Platinum Catalysts Research Articles

Influence of Ethanol Decomposition on Dispersion of PEFC Catalyst Ink

To achieve high power density operation of polymer electrolyte fuel cells (PEFCs), it is required to realize higher performance catalyst layer. Because dispersion structure of catalyst ink strongly affects the catalyst layer structure, it is crucial to understand the dispersion mechanism of PEFC catalyst ink. Though water/ethanol solution is used as solvent of the catalyst ink, decomposition of ethanol by Platinum catalyst strongly affect dispersion of the catalyst ink. In this study, influence of ethanol decomposition on dispersion of catalyst inks were investigated. Among the decomposition byproducts of ethanol, results of rheology characteristics and direct observation by scanning electron assisted dielectric microscopy clearly showed that acetaldehyde has a significant impact on aggregation of catalyst ink. To reveal the mechanism of aggregation, particle size measurement and ionomer adsorption fraction measurement of the catalyst ink were carried out. The results suggested that the acetaldehyde impede adsorption of the ionomer on Platinum catalyst.

3D Nitrogen-Doped Porous Carbon Supported Pt Catalyst for Electrocatalytic Oxidation of Glucose

Glucose fuel cells have attracted widespread attention in the biomedical field due to their ability to generate electrical energy continuously. The development of this technology has great potential in the application of powering implantable medical devices. However, the efficiency of the glucose oxidation reaction at the anode of the fuel cell is low, and a catalyst needs to be added to improve the reaction efficiency. Platinum (Pt) catalysts are prone to agglomerate during use, which limits the improvement of their properties such as catalytic activity and stability. To address this problem, in this paper, a three-dimensional ( 3D) N-doped porous carbon (NCZIF-8) material with a large specific surface area was prepared as a catalyst carrier using ZIF-8 as a precursor. Low loading rate of platinum (10 wt. %) was prepared (10% Pt/NCZIF-8) and used as catalysts for glucose oxidation reaction. The materials were structurally characterized by XRD, SEM, TEM, Raman and FT-IR, etc. The electrocatalytic properties of the materials were characterized using an electrochemical workstation. It was shown that the incorporation of NCZIF-8 carrier promotes the dispersion of Pt nanoparticles (NPs) and the utilization of the catalyst, which enhances the catalytic activity and stability of catalysts during electrocatalytic glucose oxidation. After 300 times cyclic voltammetry (CV) tests, the peak current density of 10% Pt/NCZIF-8 only decreased by 21. 12% and 8. 59% in the double-layer region and oxygen region, respectively, indicating the excellent stability of the catalyst. This kind of catalyst with low loading rate of precious metal has great potential for its practical application by improving catalyst utilization, which not only improves the catalytic efficiency but also reduces the material cost.

Nitrogen vacancies in monolayer WSi2N4 for hydrogen evolution reaction: A first-principles study

The recent synthesis of two-dimensional layered WSi2N4 has attracted considerable attention owing to its potential applications in diverse fields. In this study, we use first-principles density functional theory calculations to investigate the catalytic performance of WSi2N4 monolayers with nitrogen (N) vacancies in the hydrogen evolution reaction. The calculated Gibbs free energies of the WSi2N4 monolayers are –0.09 eV and –0.10 eV at the vacancy concentrations of 5.6 % and 12.5 %, respectively, which are close to the zero optimal value. The results indicate that the defective WSi2N4 monolayers can exhibit remarkably high catalytic activity comparable to that of platinum catalysts in the hydrogen evolution reaction. In addition, our electronic structure calculations demonstrate the emergence of spin-polarized states near the Fermi level upon introducing N vacancies, which can be attributed to isotropic Zeeman-type spin-splitting.

