Activity For O2 Reduction Research Articles

Dispersive Single-Atom Metals Anchored on Functionalized Nanocarbons for Electrochemical Reactions.

The use of dispersive single-atom metals anchored on functionalized carbon nanomaterials as electrocatalysts for electrochemical energy conversion reactions represents a burgeoning area of research, due to their unique characteristics of low coordination number, uniform coordination environment, and maximum atomic utilization. Here we highlight the advanced synthetic methods, characterization techniques, and electrochemical applications for carbon-based single-atom metal catalysts, and provide illustrative correlations between molecular/electronic structures and specific catalytic activity for O2 reduction, water splitting, and other emerging reactions including CO2 reduction, H2O2 production, and N2 reduction. We also discuss fundamental principles for the future design of carbon-based single-atom metal catalysts for specific electrochemical reactions. In addition, we explore the challenges and opportunities that lie ahead in further work with carbon-based single-atom metal electrocatalysts.

Efficient Solar‐Assisted O2 Reduction Using a Cofacial Iron Porphyrin Dimer Catalyst Integrated into a p‐CuBi2O4 Photocathode

A cofacial iron porphyrin heterodimer, Fe2 TPFPP-TMP showed high electrocatalytic activity, selectivity, and stability for O2 reduction to H2 O both in homogeneous non-aqueous and heterogeneous neutral aqueous solutions. When it is integrated to FTO/p-CuBi2 O4 (FTO=fluorine doped tin oxide) photocathode prepared by a simple novel method, a remarkable efficient solar-assisted O2 reduction is achieved in neutral potassium phosphate (KPi) or basic NaOH solutions saturated with O2 .

Structural and functional heterogeneity of cytochrome c oxidase in S. cerevisiae

Respiration in Saccharomyces cerevisiae is regulated by small proteins such as the respiratory supercomplex factors (Rcf). One of these factors (Rcf1) has been shown to interact with complexes III (cyt. bc1) and IV (cytochrome c oxidase, CytcO) of the respiratory chain and to modulate the activity of the latter. Here, we investigated the effect of deleting Rcf1 on the functionality of CytcO, purified using a protein C-tag on core subunit 1 (Cox1). Specifically, we measured the kinetics of ligand binding to the CytcO catalytic site, the O2-reduction activity and changes in light absorption spectra. We found that upon removal of Rcf1 a fraction of the CytcO is incorrectly assembled with structural changes at the catalytic site. The data indicate that Rcf1 modulates the assembly and activity of CytcO by shifting the equilibrium of structural sub-states toward the fully active, intact form.

Biomimicking vitamin B12. A Co phthalocyanine pyridine axial ligand coordinated catalyst for the oxygen reduction reaction

CoN4 complexes like Co phthalocyanines (CoPc) have been extensively studied as electrocatalysts for the oxygen reduction reaction (ORR) but they only promote the 2-electron reduction of O2 to give peroxide. In contrast, vitamin B12 a Co macrocyclic naturally occurring molecule has attracted the attention of the scientific community because instead of catalysing the 2-electron reduction of O2 to H2O2 like the other Co macrocycles it promotes the 4-electron reduction to H2O. Vitamin B12 possesses an axial back ligand and this seems to be the reason for its higher activity and selectivity for the 4-electron reduction of O2. To test this hypothesis, we synthetized a CoPc axially coordinated to pyridine anchored to carbon nano-tubes (CoPc-Py-CNT). The Co centre is therefore coordinated to 5 N as in vitamin B12. The modified CoPc containing catalytic material was characterized by EPR and XPS spectroscopy. Ab initio calculations, Koutecky– Levich extrapolation and Tafel plots well describe the similarities between the 2 complexes and reveal insights into the mechanism of action of Co penta-coordinated complexes. According to our results the pyridine back ligand increases the Co-O2 binding energy and making it more similar to that of Vitamin B12, favouring the splitting of the O-O bond. The back ligand then plays a crucial role in modifying Co-O2 binding energy which is a well know reactivity descriptor.

