Mass Activity Loss Research Articles

Fabrication and Scale-up of Highly Durable Heavy Duty Fuel Cell MEAs

Medium and heavy-duty PEM fuel cells operate under much harsher conditions than light duty fuel cells and are expected to last 25,000 hours in the field. These systems must therefore operate successfully in the presence of impurities, starting and stopping, freezing and thawing, humidity and load cycling. Therefore, materials, components, and interfaces used in such systems need to be highly resistant to severe mechanical and chemical stress.Novel, highly active stable Pt and ordered PtCo intermetallic nanoparticles with well-controlled particle size and composition have been synthesized on a highly efficient PGM-free single metal active site rich carbon, to maximize their synergistic effects for enhanced performance and durability. These catalysts were integrated with a variety of ionomers (Aquivion, Nafion, HOPI and high O2 permeability ionomer (HOPI)) to further improve fuel cell performance and to achieve >600 mA/mgPt at 0.9 VIR-free with a mass activity loss less than 30% after 150k square wave accelerated durability cycles; and > 600 mA/cm2 (~65% efficiency) at 0.8 V, with a performance loss < 40 mV after 150K cycles (0.6 to 0.95 V).In a PEM fuel cell, the catalyst ink formulation and mixing processes control catalyst layer coating quality, electrode morphology, and the resulting fuel cell performance and durability. Catalyst ink properties are a result of complex solvent-catalyst-ionomer interactions that depend on the mixing method employed. Here, we will compare the performance and durability of electrodes made from bath sonicated inks for ultrasonic spray coating vs. ball milled inks for Meyer rod coating. Ink rheology and catalyst particle size will be used to correlate ink properties to electrode morphology and structure and ensure consistency from batch to batch, and from small lab scale to subsequent scale-up. We will evaluate and discuss the challenges that arise when transitioning from spray coating catalyst ink on a small scale, directly on a membrane, to coating more viscous inks on gas diffusion layers (GDLs), and finally developing a roll-to-roll (R2R) fabrication process. The MEA performance and durability of the novel catalyst will be evaluated under heavy duty operating conditions. Finally, the electrode performance and durability of R2R fabricated GDEs will be tested, and compared to small scale GDEs made at Giner.This work provides a comprehensive understanding of interactions between Pt, PtCo, carbon, ionomer, membrane, and GDLs and their impact on electrode structure, fuel cell performance and durability, as well as considerations for scale up to a R2R fabrication process. The attained information will be used to improve fuel cell electrode design, fabrication and scale-up.Acknowledgement: The project is financially supported by the Department of Energy’s Fuel Cell Technology Office under the Grant DE-FOA-0002360.

Unravelling the Influence of Oxygen on the Degradation Mechanisms of Fe-N-C Oxygen Reduction Reaction Catalysts

Pyrolyzed iron-nitrogen-carbon materials (Fe-N-C) comprising mostly atomic Fe-Nx moieties are the most mature class of noble metal free catalysts for the oxygen reduction reaction (ORR) in acidic media. Such catalysts show excellent performance in proton exchange membrane fuel cell (PEMFC), approaching that of platinum-based catalysts. [1] However, an important performance loss is observed during operation, in conditions mimicking those of a PEMFC. [2] To shed fundamental light onto the degradation mechanisms at stake, two different Fe-N-C materials were prepared, one using a metal organic framework (MOF) and the other a sacrificial support method (SSM), and are labelled Fe-N-C_MOF and Fe-N-C_SSM, respectively. These materials were characterized before and after two different accelerated stress tests (ASTs: 10 k cycles, 0.6-1.0 V vs. RHE, 3s-3s, 0.1 M H2SO4, 80°C) under Ar or O2 atmosphere. Stronger degradation and higher ORR mass activity loss were observed when the AST is performed in O2 vs. Ar-saturated acidic electrolyte. For AST under Ar condition, physicochemical characterisations revealed a demetallation process and the eventual occurrence of a clustering mechanism whereas for AST performed in O2 atmosphere, a decrease of the Fe content and the formation of Fe oxide particles was observed (Figure 1).Keywords: Electrocatalysis, Fe-N-C, Oxygen Reduction Reaction, Durability, PEMFC Acknowledgements These studies were financed by the French National Research Agency in the frame of the CAT2CAT (grant number n°ANR-16-CE05-0007) and the ANIMA (grant number n°ANR-19-CE05-0039) projects.

