Carbon-supported Platinum Catalysts Research Articles

Water Condensation in the Nanoscale Pores of Pt/C Catalyst Particles and Its Impact on Catalyst Utilization: A Simulation Based on a Reconstructed Structure from Nanoimaging.

In polymer electrolyte membrane fuel cells, carbon-supported platinum (Pt/C) catalyst particles require sufficient water condensation within the nanoscale pores to effectively utilize the interior Pt catalysts. Since experimental visualizations with nanoscale precision of this phenomenon are not yet possible, we utilized a Pt/C catalyst particle reconstructed from segmented nanoimaging of a catalyst powder, which served as the computational domain for lattice density functional theory (LDFT) simulation of water condensation. Paired with experimental water uptake data, LDFT successfully simulated high-resolution water condensation, capturing both thin-film and capillary water condensation phenomena. Using a simple proton movement method within the water network, we reproduced the Pt utilization data from a CO stripping experiment. Our findings highlight that at low relative humidity (RH), Pt utilization is influenced by thin water film formations, mainly dictated by the wettability properties of surfaces within primary pores and the Pt/C catalyst particle's exterior. Conversely, at high RH, Pt utilization is attributed to capillary water condensation in medium-to-large sized pores. This approach contributes a qualitative and quantitative discussion on hypotheses regarding the mechanism of Pt utilization, supporting recent studies (e.g., Girod, R.; Nat. Catal. 2023, 6, (5), 383-391).

Research on preparation of high activity and durable carbon-supported platinum catalyst for methanol electro-oxidation by a facile continuous microwave pipeline method

In methanol oxidation reaction (MOR), it is crucial for the catalyst that Pt particles uniformly cover the surface of the carrier and the Pt surface active sites can effectively remove the binding with CO. This article develops a simple and effective continuous microwave technology. Carbon loaded nano platinum was synthesized by rapidly and uniformly heating a ethylene glycol mixture containing carbon black (CB) H2PtCl6 using microwave radiation, with a Pt content of 49.5%. The experimental results indicate that platinum particles are uniformly loaded onto the carbon surface, with uniform shape and size, and an average particle size of 3.02 nm. And the Pt/C catalyst prepared by continuous microwave technology showed enhanced electrocatalytic activity (peak current density of 76.95 mA/cm2) in MOR after heating at appropriate temperature in N2 atmosphere, which exceeded the commercial catalyst TKK (47.07 mA/cm2) by 63.6%. And the catalyst's resistance to CO toxicity and durability; Higher than commercial Pt/C catalysts. Compared with traditional methods, continuous microwave technology exhibits higher energy utilization efficiency and faster reaction speed in the catalyst preparation process. This technology also has the ability to achieve continuous preparation, which is one of the effective technological approaches to achieve large-scale catalysts production.

Nonporous Carbon-Supported Platinum Catalyst for Polymer Electrolyte Membrane Fuel Cell

Nonporous Carbon-Supported Platinum Catalyst for Polymer Electrolyte Membrane Fuel Cell

Performance and Durability of Carbon-Free Ionomer-Free PEFC Cathode Using Pt Nanosheet Catalyst

Polymer electrolyte fuel cells (PEFCs) have been attracting attention as highly efficient power sources and have been commercialized for use in residential power plants and automobiles. However, further widespread adoption requires the development of low-platinum catalysts. Additionally, for installation in heavy duty vehicles such as large trucks, high durability at high temperatures is necessary. Pt nanosheets (Pt(ns)), consisting of several atomic layers of Pt with a flat structure, possess high mass activity and durability due to the high specific surface area and low surface energy [1]. Conventional PEFC electrodes consisting of carbon-supported platinum (Pt/C) catalyst and ionomer suffer from degradation due to dissolution/redeposition, Ostwald ripening, and agglomeration of Pt, corrosion of the carbon support, and Pt poisoning by ionomer. Therefore, using unsupported Pt(ns) for an electrode that consists of neither carbon nor ionomer is expected to eliminate the degradation factors, resulting in a highly active and durable electrode. The purpose of this study is to develop highly active and durable electrodes by using Pt(ns) and eliminating degradation factors by making them carbon-free and ionomer-free.Polycrystalline Pt(ns) was synthesized by interlayer oxidation of graphene, as described elsewhere [2]. Catalyst ink was prepared, and cathode catalyst layers were created by dropping or spraying it onto carbon paper. A membrane-electrode assembly (MEA) was made by hot-pressing the cathode catalyst layer together with an anode made of Pt/C onto an electrolyte membrane. Power generation was conducted at 80˚C by supplying H2 to the anode and O2 or air to the cathode, each humidified under ambient pressure. Durability was evaluated by repeatedly applying cyclic potentials between 1.0 V and 1.5 V, supplying N2 to the anode and cathode, and examining changes in the cyclic voltammogram.The I-V curves of MEAs with ionomer-free carbon-free Pt(ns) cathodes fabricated using drop-coating and spray-coating methods and measured using air and oxygen as the cathode supply gases are shown in Fig. 1. As demonstrated in the figure, the activation overpotential at low current density was high, suggesting a low Pt utilization. The shape of the I-V curve of MEA using the spray method at high current density indicated that the concentration overpotential was suppressed under oxygen conditions but was high under air conditions. On the other hand, the concentration overpotential of the MEA using the drop method was high even under oxygen conditions. This may be attributed to the small spaces between the restacked nanosheets, which inhibited diffusion.A start-stop simulated potential cycle test was conducted for the MEA using ionomer-free carbon-free Pt(ns) cathode. The CV curves measured after a certain number of cycles are shown in Fig. 2. As shown in the figure, the change in the shape of the CV was small, and the ECSA remaining rate of the electrode was above 80% even after 8000 cycles, whereas that of the Pt/C cathode was less than 50% after 4000 cycles. This suggests that carbon-free ionomer-free Pt(ns) electrode has the potential as highly durable low Pt electrodes.AcknowledgementPart of this paper is based on results obtained from a project, JPNP20003, subsidized by the New Energy and Industrial Technology Development Organization (NEDO).

