Multimetallic Electrocatalysts of Pt, Ru, and Ir Supported on Anatase and Rutile TiO[sub 2] for Oxygen Evolution in an Acid Environment

Abstract

Anatase and rutile TiO 2 were investigated as stable supports for different multimetallic nanoparticles ͑i.e., Pt:Ru, Pt:Ir, Pt:Ru:Ir, and Ir:Ru͒ and tested for activity toward the oxygen evolution reaction ͑OER͒. Overall, Ir:Ru had the highest activity toward OER ͑i.e., current per gram of metal͒ compared to the other multimetallic combinations studied. This bimetallic supported on anatase TiO 2 had a 53% higher current per gram of metal than an unsupported electrocatalyst of the same composition. The higher catalyst utilization of the supported electrocatalysts for OER is consistent with small, well-dispersed nanoparticles, which were observed in high resolution transmission electron microscopy images.The electrolysis of water is a convenient method to obtain pure hydrogen. Two commercial types of water electrolyzers are based on either an alkaline or a proton exchange membrane ͑PEM͒. 1-7 PEM electrolyzers have many advantages over the alkaline system such as higher power densities and efficiencies at low temperatures ͑80°C͒, compact stack design that allows high-pressure operation and excellent partial-load range, and rapid response to fluctuating power inputs. 4,5 Also, there is greater safety and reliability because no caustic electrolyte is circulated in the cell. 6 However, one of the main problems of a PEM electrolyzer is the high costs of the electrocatalyst, 7 because nonprecious metals are not stable in an acidic environment.Electrocatalysts used for the oxygen evolution reaction ͑OER͒ consist of combinations of precious metals such as platinum, ruthenium, and iridium. Platinum forms a poorly conductive oxide film and shows a high overpotential. 8 However, electrocatalysts consisting of iridium and ruthenium 9 and their oxides 9-12 have been shown to possess high electroactivity for OER. Song et al. 9 argued that Ir and Ru oxide forms are preferred because unsupported metallic forms were observed to be unstable. Pure ruthenium metal in particular was shown to be the most active catalyst for OER, but very unstable. Iridium oxide was found to be the next most active and stable at higher current densities. 9 Based on these findings, Siracusano et al. 11 used IrO 2 as the anode electrocatalyst for a PEM electrolyzer. Several researchers found that mixtures of Ir and Ru oxides are even more active than pure IrO 2 for OER. 12-14 They added Ta 2 O 5 , 12 SnO 2 , 13 or MoO 3 ͑Ref. 14͒ to stabilize the structure of Ir:Ru oxide, because RuO 2 is less stable than IrO 2 . The addition of MoO 3 enhanced activity, but Ta 2 O 5 and SnO 2 reduced performance in a PEM electrolyzer compared to Ir:Ru oxide.The use of a support for metal electrocatalysts used in OER was discussed by Ma et al. 15,16 They prepared iridium metals supported on titanium carbide. Using cyclic voltammetry ͑CV͒ and PEM electrolyzer tests, they found that supported iridium metals are more active and more stable than unsupported iridium. Still, it has not been studied extensively in the literature if a support can provide both stability for the me...

Current Challenges in Catalyst Development for PEM Water Electrolyzers

“…On the other hand, titanium dioxide (TiO 2 ) is a stable, commercially available, and inexpensive material , and is frequently used as a catalyst support for Ir , . However, a relatively high amount of Ir or IrO 2 (> 40 wt %) is required to generate sufficient electric conductivity by forming a contiguous network/film of Ir or IrO 2 nanoparticles , , since TiO 2 itself is not conductive. A conductive and stable support material would eliminate the need for a percolating network of Ir or IrO 2 to provide sufficient conductivity across the catalyst layer and, hence, enable lower Ir loadings.…”

Iridium–Ruthenium–gold cluster complexes: Structures, and skeletal Rearrangements

“…Iridiumeruthenium complexes have been shown to serve as precursors to catalysts for the carbonylation methanol [5]. Supported bimetallic iridiumeruthenium catalysts have been shown to produce C 2 oxygenates from syngas [6] and also to exhibit unusually high catalytic activity for the oxygen evolution reaction in the electrolysis of water [7]. Recently, gold nanoparticles have been shown to exhibit significant catalytic activity for the oxidation of CO and certain olefins [8].…”

Die Elektrochemie des Sauerstoffs als Meilenstein für eine nachhaltige Energieumwandlung

“…[230] Es sei darauf hingewiesen, dass der Träger Auswirkungen auf die katalytische Aktivität von Nanopartikeln hat, was auf eine bessere Nutzung der aktiven Zentren und/oder Wechselwirkungen zwischen dem Katalysator und dem Träger zurückzuführen ist. [163,235,236] Darüber hinaus sind die räumliche Verteilung der aktiven Zentren und die Vermeidung von Oberflächensegregation von großer Bedeutung für die Leistungsfähigkeit gasentwickelnder Elektroden. [237][238][239] Eine direkte Überwachung der lokalen Aktivität für die OER an der Fest-flüssig-Grenzfläche wird notwendig, um diese nanostrukturellen Effekte eindeutig zu zeigen.…”