Oxygen Reduction Catalysis Research Articles

Sn Nanoclusters Confined in COP‐Derived Carbon for Catalytic Oxygen Reduction Reaction

AbstractThe development of catalysts composed of single atoms is crucial for enhancing the performance of oxygen reduction reaction (ORR). However, the unsatisfactory intrinsic activity of these catalysts still poses a major challenge, limiting their overall effectiveness. One approach to addressing this challenge is the introduction of metal clusters, which can form a synergistic effect with the single atoms, ultimately improving their performance. In this study, core‐shell structured carbon polymer is constructed with Zn atoms and Sn nanoclusters by directly subjecting pyrolysis of the covalent organic polymer (COP) and metal organic framework (MOF) (COP@MOF). The thin COP shell serves a dual purpose: it prevents the collapse and aggregation of zeolitic imidazolate framework‐8 (ZIF‐8) and promotes the formation of mesopores, facilitating mass transport and enhancing the graphitization degree to improve conductivity. The resulting Sn‐COP@MOF800 exhibits promising catalytic performance in the ORR, demonstrating a half‐wave potential of 0.81 V and current density of 5.56 mA cm−2 in 0.1 m KOH, which is comparable to that of Pt/C. This study provides new ideas for exploring the application of metal single atoms and metal nanoclusters in ORR catalysis through synergistic effects.

Small amount but big impact: Trace oxygen interstitially inserted PtCu alloys by microalloying for efficient oxygen reduction catalysis

Small amount but big impact: Trace oxygen interstitially inserted PtCu alloys by microalloying for efficient oxygen reduction catalysis

Core-shell Co-NC@NC nanomaterial for efficient oxygen reduction reaction

Transition metal and nitrogen doped carbons (M-N-C) catalysts present significant potential as substitutes for platinum-carbon (Pt/C) in catalyzing oxygen reduction reaction (ORR). Hence, we employ an epitaxial growth strategy to prepare Zn/Co-ZIF@ZIF-8 crystals with core-shell structure. Subsequent pyrolysis and acid etching produce highly porous cobalt-doped nitrogen materials for ORR investigation. The resulting Co-NC@NC catalyst demonstrates a graded porous structure alongside remarkable conductivity, possessing a specific surface area measuring 623 m2 g−1. It showcases heightened ORR activity with a half-wave potential (E1/2) of 0.886 V, superior kinetic performance (illustrated by an extremely low Tafel slope measuring 45.98 mV/dec), and strengthened stability (with mere 25 mV day after 40,000 cycles) when contrast with Pt/C catalysts in 0.1 M KOH. Additionally, it exhibits notable activity and stability in acidic environments. These remarkable attributes are attributable to the graded structure, which facilitates rapid mass transfer, a high electrochemically active area that exposes highly dispersed active sites, and a conductive carbon skeleton network that promotes electron transfer.

Surface modified FeCoZn-ZIF derived polyhedral electrocatalysts for ORR under alkaline and acidic conditions

Electrocatalysts for catalyzing oxygen reduction reactions at variable pH conditions are essential for energy conversion and storage. Herein, Fe@FeCoZn–CN electrocatalysts were prepared with internal and external doping approach. The Fe@FeCoZn–CN electrocatalyst exhibits a desirable ORR performance in both acid and alkaline electrolytes. Specifically, the half-wave potential (E1/2) of Fe@FeCoZn–CN electrocatalyst is 0.890 V which far beyond Pt/C electrocatalyst (0.839 V) in alkaline electrolyte. In addition, Fe@FeCoZn–CN electrocatalyst also exhibits improved ORR activity (E1/2 = 0.801 V) compared to Pt/C (0.797 V) electrocatalysts in acidic electrolytes. What's exciting is that the rechargeable ZABs based on Fe@FeCoZn–CN electrocatalysts exhibit an impressive performance with a favorable open-circuit potential of 1.517 V and a promising specific capacity is 833.7 mA h gzn−1, good charge/discharge cycle stability. The remarkable ORR catalytic performance of Fe@FeCoZn–CN electrocatalysts can be traced to the internal doping of metals which prevent excessive metal aggregation and surface modified which can increase the metal loading to expose more active sites.