Confined tuning of the charge distribution of Pt electrocatalyst for reinforcing anti-poisoning ability: Toward efficient separation of hydrogen from gases containing ammonia

The development of catalysts for hydrogen oxidation reaction (HOR) with enhanced resistance to ammonia poisoning is an important factor in the practical application of hydrogen electrochemical purification devices (HEPDs). This paper reports on the creation of a highly active and anti-ammonia HOR catalyst developed by tuning the charge distribution of the support material through nitrogen-doping of carbon. The nitrogen-doped carbon-supported platinum catalyst (Pt-N2/KB, 2.03 wt% Pt) achieves a high mass activity and exchange current density of 2788 mA mgpt-1 and 1020 mA mgpt-1, respectively, which are 5.4 and 4.7 times higher than that of the comm. 20% Pt/C. The Pt-N2/KB catalyst also displays a lower percentage of current decay and enhanced electrochemical stability, indicating superior anti-ammonia toxicity in the tests with HEPD. Density functional theory (DFT) calculations reveal that the hydrogen adsorption free energy (ΔGH*) on the surface of Pt-N2/KB is close to zero and has a lower ammonia adsorption energy, thus accounting for its superior HOR activity and anti- ammonia poisoning ability. Consequently, this work facilitates the implementation of HOR catalysts for anti-ammonia poisoning in the HEPDs, thus accelerating the advancement of ammonia cracking for hydrogen production.

Accelerated Stress Test Study on PtRu Anode Catalysts for Reformate PEM Fuel Cells

Proton-exchange membrane fuel cells (PEMFCs) are interesting candidates for heavy duty applications, e.g. in the maritime or bus and truck sector, since they convert renewable fuels into electricity efficiently [1]. Moreover, PEMFCs are flexible with respect to fuels, since they can be operated not only with hydrogen but also with reformate gas, originating from steam reforming of carbohydrates such as renewable methanol [2]. Compared to state-of-the-art carbon-supported Platinum catalysts (Pt), which are severely poisoned by CO, a side product from reforming, carbon-supported Platinum-Ruthenium catalysts (PtRu) prevail in reformate applications due to their promoting effects towards CO oxidation [3]. However, PtRu catalysts are less stable than Pt catalysts due to a higher susceptibility to dissolution [4]. Since the durability of materials in heavy duty applications is crucial to reach long operating times (> 30000 h), major efforts have to be taken to improve the stability of PtRu anode catalysts.To be able to evaluate the stability of catalysts and to investigate, identify, and understand degradation mechanisms with little time and costs, so-called accelerated stress tests (ASTs) are deployed, which induce fast electrode aging and ideally simulate electrode degradation that can be transferred to real operating conditions. For Pt cathode catalysts in PEMFC application, the U.S Department of energy proposed an AST based on square wave potential cycling between 0.6 V and 0.95 V for 30000 cycles [5]. As Ru and possibly PtRu have different dissolution potentials than Pt and are used on the anode side (therefore exposed to different potentials compared to the cathode), an AST designed for PtRu anode catalysts is required.In this work, several AST protocols based on square cycling the anode potential for 30000 cycles were developed and tested on cells with the same material composition. The carbon-supported PtRu anode electrodes were manufactured in-house with a patented technique [6], while for membranes, cathode catalysts, and GDLs commercial available products were applied. The ASTs differ by the upper potential limit, which was chosen at 0.2 VRHE, 0.65 VRHE, 0.8 VRHE, and 1.0 VRHE, respectively. The lower potential limit was set at 0.06 VRHE, (cf. Figure 1b). Before, during, and after the AST, electrochemical characterization was conducted via cyclic voltammetry, CO-stripping, and recording U-I curves (cf. Figure 1a). After the AST, post-mortem analyses were performed by means of transmission electron microscopy, X-ray diffraction, and cross-sectional scanning electron microscopy coupled with energy dispersive X-ray spectroscopy to analyze the prominent degradation mechanisms occurring for the different testing conditions.Strong differences in the degradation of the cells between the different ASTs could be observed. With increasing upper potential limit, the severity of degradation and the observed degradation phenomena increased. For example, Ru leaching occurred at ASTs with upper potentials beyond 0.65 VRHE, and increased with increasing potential, resulting in a reduced CO-tolerance. At the same time, the consequent Ru crossover to the cathode, which lowers the overall cell performance, could be only detected by EDX for ASTs beyond 0.8 VRHE, implying a correlation between Ru crossover and upper potential limit. Moreover, the data indicate that an upper potential limit of 1.0 VRHE may be too high to investigate the stability of Ru in PtRu catalysts, as an additional strong Pt degradation makes the evaluation difficult. Future work will address the correlation of these ASTs to long-term testing at constant potential.