Hierarchical porous N-doped carbon-supported PtCu nanoparticles as an efficient catalyst for oxygen reduction reaction

The catalyst of PtCu bimetallic nanoparticles anchored on hierarchical porous N-doped carbon (PtCu/NHPC) is successfully fabricated through a simple pyrolysis synthesis. The high surface area (827 m2 g−1) of N-doped porous carbon (NHPC) can effectively favor the high distribution of PtCu particles on carbon. The high mesopore ratio of NHPC helps to reduce mass transfer resistance. Furthermore, homogeneously distributed nitrogen in carbon can not only uniformly disperse nanoparticles but also optimize catalyst oxygen affinity, significantly improving catalytic efficiency for oxygen reduction reaction. PtCu/NHPC shows excellent electrocatalytic activity with a high half-wave potential (0.915 V vs. RHE) compared with commercial Pt/C (0.864 V) in half-cell test. In the single-cell system, PtCu/NHPC also behaves good performance, and its initial current density is 595 mA cm−2 at 0.85 V. PtCu/NHPC shows better durability (only 6.6% mass activity loss) after 10,000 potential cycles compared to JM Pt/C catalyst (30%). The research provides a simple preparation strategy for improving the oxygen reduction reaction activity and stability of fuel cell platinum-based catalysts.

Sublayer Stable Fe Dopant in Porous Pd Metallene Boosts Oxygen Reduction Reaction.

Engineering the morphology and electronic properties simultaneously of emerging metallene materials is an effective strategy for enhancing their performance as oxygen reduction reaction (ORR) electrocatalysts. Herein, a highly efficient and stable ORR electrocatalyst, Fe-doped ultrathin porous Pd metallene (Fe-Pd UPM) composed of a few layers of 2D atomic metallene layers, was synthesized using a simple one pot wet-chemical method and characterized. Fe-Pd UPM was measured to have enhanced ORR activity compared to undoped Pd metallene. Fe-Pd UPM exhibits a mass activity of 0.736 A mgPd-1 with a loss of mass activity of only 5.1% after 10 000 cycles at 0.9 V versus the reversible hydrogen electrode (vs RHE) in 0.1 M KOH solution. Density functional theory (DFT) calculations reveal that the stable Fe dopant in the inner atomic layers of Fe-Pd UPM delivers a much smaller overpotential during O* hydrogenation into OH*. The morphology, porous structure, and Fe doping were verified to have enhanced ORR activity. We believe that the rational design of metallene materials with porous structures and interlayer doping is promising for the development of efficient and stable electrocatalysts.

Trace doping of early transition metal enabled efficient and durable oxygen reduction catalysis on Pt-based ultrathin nanowires

Discovering an active and durable catalyst for oxygen reduction reaction is crucial to the commercialization of fuel cells, but remains grand challenging. Here we report, for the first time, the trace doping of early transition metal (ETM) Re into ultrathin PtNiGa nanowires (Re-PtNiGa NWs) to construct a novel catalyst integrating the superior activity, long-time durability, and high utilization efficiency of Pt atoms. Impressively, the Re-PtNiGa tetrametallic NWs present a 19.6-fold enhancement in mass activity (3.49 A mg−1Pt) compared to commercial Pt/C catalyst and only a 10.6% loss in mass activity after 20,000 cycles of durability test. Moreover, the real fuel cell assembled by Re-PtNiGa NWs on the cathode strongly supports its great potential in fuel cells. The density functional theory calculations reveal that introduction of ETM Re into PtNiGa NWs could weaken binding strength of oxygenated species and elevate dissolution potential, well rationalizing the great enhancements in activity and durability.

