Anode catalyst for direct hydrocarbon alkaline fuel cell

Abstract

The direct oxidation of hydrocarbons in the fuel cell has attracted increasing interest as a power source for portable applications as compared to that fed with hydrogen fuel. Hydrocarbons such as methanol, ethanol, ethylene glycol, and glucose exhibit high volumetric energy density, easy storing and delivery system, renewable in nature and are economically and environmentally friendly as compared to hydrogen fuel. Based on the oxidation of the hydrocarbons directly in the fuel cell, they are termed as the direct methanol fuel cell (DMFC), direct ethanol fuel cell (DEFC), direct ethylene glycol fuel cell (DEGFC), and direct glucose fuel cell (DGFC), which are discussed in the chapter. The performance of these fuel cell is better in alkaline electrolyte than that in the acid electrolyte at low temperature (25 °C) and are fascinating owing to use of low-cost alkaline exchange membrane, non-platinum catalyst, no fuel crossover and low CO poisoning. The anode catalysts such as noble (Pt, Ru, Pd) and non-noble metals (Co, Ni), binary and ternary alloys (PtRu, PtPdRu, PdBiRu, PdPtCo), oxides (PdCeO2, PdNiO), different nanostructures (Pd@Pt) developed for direct oxidation of the hydrocarbons in the presence of different forms of support such as functionalised carbon nanotubes, graphene, metal (N, P, B) doped graphene, ordered mesoporous carbon in alkaline medium at low temperature are discussed. Recent development in the alkaline fuel cell using methanol, ethanol, ethylene glycol and glucose directly as fuel and various anode catalysts with the corresponding reaction mechanism in fuel oxidation in alkaline medium is elaborated. The best performance is achieved in a typical DMFC using PtRu as anode catalyst with maximum peak power density of 168 mW cm−2 in alkaline medium. The performance of Pd based binary and ternary catalysts are much superior to Pt-based catalysts in DEFC, DEGFC, and DGFC in alkaline medium. A DEFC using PdNi/C as anode catalyst, a cation exchange membrane as electrolyte membrane shows peak power density of 360 mW cm−2, a DEGFC using PdNi/C as anode catalyst, KOH doped PBI membrane as electrolyte membrane gives peak power density of 112 mW cm-2 and a DGFC using PdNi/C as anode catalyst, Tokuyama A201 as anion exchange membrane electrolyte demonstrates peak power density of 38 mW.cm−2. The chapter also includes the detailed comparison of cell parameters (fuel concentration, fuel flow rate, catalyst loading, operating temperature etc.), cell performance, current-voltage characteristics, stability and durability of the alkaline fuel cell using methanol, ethanol, ethylene glycol and glucose as fuel.