(Invited) Lowering the Noble Metal Requirement for PEM Water Electrolysis: Membrane Electrode Assembly and Porous Transport Layer Design Considerations

The Net Zero Emission scenario proposed by the International Energy Agency projects a required electrolytic generation of hydrogen equivalent to 3600 GW by 2050 [1], averaging to an annual installation of ~130 GW/a between 2023 and 2050. If this were to be provided by proton exchange membrane based water electrolyzers (PEM-WEs) based on platinum catalysts for the hydrogen evolution reaction (HER) and iridium catalysts for the oxygen evolution reaction (OER), the current PEM-WE noble metal requirements of ~0.7 gIr/kW and ~0.3 gPt/kW [1] would have to be drastically reduced in view of the noble metal supply constraints. As argued previously, for PEM-WEs to be sustainable on such a large scale would require to achieve platinum and iridium loadings of ~0.05 mg/cm2 electrode [2,3]. While the former can be easily achieved due to the fast HER kinetics on Pt, the latter requires either ultra-thin OER catalyst layers or improved OER catalysts with a substantially reduced iridium packing density (in units of gIr/cm3 electrode) [2], like the recently developed catalyst with a hydrous iridium oxide shell supported on a titanium oxide core (IrOx/TiO2) [4,5].In this contribution, we will discuss the effect of the design of membrane electrode assemblies (MEAs) and of the adjacent porous transport layers on PEM-WE performance. In general, the preparation of MEAs with low platinum loading cathodes is straightforward, due to the availability of carbon supported platinum catalysts (Pt/C) with a low Pt packing density. For the optimization of the ionomer content in the cathode electrode, however, its effect on the high current density performance and on the hydrogen permeation rate from cathode to anode have to be considered [6,7].With regards to the anode electrode, we will further discuss the MEA design challenges when targeting ultra-low iridium loadings. In the case of the ultra-thin catalyst layers that result when using conventional OER catalysts, additional contact resistances between the anode catalyst layer and the titanium based porous transport layer (Ti-PTL) are observed [2]. As will be shown, these can be largely mitigated by the use of a titanium based microporous layer (MPL) coated on the Ti-PTL, highlighting the importance of the interface between the PTL and the anode catalyst layer. In case of using the above described IrOx/TiO2 catalysts with low iridium packing density, their typically lower electrical conductivity also results in apparent contact resistances within and across the anode catalyst layer [4], which poses an additional constraint on the allowable range of the catalyst/ionomer ratio in the anode electrode. The interplay between the anode catalyst type, the anode ionomer content, and the type of interface between the anode electrode and the PTL (i.e., with and without MPL) will be discussed.

Preparation of Membrane Electrode Assemblies Using Waste Tire Derived Carbon Supported Platinum Catalyst

Since the world’s population and energy demand are constantly growing and energy is largely based on the use of non-renewable energy sources, it would be necessary to find an alternative, more environmentally friendly energy carrier [1]. One of the most important alternative energy carriers is hydrogen, which is used in the operation of the polymer electrolyte membrane fuel cell (PEMFC), where chemical energy is converted into electrical energy, and only heat and pure water are released during operation [2]. As the demand for means of transport is also increasing in the world, more and more old tires are generated every year (5 billion are predicted for 2030 ) [3]. Waste tires do not decompose and generally end up in landfills, which is not a sustainable solution. Therefore, opportunities are being sought for the recycling of waste tires in various fields. In this work, a Pt catalyst material is synthesized using carbon made from waste tires as a support material [4].The aim of this work was to investigate the activity of oxygen reduction reaction (ORR) of synthesized platinum catalysts. The Pt deposition was performed by two different methods. Synthesized catalyst materials (S1 and S2) and commercial catalyst (K) for comparison were characterized physically to obtain information on Pt weight percent and Pt crystallite size, material elemental composition, specific surface area, and porosity. Catalysts were characterized electrochemically using rotating disk electrode and cyclic voltammetry methods to determine their ORR kinetics. Measurements of PEMFC performance in air showed that catalyst materials with smaller Pt crystallite size and higher ECA values also had higher ORR activity. In addition, it was found that the power density depends significantly on the carbon used in the synthesis of the Pt catalyst and the method of preparation of the membrane electrode assembly (MEA). Based on the PEMFC measurements of the optimized MEAs, the power density increased in the order S1 < S2 < K.