Synthesis of modified, ordered mesoporous carbon-supported Pt3Cu catalyst for enhancing the oxygen reduction activity and durability

The modification of carbon-supported components plays an important role in increasing the interaction between carbon-supported and metal-active components in the application of PEMFC catalysts. Here, we propose a strategy for designing a catalyst by covalently modifying ordered mesoporous carbon (MC) CMK-3 and loading Pt3Cu onto modified, ordered mesoporous carbon. Ammonium persulfate (APS) was used as a modifying agent. The surface chemistry and structural properties of the modified mesoporous carbon (MMC) were characterized by BET, XPS, Raman, etc. As a result, the MMC retains the original ordered structure and introduces many oxygen-containing functional groups on the surface of MMC. Due to the optimized properties of MMC, the Pt3Cu/MMC have shown excellent mass activity of 0.58 A/mgPt, which are twice that of Pt3Cu/MC and 4.8 times of JM Pt/C. Besides, the durability test showed that after 10 K cycles, the mass activity loss was only 12.06%, exhibiting excellent electrochemical stability. In addition, the MEA shows a high power density up to 641 mW cm−2, which demonstrate a great potential of modified mesoporous carbon catalyst in practical application.

High activity and durability of carbon-supported core-shell PtPx@Pt/C catalyst for oxygen reduction reaction

Alloying Pt with transition metals can significantly improve the catalytic properties for the oxygen reduction reaction (ORR). However, the application of Pt-transition metal alloys in fuel cells is largely limited by poor long-term durability because transition metals can easily leach. In this study, we developed a nonmetallic doping approach and prepared a P-doped Pt catalyst with excellent durability for the ORR. Carbon-supported core-shell nanoparticles with a P-doped Pt core and Pt shell (denoted as PtPx@Pt/C) were synthesized via heat-treatment phosphorization of commercial Pt/C, followed by acid etching. Compositional analysis using electron energy loss spectroscopy and X-ray photoelectron spectroscopy clearly demonstrated that Pt was enriched in the near-surface region (approximately 1 nm) of the carbon-supported core-shell nanoparticles. Owning to P doping, the ORR specific activity and mass activity of the PtP1.4@Pt/C catalyst were as high as 0.62 mA cm−2 and 0.31 mA μgPt−1, respectively, at 0.90 V, and they were enhanced by 2.8 and 2.1 times, respectively, in comparison with the Pt/C catalyst. More importantly, PtP1.4@Pt/C exhibited superior stability with negligible mass activity loss (6% after 30000 potential cycles and 25% after 90000 potential cycles), while Pt/C lost 46% mass activity after 30000 potential cycles. The high ORR activity and durability were mainly attributed to the core-shell nanostructure, the electronic structure effect, and the resistance of Pt nanoparticles against aggregation, which originated from the enhanced ability of the PtP1.4@Pt to anchor to the carbon support. This study provides a new approach for constructing nonmetal-doped Pt-based catalysts with excellent activity and durability for the ORR.

Nanocomposite of platinum and prussian blue: A highly active and stable electrocatalyst towards oxygen reduction reaction in acidic media

Deployment of proton exchange membrane fuel cells (PEMFCs) are of vital importance for the mitigation of fossil energy shortage and environment pollution. A significant amount of Pt on cathode is highly needed to accelerate the process of sluggish oxygen reduction reaction (ORR) and maintains a stable long-term performance. During ORR, the yield of undesirable hydrogen peroxide through a two-electron pathway not only decreases outer power but also weakens the long-term stability. Herein, Pt-prussian blue (PB) composite, featuring around structure, is firstly proposed and facilely fabricated via electrostatic self-assembly strategy. Pt1PB0.25/C shows 50% higher activity than commercial Pt/C, rationally ascribed to modulated electronic structure and higher selectivity towards four-electron pathway. Moreover, in contrast with the striking 38% loss in mass activity for Pt/C after accelerated degradation tests (ADTs), Pt1PB0.25/C shows only a 15% decrease possibly due to the elimination of hydrogen oxide and the anchor interaction between Pt and PB. The employment of PB with a synergy role paves an efficient way for the fabrication of brand-new Pt-based catalysts with high activity and stability.

