Fuel Cell vs Batteries

Until new batteries that can provide much higher energy densities without compromising safety are discovered, fuel cells will continue to outperform today’s heavy and large storage batteries. On the other hand, it is less expensive to build electric cars with batteries than with fuel cells.

Today’s batteries are less expensive than fuel cells, but their energy density is insufficient, and their weight and size are too high to provide the required driving range. The final outcome of the battery-versus-fuel cell race cannot be predicted. All that is obvious right now is that there are substantial developments in both fields.

In the area of fuel cells, reliability and availability have much improved. Recent U.S. military experience with phosphoric acid fuel cells found that the mean time between failure (MTBF) was almost 1,800 h and the availability was 67%. This is comparable with the MTBF service intervals for diesel generators. These fuel cells also favorably compare with the service interval needed for a typical gas turbine generation set. Still, much more development is required to obtain a commercially viable product. Today, the typical fuel cell system still requires servicing every 3–4 days to replace its scrubber packs.

The early electric cars used the old lead–acid batteries. Today’s hybrids are provided with more robust nickel–metal units. The EVs of the future are likely to be provided with lithium–iron batteries, found in today’s laptops and cell phones. Much work remains to be done in this area to increase safety and life span (to 100,000 mi of driving), while reducing their cost. Nissan and Mitsubishi are both making major investments in building lithium-ion battery mass production plants.

New battery developments include the ultracapacitor hybrid barium titanate powder design (EEStors). These devices can absorb and release charges much faster than electrochemical batteries. They weigh less, and some projections suggest that in electric cars they might provide 500 mi of travel at a cost of $9 in electricity. But these are only the projections of researchers.

Another direction of battery development involves high temperature and larger units. NGK Insulators, Ltd., in Japan uses sodium–sulfur batteries operating at 427°C (800°F) that are able to deliver 1 mW for 7 hours from a battery unit. The size of these units is about the size of a bus. Such units could be used at electric filling stations that are not connected to the grid.

Hydrogen Storage

One of the most important factors in introducing hydrogen as future fuel is transportation and on-vehicle storage of hydrogen. Storing hydrogen that flexibly links its production and user are key factor of the hydrogen fuel utilization. The major contribution to the problem is from low gas density of hydrogen. For example, to store energy equivalent to one gasoline tank, an ambient pressure hydrogen gas tank would be more than 3000-fold the volume of the gasoline tank.

Various storage options have been introduced by many researchers and institutions for last two decades. Here is a brief desription for some of them.

• Compressed Hydrogen. Considering both storage and refueling technologies, probably compressed gas storage is the most promising alternative. High strength steel or other metals are an option from a strength perspective, however, diffusivity of hydrogen through the steel and weight of the steel are major issues for vehicular storage.
  

• Liquid Hydrogen. Storing of hydrogen in liquid form at cryogenic condition is attractive in that it offers low weight and volume per unit energy when compared to compressed hydrogen. But, main issues are hydrogen boil-off, the energy required for liquefaction, and tank cost.

• Metal Hydride. Metal hydrides are specific combinations of metallic alloys, which possess the unique ability to absorb hydrogen and release it later. The life of a metal hybride storage tank is directly related to the purity of the hydrogen it is storing. The alloys act as a sponge, which absorbs hydrogen, but it is also absorbs any impurities together with hydrogen. Thus, the hydrogen released from the tank is highly pure, but the tank’s lifetime and ability to store hydrogen is reduces as the impurities are deposited in the metal pores.

• Carbon Nanotubes. Hydrogen can be adsorbed on a carbon surface. Various forms of carbon with high surface area may be utilized for the storage of hydrogen. Research on this technology has focused on the areas of improving manufacturing techniques and reducing costs as carbon nanotubes move toward commercialization.
  

Welcome to Hydrogen Study Blog

Hydrogen represents one of the most promising ways to realise sustainable energy, whilst fuel cells provide the most efficient conversion device for converting hydrogen, and possibly other fuels, into electricity. Hydrogen can be produced from carbon-free or carbon-neutral energy sources or from fossil fuels with CO2 capture and storage. Thus, the use of hydrogen could drastically reduce greenhouse gas emissions from the energy sector.

Fuel cells are intrinsically clean and very efficient (up to double the efficiency of Internal Combustion Engines (ICE)) and capable of converting hydrogen and other fuels to electricity, heat and power. They can also be sited close to the point of end-use, allowing exploitation of the heat generated in the process.

Through this Hydrogen Study Blog, I will be in position to deliver information, news, and research progress related with Hydrogen as a energy for our better future. The study will be covered many aspects about Hydrogen, such as: hydrogen production, hydrogen storage, fuel cell, and many other aspects.