Dealloyed Pt74Ni26 and Pt26Ni74 Electrodeposited Thin Film Electrocatalysts for Oxygen Reduction

Electrodeposition and microstructure of thin films close to Pt75Ni25 and Pt25Ni75 stoichiometry are described and their catalytic oxygen reduction reaction performance, dealloying, and strain evolution detailed. Multiple techniques are used to characterize the morphology, crystalline structure, and chemical homogeneity of the as-deposited and dealloyed films. A fine-scale percolating network of lower-density regions is evident in the as-deposited Pt74Ni26 films while the as-deposited Pt26Ni74 films are more homogenous and compact. Electrodeposition is accompanied by development of significant in-plane tensile stress that increases at more negative growth potentials to reach 1.28 GPa for as-deposited Pt26Ni74. Dealloying of the near-surface regions of Pt74Ni26 is accompanied by limited expansion or opening of the low-density regions while massive dealloying of the highly stressed Pt26Ni74 results in shrinkage, extensive cracking, and formation of a bi-continuous nanoporous structure with an average pore diameter close to 5 nm. Relative to electrodeposited Pt, the alloy films exhibit enhanced area-specific oxygen reduction reaction activity (at 0.95 V vs RHE, iR-corrected) that amounts to a factor of 3.4 for dealloyed Pt74Ni26 and 5.1 for dealloyed Pt26Ni74 while the Pt-based mass activity increased by a factor of 5.1 and 12.3, for the respective films.

Inducing Microstrain in Electrodeposited Pt through Polymer Addition for Highly Active Oxygen Reduction Catalysis

Inducing Microstrain in Electrodeposited Pt through Polymer Addition for Highly Active Oxygen Reduction Catalysis

Catalyzing oxygen reduction reaction with a worm-like oxide Ca3Co2O6 in solid-oxide fuel cells

Catalyzing oxygen reduction reaction with a worm-like oxide Ca3Co2O6 in solid-oxide fuel cells

Subnanometric Osmium Clusters Confined on Palladium Metallenes for Enhanced Hydrogen Evolution and Oxygen Reduction Catalysis.

Highly efficient, cost-effective, and durable electrocatalysts, capable of accelerating sluggish reaction kinetics and attaining high performance, are essential for developing sustainable energy technologies but remain a great challenge. Here, we leverage a facile heterostructure design strategy to construct atomically thin Os@Pd metallenes, with atomic-scale Os nanoclusters of varying geometries confined on the surface layer of the Pd lattice, which exhibit excellent bifunctional properties for catalyzing both hydrogen evolution (HER) and oxygen reduction reactions (ORR). Importantly, Os5%@Pd metallenes manifest a low η10 overpotential of only 11 mV in 1.0 M KOH electrolyte (HER) as well as a highly positive E1/2 potential of 0.92 V in 0.1 M KOH (ORR), along with superior mass activities and electrochemical durability. Theoretical investigations reveal that the strong electron redistribution between Os and Pd elements renders a precise fine-tuning of respective d-band centers, thereby guiding adsorption of hydrogen and oxygen intermediates with an appropriate binding energy for the optimal HER and ORR.

Catalyzing oxygen reduction by morphologically engineered ZIF-derived carbon composite catalysts in dual-chamber microbial fuel cells

From the past decades, microbial fuel cells (MFCs) have evolved as a green alternative to produce electrical energy from organic matter degradation. Cathode modification significantly enhances the overall MFC performance. In this work, we report on ZIF-8 and carbon nanotubes (CNTs) derived catalyst materials as cathode for MFC. The catalysts were prepared via high-temperature pyrolysis at 900 °C and were physically characterized by various analytical techniques. All the catalyst materials carry tubular arrangements of CNTs covering the ZIF-8 crystals and exhibit highly micro-mesoporous texture. The electrocatalytic activity for oxygen reduction reaction (ORR) was studied in 0.1 M phosphate buffer at a catalyst loading of 0.2 mg cm−2. The FeCo-N-C@900 catalyst showed the highest ORR activity with half-wave potential of 0.71 V vs RHE and limiting current density of −5.62 mA cm−2 at 1900 rpm. When tested in MFC, FeCo-N-C@900 coated cathode delivered the maximum power density of 1557 mW m−2 (comparable to Pt/C catalyst reaching Pmax of 1681 mW m−2) with chemical oxygen demand (COD) removal efficiency of 87.3%. The Next generation DNA sequencing analysis revealed the accumulation of various exoelectrogenic bacterial strains i.e., Bacillus, Desulfovibrio, Comamonadaceae sp. etc. commonly found in anaerobic biomass and showing the successful enrichment of the biofilm responsible for oxidizing organic matter at the anode. The present study illustrates the potential of transitional metal-doped ZIF-8 and CNTs composite electrocatalysts for enhancing the power output of MFC with generating promising power and current densities.

