Pt-enriched Surface Research Articles

Dynamic Surface Dealloying for Pt3Co/C Catalysts with a Pt-Enriched Surface for the Oxygen Reduction Reaction

Dynamic Surface Dealloying for Pt₃Co/C Catalysts with a Pt-Enriched Surface for the Oxygen Reduction Reaction

Ligand effect of PdRu on Pt-enriched surface for glucose complete electro-oxidation to carbon dioxide and abiotic direct glucose fuel cells.

The development of advanced electrocatalysts for the abiotic direct glucose fuel cells (ADGFCs) is critical in the implantable devices in living organisms. The ligand effect in the Pt shell-alloy core nanocatalysts is known to influence the electrocatalytic reaction in interfacial structure. Herein, we reported the synthesis of ternary Pt@PdRu nanoalloy aerogels with ligand effect of PdRu on Pt-enriched surface through electrochemical cycling. Pt@PdRu aerogels with optimized Pt surface electronic structure exhibited high mass activity and specific activity of Pt@PdRu about 450 mA·mgPt-1 and 1.09 mA·cm-2, which were 1.4 and 1.6 times than that of commercial Pt/C. Meanwhile, Pt@PdRu aerogels have higher electrochemical stability comparable to commercial Pt/C. In-situ FTIR spectra results proved that the glucose oxidation reaction on Pt@PdRu aerogels followed the CO-free direct pathway reaction mechanism and part of the products are CO2 by completed oxidation. Furthermore, the ADGFC with Pt@PdRu ultrathin anode catalyst layer showed a much higher power density of 6.2 mW·cm-2 than commercial Pt/C (3.8 mW·cm-2). To simulate the blood fuel cell, the Pt@PdRu integrated membrane electrode assembly was exposed to glucose solution and a steady-state open circuit of approximately 0.6 V was achieved by optimizing the glucose concentration in cell system.

Pt-Ni contact engineering in carbon nitride based photocatalysts for hydrogen production

The effect of a binary PtNi co-catalyst supported on graphitic carbon nitride nanosheets is studied in the photo-production of hydrogen from methanol:water mixtures. The physicochemical analysis provides evidence that the carbon nitride support allows the formation of highly dispersed PtNi nanoparticles with an average composition of Pt 85 % Ni 15 %. The binary system outperforms the monometallic Pt and Ni counterparts and renders an extraordinary quantum efficiency of 8.8 % for hydrogen photo-production. The formation of a PtNi alloy, with a Pt-enriched surface and electronic properties influenced by the heterometallic contact, provides high and stable activity, mostly as a consequence of the effects that the co-catalyst exerts on the charge carrier handling capability of the solid.

In situ shaped PtPd nanocubes on common carbon powder for efficient methanol electrooxidation in practical fuel cells

Platinum-group-metal-based polyhedral nanostructures generally possess high catalytic activity for electrochemical reactions owing to their numerous edges, corners, and well-defined lattice planes. However, their direct synthesis on common carbon powder is difficult, which considerably hinders their applications in practical devices. Herein, we report PtPd nanocubes (NCs) grown in situ on commercial carbon powder (Vulcan XC-72R) using a facile one-pot method. The as-prepared PtPd NCs/C (∼20 wt% metal) possess Pt-enriched surfaces, enabling the mass activity (MA) of methanol oxidation reaction (MOR) up to 1.77 A mgPt−1, which is 3.34/3.69 times that of commercial PtRu/C and Pt/C, respectively. With an average size of 8–10 nm, the PtPd NCs/C exhibit high stability, retaining over 80% initial MA against MOR in an accelerated durability test. For practical direct-methanol fuel cell (DMFC) operation, the PtPd NC/C as an anode catalyst delivered a maximum power density of 0.232 W cm−2 with high-concentration methanol (10 M) flow, which is 1.6 times higher than that for commercial PtRu/C under the same conditions. Moreover, the PtPd NCs/C demonstrated excellent durability for DMFC operation with much lower voltage decay than commercial PtRu/C, indicating its excellent potential for practical DMFC applications.

