February 2020 Issue Table of Contents
I would like to know, now that we’ve reached the year 2020, where is the hydrogen economy I was promised? Hydrogen fuel cell cars lurk at the margins of the marketplace, and several governments and corporations continue to make large bets on hydrogen’s future, but as I look out the window at my battery assisted, hybrid car, I’m still left wondering “what went wrong”?
Twenty years ago, the hydrogen-based economy was among the most eagerly anticipated ideas in alternative energy. The appeal of hydrogen as a commodity stems from its almost limitless mutability. This simplest of molecules can be made from many different things in many different ways, and once made can be used for many purposes. It is a transportation fuel with the energy density to propel everything from cars to hypersonic aircraft; it can be converted to electrical power at scales from laptops to houses to cities; and it is a critical chemical reagent for several industrial processes. Most importantly from the perspective of carbon emissions and renewable resources, it can be made from water alone and emits only water when it is consumed. So, if hydrogen is made using some renewable form of energy (e.g., solar-voltaic electricity), every major step in the fuel cycle of a wide range of technologies can be carbon free.
Given that the cost of photovoltaic power has dropped by nearly a factor of 5 over the last decade alone, how it is possible that hydrogen technologies haven’t yet won the fight for the alternative energy marketplace? There is no simple answer, but two factors are clear. The hydrogen economy suffers from a kind of ‘tragedy of the commons’, in that it can only flourish after we make major investments to adapt our collective energy infrastructure to meet hydrogen’s unique demands. And, the unforeseen success of fracking and other unconventional oil and gas extraction technologies have shifted the goal posts on the economic playing field, pushing clean hydrogen technologies further to the margins, and even promoting a kind of ‘dirty’ hydrogen economy in its place.
Ironically, economic uses of hydrogen have expanded in recent years, but in ways that contribute to, rather than diminish, our carbon footprint. Hydrogen is used in the Haber–Bosch process to produce ammonia fertilizers, and is reacted with low-value, refractory components of oil to create smaller, more useful hydrocarbons. Therefore, demand for hydrogen as an industrial chemical has increased with the growth of populations and economies over the last 20 years. Both of these uses of hydrogen are carbon-emitting processes in and of themselves. And, the dramatic expansion of unconventional gas production has meant that we are meeting our needs for hydrogen by steam reforming of inexpensive methane and other hydrocarbons—another CO2 producing process. If you recently purchased one of the first few commercially available hydrogen fuel cell cars, the odds are good that you are fueling your vehicle with hydrogen made by steam reforming of natural gas. Thus, a kind of hydrogen economy was, in fact, delivered, but it isn’t the one we thought we were ordering.
So what are the paths forward that remain for a ‘green’ hydrogen economy? Coupling large-scale hydrogen production from inexpensive steam reforming with capture of the produced CO2 is one possibility. In this issue of Elements, Eric Gaucher (see page 8) calls our attention to another path—recent discoveries raise the possibility of economic hydrogen gas reservoirs that form in the crust, perhaps through water–rock reactions, and that accumulate beneath impermeable geological ‘traps’. It is imaginable that discovery and exploitation of such deposits could provide a way to ground the hydrogen economy on a zero-emission source, obviating photovoltaic or other engineered production or CO2 sequestration. But whether or not these are game changing must depend on the other major factor that has held us back from this vision of a hydrogen-based 21st century energy economy: the fact that most of us still depend on a 20th century infrastructure built to meet the needs of fossil-carbon energy sources. So look to (and perhaps follow) the leadership of those few places, such as Japan, California, and Denmark, where significant investments aim to create the first large, effective hydrogen delivery networks.
John M. Eiler