Zeolite Imidazolate Framework-Derived N-Doped Carbon-Supported Ultra-Low Platinum Catalyst for Enhancing Methanol Oxidation Reactions

Direct methanol fuel cells (DMFCs) have a broad application market due to their merits of high power density, wide source of raw materials, and convenient storage and transportation. At present, the common platinum (Pt) catalysts have some problems, such as low reserves, and expensive and poor reaction kinetics. Therefore, a zeolite imidazolate framework (ZIF) derived N-doped carbon-supported ultra-low platinum catalysts (Pt-Co@ZCN) are prepared using ZIF-67@ZIF-8 as the support. The effects of heating rate on the morphology and electrocatalytic performance of the synthesized materials are investigated. The characterization results reveal that the morphology and structure of Pt-Co@ZCN-900-2 are superior to other samples. The mass activity and stability toward methanol oxidation of the synthesized samples are also better than those of commercial Pt/C catalysts.

Facile Synthesis of Nitrogen Doped Porous Carbon Supported Platinum Catalyst and Improvement of Electrocatalytic Ethanol Performance

Direct ethanol fuel cells (DEFCs) have become an alternative to traditional fossil fuels because of their low emissions, fast start-up and high energy density. Platinum (Pt)-based catalysts are the most effective catalysts for DEFCs, but their high cost and poor electrocatalytic performance hinder their practical application. Therefore, there is an urgent need to design Pt-based catalysts with low platinum content, high electrochemical activity and stability. Herein, nitrogen-doped porous carbon-loaded Pt catalysts (Pt@Co-CN) were prepared by in situ polymerization and high-temperature calcination using the metal-organic framework materials (MOFs) ZIF-8@ZIF-67 as the carriers. The effects of the addition of pyrrole monomer on the morphology and electrocatalytic properties of the samples were investigated. The sample with the complete coating layer and uniformly dispersed Pt nanoparticles (Pt@Co-CN) could be obtained by adding an appropriate amount of pyrrole monomer. The results of the electrochemical tests showed that the electrochemical activity of Pt@Co-CN catalytic ethanol is superior to that of commercial catalysts and samples with insufficient or excessive addition of pyrrole monomers. The content of this study provides a new method for the electrocatalyst of DEFCs.

Preparation of Membrane Electrode Assemblies Using Waste Tire Derived Carbon Supported Platinum Catalyst

Carbon supported Pt catalyst materials were synthesized from waste tire derived carbon by two different methods (microwave and refluxing). Catalysts and carbons were physically (XRD, N2 sorption analysis, TGA) and electrochemically characterized (RDE, CV, PEMFC single cell measurements). The RDE measurements were performed in 0.1 M HClO4 solution. For PEMFC single cell measurements, membrane-electrode assembly systems (MEAs) were prepared from catalyst materials by using different methods of coating the cathode layer and additional treatments. Catalysts were sprayed onto the membrane or GDL. In addition, MEAs were prepared where the catalyst was pipetted into GDL in several drops. Some of the MEAs were additionally treated with extra layer of Nafion and hot-pressed. The highest power density (0.42 W cm−2) was achieved with the MEA where the Pt catalyst synthesized via refluxing method was coated on the GDL with multiple drops and additional treatments were applied.

Effect of hydrogen impurities on hydrogen oxidation activity of Pt/C catalyst in proton exchange membrane fuel cells

AbstractHigh-purity of hydrogen is vital to the guarantee of end usage in proton exchange membrane fuel cell (PEMFC) electric vehicles (EVs) with superior durability and low expense. However, the currently employed hydrogen, primarily from fossil fuel, still contains some poisoning impurities that significantly affect the durability of PEMFCs. Here, we investigate the poisoning effect of several typical hydrogen impurities (S2–, Cl–, HCOO– and CO32–) on the hydrogen oxidation reaction (HOR) of the state-of-the-art carbon-supported platinum (Pt/C) catalyst used in the PEMFC anode. Electrochemical results indicate that the electrochemically active surface area of Pt/C is hampered by these hydrogen impurities with reduced effective Pt reactive sites due to the competitive adsorption against hydrogen at Pt sites showing the extent of the poisoning on Pt sites in the order: S2– &amp;gt; Cl– &amp;gt; HCOO– &amp;gt; CO32–. Density functional theory calculations reveal that the adsorption energy of S2– on Pt (111) is greater than that of Cl–, HCOO– and CO2, and the electronic structure of Pt is found to be changed due to the adsorption of impurities showing the downshift of the d-band centre of Pt that weakens the adsorption of hydrogen on the Pt sites. This work provides valuable guidance for future optimization of hydrogen quality and also emphasizes the importance of anti-poisoning anode catalyst development, especially towards H2S impurities that seriously affect the durability of PEMFCs.

Pt-Bi on carbon aerogels as efficient electrocatalysts for ethanol oxidation reaction in alkaline medium

Platinum-containing multimetallic catalysts supported on carbon materials have become one of the main choices for direct ethanol fuel cells (DEFCs) due to their high catalytic activity for the ethanol oxidation reaction (EOR). In this study, a platinum-bismuth alloy catalyst (PtBi@CA) with uniform distribution and small particles was provided by a one-step reduction method without the addition of structure directing agents and stabilizers. In the half-cell test, PtBi@CA(50−50) with the smallest crystallite size has high peak current density and pseudo-steady current density of 64.336 mA/cm2 and 0.096 mA/cm2, respectively, which is 11.22 times and 1.85 times the high of the most advanced commercial carbon-supported platinum catalysts (Pt/C). The method is simple and feasible, greatly reduces the amounts of precious metals, and has broad application prospects in the synthesis of anode electrocatalysts for direct ethanol fuel cells.

