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Elementary kinetics of nitrogen electroreduction to ammonia on late transition metals

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Abstract

Developing small scale nitrogen to ammonia conversion devices could greatly help sustainable agriculture. The lack of effective cathode materials for reduction of nitrogen to ammonia puts a major limitation on developing small scale electrochemical ammonia production devices that can operate at low pressures and temperatures. In this study, the electrochemical nitrogen reduction reaction (NRR) mechanism is investigated over late transition metals. Activation barriers for possible rate limiting steps are calculated using density functional theory (DFT) methods and are converted to potential dependent electrochemical barriers. Associative and dissociative paths are evaluated and the associative path shows lower barriers on all metals considered at NRR potentials. Brønsted–Evans–Polanyi (BEP) relationships are evaluated for rate limiting steps and a “kinetic volcano” is demonstrated for catalyst optimization. Rhodium (Rh) and iron (Fe) appear to have the lowest kinetic barriers to convert N2 to NH3. A large over-potential, however, is required to convert nitrogen to ammonia over all the surfaces considered. The hydrogen evolution reaction (HER) has a lower activation barrier compared to NRR, demonstrating the kinetic selectivity challenge.

Graphical abstract: Elementary kinetics of nitrogen electroreduction to ammonia on late transition metals

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Publication details

The article was received on 03 Sep 2018, accepted on 27 Nov 2018 and first published on 28 Nov 2018


Article type: Paper
DOI: 10.1039/C8CY01845F
Citation: Catal. Sci. Technol., 2019, Advance Article
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    Elementary kinetics of nitrogen electroreduction to ammonia on late transition metals

    G. Rostamikia, S. Maheshwari and M. J. Janik, Catal. Sci. Technol., 2019, Advance Article , DOI: 10.1039/C8CY01845F

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