Electrochemical NRR with noble metals-free catalysts

Ammonia, as one of the most important chemicals, relies on the Haber–Bosch process for massive producing leading to a large consumption of fossil fuels due to the critical reaction environments, high pressure associated with high temperature; thus, the development of sustainable method for ammonia synthesis is of significance important to alleviate environmental pollution and energy crisis. Nitrogen reduction reaction (NRR) to generate ammonia has received considerable attention due to its ambient operation condition. In this chapter, we summarize the recently reported noble metal-free electrocatalysts for electrosynthesis of ammonia, including transition metal oxides, sulfides, nitrides, phosphides, carbides, and metal-free (heteroatom doped carbons) electrocatalysts. The suppression of competitive hydrogen evolution reaction and improvement in electroadsorption of nitrogen molecules are vital to construct a high-performance NRR electrocatalyst; in this case, adjustment in morphology, introduction of foreign atoms, and manufacturing of heterostructures have been adopted to obtain superior NRR electrocatalysts. Also, the mechanism of boosted NRR catalytic activity has been proposed.