Study on durability of proton exchange membrane fuel cell stack based on mesoporous carbon supported platinum catalysts under dynamic cycles conditions

Insufficient durability still restricts the large-scale commercialization of fuel cells, rapid degradation of catalyst is considered to be the main reason, while support also plays an important role.In this study, the cyclic potential scanning with varies harshness to the catalysts are performed firstly. The membrane electrode assemblies (MEAs) are assembled to stack to perform the accelerate durability test (ADT) under New European Driving Cycle (NEDC) for 1000 h. The results show that, the durability of self-made catalysts is better than the commercial, and the voltage decay rate of commercial-MEA-Stack (35 μV h−1) is significantly higher than the self-made-MEA-Stack (5 μV h−1). Before and after the durability test, the charge and mass transfer impedance of S-MEA-Stack changes little, while that of C-MEA-Stack increases. Post-characterizations show that the self-made catalysts have better stability. In conclusion, the catalyst layer binding network based on mesoporous carbon has a more stable structure, which ensures the effective gas transport, while the high specific surface area structure is conducive to uniform distribution and stability of ionomers. Pt nanoparticles in mesoporous carbon can avoid the agglomeration and sintering, and the poisoning effect of sulfonate, thus improves the durability of the catalyst layer.

(Digital Presentation) Effect of Iron Doping on Oxygen Reduction Activity of Zirconium Oxides Containing Carbon and Nitrogen Using Pyrazine Carboxylic Acid As Platinum Alternative Cathodes for PEFC

The use of carbon-supported platinum catalysts as cathode of present polymer electrolyte fuel cells (PEFCs) have some problems such as high cost and low amount of resources of platinum. Therefore, we have attempted to develop substitute of platinum based on group 4 transition metal oxides. We found that stable oxygen vacancies on the surface and lattice distortion by doping foreign elements of these metal oxides could act as active sites of oxygen reduction reaction (ORR) [1]. However, although zirconium oxides show some ORR activity, the onset potential of the ORR still remains low. Then, we focused on the improvement of the ORR activity by an addition of iron ions to zirconium oxides according to the research of P. Madkikar et. al. [2]. In this study, we used pyrazine carboxylic acid as ligand of metal ions to prepare zirconium-iron complexes including carbon and nitrogen as precursors. The precursors were heat-treated under low oxygen pressure to obtain the iron-added zirconium oxide-based catalysts, which are designated as ZrOx-Fe. We investigated the correlation between the ORR activity and physical characteristics such as crystalline phase.ZrOx-Fe catalysts were synthesized according to the previous patent [3]. We prepared zirconium complexes solutions by mixing zirconium butoxide and acetic acid in acetylacetone as a solvent. On the other hand, we also prepared iron complexes solutions by mixing iron acetic acid and pyrazine carboxylic acid in mixed solvents of water, ethanol and acetic acid. The amount of the iron addition was changed in atomic ratios of 0, 0.004, 0.01, 0.1, and 0.2 against Zr atoms. The iron atomic ratio of 0.004 was selected according to P. Madkikar’s results, because Fe atomic ratio of 0.0036 caused the highest ORR activity in the report [2]. After mixing of two solutions, the solutions were stirring several days, and the precursors were obtained by evaporation and vacuum drying. These precursors were heat-treated under argon including 2 % hydrogen and 0.05 % oxygen for low oxygen pressure oxidation, and finally ZrOx-Fe catalysts were obtained. To investigate the effect of Fe addition to zirconium oxides, we also synthesized iron-based catalyst without Zr in the same way. Electrochemical measurements were conducted in the solution of 0.5 M H2SO4 at 30 oC. In this study, we used the ORR onset potential as the parameter of the ORR activity, which was defined as the potential when the ORR current (i ORR) was 0.01 ampere per a mass of the whole catalysts.Among the ZrOx-Fe catalysts prepared in this study, ZrOx-Fe with the Fe atomic ratio of 0.1 showed the highest E ORR, which was designated as ZrOx-Fe(0.1). Therefore, we compared with ZrOx and FeOx prepared by the same way as well as conventional catalysts. Fig. 1 shows the ORR polarization curves of the ZrOx, ZrOx / CNT [1], ZrOx-Fe / KB [2], FeOx and ZrOx-Fe(0.1) catalysts. As shown in Fig.1, the ZrOx-Fe(0.1) catalyst had highest ORR onset potential among these catalysts. Comparing with ZrOx, FeOx and ZrOx-Fe(0.1), the Fe addition into zirconium oxide was essential to increase the ORR onset potential. In addition, the onset potential of the ZrOx-Fe(0.1) was higher than that of the ZrOx-Fe / KB [2] and our previous ZrOx / CNT [1]. The onset potential of the ZrOx-Fe(0.1) was exceeded 0.9 V that we have never been able to reach with zirconium oxides. Therefore, the addition of iron to zirconium oxides improved drastically the quality of the active sites of the ORR.Next, we examined crystalline phase of all ZrOx-Fe catalysts with XRD. All ZrOx-Fe catalysts were consisted of ZrO2 monoclinic or tetragonal phase. We calculated monoclinic rate in each catalyst using the equation in the literature [4]. The change of atomic ratio of Fe caused the different monoclinic rate. A positive correlation between the ORR onset potentials and the monoclinic rates of the ZrOx-Fe was obtained. Thus, the ORR onset potential increased with increasing the monoclinic rate in the catalysts, suggesting that the monoclinic phase formed the active sites of the ORR.AcknowledgementThe authors thank the financial support of the New Energy and Industrial Technology Development Organization (NEDO), JSPS grants-in-aid for scientific research, and ENEOS Tonen General Sekiyu Research / Development Encouragement & Scholarship Foundation.References(1) A. Ishihara et. al., Int. J. Hydro. Energy, 45, 5438 (2019).(2) P. Madkikar et. al., J. Electrochem. Soc., 166, F3032 (2019).(3) Showa Denko Corp., R. Monden et. al., Oxygen reduction catalysts, the methods of these, and polymer electrolyte fuel cells, JP 2013-240785, 2013-12-05.(4) H. Toraya et. al., J. Am. Ceram. Soc., 67, C119 (1984). Figure 1