Study on the bioelectrochemistry of a horseradish peroxidase-gold nanoclusters bionanocomposite

A horseradish peroxidase (HRP)-Au nanoclusters (AuNCs) bionanocomposite was prepared simply by mixing HRP and NaAuCl4 in an alkaline aqueous solution (pH12) at 37°C for 12h under vigorous stirring. Cast-coating the HRP-AuNCs bionanocomposite and then Nafion on a glassy carbon electrode (GCE) yielded a Nafion/HRP-AuNCs/GCE. This electrode exhibited a pair of well-defined cyclic voltammetric peaks of the immobilized HRP with a formal potential of −0.389V vs SCE and an electron transfer rate constant of 3.19s−1 in pH7.0 phosphate buffer. The HRP also exhibits a high bioactivity. This electrode showed high electrocatalytic activity for reduction of both O2 and H2O2, as a result of the synergistic effects of HRP and nearby AuNCs. This electrode gave a linear amperometric response to H2O2 from 0.01 to 3.27mmolL−1 with a sensitivity of 0.86μAmM−1cm−2 and a limit of detection (LOD, S/N=3) of 0.99μM.

Isolation of yeast complex IV in native lipid nanodiscs

We used the amphipathic styrene maleic acid (SMA) co-polymer to extract cytochrome c oxidase (CytcO) in its native lipid environment from S. cerevisiae mitochondria. Native nanodiscs containing one CytcO per disc were purified using affinity chromatography. The longest cross-sections of the native nanodiscs were 11nm×14nm. Based on this size we estimated that each CytcO was surrounded by ~100 phospholipids. The native nanodiscs contained the same major phospholipids as those found in the mitochondrial inner membrane. Even though CytcO forms a supercomplex with cytochrome bc1 in the mitochondrial membrane, cyt. bc1 was not found in the native nanodiscs. Yet, the loosely-bound Respiratory SuperComplex factors were found to associate with the isolated CytcO. The native nanodiscs displayed an O2-reduction activity of ~130 electrons CytcO−1s−1 and the kinetics of the reaction of the fully reduced CytcO with O2 was essentially the same as that observed with CytcO in mitochondrial membranes. The kinetics of CO-ligand binding to the CytcO catalytic site was similar in the native nanodiscs and the mitochondrial membranes. We also found that excess SMA reversibly inhibited the catalytic activity of the mitochondrial CytcO, presumably by interfering with cyt. c binding. These data point to the importance of removing excess SMA after extraction of the membrane protein. Taken together, our data shows the high potential of using SMA-extracted CytcO for functional and structural studies.

Synthesis and electrochemistry of A2B type mono- and bis-cobalt triarylcorroles and their electrocatalytic properties for reduction of dioxygen in acid media

Two A2B mono-cobalt corroles and the corresponding bis-cobalt derivatives linked by a xanthene acyl group were synthesized, characterized as to their electrochemistry and spectroelectrochemistry in nonaqueous media and then examined as catalysts for the electroreduction of O2 in 1.0 M HClO4. The investigated mono- and bis-corroles are represented as (NH2Ph)(YPh)2CorCo(PPh[Formula: see text] and [(YPh)2CorCo(PPh[Formula: see text]]2Xac, respectively, where Cor is the trianion of the corrole, Y is a CH3 or Cl substituent on the para-position of the 5- and 15-meso-phenyl rings of the macrocycle and Xac is the xanthene acyl group linking the two macrocycles in a face-to-face arrangement. The neutral compounds were characterized by cyclic voltammetry while thin-layer spectroelectrochemistry was used to elucidate UV-visible spectra of the compounds in their electrooxidized or electroreduced forms. Rotating disk and rotating ring-disk electrode measurements were also utilized to examine the electrocatalytic activity for reduction of O2 when the face-to-face corroles were adsorbed on the electrode surface in 1.0 M HClO4. The number of electrons transferred in the catalytic electroreduction of dioxygen was calculated from currents at the disk electrode using Koutecky–Levich plots. The effect of linking the two cobalt corrole macrocycles on UV-visible spectra, redox potentials and electrocatalytic activity for the reduction of dioxygen is discussed.

