Hydrogen fuel cell vehicles -- test drive

Last weekend I attended an open house at the California Fuel Cell Partnership in West Sacramento. It was interesting to learn how hydrogen fuel cells work to power a vehicle and to see a working hydrogen fueling station up close, but the coolest opportunity was to actually drive a vehicle powered by hydrogen. None of the vehicles they had were commercially available, but all were fully functional and appeared to be pretty normal.

I drove the Mercedes A-Class car called the "F-Cell:"There are cars that actually combust liquid hydrogen, like the BMW Hydrogen 7, but all of the vehicles available for test driving last weekend were hybrid-electric, meaning the main drive engine was electric, which was powered by electricity from a hydrogen fuel cell where the hydrogen used is in the form of a gas. This is a hydrogen fuel cell that was in Ford's garage at the facility:Apparently there are hundreds of individual "cells" stacked inside of a unit like this. The simplest explanation of how electricity is produced by a hydrogen fuel cell is that the fuel cell has a negative electrode/catalyst plate inside of it that the hydrogen passes through, which strips off its electrons. The then positively-charged hydrogen passes through a membrane and interacts with a positive electrode/catalyst plate which combines the hydrogen with oxygen that is brought into the fuel cell, producing heat and water. The flow of the stripped electrons from the negative side to the positive side produces electricity.

The cars were virtually silent, though the Mercedes I drove had a distinct high-pitched sound associated with acceleration that the representative in the car said was an air compressor pumping extra air into the fuel cell, apparently to provide a bit more "juice." The transmission was continuous, meaning there were no gears or hesitations. I didn't really test out acceleration, but it seemed like just about any other car.

There are two sticking points to the widespread use of hydrogen to power vehicles on a large scale: 1) distribution infrastructure; and 2) efficiency. For infrastructure, there are currently only 24 working hydrogen fueling stations in the state of California. There are only two in the Sacramento area. Here's the one at the facility I toured:
For efficiency, I learned some new terms: "well-to-tank" efficiency, meaning how efficient the process is that produces the energy (here, hydrogen) and transports it to the individual vehicle's tank. Also, "tank-to-wheel" efficiency, meaning how efficiently the car converts that energy from its own tank to the wheels.

Currently hydrogen's "well-to-tank" efficiency is lower than that for gasoline (Toyota quotes 58% to 88%, respectively). Hydrogen's "tank-to-wheel" efficiency is greater than gasoline (38-50% versus 16-37%, respectively). Combining those measures, Toyota estimates that gasoline vehicles have a "well-to-wheel" overall efficiency of about 14%, a gas-powered hybrid like the Toyota Prius has an overall efficiency of about 32% and Toyota's hydrogen fuel cell vehicles range in overall efficiency from about 22 to 29%.

Undoubtedly these efficiencies for obtaining hydrogen and operating hydrogen fuel cells will improve and the fueling infrastructure will be built out, so at some point this will become a viable option for mainstream use.