Fuel cells have now been under development for several decades. Since I first became interested in fuel cells in the 1990’s, I have seen waves of excitement and investment followed by periods of skepticism and disillusionment. Only a few companies have stayed in the game, with Ballard in Canada and the large automakers such as Toyota being a critical and essential part for keeping fuel cell technology funded and growing. Several notable people, such as Elon Musk, have made negative comments about fuel cells calling them “silly and inefficient.” Although I respect Musk’s opinion, there is a place for both technologies in our energy supply and infrastructure. Of course, it is easy to plug-in a car, but that does not mean the fuel cells are silly.
Hydrogen is the most abundant element in the universe – it makes up 74% of all matter. Hydrogen is a clean fuel that can be produced abundantly and safely. It can be created from many types of energy sources (i.e., natural gas, biomass, solar, wind), unlike gasoline, which can only be refined from crude oil. Hydrogen can also be used like gasoline, directly in an internal combustion engine. Hydrogen can be made from sources such as:
• Water (using solar or wind energy)
• Coal (coal gas, town gas, water gas, synthesis gas
Hydrogen can be produced using numerous methods at large scale (i.e., steam reforming plants, chemical plants) and delivered by cylinder, truck or pipeline. Initial critics of fuel cell technology said that hydrogen is not “green” because it is made from fossil fuels. However, if you plug-in your car to recharge the battery in your car, you are using electricity from the grid, which is created primarily from natural gas, coal or nuclear power. The distribution of U.S. electricity generation by plant type is shown in Figure 1.
Figure 1. U.S. Electricity Generation by Plant Type.
• Natural Gas-Powered Electricity Plants: In the United States, there are 1,793 natural gas-powered electricity plants, and they generated 34% percent of the electricity in the nation.
• Coal: There are 400 coal-powered electric plants in the United States. These plants generated 30 percent of the nation's electricity.
• Nuclear: There are 61 nuclear plants in the U.S., and these plants generated 20 percent of the nation’s electricity.
• Hydro: There are 1444 hydroelectric plants which generated 7 percent of the nation’s electricity.
• Wind and Solar: There are 999 wind-powered electric plants and 1721 solar-powered plants, which generated a total of 7 percent of the nation’s electricity last year.
Today, most hydrogen is produced from various fossil fuels such as oil, natural gas, and coal. Most of the hydrogen (96%) produced in the U.S. is made by natural gas reforming in large central plants. Some of the current uses of hydrogen include hydrotreating and hydrocracking, which are processes used in refineries to upgrade crude oil. It is used in the chemical industry to make various chemical compounds, such as ammonia and methanol, and in metallurgical processes. Some of the technologies to produce hydrogen include steam reforming of natural gas, partial oxidation of hydrocarbons, and coal gasification. However, these technologies will not help to decrease the dependence on fossil fuels.
The electrolysis of water is a mature technology that was developed for hydrogen production. It is efficient but requires large amounts of electricity. This can be solved, however, by using solar energy to produce the electricity required to break the hydrogen. This technology is mature enough to be used on a large scale for electricity and hydrogen generation. Other options for generating hydrogen include hydropower, nuclear plants during off-peak hours, direct thermal decomposition, thermolysis, thermochemical cycles, and photolysis. Many of these technologies are at various stages of development, and a few have been abandoned.
Steam reforming. The cheapest method of producing hydrogen on a large scale is through steam reforming of fossil fuels. The current methods use a nickel catalyst. Methane first reacts with steam to produce carbon monoxide and hydrogen. The carbon monoxide passes over the catalyst, then reacts with the steam to produce carbon dioxide and hydrogen according to the following reaction. Natural gas is the cheapest feedstock for producing hydrogen from steam reforming, but this cost is still two to three times higher than producing gasoline from crude oil. Currently, a lot of research is being conducted on how to improve the efficiency and lower production costs of steam reforming.
Partial oxidation. Another method used to produce hydrogen is partial oxidation. This process involves reacting the membrane with oxygen to produce hydrogen and carbon monoxide. The conversion efficiency is lower than steam reforming, which is why that process still dominates commercial hydrogen production.
