With the development of the Haber process and the subsequent work done by Bosch, ammonia production become an industrially and economically viable way to fix nitrogen. Ammonia used as a fertilizer has helped increase the global food production and estimates put it at about 40% of the global population’s food needs the ammonia fertilizer from the Haber process[1]. However, the Haber-Bosch process is an energy intensive process requiring high pressure (15-30 MPa) and relatively high temperature (430 °C – 480 °C) and is highly centralized with only about 13 companies producing at about 29 plants[2, 3]. Renewable energy resources offer a possible alternative way to fix nitrogen at low temperature and lower pressure to produce ammonia in a decentralized way. High temperature solid proton conductors have been used to produce ammonia selectively, but the high temperature can degrade the ammonia[5]. Low temperature polymer electrolyte membranes can be used which might reduce the overall energy input. Proton exchange membrane (PEM) suffers from conductivity loss due to the ammonia converting to ammonium[6], which reduces the cation conductivity. The other issue is the competing hydrogen evolution reaction (HER) which is especially fast in the acidic environment[7]. By moving to an alkaline environment, ammonia will not affect the conductivity because hydroxide exchange membranes (HEMs) use anions as the charge carriers. HEMs also allow the use of non-precious metal catalysts which could reduce the overall cost of these electrochemical devices. In this presentation, we will discuss the activity of a variety of catalyst, PGMs, metal nitrides, and non-precious metals in both HEM and PEM electrolyzers for their ammonia production. We utilized the hydrogen oxidation reaction (HOR) as the counter electrode which can also be utilized as a reference. This study allows for the direct comparison of PEM and HEM for electrochemical nitrogen reduction.

References:

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2. Mineral Commodity Summaries 2015, U.S.G. Survey, 2015: Reston, Virginia. p. 196.

3. Marnellos, G. and M. Stoukides, Science, 282(5386): p. 98.(1998).

4. Kordali, V., G. Kyriacou, and C. Lambrou, Chem. Commun., (17): p. 1673.(2000).

5. Amar, I.A., et al., J Solid State Electrochem, 15(9): p. 1845.(2011).

6. Lan, R. and S. Tao, RSC Advances, 3(39): p. 18016.(2013).

7. Sheng, W., H.A. Gasteiger, and Y. Shao-Horn, J. Electrochem. Soc., 157(11): p. B1529.(2010).