Combinatorial and High Throughput Screening of DMFC Electrocatalysts

Abstract

Portable power sources play an important role in our daily life due to the increasing needs of using various power consuming electronics such as notebook computers, cell phones and digital cameras. Currently, the most widely used portable power sources are batteries. The high cost and low energy density of batteries are far behind our demands for power requirement. Even for the state-of-the-art battery, such as lithium ion battery, the energy density is less than 180 Wh/Kg. Innovative power sources are urgently needed to be an alternative to batteries. In recent years, fuel cells have attracted much attention, as they can directly convert the chemical energy of fuel to electric energy through electrochemical reactions. A fuel cell consists of an anode, a cathode, and an electrolyte membrane between the anode and the cathode. The most common type of fuel cell is polymer electrolyte membrane (PEM) fuel cell, which uses hydrogen or alcohol as fuel. Direct methanol fuel cells (DMFCs) directly uses methanol as fuel. Because of the high theoretical fuel energy density (6081 Wh/kg), and the ease of storage and transport of the liquid fuel, DMFC has become one of the more promising energy conversion sources for portable applications. People began to study direct use of methanol to generate electricity by a fuel cell early in 1960s [1][2][3][4]. However, the research on DMFC was relatively slow during the first 30 years [5-10] due to two main technical barriers: slow catalytic kinetic rates for methanol oxidation at the anode and oxygen reduction at the cathode; as well as methanol crossover from the anode to the cathode through the electrolyte membrane. Methanol crossover causes not only fuel waste, but also cathode electrode depolarization. The application of Nafion perfluorosulfonic acid as a solid polymeric electrolyte membrane has largely blocked the methanol crossover in comparison to using liquid electrolyte [11][12][13][14][15].Much effort has been made in seeking electrode catalysts. Various non-platinum catalysts, such as metallo-porphyrins and metallo-phthalocyanines [16][17][18][19] were investigated for catalytic reduction of oxygen. For example, Anson and Collman et al. [20,21] have synthesized and studied dimeric cofacial cobalt porphyrins, which