Oxygen Reduction Reaction Rate Research Articles

Stress-Affected Oxygen Reduction Reaction Rates on UNS S13800 Stainless Steel.

This work investigates the previously unexplored impact of tensile stress on oxygen reduction reaction (ORR) kinetics of a precipitation-hardened, stainless-steel fastener material, UNS S13800. ORR is known to drive localized and galvanic corrosion in aircraft assemblies and greater understanding of this reaction on structural alloys is important in forecasting component lifetime and service requirements. The mechano-electrochemical behavior of UNSS13800 was examined using amperometry to measure the reduction current response to tensile stress. Mechanical load cycles within the elastic regime demonstrated reversible electrochemical current shifts under chloride electrolyte droplets that exhibited a clear potential dependence. Strain ramping produced current peaks with a strain rate dependence, which was distinct from the chronoamperometric shifts during static tensile load conditions. Finally, mechanistic insight into the dynamic and static responses was obtained by deoxygenation, which demonstrated ORR contributions that were distinct from other reductive processes.

Achievement of a novel organometallic electrocatalyst based on nickel and poly para-aminophenol with excellent oxygen reduction reaction activity: Promoting the commercialization of low temperature fuel cells

The fuel cell is a clean system for generating electrical energy. The rate of oxygen reduction reaction at the fuel cell cathode has a significant effect on the efficiency of the fuel cell. Organometallic catalysts are a new area of research to reduce the cost and increase efficiency of low temperature fuel cell systems. In this study, an organometallic electrocatalyst of poly para-aminophenol and nickel was synthesized by solvothermal method for oxygen reduction reaction in acidic medium. The structure of compound is a new mesoporous polymer of para-aminophenol containing nickel, which is resistant to temperature (180οC) and the average particle size is 68 nm and the pore diameter is 12.39 nm. Poly para-aminophenol with Nickel (Ni/PPAP) loading on carbon black-Vulcan (XC-72R) with weight ratio of 10 to 90% were optimized for the oxygen reduction reaction in 2.5 M H2SO4 at 25 °C in saturated oxygen solution. The results showed that the presence of 10% of the synthesized material in the electrode reaction layer improves the oxygen reduction reaction kinetics with an exchange current density of 1.305 mA cm−2, which can be used as an electrocatalyst with low cost and high efficiency compared to platinum as a low temperature fuel cell.

Analysis Method of Oxygen Reduction Reaction Rate in PEFC Using Pt-Sputtered Catalyst

