Pt–W bimetallic alloys as CO-tolerant PEMFC anode catalysts (original) (raw)
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Nanomaterials, 2021
The effect of the nature of the catalyst on the performance and mechanism of the hydrogen oxidation reaction (HOR) is discussed for the first time in this work. HOR is an anodic reaction that takes place in anionic exchange membrane fuel cells (AEMFCs) and hydrogen pumps (HPs). Among the investigated catalysts, Pt exhibited the best performance in the HOR. However, the cost and the availability limit the usage. Co is incorporated as a co-catalyst due to its oxophylic nature. Five different PtCo catalysts with different Pt loading values were synthesized in order to decrease Pt loading. The catalytic activities and the reaction mechanism were studied via electrochemical techniques, and it was found that both features are a function of Pt loading; low-Pt-loading catalysts (Pt loading < 2.7%) led to a high half-wave potential in the hydrogen oxidation reaction, which is related to higher activation energy and an intermediate Tafel slope value, related to a mixed HOR mechanism. Howev...
Pt/WC as an anode catalyst for PEMFC: Activity and CO tolerance
Catalysis Today, 2008
A mesoporous tungsten carbide of WC-phase was synthesized by using ammonium meta tungstate as tungsten precursor and resorcinolformaldehyde polymer as carbon source in the presence of a surfactant. The platinum supported on this material with a low loading (7.5 wt%) served as an effective CO tolerant electro anode catalyst. The Pt/WC catalyst showed two times higher activity per mass of Pt for hydrogen electrooxidation compared to a commercial Pt/C catalyst (E-Teck). In addition, it exhibited much improved resistance to CO poisoning relative to the Pt/C catalyst. Since the catalyst is also stable in electrochemical environment, it could become an alternative anode catalyst for PEMFC.
Polymer electrolyte membrane fuel cells are a promising alternative for future energy provision. However, their wider utilization is hindered by the slow rate of the oxygen reduction reaction (ORR) taking place at the cathode. In order to improve the ORR kinetics, alloys of Pt with late transition metals and lanthanides have been studied extensively, as they offer enhanced activity and in some cases acceptable stability. Nevertheless, many of these alloys are far from being “model objects”; and their surface composition and structure are not stable under operating conditions in PEMFCs. The solute metal can dissolve from the surface and near-surface layers. This process often results in a structure in which several Pt-enriched llayers cover the bulk alloy and protect it from further dissolution. In this work, we analyze the literature results on the properties of these alloys, from single crystals and polycrystalline materials to nanoparticles, gathered in the recent decades. As a result of this analysis, we additionally propose a relatively simple method to overview the activities of de-alloyed PtnX type alloys towards the ORR. Given that the Pt-overlayer is several atomic layers thick, the so-called strain effects should primarily determine the behavior of these catalysts. The strain in the system is the result of the differences between the lattice parameters of the alloy and Pt rich overlayers, causing dissimilar compressive strains in the lattice of the Pt-rich layer. This causes changes in the electronic structure, and, consequently, in the binding properties of the surface. We propose that the atomic radius of the solute metal can be used in some particularly complex systems (e.g. polycrystalline and nanostructured alloys) as a simple semi-empirical descriptor, statistically connected to the resulting lattice strain. The implications of this phenomenon can be used to qualitatively explain the behavior of e.g. some active Pt-alloy nanoparticles so far considered “anomalous”.
Oxygen reduction reaction on nanostructured Pt-based electrocatalysts: A review
International Journal of Hydrogen Energy, 2020
h i g h l i g h t s ORR activity and durability of nanostructured Pt-based catalysts are reviewed. Activity of Pt catalysts is discussed with respect to the deposition method. Effects of deposition parameters on the activity and durability are emphasised. The application of nanostructured Pt catalysts as PEMFC cathodes is highlighted.
