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Abstract: Owing to the high cost of technologies utilizing the oxygen reduction reaction (ORR) in fuel cell applications, considerable efforts have been recently made to develop non‐precious metal electrocatalysts for the commercialization of the low‐temperature polymer electrolyte membrane fuel cells (LT‐PEMFCs). By extension, non‐precious‐metal electrocatalysts can be a cost‐effective solution for the commercialization of high‐temperature PEMFCs (HT‐PEMFCs). However, no previous reports have been published regarding the applicability. Herein, we demonstrate that a hierarchical mesoporous iron and nitrogen co‐doped carbon (Fe/N/C) electrocatalyst is able to efficiently electrocatalyze the ORR in a phosphoric acid electrolyte with a half‐wave potential of 0.72 V (only 170 mV deviation from conventional Pt/C) and high selectivity (electron‐transfer number >3.95) with a mild overpotential. Furthermore, we fabricated HT‐PEMFC devices on the basis of hierarchical mesoporous Fe/N/C electrocatalysts and non‐aqueous electrolytes, which exhibited a high performance, over 20 mW/cm2. Besides, the optimal hierarchical porosity of the mesoporous Fe/N/C catalyst contributes to its high ORR activity. It is considered that it provides a large surface area for electrocatalytic ORR, and improves the proton and oxygen transport properties. [ABSTRACT FROM AUTHOR]

Direct electrostatic interactions between a charged Pt surface and oppositely charged spectator ions are utilized for the enhancement of oxygen reduction reaction (ORR) activity in both KOH and H 3 PO 4 solutions. Zwitterionic L-cysteine molecules functionalized on a Pt surface are turned outwards to afford differing surface charges in either alkaline (−) or acid solutions (+). In KOH solution, this leads to the selective impediment of interactions between OH − and K + with the Pt surface through repulsive and attractive interactions of the negatively charged –COO − group of L-cysteine, respectively. In H 3 PO 4 solution, the phosphoric acid molecule and its anion are effectively captured by the positively charged –NH 3+ moieties of L-cysteine. Behaviors of the spectator species hindering the ORR are systematically controlled through direct electrostatic interactions with the functional groups of L-cysteine in each electrolyte, resulting in a Janus Pt catalyst for superior ORR in both alkaline and acid electrolytes. [ABSTRACT FROM AUTHOR]

It is demonstrated that the electroactivity of the oxygen reduction reaction (ORR) of Pt depends on the structure of a support. Highly conductive two-dimensional titanium carbide (Ti 3 C 2) was selected as the support for Pt because of the expected strong metal-support interaction (SMSI) between Pt and Ti. To control the edge-to-basal ratio, the number of Ti 3 C 2 layers was modulated by exfoliation. Pt nanoparticles (4 nm) were loaded on three different Ti 3 C 2 supports including multi-, few-, and mono-layered Ti 3 C 2 (22L-, 4L-, and 1L-Ti 3 C 2 , respectively). The edge-to-basal ratio of layered Ti 3 C 2 increased as the number of layers increased. The edge-dominant support (22L-Ti 3 C 2) donated more electrons to Pt than the basal-dominant supports (4L-Ti 3 C 2 and 1L-Ti 3 C 2). As a result, electron-rich Pt with less d-band vacancies (e.g., Pt/22L-Ti 3 C 2) showed higher ORR activity. In addition, the electron transfer from the support to Pt inducing the strong interaction between Pt and Ti improved the durability of the ORR electroactivity of Pt. Image 1 • Effects of the support structure-activity relationship on ORR were demonstrated. • Pt was deposited on edge-dominant Ti3C2 to basal-dominant Ti3C2. • Edge-dominant Ti3C2 donates more electrons to Pt compared to basal-dominant Ti3C2. • Electron-rich Pt on edge-dominant Ti3C2 shows superior activity and stability. [ABSTRACT FROM AUTHOR]

