Carbon-supported Platinum Nanoparticles Research Articles

Effect of Reduction Method for Carbon Supported Platinum Nanosheet with High Surface Area and Activity

Carbon supported platinum nanoparticle is utilized as the cathode catalyst for polymer electrolyte fuel cells. However, the efficiency is about 40% (60% of platinum exist inside nanoparticle) for commercial 2-3 nm diameter platinum and thus there is still room for improvement. One of the approaches to enhance the platinum efficiency is the use of smaller sized nanoparticles. However, smaller nanoparticles generally have lower specific activity and durability. Therefore, one must overcome the trade-off between high surface area and high stability.We have succeeded in the exfoliation of layered platinic acid to platinum oxide nanosheets and subsequent reduction to platinum nanosheets with an average thickness of ~0.5 nm (2 atomic layers). The carbon supported platinum nanosheets showed higher electrochemically active surface area (ECSA) and ORR mass activity than conventional carbon supported 3 nm platinum nanoparticles. Moreover, the carbon supported platinum nanosheets exhibited higher load-cycle durability owing to the high coordination number of surface atoms of platinum nanosheets. However, the nanosheets were partially aggregated and transformed to nanoparticles, resulting in platinum efficiency of about 60% of theoretical surface area. In this study, we discuss the topotactic reduction of carbon supported platinum oxide nanosheets via mild treatment such as vapor phase reduction with hydrogen gas and/or carbon monoxide for further improvement of ECSA and ORR activity.The ECSA of the carbon supported platinum nanosheets reduced by the thermal treatment under hydrogen gas at 100 ℃ (Pt(ns)/C-H2) was 100 to 120 m2 (g-Pt)-1, which is higher than 3 nm platinum nanoparticles (80 m2 (g-Pt)-1). The ECSA of the carbon supported platinum nanosheets reduced by carbon monoxide gas at 25 ℃ (Pt(ns)/C-CO) was 133 m2 (g-Pt)-1. It is considered that carbon monoxide adsorbed on reduced platinum atoms, leading to suppression of aggregation and growth of platinum.The ORR specific activity of Pt(ns)/C-H2 was 300-350 μA cm-2, while that of Pt(ns)/C-CO was 150 μA cm-2 which is half of Pt(ns)/C-H2. From cyclic voltammograms (Figure 1), the peak potential for the reduction of platinum oxide of Pt(ns)/C-CO showed lower potential than that of Pt(ns)/C-H2. This suggests that Pt(ns)/C-CO has a more unstable surface than Pt(ns)/C-H2, and Pt−OHad and/or Pt−Oad formed more on platinum surface, lowering the ORR. As a result of the high ECSA, the ORR mass activity of Pt(ns)/C-H2 was 1.7 times higher compared to that of 3 nm platinum nanoparticles, while that of Pt(ns)/C-CO was almost same as 3 nm platinum nanoparticles despite the higher ECSA.This work was supported in part by the “Polymer Electrolyte Fuel Cell Program” and the FC-Platform projects from the New Energy and Industrial Technology Development Organization (NEDO) of Japan (20001201-0, 22101136-0).[1] D. Takimoto, S. Toma, Y. Suda, T. Shirokura, Y. Tokura, K. Fukuda, M. Matsumoto, H. Imai and W. Sugimoto, Nat. Commun. 14, 19 (2023). Figure 1