Development of Non-Spherical Platinum Nanoparticles on Carbon Supports for Oxygen Reduction Reaction

Proton exchange membrane fuel cells are anticipated to play an important role in decarbonizing the global energy system, but the performance of platinum (Pt) catalysts must be improved to make this technology more economical. Studies have identified non-spherical Pt nanoparticles on carbon supports as promising approaches to address this challenge. However, to realize the full benefits of these strategies, the catalyst synthesis procedures must be successfully simplified and scaled up, and the catalyst must perform well in half and full-cell tests. In this study, a surfactant-free one-pot method is developed to synthesize non-spherical Pt nanoparticles on Ketjen Black carbon, which is either non-treated (Pt/KB), acid-treated (Pt/KB-O), or nitrogen-doped (Pt/KB-N). The catalysts are synthesized in both small and large batches to determine the effect of scaling up the synthesis procedure. The nitrogen-doped carbon support shows a nearly identical morphological structure with uniform distribution of non-spherical Pt nanoparticles for both small and large batches’ synthesis compared with non-treated and acid-treated carbon samples. The comparative oxygen reduction reaction (ORR) activity shows that the Pt/KB-N prepared in small and large batches has better ORR activity, which is likely caused by uniformly distributed non-spherical Pt nanoparticles on the nitrogen-doped carbon support. All three catalysts show similar ORR durability, testing from 0.5–1.0 V, while Pt/KB-O displays slightly better durability from 1.0–1.5 V for carbon corrosion. These results will help inform the implementation of shape-controlled Pt catalysts on modified carbon supports in large scale.

Melamine Modification of the Carrier Regulating the Performance of PtBi/AC in Heptanol Oxidation

AbstractDifferent bimetallic platinum and bismuth catalysts supported on melamine‐modified activated carbon (AC) are designed by a co‐impregnation method. Through controlling the activation temperatures of the melamine−AC mixture, a series of N‐doped and C3N4‐modified AC (N−AC and C3N4−AC) are prepared. Combined powder X‐ray diffractions, X‐ray photoelectron spectroscopic, and high‐angle annual dark‐field scanning transmission electron microscopic studies demonstrate that the introduction of C3N4 favors the formation of PtBi alloy and leads to increased particle sizes in comparison to the pristine and N‐doped AC‐supported bimetallics. The catalytic performance of the developed catalysts is evaluated in the oxidation of n‐heptanol oxidation in a batch mode using O2 as the oxidant. PtBi/C3N4−AC exhibits significantly boosted activity as well as selectivity to heptanoic acid as compared with the other catalysts. A high yield of heptanoic acid of 69 % can be achieved under the optimized reaction conditions. Furthermore, our work points to the PtBi alloy as the most active sites for the alcohol oxidation. Catalyst deactivation occurs in the cycling tests, mainly due to the collapse of the alloy phase and likely the decrease in particle sizes.

Evaluation of Structural and Compositional Changes of a Model Monoaromatic Hydrocarbon in a Benchtop Hydrocracker Using GC, FTIR, and NMR Spectroscopy.

Hydrogenation is a catalytic process that has the potential to facilitate sustainable chemical production. In this work, a model monoaromatic hydrocarbon, phenyldodecane (PDD), comprising an aromatic ring with a long aliphatic side chain has been chosen as representative of a typical species involved in hydrogenation and hydrocracked at a high pressure and temperature over a platinum catalyst in a bespoke benchtop mini-reactor. Gas chromatography-mass spectrometry (GC-MS), Fourier transform infrared (FTIR) spectroscopy, UV-vis spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy were employed to analyze the changes that took place after hydrocracking for different time periods. By combining the results from these sensitive spectroscopic tools, it was found that along with the saturation of the aromatic ring of PDD by hydrogen addition, new molecules were formed via ring opening and catalytic cracking. For comparison purposes, the spectra of the samples post hydrogenation were compared with those of cyclohexylnonadecane (CHND), which has a saturated six-membered ring and a long aliphatic tail.

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.

