TOC decomposition was determined from the Arrhenius equation; it was 56.1 kJ/mol. These results indicate that catalytic oxidation in superheated steam is useful for wastewater treatment.

Understanding the Enhanced Methanol Oxidation Reactivity on Sulfur-Organic Compound Decorated Pt Electrode in Alkaline Media

Due to the rapid increase in environmental and energy issues, it is required to replace fossil fuel-driven conventional internal combustion engines with an energy conversion system using sustainable fuels. Although fuel cell is one of the possible candidates due to its high efficiency, the storage and transportation of hydrogen fuel hinder its widespread use.1 To overcome this problem, hydrogen careers, hydrogen-rich liquid and solid-phase materials, have been proposed as alternative fuels for fuel cell systems. Among the hydrogen carriers, methanol is one of the promising candidates due to its low production cost and high energy density. However, the slow kinetics of the methanol oxidation reaction (MOR), which proceeds via a complex six-electron pathway, limits the overall efficiency of the direct methanol fuel cell (DMFC).2 Much effort has been put into improving the MOR activity, including the development of electrocatalyst by metal alloying and surface modification of the electrocatalyst by thiol derivatives.3 Here, we focused on using sulfur-organic compound copolymer synthesized from S8 and organic molecules as a surface modifier. We then explored the reaction mechanisms on Pt surface in the alkaline environment by tracking the surface-bound intermediates using in situ surface-enhanced infrared absorption spectroscopy (SEIRAS). We selected styrene as an organic component and synthesized sulfur-organic compound copolymer (poly(s-st)). Synthesized poly(s-st) was decorated on the Pt surface by simply immersing the electrode into the poly(s-st)-contained solution. Cyclic voltammogram and X-ray photoelectron spectroscopy confirm the surface modification of the Pt surface by poly(s-st), which was stable after 5 cycles of potential cycling in 0.1 M KOH electrolyte. The oxidation current at 0.78 V vs. RHE, which is related to the MOR, was more significant than the pristine Pt electrode, which confirms the improvement of the MOR activity by poly(s-st) modification. The degree of activity enhancement became more substantial with the increase in alkyl chain length of alcohol fuels (methanol < propanol < 1-butanol), suggesting the reason of the enhanced activity to be the hydrophobic interaction between phenyl group of a surface modifier and alkyl portion of alcohol fuels which could facilitate the fuel supply on Pt electrode. In order to support our hypothesis, we performed SEIRAS measurement, where we observed a peak corresponds to the site-blocking species at ca. 1500 cm-1 for pristine Pt surface, while no corresponding peak was observed for poly(s-st) modified Pt surface. We will discuss the changes in the surface reaction mechanism based on the direct observation of the reaction intermediates by SEIRAS. It will also be demonstrated that the holistic information about the nature of the adsorbed species can provide a strategy to design the surface modifier to tune the energetics of key reaction intermediates, leading to further improvements in electrocatalytic activity for the methanol oxidation reaction.[1] Z-F. Li et al. Electrochim. Acta. 2017, 228, 351–360.[2] C. Lamy et al. J Appl. Electrochem. 2001, 31, 799–809.[3] H. Zimmermann et al. Chem. Eur. J. 2000, 4, 592–599.

Pressure Dependency of the Hydrogen Oxidation and Evolution Reaction Kinetics on Carbon Supported Pt Catalysts Using a PEMFC Based Hydrogen Pump Approach

