Tandem electrocatalytic N₂ fixation via proton-coupled electron transfer

Area of Science:

• Electrochemistry
• Catalysis
• Materials Science

Background:

• Electrochemical ammonia (NH3) synthesis offers a sustainable alternative to the Haber-Bosch process for fertilizer production and zero-carbon fuel generation.
• Current research focuses on heterogeneous electrocatalysts for nitrogen reduction reaction (N2RR), but these often suffer from poor stability and selectivity, with hydrogen evolution reaction (HER) dominating.
• Molecular catalyst systems show promise but face similar selectivity challenges.

Purpose of the Study:

• To develop a novel tandem catalysis strategy for efficient and selective electrochemical ammonia synthesis.
• To overcome the limitations of HER outcompeting N2RR in electrochemical systems.
• To demonstrate the generality of the proposed tandem approach across various metal complexes.

Main Methods:

• A tandem catalysis system was designed, combining a molecular complex for N2 reduction with a co-catalyst for proton-coupled electron transfer.
• The system facilitates N-H bond formation at a favorable applied potential (-1.2 V vs Fc+/0).
• Diverse metal complexes (W, Mo, Os, Fe) were tested within the tandem strategy.

Main Results:

• The tandem catalysis strategy successfully mediated N2RR at a favorable potential, improving thermodynamic efficiency.
• The approach facilitates the formation of key N2RR intermediates that are otherwise unreactive.
• Structurally diverse metal complexes demonstrated N2RR electrocatalysis when used with the mediator.

Conclusions:

• The developed tandem catalysis strategy provides a viable solution for selective electrochemical ammonia synthesis.
• This approach enhances the efficiency and stability of N2RR, overcoming competition from HER.
• The generality of the tandem strategy suggests broad applicability for future electrocatalyst development.