Conversion of Pt nanoparticles encapsulated within MIL-101(Fe) to FePt intermetallic nanoparticles supported on carbon promotes formic acid electrooxidation

Pt-based catalysts have limited usefulness in direct formic acid fuel cells (DFAFCs) due to their susceptibility to CO poisoning. Combining Pt with Fe atoms is an effective approach for suppressing Pt poisoning by CO. In this work, we fabricate novel carbon-supported FePt alloy nanoparticles (FePt@C) by pyrolyzing Pt nanoparticles encapsulated within mesoporous MIL-101(Fe) (Pt@MIL-101(Fe)). The resulting FePt nanoparticles (Fe3Pt (111)) possess a lower CO adsorption energy (0.64 eV) than the (111) surfaces of Pt, indicating that the FePt nanoparticles are far less susceptible to CO poisoning. The mass activity and current density of a 9.6 wt% FePt@C catalyst are 4.2 and 4.5 times, respectively, higher than those of a commercial Pt/C catalyst. Furthermore, the 9.6 wt% FePt@C catalyst exhibits excellent durability, with only a 0.1% loss of mass activity after 1000 cycles. These results should guide the development of improved anode catalysts for DFAFCs based on MOF precursors.

De-alloyed ternary electrocatalysts with high activity and stability for oxygen reduction reaction

Proton exchange membrane fuel cell is a viable technology for clean energy production, however developing a cost-effective and highly efficient catalyst for oxygen reduction reaction (ORR) is a challenge to overcome. A promising strategy is alloying Pt with transition metals where synergistic effects and strain induced on Pt adatoms can lead to unprecedent activity. Controlling alloy composition and particle structure are highly complex as alloying order increases. Herein, we report a facile and simple one-pot synthesis method, to synthesize carbon-supported PtCuFe nanoparticles surpassing DOE technical requirement of ORR catalyst for PEMFC application. After voltammetric dealloying, a Pt-rich shell is exposed on the surface of the PtCuFe nanoparticles. The elemental composition and electronic environment of PtCuFe nanoparticles are characterized using high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The condition of dealloying affects catalytic activity for ORR. Dissolution of non-noble metals exhibits significant improvement of PtCuFe ORR activity, as well as, an enhancement in their stability. D-Pt2CuFe/C-150 catalyst shows an ORR mass activity of 0.99 A mg−1Pt at 0.90 V vs. RHE, records 2.9 fold enhancement over state-of-the-art commercial TKK catalyst. Furthermore, D-Pt1CuFe/C-150 exhibits prolonged stability, with a mass activity loss of only 7.6% after 5000 durability cycles, whereas TKK catalyst suffers for a 29.4% loss under the same conditions.

Raw and pyrolyzed (with and without melamine) graphene nanoplatelets with different surface areas as PEM fuel cell catalyst supports

Platinum (Pt) catalysts dispersed on carbon-based support materials are generally used in the polymer electrolyte membrane (PEM) fuel cells. In this study, commercial graphene nanoplatelets (GNPs), with different surface areas (320, 530, 800 m2 g−1), were used as catalyst supports in PEM fuel cells. These GNPs were also pyrolyzed under the inert atmosphere, with and without melamine, as the nitrogen (N) source. Various characterizations (Elemental analysis, FTIR, Raman spectroscopy, BET, TEM, HRTEM, SAED, XRD, TGA, ICP-MS, contact angle measurement, CV, ORR, chronoamperometry, EIS, PEM fuel cell performance test) were performed for the detailed analysis of Pt/GNPs. Based on the three-electrode cell system, the lowest electrochemical surface area (ECSA) loss (29.9%), Pt mass activity loss (20.3%) and overall (charge and mass) resistance (42.2 Ω) were obtained with the Pt/M-530 catalyst. According to the in-situ PEM fuel cell performance results, the specific peak power density was recorded as (450 mW mg Pt−1) for the Pt/R-530 catalyst, which has also the second most hydrophobic catalyst layer surface with the 146.5° ± 1.28° contact angle value. On the heels of Pt/R-530, the two best performances also belong to the Pt/M-530 (391 mW mg Pt−1) and Pt/P-530 (378 mW mg Pt−1) catalysts of the same group.