Role of Carbon Support Structure on PEMFC Durability

Proton exchange membrane fuel cells (PEMFCs) are the electrochemical generators increasingly being studied as part of the energy transition. Among the key components of these systems, catalysts based on carbon-supported platinum nanoparticles (Pt/C) for PEMFC applications in the transport sector are the focus of numerous research efforts aimed at improving their durability1,2. Indeed, catalyst durability depends on the nature of carbon support used : in real systems, these materials undergo significant degradation phenomena, such as corrosion of the carbon support or deterioration of the Pt active sites (nanoparticle migration, dissolution, coalescence, Ostwald ripening)3, particularly at the cathode where water (a degradation factor) is present and the limiting ORR reaction occurs. Faced with the challenges of performance and durability, mesoporous carbon supports could meet the needs for PEMFC catalyst applications. These carbons offer a number of advantages for improving performance (high specific surface area) and durability (Pt nanoparticles anchored inside pores that are less exposed to degradation and ionomer poisoning)4,5. Thus, the properties of the carbon used as a catalyst support and in particular its structure, can play a crucial role in mitigating degradation processes, and consequently in improving the stability of PEMFC electrodes.The aim of this study is to analyze the influence of mesoporous carbon structures on the durability of PEMFC catalysts. To this end, two major parameters are explored: mesoporosity tuning and carbon hydrophilicity, since it has been reported that wettability has repercussion on catalyst layer performance and durability6. The structural and physico-chemical properties of different types of mesoporous carbon supports are analyzed before and after electrochemical tests assessed by AST ("Accelerated Stress Tests", protocol inspired by the US DOE7).To this end, three carbon supports with variable grain size, graphitization, hydrophilicity, BET surface area and mesoporous volumes were chosen to synthesize 40 wt% Pt/C catalysts by a polyol route. Synthesized carbons and catalysts are characterized using various physico-chemical analysis tools in order to evaluate and compare their structural and chemical properties. As water plays a major role in the MEA (membrane electrode assemblies) operation, we also chose to carry out dynamic vapour sorption (DVS) measurements, which are rarely used for PEMFC applications, to analyze the hydrophilicity of the materials (carbons, catalysts and active layers) and their sorption behavior. Catalysts are then integrated into similar cathodic catalyst layers (ink formulation, coating and transfer onto PEM membranes) and electrochemically degraded in a 1.8cm² differential cell (small active surface area) using the AST protocol simulating carbon support degradation in particular (corrosion during system start-up/shut-down phases). Accelerated degradation is monitored using various advanced electrochemical characterization techniques at different cycles at the cathode. Post-mortem analyses are also carried out from time to time to complement the electrochemical observations made. Taken together, the results provide first promising trends and new insights into the impact of mesoporous structures on the durability of catalytically active layers. They suggest that the choice of critical structural and physico-chemical properties is favorable to electrode longevity. References (1) Gröger, O.; Gasteiger, H. A.; Suchsland, J.-P. Review—Electromobility: Batteries or Fuel Cells? J. Electrochem. Soc. 2015, 162 (14), A2605–A2622. https://doi.org/10.1149/2.0211514jes.(2) Yoshizumi, T.; Kubo, H.; Okumura, M. Development of High-Performance FC Stack for the New MIRAI; 2021; pp 2021-01–0740. https://doi.org/10.4271/2021-01-0740.(3) Meier, J. C.; Galeano, C.; Katsounaros, I.; Witte, J.; Bongard, H. J.; Topalov, A. A.; Baldizzone, C.; Mezzavilla, S.; Schüth, F.; Mayrhofer, K. J. J. Design Criteria for Stable Pt/C Fuel Cell Catalysts. Beilstein J. Nanotechnol. 2014, 5, 44–67. https://doi.org/10.3762/bjnano.5.5.(4) Sakthivel, M.; Drillet, J.-F. An Extensive Study about Influence of the Carbon Support Morphology on Pt Activity and Stability for Oxygen Reduction Reaction. Applied Catalysis B: Environmental 2018, 231, 62–72. https://doi.org/10.1016/j.apcatb.2018.02.050.(5) Daimon, H.; Yamazaki, S.; Asahi, M.; Ioroi, T.; Inaba, M. A Strategy for Drastic Improvement in the Durability of Pt/C and PtCo/C Alloy Catalysts for the Oxygen Reduction Reaction by Melamine Surface Modification. ACS Catal. 2022, 12 (15), 8976–8985. https://doi.org/10.1021/acscatal.2c01942(6) Nagamori, K.; Aoki, S.; Ikegawa, M.; Tamoto, K.; Honda, Y.; Seki, Y.; Igarashi, H.; Uchida, M. Impacts of Pt/Carbon Black Catalyst Surface Hydrophilicity on Ionomer Distribution and Durability during Water-Generating Load Cycling of Polymer Electrolyte Fuel Cells. ACS Appl. Energy Mater. 2023, 6 (22), 11481–11496. https://doi.org/10.1021/acsaem.3c01706(7) U.S. DRIVE Fuel Cell Tech Team. Cell Component Accelerated Stress Test and Polarization Curve Protocols for PEM Fuel Cells. U.S. Department of Energy January 14, 2013. https://www.energy.gov/eere/fuelcells/articles/fuel-cell-tech-team-accelerated-stress-test-and-polarization-curve. Figure 1