Multifunctional Pt3Rh–Co3O4 alloy nanoparticles with Pt-enriched surface and induced synergistic effect for improved performance in ORR, OER, and HER

Engineering high-performance electrocatalysts to improve the kinetics of parallel electrochemical reactions in low-temperature fuel cells, water splitting, and metal-air battery applications is important and inevitable. In this study, by employing a chemical co-reduction method, we developed multifunctional Pt3Rh–Co3O4 alloy with uniformly distributed ultrafine nanoparticles (2–3 nm), supported on carbon. The presence of Co3O4 and the incorporation of Rh led to a strong electronic and ligand effect in the Pt lattice environment, which caused the d-band center of Pt to shift. This shift improved the electrocatalytic performance of Pt3Rh–Co3O4 alloy. When Pt3Rh–Co3O4/C was used to catalyze the oxygen reduction reaction (E1/2: 0.75 V), oxygen evolution reaction (η10: 290 mV), and hydrogen evolution reaction (η10: 55 mV), it showed greater endurance (mass activity loss of only 7%–17%) than Pt–Co3O4/C and Pt/C catalysts up to 5000 potential cycles in perchloric acid. Overall, the as-prepared Pt3Rh–Co3O4/C showed high multifunctional electrocatalytic potency, as demonstrated by typical electrochemical studies, and its physicochemical properties endorse their extended performance for a wide range of energy storage and conversion applications.

Tuning oxygen reduction reaction activity via structure orientation and surface arrangement: A study on ordered PtCo/C catalysts

A facile and general strategy for the preparation of highly dispersed PtCo/C catalysts with a Pt-enriched surface is reported. The thermal treatment of the PtCo/C catalyst changes the structure orientation from disordered to ordered phase. Ordered PtCo/C intermetallic catalyst exhibits significantly enhanced electrocatalytic activity and durability toward oxygen reduction reaction (ORR) compared with its disordered counterpart and commercially available PtCo/C, with a mass activity and specific activity of 0.68 A mg Pt−1@0.90 V and 1.15 mA cm−2, respectively. In addition, the mass activity only decreased by 25.1% after 30,000 potential cycles from 0.60 to 1.00 V at a scan rate of 100 mV s−1. Therefore, the improved ORR activity and stability can be ascribed to the atomic ordered surface arrangement and reasonable surface compress strain originated from Pt-enriched surface.

Multi-skeletal PtPdNi nanodendrites as efficient electrocatalyst with high activity and durability towards oxygen reduction reaction

Engineering alloy nanostructures with a combination of highly active noble metals (Pt and Pd) and less electronegative non-noble metal (Ni) is found to be crucial for improving surface reactivity by enriching with active Pt sites. Herein, a multi-skeletal PtPdNi nanodendrites (NDs) was successfully formed by a simple one-pot method with structure directing agent. The modification of Pt electronic structure and their interaction due to compressive strain were explored using benchmark characterization techniques, which showed that the PtPdNi NDs possess Pt-enriched surface, corroborating to more active catalyst sites for oxygen reduction reaction (ORR) in acidic medium. The PtPdNi NDs have a higher electrochemical surface area (63 m2 g−1) and an earlier onset potential (1.01 V) than PtPd NDs, PtNi NDs, and commercial Pt/C catalysts, indicating the outstanding ORR performance. The high mass and specific activities, as well as superior durability after accelerated degradation test (ADT), highlight the remarkable electrocatalytic performance of PtPdNi NDs over others. As a result, enhancing Pt utilization through the formation of PtPdNi NDs could be a reliable strategy to improve ORR electrocatalysis for polymer electrolyte membrane fuel cell (PEMFC) applications.