Pseudocapacitance behavior enables efficient and stable electrochemical energy conversion and storage in glucose/air enzymatic biofuel cells

Constructing an integrated system with high-efficiency and stable energy conversion and storage (ECS) is of great significance but remains challenges. Herein, we report a biodevice consisting of a bioanode of tetrathiafulvalene/glucose oxidase (TTF/GOx) immobilized on asphalt-derived porous carbon (APC) for catalyzing glucose oxidation and a biocathode of 2,2’-azinobis(3-ethylbenzothiazoline-6-sulfonate)/bilirubin oxidase (ABTS/BOD) immobilized on APC for catalyzing oxygen reduction, to achieve ECS with high-efficiency and excellent stability. The redox mediators, TTF and ABTS, used at the bioanode and biocathode, respectively, simultaneously mediate electron transfer to release electric current on discharging and serve as pseudocapacitors to achieve charge storage at open-circuit conditions, enabling high power density and self-charge capability. The biodevice of the above configuration delivers a peak power output of 5.01 mW cm−2 in the pulse discharge mode with cell voltage remaining 93.7 % of its initial value after 100 pulse discharge/self-charge cycles. This work provides a highly efficient solution to address the low power density and poor stability of the conventional enzymatic biofuel cells, showing great implications for small, implantable and wearable electronics.

First-principle calculations study of oxygen reduction electrocatalyst: Single transition metal supported on a brand-new graphitic carbon nitride (g-C7N3) substrate

Single-atom catalysts (SACs) possess promising potential as materials to catalyze oxygen reduction reaction (ORR) on account of high atomic utilization efficiency, tunable electronic structure, and exceptional catalytic performance. The ORR activities of graphite carbonitride (g-C7N3) supported 3d, 4d, and 5d transition metals are investigated. Eleven kinds of TM-C7N3 structures have been found to have good stability by computing formation energy and dissolution potential. Furthermore, density of states analysis shows a strong interaction of the metal atom and the coordination N atoms, which gives satisfactory stability of TM-C7N3. Among eleven TM-C7N3, the binding energy of reaction species on Rh-C7N3, Ni-C7N3, and Pt-C7N3 are closer to those of Pt(111), showing that they have good ORR activity. In addition, good linear relationships exist between the adsorption free energy of *OH (∆G*OH) and that of *OOH and *O, implying that ∆G*OH can be put forward as a trustworthy activity descriptor. Promisingly, the ηORR values of Rh-C7N3, Ni-C7N3, and Pt-C7N3 are 0.32, 0.38, and 0.44 V, respectively, even lower than the overpotential value of Pt(111). This suggests that these three catalysts demonstrate superior catalytic activity compared to Pt(111).

Amorphization Activated Multimetallic Pd Alloys for Boosting Oxygen Reduction Catalysis.

Amorphous nanomaterials have drawn extensive attention owing to their unique features, while amorphization on noble metal nanomaterials still remains formidably challenging. Herein, we demonstrate a universal strategy to synthesize amorphous Pd-based nanomaterials from unary to quinary metals through the introduction of phosphorus (P). The amorphous Pd-based nanoparticles (NPs) exhibit generally promoted oxygen reduction reaction (ORR) activity and durability compared with their crystalline counterparts. Significantly, the quinary P-PdCuNiInSn NPs, benefiting from the amorphous structure and multimetallic component effect, exhibit mass activities as high as 1.04 A mgPd-1 and negligible activity decays of 1.8% among the stability tests, which are much better than values for original Pd NPs (0.134 A mgPd-1 and 28.4%). Experimental and theoretical analyses collectively reveal that the synergy of P-induced amorphization and the expansion of metallic components can considerably lower the free energy changes in the rate-determined step, thereby explaining the positive correlation with the catalytic activity.

Catalytic reduction of oxygen to water by non-heme iron complexes: exploring the effect of the secondary coordination sphere proton exchanging site.

