After carbon, hydrogen, and oxygen, nitrogen is the next most abundant element in the human body. Inorganic and organic compounds of nitrogen feature prominently in many biological and environmental, as well as industrial, processes. In nature, the inorganic compounds of nitrogen are controlled by a reaction cycle called the nitrogen cycle (Figure 1).1 The denitrification pathway in this cycle, that is, the conversion of nitrate to dinitrogen, is employed by certain bacteria to produce ATP anaerobically and gain energy for cell growth. All organisms use ammonia as one of the starting building blocks for the synthesis of amino acids, nucleotides, and many other important biological compounds. Nitric oxide is * Corresponding author. E-mail: m.koper@chem.leidenuniv.nl. † Present address: Energy research Centre of The Netherlands (ECN), P.O. Box 1, 1755 ZG Petten, The Netherlands. ‡ Present address: Research, Development & Innovation, AkzoNobel Chemicals bv, Velperweg 76, P.O. Box 9300, 6800 SB Arnhem, The Netherlands. Chem. Rev. 2009, 109, 2209–2244 2209

Nitrogen cycle electrocatalysis.

Nitrogen is a fundamental constituent for all living creatures on the Earth and modern industrial society. The current nitrogen industry is largely powered by fossil fuels with huge energy consumption and carbon dioxide emission, and nitrogen pollution in surface water bodies induced by the indiscriminate discharge of industrial and domestic wastewater has become a worldwide environmental concern. Electrochemical techniques for nitrogen fixation and transformation under mild conditions are promising approaches to meet the challenge of efficiently managing and balancing the nitrogen cycle, where the rational design of advanced electrocatalysts from both structural and compositional aspects down to the nanoscale plays the most essential role. Herein, important nitrogen species including dinitrogen (N2), ammonia (NH3) and hydrazine (N2H4), their transformation processes between each other including the nitrogen reduction reaction (NRR), ammonia oxidation reaction (AOR) and hydrazine oxidation reaction (HzOR), and research progress on the development of related electrocatalysts are systematically summarized, aiming at establishing a general picture of the whole nitrogen cycle instead of a certain single reaction. Strategies combining theoretical computations and experimental optimizations are proposed to improve the catalytic performance including activity, efficiency, selectivity and stability, finally contributing to a self-sufficient and carbon-free "green" nitrogen economy.

Electrochemical nitrogen fixation and utilization: theories, advanced catalyst materials and system design.

https://iopscience.iop.org/article/10.1149/1.1488651/pdf

E. J. Cairns

Papers

The Performance of Direct Ammonia Fuel Cells