Improved bi-functional oxygen electrocatalytic performance of Pt–Ir alloy nanoparticles embedded on MWCNT with Pt-enriched surfaces

Multi-walled carbon nanotube supported Pt–Ir nanoparticles (Pt–Ir/MWCNT) with different elemental ratios were synthesized by one-pot co-reduction approach under ambient conditions. The Pt–Ir catalysts exhibit improved bi-functional activity towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) and its electrocatalytic performance was clearly established using different physiochemical characterization techniques. The Pt–Ir composition of 2:1 has a higher electrochemical surface area (ECSA) of about 85.3 m2/g compared to other compositions (3:1 and 1:1) and Pt/MWCNT due to the effect of particle size distribution. The improved ORR/OER activity was found to be 139.4 and 740 mA/mg, respectively, for Pt–Ir(2:1)/MWCNT with the potential difference of 760 mV for oxygen bi-functional activity. Furthermore, Pt–Ir(2:1)/MWCNT showed much better stability for ORR compared to other compositions and Pt/MWNCT catalysts, i.e., around 76% of its initial ECSA retained with <20 mV shift in half-wave potential was obtained even after 10,000 potential cycles in acidic medium. It is believed that the Pt enriched surface, amount of Ir content, induced electronic and geometric effects play a vital role on the electrocatalytic activity enhancement of Pt–Ir(2:1)/MWNCT as effective bi-functional oxygen electrode.

Evolution of composition and structure of PtRh/C in the acidic methanol electrooxidation process

PtRh alloys are highly active in the anodic methanol oxidation reaction (MOR) but few studies have looked at their evolution in the composition and structure during the catalytic process. Herein, a uniformly dispersed carbon-supported PtRh (PtRh/C) catalyst with Rh-enriched surface was synthesized via a facial hydrothermal method. By recording the performance of different cyclic voltammetry (CV) cycles during electrocatalytic MOR process in acid, the evolution of PtRh/C in composition and structure was elucidated. During the first 80 CV cycles, the rapid dissolution of the surface Rh atoms and the exposure of active Pt sites lead to the dramatic enhancement of the current density. When further continue the CV cycling, Pt atoms on the surface have aggregated and recombined to form a tightly aligned Pt-enriched surface. But Rh tends to be stable and catalytic performance reaches a relatively stable status with slightly decreased activity. Compared with the performance of PtRu/C catalyst, it can be concluded that PtRh/C has better stability and higher activity based on the less soluble property of Rh than Ru.

Facile Preparation of a Surface-Enriched Pt Layer Over Pd/C as an Efficient Oxygen Reduction Catalyst With Enhanced Activity and Stability

Abstract Pt-enriched surface layer formation on Vulcan carbon-supported Pd (Pt@Pd/C) was successfully prepared through a simple and one-pot formic acid reduction approach without any stabilizing agent. The electrocatalytic performance of Pt@Pd/C catalyst toward an oxygen reduction reaction (ORR) in alkaline medium was studied and also compared with standard carbon-supported Pt (Pt/C) and Pd (Pd/C) catalysts. The Pt@Pd/C exhibits higher electrochemical active surface area (74.7 m2/g) and mass activity (1.38 mA/µg) than Pt/C, Pd/C, and contending with standard reported catalysts. In durability tests, Pt@Pd/C showed negligible loss of intrinsic activity (∼10%) after 10,000 cycles which confirmed improved stability than Pt-based catalysts for ORR in KOH medium. This improved electrocatalytic performance could be attributed to their structural characteristics of the Pt-enriched surface layer on Pd/C-core and the compressive lattice strain on Pt. The present investigation demonstrates the simple preparation procedure for surface-enriched Pt on Pd/C and its improved performance for ORR, suggesting that it is a promising contender to benchmark ORR catalysts for alkaline fuel cells.