Zigzag PtCo nanowires modified in situ with Au atoms as efficient and durable electrocatalyst for oxygen reduction reaction

Pt-based nanowires are often used as efficient electrocatalysts for oxygen reduction reaction (ORR) but limited by poor stability. Herein, we prepare zigzag PtCo nanowires (PtCo NWs) by a facile one-pot method, and then modify their surface in situ with Au atoms through galvanic replacement and annealing process. The mass activity of as-prepared PtCoAu1.5 NWs (the Au/Pt atomic ratio is 1.5%) reaches 1.94 A mgPt−1, which is about 11 times higher than that of commercial Pt/C, attributing to the integrated advantages of ultrathin nanowire structure, high-index facets, and alloy effect. And the surface modification by trace Au atoms can suppress the leaching of Co atoms and preserve the nanowire structure without agglomeration. The PtCoAu1.5 NWs behave improved stability (only 21% mass activity loss) after 20,000 potential cycles in half-cell test, compared to PtCo-T NWs (35%) and Pt/C catalysts (59%). In single-cell test, the PtCoAu1.5 NWs also show improved stability compared to PtCo-T NWs and Pt/C catalyst. This work provides a strategy to further improve the performance of Pt-based catalysts for fuel cells.

Anisotropic Strain Tuning of L10 Ternary Nanoparticles for Oxygen Reduction.

Tuning the performance of nanoparticle (NP) catalysts by controlling the NP surface strain has evolved as an important strategy to optimize NP catalysis in many energy conversion reactions. Here, we present our new study on using an eigenforce model to predict and experiments to verify the strain-induced catalysis enhancement of the oxygen reduction reaction (ORR) in the presence of L10-CoMPt NPs (M = Mn, Fe, Ni, Cu, Ni). The eigenforce model allowed us to predict anisotropic (that is, two-dimensional) strain levels on distorted Pt(111) surfaces. Experimentally, by preparing a series of 5 nm L10-CoMPt NPs, we could push the ORR catalytic activity of these NPs toward the optimum region of the theoretical two-dimensional volcano plot predicted for L10-CoMPt. The best ORR catalyst in the alloy NP series we studied is L10-CoNiPt, which has a mass activity of 3.1 A/mgPt and a specific activity of 9.3 mA/cm2 at room temperature with only 15.9% loss of mass activity after 30 000 cycles at 60 °C in 0.1 M HClO4.

Boosting alcohol electro-oxidation reaction with bimetallic PtRu nanoalloys supported on robust Ti0.7W0.3O2 nanomaterial in direct liquid fuel cells

In this work, an anatase Ti0.7W0.3O2-supported Pt3Ru nanoparticles (NPs) were fabricated by combining the advantages of the non-carbon Ti0.7W0.3O2 nanosupport and the synergistic effect of the bimetallic Pt3Ru nanoalloy that was investigated as electrocatalyst toward alcohol electrochemical oxidation. The bimetallic Pt3Ru nanoparticles with ~3 nm in diameter were relatively well-dispersed on the surface of the anatase Ti0.7W0.3O2 nanosupport via a surfactant-free microwave-assisted polyol route that, which was attributable to the good dispersibility of ethylene glycol and the rapid, uniformity of the microwave heating. For methanol and ethanol electrochemical oxidation, the as-obtained Pt3Ru (NPs)/Ti0.7W0.3O2 electrocatalyst exhibited the low onset potential (~0.10 V vs. NHE for MOR and ~0.35 V vs. NHE for EOR) and high mass activity (~350.84 mA mgPt−1 for MOR and ~274.59 mA mgPt−1 for EOR) compared to the commercial Pt (NPs)/C (E-TEK) electrocatalyst. Additionally, the CO-stripping and CA results indicated the remarkably enhanced CO-tolerance of the Pt3Ru (NPs)/Ti0.7W0.3O2 catalyst. After the 5000-cycle accelerated durability test (ADT) in acidic ethanol media, the bimetallic Pt3Ru (NPs)/Ti0.7W0.3O2 catalyst only showed the mass activity loss of 19.11% of its initial mass activity, compared with the severe deterioration of 44.04% of the commercial Pt (NPs)/C (E-TEK) catalyst. The outstanding results could be interpreted due to the bifunctional mechanism of the Pt3Ru nanoalloys combining with the synergistic effect between the bimetallic nanoalloy and the mesoporous Ti0.7W0.3O2 nanosupport as well as the superior anti-corrosion of the TiO2-based nanosupport under acidic and oxidative environments.