The hydrogen oxidation and evolution reaction (HOR/HER) has been widely investigated in electrocatalysis due to its importance for a broad variety of applications especially in electrolysis and fuel cells (FC). While the HOR/HER reaction rates on platinum and platinum alloy catalysts in alkaline environment can be determined precisely with rotating disk electrode (RDE) measurements,1-3 this is not possible at low pH due to the two orders of magnitude higher reaction rates that far exceed the slow mass transport limited rates afforded by the RDE configuration.4 As a result, meaningful measurements are limited to setups with much faster mass transport rates, such as floating electrodes or proton exchange membrane (PEM) fuel cell based electrochemical H2-pumps,4, 5 but the effect of hydrogen partial pressure and kinetic limitations at higher overpotentials are not yet fully understood.Here we report detailed kinetic investigations on the temperature and pressure dependence of the HOR/HER kinetics on carbon supported platinum (Pt/C) using the PEMFC based H2-pump approach. The measurements were performed on assymmetric membrane electrode assemblies (MEAs), where the working electrode has an ultra-low loading of only 1-2 µgPt cmMEA -2 (resulting in roughness factors of ≈1.5 cmPt 2 cmMEA -2), while the counter electrode has a much higher loading of 0.4 mgPt cmMEA -2. Using a fuel cell test station that allows for the feed of humidified hydrogen on both the anode and the cathode, we were able to show that the apparent activation energy of the HOR/HER on platinum increases with increasing partial pressure of hydrogen, which we ascribe to a decreasing effect of the hydrogen adsorption enthalpy with increasing coverage by adsorbed hydrogen atoms on the Pt surface. Consequently, the HOR/HER reaction order with respect to H2 partial pressure is also depending on the temperature. We further observed that the HOR quickly reaches a limiting current with increasing HOR overpotential, ηHOR (orange area in Fig. 1), which we ascribe to a change in the rate-determining step (rds) from the Volmer reaction (i.e., the electrochemical oxidation of adsorbed H) at low ηHOR to the Tafel reaction (i.e., the dissociative adsorption of H2 on the Pt surface) at higher ηHOR. The Tafel-limited current shows a pressure-independent activation energy and a direct proportionality to the partial pressure of hydrogen, which is exactly what one would expect for the dissociative Langmuir adsorption as the rds. Finally, the HOR/HER reaction rates on a Pt3Co alloy and a Ru@Pt core-shell catalyst will be compared to that on a Pt/C catalyst.

Effect of Varying Carbon Supports on Pt Based HOR Electrocatalysts for Alkaline Media Synthesized By CVD

The synthesis of electrocatalysts for the chemical reactions of hydrogen systems (e.g. fuel cells and electrolyzer systems) continues to be a significant area of research in the renewable energy community. The kinetics of hydrogen reactions decrease by two orders of magnitude in alkaline environments compared to acidic, which has rendered significant challenges in the development as catalysts of alkaline fuel cell systems[1,2]. Chemical vapor deposition (CVD) is a conventional synthesis process applied to manufacture electrocatalysts[3,4]. In this study, a modified form known as “Poor Man’s” CVD (PMCVD) is utilized, to further its impact in electrochemical catalyst development. This work assesses the deposition mechanism as well as its ability to develop tuneable catalysts for the hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) for alkaline media.In our last efforts, we showed Pt based catalysts synthesized using the PMCVD method exhibited higher activities for the HOR/HER in alkaline media than commercially available catalysts[5]. The performance was attributed to the tunability of crystallite size by varying the temperature and pressure of the PMCVD process. In an effort to further understand the deposition mechanism of this processes, we investigated Pt catalysts on various carbon supports. In doing so, Pt was deposited on three supports: XC-72, Acetylene Black, and Graphitized Nanoplatelets with 30% Pt by weight. The carbons varied in both surface areas and degree of graphitization. This work will summarize the HOR/HER activities of these three Pt/C catalysts in alkaline media. It will also help elucidate the impact of the deposition mechanism as a function of each support based on their material properties.[1] Durst, J. et al. New insights into the electrochemical hydrogen oxidation and evolution reaction mechanism. Energ. Environ. Sci. 7, 2255–2260 (2014).[2] Sheng, W. et al. Hydrogen Oxidation and Evolution Reaction Kinetics on Platinum: Acid vs Alkaline Electrolytes.” Electrochem. Soc. 2010 volume 157, issue 11, B1529-B1536[3] Garcia, Vargas, et al., “Chemical Vapor Deposition of Iridium, platinum, Rhodium, and Palladium.” Materials Transactions, Vol. 44, No. 9 (2003) pp. 1717 to 1728[4] Serp, Philppe, et. al., “Chemical Vapor Deposition Methods for the Controlled Preparation of Supported Catalytic Materials.” Chem. Rev. 2002, 102, 3085−3128[5] Williams, S. et. al. “Synthesis and Characterization of Electrocatalysts for the Hydrogen Evolution Reaction in Alkaline Environment.” ECS Fall 2019. Figure 1

