Bifunctional Pt-IrO2 Catalysts for the Oxygen Evolution and Oxygen Reduction Reactions: Alloy Nanoparticles vs. Nanocomposite Catalysts

Abstract

<p>In the present study different concepts for the development of bifunctional oxygen reduction reaction / oxygen evolution reaction (ORR / OER) electrocatalysts are explored and compared. Bifunctional ORR / OER catalysts are often suggested to improve the stability during startup and shutdown of fuel cells. Furthermore, they are proposed for so-called unitized regenerative fuel cells (URFCs) that would allow a closed loop system to use and produce hydrogen on demand. We compare the electrocatalytic performance of conventional Pt<sub>x</sub>Ir<sub>y</sub> alloy nanoparticles (NPs) with Pt – IrO<sub>2</sub> NP composites (nanocomposites), both immobilized onto a commercial carbon support. The Pt – IrO<sub>2</sub> nanocomposites thereby consist of a mixture of Pt NPs and IrO<sub>2</sub> NPs. By probing the electrocatalytic performance before and after exposing the electrocatalysts to accelerated degradation tests (ADTs) it is shown that the Pt – IrO<sub>2</sub> nanocomposite concept offers advantages but also some disadvantages over the conventional alloy concept. In particular it is shown that while the nanocomposites are initially less active for the ORR due to an interparticle effect, their performance is less affected by the ADTs. However, all tested catalysts experience a decline of the Ir / Pt ratio upon the ADTs treatment, highlighting the challenging stability requirements for URFCs.</p>

Iridium‐based electrocatalysts toward sustainable energy conversion

“…As for the example of alloying Ir with noble metal, Pt is one of the most promising choices to be selected. Arenz and coworkers studied the OER performance of Ir and Pt co‐catalyst from the viewpoint of alloy nanoparticles vs. nanocomposites 184 . The result indicates that the PtIr alloy catalyst can deliver enhanced electrocatalytic property but it also faces the question that the increase of Ir leads to the additional Ir loss, which will influence the activity and stability of the whole catalyst.…”

Nanocomposite Concept for Electrochemical In Situ Preparation of Pt–Au Alloy Nanoparticles for Formic Acid Oxidation

“…51,52 For the preparation of the Pt NPs, a surfactantfree colloidal approach was applied, 53 which was outlined in our recent work. 33,34 Briefly, the same volumes of NaOH EG solution (400 mM) and H 2 PtCl 6 •6H 2 O EG solution (40 mM) were mixed and heated to 160 °C in a microwave reactor for 3 min to obtain colloidal Pt NPs in EG with a concentration of 3.90 g Pt L −1 . To support the Pt NPs onto carbon, the Pt colloid in EG was flocculated with 1 M HCl and centrifuged, whereafter the Pt NPs could be separated from the EG and re-dispersed in acetone (3.90 g Pt L −1 ).…”

“…30 However, Guay and co-authors reported a laser ablation method to prepare surfactant-free Pt−Au bimetallic catalysts, avoiding a surfactant-removal process, and the obtained Pt−Au mixed and Pt−Au alloyed nanoparticles are used for FAO study. 32 In the present study, we use our previously introduced nanocomposite concept 33,34 to prepare Pt + xAu/C bimetallic nanocomposites with tunable Pt to Au ratio. Surfactant-free, metallic Pt and Au nanoparticles serve as starting blocks.…”