Around the Block: Fuel Cell Alternatives And The Myth of Clean Energy
By Don Fedak
For most of our existence, human beings have used their muscles or domesticated animals to move around, lift and carry things. Our bodies process, via respiration (breathing), Earth’s most ubiquitous element, oxygen, and the chemicals (fuels) in foods to produce the energy and products essential to life, e.g., electrical (nerve) energy, mechanical energy, heat and waste. Most of these life-defining chemical oxidation reactions tend to be slow because they are heterogeneous, i.e., they occur on two-dimensional surfaces and require catalysts (enzymes).
Eventually, our ancestors discovered how to start and control the rapid oxidation of natural hydrocarbons, e.g., wood, in reactions with atmospheric oxygen, i.e., fire. Humans continue to exploit external combustion reactions and burn whatever gaseous, liquid or solid fuel is convenient to produce heat, light and/or mechanical energy.
When we burn fuel in a confined space, internal combustion, oxidation occurs at much higher rates. Whether the fuel is a gas, a liquid aerosol or a finely divided solid, internal combustion involves many simultaneous exothermic chain (explosive) homogeneous reactions accompanied by a significant change in volume (mechanical energy) and does not require a catalyst. Compared to external combustion, internal combustion releases and delivers energy at a higher rate so engines tend to have a higher power density.
Internal combustion engines are not inherently dirty. The contents of exhaust gases produced by internal combustion engines are directly related to the composition of the fuel and the oxidant. For example, piston, jet or rocket engines fueled with pure hydrogen and oxygen will only produce an environmentally friendly exhaust of water vapor.
Unfortunately, there are no convenient large natural sources of pure hydrogen and oxygen. The lightest, simplest and most prevalent element, hydrogen, the fuel of solar fusion that heats the earth via radiation, indeed, the fundamental atomic building block of the universe, reacts with most other elements. A lot of energy is required to reverse the process, called reduction, and break these compounds down. So pure hydrogen must be artificially produced and then isolated to suppress oxidation reactions with other elements and compounds. This is why most of the earth’s hydrogen is found combined with oxygen, as water, or with carbon as carbohydrates or hydrocarbons; there are no hydrogen wells.
Many years ago, John D. Rockefeller (1839-1937), responding to a growing demand for lubricating oils for horse- and steam-powered machines, discovered and developed the large commercial crude oil deposits in upper Pennsylvania. Initially, the gasoline and diesel fuel obtained when these deposits were refined were considered nuisance leftovers with little or no value. But Rockefeller’s fortune would be quickly assured and compounded. These byproducts of lubricating oil refineries were found to be suitable fuels for the horseless carriages powered by new internal combustion engines.
Our oil dependent transportation industry evolved and we continue to fuel diesel and gasoline engines with a variety of hydrogen/carbon/oxygen compounds. Fuels derived from crude oil or natural gas are mixed with a gas containing 80 percent nitrogen and 20 percent oxygen (air), ignited and burned. This produces exhaust gases that consist of water vapor and carbon dioxide/monoxide along with trace amounts of nitrogen oxides and unburned hydrocarbon fuels. As long as we choose to burn mixtures of hydrocarbons and air in internal combustion engines, we will have to deal with these exhaust gas reaction products.
If they were readily available, we could burn mixtures of pure hydrogen and oxygen, i.e., rocket fuel, in our engines and the exhaust would consist entirely of water vapor. This relatively simple reaction is also reversible. With an appropriate source of electrical energy, molecular hydrogen and oxygen can be produced by chemical reduction of water, a process known as electrolysis. The pure gases can be collected, compressed and stored. And when they are subsequently mixed and ignited, most of the energy supplied to produce them is released as heat.
At or near ambient temperature, if hydrogen and oxygen are exposed to separate specific catalytic conductor surfaces, oxidation will occur – producing water and some heat – releasing electrical energy to an external circuit. According to Webster, this ‘electromechanical device’ which converts the chemical energy of fuel oxidation directly into electricity without combustion and which is a relatively light, efficient and quiet source of power, is a fuel cell.
Commercial hydrogen-oxygen fuel cells have been available for decades. But they tended to be large and have low power density because the heterogeneous reactions are slow and require large surface areas. To date, commercial applications to motive power have been limited by fuel storage capacity and distribution issues.
Other fuels have also been considered. Recent and current fuel cell research has examined different catalysts, fuels and materials and the development of higher energy density stacks, compressors, electrical drives and fuel storage devices.
Since oxygen is abundantly available and water is the only reaction product, hydrogen remains the ideal fuel for these clean, green, environmentally friendly motive and stationary power sources. All we need to complete this scenario is an abundant, convenient, economical, portable and safe source of hydrogen, or some other equally benign fuel.
Actually, we have been using hydrogen as a source of heat, electrical and mechanical power since the discovery of fire. The hydrocarbons in wood, coal and oil all contain hydrogen along with substantial amounts of carbon, oxygen and other elements that all react during combustion. Unfortunately, these other elements form oxides, e.g., carbon oxides and sulfur oxides that are less benign than water. So our traditional hydrocarbons are a source of ‘dirty’ hydrogen. And even if clean hydrogen was abundantly available, it is not clear that it should be dedicated to fuel-motive power.
In the early 1960s experts suggested that, as soon as natural gas (a carbon-hydrogen compound) became scarce, an alternative ‘Hydrogen Economy’ would quickly evolve, and that we would adapt our existing natural gas pipeline infrastructure to the substitution and distribution of hydrogen gas produced at a few efficient large remote sites.
The prevailing wisdom assumed that the large remote fossil- or nuclear-fueled hydrogen plants would efficiently control, localize and minimize any and all environmental problems. While energy costs have escalated in the intervening four decades, so have the discoveries of new fossil fuel reserves, including natural gas.
It sometimes seems that vehicle engines are no longer engineered but are rather being designed and regulated by well-intentioned politicians and voters who couldn’t tell you which end of a screwdriver is the handle. Meanwhile, the popular press reports of significant advances in fuel cell development attracting even more investor capital and, as long as their vehicle does not dump noxious gases into their local environment, their increased greenness is assured.
But there is no free lunch. Clean energy from fuel cells is a myth. We must continue to think globally. Zero local emissions require excessive emissions in someone else’s environment. Or, as the Lung Association points out: "If we can’t breathe, nothing else matters."
P.S. (Possible Scenario) Of course, it may be that long before we run out of fossil fuels we will all have choked to death, drowned or died of starvation ... like the dinosaurs!