Degradation of odorous sulfide compounds by different oxidation processes in drinking water: Performance, reaction kinetics and mechanism

Swampy/septic odor caused by various sulfides is one of the most frequently encountered odor problems in drinking water. However, even though it is much more offensive, few studies have specifically focused on swampy/septic odor compared to the extensively studied musty/earthy problems. In this work, four sulfide odorants, diamyl sulfide (DAS), dipropyl sulfide (DPS), dimethyl disulfide (DMDS) and diethyl disulfide (DEDS), were selected to evaluate the treatment performance of different oxidation processes in drinking water. The results demonstrated that DMDS, DEDS, DPS and DAS could be oxidized effectively by KMnO4, NaClO and ClO2. The oxidation processes could be well described by the second-order kinetic model, in which k values of selected sulfides followed the order DMDS≈DEDS ≪ DPS≈DAS. As for the three oxidants, the order of reactivity was KMnO4 ≪ ClO2 < NaClO, which was also verified in raw water. The results of oxidation treatability, reaction kinetics and mechanisms confirmed that the characteristics of the central sulfur atom rather than the side chain is the decisive factor in controlling the oxidation rate and transformation pathway of sulfides. The transformation products and pathways were significantly different for the three oxidants. Sulfones (DPSO, DASO) were always formed by cycloaddition reactions during KMnO4 oxidation, yet recombination reactions proceeded during ClO2 oxidation and formed more products, such as MADS, DADS and EADS. Density functional theory (DFT) calculations confirmed that the differences in transformation pathways were caused by the variations in the activity of the oxidants and sulfides. Finally, NaClO was certified as the most effective oxidant for controlling sulfide odorants in drinking water treatment.

Acetonitrile’s Effect on the Efficiency of Ethanol Electrooxidation at a Polycrystalline Pt Electrode in Relation to pH-Dependent Fuel Cell Applications

The present paper reports cyclic voltammetric and a.c. impedance spectroscopy investigations on the influence of the acetonitrile concentration on the kinetics (and individual product’s efficiency) of the ethanol oxidation reaction (EOR), performed on a polycrystalline Pt electrode surface in 0.5 M H2SO4 and 0.1 M NaOH supporting solutions. The kinetics of the EOR were examined at room temperature over the voltammetric potential range, which covers the electrooxidation of surface-adsorbed COAds species, as well as the formation of acetaldehyde molecules. In addition, the time-dependent efficiency of acetate and acetaldehyde formation in relation to the initial acetonitrile content for both acidic and alkaline electrolytes was evaluated by means of spectrophotometric Ultraviolet/ Visible Spectroscopy (UV-VIS) instrumental analysis.

Dinuclear nickel(II) complexes with ONO-pincer and coordinated aquo ligands as a robust homogeneous water oxidation catalyst

A nickel(II) complex with the newly synthesized dicarboxamide ligand [H2LBZ][(CF3SO3)Cl] was explored as a water oxidation catalysis. All the synthesized compounds were characterized by IR and NMR spectroscopy, thermogravimetry, and single-crystal XRD analysis. The superior kinetics of the water oxidation reaction in the presence of the NiII catalyst was shown by an enhanced current of 4535 µA (pH 8) or 8900 µA (pH 10) at an overpotential of 186 mV in a cyclic voltammogram. Controlled potential electrolysis demonstrated that the catalyst was stable during the water oxidation experiment. These results are akin to those for other reported nickel catalysts.