Double layer capacitance of a platinum electrode in a protic ionic liquid: The influence of cation acidity

Protic ionic liquids (PILs) are promising candidates as electrolytes for future intermediate-temperature polymer electrolyte membrane fuel cells (PEMFCs). A deeper understanding of their double layer properties is essential for the improvement of oxygen reduction reaction (ORR) kinetics in the interface of the platinum catalyst and PIL. In this study, we investigate the double layer differential capacitance of platinum in the presence of PILs with acidic cations of various proton donor strengths as a function of the electrode potential, bulk water content, and temperature. Complex capacitance plots of impedance spectra enable the evaluation of a high-frequency double layer capacitance, C1, and a mid-frequency pseudo-double layer capacitance, C2. The C1-capacitance curves were simulated by two mean field models that account for the presence of water, short range correlations of ions, and, in the case of the second model, also for the non-monotonic charging of the Pt surface that has a strong impact on the double-layer structure and properties. The simulations reveal different double-layer properties of [2-Sema][TfO], a PIL with a highly acidic cation, compared to the less acidic [1-EIm][TfO] and [Dema][TfO]. These variations are associated with differences in interionic forces, degrees of ion pairing, and the compactness of ionic layers. Most likely, these effects correlate with hygroscopicity and ability to form the hydrogen bonds of the cation, rather than with its acidity. The different pseudo-double layer capacitances of [2-Sema][TfO] and of the less acidic PILs at higher potentials are explained by different mechanisms of oxide formation.

Microbial Fuel Cell Using a Novel Ionic Liquid-Type Membrane–Cathode Assembly for Animal Slurry Treatment and Fertilizer Production

The implementation of a microbial fuel cell for wastewater treatment and bioenergy production requires a cost reduction, especially when it comes to the ion exchange membrane part and the catalysts needed for this purpose. Ionic liquids in their immobilized phase in proton exchange membranes and non-noble catalysts, as alternatives to conventional systems, have been intensively investigated in recent years. In the present study, a new microbial fuel cell technology, based on an ionic liquid membrane assembly for CoCu mixed oxide catalysts, is proposed to treat animal slurry. The new low-cost membrane–cathode system is prepared in one single step, thus simplifying the manufacturing process of a membrane–cathode system. The novel MFCs based on the new low-cost membrane–cathode system achieved up to 51% of the power reached when platinum was used as a catalyst. Furthermore, the removal of organic matter in suspension after 12 days was higher than that achieved with a conventional system based on the use of platinum catalysts. Moreover, struvite, a precipitate consisting of ammonium, magnesium, and phosphate, which could be used as a fertilizer, was recovered using this membrane–cathode system.

Comparison of different synthesis techniques of supported platinum catalysts and their sintering studies

Comparison of different synthesis techniques of supported platinum catalysts and their sintering studies

Synthesis and characterization of nickel boride nanoparticles for energy conversion catalyst materials – The effect of annealing temperature

In the recent technology development, fuel cell has been widely used in many applications, including transportation and industry. Platinum catalysts are used to catalyst the reaction at the oxygen electrode, but they are expensive and has limited supply. A nickel-boron nanoparticle catalyst is proposed as a substitute for fuel cell catalyst material. The objectives are to evaluate the effect of the annealing process and to determine the characteristics of the annealed nanoparticles using scanning electron microscopy - energy dispersive X-ray (SEM-EDS), inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis, total organic carbon (TOC) analysis and X-ray diffraction (XRD). A wet chemical method was used to synthesize nickel-boron nanoparticles by chemical reduction (co-reduction) of nickel chloride and sodium borohydride. As-synthesized nickel-boron nanoparticles were annealed at temperatures of 200, 300, 400, 500, and 700 °C in an argon atmosphere for 2 h. From the experimental results, nickel-boron nanoparticles annealed at 300 °C with equal dispersion of crystalline Ni and crystalline Ni3B showed the highest catalyst performance. The yield of nickel-boron nanoparticles sized 1.1364 nm was smaller than in the literature (37 nm). The size of Ni-B nanoparticles was calculated by using the Scherrer equation with the values of full width half maximum (FWHM) obtained by peak fitting following the Gaussian model. Smaller Ni-B nanoparticles have a higher surface-area-to-volume ratio, which increases the exposure of the active sites (crystalline Ni and crystalline Ni3B phase) to the reactants (methanol) and improves catalytic activity.