IntroductionTo establish the generic model of the cathode catalyst layer (CCL),[1] the intrinsic oxygen reduction reaction (ORR) rate which does not include mass transfer resistance through the CCL should be formulated. Neglecting the backward reaction, the ORR rate per geometric area, r gc, is proportional to oxygen partial pressure, p O [Pa], as follows: r gc = k gc p O [mol/(m2·s)][1] (1) k gc = k gc0exp(–E/RT–E c/b c) = k gc0exp{–(E+4aFE c)/RT} (2)where k gc is the reaction rate constant per geometric area [mol/(Pa·m2·s)], E c is the cathode electromotive force [V], E is the activation energy [J/mol], T is temperature [K], b c is the Tafel slope [V] which is proportional to temperature, and 4a is the transfer coefficient.The objective of this study is to develop a measurement method of temperature, relative humidity (RH) and E c dependencies of the intrinsic ORR rate constant using platinum-sputtered catalyst.ExperimentalA Japan Automobile Research Institute (JARI) standard cell whose active area was 50 mm × 50 mm or modified to 20 mm × 20 mm was used in experiments. The membrane-anode assembly (MAA, Eiwa Corp.) was composed of a proton exchange membrane (PEM, Nafion® NR-212), an 8.3‒9.8 μm thick (0.19–0.24 mg/cm2) anode which was made of Pt/Vulcan® XC-72 catalyst (Pt/C weight ratio: 1) with a Nafion® ionomer (ionomer/carbon weight ratio: 0.74). Pt thin-layer cathode (0.054 mg/cm2) was prepared by sputtering (AOV, SPAD-4240UM, Ar atmosphere, 5 Pa, 100 ℃, for 50 minutes) on the microporous layer (MPL) on a carbon paper (SIGRACET-GDL 29 BC, 235‒238 μm thick) to eliminate mass transfer resistance through the CCL.[2] Before sputtering, MPL substrates were cleaned using argon plasma in order to eliminate the hydrophobized coatings on the MPL surface. The MAA and Pt thin-layer cathode were stacked as shown in Fig. 1. A carbon current collector had a single serpentine flow channel, the width and depth of which were 1.0 mm and the pitch of the ribs was 2.0 mm. H2 and O2 were humidified at 60–80 oC. H2 and O2 flow rates were 600 and 300 cm3/min, respectively. The cell was operated at 65–80 oC. The pressure at the cell outlet was ambient pressure (ca. 1 atm).Results and DiscussionFig. 2 shows the SEM images of the surface of MPL on a carbon paper before and after 50 min sputtering. Pt particles whose diameter is approximately 10 nm are observed. Next, Fig. 3 shows the temporal changes in the substrate weight (MPL) while ion cleaning. The slope from 25 to 135 minutes is less than a half of the slope from 0 to 25 minutes. It indicates that 30 minutes is enough to remove almost all of hydrophobized coatings on the MPL surface. In addition, Fig. 4 shows Pt loading is proportional to the sputtering time.[3] 40-minute ion cleaning and 50-minute sputtering were employed in this study.Fig. 5 shows the Tafel plot at different temperatures. The current density at a fixed E c increased with raising temperature as expected from Eq. (2). From these polarization curves, the k gc parameters, E, 4a and k gc0 were determined by using nonlinear least square method under the assumption that ORR rate is proportional to RH. As a result, E = 25 kJ/mol, 4a = 0.48 and k gc0 = 1.3 mol/(Pa m2 s) are determined. Fig. 6 shows the Arrhenius plot of recalculated results shown by dashed lines with observed values. The ORR rate dependencies on temperature, RH and E c were properly reproduced so the ORR rate parameters were appropriately determined.Conclusions Temperature, RH and E c dependencies of ORR rate constant, k gc, were measured using platinum-sputtered catalyst in order to determine ORR parameters, E, 4a and k gc0 which do not include the effect of mass transfer resistance through the CCL. From experimental results at different temperatures, ORR dependency on temperature was measured and ORR rate parameters were appropriately determined.AcknowledgementThis work was supported by the New Energy and Industrial Technology Development Organization (NEDO), Japan.References Kawase et al., AIChE J., 63(1), 249–256 (2017).Kageyama et al., 232nd ECS Meeting (National Harbor, Oct., 2017), #1387.Murase et al., 31st ISChE (Chiang Mai, Dec. 1, 2018), OC06.Hu et al., ChemElectroChem, 6(10), 2659‒2666 (2019). Figure 1

Decoration of Graphenated Carbon Nanotube Electrodes with Platinum Nanoparticles via Atomic Layer Deposition

Platinum electrodes are commonly used in devices such as fuel cells, neurostimulators, and sensors. Device performance can be improved by increasing the electrochemically active surface area of the platinum, which increases the charge storage capacitance, oxygen reduction reaction (ORR) rates, and catalytic activity. Therefore, there is significant motivation to fabricate platinum 3D structures, but it is challenging to accomplish successfully. In this study, graphenated carbon nanotubes (gCNTs), a type of carbon nanotube with leaf-like graphene foliates, were decorated with platinum nanoparticles to fabricate a 3D structure with increased Pt surface area. The carbon nanotubes act as a conductive scaffold and the foliates provide increased surface area and highly reactive edge sites.The development of gCNTs was accomplished by systematically adjusting growth parameters in a microwave plasma enhanced chemical vapor deposition system. The primary growth parameters were growth temperature, growth time, process gas composition (methane flow rate vs ammonia flow rate), and microwave power. gCNTs were characterized to obtain the best relevant electrochemical properties, i.e., impedance, voltage window, stability, and charge storage capacity. Compared to platinum, typical gCNT electrodes had lower impedance at 100 Hz at 230 Ω vs 375 Ω for Pt. The electrochemical properties of the gCNTs were compared to scanning electron microscope images (Fig. 1) and it was found that a medium foliate density (3.0 CH4: 1 NH3) had the best electrochemical properties.Next, the gCNTs electrodes can be further enhanced by decoration with nanoparticles of platinum via atomic layer deposition (ALD). Atomic layer deposition alternates two reagents so that the first adsorbs on the surface in a monolayer and the second reacts with the monolayer. The most reactive sides tend to nucleate first, so that at low deposition density, particles preferentially deposit at the edges of the graphene foliates. A major advantage of ALD is that it produces much more monodispersed nanoparticles, which yields more uniform properties. The combined electrodes will have the larger electrochemical surface area of gCNTs and the catalytic and charge storage properties of platinum electrodes. Electrochemical properties of Pt-gCNTs will be compared to gCNTs and planar Pt electrodes. Figure 1