Platinum Nanoparticles Supported on Nitrogen-Doped Graphene Nanosheets as Electrocatalysts for Oxygen Reduction Reaction

This paper deals with nitrogen-doped graphene nanosheets prepared using dicyandiamide precursor as a catalyst support for oxygen reduction reaction (ORR). Platinum nanoparticles supported on N-doped graphene nanosheets (Pt/NG) were studied as electrocatalysts for ORR in acid and alkaline solutions employing the rotating disk electrode (RDE) technique. Pt/NG nanomaterials were synthesised by chemical reduction of hexachloroplatinic acid using sodium borohydride or ethylene glycol as reducing agents. Surface morphology and composition of the prepared catalysts were examined by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The TEM images showed a high dispersion of Pt nanoparticles on N-doped graphene nanosheets due to strong interaction of Pt with nitrogen functionalities. The average nitrogen content was between 6 and 7 at.% according to the XPS analysis. In acidic solution, 20 wt% Pt/NG catalyst prepared by borohydride reduction showed the highest specific activity for O2 reduction from all the Pt/NG materials studied. Pt/NG nanomaterials exhibited excellent electrocatalytic activity in alkaline media, and their half-wave potentials were similar to that of commercial Pt/C catalyst. The RDE data analysis showed that the ORR on the Pt/NG catalysts proceeded via four-electron pathway.

Non-Precious Metal Catalyst That Combines Perovskite-Type Oxide and Iron Phthalocyanine for Use as a Cathode Catalyst in an Alkaline Fuel Cell

A non-precious metal catalyst was obtained by combining a perovskite-type oxide-carbon mixture (La0.6Sr0.4MnO3/C, La0.6Sr0.4CoO3/C, and La0.6Sr0.4Mn0.7Co0.3O3/C) and an iron phthalocyanine complex (Fe-Pc) with two-by-two electron O2 reduction activity. The oxygen reduction reaction (ORR) activities of the Fe-Pc/perovskite/C catalysts were investigated in alkaline media using rotating ring-disk electrode (RRDE) method. Although all of the Fe-Pc/perovskite/C catalysts showed enhanced ORR activities with a positive shift of the onset potential compared to perovskite/C and Fe-Pc/C, the number of electrons during ORR was different due to the HO2− reduction activity of the perovskite/C. Among the prepared catalysts, the Fe-Pc/La0.6Sr0.4Mn0.7Co0.3O3/C catalyst exhibited the highest catalytic activity, which was comparable to that of the Pt/C catalyst. Furthermore, oxygen reduction on this catalyst proceeds thorough an efficient 2+2 pathway with the formation of only a very small fraction of HO2− (0.5–3%).

Metalloporphyrin-modified perovskite-type oxide for the electroreduction of oxygen

Perovskite-type oxide-carbon (Vulcan XC72) mixture (La0.6Sr0.4Mn0.6Fe0.4O3/C) was modified by a metalloporphyrin (cobalt octaethylporphyrin: Co-OEP) having two-electron O2 reduction activity, and its electrochemical reduction activity for O2 (ORR) was investigated in an alkaline solution by rotating ring disk electrode (RRDE) voltammetry. The Co-OEP/La0.6Sr0.4Mn0.6Fe0.4O3/C catalyst showed improved ORR activity, with a positive shift of the onset potential. In addition, a decreased ring current compared to Co-OEP/C suggested that the quasi-four-electron reduction of O2 was also enhanced. Further experiments showed that ORR activity was also enhanced by Co-OEP-modification of other types of carbon (Ketjenblack EC600JD, Denka Black) or perovskite-type oxide (La0.6Ca0.4Mn0.6Fe0.4O3, La0.8Sr0.2Co0.6Fe0.4O3). In the case of the addition of other porphyrin complexes (cobalt tetraphenylporphyrin (Co-TPP), iron octaethylporphyrin (Fe-OEP)) to a La0.6Sr0.4Mn0.6Fe0.4O3/C catalyst, the onset potential did not shift to the positive side due to the lower activity compared to Co-OEP.