ACS Sustainable Chemistry & Engineering, 2019
Although, Pt 3 M (M = transition metals like Co, Ni, Cu) binary alloy nanostructures have been well established with reference to their unique composition (chemically ordered) and electrocatalytic property relationship, further improvement in their catalytic efficiency could be possible by tuning the surface properties. Herewith, to improve the sluggish kinetics of electroreduction of oxygen, we demonstrate an effective way to prepare carbon supported Pt 3 M nanostructures, especially Pt 3 Co using single step, molten-salt synthesis (MSS) method, without using any capping or stabilizing agent. XRD studies confirmed an alloy formation in Pt 3 Co with fcc structure (but surprisingly not a chemically ordered structure or L 12 phase) and the transmission electron microscopy (TEM) revealed the formation of hexagonal nanoplates with an approximately 2 nm thick and 17 nm diameter. The specific geometry and facets (surface property) has been responsible for boosting the specific activity of 4.2 mA cm Pt-2 , which is almost 21 times greater than that of the state-of-the-art Pt/C catalyst and even superior to Pt 3 Ni/C and Pt 3 Cu/C catalysts (prepared by similar process). Moreover, increase in the electrocatalytic activity has been observed during the durability test that is perceptible due to the
Electrocatalysis, 2016
Pt 3 M (M: Co, Ni and Fe) bimetallic alloy nanoclusters were synthesized by a novel and simple chemical reduction approach, and employed as the promising electrocatalyst to accelerate the kinetics of oxygen reduction reaction (ORR) for polymer electrolyte membrane fuel cells. From XRD, the positive shift of diffraction angle confirms the alloy formation between Pt and M and the elemental composition was confirmed by energy dispersive X-ray spectroscopy analysis. The nanocluster morphology and particle size was determined using scanning and transmission electron microscopy analysis. The ORR kinetic parameters for Pt-M electrocatalysts were calculated and compared with reported Pt/C catalysts. Among the Pt-M electrocatalysts, Pt-Co was found to be the most efficient catalyst having the higher mass and specific activity (at 0.9 V vs. RHE) of 0.44 mA/μg and 0.69 mA/cm 2 , respectively. The accelerated durability test reveals that the Pt-M bimetallic alloy nanoclusters retain appreciable surface area and mass activity after 8000 potential cycles confirms good long-term durability, and also competing with the reported benchmark ORR catalysts.
Electrochimica Acta, 2002
Electrocatalysis of CO tolerance and direct methanol oxidation on PtMo/C (3:1 a/o) has been investigated in a PEM fuel cell environment. While a 3-fold enhancement is observed for CO tolerance when compared with PtRu/C (1:1), no such enhancement occurred for methanol oxidation. In situ XAS at the Pt L and alloying element K edges for Pt/C, PtRu/C and PtMo/C showed that in contrast to PtRu/C, both Mo and Pt surfaces play a distinct role for CO oxidation. While on the Ru surface there is a competition between oxide formation (from activation of water) and CO adsorption, Mo oxide surface showed no affinity for CO. This provided for efficient CO oxidation at low overpotentials on PtMo/C. However, the corresponding behavior for methanol oxidation showed that Mo oxy-hydroxides were inhibited from efficient removal of CO and CHO species in contrast to Ru oxides. The Mo surface oxides also showed a redox couple involving (V to VI) oxidation states in the presence of both CO and methanol. #
Pt-Co alloys prepared by high energy ball milling synthesis were tested as electrocatalysts for hydrogen fueled Polymer Electrolyte Membrane Fuel Cells (PEMFC). In the present contribution we report on the first results regarding the electrochemical behaviour of two samples of Pt-Co alloys. One sample contains 20 wt.% alloy Pt:Co in the molar ratio 0.25:0.75 and C 80 wt.% and the second one Pt:Co in the molar ratio 0.75:0.25 and C 80 wt.%. The electrochemically active surface (EAS) was determined by cyclic voltammetry data while the electrocatalyst performance in a real cell was obtained by assembling Membrane Electrode Assemblies (MEAs) with the considered sample at the cathode. The results obtained, though indicating a lower performance than all-Pt catalysts, are quite interesting as they point out the importance of the C/Pt, Nafion/Pt and Pt/Co ratios that exert a deep influence onto the cell performance.
Pt/C catalyst impregnated with tungsten-oxide – Hydrogen oxidation reaction vs. CO tolerance
International Journal of Hydrogen Energy, 2019
Hydrogen Oxidation Reaction (HOR) is anode reaction in Proton exchange membrane fuel cells (PEMFCs) and it has very fast kinetics. However, the purity of fuel (H 2) is very important and can slow down HOR kinetics, affecting the overall PEMFC performance. The performance of commercial Pt/C catalyst impregnated with WO x, as a catalyst for HOR, was investigated using a set of electrochemical methods (cyclic voltammetry, linear scan voltammetry and rotating disk electrode voltammetry). In order to deepen the understanding how WO x species can contribute CO tolerance of Pt/C, a particular attention was paid to CO poisoning. In the absence of CO, HOR is under diffusion limitations and HOR kinetics is not affected by WO x species. Appreciable HOR current on the electrodes pre-saturated with CO ads at potentials above 0.3 V vs. RHE, which is not observed for pure Pt/C, was discussed in details. HOR liming diffusion currents for higher concentrations of W are reached at high anodic potentials. The obtained results were explained by donation of OH ads by WO x phase for CO ads removal in the mid potential region and reduced reactivity of Pt surface sites in the vicinity of the PtjWO x interface. The obtained results can provide guidelines for development of novel CO tolerant PEMFC anode catalysts.