Coal gasification. The gasification of coal is one of the oldest methods for producing hydrogen. It was used to produce “town gas” before natural gas became available. The coal is heated to a gaseous state, then mixed with steam in the presence of a catalyst to produce synthesis gas. This gas can be processed to extract hydrogen and other chemicals or burned to produce electricity. Current R&D on coal gasification is focusing on the lowering of pollutants, such as nitrogen and sulfur oxides, mercury, and carbon monoxide.
Small-scale reforming: Several studies have assessed the cost and feasibility of building a hydrogen-refueling infrastructure for vehicles and these studies have found that small-scale reforming at the refueling station may offer the lowest delivered hydrogen cost and most practical solution to developing the hydrogen economy. Therefore, small-scale reformers are a key technology for the early stages of a hydrogen economy. Reformer technology is commercially available today; however, scale economies in capital cost can be significant. Lower pressure, temperature and cost materials are needed to make small-scale, distributed reforming competitive. Minimizing CO2 emissions must also be addressed, as carbon capture and sequestration can be costly at the small scale.
There are multiple methods of producing hydrogen if an electrolyzer is used with a renewable energy source. Electrolyzers use electricity to break water into hydrogen and oxygen. The electrolysis of water occurs through an electrochemical reaction that does not require external components or moving parts. It is very reliable and can produce ultra-pure hydrogen (> 99.999%) in a non-polluting manner when the electrical source is renewable energy. The reactions that take place in an electrolyzer are very similar to the reaction in fuel cells, except the reactions that occur in the anode and cathode are reversed. Ideally, the electrical energy needed for the electrolysis reaction should come from renewable energy sources such as wind, solar or hydroelectric sources. There are several hydrogen gas stations for vehicles that produce hydrogen at the site via electrolysis using solar panels.
Wind: Wind is a 100% renewable resource for generating electricity. In a wind-electric turbine, the turbine blades capture the kinetic energy of the wind. The captured wind energy moves the blades, which spins a shaft connected to a generator. In this way, rotational energy is turned into electrical energy. Wind power generates electricity by transferring energy from one medium to another. Electricity generated from the wind can be used for water electrolysis to produce hydrogen. This hydrogen can be stored and used to generate electricity when needed.
Solar: Solar power can be used in conjunction with an electrolyzer to produce hydrogen. When a photovoltaic (PV) cell is exposed to sunlight, the photons of the absorbed sunlight dislodge the electrons from the atoms of the cell. The free electrons then move through the cell, creating and filling in holes. It is this movement of electrons and holes that generate electricity. The process of converting sunlight into electricity is known as the “photovoltaic effect.”
Biomass: Fuels can be derived from many sources of biomass, including methane from municipal wastes, sewage sludge, forestry residues, landfill sites, and agricultural and animal wastes. Therefore, biomass is an abundant resource that can be converted to hydrogen and other byproducts through a number of methods. In addition, growing biomass removes carbon dioxide from the atmosphere, so the net carbon emissions of these methods can be low. Hydrogen can be produced from many types of biomass such as agricultural and animal residues using pyrolysis and gasification processes. These produce a carbon-rich synthesis gas. Using biomass instead of fossil fuels produce no carbon dioxide emissions. Unfortunately, biomass hydrogen production costs are much higher than hydrogen production costs from fossil fuels. Biological processes for producing hydrogen from biomass includes fermentation, anaerobic digestion, and metabolic processing techniques, but these are far from being competitive with traditional hydrogen-producing techniques.
To obtain the goal of transitioning from our traditional fossil-fuel based economy to a renewable energy economy, one or more intermediate steps may be necessary, such as using propane or methanol as fuels, and/or initially processing hydrogen from fossil-based fuels and coal. Although hydrogen will most definitely be made initially from fossil fuels, many non-fossil fuel–based methods can be used in the future to obtain hydrogen, such as nuclear, biological, wind, and, ultimately, solar power. Hydrogen technologies for production, utilization, and storage are already in use, and although many improvements need to be made. Additional research and development need to be conducted on solar hydrogen for future applications since hydrogen can be produced at lost cost with no pollution after the infrastructure has been set up.