Niobium was doped into anatase TiO 2 support at 10 mol % ͑Nb 0.1 Ti 0.9 O 2 ͒ using sol-gel chemistry. A PtRu/Nb 0.1 Ti 0.9 O 2 catalyst was synthesized by LiBH 4 reduction in tetrahydrofuran. The methanol electro-oxidation activity of the catalyst shows that this oxide support was electrically conductive. The current ͑A/g Pt ͒ was 6% higher on the PtRu/Nb 0.1 Ti 0.9 O 2 catalyst compared to a commercial PtRu/C catalyst at 25°C. The electrochemically active surface area of the PtRu/C was 94% higher than PtRu/Nb 0.1 Ti 0.9 O 2 , thus the current per active site was 100% higher on PtRu/Nb 0.1 Ti 0.9 O 2 . A membrane electrode assembly with PtRu/Nb 0.1 Ti 0.9 O 2 had 46% higher current ͑A/g Pt ͒ than an equivalent E-TEK membrane electrode assembly at 70°C.Electrochemical cells that have porous electrodes require an electrically conductive matrix material to facilitate transportation of electrons between the electrodes. In many applications, the conductive matrix phase also serves as a support for catalyst particles that facilitate the reaction. Most traditional heterogeneous catalysts used for nonelectrochemical reactions are supported on insulating metaloxide materials that have a high surface area and promote catalytic activity ͑i.e., enhanced catalyst-support interactions͒. In electrochemical applications ͑e.g., proton-exchange membrane fuel cells͒, the typical support material is carbon due to its high surface area and high electron conductivity rather than any enhanced catalyst-support interactions. However, carbon-supported electrodes that operate at voltages above ϳ0.9 V in the presence of water are known to undergo the carbon corrosion via the reaction 1 C + 2H 2 O → CO 2 + 4H + + 4e − ͓1͔ Figure 1 illustrates the three phase contact that is necessary in porous electrodes for an active reaction site and shows how carbon corrosion can deactivate the reaction site at high potentials. One method of increasing the durability of porous electrodes is the development of inert electrocatalyst supports.Unfortunately, replacing carbon with traditional metal-oxide supports is not possible due to their electrical-insulating properties at temperatures below 200°C. However, metal oxides such as reduced oxidation state titania ͑e.g., Ti 4 O 7 and Ebonex͒ and Niobium-doped TiO 2 ͑e.g., Nb 0.1 Ti 0.9 O 2 ͒ have shown promise for electrically conductive supports. 2,3 Titanium-oxide-based supports may also provide catalytic advantages for the electrochemical oxidation of methanol because anatase TiO 2 is an active photocatalyst for the destruction of organic compounds. 4 It has been shown that mixtures of NbO 2 and TiO 2 sintered at 1000°C lead to the formation of an electrically conducting material. 3,5 with an electrical conductivity in the range of 0.2-1.5 S/cm and a surface area of ϳ1 m 2 /g. 3 This hightemperature synthesis method shows promising results, but it leads to a low surface area material that requires long synthesis times. Because TiO 2 undergoes a phase transition from anatase to the less catalytically active ...
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...
Electrocatalysts for the bifunctional oxygen electrode for a PEM fuel cell/electrolyzer process need to be active and stable toward the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In this work, Pt-Ir was synthesized supported on TiC and studied as a viable candidate to use as an oxygen electrode. Linear sweep voltammetry (LSV) and cyclic voltammetry (CV) were performed to measure electrochemical activity and compared with supported Pt and Ir on TiC, as well as commercial forms of unsupported Pt and Ir. It was determined that Pt-Ir on TiC outperformed the other electrocatalysts studied with a round trip efficiency of 65%.
Revision 0 vi 4. Liquid air interface tests at the new SCC limits LAI tests of carbon steel coupons exposed to simulants with different ratios of nitrite and nitrate were performed. Coupons exposed to simulants with a ratio of nitrite to nitrate of 1.66 showed negligible corrosion rates or pitting susceptibility. This can be expected since this inhibitor ratio meets the SRS requirement for pitting control. None of the coupons showed any signs of LAI. Minor areas of general surface attack were seen in the vapor space area. However, no pits or general corrosion areas were observed in the weld area of the coupons. There was also no correlation between heat treatment and the degree of corrosion observed. 5. Pitting corrosion studies using the standardized CPP protocol for the Argentinian work and additional dilute test solutions The results of the 18 repeated Argentina tests compared relatively well to original CPP test results. A second series of tests in simulants with nitrate concentrations ranging between 0.5-2 M resulted in 11 of the 12 cases indicating pitting. These results indicate that a pH of 12 is not always sufficient to prevent pitting initiation particularly if higher than normal quantities of chloride and sulfate are present. The results from these tests, along with other previous testing, will be utilized during FY16 for the development of new corrosion chemistry limits for pitting prevention. 6. Pitting corrosion studies using the standardized CPP protocol of new vs. legacy stock of A-537 steel for vitrification return stream All five heats of A-537 carbon steel underwent aggressive pitting corrosion in the two test simulants during the CPP test. To determine if there is an appreciable effect of the different heats of material, CPP testing in a simulant that is not aggressive and in one that produces mixed results may reveal differences (i.e., similar to the test protocol development).
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