Platinum–Dysprosium Alloys as Oxygen Electrodes in Alkaline Media: An Experimental and Theoretical Study (original) (raw)
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Understanding the electrocatalysis of oxygen reduction on platinum and its alloys
Energy & Environmental Science, 2012
The high cost of low temperature fuel cells is to a large part dictated by the high loading of Pt required to catalyse the oxygen reduction reaction (ORR). Arguably the most viable route to decrease the Pt loading, and to hence commercialise these devices, is to improve the ORR activity of Pt by alloying it with other metals. In this perspective paper we provide an overview of the fundamentals underlying the reduction of oxygen on platinum and its alloys. We also report the ORR activity of Pt 5 La for the first time, which shows a 3.5-to 4.5-fold improvement in activity over Pt in the range 0.9 to 0.87 V, respectively. We employ angle resolved X-ray photoelectron spectroscopy and density functional theory calculations to understand the activity of Pt 5 La. † We estimate the average autocatalyst loading in motor vehicles to be $3.4 g, obtained by dividing the total amount of platinum group metals used for autocatalysts by the global production of motor vehicles in 2010, i.e. (2.66 Â 10 8 )/(77.9 Â 10 6 ). 2,3 The loading is dependent on the type of vehicle, and can vary between 1 g and 15 g. 4
Alloys of platinum and early transition metals as oxygen reduction electrocatalysts
Nature Chemistry, 2009
The widespread use of low-temperature polymer electrolyte membrane fuel cells for mobile applications will require significant reductions in the amount of expensive Pt contained within their cathodes, which drive the oxygen reduction reaction (ORR). Although progress has been made in this respect, further reductions through the development of more active and stable electrocatalysts are still necessary. Here we describe a new set of ORR electrocatalysts consisting of Pd or Pt alloyed with early transition metals such as Sc or Y. They were identified using density functional theory calculations as being the most stable Pt-and Pd-based binary alloys with ORR activity likely to be better than Pt. Electrochemical measurements show that the activity of polycrystalline Pt 3 Sc and Pt 3 Y electrodes is enhanced relative to pure Pt by a factor of 1.5-1.8 and 6-10, respectively, in the range 0.9-0.87 V.
Structure sensitivity of oxygen reduction on platinum single crystal electrodes in acid solutions
Journal of Electroanalytical Chemistry, 1997
The oxygen reduction reaction (orr) on the low index planes of single crystal Pt electrodes has been studied in HClO4 and H2SO4 solutions using the hanging meniscus rotating disk technique (HMRD). Significant structural sensitivity of the reaction rate has been found in both electrolytes. Results are compared with published data. The importance of controlling the conditions of the experiments, as
The Journal of Physical Chemistry, 1995
The effect of different alloying conditions (alloying temperature, annealing period) on the electrocatalytic activities for the oxygen reduction reaction (ORR) by three carbon-supported Pt alloy electrocatalysts (WCr, WCo, m i) was investigated and correlated with electronic and structural parameters determined by in-situ XAS. The results indicate that all the Pt alloys show enhanced ORR activities relative to a W C electrocatalyst. However, the electrocatalytic activity and activation energy for ORR in the case of Pt/Ni and Pt/Co alloys show marked effect due to different alloying conditions. This was in contrast to W C r alloy, where both parameters remained unchanged over the range of alloying conditions. Those electrochemical results were correlated with those obtained from in-situ X-ray absorption spectroscopic (XAS) investigations, which provided information on the electronic (Pt 5d-orbital vacancy, from the X-ray absorption near-edge structure) and geometric (Pt-Pt bond distances, from the extended X-ray absorption fine structure) factors. In-situ XAS results indicate that the supported alloys possess higher P t Sd-orbital vacancies and shorter Pt-Pt bond distances. In addition, the XAS results showed that alloying inhibited chemisorption of oxygenated species (OH) on the Pt at potentials above 0.8 V vs RHE. Correlation of electrocatalytic activities and activation energies for ORR with parameters obtained from in-situ XAS studies indicates that, in the case of m i and Pt/Co alloys, higher alloying temperature and longer annealing periods result in higher Pt 5d-orbital vacancies with the geometric parameters remaining unchanged. The W C r alloy on the other hand revealed no dependence of either the Pt d-orbital vacancies or the geometric parameters on alloying temperature. These observations indicate that the dependence of electrocatalytic activities and activation energy for Pt/Co and Pt/Ni alloys on the thermal history and the absence of such an effect in the W C r alloy could be related to the differences in the Pt Sd-orbital vacancies.