Abstract: To investigate the enhancement of the oxygen reduction reaction (ORR) activity on a carbon-supported PtAu alloy nanoparticle catalyst, the catalyst was subject to heat treatment at 423K under a CO or Ar atmosphere. The surface composition was analyzed by XPS and the composition was shown to increase from 66±2% (PtAu-AP) to 74±2% (PtAu-CO) after heat treatment under a CO atmosphere, which was confirmed by electrochemical techniques, while the bulk composition was invariant at 55%. For the oxygen reduction reaction (ORR), the mass activity of PtAu-CO increased by 75.6% (33.2 A/gPt) when compared to that of PtAu-AP (18.9 A/gPt). Since the increase in EAS was only 15.8%, it was concluded that the specific activity was enhanced by 52.6% due to surface Pt segregation after heat treatment under a CO atmosphere. The enhanced specific activity was attributed to the reduced OH adsorption energy which was characterized by measuring the potential of total zero charge. The weaker OH adsorption was resulted from the higher Pt/Au ratio at the surface layers. [Copyright &y& Elsevier]

As cathode electrocatalysts for alkaline anion exchange membrane fuel cells (AAEMFCs), La 0.8 Sr 0.2 MnO 3 + δ electrocatalysts were synthesized by Pechini's method at various heat treatment temperatures (HTT). With HTT increase from 600 to 900 °C, the surface area gradually decreased 30.6 to 6.0 m 2 g − 1 , while impurity phase was not detected for all HTTs. The specific activity for the oxygen reduction reaction was analyzed to increase with HTT up to 45.8 ± 6.4 μA cm − 2 at 0.8 V vs. RHE, which could be correlated with the Mn e g filling increase from 0.52 (600 °C) to 0.70 (900 °C). Therefore, the mass activity, which equals to the product of specific activity and surface area, showed maximum value (6.33 ± 0.63 A g − 1 ) at HTT of 700 °C. [ABSTRACT FROM AUTHOR]

For carbon-supported Pt-enriched Pt 3 Au nanoparticles (Pt 3 Au/C), the effect of oleylamine (OA) concentration during nanoparticle synthesis is investigated. When the OA concentration is increased from 0.12 mM to 1.2 mM, the particle size of Pt 3 Au gradually decreased from 5.1 nm to 3.3 nm, whereas the crystal structure and surface Pt concentration are not significantly influenced. With higher OA concentration, the oxygen reduction reaction activity of the Pt 3 Au/C is largely enhanced, which can be explained by the combined effect of increased specific activity and electrochemical surface area of Pt. It is experimentally confirmed using a bulk CO-oxidation technique that smaller particle size (larger OA concentration) leads to decreased OH adsorption strength, which originates from the double layer overlapping effect of closely adjacent nanoparticles. [ABSTRACT FROM AUTHOR]

In the present work, we have accomplished morphology-controlled synthesis of ternary Pt–Pd–Cu alloy nanoparticles, particularly for efficient electrocatalytic oxygen reduction reactions. By controlling over the degree of galvanic displacement at room temperature, we selectively introduced porous and hollow architectures into Pt-decorated Pd–Cu alloy nanoparticles. Porous morphology was accompanied with partially facilitated Pt substitution reaction while hollow shape was exclusively achieved when the galvanic reaction was coupled with additional pre-treatment process which could eventually make the following displacement reaction more facile. Not only the both porous and hollow Pt@PdCu/C catalysts exhibited enhanced ORR performances compared to commercial Pt/C, but also they displayed outstanding durability. In addition, we investigated the alloying effects between Pt and Pd–Cu composite and the presumable influences of lattice strain through preliminary theoretical calculation to account for the enhanced ORR efficiency and durability of the present catalysts. [ABSTRACT FROM AUTHOR]