Optimising PtFe nanoparticle structure to enhance catalytic activity and stability for propane oxidation

Although the development of highly active and stable platinum catalysts for the complete oxidation of hydrocarbons is crucial, there are still significant challenges that need to be addressed. Herein, the surface structure of PtFe nanoparticles (NPs) on PtFe/CeO2-x (x = CO, H, O) catalysts was precisely tuned via thermal treatment in CO, H2 and O2 atmospheres. The structure of the PtFe NPs on the PtFe/CeO2-O catalyst consisted of dispersed FeOx nanoclusters anchored on the PtFe NPs core. As a result, the PtFe/CeO2-O exhibited superior activity and water resistance for propane oxidation among all catalysts, which stems from the cooperation among robust metallic Pt sites, abundant active oxygen species, and FeOx nanoclusters as additional sites for oxygen supply. However, the reaction path of propane oxidation was similar among the PtFe/CeO2-x catalysts. This study offers encouraging insights for the deliberate development of robust and high-performing bimetallic catalysts to eradicate volatile organic compound pollutants. SynopsisThe CeO2‑supported core-shell-like PtFe-FeOx NPs catalyst synthesised via calcination treatment in oxygen atmosphere exhibits the excellent activity, good durability and water resistance for propane oxidation at low temperature.

Nitrogen-doped porous alumina for supported metal catalysts: Sintering resistance effect

A protocol has been proposed for modifying a porous alumina support by NO treatment to increase the resistance of metal particles on the support to sintering. The stabilization effect by forming AlNxOy species has been clearly demonstrated for supported platinum catalysts.

(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.

(Digital Presentation) An Efficient and Stable of Low-Pt Catalysts for Full Water Splitting in Acidic

Designing efficient platinum-based catalysts is of great interest for the lowering of Pt dosage and the enhance of catalytic activity on the full water splitting. However, it is still challenging to develop low-Pt catalysts with evenly distributed, proper sized particles on supports. Here, Metal-Organic Frameworks (MOF) derivatives were used as supports to prepare ultra-low platinum catalysts of uniform particle size. MOF derived transition metal heteroatom-doped carbon is a promising support for precious metal nanoparticles of electrocatalytic activity, because it provides abundant anchor points that enhance their adhesion, transition metals on the MOF skeleton can effectively prevent further growth of platinum particles, more importantly, through the proof-metal electron interaction, improve their intrinsic catalytic activity to achieve high activity and stable hydrogen evolution reaction. We will characterize the characteristics of the catalyst from several aspects, such as morphology, pore size and composition. Finally, we will verify the catalytic ability, rate ability and stability of low platinum catalyst with MOF derivatives support, through a comprehensive characterization of the catalyst HER and OER performance.

(Digital Presentation) The Utilization of Platinum Catalysts Deposited on Carbon Support Synthesized from Coffee Grounds in a Polymer Electrolyte Membrane Fuel Cell

