Operando Spectroscopic Study of the Dynamics of Ru Catalyst during Preferential Oxidation of CO and the Prevention of Ammonia Poisoning by Pt

Abstract

Hydrogen is a promising clean energy source. In domestic polymer electrolyte fuel cell systems, hydrogen is produced by reforming of natural gas; however, the reformate contains carbon monoxide (CO) as a major impurity. This CO is removed from the reformate by a combination of the water–gas shift reaction and preferential oxidation of CO (PROX). Currently, Ru-based catalysts are the most common type of PROX catalyst; however, their durability against ammonia (NH 3 ) as an impurity produced in situ from trace amounts of nitrogen also contained in the reformate is an important issue. Previously, we found that addition of Pt to an Ru catalyst inhibited deactivation by NH 3 . Here, we conducted operando XAFS and FT-IR spectroscopic analyses with simultaneous gas analysis to investigate the cause of the deactivation of an Ru-based PROX catalyst (Ru/α-Al 2 O 3 ) by NH 3 and the mechanism of suppression of the deactivation by adding Pt (Pt/Ru/α-Al 2 O 3 ). We found that nitric oxide (NO) produced by oxidation of NH 3 induces oxidation of the Ru nanoparticle surface, which deactivates the catalyst via a three-step process: First, NO directly adsorbs on Ru 0 to form NO-Ru δ+ , which then induces the formation of O-Ru n + by oxidation of the surrounding Ru 0 . Then, O-Ru m + is formed by oxidation of Ru 0 starting from the O-Ru n + nuclei and spreading across the surface of the nanoparticle. Pt inhibits this process by alloying with Ru and inducing the decomposition of adsorbed NO, which keeps the Ru in a metallic state.

Evaluation of Novel Fuel Cell Catalysts with Ultra-Low Noble Metal Contents towards Electrochemical Catalysis

“…[23][24][25]28 For ORR, alloys, core-shell structures and cage structures have recently been created and explored. [1][2][3][4][5] Pt-based bimetallic electrocatalysts.-Pure Pt NPs used to be the most cutting-edge materials for fuel cell cathodes and anodes, but they are no longer since they are too costly and do not give enough catalytic efficiency under real-world loads. When Pt is employed in isolation as a catalyst, intermediate electrocatalytic oxidation reactions (such as the oxidation of CO) take place on its surface, occupying the catalyst's active sites and lowering the effectiveness of the Pt catalyst.…”

“…The kinetics of the reaction will be dramatically improved by adding a second metal, which will also significantly boost its desorption and oxidation of the adsorbed CO. 45,[46][47][48][49] The catalytic activity of Pt and CO tolerance will be further enhanced by the cooperation of additional catalyst components or by using electrons. 11 The fine three-dimensional structure of catalysts Pt-M (M = Au, Ru, Co, Fe, Cu, or Ni) discloses additional active sites by lowering the amount of accessible precious metal atoms, [3][4][5] has recently gained interest. Pt and Pt 3 trend M's and oxygen-binding ability are shown in Fig.…”

“…Cu's metastable nature makes it possible to develop sophisticated electrocatalysts with astronomically large surface areas. [1][2][3][4]51 Cu, for instance, may be utilized to make Pt-Cu nanocatalysts both as an alloy component and as reusable in the situ-shaped template. A core-shell structure made of a Pt-Cu core and a Pt-rich shell can emerge because of the selective dissolution of Cu on the Pt-Cu surface, causing geometrical effects and ligand effects that have high catalytic reactivity to ORR.…”

“…Therefore, more durable and practical electrical energy conversion and storage methods are required to achieve more sustainable colonies with adequate renewable energy and a significant pollution reduction. [1][2][3][4] Researchers are concentrating on nuclear power and the different renewable energy sources (sunlight, wind, rain, tides, waves, geothermal energy, etc.) as alternatives to fossil fuels.…”

“…4,20 PEMFCs must be operated at a temperature of less than 100 o C. Due to their low-temperature functioning and water requirement, pure hydrogen (with a low CO concentration) must be utilized in PEMFCs. [1][2][3]21 A membrane electrode assembly (MEA) is the brain of a PEMFC. MEA is a seven-layered made up of porous carbon paper covered with carbon and sandwiched between a polymer electrolyte membrane and an electrocatalyst (Fig.…”