Suppression of Hydrogen Peroxide Formation on Pt Using WO3 as Anode Co-Catalysts

Polymer electrolyte fuel cells (PEFCs) are emerging as promising candidates for next-generation energy systems, particularly for hydrogen vehicles and clean energy applications, due to their advanced high-power density production and efficiency. However, the commercialization of PEFCs is hindered by issues related to fuel cell durability, primarily caused by the chemical degradation of proton exchange membranes (PEMs) due to reactive oxygen-related radical attacks, notably generated through the production of hydrogen peroxide (H2O2). Anode catalysts, such as carbon-supported platinum nanoparticles (Pt/C), play a vital role in facilitating the hydrogen oxidation reaction (HOR), which is accompanied by the undesired formation of H2O2 due to oxygen gas (O2) crossover from the cathode. As for the Pt surface, the structure is sensitive to H2O2 production. Hence, minimizing H2O2 generation while maintaining HOR activity by developing anode catalysts is necessary to suppress degradation. Tungsten oxide (WO3) has emerged as an interesting active material due to its stability in acidic solutions and its ability to increase the rate of hydrogen oxidation by facilitating hydrogen spill-over from the Pt surface to WO3 to generate hydrogen tungsten bronze (HxWO3). [1, 2] This process enhances the availability of hydrogen on the Pt surface by effectively transferring hydrogen atoms from Pt to WO3. With more active sites available on the Pt surface, there is a higher likelihood of hydrogen oxidation, reducing the formation of H2O2 as an intermediate product.This study aims to develop an anode catalyst by incorporating WO3 nanoparticles into the Pt/C to suppress H2O2 production during HOR, particularly in the presence of oxygen. The rotating ring-disk electrode (RRDE) technique was utilized to evaluate catalyst performance and detect H2O2 generation during HOR. HOR activity and H2O2 production rate measurements were conducted in H2-sat. and H2/air-sat. 0.1 M HClO4 electrolyte at different temperatures (25, 40, and 60 ℃). The electrochemical measurements demonstrated that both Pt/C and WO3-Pt/C catalysts exhibited enhanced H2O2 formation rates with increasing temperature. This observation underscores the significance of temperature as a modulator of catalytic performance and suggests the existence of temperature-dependent kinetic mechanisms governing H2O2 generation during HOR. Moreover, the comparative analysis between Pt/C and WO3-Pt/C catalysts reveals distinct temperature-dependent behaviors. While both catalysts exhibit temperature-enhanced H2O2 formation, the WO3-Pt/C catalyst demonstrated significantly reduced H2O2 production at 0 V vs reversible hydrogen electrode (RHE) approximately 40% at 60 ℃ as compared with Pt/C, and it exhibited high HOR mass activity and surface activity across a broad temperature range. This suppression is attributed to the synergistic effect between platinum and tungsten oxide species, which facilitates improved HOR kinetics and H2O2 selectivity.This study was supported in part by funds for the “R&D of novel anode catalyst” project in the “Collaborative industry-academia-government R&D project for solving common challenges toward dramatically expanded use of fuel cells” from the New Energy and Industrial Technology Development Organization (NEDO) of Japan. The authors thank Prof. Hiroyuki Uchida (The University of Yamanashi) for his kind advice.

Fusarium oxysporum mediated synthesis of nitrogen-doped carbon supported platinum nanoparticles for supercapacitor device and dielectric applications

A scalable method has been developed for synthesizing nitrogen-doped carbon-supported platinum nanoparticles. Fusarium oxysporum was utilized as reducing and stabilizing agent, and calcination was employed to produce the carbon support. The unique properties of Fusarium oxysporum facilitate the reduction of metal ions while preventing agglomeration and maintaining nanoparticle stability. An extensive investigation of the electrochemical supercapacitor and temperature-dependent dielectric properties of the nanoparticles demonstrates their suitability for supercapacitor applications. Electrochemical analysis showed N-doped C/Pt NPs with high specific capacitance, 482.77F/g at 2.0 A/g, retaining 94 % capacitance even under 20 A/g after 10,000 cycles. The symmetric supercapacitor device displayed 275F/g at 2 A/g, maintaining 61.10 Wh/kg energy density at 1000 W/kg power density, with ∼ 92 % capacitance retention after 10,000 cycles. Dielectric properties of N-doped C/Pt NPs were analyzed at both ambient (300 K) and elevated (450 K) temperatures, revealing temperature-dependent characteristics and alternating current conductivity. At 0.75 MHz, the dielectric permittivity (ɛ’) was measured at 31, with tangent loss at 2.01 and a.c. conductivity at 2.597 × 10-3 O−1 m−1. Increasing the frequency to 6.0 MHz resulted in a 2.38-fold rise in dielectric permittivity and a decrease in tangent loss to 0.77, demonstrating the temperature-sensitive nature of dielectric relaxation.