Exploring alternative sources for platinum catalyst carbon support material is vital for the further development of polymer electrolyte membrane fuel cells (PEMFC).1 The support material and the method of depositing Pt nanoparticles are crucial for defining the catalytic properties of the catalyst. In this study, carbon support material, derived from coffee grounds was used in the preparation of Pt catalysts for PEMFC application. The carbon material was synthesized using ZnCl2 activated pyrolysis method2 and the Pt nanoparticles were deposited onto carbon support by two methods: using ethylene glycol3 or hydrogen4 as a reducing agent.The physical properties of the support material, as well as catalysts were analysed through thermogravimetric analysis (TGA), dynamic light scattering, X-ray diffraction (XRD), N2 sorption analysis and high-resolution scanning electron microscopy (HR-SEM) methods. The electrochemical activity, as well as the electrochemically active surface area (ECSA) of the catalysts were determined in a completed PEMFC. The properties and performance of catalysts synthesised were compared with the catalyst which was deposited onto commercial carbon (Ketjenblack, EC-300J).TGA displayed that carbon derived from coffee grounds contained 6.9 % of impurities by mass in the form of metal oxides and that the coffee carbon Pt catalyst contained 60 wt% of Pt. The Pt crystallite size was determined through XRD and it was 1.4 nm. HR-SEM analysis displayed that the average particle size of Pt nanoparticles on the coffee carbon catalyst was 4.7±2.5 nm. Results from N2 sorption analysis showed that all materials were micro-mesoporous, with coffee ground carbon having a specific surface area of 590 m2 g-1. The coffee carbon Pt catalyst produced smaller results of 370 m2 g-1 compared to the carbon support, due to the Pt nanoparticles depositing in the micropores, however still had a larger specific surface area than the commercial carbon catalyst with a specific surface area of 300 m2 g-1.Catalysts deposited on coffee ground carbon produced comparable electrochemical results to catalysts deposited on commercially available carbon. The coffee carbon catalyst produced a higher ECSA of 64 mPt 2 gPt -1, compared to the commercial carbon catalyst with an ECSA of 51 mPt 2 gPt -1. The current density of the Pt catalyst deposited onto coffee carbon was 0.68 A cm-2 at 670 mV, whilst in the same conditions commercial carbon peaked at 0.70 A cm-2. Both coffee and commercial carbon Pt catalysts produced similar power density maximums with the coffee Pt catalyst producing 0.56 W cm-2 and the commercial Pt catalyst producing 0.60 W cm-2.Physical and electrochemical characterizations displayed that higher ECSA values were strongly correlated to smaller Pt crystallite size. Other techniques to increase fuel cell performance were also experimented with, such as covering the gas diffusion layer with catalyst instead of Nafion membrane and adding additional Nafion layers, with both methods producing promising results.This study displays that there is a lot of potential in improving the catalytic performance of Pt catalysts by depositing on support materials derived from alternative sources. The methods of boosting PEMFC performance could be further investigated for catalysts deposited on different carbon supports. Acknowledgements This work was supported by the EU through the European Regional Development Fund TK141 “Advanced materials and high-technology devices for energy recuperation systems” (2014-2020.4.01.15-0011), Personal Research Grant PRG676 and by private limited company AuVe Tech LLTKT20148 “Production of Polymer Electrolyte Membrane Fuel Cells”. The SEM measurements were conducted using the NAMUR+ core facility funded by the Estonian Research Council (TT 13). References S. Shahgaldi and J. Hamelin, Carbon, 94, 705-728 (2015). M. Härmas, PhD thesis, University of Tartu, Tartu, Estonia (2020). Y. Shao, S. Zhang, R. Kou, X. Wang, C. Wang, S. Dai, V. Viswanathan, J. Liu, Y. Wang, Y. Lin, J. Power Sources 195, 1805-1811 (2010). Y. Zheng, Z. Dou, Y. Fang, M. Li, X. Wu, J. Zeng, Z. Hou, S. Liao, J. Power Sources, 306, 448-453 (2015).

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.

Electrochemical Ethylamine Dehydrogenation to Acetonitrile on Platinum-Based Catalysts

