PtRu Nanoparticles on Nitrogen-Doped Carbon Nanotubes As Efficient Anode for High Performance Direct Methanol Fuel Cells

Abstract

Growing energy demand has attracted the investigation of renewable energy conversion devices such as Direct Methanol Fuel Cells (DMFCs). It has several advantages as energy conversion device due to the low cost, higher energy density (6.08 kWh/kg) and easy handling of methanol. In DMFCs, methanol is oxidized to CO2 at the anode and oxygen is reduced to water at the cathode to produce electricity. Platinum (Pt) supported on Vulcan carbon is the state-of-the-art electrocatalyst for Methanol Oxidation Reaction (MOR). Conventionally, DMFCs cannot be fed with pure methanol as fuel, owing to the methanol crossover through polymer electrolyte membrane to the cathode side. However, using dilute methanol solutions causes the deliverable power density substantially lower than the theoretical value. In addition, the high cost of Pt, sluggish MOR kinetics and CO poisoning also hinder the commercialization of DMFCs. Therefore, design and development of robust anode materials are of compelling necessity. To address these issues, typically an oxophilic metal like Ruthenium (Ru) is alloyed with Pt, which replenishes the CO poisoned Pt surface by providing OH species which accelerates the oxidation of CO to CO2. Here, we demonstrate PtRu nanoparticles deposited on Nitrogen-doped Carbon Nanotube (N-CNT) supports by microwave-assisted synthesis. The N-CNTs possess conically stacked graphitic nanostructured side walls, which can strongly anchor PtRu nanoparticles. The 3D N-CNTs support was utilized to improve the methanol mass transport at the anode side. The PtRu/N-CNTs showed enhanced CO oxidation and durability comparing to commercial PtRu/C. A DMFC prototype (5 cm2 MEA) fabricated with PtRu/N-CNTs anode, showed a power density of 102 mW/cm2 with < 4 mg/cm2 of catalyst loading using 1M methanol with 50 kPa backpressure at 90°C and maintained nearly the same power density as the methanol concentration was increased to 3M. The prototype maintained good performance up to 8M methanol.