Abstract: A graphene-oxide-intercalated layered manganese oxide (GO-HLMO) was prepared by intercalating graphene oxide (GO) into the protonated layered manganese oxide (HLMO, H0.32MnO2), and its enhanced activity towards oxygen reduction reactions (ORR) in alkaline media was demonstrated. As a result of GO intercalation, decreases in interlayer distance and in Mn oxidation state were experimentally confirmed by X-ray diffraction (XRD), X-ray absorption near-edge structure (XANES), and X-ray photoelectron spectroscopic (XPS) analysis. Cyclic voltammetry (CV) analysis indicated that GO-HLMO had more accessible Mn(III)/Mn(IV) sites than HLMO, which probably resulted in the large enhancement in ORR activity in alkaline media, from 0.236Ag−1 (HLMO) to 0.735Ag−1 (GO-HLMO) at 0.8V vs. RHE. [Copyright &y& Elsevier]

Abstract: Carbon-supported Se-modified-Ru catalysts (RuSey/C) were synthesized, and their phosphate adsorption characteristics were evaluated using electrochemical techniques and in-situ X-ray absorption spectroscopy (XAS). When phosphoric acid was added, the ORR activity of unmodified Ru/C decreased by 26.8% because the active sites were blocked by electrochemical adsorption, as confirmed by CV. However, for RuSey/C, the ORR activity was enhanced with phosphoric acid (RuSe1.56/C: 63.8%), which indicates that the kinetics at each site increased to compensate for the site blocking effect. The XAS results demonstrated that, for RuSey/C, phosphoric acid molecules or phosphate anions primarily interacted with Se atoms, and the oxidation state of Ru atoms decreased. Therefore, it was concluded that the enhanced ORR kinetics originated from the decreased oxygen binding energy with larger electrostatic repulsion. [Copyright &y& Elsevier]

Abstract: The phosphate adsorption characteristics and its effect on oxygen reduction reaction (ORR) were examined for various carbon-supported catalysts (Pt/C, Pt3Co/C, PtCo/C, and Aucore–Ptshell/C). Using cyclic voltammetry (CV) and the addition of phosphoric acid, the degree of phosphate adsorption for each catalyst was evaluated based on the intensity of the phosphate adsorption peaks (0.25–0.3V and 0.5–0.65V) and on the decrease in the platinum oxidation current (0.9V). In the N2O reduction technique, the surface structures were analyzed using N2O as an electrochemical probe, which showed that as the Co content increased, (i) steps or defects were introduced by surface reconstruction, (ii) the phosphate adsorbed more strongly compared to Pt/C with a preference for the terrace sites, and (iii) the potential of zero total charge (PZTC) shifted to negative potentials. In the case of the Aucore–Ptshell/C, the phosphate adsorption was found to be weaker than other catalysts, including Pt/C catalyst. The relative ORR activity with PA addition, normalized by that with no phosphate adsorption, was significantly smaller for Co containing alloy catalysts (PtCo/C: 18.2%) and larger for Aucore–Ptshell (30.2%) compared with the Pt/C catalyst (27.8%), confirming the phosphate adsorption characteristics of each catalyst, as measured by CV and N2O reduction analysis. [Copyright &y& Elsevier]

Abstract: Pt3Cox/C electrocatalysts for use as cathodes in proton exchange membrane fuel cells are fabricated using various stabilizers to control the different reduction speeds between Pt and Co ions. Four different types of stabilizers—sodium acetate, oleylamine, tetraoctylammonium bromide (TOAB), and hexadecyltrimethylammonium bromide (CTAB)—differing in molecular structures and ionic states are tested. Primarily, Pt3Cox/C alloy nanoparticles are synthesized with 0.6 < x < 0.8 after heat treatment to remove the residual stabilizers. A significant improvement in the activity for oxygen reduction reaction is observed in the case of TOAB- and CTAB-mediated Pt3Cox/C catalysts. In particular, CTAB-mediated catalysts exhibit the best activity, which is about 2-times higher mass activity than commercial Pt/C catalyst. The higher mass activity is believed to result from not only the alloying effects with small atomic size Co but also better dispersion and smaller particle size after heat treatment at relatively low temperature. [Copyright &y& Elsevier]