Progress in Development of Nanostructured Manganese Oxide as Catalyst for Oxygen Reduction and Evolution Reaction

The rise in energy consumption is largely driven by the growth of population. The supply of energy to meet that demand can be fulfilled by slowly introducing energy from renewable resources. The fluctuating nature of the renewable energy production (i.e., affected by weather such as wind, sun light, etc.), necessitates the increasing demand in developing electricity storage systems. Reliable energy storage system will also play immense roles to support activities related to the internet of things. In the past decades, metal-air batteries have attracted great attention and interest for their high theoretical capacity, environmental friendliness, and their low cost. However, one of the main challenges faced in metal-air batteries is the slow rate of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) that affects the charging and the discharging performance. Various types of nanostructure manganese oxide with high specific surface area and excellent catalytic properties have been synthesized and studied. This review provides a discussion of the recent developments of the nanostructure manganese oxide and their performance in oxygen reduction and oxygen evolution reactions in alkaline media. It includes the experimental work in the nanostructure of manganese oxide, but also the fundamental understanding of ORR and OER. A brief discussion on electrocatalyst kinetics including the measurement and criteria for the ORR and the OER is also included. Finally, recently reported nanostructure manganese oxide catalysts are also discussed.

Analysis Method of Oxygen Reduction Reaction Rate in PEFC Using Pt-Sputtered Catalyst

For widespread use of polymer electrolyte fuel cell (PEFC), it is necessary to reduce the amount of platinum by optimizing the cathode catalyst layer (CCL) structure. Therefore, oxygen reduction reaction (ORR) rate which does not include the mass transfer resistance in CCL should be formulated. To measure the ORR rate which does not include the mass transfer resistance in the CCL, a thin layer electrode was prepared by directly sputtering platinum to microporous layer (MPL) on gas diffusion layer. Dependencies of ORR rate on temperature and relative humidity (RH), were measured and analyzed. From the measurement results, ORR parameters which do not include the effect of mass transfer resistance through the CCL were appropriately determined. The ORR rate and electrochemical surface area (ECSA) depend on RH and a half of RH dependency of ORR rate is ascribed to change in ECSA.

Boosting the ORR active and Zn-air battery performance through ameliorating the coordination environment of iron phthalocyanine

Iron phthalocyanine (FePc) with unique iron-pyrrolic nitrogen (Fe-N) structure has attracted an increasing attention on the oxygen reduction reaction (ORR). Unfortunately, the Fe-N site is not “active” because of its symmetry in the plane and always exhibits unsatisfactory ORR activity. Herein, we design a non-contact scheme of axial carbon substrate induced Fe-N electron localization to improve its ORR performance. Theoretical calculation indicates that the addition of MWCNTs causes the aggregation of electron cloud around Fe-N, enhances the oxygen adsorption capacity and accelerates the ORR rate. The obtained catalyst shows a Tafel slope of 35.8 mV·dec−1, an initial potential of 0.979 V vs. RHE, a half-wave potential of 0.902 V vs. RHE and a limiting current density of 5.42 mA·cm−2 in alkaline medium. The Zn-air battery assembled by this catalyst also demonstrates a large discharge voltage of 1.296 V, considerable power density of 102 mW·cm−2 and superior cycling stability (500 cycles). This work not only simplifies the process of preparing high efficiency transition metal catalysts but also does some tentative explore for realizing the practical use of Zn-air battery.