Hydrogen storage is a crucial link between green hydrogen generation by water electrolysis and hydrogen application in fuel cells. We very recently reported a new, electrochemical ethylamine/acetonitrile redox method for hydrogen storage [1]. This method realizes hydrogen uptake by pairing acetonitrile hydrogenation to ethylamine reaction (AHR) on cathode and hydrogen oxidation reaction (HOR) on anode, and realizes hydrogen release by pairing ethylamine dehydrogenation to acetonitrile reaction (EDR) on anode and hydrogen evolution reaction (HER) on cathode. With 8.9 wt.% theoretical storage capacity and ambient reaction conditions being demonstrated in the study, this method shows a great potential to advance hydrogen storage technology and meet the DOE target. One remaining challenge of this method was a rapid activity decay of the used commercial platinum catalyst (Pt/C) in the EDR, which caused a long-term durability issue.In this work, we report our fundamental study of Pt catalyst deactivation mechanism in EDR and the discovery of new Pt-based catalysts. Attenuated total reflection infrared spectroscopy (ATR-IR) was employed for characterizing working catalyst surface under reactive conditions. Partially dehydrogenated intermediate species were observed to generate on Pt surface, which strongly adsorbed and caused an accumulation and blockage of the active sites. Interestingly, the catalyst showed a self-cleaning property where the intermediates can be hydrogenated back to ethylamine and released from Pt surface below 0 V vs. RHE. A group of Pt-Ni alloy catalysts were prepared and investigated the composition effect in this reaction, among which Pt3Ni exhibited 75% higher activity and significantly improved stability compared to Pt. ATR-IR experiments showed that the accumulation of intermediates on the Pt3Ni surface was much slower than that on the Pt, attributed to weakened adsorption. This work provides mechanistic insights into EDR reaction pathways and the cause of Pt catalyst deactivation and offers a Pt alloy strategy for active and stable catalyst design.[1] Wu, D.; Li, J.; Yao, L.; Xie, R.; Peng, Z. ACS Appl. Mater. Interfaces 13, 55292 (2021).

Oxidative Desorption of Adsorbed Sulfur on Platinum Surfaces Modified with Cerium Species

In polymer electrolyte membrane fuel cells, hydrogen oxidation and oxygen reduction reaction occur at platinum (Pt) catalyst surface. Pollutants in air and hydrogen fuel, especially, sulfur (S) species, often strongly adsorb on the Pt surface, resulting in reduced electrochemically active surface area, namely poisoning effect. Because such poisoning causes the significant deterioration of cell performance and durability, understanding and control of adsorption behavior of S species are very important. Thus, it is necessary to develop a new method or material for recovery from S poisoning in anode.In this study, a Pt(111) single crystal electrode was modified with a Ce species and its electrochemical property was compared with a bare Pt electrode. The modification with Ce species was accomplished by immersion in a Ce (NO3)3 + HClO4 aqueous solution with bubbling Ar + H2 gas through the solution for 1 h or applying the potential at -0.2 V in a Ce (NO3)3 + HClO4 aqueous solution. The modification of Pt(111) electrode with Ce species drastically changed the electrochemical responses; hydrogen adsorption/desorption waves become smaller and adsorption/desorption waves of hydroxy group disappeared because of the presence of adsorbed Ce species. Adsorbed species was identified as a Ce3+ ion by XANES spectrum.After the bare Pt(111) electrode was immersed in an aqueous solution containing sodium sulfide, three types of adsorbed S species, HS and S/Sn were detected by XPS. HS was reductively desorbed from Pt electrode surface at potential cycling between 0.0 and 0.2 V vs. RHE (-0.2 and 0.0 V vs. Ag/AgCl). S/Sn species remained during this potential cycling but oxidatively desorbed when the positive limit of potential cycling was 0.6 V vs. RHE (0.8 V vs. Ag/AgCl). The hydrogen adsorption/desorption current gradually increased as repeating potential cycling between 0.0 and 1.0 V vs. RHE (-0.2 V and 0.8 V vs. Ag/AgCl).After the Ce-modified Pt(111) electrode was immersed in an aqueous solution containing sodium sulfide, an anodic current assignable to the oxidative desorption of S species appeared at 0.3 V. The peak current decreased as repeating potential cycling between 0.0 and 0.7 V vs. RHE (-0.2 V and 0.5 V vs. Ag/AgCl). After this potential cycling, the peak area of S2p region of XPS spectra decreased as well as Ce 3d peak. The oxidative desorption of S and Sn on the Ce-modified Pt(111) electrode took place at 0.5 V vs RHE (0.3 V vs. Ag/AgCl) which is much more negative than that of bare Pt(111) electrode (1.0 V vs. RHE (0.8 V vs. Ag/AgCl)). Thus, modification of Pt(111) electrode with Ce species promoted the oxidative desorption of S species.

