Rutile phase niobium-doped titanium oxide [NbxTi(1 − x)O2, x = 0.25] with a high electrical condu... more Rutile phase niobium-doped titanium oxide [NbxTi(1 − x)O2, x = 0.25] with a high electrical conductivity (1.11 S cm−1) was synthesized and investigated as a cathode catalyst support material for polymer electrolyte membrane fuel cells (PEMFCs). The TEM image of the Pt/NbxTi(1 − x)O2 catalyst revealed that Pt particles (dPt = 3–4 nm) were deposited on the NbxTi(1 − x)O2 support using a borohydride reduction method. The Pt/NbxTi(1 − x)O2 catalyst showed comparable oxygen reduction reaction (ORR) activity to that of a commercial Pt/C catalyst (E-TEK) when tested in rotating ring-disk electrode (RRDE). The results of an accelerated durability test (ADT, continuous cycling between 0.6 and 1.4 V) in RRDE indicated high stability for the Pt/NbxTi(1 − x)O2 electrocatalysts at high potentials in terms of minimum loss in Pt electrochemical surface area (ECSA). Furthermore, the Pt/NbxTi(1 − x)O2 showed nearly 10-fold higher ORR activity after potential cycling tests when compared to the Pt/C catalyst (1.19 and 0.13 mA cm−2 for Pt/NbxTi(1 − x)O2 and Pt/C, respectively). The Pt/C catalyst showed no activity in fuel cell testing after 1000 cycles due to severe carbon corrosion and subsequent disintegration of the catalyst layer. Conversely, the Pt/NbxTi(1 − x)O2 catalyst showed only a small voltage loss (0.11 V at 0.6 A cm−2) even after 3000 cycles. Based on the ADT results, the Pt/NbxTi(1 − x)O2 electrocatalyst synthesized in this investigation offers a new approach to improve the reliability and durability of PEM-based fuel cell cathode catalysts.
Supported samples of 8 wt % monometallic Pt/C and Ru/C, as well as 12 wt % bimetallic Pt50Ru50/C,... more Supported samples of 8 wt % monometallic Pt/C and Ru/C, as well as 12 wt % bimetallic Pt50Ru50/C, were prepared by the method of incipient wetness impregnation. Impregnated samples were subsequently reduced by hydrogen and then oxidized in air at different To temperatures. TEM and XRD examinations indicated that metal crystallites were finely dispersed with a diameter of dM < or = 3 nm on the reduced samples. Reductive behavior of the oxidized samples by hydrogen was pursued with the technique of temperature programmed reduction (TPR). The temperature of the reduction peaks (Tr) noticed in the TPR profiles varied with the metal composition of catalysts and To temperature of oxidation. At To = 300 K, oxidation was confined to the surface layer of metallic crystallites. As a result, Pts O (with a peak at Tr = 230 K) or PtsO2 (Tr = 250 K) was formed on monometallic Pt/C while RusO2 (Tr approximately 380 K) was formed on Ru/C. A reductive peak with Tr = 250 K was found from the bimetallic sample from Pt50Ru50/C oxidized at To = 300 K. The reductive peak suggests bimetallic crystallites were dispersed with cherry type structure, with Pt exposed at the surface and Ru in the core. On increasing the To temperature of oxidation treatment to 370 K and higher, Tr peaks between 270 and 350 K were gradually noticed on the oxidized bimetallic sample. Peaks in this Tr region are assigned to reduction of the oxidized alloy surface (AsO). Evidently, a segregation of Ru to the surface of the bimetallic crystallites is indicated upon oxidation at To > 380 K.
The corrosion of the carbon-based bipolar plate was studied under unitized regenerative fuel cell... more The corrosion of the carbon-based bipolar plate was studied under unitized regenerative fuel cell (URFC) operation conditions. At overpotentials higher than 2.0 V vs. normal hydrogen electrode (NHE), cell performance in the electrolyzer mode significantly decreases with time due to the increased ohmic resistance of the carbon-based bipolar plates. During fuel cell operation, the unit cell shows an ohmic resistance of approximately 0.15 Ω. After the operation in the electrolyzer mode, the ohmic resistance of the cell increases up to 1.24 Ω. The surface image of the carbon-based bipolar plate after water electrolysis reaction at 2.0 V shows a drastic corrosion at the contact area of the bipolar plate with the electrode. The corrosion of the rib in the flow-field increases the contact resistance between the electrode and the bipolar plate, which leads to the observed decrease in cell performance. A gold coating of 1 μm on the titanium bipolar plates is very effective in preventing titanium oxidation during the URFC operation. The ohmic resistance of the cells that are prepared with bare titanium and gold-deposited titanium bipolar plates is 0.40 Ω and 0.18 Ω, respectively. In fact, the gold coating serves as a barrier layer, which inhibits the formation of the passive layer on the surface of titanium-based bipolar plates. The cycling experiments in the fuel cell and in the electrolyzer mode indicate that the gold-coated titanium bipolar plates exhibit a stable performance.
