K.G. Nishanth

A DMFC with Methanol-Tolerant-Carbon-Supported-Pt-Pd-Alloy Cathode

Methanol-tolerant Pt-Pd alloy catalysts supported on to carbon with varying Pt:Pd atomic ratios of 1:1, 2:1 and 3:1 are prepared by a novel wet-chemical method and characterized using powder XRD, XPS, FESEM, EDAX and TEM techniques. The optimum atomic weight ratio for Pt to Pd in the carbon-supported alloy catalyst as established by linear-sweep voltammetry (LSV) and cell polarization studies is found to be 2:1. A direct methanol fuel cell (DMFC) employing carbon-supported Pt-Pd (2:1) alloy (Pt-Pd/C) catalyst as the cathode catalyst delivers a peak-power density of 115 mW/cm(2) at 70 degrees C as compared to peak-power density of 60 mW/cm(2) obtained with the DMFC employing carbon-supported Pt (Pt/C) catalyst operating under similar conditions. In the literature, DMFCs operating with Pt-TiO2 (2:1)/C and Pt-Au (2:1)/C methanol-tolerant cathodes are reported to exhibit maximum ORR activity among the group of these methanol-tolerant cathodes with varying catalysts compositions. Accordingly, the present study also provides an effective route to design methanol-tolerant-oxygen-reduction catalysts for DMFCs

DMFCs with Enhanced Catalytic Activity and Durability Using Transition-Metal Carbides as Catalyst Support

Molybdenum carbide (MoC) and Tungsten carbide (WC) are obtained by direct carbonization method. Pt-Ru supported on MoC, WC and Vulcan XC-72R are prepared, and characterized by XRD and TEM techniques. Electrochemical activity for methanol electro-oxidation is studied by cyclic voltammetry (CV) and durability study on all the electro-catalysts is conducted by accelerated durability test (ADT). The electrochemical activity for methanol electro-oxidation of carbide-supported electro-catalysts is found to be higher than carbon-supported catalysts before and after ADT. Direct methanol fuel cells (DMFCs) employing carbide-supported Pt-Ru exhibit higher performance towards methanol oxidation in relation to carbon-supported Pt-Ru.

Enhanced Methanol Electro-Oxidation on Pt-Ru Decorated Self-Assembled TiO2-Carbon Hybrid Nanostructure

Direct Methanol Fuel Cells (DMFCs) are attractive for portable power applications owing to the easy transportation, storage and refueling of methanol in conjunction with the reduced system-weight, size, highenergy-efficiency and low-temperature operation (1). However, to improve the commercial viability of DMFCs, there are several scientific issues, such as methanol crossover, sluggish electrode kinetics and durability that need to be addressed with concomitant improvements in performance characteristics. One of the problems with the DMFCs is the limited activities of the pure platinum anode catalysts as pure platinum is easily poisoned by carboxylic reaction-intermediates produced during the methanol oxidation reaction (MOR). The use of alloy catalysts such as Pt:Ru has helped mitigating the aforesaid problem substantially. But the CO tolerance of PtRu alloy catalyst is still unsatisfactory for practical DMFC applications (2). Accordingly, it is imperative to further the catalytic activity of Pt-Ru alloy catalyst. It has been reported that the addition of transition metal oxides, such as, CeO2, TiO2, WO3, MoO3, etc., to PtRu alloy catalyst can improve its CO tolerance and activity towards MOR due to the “spillover” effect. Among these metal oxides, TiO2 seems most promising due to its natural abundance, cost and stability in acidic environment. Homogeneously-dispersed composite of PtRu alloy catalyst with TiO2 could be realized by (a) intimate mixing of Pt, Ru, and TiO2 precursor solutions, (b) impregnation and colloidal methods using Pt-Ru/C or TiO2 particles, and (c) physical mixing of PtRu/C with TiO2 particles. Among these colloidal methods and solgel routes are more effective to achieve homogenous nanoscale mixing of the metal and metal oxide phases. However, these methods need pyrolysis at high temperatures that affects the performance of the catalyst. Accordingly, it is desirable to develop an effective synthetic route to realize a homogenous nanocomposite catalyst devoid of any post-heat treatment. In the present study, a porous titanium oxide-carbon hybrid nanocomposite is directly synthesized using a supramolecular self-assembly concept with in situ crystallization process. The microstructure of the catalyst including surface area, morphology and crystallinity are characterized by Brunauer–Emmett–Teller (BET), Transmission electron microscope (TEM), X-ray diffraction (XRD) and Raman spectroscopy. Pt-Ru on titanium oxide-carbon composite is prepared by treating with chloroplatinic acid and ruthenium chloride followed by reduction with NaBH4. The crystalline nature and alloy formation are confirmed by XRD studies, and the morphology and particle-size distribution are studied by TEM. Methanol electro-oxidation and Accelerated Durability Test (ADT) are performed using Cyclic Voltammetry (CV). The catalysts have also been performance tested in DMFCs at 65C using methanol and oxygen. Fig. 1 shows electro-catalytic activities for PtRu/C and Pt-Ru decorated Titanium oxide-carbon towards methanol oxidation reaction. It is clear that titanium oxide-carbon composite supported electrocatalyst exhibit enhanced catalytic activity in relation to Pt-Ru/C. Besides the peak potentials for methanol oxidation are 0.52V and 0.56V for Pt-Ru supported on titanium oxide-carbon composite and Pt-Ru/C, respectively, suggesting that methanol oxidation occurs at a lower potential on titanium oxide-carbon composite supported catalyst in relation to carbon supported catalyst.

Insights into the effect of structure-directing agents on structural properties of mesoporous carbon for polymer electrolyte fuel cells

Synthesis of mesoporous carbon (MC) with well-defined morphologies and, wide range of surface area and pore size, is reported by organic–organic interaction between thermally decomposable surfactants (structure-directing agents) and the cost-effective carbon precursors, such as phloroglucinol and formaldehyde. Selected surfactants based on tri-block co-polymer, non-ionic and ionic, are used for synthesis of MCs with wide variation in their physical properties. The present method could be applied to large-scale production of porous carbon with desired surface area and pore morphology and would practically be relevant to many emerging technologies including electrochemical power sources such as super-capacitors and fuel cells. In the present study, we have successfully used MCs as gas-diffusion layers in fuel cell electrodes and established proper balance between air permeability and water management. The porous carbon contributes significantly to reduce mass transfer existing at high current density region resulting in improved performance of the polymer electrolyte fuel cells.

Carbon-Supported Pt-Pd Alloy as a Methanol-Tolerant-Oxygen-Reduction Electro-Catalyst for DMFCs

Methanol-tolerant Pt-Pd alloy catalysts supported on to carbon with varying Pt:Pd atomic ratios of 1:1, 2:1 and 3:1 are prepared by a novel wet-chemical method and characterized using powder XRD, FESEM and EDAX techniques. The optimum atomic weight ratio of Pt to Pd in the carbon-supported alloy catalyst as established by linear-sweep voltammetry (LSV) and cellpolarization studies is found to be 2:1. A direct methanol fuel cell (DMFC) employing the carbon-supported Pt-Pd(2:1) alloy catalyst as the cathode catalyst delivers a peak-power density of 115 mW/cm at 70°C as compared to the peak-power density value of 60 mW/cm obtained with the DMFC employing carbon-supported Pt (Pt/C) catalyst operating under similar conditions.