I write in connection with the article “It’s a Heat Wave” in the July/August 2014 issue of the Canadian Chemical News (ACCN). The opening paragraphs of the article are reproduced below.

“It is a dream that fell short of its early optimism and hype: use abundant hydrogen to supply the planet’s energy needs to eliminate the global dependence on fossil fuels and reduce the greenhouse gases (GHG) implicated in climate change.

But the trajectory towards the widespread use of hydrogen stumbled due to numerous marketing and commercialization challenges. Still, continued innovation in hydrogen production holds enormous promise, not only for the existing global hydrogen market, but also for fuel cells that could power vehicles or provide distributed electricity generation.”

My concern is that articles about a hydrogen economy tend to gloss over several problems associated with this “dream.” For example, although hydrogen is indeed abundant on our planet, it is found only in combined form, mostly as water, and to a lesser extent as hydrocarbons. Energy is required to access elemental hydrogen, which therefore should be considered as an “energy currency” rather than as a fuel per se. In addition, the attraction of the high energy density of hydrogen per kilogram is compromised by the additional mass involved in transporting or storing it as a compressed gas or in combined form such as a metal hydride.

In the 1970s, much effort was expended in trying to produce hydrogen photochemically, with the idea of using sunlight as a “free” source of energy. However, none of these efforts was ultimately successful. The article in ACCN describes a new technology involving the generation of hydrogen from methane; however, this approach does not “eliminate the global dependence on fossil fuels,” because it is a method of converting one fuel (methane) into another (hydrogen).

Several aspects of the story would have been interesting to cover in more detail in order to demonstrate the viability of the technology. The ACCN article explained that the conversion of methane to hydrogen is achieved by means of microwave radiation at 700-900 C to break down methane (Equation 1).

(1) CH4(g) → C(s) + 2H2(g)

The energetics of Equation 1 are ΔH°(1100 K) = +75 kJ mol-1, ΔG°(1100 K) = -14 kJ mol-1, using approximate calculations. In the CarbonSaver process, the energy to liberate elemental hydrogen is supplied by 100 kilowatts of microwave energy (requiring electricity), which can be considered to contribute to the internal energy of the system. The process was described as “efficient” but no details were provided, such as the cost in terms of kilowatt hours consumed per kilogram of hydrogen produced.

The article went on to suggest that using the hydrogen to make electricity in a fuel cell (Equation 2): ΔH°(298 K) = -572 kJ mol-1, ΔG°(298 K) = -475 kJ mol-1.

(2) 2H2(g) + O2(g) → 2H2O

The overall cost and energy efficiency of converting the energy inherent in methane into electricity using a fuel cell is determined by combining total costs (including capital and personnel) and efficiencies of both processes (1) and (2). Not included is the enormous technical challenge (and cost) of upgrading the 97 percent hydrogen produced in reaction (1) into “five decimal points” of purity for use in a fuel cell. This proposition is very different than introducing 97 percent hydrogen into an existing steam-methane reforming source of hydrogen at an oil refinery.

I look forward to a follow-up article with more technical and economic details of this interesting technology.