Preparation of porous PtAuCu@Pt core-shell catalyst for application to oxygen reduction

Designing a Pt-based catalyst with high oxygen reduction reaction (ORR) performance is very important for the improvement of the economic feasibility of polymer electrolyte fuel cells. Herein, we suggest a method to prepare a Pt-based core-shell catalyst with high ORR activity and durability by galvanic displacement between Cu on a thermally annealed sample of (PtxAuy)1Cu5/C-HT and Pt ions. The resultant catalysts ((PtxAuy)1Cu5@Pt/C) showed a porous core–shell structure with a Pt-enriched surface. The composition of (PtxAuy)1Cu5/C-HT influenced the physical properties of the resultant (PtxAuy)1Cu5@Pt/C catalysts. (PtxAuy)1Cu5@Pt/C catalysts exhibited better ORR performance than a commercial Pt/C one and their performance varied with the composition. Among the catalysts examined, (Pt1Au0.1)1Cu5@Pt/C showed the best ORR activity. Specifically, it delivered a mass and specific activity of 0.660mA/mgPGM and 1506.2mA/cm2Pt at 0.9V (vs. RHE), respectively. These are 2.7 and 4.2 times higher than corresponding values obtained for Pt/C. In an accelerated degradation test, addition of Au proved beneficial for the design of a highly durable catalyst. The effect of the Au content on the physical properties and ORR performance of catalysts was interpreted in detail.

Core/shell Cu/FePtCu nanoparticles with face-centered tetragonal texture: An active and stable low-Pt catalyst for enhanced oxygen reduction

Low-Pt based nanocrystals demonstrate potential as highly active catalysts for the oxygen reduction reaction (ORR), but they suffer from undesirable structural degradation. Therefore, it is highly challenging to optimize their surface and interfacial structures to tune their catalytic properties for both activity and stability. Here core–shell Cu/FePtCu nanoparticles with a face-centered-tetragonal phase are prepared by a facile one–pot polyol method at 320 °C. The optimized core–shell Fe45Pt35Cu20 catalyst with Pt-enriched surface exhibits 0.5 A/mgPt mass activity, which is a factor of 4 better than that of commercial Pt/C (0.13 A/mgPt). In addition, the current density of the catalyst drops only 3.0% after 1000 cycles, which is much better than Pt/C (34.2% decay). Using aberration-corrected scanning transmission electron microscopy and atomically resolved elemental mapping, the morphology and structure evolving between the FePtCu alloy and core–shell Cu/FePtCu could clearly be explained. This work demonstrates that an ordered and core–shell FePtCu catalyst is highly promising for ORR and other electrochemical processes.

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.

Catalytic performance of Pt–Rh/CeZrYLa+LaAl with stoichiometric natural gas vehicles emissions

The composite support CeZrYLa+LaAl was prepared by a co-precipitation method, and Pt–Rh bimetallic catalysts were fabricated on this support using different preparation procedures. The catalytic activities of these materials were tested in a gas mixture simulating the exhaust from a stoichiometric natural gas vehicle. The as-prepared catalysts were also characterized by X-ray photoelectron spectroscopy, X-ray diffraction, N2 adsorption-desorption and H2-temperature-programmed reduction. It was found that the order of activities for CH4, CO and NO conversion was Cat3 ≈ Cat2 > Cat1, where Cat3 had the lowest light-off temperature (T50) for CO (114 °C) and NO (149 °C), the lowest complete conversion temperature (T90) for CH4 (398 °C) and CO (179 °C), and the lowest ΔT (T90–T50) for CH4 (34 °C) and CO (65 °C). Cat2 showed the lowest T50 for CH4 (342 °C), the lowest T90 for NO (174 °C), and the lowest ΔT for NO (17 °C). Cat1 had the highest T50 and T90 and the largest ΔT out of all three catalysts. Indicating that Pt–Rh bimetallic catalysts (Cat2 and Cat3) prepared by physically mixing Pt and Rh powders exhibited much better catalytic activity than those (Cat1) prepared by co-impregnation, since homogeneous Pt and Rh sites made a significant contribution to CH4/CO/NO conversions. In contrast, strong Pt–Rh interactions in the co-impregnation materials affected the oxidation states of Pt, and the Pt-enriched surface blocked active Rh sites. Moreover, Cat3 was prepared by adding additives (La3+, Zr4+ and Ba2+) into the physically mixed Pt–Rh catalysts. XRD results demonstrated that the additive cation (Zr4+) was incorporated into the CeO2–ZrO2 lattice, thus creating a higher concentration of defects and improving the O2-mobility. XPS results showed that the Cat3 had the highest Ce3+/Ce ratio, suggesting the presence of a significant quantity of oxygen vacancies and cerium in the Ce3+ state. All of these further promoted the three-way catalytic activity and widened the air-to-fuel working-window.