Multi-sites synergistic modulation in oxygen reduction electrocatalysis

Revealing the types of and interplays among multiple active-sites in iron-nitrogen-carbon (FeNC) materials is of great significance for developing high-performance, Fe-based non-precious metal catalysts for oxygen reduction reaction (ORR). In this paper, a single-atom FeNC catalyst is prepared through high-temperature pyrolyzing of melamine foam (MF), iron phthalocyanine (FePc), phthalocyanine (Pc), and zinc (Zn)-salts composite. The catalyst is found to contain a variety of active-sites, including carbon atom next to pyridinic-N (pyridinicNC), Fe-N4 and pore defect. It is shown that MF with high N-content is responsible for the formation of the main pyridinicNC sites and in the meantime acts as the self-sacrificed template for framework of the catalyst. The presence of Pc can facilitate the formation of the predominant Fe-N4 sites, since the interplay between Pc and FePc results in a confinement of Fe-N4. Zn-salts serve as the pore-forming additives to create sufficient pore defects which can also anchor pyridinicNC and Fe-N4 structures. The results of density functional theory (DFT) calculations suggest that the multiple active-sites function synergistically to enable high-efficiency ORR electrocatalysis. The optimal FeNC catalyst shows superior ORR activity with a half-wave potential of ∼0.88 V (vs. RHE), as well as high methanol tolerance and electrochemical stability compared to the commercial carbon-supported platinum (Pt/C) catalyst.

Batch synthesis of high activity and durability carbon supported platinum catalysts for oxygen reduction reaction using a new facile continuous microwave pipeline technology

Traditional synthesis methodologies for fuel cell catalyst production involve long reactions and uncontrollable reaction processes. Synthesis methods for the production of catalysts typically have difficulties to achieve catalysts materials with consistency, high activity, and durability. In this study, a fast, simple, and suitable continuous pipeline microwave method for catalyst mass production was developed, with the carbon carrier being treated at different temperatures simultaneously. The method herein developed resulted in carbon-supported platinum (Pt) catalysts with high activity and high durability. In addition, the half-wave potential of the catalyst exceeded 0.9 V, the electrochemical active surface area reached 85.7 m2-gPt−1, and the mass specific activity reached 171.1 mA-mg−1. Remarkably, after 30,000 cycles of Pt attenuation tests and 30,000 cycles of carbon carrier attenuation tests, the retention rate of the annealed carbon carrier catalyst reached 80 %. As a membrane electrode, the catalyst generated a single cell maximum power density of 1.4 W-cm−2, and the Pt content reached 0.286 gPt-kW−1. The work provides an effective and practical method for the mass production of high-performance and high-durability catalysts, which guiding significance for mass production of catalysts.

Investigation of IrO2 Stability As a Cell-Reversal Mitigation Catalyst in PEMFC Anodes