Investigation of a cost-effective strategy for polymer electrolyte membrane fuel cells: High power density operation

Polymer electrolyte membrane (PEM) fuel cell technology needs to overcome the cost barrier in order to compete with the internal combustion engines (ICEs) for transportation application. A viable approach is to raise fuel cell's power output without increasing its size and Pt loading in the catalyst layers (CLs). In this strategy, the cost per kW power output can be proportionally reduced due to the increased power density. This paper examines this strategy by exploring several important aspects that influence fuel cell performance under high power or current density using a three-dimensional (3-D) fuel cell model. It is shown that local CLs may be subject to low oxygen concentration under a high current density of 2 A/cm2, causing low reaction rate near the outlet, especially under the land. Additionally, the oxygen reduction reaction (ORR) rate may be subject to a large through-plane variation under 2 A/cm2, raising ohmic voltage loss in the CL. Two additional cases are investigated to improve fuel cell performance under 2 A/cm2: one has a 5 times thinner CL with the same ORR kinetics per membrane electrode assembly (MEA) area and the other has a 5 times thinner CL with 5 times higher ORR kinetics. The results show the output voltage is raised approximately from 0.5 V to 0.554 V in the former CL case and further to 0.606 V for the latter CL. To enable high-efficiency operation (e.g. >50%), thinner CLs with high ORR kinetics and GDLs with better transport properties are one research and development (R&D) direction.

Synthesis of Co/Ni @ Al2O3-GO as novel oxygen reduction electrocatalyst for sustainable bioelectricity production in single-chambered microbial fuel cells

In this work, the synthesis of cobalt (Co) -nickel (Ni) nanoparticles supported on the matrix of alumina-graphene oxide (Al2O3-GO) and studies of their oxygen reduction reaction (ORR) activity in single-chambered microbial fuel cells (MFCs) were reported. A study of different weight ratios of Co-Ni nanoparticles with support material is accomplished to determine the catalyst performance. It is revealed that the catalyst Co-Ni (2:1)/Al2O3-GO (catalyst S2) with a weight ratio of 2:1 of nanoparticles shows optimized properties among other electrocatalysts. The ORR study of hybrid catalysts suggested that the catalyst S2 (reduction potential at 542 mV with −0.252 mA current) showed higher stability and electrocatalytic activities compared to catalyst Pt/C (reduction potential at 466 mV with −0.210 mA current) towards ORR. Al2O3-GO supported Co-Ni (2:1) catalyst revealed an improved ORR rate in single-chambered MFCs with a maximum power density of ~168 mW/m2 compared to 102 mW/m2 for Pt/C. The enhanced electrocatalytic activity of catalyst S2 was accredited to the high electronic conductivity and longer stability of the nanocomposite. MFCB (catalyst S2) showed the highest OCV values (668 ± 15 mV), corresponding to the maximum electrochemical activity. Higher OCV values signified a stable biofilm developed on anode surface resulting in high electron transfer from microbes to anode surface, leading to maximum power production by catalyst S2 in MFCB. The experimental consequences confirmed the employments of Al2O3-GO as a beneficial support matrix in constructing inexpensive and efficient cathode catalysts over standard Pt/C catalysts for single-chambered MFCs.

Enhanced oxygen reduction electrocatalysis on PtCoSn alloy nanocatalyst mediated by Ta-doped SnO2 support for polymer electrolyte fuel cells

For polymer electrolyte fuel cells (PEFCs), platinum-based catalysts for the air cathode supported on metal oxides such as SnO2 exhibit highly promising durability. Yet, the activity for the oxygen reduction reaction (ORR) has still not been sufficiently high toward widespread application. Here, we report a new type of catalyst with significantly boosted ORR activity, based on PtCoSn alloy nanostructures formed on Ta-doped SnO2 support (PtCoSn/Ta-SnO2). The ORR activity of the PtCoSn/Ta-SnO2 catalyst is evaluated in acidic media (0.1 M HClO4) from 20 to 80 °C. The apparent rate constants (kapp) for the ORR on PtCoSn/Ta-SnO2 are found to be about 4.5 and 1.5 times greater than those of commercial Pt and Pt3Co alloy catalysts supported on carbon black (c-Pt/C and c-Pt3Co/C), respectively, and increase with temperature, in accordance with an Arrhenius-type relation from 20 to 60 °C. The enhanced ORR rates of the PtCoSn/Ta-SnO2 catalyst can be correlated with an increase in the preexponential factor of the Arrhenius equation, together with a lowered activation energy. Experimental and density functional theory results reveal that the incorporation of Sn facilitates O2 adsorption and dissociation, which is beneficial to overcome the kinetic limitation of ORR. Moreover, the durability of PtCoSn/Ta-SnO2 examined by potential-step cycling between 0.6 and 1.0 V at 80 °C has been found to be much higher as compared with c-Pt/C and c-Pt3Co/C.