Hollow ternary PtPdCu nanoparticles: a superior and durable cathodic electrocatalyst.

Hollow alloyed nanoparticles (NPs) represent one kind of promising fuel cell electrocatalyst. However, the formation of single-cavity hollow structures by a dealloying process is quite challenging owing to the random leaching/dissolution of transition metals, surface passivation and the limited diffusion distance of the noble metals. Here we present a facile method to prepare hollow PtPdCu NPs derived from monodisperse alloy NPs by an acetic acid-assisted dealloying process. Here, acetic acid not only acts as a chemical etching agent but also plays an important role in the removal of the residual surfactants for colloidal NPs. Our findings rectify the current knowledge that hollow alloyed NPs cannot be prepared by a dealloying strategy and provide further understanding of the dealloying process in a ternary system. Such unique hollow ternary PtPdCu NPs exhibit outstanding durability and improved catalytic activity toward the oxygen reduction reaction.

One-pot sonication-assisted polyol synthesis of trimetallic core–shell (Pd,Co)@Pt nanoparticles for enhanced electrocatalysis

In this report, the synthesis and characterization of trimetallic (Pd,Co)@Pt nanoparticles (NPs) with Pt-enriched surfaces are detailed. (Pd,Co)@Pt NPs supported on carbon with different elemental compositions (Pd50Co20Pt30, Pd34Co27Pt39, and Pd21Co34Pt45) are synthesized by sonochemical reactions of Pt(acac)2, Pd(acac)2, and Co(acac)2 in ethylene glycol. The NPs are subsequently characterized by X-ray diffractometry, transmission electron microscopy, and inductively coupled plasma − atomic emission spectroscopy to determine their particle size, morphology, and elemental composition. The existence of a Pt-enriched surface on the (Pd,Co)@Pt NPs is demonstrated by line profiles obtained via scanning transmission microscopy − energy dispersive spectroscopy. The NPs are applied to electrocatalysis for oxygen reduction reactions. When compared to a commercial Pt catalyst, the onset potential of the NPs increased by 22 mV, while the specific and mass activities were enhanced by factors of ∼ 2.7–4.9 and 4.3–6.3, respectively. The (Pd,Co)@Pt NPs also showed superior stability, as the onset potential was reduced by 11–19 mV after 5000 potential cycles when compared to the 45 mV reduction observed for a commercial Pt catalyst.

Surface modification of commercial PtRu nanoparticles for methanol electro-oxidation

The surfaces of commercially available PtRu nanoparticles (PtRu/C) have been successfully modified via a displacement reaction between the Ru atoms on the PtRu/C and the Pt ions in an aqueous hexachloroplatinic acid solution. The concentration of the hexachloroplatinic acid solution was deliberately formulated to allow for the formation of sub-monolayered Pt (Pt(1/16)) and monolayered Pt (Pt(1/8)) on the surface of PtRu/C. Material characterization, including X-ray diffraction patterns and transmission electron microscopy images, showed that the PtRu phases of the samples were identical but that the particle sizes increased slightly after the surface modification. Data from inductively coupled plasma mass spectrometry confirmed the deposition of Pt with negligible loss of Ru. X-ray absorption spectroscopy showed Pt-enriched surfaces, and the surface Pt content decreased in the order Pt(1/8) > Pt(1/16) > PtRu/C. Cyclic voltammetry and chronoamperometry were conducted for methanol electro-oxidation, and our results indicated impressive catalytic ability and carbon monoxide tolerance for Pt(1/16), followed by Pt(1/8) and PtRu/C. The mass activities of Pt(1/16) and Pt(1/8) increased 223% and 135% over that of PtRu/C. We attributed the observed improvements to the reduced amount of Ru on the PtRu surface, which resulted in an optimized PtRu ratio with enhanced catalytic ability.

