Hydrogen Drives Future Automobile Industry

Hydrogen Drives Future Automobile Industry

Introduction

There is growing confidence among many energy experts that hydrogen has the potential to become an important energy system for the 21st century. Hydrogen, chemical symbol H, is the simplest element on earth. An atom of hydrogen has only one proton and one electron. Hydrogen gas is a diatomic molecule; each molecule has two atoms of hydrogen (which is why pure hydrogen is commonly expressed as “H2”). At standard temperature and pressure, hydrogen exists as a gas. It is colorless, odorless, tasteless, and lighter than air (Hydrogen. [Art]).

Figure 1. Hydrogen Molecule

Like electricity, hydrogen is an energy carrier (not an energy source), meaning it can store and deliver energy in an easily usable form (Fischer & Finnell, 2006).

. Although abundant on earth as an element, hydrogen combines readily with other elements and is almost always found as part of some other substance, such as water (H2O), or hydrocarbons like natural gas (which consists primarily of methane, with the chemical formula, CH4). Hydrogen is also found in biomass, which includes all plants and animals.

Historical Overview

The United States currently produces about nine million tons of hydrogen per year (National Academy of Sciences/ national research Council, 2004). This hydrogen is used primarily in industrial processes including petroleum refining, petrochemical manufacturing, glass purification, and in fertilizers. It is also used in the semiconductor industry and for the hydrogenation of unsaturated fats in vegetable oil. Only a small fraction of the hydrogen produced in the United States is used as an energy carrier, most notably by the National Aeronautics and Space Administration (NASA). This could change, however, as our nation’s leader’s look to increase our energy security by reducing our dependence on imported oil and expanding our portfolio of energy choices. Hydrogen is the optimum choice for fuel cells, which are extremely efficient energy conversion devices that can be used for transportation and electricity generation.

Production

Although hydrogen is the most abundant element in the universe, it does not naturally exist in its elemental form on Earth. Pure hydrogen must be produced from other hydrogen-containing compounds, such as fossil fuels, biomass, or water. Each production method requires a source of energy, i.e., thermal (heat), electrolytic (electricity), or photolytic (light) energy. Researchers are developing a wide range of technologies to produce hydrogen in economical, environmentally friendly ways so that we will not need to rely on any one energy resource. The great potential for diversity of supply is an important reason why hydrogen is such a promising energy carrier.

The overall challenge to hydrogen production is cost reduction. For transportation, hydrogen must be cost-competitive with conventional fuels and technologies on a per-mile basis to succeed in the commercial marketplace. This means that the cost of hydrogen (which includes the cost of production as well as delivery to the point of use) should be between $2.00 -$3.00 per gallon gasoline equivalent (untaxed).

Delivery

Infrastructure is required to move hydrogen from the point of production to the dispenser at a refueling station or stationary power site. Options and trade-offs for hydrogen delivery from central, semi-central, and distributed production facilities to the point of use are complexвЂ"the choice of a hydrogen production strategy greatly affects the cost and method of delivery. For example, larger, centralized facilities can produce hydrogen at relatively low costs due to economies of scale, but the delivery costs are high because the point of use is farther away. In comparison, distributed production facilities have relatively low delivery costs, but the hydrogen production costs are likely to be higherвЂ"lower volume production means higher equipment costs on a per-unit-of-hydrogen basis.

Hydrogen has been used in industrial applications for decades, but today’s delivery infrastructure and technology are not sufficient to support widespread consumer use of hydrogen. Because hydrogen has a relatively low volumetric energy density, its transportation, storage, and final delivery to the point of use comprise a significant cost and results in some of the energy inefficiencies associated with using it as an energy carrier. Key challenges to hydrogen delivery include reducing delivery cost, increasing energy efficiency, maintaining hydrogen purity, and minimizing hydrogen leakage. Further research is needed to analyze the trade-offs between hydrogen production and delivery options taken together as a system. Building a national hydrogen delivery infrastructure is a big challenge. It will take time to develop and will likely include combinations of various technologies. Delivery infrastructure needs and resources will vary by region and type of market (e.g., urban, interstate, or rural). Infrastructure options will also evolve as the demand for hydrogen grows and as delivery technologies develop and improve.

Storage

Hydrogen has the highest energy content per unit weightвЂ"but not per unit volume of any fuel. Its relatively low volumetric energy content poses a significant challenge for storage. Under most scenarios, stationary hydrogen storage systems have less stringent requirements than vehicular storage. Stationary systems can occupy a relatively large area, operate at higher temperatures, and compensate for slower refueling times with larger storage systems. Storage systems for vehicles, however, face much tougher challenges. They must operate within the size and weight constraints of the vehicle, enable a driving range of more than 300 miles (generally regarded as the minimum for widespread driver acceptance based on the performance of today’s gasoline vehicles), and refuel at near room temperature and at a rate fast enough to meet drivers’ requirements (generally only a few minutes). Because of these challenges, hydrogen storage research is focused primarily on vehicular applications.

Many consider on-board hydrogen storage to be the greatest technical challenge to widespread commercialization of hydrogen fuel cell vehicles. Current approaches include compressed hydrogen gas tanks, liquid hydrogen tanks, and hydrogen storage in materials. Researchers in government, industry, and academia are working toward technical targets specific to the entire storage system which