Regulation of Cathode Mass and Charge Transfer by Structural 3D Engineering for Protonic Ceramic Fuel Cell at 400 °C

AbstractLowering the operating temperature (ideally below 400 °C) for solid oxide fuel cell (SOFC) technology deployment has been an important transition that introduces the benefit of reduced operational costs and system durability. However, the key technical issue limiting the transition is the sluggish cathodic performance, namely the oxygen reduction reaction (ORR) rate of the conventional sponge‐like cathode dramatically drops as the temperature reduces. In this paper, 3D engineering of a cathode is conducted on a protonic ceramic fuel cell to obtain an enhanced ORR between 400 and 600 °C. Compared with a cell using a conventional sponge‐like cathode, 3D engineering improves the cathode ORR by 41% at 400 °C with a peak power density of 0.410 W cm−2. A phase field simulation is applied to assist the engineering by understanding the competition between the cathode mass and charge transfer with different cathode porosities. The results show that structural engineering of existing well‐developed cathodes is a simple and effective method to promote cathode ORR for low temperature SOFC by regulating the mass and charge transfer.

Modelling of Patterned Cathode-Membrane Interfaces with Random Roughness for PEMFCs

Proton Exchange Membrane fuel cells (PEMFCs) are becoming an increasingly promising piece of power generation technology that can fit into the changing economy as we strive towards a sustainable energy-based future. However, PEMFCs struggle to meet the energy demands of the world, falling short of the capability of other energy sources such as fossil fuels, mainly due to price and energy output compared to the already establish combustion engines. Looking internally into the PEMFC itself, one of the main issues is the limitations of the electrode-membrane interface leading to low ion transfer performance from the catalyst layer to polymer electrolyte membrane. If we can improve the cathode-membrane interface facilitating the oxygen reduction reaction (ORR) rate at the cathode, the rate limiting step, we can increase the overall performance of the fuel cell.It is believed that by increasing the interfacial area of the cathode-membrane interface, such as applying a prismatic pattern to the morphology, we can increase the active surface area for the membrane electrode assembly (MEA). By varying the prism frequency and relative height, the interfacial area can be tuned to improve the overall power performance of PEMFCs.In this work, with a LiveLink connection between Matlab and multiphysics software COMSOL, we model the electrode-membrane interface to investigate its influence on the ion-transfer performance of PEMFCs. By varying the number and size of prism peaks applied to the interface, it is shown that we can influence the fuel cell performance whilst maintaining a constant membrane and catalyst loading. The results showed, at an optimal peak frequency and relative height, an improvement of up to 25% was achieved in the power density.Although research into the prismatic morphology looks promising, there are many other potential options when looking for which morphology could yield the best overall power performance out of a PEMFC. As such, looking not only into prismatic patterning, but also a pyramidal morphology could prove beneficial. We're also looking into how the application of the roughness to the interface, created using a combination of Gaussian and Uniform wave functions, will impact any previous results observed, and allow us to simulate a model that fits better with the real-world findings. Figure 1

Lattice contraction tailoring in perovskite oxides towards improvement of oxygen electrode catalytic activity

Tailoring the charge density of active metal center is one effective approach to improve the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) performance by accelerating the rate-determining step. Herein, we propose a novel strategy, that is, lattice contraction tailoring to modulate the charge density of active Co atom in LaCoO3 by doping Ce ions into the host lattice. The introduction of Ce can boost the bifunctional oxygen electrode activity (0.81 V) with better durability, surpassing the pure LaCoO3 (1.00 V) catalyst. Due to the improved catalysis performance, the Zn-air battery based on lattice constrain tailoring strategy has demonstrated the 1.2- and 2.0-fold enhancement for current and power densities, respectively. The theoretical calculation reveals that the lattice contraction tailoring in LaCoO3 can effectively increase the electrical conductivity, decrease the reaction free energy and enhance the rate-determining step rate, which causes the accelerated ORR and OER rates. This study provides a novel insight into designing high-performance oxygen electrocatalyst through engineering the crystal parameters of catalysts.