In this study, we prepared non-heme FeIII complexes (1, 2, and 3) of an N4 donor set of ligands (H2L, Me2L, and BPh2L). 1 is supported by a monoanionic bispyridine-dioxime ligand (HL). In 2 and 3, the primary coordination sphere of Fe remained similar to that in 1, except that the oxime protons of the ligand were replaced with two methyl groups and a bridging -BPh2 moiety, respectively. X-ray structures of the FeII complexes (1a and 3a) revealed similar Fe-N distances; however, they were slightly elongated in 2a. The FeIII/FeII potential of 1, 2, and 3 appeared at -0.31 V, -0.25 V, and 0.07 V vs. Fc+/Fc, respectively, implying that HL and Me2L have comparable donor properties. However, BPh2L is more electron deficient than HL or Me2L. 1 showed electrocatalytic oxygen reduction reaction (ORR) activity in acetonitrile in the presence of trifluoroacetic acid (TFAH) as the proton source at Ecat/2 = -0.45 V and revealed selective 4e-/4H+ reduction of O2 to H2O. 1 showed an effective overpotential (ηeff) of 0.98 V and turnover frequency (TOFmax) of 1.02 × 103 s-1. Kinetic studies revealed a kcat of 2.7 × 107 M-2 s-1. Strikingly, 2 and 3 remained inactive for electrocatalytic ORR, which established the essential role of the oxime scaffolds in the electrocatalytic ORR of 1. Furthermore, a chemical ORR of 1 has been investigated using decamethylferrocene as the electron source. For 1, a similar rate equation was noted to that of the electrocatalytic pathway. A kcat of 6.07 × 104 M-2 s-1 was found chemically. Complex 2, however, underwent a very slow chemical ORR. Complex 3 chemically enhances the 4e-/4H+ reduction of O2 and exhibits a TOF of 0.24 s-1 and a kcat value of 2.47 × 102 M-1 s-1. Based on the experimental observations, we demonstrate that the oxime backbone of the ligand in 1 works as a proton exchanging site in the 4e-/4H+ reduction of O2. The study describes how the ORR is affected by the tuning of the ligand scaffold in a family of non-heme Fe complexes.

Pore-edge graphitic nitride-dominant hierarchically porous carbons for boosting oxygen reduction catalysis

The construction of pore structures at different scales (atomic defect and molecular porous structures) is the most promising method to achieve excellent ORR catalytic activity for carbon-based catalysts.

Orbital electron delocalization of axial-coordinated modified FeN4 and structurally ordered PtFe intermetallic synergistically for efficient oxygen reduction reaction catalysis.

Regulating the chemical environment of materials to optimize their electronic structure, leading to the optimal adsorption energies of intermediates, is of paramount importance to improving the performance of electrocatalysts, yet remains an immense challenge. Herein, we design a harmonious axial-coordination Pt x Fe/FeN4CCl catalyst that integrates a structurally ordered PtFe intermetallic with an orbital electron-delocalization FeN4CCl support for synergistically efficient oxygen reduction catalysis. The obtained Pt2Fe/FeN4CCl with a favorable atomic arrangement and surface composition exhibits enhanced oxygen reduction reaction (ORR) intrinsic activity and durability, achieving a mass activity (MA) and specific activity (SA) of 1.637 A mgPt -1 and 2.270 mA cm-2, respectively. Detailed X-ray absorption fine spectroscopy (XAFS) further confirms the axial-coupling effect of the FeN4CCl substrate by configuring the Fe-N bond to ∼1.92 Å and the Fe-Cl bond to ∼2.06 Å. Additionally, Fourier transforms of the extended X-ray absorption fine structure (FT-EXAFS) demonstrate relatively prominent peaks at ∼1.5 Å, ascribed to the contribution of the Fe-N/Fe-Cl, further indicating the construction of the FeN4CCl moiety structure. More importantly, the electron localization function (ELF) and density functional theory (DFT) further determine an orbital electron delocalization effect due to the strong axial traction between the Cl atoms and FeN4, resulting in electron redistribution and modification of the coordination surroundings, thus optimizing the adsorption free energy of OHabs intermediates and effectively accelerating the ORR catalytic kinetic process.

Machine learning enabled exploration of multicomponent metal oxides for catalyzing oxygen reduction in alkaline media

Machine learning can map and predict the oxygen reduction reaction performance of multicomponent metal oxides in alkaline media.

