ABSTRACT
Development of alternative energy sources over the traditional ones is an urgent need because of the continuous depletion of fossil fuels. Currently, people have grown interest in fuel-based technologies because of their high efficiency, very low emission and noise, modular design, and low maintenance cost of the fuel cells [1]. Among several fuel-cell-based technologies, direct methanol fuel cells (DMFCs) have been considered a promising energy conversion system because they have high conversion efficiency and are environmentally benign. DMFC is a low temperature (60° C–120° C) proton exchange membrane fuel cell (PEMFC) with high energy density 238(5.04 kWh L-1), simple confguration, easy portability, and light weight; however, DMFC has some serious issues that limit its wide-scale commercialization. Platinum (Pt) has long been known as the most effective cathode catalyst in DMFC to reduce high overpotential of oxygen reduction reaction (ORR), however, the high cost of Pt inhibits the large-scale use of DMFC. Methanol crossover from the anode to the cathode side of the cell is the major drawback of DMFC. Therefore, intense research efforts have been made recently to develop non-Pt-based methanol-tolerant cathode catalysts at a low cost. Recently, many Pt-free cathode catalysts have been designed using carbon-based compounds, transition metals, macrocycle-based materials, etc.; however, these cathode catalysts may not show much improved ORR in comparison to Pt-based compounds, although these can reduce the crossover loss than that of many Pt-based materials.