Gold particle effect on high temperature oxygen reduction reaction via lanthanum strontium cobaltite ferrite electrocatalyst

Gold is generally considered to be inert for electrochemical reactions in solid oxide fuel cells (SOFCs). It is thus used as the standard current collector to characterize the catalytic activity of various cathode materials including the state-of-the-art lanthanum strontium cobalt iron oxide (LSCF). This work shows that gold is not inert but active for oxygen reduction reaction (ORR) via LSCF. Electrical conductivity relaxation measurement shows that scattered gold particles on LSCF surface can greatly increase the ORR rate. Gold improves the chemical oxygen surface exchange coefficient by a factor up to 27.5. The improvement is much high at reduced temperature from 800 to 650 °C. In addition, gold particles with smaller size show better performance in enhancing the ORR activity.

Reduced graphene oxide-carbon black composite supported iron phthalocyanine as a high-efficiency and stable catalyst for oxygen reduction reaction

It has been found that only catalytic sites are situated on the surfaces or sub-surfaces of supports to accelerate oxygen reduction reaction (ORR) rates, whereas those situated within the interior regions of supports do not actually participate in catalysis ORR. Therefore, catalyst support technology has been regarded as another effective tactic for improving the catalytic activities of catalysts. In the present study, ORR catalysts supported by composite materials were created by uniformly mixing super-conducting carbon black with tetra-β-(8-quinolinoxy) iron phthalocyanine-loaded reduced graphene oxides (rGO). The morphologic structures of the prepared material were investigated using AFM, SEM, FTIR, UV, XPS, and Raman spectroscopic methods. The catalytic activities and stabilities toward the ORR in alkaline electrolyte were assessed using CV and LSV processes. The experimental results demonstrated that insertions of the carbon black (CB) nanospheres between the rGO sheets not only impeded the stacking of the rGO nanosheets, but also achieved the full utilization of the synergistic effects between them. The improved electrochemical catalytic activities of the tetra-β-(8-quinolinoxy) iron phthalocyanine (TQFePc) via CB/rGO hybrid support were mainly attributed to the strong π-π interaction between the TQFePc molecules and the rGO nanosheets, as well as the novel 3D sandwiched graphene/carbon nanosphere/graphene structures.

Influence of copper surface pretreatment on the kinetics of oxygen reduction reaction in 0.5 M NaCl solution: Surface characterization and electrochemical studies

The study of oxygen reduction reaction (ORR) in 0.5 M NaCl on copper revealed that oxygen reduction reaction rates are markedly influenced by the surface condition and increased in the following order: covered with PDTC < pre-reduced < passivated surfaces. On pre-reduced and passivated surfaces, the ORR proceeded via a four electron pathway limited by oxygen diffusion. When the surface is passivated, the ORR is influenced by a combination of the reduction of copper oxide and the normal kinetics of ORR at a pre-reduced surface. The partial reduction of Cu2O oxide enhances the ORR kinetics. A surface covered with PDTC represents the least reactive site towards ORR process. The current densities decreased significantly due to the limitation of O2 access to the surface by the formation of a protective barrier layer. PDTC molecules are bonded on copper surface and form an inhibitive adsorption layer, which plays a major role in slowing down O2 reduction by blocking the active cathodic sites.

Molecular Insight of the Critical Role of Ni in Pt-Based Nanocatalysts for Improving the Oxygen Reduction Reaction Probed Using an In Situ SERS Borrowing Strategy.