Elimination of volatile organic compounds in paint drying by absorption reaction in water combined with the ozone oxidation technique

The aim of this work was to evaluate the treatment of Volatile Organic Compounds (VOCs) released during the painting and drying process of an industrial paint by absorbing them in a water curtain and then oxidizing them with ozone. For this purpose, laboratory equipment was built consisting of a paint drying cabin and a bubble column where the VOCs were absorbed and treated. Tests were carried out with simulated effluents using distilled water and service water, to which 3.5 µg/L of formaldehyde, 11.6 mg/L of butyl acetate, 5.3 mg/L of ethanol and 5.6 mg/L of methyl ethyl ketone were added, according to data provided by the paint manufacturer; these tests were then repeated using the industrial paint currently used in the processes. The water saturation with the VOCs and the simultaneous treatment by means of ozone dosage was studied, taking the Chemical Oxygen Demand (COD) value as a treatment effectiveness parameter. VOC saturation is achieved for exposure times between 5 and 15 min in the aqueous effluent. The system of absorption and ozonation is effective for the elimination of the released VOCs, achieving a 94% reduction in the COD of the wastewater. Finally, it was observed that when O3 is injected together with the paint, the reduction of COD in the effluent is favored due to a first instance of direct ozonation of the VOCs, and a second, slower indirect stage, generated by the presence of free radicals from the reaction of O3 with water [hydroxyl radical (HO•), superoxide anion radical (O2–•) and hydroperoxyl radical (HO2•)] favored by the pH of the solution. The reaction kinetics of VOC oxidation is of first order.

Fabrication of BiVO4-Ni/Co3O4 photoanode for enhanced photoelectrochemical water splitting

The low efficiency of charge separation and slow kinetics of water oxidation of BiVO4 limit its application in the PEC water splitting. Here, an effective strategy is explored with Ni-doped Co3O4 (Ni/Co3O4) decorated BiVO4 photoanode by a simple route. The photocurrent of the BiVO4-Ni/Co3O4 (2.23 mA/cm2 at 1.23 VRHE biases) has significantly increased up to 4.4 times of that of bare BiVO4, and the Vonset of BiVO4-Ni/Co3O4 shows a significant negative shift (180 mV) to 0.23 V. The IPCE value of BiVO4-Ni/Co3O4 (27%, 380 nm) is about 5 times that of the BiVO4 (5%). The ηinjection and ηseparation of BiVO4-Ni/Co3O4 at 1.23 VRHE reaches 75.82% and 37.08%. The results demonstrate that the Ni/Co3O4 could enhance the charge transfer and accelerate the kinetics of water oxidation reaction, leading to the excellent PEC water splitting performance of the photoelectrode.

Reduced graphene oxide supported nickel tungstate nano-composite electrocatalyst for anodic urea oxidation reaction in direct urea fuel cell

In recent time direct urea fuel cell (DUFC) emerges as a potential candidate for sustainable urea reach wastewater treatment and power generation. The efficiency of DUFC mainly governed by the anodic urea oxidation reaction (UOR) kinetics. The design and development of efficient electrocatlysts for UOR remains a key factor for practical utilization of DUFC. In current study, we present a single step hydrothermal synthesis of NiWO4 NPs/rGO (h-NiWO4 NPs/rGO) composite for UOR catalysis in alkaline medium. The synthesized NiWO4 NPs/rGO composite offers a 218 mA/cm2 UOR catalytic current density. Moreover, the h-NiWO4 NPs/rGO composite retains its 94% UOR catalytic current after 1000 cyclic voltammetric cycles. Further, h-NiWO4 NPs/rGO composite shows superior UOR catalytic performance than physical mixture of NiWO4 NPs and rGO, NiWO4 NPs, NiO/WO3 physical mixture and only NiO with reference to catalytic current density, onset potential, and durability. The enhanced electrocatalytic activity of the h-NiWO4 NPs/rGO composite attributed to the synergetic coupling of physiochemical properties of NiWO4 NPs and rGO which improves the charge transfer generates larger electroactive surface and reduces catalyst poisoning. An air cathode DUFC with h-NiWO4 NPs/rGO composite modified anode and Pt/C cathode produces a maximum power density of 5.1 mW/cm2 and 927 mV open circuit potential.

