Conceptually, replacing the current oil-based infrastructure with hydrogen would cost billions, maybe trillions, of dollars.
Although abundant in the universe, hydrogen is fairly rare in our atmosphere, meaning that it has to be extracted (for example through electrolysis, as explained above) and currently, the process is cost prohibitive and inefficient.
Its production at energy plants creates excessive carbon dioxide.
When it burns, a hydrogen flame is virtually invisible; coupled with the gas’s propensity for escaping, in small amounts, almost any tank, there are concerns about explosions. On the plus side, hydrogen is so light it typically is dispersed in the air very quickly.
On-board storage is a major issue; a hydrogen tank would currently be too large for a car.
It is a very flammable gas (think of the Hindenburg), which further adds to the on-board storage problems.
"The first hard core environmentalist I ever encountered in life taught my 8th grade energy class at Estacada Junior High, a course that President Carter's brand new Department of Education had mandated upon us a decade before as a symbolic gesture to show he cared about America's energy future. Despite an overall policy of separating church and state, in this class it was the gospel that we would deplete all fossil fuels by the year 2000. Back when "2000" was preceded by "THE YEAR" it seemed so far away didn't it? The only lasting lesson this course taught me was a healthy skepticism of government mandated indoctrination."
