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...
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