4.1 Hydrogen Fuel Cell Engines
Invented in 1839, the hydrogen fuel cell has been employed widely since the early 1960s in space probes to generate onboard electricity, water and heat.
Indeed, in the fuel cell the controlled reaction of hydrogen with oxygen yields electricity, heat, and water, directly converting into electrical energy the chemical energy of the bound H2 molecule.
In most fuel cells developed thus far the H2 dissociation reaction is usually catalyzed by platinum at the anode’s surface and takes place at a temperature of approximately 80 °C (Figure 4.1).
The presence of easily poisoned platinum requires the use of high purity ‘‘technical-grade’’ (purity as high as 99.999%) H2 because the carbon – and sulfur-containing impurities of ‘‘commercial-grade’’ hydrogen would quickly degrade, reducing the life of the fuel cell stack (Figure 4.2).
Indeed, similar to what happens with solar cells, an individual fuel cell (about 2 mm thick) generates a comparatively low potential of less than 1 V. Hence, for practical application several hundred cells are connected in series to form a so-called ‘‘stack’’. A 200 V system potential, for example, is used to power a fuel cell vehicle (FCV) such as the Mercedes B-Class F-CELL, the first fuel cell passenger car to be produced under series conditions, which attains an operating range of around 400 km with its 700 bar hydrogen tank in the sandwich floor unit.1
From a technical viewpoint only, the clean, efficient and compact H2- fueled fuel cell fits excellently into the ongoing electrification trend;2 it
Solar Hydrogen: Fuel of the Future Mario Pagliaro and Athanasios G. Konstandopoulos © Mario Pagliaro and Athanasios G. Konstandopoulos 2012 Published by the Royal Society of Chemistry, www. rsc. org
serves as a battery recharging device for long-life power packages in portable electronics, as stationary combined heat and power (CHP) facilities, and as an electrical generator to replace the current poorly efficient mobile electrical generators (lead batteries and diesel gensets).3
Moreover, the H2-fueled fuel cell is without moving parts and, thus, is vibration-free and noiseless; it is no heavier than the internal combustion engine (ICE), and fits into a conventional engine compartment without major modifications. Overall, the combination of the fuel cell and an electric motor is 2-3 times more efficient than an ICE.4
The installed cost of a hydrogen fuel cell system depends on the technology, configuration and size. In general, installation costs of a fuel cell system range from $5000 kW-1 to $10 000kW-1,5 meaning that the fuel cell is technically, but not economically, more efficient than an internal combustion engine.
Currently, H2 fuel cells are mostly present in German, Greek and Italian submersibles of the respective navies. The main reason for this market failure is due to their inherently high costs. Legacy fuel cell technologies such as proton exchange membranes (PEMs), phosphoric acid fuel cells (PAFCs), and molten carbonate fuel cells (MCFCs) have all required expensive precious metals, corrosive acids, or hard to contain molten materials. From an environmental viewpoint, hydrogen – powered fuel cell vehicles achieve reductions in greenhouse gas emission below 1990 levels by 80% or more (hydrogen ICE hydrogen powered vehicles by 60%) with near elimination of urban air pollution.6 The car maker Honda, for example, in 2007 unveiled the world’s first fuel cell vehicle (Figure 4.3), an electric car powered by H2 but only offering a driving range of 240 miles, which is currently available to lease in the USA.
After all, on average a vehicle exhaust catalyst (Figure 4.4) contains around 1-3 g of platinum group metals (PGM; about 1.5 g platinum, 0.5 g palladium and 0.1 g rhodium).7 Perhaps it would be more logical to
use this platinum in fuel cells for energy generation and pollution prevention, rather than in cars forЧ pollution reduction.8