Selective formation of hydrogen peroxide by oxygen reduction on TiO2 nanotubes in alkaline media

The oxygen electrochemical reduction at nitrogen treated TiO2 nanotubes electrode shows distinctive and well-separated 2-electrons reduction peaks. The oxygen reduction was investigated in alkaline solution at titanium oxide nanotube (TON) arrays fabricated by anodizing of titanium foil in hydrogen fluoride solution followed by annealing at 450°C in nitrogen (TON-N2) atmosphere. The morphology of the arrays was characterized by SEM and the electrochemical behavior was studied by cyclic voltammetry in potassium ferrocyanide and alkaline solutions. The treated TON arrays showed a significant enhancement in conductivity and in the activity for reduction of O2 in alkaline media in comparison to the data of plain TiO2. TON arrays annealed in N2 showed a unique electrochemical behavior of two well-resolved 2-electrons O2 reduction peaks in contrast to TON arrays annealed air, which only showed a single reduction peak at more negative potential. At TON-N2 arrays, hydrogen peroxide was detected as the main product during the first reduction. The switch in mechanism is proposed to be due to the presence of oxygen vacancies at the surface of titania nanotube arrays. The finding is of a high importance for the selective production of hydrogen peroxide by electrochemical reduction of oxygen in alkaline media using TiO2 nanotubes electrode.

High‐Yield Electrosynthesis of Hydrogen Peroxide from Oxygen Reduction by Hierarchically Porous Carbon

AbstractH2O2 production by electroreduction of O2 is an attractive alternative to the current anthraquinone process, which is highly desirable for chemical industries and environmental remediation. However, it remains a great challenge to develop cost‐effective electrocatalysts for H2O2 synthesis. Here, hierarchically porous carbon (HPC) was proposed for the electrosynthesis of H2O2 from O2 reduction. It exhibited high activity for O2 reduction and good H2O2 selectivity (95.0–70.2 %, most of them >90.0 % at pH 1–4 and >80.0 % at pH 7). High‐yield H2O2 generation has been achieved on HPC with H2O2 concentrations of 222.6–62.0 mmol L−1 (2.5 h) and corresponding H2O2 production rates of 395.7–110.2 mmol h−1 g−1 at pH 1–7 and −0.5 V. Moreover, HPC was energy‐efficient for H2O2 production with current efficiency of 81.8–70.8 %. The exceptional performance of HPC for electrosynthesis of H2O2 could be attributed to its high content of sp3‐C and defects, large surface area and fast mass transfer.

High-yield electrosynthesis of hydrogen peroxide from oxygen reduction by hierarchically porous carbon.

H2O2 production by electroreduction of O2 is an attractive alternative to the current anthraquinone process, which is highly desirable for chemical industries and environmental remediation. However, it remains a great challenge to develop cost-effective electrocatalysts for H2O2 synthesis. Here, hierarchically porous carbon (HPC) was proposed for the electrosynthesis of H2O2 from O2 reduction. It exhibited high activity for O2 reduction and good H2O2 selectivity (95.0-70.2%, most of them >90.0% at pH 1-4 and >80.0% at pH 7). High-yield H2O2 generation has been achieved on HPC with H2O2 concentrations of 222.6-62.0 mmol L(-1) (2.5 h) and corresponding H2O2 production rates of 395.7-110.2 mmol h(-1) g(-1) at pH 1-7 and -0.5 V. Moreover, HPC was energy-efficient for H2O2 production with current efficiency of 81.8-70.8%. The exceptional performance of HPC for electrosynthesis of H2O2 could be attributed to its high content of sp(3)-C and defects, large surface area and fast mass transfer.