Agglomeration behavior of carbon-supported platinum nanoparticles in catalyst ink: modeling and experimental investigation

Within catalyst inks, the agglomeration of carbon-supported Pt nanoparticles (Pt/C NPs) stands out as a primary destabilizing factor. This study simulates the agglomeration process of particles under varying ionic strengths (ISs), employing the Brownian motion of Pt/C NPs and inter-particle forces. The energy barriers (EBs) within particles govern particle interactions, subsequently translating into the adhesive efficiency of particle collisions (α). By modulating the ISs in Ink-P (IS = 0.00182), Ink-01 (IS = 0.01), and Ink-001 (IS = 0.001), the Zeta potential and EBs are diminished, thereby increasing α. Structural parameters of agglomerates during the agglomeration process, such as fractal dimension (df) and porosity, are computationally assessed using Matlab. The simulated df for Ink-P, Ink-001, and Ink-01 are 1.82, 1.62, and 1.54, respectively, while the experimentally measured df are 1.92–1.95, 1.67–1.7, and 1.56–1.59, confirming the effectiveness of the simulation method. High α led to isotropic growth of agglomerates, resulting in higher df. Increased IS causes compression of the electric double layer and higher α, ultimately leading to rapid destabilization of the ink. This method not only enhances comprehension of nanoscale particle agglomeration, explaining variations in ink stability and agglomerate structures, but also broadens its applicability to diverse nanoparticle dispersion systems.

Facilitating alkaline hydrogen evolution reaction on the hetero-interfaced Ru/RuO2 through Pt single atoms doping

Exploring an active and cost-effective electrocatalyst alternative to carbon-supported platinum nanoparticles for alkaline hydrogen evolution reaction (HER) have remained elusive to date. Here, we report a catalyst based on platinum single atoms (SAs) doped into the hetero-interfaced Ru/RuO2 support (referred to as Pt-Ru/RuO2), which features a low HER overpotential, an excellent stability and a distinctly enhanced cost-based activity compared to commercial Pt/C and Ru/C in 1 M KOH. Advanced physico-chemical characterizations disclose that the sluggish water dissociation is accelerated by RuO2 while Pt SAs and the metallic Ru facilitate the subsequent H* combination. Theoretical calculations correlate with the experimental findings. Furthermore, Pt-Ru/RuO2 only requires 1.90 V to reach 1 A cm−2 and delivers a high price activity in the anion exchange membrane water electrolyzer, outperforming the benchmark Pt/C. This research offers a feasible guidance for developing the noble metal-based catalysts with high performance and low cost toward practical H2 production.

A sulfur-modified pore-blocking method to enhance the electrocatalytic stability of carbon-supported platinum nanoparticles.

Currently, the durability of electrode materials remains a big obstacle to the widespread adoption of proton exchange membrane fuel cells (PEMFCs). Herein thiourea and sodium dodecyl benzene sulfonate (SDS) were employed as sulfur source and carbon source to modify the pristine carbon black (Ketjen black EC300 J). A highly durable carbon supported Pt nanosized catalyst with higher platinum utilization for oxygen reduction reaction (ORR) in PEMFCs was produced by doping elemental sulfur into carbon supports and decreasing the carbon pore sizes and volume through a successive impregnation technique. The catalyst exhibits an initial activity of 0.167 A mgPt -1 at 0.90 V and demonstrates minimal activity loss after acceleration stress test (30,000 cycles of AST). The half-wave potential loss for representative sample (Pt/S-C-3) is only 14 mV with only 21.8 % ECSA decrease, 27.5 % MA loss and 5.9 % SA loss. A sintering test at various temperature shows a minor average size increase for sulfur-doped carbon (S-C) supported one (from 2.09 to 2.52 nm). In single-cell test, the MEA sample employing the platinum catalyst on modified carbon as cathode exhibited almost negligible performance loss after 30,000 cycles of AST.

Electrochemical recovery of Pt/C electrocatalyst: optimization of the potential range on the leaching process and application to an aged MEA

An optimized potential window for efficient platinum electrodissolution, the first step of a Pt recycling process, is proposed.

