ABSTRACT
Incomplete methanol oxidation and rapid activity degradation of electro-catalysts are key barriers to successful commercialization of direct methanol fuel cell (DMFC). To address these problems, we report the synthesis of platinum-copper (PtCu) alloy nanoparticles supported on nitrogen doped reduced graphene oxide (N-rGO) as the anode catalyst for the efficient electro-oxidation of methanol. Catalysts with varying molar ratios of PtCu were fabricated using impregnation reduction method and their electrochemical performance was compared with the commercially available Pt/C (20 wt%) anode catalyst. The electro-catalytic activity of the synthesized PtCu (1:2)/N-rGO catalyst was found to be much higher to those that observed for Pt/N-rGO and Pt/C catalyst as revealed by cyclic voltammetry, electrochemical impedance spectroscopy and electron transfer measurements. The enhanced electrochemical activity of PtCu (1:2)/N-rGO catalyst is not only attributed to strong interfacial interaction between the nitrogen group of N-rGO and PtCu active metal phase but also to the altered electronic structure of Pt as a result of Cu alloying. This reduces the adsorption of CO and OH- species on Pt surface, thereby creating more Pt active sites for methanol electro-oxidation; thus faster kinetics is exhibited. These results indicate the potential application of PtCu/N-rGO catalyst as an anode material in a DMFC.
ABSTRACT
The higher methanol utilization efficiency in direct methanol fuel cell (DMFC) is one of the key parameter to show the performance of an anode catalyst. Here in, we have synthesized a highly efficient and stable PtCo anode nanocatalysts (2-4 nm size) supported on reduced graphene oxide (rGO) for the electro-oxidation of methanol in a DMFC. Three different compositions of anode catalysts PtCo (1:7)/rGO, PtCo (1:9)/rGO and PtCo (1:11)/rGO comprising of 20% metal loading by weight of rGO are being investigated for methanol electro-oxidation in acidic medium with different methanol concentration using cyclic voltammetry. The electrochemical response from three different catalysts revealed that the PtCo (1:9)/rGO catalyst has efficiently oxidized 5 M methanol in a half cell configuration. A peak anodic current density of 46.8 mA/cm² and a power density of 136.8 mW/cm² are achieved using PtCo (1:9)/rGO anode catalyst at 100 °C for DMFC with 5 M methanol supply with negligible amount of methanol crossover. About 34% Faradaic efficiency and 22% energy efficiency is attained using PtCo (1:9)/rGO anode catalyst for a DMFC. Further, the 3% methanol oxidation reaction (MOR) efficiency is attained as revealed by evaluating the MOR by-products i.e., formic acid and formaldehyde formation. The results indicate excellent catalytic behavior of PtCo (1:9)/rGO towards MOR and its potential application as anode catalyst in DMFC.
ABSTRACT
Amino functionalized boron nitride nanotubes were used as the reinforcement material for the fabrication of Al-matrix composites using powder metallurgy process. It was found that the mechanical properties of these composites were improved significantly as compared to pure Al composites fabricated under similar conditions. The microhardness of these composites was found to improve by five times and compressive strength by 300% as compared to pure Al composites under similar processing conditions. The enhanced mechanical properties of these composites can be attributed to the proper dispersion of boron nitride nanotubes (BNNTs) in Al matrix and the formation of a strong interfacial bonding between BNNTs and Al matrix under the processing conditions. High-resolution transmission electron microscopy studies revealed the formation of transition layer of AlB2 which might lead to a better load transfer from Al matrix to the BNNTs. Further, these composites are believed to withstand high temperatures as compared to Al matrix composites reinforced with carbon nanotubes and, therefore, can be used for applications where lightweight and high strength materials are desired with stability at elevated temperatures.