Defining the role of tyrosine and rational tuning of oxidase activity by genetic incorporation of unnatural tyrosine analogs.

While a conserved tyrosine (Tyr) is found in oxidases, the roles of phenol ring pKa and reduction potential in O2 reduction have not been defined despite many years of research on numerous oxidases and their models. These issues represent major challenges in our understanding of O2 reduction mechanism in bioenergetics. Through genetic incorporation of unnatural amino acid analogs of Tyr, with progressively decreasing pKa of the phenol ring and increasing reduction potential, in the active site of a functional model of oxidase in myoglobin, a linear dependence of both the O2 reduction activity and the fraction of H2O formation with the pKa of the phenol ring has been established. By using these unnatural amino acids as spectroscopic probe, we have provided conclusive evidence for the location of a Tyr radical generated during reaction with H2O2, by the distinctive hyperfine splitting patterns of the halogenated tyrosines and one of its deuterated derivatives incorporated at the 33 position of the protein. These results demonstrate for the first time that enhancing the proton donation ability of the Tyr enhances the oxidase activity, allowing the Tyr analogs to augment enzymatic activity beyond that of natural Tyr.

Reversible Ca(2+) switch of an engineered allosteric antioxidant selenoenzyme.

A Ca(2+) -responsive artificial selenoenzyme was constructed by computational design and engineering of recoverin with the active center of glutathione peroxidase (GPx). By combining the recognition capacity for the glutathione (GSH) substrate and the steric orientation of the catalytic selenium moiety, the engineered selenium-containing recoverin exhibits high GPx activity for the catalyzed reduction of H2 O2 by glutathione (GSH). Moreover, the engineered selenoenzyme can be switched on/off by Ca(2+) -induced allosterism of the protein recoverin. This artificial selenoenzyme also displays excellent antioxidant ability when it was evaluated using a mitochondrial oxidative damage model, showing great potential for controlled catalysis in biomedical applications.

Systematic tuning of heme redox potentials and its effects on O2 reduction rates in a designed oxidase in myoglobin.

Cytochrome c Oxidase (CcO) is known to catalyze the reduction of O2 to H2O efficiently with a much lower overpotential than most other O2 reduction catalysts. However, methods by which the enzyme fine-tunes the reduction potential (E°) of its active site and the corresponding influence on the O2 reduction activity are not well understood. In this work, we report systematic tuning of the heme E° in a functional model of CcO in myoglobin containing three histidines and one tyrosine in the distal pocket of heme. By removing hydrogen-bonding interactions between Ser92 and the proximal His ligand and a heme propionate, and increasing hydrophobicity of the heme pocket through Ser92Ala mutation, we have increased the heme E° from 95 ± 2 to 123 ± 3 mV. Additionally, replacing the native heme b in the CcO mimic with heme a analogs, diacetyl, monoformyl, and diformyl hemes, that posses electron-withdrawing groups, resulted in higher E° values of 175 ± 5, 210 ± 6, and 320 ± 10 mV, respectively. Furthermore, O2 consumption studies on these CcO mimics revealed a strong enhancement in O2 reduction rates with increasing heme E°. Such methods of tuning the heme E° through a combination of secondary sphere mutations and heme substitutions can be applied to tune E° of other heme proteins, allowing for comprehensive investigations of the relationship between E° and enzymatic activity.