Hierarchically skeletal multi-layered Pt-Ni nanocrystals for highly efficient oxygen reduction and methanol oxidation reactions

Pt based materials are the most efficient electrocatalysts for the oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) in fuel cells. Maximizing the utilization of Pt based materials by modulating their morphologies to expose more active sites is a fundamental objective for the practical application of fuel cells. Herein, we report a new class of hierarchically skeletal Pt-Ni nanocrystals (HSNs) with a multi-layered structure, prepared by an inorganic acid-induced solvothermal method. The addition of H2SO4 to the synthetic protocol provides a critical trigger for the successful growth of Pt-Ni nanocrystals with the desired structure. The Pt-Ni HSNs synthesized by this method exhibit enhanced mass activity of 1.25 A mgpt−1 at 0.9 V (versus the reversible hydrogen electrode) towards ORR in 0.1-M HClO4, which is superior to that of Pt-Ni multi-branched nanocrystals obtained by the same method in the absence of inorganic acid; it is additionally 8.9-fold higher than that of the commercial Pt/C catalyst. Meanwhile, it displays enhanced stability, with only 21.6% mass activity loss after 10,000 cycles (0.6–1.0 V) for ORR. Furthermore, the Pt-Ni HSNs show enhanced activity and anti-toxic ability in CO for MOR. The superb activity of the Pt-Ni HSNs for ORR and MOR is fully attributed to an extensively exposed electrochemical surface area and high intrinsic activity, induced by strain effects, provided by the unique hierarchically skeletal alloy structure. The novel open and hierarchical structure of Pt-Ni alloy provides a promising approach for significant improvements of the activity of Pt based alloy electrocatalysts.

Biaxial Strains Mediated Oxygen Reduction Electrocatalysis on Fenton Reaction Resistant L10‐PtZn Fuel Cell Cathode

AbstractPtM alloy catalysts (e.g., PtFe, PtCo), especially in an intermetallic L10 structure, have attracted considerable interest due to their respectable activity and stability for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). However, metal‐catalyzed formation of ·OH from H2O2 (i.e., Fenton reaction) by Fe‐ or Co‐containing catalysts causes severe degradation of PEM/catalyst layers, hindering the prospects of commercial applications. Zinc is known as an antioxidant in Fenton reaction, but is rarely alloyed with Pt owing to its relatively negative redox potential. Here, sub‐4 nm intermetallic L10‐PtZn nanoparticles (NPs) are synthesized as high‐performance PEMFC cathode catalysts. In PEMFC tests, the L10‐PtZn cathode achieves outstanding activity (0.52 A mgPt−1 at 0.9 ViR‐free, and peak power density of 2.00 W cm−2) and stability (only 16.6% loss in mass activity after 30 000 voltage cycles), exceeding the U.S. DOE 2020 targets and most of the reported ORR catalysts. Density function theory calculations reveal that biaxial strains developed upon the disorder‐order (A1L10) transition of PtZn NPs would modulate the surface PtPt distances and optimize PtO binding for ORR activity enhancement, while the increased vacancy formation energy of Zn atoms in an ordered structure accounts for the improved stability.

Superior CO-tolerance and stability toward alcohol electro-oxidation reaction of 1D-bimetallic platinum-cobalt nanowires on Tungsten-modified anatase TiO2 nanostructure

Direct alcohol fuel cells (DAFCs) use liquid and renewable fuels that have been sparked significant interest in a variety of applications; however, the poor catalytic performance of the state-of-the-art Pt nanoparticles (NPs) over carbon support is a major challenge for further DAFC utilization. Herein, the 1D-bimetallic Pt3Co nanowires with a diameter of ~4 nm and the lengths of up to several tens nanometers were grown firstly on the non-carbon Ti0.7W0.3O2 nanoparticles via a template- and surfactant-free chemical reduction preparation at room temperature. Electrochemical results indicated that the bimetallic Pt3Co NWs/Ti0.7W0.3O2 catalyst was an effective electrocatalyst toward alcohol (methanol, ethanol) electrochemical oxidation. For instance, the bimetallic Pt3Co NWs/Ti0.7W0.3O2 catalyst exhibited high mass activity (MOR of ~393.29 mAmgPt-1and EOR of ~341.76 mAmgPt-1), low onset potential (~0.01 V vs. NHE for MOR and ~0.20 V vs. NHE for EOR) and superior CO-tolerance (If/Ib value for MOR of ~3.11 and EOR of ~1.54) in comparison with the conventional carbon-supported Pt nanoparticles (NPs) catalyst. Additionally, the mass activity loss of the Ti0.7W0.3O2-supported Pt3Co (NWs) catalyst was ~10.68% of the initial mass activity, which ~4.18-time lower than that of the carbon-supported Pt (NPs) catalyst (~44.66% of the initial mass activity) after 5000 cycles test, indicating the superior stability retention of the as-obtained Pt3Co NWs/Ti0.7W0.3O2 electrocatalyst. These enhancements were attributable to the combination of the advantageous 1D nanostructures with the internal effect of the Pt3Co nanowires, the synergistic effect between Pt-M alloy and TiO2-based nanomaterials and the superior anti-corrosion possibility of the non-carbon support.

