Nanocarbon for Energy Material Applications: N$_2$ Reduction Reaction

TL;DR

This paper reviews nanocarbon-based electrodes for N2 reduction to ammonia, emphasizing the importance of active site engineering and a holistic approach to improve performance in photo- and electrocatalytic methods.

Contribution

It highlights the need for a new perspective and holistic strategies to advance nanocarbon catalysts for nitrogen reduction reactions.

Findings

Active sites relate to charge density differences on defected/strained C atoms.

Doping and metal ion introduction influence catalytic activity.

Current performance levels are far from target benchmarks.

Abstract

Nanocarbons are an important class of energy materials and one relevant application is for the nitrogen reduction reaction, i.e., the direct synthesis of NH3 from N2 and H2O via photo- and electrocatalytic approaches. Ammonia is also a valuable energy or hydrogen vector. This perspective paper analyses developments in the field, limiting discussion to nanocarbon-based electrodes. These aspects are discussed: i) active sites related to charge density differences on C atoms associated to defects/strains, ii) doping with heteroatoms, iii) introduction of isolated metal ions, iv) creation and in situ dynamics of metal oxide(hydroxide)/nanocarbon boundaries, and v) nanocarbon characteristics to control the interface. Discussion is focused on the performances and mechanistic aspects. Aim is not a systematic state-of-the-art report but to highlight the need to use a different perspective in studying this challenging reaction by using selected papers. Notwithstanding the large differences in the proposed nature of the active sites, fall all within a restricted range of performances, far from the targets. A holistic approach is emphasized to make a breakthrough advance.