Reaction characteristics and kinetics of the low-temperature oxidation and weight gain of coal

ABSTRACT The study of coal oxidation and weight gain at low temperatures is helpful in understanding the spontaneous combustion of coal and its mechanisms. In this study, we comprehensively investigated the low-temperature oxidation properties and the oxygen adsorption weight gain kinetics of Chinese Shenhua subbituminous coal (SH). Using thermogravimetric experiments with various particle sizes, heating rates, and coal ranks, the oxygen adsorption mass gain stages of coal oxidation at low temperatures were investigated. According to the results of these experiments, as the particle size of SH coal decreased, the dry cracking temperature (T1) decreased, the ignition temperature (T2) changed slightly, the weight gain increased, and the spontaneous combustion tendency increased. The three-dimensional diffusion model (Zhuralev-Lesokin-Tempelman) (D5) is suitable for SH coal samples with different particle sizes. A higher heating rate is not conducive to the formation of carbon-oxygen complexes. The D5 model can also be used to fit the kinetics of the SH coal samples at 5 K/min, 10 K/min, and 30 K/min. Unlike the SH coal samples, the Shengli lignite (SL) and Tavan Tolgoi anthracite (TT) samples fit the three-dimensional diffusion model (Jander) (D3). Based on the fitting results of the Achar differential method and the Coats-Redfern integral method, the activation energy E of the low-temperature oxidation weight gain of the coal samples decreases with decreasing coal particle size and with increasing oxidation rate and coal rank.

Bell shape vs volcano shape pH dependent kinetics of the electrochemical oxidation of formic acid and formate, intrinsic kinetics or local pH shift?

The interfacial pH at the electrode/electrolyte interface (pHs) and reaction kinetics of electrochemical oxidation of formic acid in the presence or absence of buffers are carried out. The transform from bell shape to volcano shape pH dependence of formic acid oxidation reaction (FOR) is clarified by considering both pHs drift and buffer effect. The Diagram of pHs as a function of FOR current density (j) in solutions with bulk pH (pHb) from 0 to 14 with/without buffers are constructed by numeral calculations, which are compared with experimental results of FOR on Pt and Au. Our study reveals that i) In solutions with 5< pHb <10 free of buffer or with limit buffer capability, there is significant pHs drop and drift of the thermodynamic equilibrium potential (Eeq); ii) FOR on both Pt and Au has a bell shape intrinsic pH dependence with maximum activity close to the pKa of HCOOH; iii) The observed volcano shape pH dependence of FOR activity with a plateau at 5<pHb<10 on top of the volcano is a coincidence related to pHs drift.

Insights of temperature dependent catalysis and kinetics of electro-oxidation of nitrite ions on a glassy carbon electrode

Influence of temperature on the catalysis and kinetics of nitrite oxidation reactions has been investigated on a glassy carbon (GC) electrode surface in a slightly basic medium. To elucidate the kinetics of oxidation reaction, diffusion coefficient, electron transfer coefficient, heterogeneous rate constant and free energy of activation were systematically evaluated within the temperature range of 0–60 °C. Nitrite oxidation involves single electron transfer and first order reaction forming nitrogen dioxide as a product. The electrode process was found most efficient at 60 °C with a standard rate constant (ko) of 4.63 × 10−5 cm s−1 at 0. 0.84 V vs. Ag/AgCl (sat. KCl) reference electrode. Above 60 °C, predominant desorption step negatively influences the overall reaction rate. It has been proposed that at the lower temperatures (≤ 30 °C), the chemical step is concerned with an electron transfer step at the RDS and above this temperature, the reaction simply follows a stepwise mechanism. The decrease of solvent reorganization energy (λ) at higher temperatures minimizes the activation free energy (ΔG‡) which accelerates the reaction rate using catalytically different route.