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.

Synthesis and characterization the multifunctional nanostructures TixW1-xO2 (x = 0.5; 0.6; 0.7; 0.8) supports as robust non-carbon support for Pt nanoparticles for direct ethanol fuel cells

In the present study, various mesoporous TixW1-xO2 (x = 0.5; 0.6; 0.7; 0.8) supports were fabricated via a facile solvothermal approach and explored the effect of doping tungsten concentration on electrochemical properties of TixW1-xO2-supported Pt electrocatalysts toward ethanol electrochemical reaction. Interestingly, the incorporation of tungsten into TiO2 lattices with the doping tungsten amounts (20 and 30 at %) resulted in boosting both the surface area and electrical conductivity, however, a reverse trend was observed when increasing the doped tungsten content more than 40 at %. Additionally, the relatively well-distributed Pt nanoparticles with the small particle size (ca. 3 nm) anchored on supports were achieved using a microwave-assisted polyol route. Electrochemical results indicated that various TixW1-xO2-supported Pt catalysts exhibited the catalytic performance greater than that of the commercial carbon-supported Pt (E-TEK) catalyst for ethanol electro-oxidation reaction (EOR). For as-obtained electrocatalysts, the Ti0.7W0.3O2-supported Pt catalyst showed the highest mass activity (~260.23 mA/mgPt) and greatest If/Ib ratio (~1.34), which ~2.0-fold and ~1.57-time higher than that of carbon-supported Pt (E-TEK) catalyst (~130.62 mA/mgPt for mass activity and ~0.85 for If/Ib ratio, respectively). After 5000 cycling tests, the mass activity loss of TixW1-xO2-supported Pt catalysts was around twice lower than that of the commercial Pt/C (E-TEK) catalysts, suggesting that the TixW1-xO2-supported Pt catalysts exhibited the superior stability toward ethanol electrochemical oxidation. The outstanding electrochemical activity and stability of TixW1-xO2-supported Pt electrocatalysts were owing to the synergetic effect between Pt nanocatalyst and non-carbon TixW1-xO2 supports as well as superior natural durability of TiO2-based materials.

Enhanced oxygen reduction activity of PtCu nanoparticles by morphology tuning and transition-metal doping

Developing active and durable electrocatalysts for oxygen reduction reaction (ORR) is of great significance in proton exchange membrane fuel cells (PEMFCs). Herein, we develop a facile strategy to synthesize PtCu nanoparticles with enhanced ORR performance through morphology tuning and transition-metal doping. Two distinct PtCu nanoparticles, namely nanooctahedrons (NOs) and nanospheres (NSs), are selectively synthesized in presence or absence of W(CO)6via a facile one-pot method. Furthermore, by introducing a small amount of third transition metal, M-doped (M = Sc, Y, La, Gd, Fe) PtCu NOs are obtained. Electrocatalytic results suggest that the ORR performance of PtCu NOs is better than that of PtCu NSs due to the morphology advantages. And the ORR performance of PtCuM NOs is further promoted since the doping effect of transition metals compared to that of PtCu NOs. Particularly, PtCuSc NOs exhibit remarkable mass activity (1.652 mA μg−1Pt) and specific activity (2.093 mA cm−2), which are 9.9 and 7.2 times higher than that of commercial Pt/C catalysts at 0.8 V (vs. RHE). Moreover, after accelerated stability tests, the loss of mass activity for PtCuSc NOs is only 9.2%, which is much lower than that of PtCu NOs (16.5%) and commercial Pt/C (44.3%). This work provides a feasible idea to boost the ORR performances of Pt-based nanoparticles.