PtNi alloy catalysts have excellent catalytic activity and are considered some of the most promising electrocatalysts capable of replacing pure Pt for the oxygen reduction reaction (ORR). For PtNi alloys, Ni-doping can improve performance by changing the electronic and structural properties of the catalyst surface and its interaction with reaction intermediates. However, to date there is no direct spectral evidence detecting or identifying the effect of Ni on the ORR in PtNi alloy catalysts. Herein, we introduce a surface-enhanced Raman spectroscopic (SERS) "borrowing" strategy for investigating ORR processes catalyzed by Au@PtNi nanoparticles (NPs). The bond vibration of adsorbed peroxide intermediate species (*OOH) was obtained, and the effect of Ni on the interaction between surface Pt and *OOH was studied by varying the Ni content in the alloy. The frequency of the *OOH spectral band has an obvious red-shift with increasing Ni content. Combined with density functional theory (DFT) calculations, we show that Ni-doping can optimize *OOH surface binding on the Pt surface, achieving more efficient electron transfer, thus improving the ORR rate. Notably, these results evidence the SERS borrowing strategy as an effective technique for in situ observations of catalytic processes.

Effects of mechanical stress and cathodic protection on the performance of a marine organic coating on mild steel

The separate and interactive effects of mechanical stress and cathodic protection on degradation behaviour of a marine epoxy-based organic coating on Q235 steel in 3.5% NaCl solution were investigated by employing electrochemical impedance spectroscopy technique. Results revealed that both tension stress (e.g., 120 and 200 MPa) and cathodic protection (e.g., −0.8, −1.0 and −1.2 V with respect to a saturated silver/silver chloride electrode) could greatly deteriorate coating protective performance, including barrier properties, water uptake and diffusion as well as delaminated area, and meanwhile their harmful impacts could become more pronounced with the prolongation of immersion time. The interactive effect of the two factors on coating degradation was shown to be associated with their respective contribution. In addition, the degradation rate for the coating at the potentials of −0.8 and −1.0 V depended largely on the main reaction rate of oxygen reduction and hydrogen evolution, and the predominant control procedure of the two reactions could be reversed by the critical tension stress of 120 MPa.

Promoting Electrocatalytic Activity and Stability via Er0.4Bi1.6O3-δ In Situ Decorated La0.8Sr0.2MnO3-δ Oxygen Electrode in Reversible Solid Oxide Cell.

Weak electrocatalytic activity of the La0.8Sr0.2MnO3-δ (LSM) oxygen electrode at medium and low temperatures leads to decreasing performance both in the solid oxide fuel cell (SOFC) mode and the solid oxide electrolysis cell (SOEC) mode. Herein, we design an Er0.4Bi1.6O3-δ (ESB) functionalized La0.8Sr0.2MnO3-δ (labeled as LSM/ESB) oxygen electrode via a one-step co-synthesis modified Pechini method. The unique LSM/ESB with polarization resistance of only 0.029 Ω·cm2 at 750 °C enables a highly enhanced rate of oxygen reduction and evolution reaction. The single cell with the LSM/ESB electrode achieves a maximum power density of 1.747 W cm-2 at 750 °C, 2.6 times higher than that of the mechanically mixed LSM-ESB electrode (0.667 W cm-2). In the SOEC mode, it also shows the improved performance of the LSM/ESB electrode. Furthermore, the cell exhibits admirable durability of 90 h in the fuel cell mode and excellent reversibility. The better performance can be concluded as a better surface-active state and a tighter connection between the LSM and ESB particles of LSM/ESB via a co-synthesis process. This work proposes a novel strategy to advance the application of the one-step modified Pechini technology for an efficient and stable oxygen electrode.

High rate oxygen reduction reaction during corrosion of ultra-high-purity magnesium

Comprehending the corrosion mechanism of magnesium is of major interest in diverse fields. Typically, hydrogen evolution reaction is considered as the only cathodic reaction during Mg corrosion. However, recent works demonstrate importance of considering oxygen reduction reaction (ORR) as a second cathodic process at specific conditions. With oxygen micro-optode, we show that ORR rate was higher on slower corroding ultra-high-purity Mg (UHP-Mg), while lower on faster corroding commercially pure Mg (CP-Mg), where massive hydroxide layer impeded oxygen permeation. These findings shed light on yet another facet of complex mechanism of Mg corrosion.