Electrochemical Stability of Topmost Surface of Pt-Enriched Ni/Pt(111) Prepared by Molecular Beam Epitaxy

Oxygen reduction reaction (ORR) activity and stability of a molecular beam epitaxially (MBE) prepared Pt-enriched Ni0.3nm/Pt(111) surface was investigated. Reflection high-energy electron diffraction (RHEED) patterns, and a scanning tunneling microscopic (STM) image indicated that the Pt-enriched surface has long-range-ordered six-fold symmetry with atomic-scale corrugations. ORR activity was estimated by kinetically-controlled current density at 0.9 V vs. a reversible hydrogen electrode, and the as-prepared Pt-enriched surface showed 8-times-higher ORR activity than clean Pt(111). The activity steeply reduced during potential cycling between 0.6 V and 1.0 V. After 1000 potential cycles, the enhancement factor was 2.5 and a cyclic voltammetry (CV) curve exhibited an increase in (EC) electron charge for the Had&des region accompanied by the emergence of a 0.13 V redox feature caused by (110) surface defects. These results suggest that the electrochemical stability of the underlying Ni atoms determines the durability of Pt-Ni alloy catalysts.

Platinum–copper nanotube electrocatalyst with enhanced activity and durability for oxygen reduction reactions

The activity and the durability of Pt based electrocatalysts constitute the major challenges in the current fuel cell technology. Motivated by the improved activity and ameliorated durability for Pt based cathode catalysts achieved from the compositional and morphological control, respectively, in this paper, a rationally designed, PtCu based, 1-dimensional electrocatalyst was prepared via a facile and scalable procedure. The detailed materials characterization revealed that the as-prepared nanotubes (NTs) were composed of a PtCu alloy bulk and a Pt-enriched surface with downshifted d-band center position. Towards the electrocatalysis of oxygen reduction reaction, PtCu NTs have displayed a distinguished specific activity with more than a 10-fold improvement relative to the commercial catalysts and more than a 3-fold improvement relative to the 2015 DOE technical target (0.72 mA cmPt−2 @ 0.9 V). Meanwhile, PtCu NTs have shown greatly ameliorated durability in the aspects of both ECSA and mass activity compared to Pt/C (40%) and Pt black after a 6000-cycle accelerated durability test.

Structure and Electrochemical Stability of Pt-Enriched Ni/Pt(111) Topmost Surface Prepared by Molecular Beam Epitaxy

We investigated the atomic-scale structure and electrochemical stability of a Pt-enriched topmost surface (Pt-enriched Ni/Pt(111)) prepared through monolayer Ni deposition on Pt(111) at 823 K using molecular beam epitaxy. Reflection high-energy electron diffraction patterns and an ultra-high vacuum scanning tunneling microscopic (UHV-STM) image of the Pt-enriched Ni/Pt(111) surface showed that the surface has long-range-ordered six-fold symmetry with atomic-scale corrugations. Although the oxygen reduction reaction (ORR) activity of the as-prepared Pt-enriched surface was eight times higher than that of clean Pt(111), the ORR activity degraded steeply during potential cycles between 0.6 and 1.0 V in O2-saturated 0.1 M HClO4. After 1000 potential cycles, the enhancement factor was estimated to be 2. An STM image collected after the potential cycles showed island-like structures (ca. 5–9 nm in diameter and 0.4–0.8 nm in height). Furthermore, the intensity of the Ni 2p core-level band for the as-prepared sample decreased after the 1000 potential cycles, revealing dissolution of the Ni atoms located at the subsurface layer. This experimental study clearly demonstrates that the underlying-Ni-induced specific surface strains and electronic state of the Pt-enriched topmost surface sorely contribute to the remarkable ORR activity of the Ni/Pt(111) surface.