Ernee Noryana Muhamad

Evidence of nonelectrochemical shift reaction on a CO-tolerant high-entropy state Pt-Ru anode catalyst for reliable and efficient residential fuel cell systems.

A randomly mixed monodispersed nanosized Pt-Ru catalyst, an ultimate catalyst for CO oxidation reaction, was prepared by the rapid quenching method. The mechanism of CO oxidation reaction on the Pt-Ru anode catalyst was elucidated by investigating the relation between the rate of CO oxidation reaction and the current density. The rate of CO oxidation reaction increased with an increase in unoccupied sites kinetically formed by hydrogen oxidation reaction, and the rate was independent of anode potential. Results of extended X-ray absorption fine structure spectroscopy showed the combination of N(Pt-Ru)/(N(Pt-Ru) + N(Pt-Pt)) ≑ M(Ru)/(M(Pt) + M(Ru)) and N(Ru-Pt)/(N(Ru-Pt) + N(Ru-Ru)) ≑ M(Pt)/(M(Ru) + M(Pt)), where N(Pt-Ru)(N(Ru-Pt)), N(Pt-Pt)(N(Ru-Ru)), M(Pt), and M(Ru) are the coordination numbers from Pt(Ru) to Ru(Pt) and Pt (Ru) to Pt (Ru) and the molar ratios of Pt and Ru, respectively. This indicates that Pt and Ru were mixed with a completely random distribution. A high-entropy state of dispersion of Pt and Ru could be maintained by rapid quenching from a high temperature. It is concluded that a nonelectrochemical shift reaction on a randomly mixed Pt-Ru catalyst is important to enhance the efficiency of residential fuel cell systems under operation conditions.

Effect of SnO2 Deposition Sequence in SnO2-Modified PtRu/C Catalyst Preparation on Catalytic Activity for Methanol Electro-Oxidation

SnO 2 -modified PtRu/C catalysts were prepared in a polyol process to investigate the effect of a SnO 2 deposition sequence on the catalytic activity for methanol electro-oxidation. The structure, morphology, and chemical state of the prepared catalysts were characterized by X-ray diffraction, scanning transmission electron microscopy, and X-ray photoelectron spectroscopy. The electrochemical activities were evaluated by cyclic voltammetry, linear sweep voltammetry, and chronoamperometry measurements in combination with in situ IR reflection-absorption spectroscopy (IRRAS). Compared with those in the PtRu/C catalyst, a simultaneous deposition of PtRu and SnO 2 particles or a deposition of SnO 2 prior to PtRu improved the metal dispersion and decreased the alloyed Ru fraction. The deposition sequence of SnO 2 did not alter the chemical-state distribution of Pt and Ru but resulted in a different surface atomic ratio of Pt, Ru, and SnO 2 . Electrochemical and in situ IRRAS measurements indicated that the SnO 2 -modified PtRu/C catalyst prepared by the deposition of PtRu prior to SnO 2 gave the best catalytic activity for CO ads and methanol electro-oxidation among the PtRu/C and SnO 2 -modified PtRu/C catalysts. The roles of SnO 2 deposited with different sequences in the SnO 2 -modified PtRu/C catalysts were proposed.

A Comparative Study of Variously Prepared Carbon-Supported Pt / MoO x Anode Catalysts for a Polymer Electrolyte Fuel Cell

Carbon-supported Pt/MoO x anode catalysts were prepared by the preimpregnation, postimpregnation, and chemical reduction methods. The physicochemical characteristics of all catalysts were determined by X-ray diffraction, scanning transmission electron microscopy, and CO pulse titration. The electrochemical oxidation of CO verified from CO-stripping voltammetry shows that most of the CO ads were oxidized on the Pt sites. The Pt/MoO x /C catalyst prepared by the chemical reduction method showed superior hydrogen electrochemical oxidation in pure H 2 , apparently due to the much smaller Pt particle size than those of the other Pt/MoO x /C catalysts. However, the anode performances in the presence of 500 ppm CO/H 2 mixture showed that a catalyst with high CO tolerance was derived from the Pt/MoO x /C catalyst prepared by postimpregnation method. The oxidation of CO by the water―gas shift (WGS) reaction is shown by the formation of CO 2 even under an open-circuit condition. With an increase in current, active sites for the WGS reaction is regenerated by electrochemical oxidation of hydrogen.

