An improved palladium-based DMFCs cathode catalyst

Abstract

A novel carbon-supported palladium-rich Pd 3 Pt 1 /C catalyst prepared by a modified polyol process showed a better cell performance than Pt/C in direct methanol fuel cells, which may be attributed to palladium's inactivity to methanol electro-oxidation while exhibiting good performance to oxygen reduction reaction.There has been growing interest in using direct methanol fuel cells (DMFCs) as transport and portable power sources in recent years. 1 However, polymer electrolyte membranes (PEM) commonly employed, such as Nafion 1 , suffer from high methanol crossover, which not only lowers fuel utilization efficiency but also adversely affects the cathode performance, and thus results in a loss in the overall fuel cell efficiency. One effective way to overcome the crossover problem may be to adopt oxygen reduction selective catalysts for use as the DMFC's cathode. 2 Several transition metal compounds, such as pyrolysed transition metal macrocycles and transition sulfide, have been exploited as methanol-tolerant oxygen reduction reaction (ORR) catalysts 3 because of their good selectivity (y100%) against methanol oxidation reaction (MOR). But the activity of these ORR catalysts was considerably lower than platinum-based ones. Thus, many researchers have been trying to improve DMFCs cathode performance based on platinum catalysts. 4 Li et al obtained good cell performance through adopting multi-walled carbon-nanotube as carbon support; Neergat and his co-workers tried to alloy platinum with transition metal elements such as Co, Cr, Ni and Fe to improve ORR activity; Zhou et al got good DMFCs cathode performance by increasing the mass ratio of platinum metal to carbon support. However, platinum-based catalysts have not been considered ideal DMFCs cathode because of platinum's high intrinsic activity to ORR and MOR. Therefore, it is necessary to find a novel DMFCs cathode catalyst, which has good ORR performance and high selectivity against MOR.Palladium and platinum have very similar properties because they belong to the same group in the periodic table. Savadogo had reported active palladium alloy catalysts without platinum for ORR in acid medium. 5 But the ORR on carbon supported palladium-based alloy in presence of methanol has not been announced hitherto. In this communication, carbon supported palladium-based catalyst as DMFCs cathode was investigated.Pd-Pt/C catalyst with a molar ratio of palladium to platinum of 3 : 1 was prepared by a modified polyol synthesis strategy as described in previous papers. 4d As a comparison, Pt/C was also prepared. The total metal content maintained about 20 wt.% for all the catalysts. Fig. 1 shows the X-ray diffraction (XRD) results of Pd 3 Pt 1 /C and Pt/C. The first peak at the low 2h range (2h # 26u) was associated with the XC-72 carbon support. As displayed in Fig. 1, both the catalysts exhibited the characteristic diffraction fcc. crystalline structure. An angular shift of diffraction peaks to higher positions was found in the XRD pattern of Pd 3 Pt 1 /C as compared to those...

Enhanced Methanol Tolerance of Highly Pd rich Pd-Pt Cathode Electrocatalysts in Direct Methanol Fuel Cells

“…Meanwhile, sufficient oxygen reduction activity has to be ensured and the electrocatalyst must possess considerable methanol tolerance [35][36][37]. Pd-based electrocatalysts with high oxygen reduction activity and low methanol oxidation activity have been suggested as possible DMFC cathode catalysts [38][39][40][41][42][43][44][45].…”

Anode Catalysts for Low‐Temperature Direct Alcohol Fuel Cells

“…Later, supported noble metal or noble metal/transition metal nanoparticles were prepared [60][61][62][63][64][65][166][167][168][169][170][171][172][173][174][175][176][177][178][179]. Xin and coworkers synthesized carbon-supported Pt, PtRu, PtPd, PtIr, PtSn, PtW, and PtFe catalysts with a sharp particle size distribution of 2-5 nm [60][61][62][63][64][65]166,168,[170][171][172][173]175,177]. This method is simple and very easy to scale up.…”

Pt–Au/C cathode with enhanced oxygen-reduction activity in PEFCs

“…* Author for correspondence (psridhar55@gmail.com) Accordingly, efforts are being made to find a long-lasting and active catalyst for PEFCs. In this context, introduction of second noble metal, such as palladium, gold, to Pt has received considerable attention in recent years due to their attractive stability and activity towards ORR in fuel cells (Li et al 2004;Shao et al 2006a, b;Hernandez-Fernandez et al 2007;Mathiyarasu and Phani 2007). Among the various noble metals, gold is of particular interest in view of its inertness in the bulk state but high catalytic activity at nano-scales.…”