A self-cleaning window for high-efficiency photodegradation of indoor formaldehyde

Formaldehyde (HCHO) as an indoor air pollutant released by new furniture and decorative materials is of great concern. Developing a self-cleaning device to remove HCHO is an ideal way to improve indoor air quality. In this study, a self-cleaning window with a multilayered structure constructed from fluorine-doped tin oxide/bismuth tungstate/resorcinol-formaldehyde resin (FTO/Bi2WO6/RF) has been fabricated, which is capable of degrading HCHO in natural indoor condition. The as-fabricated device could utilize the natural room light and promote the generation and transfer of the photocatalytic carriers in Bi2WO6, which subsequently delivers a good catalytic oxygen reduction efficiency in RF to produce hydrogen peroxide (H2O2). The as-synthesized H2O2 could further split into hydroxyl radicals (•OH), then oxide the HCHO molecules in the air. The present study demonstrates a novel and efficient strategy to fabricate a transparent multifunctional window for self-cleaning indoor gaseous pollutants, the concept is of great importance to be expanded in a broad range of indoor furniture for in-house air pollution control.

Improvement of Oxygen Reduction Reaction Performance of Fe-N-C Catalyst

Fuel cells are gaining worldwide attention as an acceptable technology for achieving carbon neutrality. However, existing fuel cells use large amounts of precious metals, which limits their widespread adoption. Precious metal-free fuel cells have been studied in our laboratory. The oxidation-reduction reaction (ORR) at the cathode of the fuel cell must start at a higher potential and proceed smoothly in a four-electron reduction reaction without producing hydrogen peroxide1,2. We have synthesized iron-based complex catalysts using the method reported by Plamen Atanassov3 et al. Iron nitrate dihydrate is mixed in aqueous solution with glucose, 2-methylimidazole, and zinc nitrate hexahydrate, followed by hydrothermal synthesis at 200°C for 24 hours. It is then acid-treated with nitric acid to dissolve excess metallic iron, and the process is repeated twice at 950°C to complete the Fe-N-C catalyst. However, SEM and XRD analysis confirmed the presence of large amounts of metallic iron. In response to these results, the synthetic process of the Fe-N-C catalyst was repeatedly improved, and the prepared catalyst was subjected to in-situ XAFS (X-ray absorption fine structure) analysis using synchrotron radiation at SPring-8 (Fig. 1). The peak around 7110 eV is significantly different from that of metallic iron (Fe foil), indicating that iron complex, iron phthalocyanine (II), and it is like the peak of iron phthalocyanine (II), confirming that the prepared Fe-N-C catalyst forms a good complex. The performance of the Fe-N-C catalyst with the confirmed complexation was then investigated, and a cathode that exhibited ORR performance comparable to that of the Pt catalyst was successfully synthesized (Fig. 2). In the future, further improvement of the catalyst preparation process will be discussed to develop a catalyst with much better performance than Pt.Reference 1N. Yamamoto, D.Matsumura, Y. Hagihara, K.Tanaka, Y. Hasegawa, K. Ishii, H. Tanaka, “Investigation of hydrogen superoxide adsorption during ORR on Pt/C catalyst in acidic solution for PEFC by in-situ high energy resolution XAFS”, Jounal of Power Sources, 557, 15, (2023), 232508 2S. Kusano, D. Matsumura, K. Ishii, H. Tanaka, J. Mizuki, “Electrochemical Absorption on Pt Nanoparticles in alkaline Solution Observed Using in-situ High Energy Resolution X-ray Absorption Spectroscopy”, Nanomaterials, 9, 4, (2019), 642 3 R. Gokhale, L-K. Tsui, K. Roach, Y. Chen, M. M. Hossen, K. Artyushkova, F. Garzon, p. Atanassov, “Hydrothermal synthesis of platinum-Group-Metal-Free Catalysts: Structural Elucidation and Oxygen Reduction Catalysis”, ChemElectroChem, 5, 14, (2017), 1848-1853 Figure 1

(Invited) Understanding the Effects of Metal Nanoparticle Exsolution from La0.3Ca0.7Fe0.7Cr0.3O3-δ Perovskites on CO2-CO Electrocatalysis

