Batteries

Batteries are usually categorized as primary batteries, secondary batteries, or fuel cells [4]. Primary batteries cannot be recharged, because they have irreversible electrochemistry. They are single use and disposable. Examples of a primary battery include alkaline batteries (such as silver oxide/zinc, mercury oxide/zinc, and manganese oxide/zinc) [5]. Secondary batteries experience reversible elec­trochemistry, so they are reusable and can be recharged by an external power supply after the operating voltage has dropped to zero. Examples of a secondary battery include nickel-cadmium, nickel-metal-hydride, and lithium-ion batteries. Problems associated with secondary batteries are that they undergo hysteresis, which prohibits them from being recharged to their original state once used [4]. Unlike secondary batteries, fuel cells do not undergo hysteresis. A fuel cell is an electrochemical device that generates power upon fuel addition; therefore, it is not of single use nor does it need to be recharged by an external power source, but only by the addition of more fuel.

A battery is a portable, self-contained electrochemical power source that consists of one or more voltaic cells [5]. Single voltaic cells consist of two electrodes (an anode and a cathode) and at least one electrolyte. In all electro­chemical power sources, electrodes are used to donate and accept electrons in order to generate power. Oxidation of fuel occurs at the anode electrode, while reduction occurs at the cathode electrode. Traditional electrode materials utilized in batteries are metal-based, such as platinum, nickel, lead, and lithium. Employ­ment of these catalysts is limited due to the fact that they are nonrenewable resources and highly expensive. In addition, precious metal catalysts when employed at electrodes will oxidize a variety of fuels (hydrogen gas, methane, and alcohols: methanol, ethanol, propanol, butanol, other alkyl alcohols) and therefore they are nonselective catalysts.

Due to the nonspecificity of the catalysts, a salt bridge must be employed to separate the anode and cathode compartments in order to increase the operating voltage of the electrochemical cell by separating anodic fuel from cross-reacting at the cathodic electrode. Theoretically, if selective catalysts were utilized at both electrodes, the polymer electrolyte membrane that acts as a salt bridge in a typical cell can be eliminated from the system. This can result in simplifying the elec­trochemical power system as well as the manufacturing procedure, which will result in lower production costs. Elimination of resistance that is associated with the polymer electrolyte membrane results in an increase in ion conductivity that results in higher power density outputs.