BiVO4 photoanode decorated with cobalt-manganese layered double hydroxides for enhanced photoelectrochemical water oxidation

Bismuth vanadate (BiVO4) is being widely identified as a leading n-type semiconductor material for photoelectrochemical (PEC) water splitting. Nevertheless, achieving efficient PEC water oxidation process through BiVO4 photoanode still faces serious challenge such as severe electron-hole recombination. In this case, PEC activity of BiVO4 photoanode was enhanced by decoration of three-dimensional CoMn-layered double hydroxide (CoMn-LDH) nanoflakes on the BiVO4 surface via a facile electrodeposition process. It was suggested that CoMn-LDH played a synergistic effect on broadening internal light absorption, which accelerated injection of holes carrier to electrolyte and alleviated the electron-hole recombination, resulting in expediting faster PEC water oxidation reaction kinetics. Consequently, the photocurrent density of BiVO4/CoMn-LDH photoanode achieved 2.69 mA cm−2 at 1.23 VRHE, 2.45 times higher than the pristine BiVO4. What's more, 220 mV negative-shift took place on onset potential that was further decreased to 0.31 VRHE. The vastly enhanced PEC performance was also prioritized to those of Co and Mn single relatives. This work demonstrated that the synergistic BiVO4/CoMn-LDH as a capable candidate material, can be utilized for effective PEC water splitting.

Surface Modification of Hematite Photoanodes with CeOx Cocatalyst for Improved Photoelectrochemical Water Oxidation Kinetics.

Hematite is a promising photoanode for solar water splitting by photoelectrochemical (PEC) cells, but its performance is limited by the slow kinetics of water oxidation reaction or oxygen evolution reaction (OER). Surface modification of hematite photoanodes with a suitable water oxidation cocatalyst is a key strategy for improving the kinetics of water oxidation. In this study, a CeOx overlayer is deposited on the surface of the hematite photoanode by a water-based solution method with ceric ammonium nitrate (CAN) followed by heat treatment. The photocurrent of CeOx -modified hematite is 3 times higher than that of pristine hematite (at 1.23 V vs. RHE) under AM 1.5G, 1 sun conditions. Through hole-scavenger measurements, Tafel plot analysis, and electrochemical impedance spectroscopy, it is concluded that CeOx overlayer increases the hole injection efficiency, improves the surface catalytic activity, and enhances charge transfer across the photoanode/electrolyte interface. These observations are attributed to the synergistic effects of Ce3+ /Ce4+ redox species in CeOx and the oxygen vacancies. This work elucidates the role of CeOx as an efficient cocatalyst overlayer to improve the OER kinetics of photoanodes.

Bifunctional mechanism of hydrogen oxidation reaction on atomic level tailored-Ru@Pt core-shell nanoparticles with tunable Pt layers

Anion exchange membrane fuel cells (AEMFCs), as the next generation of cost-effective fuel cells, have attracted renewed attention in recent years. One of the existent challenges to the AEMFCs is the sluggish kinetics of the hydrogen oxidation reaction (HOR) in alkaline solution. The alkaline HOR mechanism is yet in debate, which would be a major barrier to the design of high-performance catalysts. Here, we explore the HOR mechanism on graphene-supported Ru@Pt core-shell nanoparticles. The Pt shell was precisely tailored at atomic monolayer level through controlling Cu underpotential deposition (UPD)-Galvanic displacement (GD) cycle. The relationship between the HOR electrocatalytic activity and the electronic structure of the catalysts has been investigated based on the results from electrochemical rotating disk electrode and X-ray photoelectron spectroscopic characterizations. We find that the hydrogen-binding energy (HBE) is not the sole descriptor of HOR activity, the reactive oxygen species on the catalyst surface also promotes the HOR kinetics through the bifunctional mechanism. This research offers the fundamentals for designing high performance HOR catalysts in alkaline solution and contributes to the commercial application of hydrogen fuel cells.