Rutile phase niobium-doped titanium oxide [NbxTi(1 − x)O2, x = 0.25] with a high electrical condu... more Rutile phase niobium-doped titanium oxide [NbxTi(1 − x)O2, x = 0.25] with a high electrical conductivity (1.11 S cm−1) was synthesized and investigated as a cathode catalyst support material for polymer electrolyte membrane fuel cells (PEMFCs). The TEM image of the Pt/NbxTi(1 − x)O2 catalyst revealed that Pt particles (dPt = 3–4 nm) were deposited on the NbxTi(1 − x)O2 support using a borohydride reduction method. The Pt/NbxTi(1 − x)O2 catalyst showed comparable oxygen reduction reaction (ORR) activity to that of a commercial Pt/C catalyst (E-TEK) when tested in rotating ring-disk electrode (RRDE). The results of an accelerated durability test (ADT, continuous cycling between 0.6 and 1.4 V) in RRDE indicated high stability for the Pt/NbxTi(1 − x)O2 electrocatalysts at high potentials in terms of minimum loss in Pt electrochemical surface area (ECSA). Furthermore, the Pt/NbxTi(1 − x)O2 showed nearly 10-fold higher ORR activity after potential cycling tests when compared to the Pt/C catalyst (1.19 and 0.13 mA cm−2 for Pt/NbxTi(1 − x)O2 and Pt/C, respectively). The Pt/C catalyst showed no activity in fuel cell testing after 1000 cycles due to severe carbon corrosion and subsequent disintegration of the catalyst layer. Conversely, the Pt/NbxTi(1 − x)O2 catalyst showed only a small voltage loss (0.11 V at 0.6 A cm−2) even after 3000 cycles. Based on the ADT results, the Pt/NbxTi(1 − x)O2 electrocatalyst synthesized in this investigation offers a new approach to improve the reliability and durability of PEM-based fuel cell cathode catalysts.
Supported samples of 8 wt % monometallic Pt/C and Ru/C, as well as 12 wt % bimetallic Pt50Ru50/C,... more Supported samples of 8 wt % monometallic Pt/C and Ru/C, as well as 12 wt % bimetallic Pt50Ru50/C, were prepared by the method of incipient wetness impregnation. Impregnated samples were subsequently reduced by hydrogen and then oxidized in air at different To temperatures. TEM and XRD examinations indicated that metal crystallites were finely dispersed with a diameter of dM < or = 3 nm on the reduced samples. Reductive behavior of the oxidized samples by hydrogen was pursued with the technique of temperature programmed reduction (TPR). The temperature of the reduction peaks (Tr) noticed in the TPR profiles varied with the metal composition of catalysts and To temperature of oxidation. At To = 300 K, oxidation was confined to the surface layer of metallic crystallites. As a result, Pts O (with a peak at Tr = 230 K) or PtsO2 (Tr = 250 K) was formed on monometallic Pt/C while RusO2 (Tr approximately 380 K) was formed on Ru/C. A reductive peak with Tr = 250 K was found from the bimetallic sample from Pt50Ru50/C oxidized at To = 300 K. The reductive peak suggests bimetallic crystallites were dispersed with cherry type structure, with Pt exposed at the surface and Ru in the core. On increasing the To temperature of oxidation treatment to 370 K and higher, Tr peaks between 270 and 350 K were gradually noticed on the oxidized bimetallic sample. Peaks in this Tr region are assigned to reduction of the oxidized alloy surface (AsO). Evidently, a segregation of Ru to the surface of the bimetallic crystallites is indicated upon oxidation at To > 380 K.
The corrosion of the carbon-based bipolar plate was studied under unitized regenerative fuel cell... more The corrosion of the carbon-based bipolar plate was studied under unitized regenerative fuel cell (URFC) operation conditions. At overpotentials higher than 2.0 V vs. normal hydrogen electrode (NHE), cell performance in the electrolyzer mode significantly decreases with time due to the increased ohmic resistance of the carbon-based bipolar plates. During fuel cell operation, the unit cell shows an ohmic resistance of approximately 0.15 Ω. After the operation in the electrolyzer mode, the ohmic resistance of the cell increases up to 1.24 Ω. The surface image of the carbon-based bipolar plate after water electrolysis reaction at 2.0 V shows a drastic corrosion at the contact area of the bipolar plate with the electrode. The corrosion of the rib in the flow-field increases the contact resistance between the electrode and the bipolar plate, which leads to the observed decrease in cell performance. A gold coating of 1 μm on the titanium bipolar plates is very effective in preventing titanium oxidation during the URFC operation. The ohmic resistance of the cells that are prepared with bare titanium and gold-deposited titanium bipolar plates is 0.40 Ω and 0.18 Ω, respectively. In fact, the gold coating serves as a barrier layer, which inhibits the formation of the passive layer on the surface of titanium-based bipolar plates. The cycling experiments in the fuel cell and in the electrolyzer mode indicate that the gold-coated titanium bipolar plates exhibit a stable performance.
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Papers by Sheng Yang Huang