In the recent years, the use of fuel cells for the propulsion of passenger vehicles and heavy-duty vehicles has gained renewed interest as alternative to internal combustion engine-powered vehicles. Particularly for the latter, the long-term durability of proton-exchange-membrane fuel cells (PEMFCs) is still a concern, which in part is governed by the catalyst layer durability during system operating conditions.1 During the operation of a PEM fuel cell system, certain transient conditions can occur that can lead to rapid degradation of the catalyst layers. On one hand, the widely studied start-up/shut-down (SUSD) phenomenon leads to significant degradation of the cathode catalyst layer due to the exposure of the cathode electrode to high potentials (>>1.0 V vs the reversible hydrogen electrode potential (VRHE)) that results from a H2/air-front passing through the anode flow field.2 On the other hand, an intermittent under-supply of hydrogen to one or several cells of a PEMFC stack can lead to a so-called cell-reversal (CR) event, resulting in the oxidation of the carbon support of the anode catalyst and in the subsequent collapse of the anode catalyst layer structure. The latter can be mitigated by the addition of an anode co-catalyst that facilitates the oxygen evolution reaction (OER) at much lower potentials than the carbon-supported platinum catalyst (Pt/C) that serves as anode catalyst for the hydrogen oxidation reaction (HOR).3 However, as shown by our recent study, the stability of the anode co-catalyst for the OER during SUSD events must be considered.4 In the present study, we examine different accelerated stress tests (ASTs) for single-cell PEMFCs that are designed to assess the stability of an anode co-catalyst for the OER in a PEMFC that is subjected to cell-reversal and SUSD events. Thus, we evaluated the stability of an anode co-catalyst under four conditions: i) subjecting the cell to extended SUSD cycles; ii) a cell-reversal protocol where a constant current is being drawn when feeding N2/air to the anode/cathode until a given cut-off cell potential is reached; iii) a protocol where cell-reversal cycling is induced by switching the anode feed gas between hydrogen and nitrogen while applying a constant current and supplying air to the cathode (later on referred as CR cycling); and, iv) an anode potential cycling protocol where the anode is supplied with N2, and its potential is cycled potentiostatically to different upper potential limits, with the cathode purged with air and serving as a counter electrode. With these ASTs, we examine the effect of the different anode potential cycles during SUSD and CR transients in order to elucidate the dependence of the IrO2 dissolution rate on operating potential.The stability of the IrO2 based anode co-catalyst is investigated by electrochemical measurements (cyclic voltammetry and polarization curves) and additionally via ex-situ XPS analysis. For example, Figure 1 shows the ex-situ XPS analysis of pristine and aged membrane electrode assemblies (MEAs). The upper two panels show the XPS data in the Pt 4f (BE>67 eV) and the Ir 4f (BE<67 eV) regions of the pristine Pt/C anode with an IrO2-based anode co-catalyst (Figure 1a) as well as the pristine Pt/C cathode (Figure 1b). The lower two panels show the cathode XPS data of the MEAs after 500 SUSD cycles (Figure 1c) and after 500 CR cycles (Figure 1d). In the case of the SUSD degraded MEA, a higher amount of Ir is observed on the cathode when compared to the CR degraded MEA. The mechanistic implications of these data will be discussed. References USDRIVE Fuel Cell Technical Team Roadmap (2017): https://www.energy.gov/eere/vehicles/downloads/us-drive-fuel-cell-technical-team-roadmap (accessed on 28.10.2021).T. Mittermeier, A. Weiß , F.Hasché, G. Hübner, H. A. Gasteiger. Journal of The Electrochemical Society, 164 (2), F127-F137 (2016).T. R. Ralph, S. Hudson, and D. P. Wilkinson, ECS Transactions, 1 (8), 67-84 (2006).M. Fathi Tovini, A. M. Damjanović, H. A. El-Sayed, J. Speder, C. Eickes, J.-P. Suchsland, A. Ghielmi, and H. A. Gasteiger, Journal of The Electrochemical Society, 168 (6), 064521 (2021). Figure 1

Investigation of Oxygen Reduction on Platinum Nanoparticles Deposited Onto Peat-Derived Carbon Carrier

Carbon supported platinum catalysts for proton exchange membrane fuel cell (PEMFC) applications have been studied intensively in the scientific community.1,2 The catalytic activity of the catalyst depends on the characteristics of the carbon support material3 and on the Pt depositing method4,5. The aim of the study was to investigate the oxygen reduction reaction (ORR) on Pt nanoparticles deposited on peat-derived carbon. The Pt nanoparticles were deposited on the carbon support material by three different methods using NaBH4 (NBH), ethylene glycol (EG) and isopropyl alcohol (IA) as a reducing agent.The studied materials were characterized using N2 sorption, X-ray diffraction (XRD) and thermogravimetric analysis (TGA). Structure of the platinum nanocatalyst on carbon support was also studied using scanning electron microscopy with energy-dispersive X-ray analysis (SEM-EDX). For electrochemical characterization, the electrochemically active surface area (ECA) of the materials were measured in a three-electrode system (0,1 M HClO4) and in a completed PEMFC. The ORR kinetics of the materials were studied by the rotating disk electrode (RDE) method as well as in a PEMFC configuration.As a result, it was found that the higher the ECA of the material, the higher the catalytic activity. The catalytic activity of the synthesized materials increases in order: IA < NBH < EG. ECA of the materials increases in the same order. Also, the special surface area of the materials increases in the same order. The catalytic activities of the synthesized materials were compared to a commercial catalyst material, 60% Pt on HSA Ketjenblack. References O. Z. Sharaf and M. F. Orhan, Renew. sust. energ. rev., 32, 810–853 (2014).Y. Wang, K. S. Chen, J. Mishler, S. C. Cho, and X. C. Adroher, Appl. Energ., 88, 981–1007 (2011).S. Sharma and B. G. Pollet, J. Power Sources, 208, 96–119 (2012).S. Sepp et al., Electrochim. Acta, 203, 221–229 (2016).P. Valk et al., J. Electrochem. Soc., 165, F315–F323 (2018). Acknowledgements The author thanks the European Union Regional Development Fund for the financial support of the project TK141 “Innovative materials and high-tech equipment for energy recovery systems” (2014-2020.4.01.15-0011); the Estonian Research Agency project (personal research support group grant project No. PRG676) and the Estonian Energy Technology Program: SLOKT10209T “. Nanomaterials – research and applications (NAMUR)” project 3.2.0304.12-0397. The author also thanks the private limited company AuVe Tech.

