Advantages and Disadvantages of Fuel Cells

With respect to other energy conversion systems, fuel cells have advantages and disadvantages:

ADVANTAGES

Zero Emissions: a fuel cell vehicle only emits water vapour if fueled with pure hydrogen, while if it has an on board reformer for the hydrogen production we have to take into account its emissions. The vehicle is a really no-noise vehicle, except for the noise of the auxiliaries (pumps, fan etc.);

High efficiency: Since fuel cells do not use combustion, their efficiency is not linked to their maximum operating temperature. As a result, the efficiency of the power conversion step (the actual electrochemical reaction as opposed to the actual combustion reaction) can be significantly higher than that of thermal engines. In addition fuel cells also exhibit higher part-load efficiency and do not display a sharp drop in efficiency as the powerplant size decreases. Heat engines operate with highest efficiency when run at their design speed and ex-hibit a rapid decrease in efficiency at part load.

Rapid load-following: Fuel cells exhibit good load-following characteristics. Fuel cell sys-tems, however, are comprised of predominantly mechanical devices each of which has its own response time to changes in load demand. Nonetheless, fuel cell systems that operate on pure hy-drogen tend to have excellent overall response.

Low temperatures: Fuel cell systems suitable for automotive applications operate at low temperatures. This is an advantage in that the fuel cells re-quire little warmup time, high temperature hazards are reduced, and the thermodynamic efficiency of the electro-chemical reaction is inherently better.

Reduced number of energy tranformations: When used as an electrical energy generating device, fuel cells require fewer energy transformations than those as-sociated with a heat engine. When used as a mechanical energy generating device, fuel cells require an equal number of conversions, although the specific transformations are different and efficiencies are higher.

Refueling time: Fuel cell systems do not require recharging. Rather, fuel cell systems must be re-fueled, which is faster than charging a battery and can provide greater range depend-ing on the size of the storage tank.


DISADVANTAGES

Hydrogen: Ironically, hydrogen which is of such benefit environmentally when used in a fuel cell, is also its greatest liability in that it is difficult to manufacture and store. Current manufacturing processes are expensive and energy in-tensive, and often derive ultimately from fossil fuels.

Contaminants sensitivity: Fuel cells require relatively pure fuel, free of specific con-taminants. These contaminants include sulfur and car-bon compounds, and residual liquid fuels (depending on the type of fuel cell) that can deactivate the fuel cell catalyst effectively destroying its ability to operate. None of these contaminants inhibit combustion in an internal combustion engine.

High-cost catalyst: Fuel cells suitable for automotive applications typically require the use of a platinum catalyst to promote the power generation reaction. Platinum is a rare metal and is very expensive.

Ice: Fuel cells must not freeze with water inside. Fuel cells generate pure water during the power generating reaction and most fuel cells suitable for automotive applications use wet reactant gases. Any residual water within the fuel cells can cause irreversible expansion damage if permitted to freeze. During operation, fuel cell systems generate sufficient heat to prevent freezing over normal ambient temperatures, but when shut down in cold weather the fuel cells must be kept warm or the residual water must be removed before freezing.

New technology: Fuel cells are an emerging technology. As with any new technology, reductions in cost, weight and size concurrent with increases in reliability and lifetime remain pri-mary engineering goals.

Lack of infrastructures: An effective hydrogen infrastructure has yet to be established.