Hydrogen Reconversion from Ammonia through Anion Exchange Membrane Electrolysis

Nitrogen-based compounds, especially ammonia, is a promising alternative for the storage and transport of renewable hydrogen over long distances [1]. Considering ammonia as a hydrogen carrier will require studying the conversion (ammonia to hydrogen) and reconversion steps (hydrogen to ammonia). The reconversion of ammonia can take place through electrolysis under alkaline conditions [2] and needs the development of more efficient catalysts. For this, we started studying the electro-oxidation of ammonia in an anion exchange membrane electrolyser over platinum-based and PGM free electrodes with KOH as electrolyte. We have prepared several catalysts, carbon supported platinum, platinum-iridium, and nickel nanoparticles using the polyol technique. Commercial carbon supported platinum nanoparticles was used as catalyst for the cathodes. Catalyst coated substrates (CCS) were then prepared by spraying a catalytic ink over stainless-steel fiber paper for the anode side. The formulation of the ink requires optimizing parameters such as the type of ionomer (nafion, sustanion) and the ratio of ionomer to carbon. Anodes obtained have been assembled with anion exchange membranes and commercial cathodes for ammonia electro-oxidation in single cell. We have compared the performance of these different membrane electrodes assemblies (MEAs) to commercially available ones integrating nickel-iron-cobalt based anodes. The performance of MEAs was analyzed based on polarization curves, cyclic voltammograms and impedance spectroscopy data. Different testing conditions were investigated by varying the ammonia concentration from 0.1 to 1 M, the temperature from 25 °C to 60°C, and the KOH concentration from 0.1 to 5 M.

Plasma-liquid synthesized carbon-supported platinum nanoparticles as active electrocatalysts

BackgroundThe preparation of carbon-supported platinum nanoparticles (Pt/C NPs) with excellent catalytic activities can greatly benefit both the fundamental research and industrial applications. However, the ability for rapid Pt/C NPs synthesis and engineering, especially in a simple, green, and controllable manner, remains essentially limited. MethodsHerein, Pt/C NPs were prepared via a microplasma-liquid interaction method from chloroplatinic acid solution and carbon black. Systematic experiments have been performed to investigate the synthesis process. Their catalytic performance was further evaluated via electrochemical reactions and measurements. Significant findingsResults revealed the successful synthesis of Pt/C nanoparticles, where small sized Pt nanoparticles (2∼3.6 nm) were well-dispersed over the carbon black. The formed Pt/C NPs have active electrocatalytic performance, and the electrochemically active surface area (ESA) can be tuned from 28.65 to 78.80 m2/g by adjusting the Pt content (3∼10%) through process control. A maximum catalytic activity of 24.23 mA/cm2 was achieved for methanol oxidation using the Pt/C-10%, better than commercial samples (ESA: 65.13 m2/g, MOR: 20.07 mA/cm2). Additionally, the Pt/C NPs for hydrogen evolution reaction (HER) exhibited small Tafel values in both the acid and alkaline solution. The demonstrated microplasma process is envisaged to be applicable for multiple functional nanomaterials synthesis.

Comments on “Size dependence of the lattice parameters of carbon supported platinum nanoparticles: X-ray diffraction analysis and theoretical considerations,” RSC Adv., 2014, 4, 35959–35965

Leontyev and colleagues presented the results of an experiment and of its theoretical consequences. The interpretations were based on model-fits to that experiment. Unfortunately, they used two demonstrably incorrect parameters in their models. When the correct parameters are used, the best fits, and the corresponding theoretical implications, are interchanged. Specifically, they deduced an inapplicability of the Laplace–Young equation to the compression of nanoparticles. After their faulty parameters are corrected, this is no longer proven. An equation based on Laplace–Young pressure was dismissed by Leontyev et al., but when recalculated with corrected parameters, it fits their experimental data points.