Shape‐Dependent Electrocatalysis: Oxygen Reduction on Carbon‐Supported Gold Nanoparticles

AbstractCubic, octahedral and quasi‐spherical (two different particle sizes) Au nanoparticles are synthesised and dispersed in a carbon‐black powder. The size and morphology of the Au nanocatalysts is confirmed by transmission electron microscopy and X‐ray diffraction. Au nanospheres are approximately 5 and 30 nm in diameter, whereas the size of Au octahedra and nanocubes is approximately 40–45 nm. The electrocatalytic activity of these carbon‐supported particles towards the oxygen reduction reaction (ORR) is studied in 0.5 M H2SO4 and 0.1 M KOH solutions by using the rotating‐disk‐electrode method. The specific activity (SA) for O2 reduction is measured, and the highest SA is observed for Au nanocubes supported on carbon. The highest mass activities are found for the smallest Au nanoparticles. Tafel analysis suggests that the mechanism of the ORR on shape‐controlled Au/C catalysts is the same as on bulk Au.

Proton pumping by an inactive structural variant of cytochrome c oxidase

The aa3-type cytochrome c oxidases (CytcOs) from e.g. Rhodobacter sphaeroides and Paracoccus denitrificans harbor two proton-transfer pathways. The K pathway is used for proton uptake upon reduction of the CytcO, while the D pathway is used after binding of O2 to the catalytic site. The aim of the present study was to determine whether or not CytcO in which the K pathway is blocked (by e.g. the Lys362Met replacement) is capable of pumping protons. The process can not be studied using conventional assays because the O2-reduction activity is too low when the K pathway is blocked. Consequently, proton pumping with a blocked K pathway has not been demonstrated directly. Here, the Lys362Met and Ser299Glu structural variants were reconstituted in liposomes and allowed to (slowly) become completely reduced. Then, the reaction with O2 was studied with μs time resolution after flash photolysis of a blocking CO ligand bound to heme a3. The data show that with both the inactive Lys362Met and partly active Ser299Glu variants proton release occurred with the same time constants as with the wild-type oxidase, i.e. ~200μs and ~3ms, corresponding in time to formation of the ferryl and oxidized states, respectively. Thus, the data show that the K pathway is not required for proton pumping, suggesting that D and K pathways operate independently of each other after binding of O2 to the catalytic site.

Experimental Challenges to the Theory of the Oxygen Reduction Reaction on Pt and Pt Alloys

The conventionally accepted reason that platinum alloys are more active for the O2 reduction reaction than pure platinum is that reaction products such as adsorbed oxygen atoms (Oad) and hydroxyls (OHad) are less strongly adsorbed on the alloy surface, allowing more O2 to adsorb [1]. This is a reasonable view, but experimental results obtained in this laboratory suggest a much different picture, one in which higher coverages of reaction products such as Oad and OHad on alloy surfaces are correlated with higher O2 reduction activity [2-4]. Specifically, with X-ray photoelectron spectroscopic measurements combined with electrochemical measurements on the same surface (EC-XPS), we find a buildup of Oad, with increasing amounts at lower potentials [2,3]. This result is just the opposite of that expected from the conventional model. Similarly, with quartz crystal microbalance/electrochemical measurements (EQCM), we find that there are elevated levels of oxygenated species on the alloy surface during active O2 reduction, even though the mass resolution is not sufficiently high to distinguish between Oad, OHad and H2Oad. The Brønsted-Evans-Polanyi (BEP) principle, which states that the activation energies of a set of similar reactions are proportional to their enthalpies [5], has become well accepted, even though it is an empirical relationship. This principle implies that the adsorption energy of two Oad atoms should be large compared to that of the undissociated O2 molecule, specifically, in an electrochemical potential region in which the overall reaction is energetically favored. Furthermore, it implies that a platinum skin/platinum alloy surface such as Pt skin/Pt3Co(111) should have a larger overall negative change in energy for the O2dissociation step than that for pure Pt(111). This simplest of all models seems consistent with our experimental results. However, most theoretical calculations have found a weakening of the adsorption strengths of all of the oxygenated species, i.e., O2, Oad and OHadon Pt skin/Pt alloy surfaces. Thus, this situation presents a highly intriguing challenge for theoreticians. Of course, it can be conceived that reaction products might be so tightly bound to the surface that the desorption process might become rate-limiting. However, our experimental results are inconsistent with this idea. Finally, we note that both our EC-XPS and EQCM results clearly show that the coverages of oxygenated species such as Oad and OHad are much different for the oxygenated vs. deoxygenated solutions in the potential region in which O2 reduction is proceeding at significant rates. This is especially true for the Pt skin/Pt3Co alloy surface. This is because a high rate of O2reduction inevitably implies a high yield of dissociated products. In our presentation, based on recent DFT calculations, we will suggest a reasonable solution to the dilemma described above. We will also comment on the need to take into account orbital energies, as well as the overall Fermi energy, in order to fully understand the energetics of key reaction such as O2 dissociation. Acknowledgement: The authors gratefully acknowledge support from the “Research on Nanotechnology for High Performance Fuel Cells” project of NEDO, Japan. References Y. Xu, A. V. Ruban, and M. Mavrikakis, J. Amer. Chem. Soc., 126, 4717-4725 (2004).M. Wakisaka, M. Watanabe, and H. Uchida, Mechanism of an Enhanced Oxygen Reduction Reaction at Platinum-Based Electrocatalysts: Identification and Quantification of Oxygen Species Adsorbed on Electrodes by X-Ray Photoelectron Spectroscopy. In Fuel Cell Science: Theory, Fundamentals, and Biocatalysis, Editors, A. Wieckowski, J. K. Nørskov, pp. 147-168, John Wiley & Sons, Inc., Hoboken, NJ, USA (2010).M. Watanabe, D. A. Tryk, M. Wakisaka, H. Yano, H. Uchida, Electrochim. Acta, 84, 187-201 (2012).J. Omura, M. Wakisaka, D. A. Tryk, H. Uchida, and M. Watanabe, submitted.T. Bligaard, J. K. Nørskov, S. Dahl, J. Matthiesen, C. H. Christensen, J. Sehested, J. Catal. 224, 206-217 (2004).