Preparation of Well-Alloyed PtRu/C Catalyst by Sequential Mixing of the Precursors in a Polyol Method

A well-alloyed and highly CO-tolerant 45 wt % PtRu/C catalyst was prepared by sequential mixing of the precursors in a polyol method. The alloying degree of the PtRu/C catalyst was much higher than that of the conventional PtRu/C catalyst prepared by simultaneous mixing of the precursors in the polyol method. In the sequential mixing approach, Pt and Ru compounds were reduced at the same time because Ru 3+ was partly reduced to Ru 2+ before the addition of H 2 PtCl 6 , which promoted PtRu alloy formation, and subsequent reduction treatment by ethylene glycol at a high temperature further improved the alloying degree. Greater CO tolerance of the well-alloyed PtRu/C catalyst was verified by a negative shift in peak potential of CO ads electro-oxidation in CO stripping voltammetry. The well-alloyed PtRu/C catalyst showed a better single-cell performance than the conventional and commercial PtRu/C catalysts when the anode was fed with CO-contaminated H 2 .

Improving CO Tolerance of Pt2Ru3/C Catalyst by the Addition of Tin Oxide

SnOx-modified Pt2Ru3/C catalysts were post-treated in different atmospheres at various temperatures to improve the catalytic activity for H2/CO electro-oxidation. The structures of the Pt2Ru3/C and SnOx/Pt2Ru3/C catalysts were characterized by X-ray diffraction. Electrochemical activities were evaluated by CO stripping voltammetry and single cell test. The SnOx/Pt2Ru3/C catalysts had a lower onset potential for CO electro-oxidation and greater cell voltage than the Pt2Ru3/C catalyst under high CO concentrations. The SnOx/Pt2Ru3/C catalyst treated in 5 % H2/Ar at 150oC exhibited the greatest CO tolerance due to that the post-treatment caused the conversion of SnO2 to SnOx (1{less than or equal to} x {less than or equal to}2) without destroying PtRu alloy structure.

Structures and CO Tolerance of Anode PtRu Catalyst for Polymer Electrolyte Fuel Cells

An anode catalyst for a polymer electrolyte fuel cell should be CO-tolerant, i.e., it should have the function of hydrogen oxidation in the presence of CO, since hydrogen fuel gas generated by the steam reforming process of natural gas contains CO. PtRu/C catalysts with the same degree of Pt-Ru alloying and with various sizes of PtRu particles were prepared, and the dependence of CO tolerance on particle size was investigated. Polarization curves were obtained with pure H2 and CO/H2 (CO concentrations of 500-2040 ppm). It was found that highly dispersed PtRu/C (HD) with small metal particles has much higher CO tolerance than that of poorly dispersed PtRu/C (LD) with large metal particles. The CO tolerance of PtRu/C (HD) was higher than that of a commercial PtRu/C catalyst. The high CO tolerance of PtRu/C (HD) is probably due to efficient concerted functions of Pt, Ru, and their alloy.

The Effect of Modification of PtRu Anode Catalyst with SnO2 on CO Tolerance

Residential polymer electrolyte fuel cell cogeneration system has recently attracted much attention, and in this system H2 is usually produced from the steam reforming of natural gas. Since the acceptable CO concentration for Pt-Ru alloy anode [1] is below 100 ppm, the CO removal units add extra cost. Consequently, it is earnestly desired to improve the performance of Pt-Ru catalyst for CO tolerance.