The effect of non-spherical platinum nanoparticle sizes on the performance and durability of proton exchange membrane fuel cells

• Developed and implemented a novel one-pot synthesis technique. • Synthesized non-spherical carbon-supported platinum nanoparticle catalysts. • Carried out physical, half- and full cell electrochemical characterizations. • Catalyst with 2 nm Pt size has excellent performance (> 1.1 W/cm 2 peak power density). • Catalyst with larger Pt size (5 nm) has excellent durability under AST. Platinum (Pt) nanoparticles with different sizes of 2 nm and 5 nm supported on functionalized high surface area carbon (HSC) have been successfully synthesized with a one-pot synthesis technique in large scale. Of the interest for the proton exchange membrane fuel cell applications, the synthesized supported catalysts are evaluated by physical characterizations, half-cell and scaled up single cell tests to study the impact of the catalyst sizes on cell performance and durability. Physical characterizations clearly demonstrate the sizes, shapes, crystallinity phases, and the total loading of the Pt nanoparticles on HSC. Half cell characterizations demonstrate higher electrochemical surface area, higher mass activity, and less durability for the working electrode prepared by the smaller Pt nanoparticle sizes (2 nm) than the larger Pt nanoparticles (5 nm). Scaled up single cell tests using air and hydrogen as the cathode and anode reactants demonstrate the membrane electrode assembly (MEA) prepared by smaller Pt nanoparticle sizes (2 nm) shows the maximum power density of 1.1 W/cm 2 , which is 7% higher than the maximum power density of MEA prepared by larger Pt nanoparticles (5 nm) under similar operational conditions. The 30,000 cycles of accelerated stress test on the membrane electrode assembly prepared by larger Pt nanoparticles (5 nm) demonstrates 13% drop at maximum power density, illustrating the excellent performance against degradation (ageing).

Direct Conversion of Polypropylene into Liquid Hydrocarbons on Carbon-Supported Platinum Catalysts.

Efforts to selectively convert polypropylene (≈30 % of all plastic waste) have not been particularly successful. Typical distributions span from gas to solid products, highlighting a challenging cleavage control. Here, carbon-supported platinum nanoparticles were designed for complete hydrocracking into liquid hydrocarbons (C5 -C45 ). The metal and carrier phases operated synergistically. The cleavage activity depended on platinum and its rate rose with decreasing particle size. The carbon carrier controlled selectivity via hydrocarbon binding strength, which depended on the chain length and on the surface oxygen concentration. An optimal binding provided by carbons with high oxygen content promoted both adsorption of long chains and desorption of short products. This strategy achieved an unprecedented 80 % selectivity toward motor oil (C21 -C45 ). Carbons exhibiting too strong binding (low oxygen content) hindered product desorption, while non-binding materials (e. g., silica or alumina) did not promote plastic-Pt contact, leading in both cases to low performance. This work pioneers design guidelines in a key process towards a sustainable plastic economy.

Strengthening oxygen reduction activity and stability of carbon-supported platinum nanoparticles by fluorination

By combining experimental and theoretical aspects, this study focuses on exploring and enhancing the activity and stability towards oxygen reduction reaction (ORR) of fluorinated carbon supported platinum nanoparticles in the acidic electrolyte. Physical characterization results revealed that fluorinated carbon support generates a C-F bonding. The interaction between Pt and fluorinated-carbon allows for a strong charge transfer from Pt to the support. This phenomenon is consistent with the density functional theory (DFT) analysis. Because of the fluorination, the electronic structure of Pt is changed, which is an advantage for improving the catalytic activity and stability of the catalyst towards ORR.

Boosting the Role of Ir in Alleviating Corrosion of Carbon Support By Alloying with Pt

