Electrochemical Ammonia Oxidation with Molecular Catalysts

Abstract

Electrocatalytic ammonia oxidation (AO) provides an attractive route to a carbonneutral fuel economy and the energy-efficient production of value-added feedstocks. The design and study of molecular catalysts can give a deeper mechanistic understanding of AO, which will aid in optimizing catalysts for overpotential, efficiency, and chemoselectivity. This Perspective introduces the topic with biological AO chemistry and then surveys the recent developments of molecular AO electrocatalysts, followed by a discussion of design strategies for new catalysts.

Temporally Decoupled Ammonia Splitting by a Zn–NH3 Battery with an Ammonia Oxidation/Hydrogen Evolution Bifunctional Electrocatalyst as a Cathode

“…The reaction mechanism is vital to explain the superior performance. Compared to the single path of HER, AOR shows more complex reaction pathways due to a wide variety of oxidation states . Currently, two typical mechanisms are reported for eAOR, including G–M and O–S mechanisms .…”

The Potential of Molecular Electrocatalysis for Ammonia‐to‐Dinitrogen Conversion

“…Some excellent reviews on molecular ammonia oxidation have recently been published. [23,24] Herein, we focus not only on the benefits of molecular AOR catalysts but also on how potential drawbacks towards practical use can be circumvented by immobilizing them at electrode surfaces. Furthermore, we dedicate the last session to paradigms for the implementation of molecular catalysts that have been uncovered for other catalytic reactions and could be transposed to AOR.…”

Selecting between Ammonia and Water Oxidation: Electrochemical Oxidation of Ammonia in Water Using an Organometallic–Inorganic Hybrid Anode

“…15 On the other hand, homogeneous catalysts can benefit from high efficiency, high atom economy, well-defined active sites, and tunability. 16,17 Combining the advantages of both molecular and heterogeneous systems, our group has developed an organometallic− inorganic hybrid anode, named "Blue Layer" (BL), for electrochemical water oxidation (WO). 18 BL is synthesized at room temperature via an electrodeposition process in which an organometallic Ir precursor, [Cp*Ir(H 2 O)]SO 4 (Cp* = pentamethylcyclopentadienyl), is electrochemically oxidized on a metal oxide anode, forming a heterogeneous layer of [IrO 2 ] x nanoclusters.…”

“…Many heterogeneous catalysts suffer from having low atom economy, a cocktail of surface sites, and low selectivity, as well as being prone to ammonia-assisted degradation . On the other hand, homogeneous catalysts can benefit from high efficiency, high atom economy, well-defined active sites, and tunability. , …”