Developing Reversal-Tolerant Anode for PEFCs by Introducing Iridium-Based Layered Structure

On the anode side of the polymer electrolyte fuel cell (PEFC), hydrogen fuel can be blocked from reaching the catalyst layer due to anode water flooding which can occur at high humidity, low current density, and rapid load changing conditions [1-3]. This can cause the cell voltage reversal phenomena where anode potential increases relative to the cathode potential resulting in severe carbon corrosion, Platinum catalyst dissolution and agglomeration, and then causing performance loss and eventually cell failure. Currently, control based strategies such as voltage monitoring or flushing excess water have been suggested to overcome this issue [4,5], but unfortunately this increases the complexity and cost of the overall system. In order to greatly reduce system cost, more passive, material-based based solutions such asdevelopment of reversal tolerant anodes (RTAs) are necessary. RTAs include a water electrolysis catalyst such as Ir, Ru, IrO2, RuO2, etc, that can preferentially promote and sustain water electrolysis reaction during cell reversal in order to delay or even prevent the anode from reaching voltages higher than ~1.7 V, [6] resulting in a passive and hence cost-effective solution for the fuel starvation problem.The standard Pt/C+IrO2 RTA catalyst was first studied to investigate its cell reversal characteristics, and several current shortcomings were identified. We found that the RTA underwent significant carbon-based performance degradation even during the water electrolysis stage, and the oxygen evolution reaction (OER) catalyst, IrO2, was found to be deactivated after every subsequent cell reversal experiments. Furthermore, a comparative study of the standard Pt/C+IrO2 RTA with other structures such as Pt/C+Ir/C and Ir(IrOx)/Pt/C hybrid catalyst revealed a new cause of performance degradationbased on Platinum and Iridium particle alloying. Therefore, it is important to manage both the carbon-based degradation and alloying-based degradation in order to make RTAs feasible, and thus tackle the fuel starvation problem.Therefore introduction of layered structure was introduced in RTA catalyst, as explained in Fig. 1. In this study two types of layered RTA catalysts were explored towards addressing these problems. Layered RTA catalysts, LRC1, was made by spray-printing IrO2 (0.24 mgIrO2/cm2) first and then Pt/C (0.3 mgPt/cm2) on the Nafion 212 membrane as shown in Fig.1 (b). In LRC2 case, Cvulcan layer was spray-printed between IrO2 and Pt/C layers as described in Fig.1 (c). Compared to the standard RTA, LRC1 showed improved OER activity and higher performance after the fuel starvation durability test. The LRC2 structure was able to suppress alloying based degradation almost completely. Our findings contribute greatly to the understanding of the fuel starvation based degradation phenomena, and will help in designing better RTAs with improved performance and durability. Fig. 1 Schematic diagram showing (a) standard mixed RTA: Pt/C+IrO2, (b) LRC1: Pt/C -> IrO2, (c) LRC2: Pt/C -> Cvulcan -> IrO2 References [1] Hong, B. K., Mandal, P., Oh, J.-G. & Litster, S. On the impact of water activity on reversal tolerant fuel cell anode performance and durability. J. Power Sources 328, 280–288 (2016).[2] Knights, S. D., Colbow, K. M., St-Pierre, J. & Wilkinson, D. P. Aging mechanisms and lifetime of PEFC and DMFC. J. power sources 127, 127–134 (2004).[3] O’Rourke, J., Ramani, M. & Arcak, M. In situ detection of anode flooding of a PEM fuel cell. Int. J. Hydrog. Energy 34, 6765–6770 (2009). [4] Kurnia, J. C., Sasmito, A. P. & Shamim, T. Advances in proton exchange membrane fuel cell with dead-end anode operation: A review. Appl. Energy 252, 113416 (2019).[5] Chen, Y.-S., Yang, C.-W. & Lee, J.-Y. Implementation and evaluation for anode purging of a fuel cell based on nitrogen concentration. Appl. Energy 113, 1519–1524 (2014).[6] Ralph, Thomas R., Sarah Hudson, and David P. Wilkinson. "Electrocatalyst stability in PEMFCs and the role of fuel starvation and cell reversal tolerant anodes." ECS Transactions1.8 (2006): 67. Figure 1