ChemCatChem, 2012
under conditions relevant for low-temperature fuel cells. The surfaces were characterised in situ by means of electrochemical methods and ex situ under ultrahigh vacuum conditions. The ORR activity was established in an electrochemical cell containing 0.1 m HClO 4 by use of a rotating ring disk electrode assembly. The surface composition was characterised before and after the electrochemical measurements by using angle-resolved X-ray photoelectron spectroscopy. The ORR activity of the electrodes increased in the following order: Pt 2 Y % Pt 3 Zr % Pt % < Pt 3 Hf < Pt 3 Sc ! Pt 5 Y < Pt 3 Y. At 23 8C, the most active catalyst, Pt 3 Y, exhibited a six-to ninefold improvement in activity over Pt in the potential range 0.9-0.87 V with respect to a reversible hydrogen electrode. Over the same potential range at 60 8C, Pt 3 Y exhibited a fourto fivefold improvement in activity over Pt. The angle-resolved X-ray photoelectron spectroscopy analyses show that Pt 3 Y and Pt 5 Y formed a Pt overlayer under ORR conditions. In contrast, the surfaces of Pt 3 Hf and Pt 3 Zr comprised a mixture of Pt and HfO x or ZrO x , respectively, which explained their poor performance.
Platinum‐Rare Earth Alloy Electrocatalysts for the Oxygen Reduction Reaction: A Brief Overview
ChemCatChem
The development of highly active and long‐term stable electrocatalysts for the cathode of proton‐exchange membrane fuel cells (PEMFC) is a paramount requirement for high performance and durable PEMFC stacks. In this regard, alloying Pt with rare earth metals (REM) has emerged as a promising approach. This short review summarizes and discusses the most relevant advances on Pt‐REM alloy electrocatalysts, from bulk polycrystalline surfaces to carbon supported nanostructures, for the oxygen reduction reaction (ORR), and their implementation in PEMFCs, and is a starting point to establish the challenges in synthesis and design and properties goals for novel Pt‐REM alloys.
Journal of Electroanalytical Chemistry, 1993
Here we demonstrate a remarkable enhancement of oxygen reduction reaction (ORR) activity on a novel Pt/ TaO x /GC electrocatalyst where at first tantalum oxide (TaO x ) and next Pt were deposited electrochemically on a glassy carbon (GC) surface. An excellent electrocatalytic activity of the Pt/TaO x / GC electrocatalyst for ORR was found to be more than 12 times that of the unmodified Pt/GC one as evaluated from the kinetic currents at 0.80 V. SEM images showed no significant differences in the size and distribution of Pt nanoparticles between these two electrocatalysts, indicating that these are not factors causing the observed ORR activity. The spillover of oxygen-containing species resulting from the electronic interaction between Pt and TaO x , which is evidently demonstrated from the XPS analysis, is strongly suggested as the crucial factor for the ORR enhancement. Interestingly, the spillover effect also results in a remarkable increase in the electrochemically active "apparent" surface area of Pt on the Pt/TaO x /GC electrocatalyst. Moreover, the rotating ring-disk electrode voltammetric measurements obviously showed the increase in limiting current as well as the decrease in ring current on this novel electrocatalyst relative to the unmodified one, confirming a complete four-electron reduction pathway. On the basis of these findings a plausible mechanism has been proposed for the observed enhancement in ORR where the role of TaO x is to reduce the formation of OH on the Pt surface by spillover effect and to promote d orbital vacancy of Pt for oxygen adsorption by electron donation to Ta.
Oxygen reduction reaction on electrodeposited Pt100−x−yNixPdy thin films
Electrochimica Acta, 2010
The kinetics of the oxygen reduction reaction (ORR) were examined on a series of Pt 100−x−y Ni x Pd y ternary alloys. Films were produced by electrodeposition that involved a combination of underpotential and overpotential reactions. For Pt-rich Pt 100−x−y Ni x Pd y alloy films (x < 0.65) Ni co-deposition occurred at underpotentials while for Ni-rich films (x > 0.65) deposition proceeded at overpotentials. Rotating disk electrode (RDE) measurements of the ORR kinetics on Ni-rich Pt 100−x−y Ni x Pd y thin films revealed up to ∼6.5-fold enhancement of the catalytic activity relative to Pt films with the same Pt mass loading. More than half of the electrocatalytic gain may be attributed to surface area expansion due to Ni dealloying. Surface area normalization based on the H upd charge reduced the enhancement factor to a value less than 2. The most active ternary alloy film for ORR was Pt 25 Ni 73 Pd 2 . Comparison of the ORR on Pt, Pt 20 Ni 80 , Pt 25 Ni 73 Pd 2 thin films indicate that the binary alloy is the most active with a H upd normalized ORR enhancement factor of up to 3.0 compared to 1.6 for the ternary alloy.