Solid Oxide Fuel Cells (SOFCs) and Solid Oxide Electrolysis Cells (SOECs) are highly useful devices, capable of generating and storing large amounts of energy, respectively.1 They can do this by catalyzing CO oxidation at a SOFC anode and CO2 reduction (CO2RR) at a SOEC cathode, while the other electrode catalyzes oxygen reduction or evolution. The conduction of oxide ions through the electrolyte completes the circuit, making Solid Oxide Cells (SOCs) an excellent choice for clean energy production and use since there are no undesired byproducts.1 While traditional SOC electrodes are composed of oxide-conducting ceramics mixed with electronically conducting metals,1 a newer category of catalysts are Mixed Ionic Electronic Conductors (MIECs), with one example being the perovskite La0.3M0.7Fe0.7Cr0.3O3-δ (M = Sr, Ca) (LMFCr), investigated heavily by our group.2,3,4 As an MIEC, the full surface of LMFCr is electrochemically active, giving excellent activity at both the cathode and anode, including for CO2RR and CO oxidation.2,3 However, efforts are being made to further improve the CO2RR-CO oxidation kinetics and durability, with the Ca analogue having a better chemical match with standard electrolytes.4 One approach used recently to improve MIEC oxide performance is B-site doping with transition metals (TMs) while also creating an A-site deficiency, resulting in nanoparticle (NP) formation (exsolution) when the perovskite is subjected to reducing conditions.2 For instance, Fe-Ni NPs of a ~20 nm average size can be exsolved from (La0.3Ca0.7)0.95Fe0.7Cr0.25Ni0.05O3-δ(LCFCrNi), even at 600 °C in 70CO2:30CO (pO2 ~10-18 atm). Furthermore, NP features can easily be tailored by changing the reducing conditions or dopant used.2 In general, higher temperatures and lower pO2 lead to larger NPs over time, and more easily reducible metals tend to exsolve first under less harshly reducing conditions.2 Recent studies have suggested that NP formation enhances electrocatalytic activity by creating additional sites of reactivity, suggesting that strong NP-substrate interactions are important to catalysis.5 However, there is no clear understanding of the role played by exsolved NPs in catalyzing SOC reactions. To gain further insights, detailed electrochemical studies of LCFCrNi electrodes were done on 1-inch diameter cells constructed using Samarium-Doped Ceria buffered Scandia-Stabilized Zirconia electrolyte substrates. LCFCrNi was made into an ink and tape-cast on 0.5 cm2 on one side (working electrode, WE) and 1 cm2 on the other (counter electrode, CE) on each substrate. The cells were sintered at 1100 °C for 2 h, coated with Au ink, and sintered at 850 °C for 1 h. Electrochemical Impedance Spectroscopy (EIS) was performed at 600 °C with 70CO2:30CO at the WE and air at the CE, followed by exsolution in 5H2:95N2 at a higher temperature, and then EIS was repeated multiple times under the same conditions at 600 °C. Cells were imaged via Scanning Electron Microscopy (SEM) after ramping down to room temperature in N2 to determine the size and distribution of the NPs for each set of exsolution conditions.Under all conditions employed, the polarization resistance (Rp) was found to be stable before exsolution occurred, but started decreasing once the NPs formed, especially via a shrinking of the low frequency resistance. The low frequency resistance has been associated with CO oxidation,2 so the fact that it improves with exsolution is an indication that the increased electrode area serves to improve CO oxidation more than CO2RR. When exsolution was carried out at 800 °C for 25 h, Rp decreased more rapidly than after exsolution at 800 °C for 14 h. Exsolution at 800 °C for 25 h also showed a more rapid decrease in Rp compared to 700 °C exsolution for 25 h. These results argue that the initial formation of larger NPs (formed after longer time or at a higher temperature) results in a faster increase in the active surface area of the electrode at the lower 600 °C temperature. Further experiments are being carried out to better understand whether it is the growth of NPs or new NP formation after higher temperature exsolution that is the reason behind this observation. The results of operando synchrotron studies in CO2/CO environments before and after exsolving, as well as the use of different transition metal dopants, are also being investigated for this purpose.

Construction of Warped Graphitic Layers from Fullerene Soot and Study of Their Catalytic Oxygen Reduction Activity

Construction of Warped Graphitic Layers from Fullerene Soot and Study of Their Catalytic Oxygen Reduction Activity