ORR Activity and Stability of a Carbon-Supported Ptxy Alloy Catalyst Evaluated in a PEM Fuel Cell

The application of proton exchange membrane fuel cells (PEMFCs) in light-duty vehicles (LDV) has dominated the fuel cell research field for the past decades. To reduce the LDV FC system cost to 30 $/kW by 2025 has driven the search for highly active cathode catalysts that could substitute the costly state-of-the-art Pt-alloy catalysts or reduce the cathode loadings to < 0.125 mgPt/cm2.1, 2 As novel ORR catalyst continue to emerge, theoretical calculations have turned the attention on Pt-rare earth (RE) alloys, such as platinum-yttrium alloys that were suggested to have superior activity for the oxygen reduction reaction (ORR) and superior long-term stability compared to conventional carbon-supported platinum catalyst (Pt/C). 3 Based on these findings, many attempts have been made to produce high electrochemical surface area (ECSA) Pt-RE alloy catalysts.4 In recent years, Hu, et al. introduced a new synthesis procedure that utilizes a carboiimide-assisted synthesis for the preparation of Pt-RE/C catalysts with an unprecedentedly high ECSAs in the range of ~50-60 m2/gPt.5 With such high ECSA PtxY/C catalysts, good PEMFC performance would be expected, but to date the ORR activity and stability of such PtxY/C catalysts has not been demonstrated in a PEMFC environment.In view of this, we reproduced the synthesis reported by Hu et al. using a Ketjen Black (KB) carbon support. The resulting PtxY/KB catalyst was characterized by X-ray diffraction, X-ray spectroscopy (EDS) in scanning transmission electron microscopy (STEM), and elemental analysis, indicating the formation of a Pt-richshell/Pt3Ycore structure that was caused by the acid washing procedure introduced before the electrochemical characterization.5 In our present study, two different Pt/KB catalysts were selected as reference materials: i) a Johnson Matthey reference catalyst consisting of small well-dispersed Pt nanoparticles on a KB support (Pt/KB-JM); ii) an in-house synthesized Pt/KB catalyst (Pt/KB-syn.) with a similar particle size distribution and ECSA as the in-house synthesized PtxY/KB catalyst (PtxY/KB-syn.). The ECSA (via CO-stripping voltammetry) and the ORR mass activity at 0.9 V vs. RHE (imass 0.9 V) of these three catalysts were first evaluated by rotating disk electrode (RDE) measurements in 0.1 M HClO4 at 25 °C. The catalysts were also incorporated as cathode catalysts in membrane electrode assemblies (MEAs), first determining their ECSA (by CO-stripping) and then their H2/O2 and H2/air performance in a 5 cm2 single-cell PEMFC hardware at 80 °C under differential flow conditions, including a quantification of the ORR mass activity at 0.9 V vs. RHE at 100 kPa O2.As can be seen in Figure 1, the relative ECSA and ORR mass activity values of the three different catalysts obtained in the RDE and the PEMFC configuration were essentially identical when evaluated at the same ionomer to carbon ratio (I/C = 0.7, g/g). Furthermore, a comparison of the RDE ORR activity at two different I/C ratios showed that the PtxY/KB-syn. and Pt/KB-syn. catalysts were more susceptible to ionomer poisoning when compared to the Pt/KB-JM catalyst. Following the approach taken in our previous publications, the voltage-cycling stability of the synthesized catalysts was also evaluated using an accelerated stress test (AST) consisting of a triangular potential scan between 0.6 and 1.0 VRHE at 50 mV/s up to 30000 cycles.5 Overall, the RDE and PEMFC data showed that the here synthesized carbon-supported Pt-richshell/Pt3Ycore catalyst does not shown an enhanced ORR activity nor a long-term stability benefit when compared to a Pt/KB catalyst with the same ECSA, contrary to what had been hypothesized earlier.3 References R. L. Borup, A. Kusoglu, K. C. Neyerlin, R. Mukundan, R. K. Ahluwalia, D. A. Cullen, K. L. More, A. Z. Weber and D. J. Myers, Current Opinion in Electrochemistry, 21, 192–200 (2020).M. Escudero-Escribano, K. D. Jensen and A. W. Jensen, Current Opinion in Electrochemistry, 8, 135–146 (2018).J. Greeley, I. E. L. Stephens, A. S. Bondarenko, T. P. Johansson, H. A. Hansen, T. F. Jaramillo, J. Rossmeisl, I. Chorkendorff and J. K. Nørskov, Nature Chemistry, 1(7), 552–556 (2009).J. N. Schwämmlein, G. S. Harzer, P. Pfändner, A. Blankenship, H. A. El-Sayed, and H. A. Gasteiger, Journal of the Electrochemical Society(165 (15)), J3173-J3185 (2018).Y. Hu, J. O. Jensen, L. N. Cleemann, B. A. Brandes and Q. Li, Journal of the American Chemical Society, 142, 953–961 (2020). Acknowledgment This work has been supported by the Fuel Cells and Hydrogen 2 Joint Undertaking under grant agreement No. 826097 (GAIA). This Joint Undertaking receives support from the European Union’s Horizon 2020 research and innovation programme, Hydrogen Europe and Hydrogen Europe Research. Figure 1