The degradation of PEMFC is a very complex phenomenon and is affected by various factors. Among the components of PEMFC, an electrode composed of a carbon-supported platinum nanoparticle catalyst (Pt/C) plays an important role in determining the durability of PEMFC. Typically, PEMFCs have an operating voltage range of 0.5–1.0V. During long-term operation under these conditions, Pt nanoparticles agglomerate, reducing the active surface area and gradually reducing electrode performance. On the other hand, abnormal conditions such as low fuel and start/shutdown (SU/SD) cycles produce abnormally high potentials above 1.4V at the electrodes. At this high potential, the carbon support corrodes to form carbon dioxide (C + 2H2O → CO2 + 4H + + 4e–, E0 = 0.207 V), leading to loss of supported Pt nanoparticles and rapid decay or catastrophic failure of electrode performance. Automotive PEMFCs, which are more often exposed to the aforementioned abnormal conditions, have a shorter life (almost thousands of hours) than stationary PEMFCs (nearly tens of thousands of hours). This clearly means that these dynamic conditions will decisively affect the degradation of PEMFC.Extensive research efforts have been made to mitigate the corrosion of carbon supports to improve the durability of PEMFC. First, it improves the corrosion resistance of these materials by modifying the surface properties and crystallinity of carbon. Second, corrosion-resistant and electrically conductive oxides and transition metal carbides have been explored as alternative supports for Pt nanoparticles to remove carbon from the electrode. Electrodes without supports, such as nanostructured thin film electrodes, have also been proposed to remove carbon from the electrode. On the other hand, operating procedures or plant balances (BOPs) have been developed to avoid exposure to cell reversal or reverse current conditions. Despite these studies, the lifetime of automotive PEMFCs is limited due to carbon corrosion, but this is not the only issue. Nevertheless, the mitigation of carbon corrosion remains an important challenge.With a new approach, iridium oxide (IrO2) is incorporated into the Pt/C electrode as an additive that protects carbon from corrosion with the help of sacrificial oxidation of water (or oxygen evolution reaction, OER) demonstrating improved durability in both half-cell and single-cell tests. However, the function of the OER catalyst was not clear in terms of composition and distribution, which is a prerequisite for further improvement of cathode durability. This study aims to gain a mechanical understanding of OER functional Ir-containing Pt/C electrodes. Carbon-supported Pt–Ir alloy catalysts (PtxIry/C) are synthesized in various compositions and are exposed to potential cycles from 1.0 to 1.5 VRHE compared to Pt/C and mixtures of Pt/C and Ir/C (Pt/C + Ir/C, Pt-Ir ratio 85:15). Pt85Ir15/C has been proven to be more resistant to carbon corrosion than Pt/C as well as Pt/C+Ir/C due to Ir atomically distributed in Pt85Ir15/C. The corrosion behavior of the carbon support is thoroughly investigated by the identical location transmission electron microscopy (IL-TEM), differential electrochemical mass spectrometry (DEMS), and X-ray photoelectron spectroscopy (XPS). As a cathode catalyst, Pt85Ir15/C exhibits much higher oxygen reduction reaction (ORR) activity than Pt/C after potential cycles, which is associated with the formation of high-index facets of Pt as revealed by high-resolution TEM (HR-TEM) and inductively coupled plasma mass spectrometry connected to a scanning flow cell (SFC/ICP-MS). This study suggests that the atomic-level distribution of Ir is a key factor in effectively mitigating carbon corrosion and improving PEMFC durability.

Oxygen-Enriched Biomass-Activated Carbon Supported Platinum Nanoparticles as an Efficient and Durable Catalyst for Oxidation in Benzene

Carbon materials have been widely utilized as supports in different catalytic reactions; however, it has been rarely reported that carbon supports were used in the catalytic oxidation of volatile organic compounds because they have no catalytic activity and poor catalytic stability compared to metal supports. Herein, fabricating optimal carbon supports to facilitate the catalytic oxidation of benzene has become a great concern of research. A novel activated carbon (biomass–HCO) was prepared from different waste biomass via a three-stage route without the participation of harmful chemical reagents. The successful synthesis of C–O bonds and C═O bonds through this method could greatly increase oxygen-enriched functional groups and defects of the biomass–HCO surface, which could effectively promote the nucleation and growth of platinum. Benzene oxidation reactions were performed to evaluate the activity of catalysts. The results demonstrated that Pt/biomass–HCO catalyst made the reaction temperature sharply decrease to 160 °C at T₉₀. The 150 h on-stream reaction exhibited great thermal stability of Pt/biomass–HCO. The DFT calculations verified the strong interaction between Pt nanoparticles and carbon supports. Moreover, our demonstration of the superior benzene oxidation activity of Pt/biomass–HCO catalysts revealed that it is feasible to utilize oxygen-enriched biomass carbon as catalytic supports toward the oxidation of volatile organic compounds.

Improved Borohydride Oxidation Reaction Activity and Stability for Carbon-Supported Platinum Nanoparticles with Tantalum Oxyphosphate Interlayers

Platinum electrocatalysts are active for the borohydride oxidation reaction (BOR) in an alkaline environment. However, high surface area carbon-supported platinum (Pt/C) electrodes are not viable long term in alkaline solutions at 60 °C, because Pt nanoparticles are dislodged from the C surface over time due to carbonate formation and the Pt is poisoned by intermediates in the BOR, causing a significant loss in activity. We demonstrate that platinum has increased BOR activity and durability when supported on a tantalum oxyphosphate (TaOPO4) interlayer on Vulcan carbon (VC) (Pt/[TaOPO4/VC]). Pt/[TaOPO4/VC] is compared to Pt/VC electrocatalysts at the anode of a hydrogen peroxide direct borohydride fuel cell (H2O2-DBFC) and using rotating disk electrode (RDE) voltammetry in a half cell measurements. Accelerated stress testing with rotating disk electrode voltammetry is carried out in both 0.10 M NaOH at 25 °C and 0.05 M NaBH4 + 1 M NaOH at 60 °C. The TaOPO4 interlayer between the Pt and VC improves performance and durability in the range of 10 to 20%, suggesting that this is a promising approach for stabilizing Pt in aggressive alkaline environments.

