Oxygen Reduction Reaction Surface Research Articles

Subnanoscale Dual-Site Pd-Pt Layers Make PdPtCu Nanocrystals CO-Tolerant Bipolar Effective Electrocatalysts for Alcohol Fuel Cell Devices.

Finding a high-performance low-Pt bipolar electrocatalyst in actual direct alcohol fuel cells (DAFCs) remains challenging and desirable. Here, we developed a crystalline PdPtCu@amorphous subnanometer Pd-Pt "dual site" layer core-shell structure for the oxygen reduction reaction (ORR) and alcohol (methanol, ethylene glycol, glycerol, and their mixtures) oxidation reaction (AOR) in an alkaline electrolyte (denoted D-PdPtCu). The prepared D-PdPtCu/C achieved a direct 4-electron ORR pathway, a full oxidation pathway for AOR, and high CO tolerance. The ORR mass activity (MA) of D-PdPtCu/C delivered a 52.8- or 59.3-fold increase over commercial Pt/C or Pd/C, respectively, and no activity loss after 20000 cycles. The D-PdPtCu/C also exhibited much higher AOR MA and stability than Pt/C or Pd/C. Density functional theory revealed the intrinsic nature of a subnanometer Pd-Pt "dual site" surface for ORR and AOR activity enhancement. The D-PdPtCu/C as an effective bipolar electrocatalyst yielded higher peak power densities than commercial Pt/C in actual DAFCs.

Ultrathin PtCo nanorod assemblies with self-optimized surface for oxygen reduction reaction

Controllable synthesis of Pt-based materials at the nanoscale can efficiently tailor their electrocatalytic performance, enabling enhancement in both activity and durability. Herein, we report the synthesis of ultrathin PtCo nanorod assemblies (NRAs) terminated with high index facets through a grain-boundary corrosion approach. Atomic insight reveals that grain boundaries and other defects are formed in PtCo nanowire assemblies (NWAs) during the hydrothermal reaction. With a further increase in reaction time, selective dissolution at these sites generated PtCo NRAs composed of shorter nanorod assemblies with larger surface areas and high index facets termination. The carbon-supported catalyst of PtCo NRAs exhibits high mass activity of 0.914 A/mgPt at 0.9 V vs RHE for ORR, 2.4 times higher than those of the smooth PtCo NWAs (0.377 A/mgPt), 5.7 times higher than those of the commercial Pt/C (0.161 A/mgPt). Most significantly, the PtCo NRAs show high stability with about 25.6% loss of mass activity after 10,000 cycles, while only 22.3% loss of mass activity from 10,000 cycles to 50,000 cycles of accelerated durability test. The high durability is mainly attributed to the jagged surface resulted from the surface reconstruction of PtCo NRAs during the electrochemical process. This self-optimization phenomenon may lead to a new effective long-life electrocatalyst.

A facile approach for constructing nitrogen-doped carbon layers over carbon nanotube surface for oxygen reduction reaction

Fabricating nitrogen-doped carbon layers over the conductive substrate is a cost-effective and efficient approach to develop practical oxygen reduction reaction (ORR) catalyst. In the current work, relying on the commercially available carbon nanotube (CNT), nitrogen-doped carbon layers over CNT is constructed by annealing the in situ formed complex over the CNT surface derived from iron ion inducing diaminonaphthalene (DAN) polymerization and DAN self-polymerization. Physical and electrochemical characterizations are carefully conducted to comparatively analyze the structure and activity relationship. The significance of iron in constructing nitrogen-doped carbon layers and tuning active sites of N types over multiwall carbon nanotube for ORR is demonstrated by X-ray photoelectron spectroscopy and Raman scattering spectrum. The excellent performance of nitrogen-doped carbon layers over CNT (catalyzed by iron) towards ORR is displayed by rotating ring-disk electrode. Specifically, the onset potential, half-wave potential, and limiting current density are 0.961 V, 0.831 V, and 5.20 mA cm−2 respectively, very close to the state-of-the-art commercial Pt/C catalyst. Both high surface area and efficient N active sites should be considered in the nitrogen-doped carbon materials design and fabrication for ORR. Considering the large-scale availability, it has significant value in fuel cells commercial applications.

Electrochemical Probing on Structural Changes of Surface Composition and Geometry of Ptni Nanoparticles with Pt-Enriched Surface

Alloying Pt with M (M = Fe, Co, Ni, Cu, etc) has been extensively studied for increasing the oxygen reduction rate owing to the decreased bond strength of hydroxyl to Pt. Formation of Pt-enriched surface on the Pt-M alloy core can enhance both activity and durability, which generates several unique features that make it the most promising candidate for active and durable ORR catalyst, such as lower d-band center and consequent weaker bond strength of oxygen-containing adsorbates, and increased dissolution potential of surface Pt. Our recent study on PtNi bimetallic nanoparticles with Pt-enriched surface for oxygen reduction reaction (ORR) will be presented with introducing conceptual understanding of electronic modification induced by the formation of Pt skin on PtM alloy.1 In particular, it will be discussed that the electrochemical properties, which were obtained from CO and reduced CO2 adlayer oxidation measurements before and after potential cycling under ORR conditions, provide us important informations for estimating the surface electronic and geometric states of pure Pt, PtNi, and Pt-enriched PtNi. 1. Jeon, T.-Y., Kim, S. K., Pinna, N., Sharma, A., Park, J., Lee, S. Y., Lee, H. C., Kang, S.-W., Lee, H.-K., Lee, H. H. Chem. Mater. 2016, 28, 1879-1887.