Electrochemical Quartz Crystal Microbalance Analysis of the Oxygen Reduction Reaction on Pt-Based Electrodes. Part 2: Adsorption of Oxygen Species and ClO4– Anions on Pt and Pt–Co Alloy in HClO4 Solutions

To gain deeper insight into the role of adsorbed oxygenated species in the O2 reduction reaction (ORR) kinetics on platinum and platinum-cobalt alloys for fuel cells, we carried out a series of measurements with the electrochemical quartz crystal microbalance (EQCM) and the rotating disk electrode (RDE) in acid solution. The effects of anion adsorption on the activities for the ORR were first assessed in HClO4 and HF electrolyte solutions at various concentrations. In our previous work (Part 1), we reported that the perchlorate anion adsorbs specifically on bulk-Pt, with a Frumkin-Temkin isotherm, that is, a linear relationship between Δm and log[HClO4]. Here, we find that the specific adsorption on the Pt-skin/Pt3Co alloy was significantly stronger than that on bulk-Pt, in line with its modified electronic properties. The kinetically controlled current density j(k) for the O2 reduction at the Pt-skin/Pt3Co-RDE was about 9 times larger than that of the bulk-Pt-RDE in 0.01 M HClO4 saturated with air, but the j(k) values on Pt-skin/Pt3Co decreased with increasing [HClO4] more steeply than in the case of Pt, due to the blocking of the active sites by the specifically adsorbed ClO4(-). We have detected reversible mass changes for one or more adsorbed oxygen-containing species (Ox = O2, O, OH, H2O) on the Pt-skin/Pt3Co-EQCM and Pt-EQCM in O2-saturated and He-purged 0.01 M HClO4 solutions, in which the specific adsorption of ClO4(-) anions was negligible. The coverages of oxygen species θ(Ox) on the Pt-skin/Pt3Co in the potential range from 0.86 to 0.96 V in the O2-saturated solution were found to be larger than those on pure Pt, providing strong evidence that the higher O2 reduction activity on the Pt3Co is correlated with higher θ(Ox), contrary to the conventional view.