Fuel Cell Automotive Drive-Cycle Cathode Catalyst (Pt/C) Layer Durability: Dependence on Low Vs. High Carbon Supports and Ionomer-to-Carbon-Ratio

The typical urban automotive drive-cycle for proton exchange membrane fuel cells (PEMFC) consists of frequent idle-to-peak power cathode voltage transients, with extremes ranging from 1.2 V to 0.6 V, respectively. Understanding the platinum electrochemical surface area (ECSA) loss mechanisms dependence on material and operational conditions have been extensively investigated with the objective of minimizing performance losses over the lifetime of PEMFC powered automobiles. Commonly, automotive accelerated stress tests (AST) are performed ex-situ on thin catalyst films. The standard catalyst consists of carbon supported platinum nanoparticles (Pt/C). This study compares triangle waveform (TW) ASTs monitoring ECSA loss for ex-situ (thin film in 0.1 HClO4) and in-situ (catalyst layers bond with ionomeric electrolyte in a complete membrane electrode assembly (MEA)). The ionomer-to-carbon ratios (I/C) of the MEAs is varied from 0.6 to 1.5 on either low surface area carbon (LSAC) or high surface area carbon (HSAC) supports. The AST profiles included 25k cycles at 10 sec intervals, between the upper potential limit of either 0.9 V or 1.2 V and the lower potential limit of 0.6V, with intermediate ECSA evaluations from the H-desorption current (0.02 V → 0.4 V).The electrolyte environment alters, liquid vs. ionomer, the dominant AST decay mechanism, Figure 1A. The decay in the liquid electrolyte is most sever upon initiation of the AST and the rate of decay decrease after the first 2000 cycles. While the MEA decay is less initial, but maintains the same rate of initial decay over 5000 cycles resulting in a higher overall loss of ECSA. ECSA decay is exacerbated at temperatures of 70°C. Increasing the I/C increases the interfacial acidity at the surface of the Pt/C and results in exacerbated ECSA loss, Figure 1B. In accordance with the Pourbaix diagram for Pt, it is less stable in a more acidic environment. The relative rate of ECSA loss is reduced on HSAC supports. Figure 1

Boosting the Role of Ir in Mitigating Corrosion of Carbon Support by Alloying with Pt

Corrosion of carbon support is one of the most crucial causes of the degradation of polymer electrolyte membrane fuel cells (PEMFCs) utilizing carbon-supported platinum nanoparticles (Pt/C) as a ca...

Space-confined catalyst design toward ultrafine Pt nanoparticles with enhanced oxygen reduction activity and durability

Carbon supported platinum nanoparticles have been widely used to catalyze oxygen reduction reaction (ORR), however, their real-world applications in polymer electrolyte membrane fuel cells (PEMFCs) is mainly bottlenecked by insufficient catalytic activity and durability due to particles agglomeration and dissociation from support material. Herein, we have developed a facile catalyst design to embed ultrafine Pt nanoparticles inside the nanopores of carbon support towards increased Pt atom utilization and suppressed Ostwald ripening through space-confinement effect. Besides, the novel strategy endows the resultant Pt nanoparticles with an optimized electronic structure, which further accelerates ORR kinetics. Due to these attributes, the as-prepared Pt nanoparticle inside pore (Ptinside/KJ600) catalyst have shown remarkable initial mass activity of 0.558 A mg−1Pt (@0.9 V vs RHE), which is 3.30 times higher than commercial Pt/C and outperforms most of the reported Pt catalysts. Beyond that, the catalyst also exhibits significantly improved durability with 9 mV negative shift in half-wave potential after 20 K cycles, while commercial Pt/C benchmark displays a 52 mV negative shift. The structural characterizations after durability test confirmed that the pore-confinement design can effectively inhibit the particle agglomeration with negligible increase in particle size. This catalyst design can be easily applicable to other metal-based catalyst and heteroatoms doping.