Exploring the catalytic activity of pristine T6[100] surface for oxygen reduction reaction: A first-principles study

The electrocatalytic activity of T6[100] surface containing both sp3 (C1) and sp2 (C2) hybridized carbon atoms is explored using first-principles density functional theory based approach. The top layered C1 atom of the surface is found to be more active towards the oxygen reduction reaction (ORR), as compared to that of C2 atom. This is attributed to the presence of dangling σ bond in the corresponding C1 atom, leading to the high electron density near the Ferrmi level. Whereas, the π electron in the top layered C2 atom forms a weak out of plane network. As estimated from free energy profile, the overpotential is much lower when C1 is considered as the active site and the final step i.e desorption of final OH− ion is found to be the potential determining step. We have also reported the effect of Si dopant on the catalytic activity of T6[100] surface and explained the origin of high overpotential value in this case. Thus in this report, we propose a new metal-free catalyst i.e T6[100] surface, having both sp2 (maintains the high metallicity needed to reduce ohmic loss) and sp3 (helps in capturing the upcoming molecules) hybridized carbon atoms, as a potential candidate for ORR.

PtCu bimetallic alloy nanotubes with porous surface for oxygen reduction reaction

PtCu bimetallic alloy nanotubes with porous surface were synthesized in aqueous solution using Te NWs as templates. The nanotubes with optimized composition present enhanced electrocatalytic performance for oxygen reduction reaction.

First-Principles Analysis of the Electrocatalytic Activity of Pt(100) Surface for Oxygen Reduction Reaction

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Synthesis and Characterization of Au-Decorated Pt Surface for Oxygen Reduction Reaction

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First-Principles Based Analysis of the Electrocatalytic Activity of the Unreconstructed Pt(100) Surface for Oxygen Reduction Reaction

We apply a rigorous computational procedure combining ab initio DFT calculations and statistical mechanics based methods to examine the electrocatalytic activity of the unreconstructed Pt(100) surface for oxygen reduction reaction. Using the cluster expansion formalism, we obtain stable interfacial water structures using Monte Carlo simulations carried out using parametrized interactions of water–water and water–metal. We find that both long-range and multibody interactions are important to describe the adsorbate interactions as a consequence of the mismatch between the preferred “hexagonal” water overlayer and the underlying square symmetry of the (100) surface. Our results indicate that the stable interfacial water structure is substantially different from that found on the Pt(111) surface. We compute the potential-dependent equilibrium coverages of oxygen-containing adsorbates, which shows that the surface is poisoned by strongly adsorbed OH. We construct the free-energy diagram of intermediates for ox...

Heterogeneous Au–Pt nanostructures with enhanced catalytic activity toward oxygen reduction

Heterogeneous Au-Pt nanostructures have been synthesized using a sacrificial template-based approach. Typically, monodispersed Au nanoparticles are prepared first, followed by Ag coating to form core-shell Au-Ag nanoparticles. Next, the galvanic replacement reaction between Ag shells and an aqueous H(2)PtCl(6) solution, whose chemical reaction can be described as 4Ag + PtCl(6)(2-)→ Pt + 4AgCl + 2Cl(-), is carried out at room temperature. Pure Ag shell is transformed into a shell made of Ag/Pt alloy by galvanic replacement. The AgCl formed simultaneously roughens the surface of alloy Ag-Pt shells, which can be manipulated to create a porous Pt surface for oxygen reduction reaction. Finally, Ag and AgCl are removed from core-shell Au-Ag/Pt nanoparticles using bis(p-sulfonatophenyl)phenylphosphane dihydrate dipotassium salt to produce heterogeneous Au-Pt nanostructures. The heterogeneous Au-Pt nanostructures have displayed superior catalytic activity towards oxygen reduction in direct methanol fuel cells because of the electronic coupling effect between the inner-placed Au core and the Pt shell.

One-pot synthesis of core–shell-like Pt3Co nanoparticle electrocatalyst with Pt-enriched surface for oxygen reduction reaction in fuel cells

2–3 nm sized Pt3Co nanoparticles (NPs) with Pt-enriched shells on a carbon support were prepared by a one-step ultrasound polyol process on Pt(acac)2 (acac = acetylacetonate) and Co(acac)2. The ultrasound facilitates the conversion of Co(acac)2 and retards the conversion of Pt(acac)2 into NPs, which can be explained with the different vapour pressures of the metal precursors. The Pt-enriched shell structure of the NPs by this method, as opposed to the alloy-like elemental distribution of the NPs synthesized in similar conditions but without ultrasound, was evidenced by transmission electron microscopy, magnetism data, extended X-ray absorption fine structure analyses, and chemical replacement tests of Co with Ru3+. Electrochemical oxygen reduction reaction data of these NPs showed improved performance from the commercial Pt/C with the NPs with Pt-enriched shells showing the highest activity.

Probing the Pt Surface for Oxygen Reduction by Insertion of Ag

We report on the probing of the Pt surface for oxygen reduction reaction (ORR) by insertion of Ag. Therefore, PtAg bimetallic nanoparticles were prepared by pulse electrodeposition. In a second step, Ag was electro-dissolved in acidic media from the particles under formation of Pt skeleton. The ORR activity of these Pt skeleton depends on two factors: (1) on the surface properties of the Pt-shell and (2) on the electronic as well as geometric influences of the remaining Ag in the particle core. By varying the conditioning procedure prior to measuring the ORR activity, we were able to differentiate between these two effects.