Literature review: Electrochemical Ammonia Synthesis and Ammonia Fuel Cells

The journal Advanced Materials recently published an article that reviews electrochemical ammonia technologies for both synthesis and power generation. In addition to presenting a range of technologies under development, the authors, based at the University of Delaware, present “perspectives in the technical challenges and possible remedies.”

Ammonia is a promising platform molecule for the future renewable energy infrastructure owing to its high energy density (when liquefied) and carbon-free nature …

Here, the latest developments in electrochemical ammonia synthesis and ammonia fuel cells are presented … N2 electrolysis, plasma‐enabled N2 activation, and electro‐thermochemical looping are three potential approaches for electrochemical ammonia synthesis; however, achieving high selectivity and energy efficiency remains challenging. Direct ammonia fuel cells are suitable for a broad range of mobile and transportation applications but are limited by the lack of active catalysts for ammonia oxidation.
Feng Jiao and Bingjun Xu, Electrochemical Ammonia Synthesis and Ammonia Fuel Cells, Advanced Materials, December 2018

Click to enlarge. Figure 2. Schematics of three key electrochemical ammonia synthesis methods. Feng Jiao and Bingjun Xu, Electrochemical Ammonia Synthesis and Ammonia Fuel Cells, Advanced Materials, December 2018.

We have written extensively on the subject of electrochemical ammonia synthesis technologies, and our 2018 Ammonia Energy Conference featured two presentations from University of Delaware researchers: Electrochemical Synthesis of Ammonia Using Metal Nitride Catalysts and Electrochemical Nitrogen Reduction Reaction on Transition Metal Nitride Nanoparticles in Proton Exchange Membrane Electrolyzers.

In our last Annual Review, we wrote about near-commercial ammonia fuel cell technology developments around the world, in Ammonia for Fuel Cells: AFC, SOFC, and PEM. And, more recently, we reviewed ammonia fuel cell technology from the University of Delaware, in More Progress for Automotive-Oriented Direct Ammonia Fuel Cells.

Note that “N2 electrolysis,” a technology under development for the direct reduction of atmospheric nitrogen using electricity, is distinct from water electrolysis, a mature technology for production of hydrogen. We have frequently written on the subject of commercially available technologies that combine water electrolysis and Haber-Bosch units to produce renewable ammonia, most recently in Green ammonia: Haldor Topsoe’s solid oxide electrolyzer.

The authors conclude their review by identifying “key challenges” for future research and development. These involve “the development of active, selective, and durable materials” to accomplish three tasks:

  1. “Catalyze the electrochemical reduction N2 to ammonia.”
  2. “Mediate the electrochemical oxidation of ammonia to N2 at modest temperatures.”
  3. “Enable durable membrane-based ammonia production and conversion devices.”

These “key challenges” build on the “grand challenges” identified in the 2016 US Department of Energy Roundtable Report on Sustainable Ammonia Synthesis, which called for the development of an “active, selective, scalable, long-lived catalyst,” as well as identifying seven other pathways for technology development.

The review article, Electrochemical Ammonia Synthesis and Ammonia Fuel Cells is available online (behind a paywall) in the December 2018 issue of Advanced Materials.

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