Single-Site Polyoxometalate Complexes with Engineered Electron Channels for Efficient Electrocatalytic Ammonia...

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Electrochemical nitrate reduction to ammonia (ENRA) offers a sustainable route for ammonia synthesis and wastewater remediation.
• Developing efficient and selective electrocatalysts is crucial for advancing ENRA technology.

Purpose of the Study:

• To synthesize and characterize novel polyoxometalate-based (POM-based) mononuclear complexes for ENRA.
• To investigate the catalytic performance and underlying mechanism of these POM-based catalysts.

Main Methods:

• Synthesis of three POM-based mononuclear complexes: [M(HNCP)2(H2O)][PW12O40]·H2O (M = Ni, Co, Zn).
• Electrochemical evaluation of ENRA performance, including Faradaic efficiency and NH3 yield rate.
• In-depth computational studies to elucidate the reaction mechanism and electron transfer pathways.

Main Results:

• The Ni-PW12 complex demonstrated outstanding ENRA performance with a Faradaic efficiency of 90.3% and an NH3 yield rate of 11.2 mg h-1 mgcat.-1 at -1.3 V vs RHE.
• Computational analysis revealed that electron transfer from the POM cluster to the metal center optimizes the reaction pathway and suppresses hydrogen evolution.
• POM-metal-hybrid systems showed a 24.1-39.3% enhancement in NH3 Faradaic efficiency compared to POM-only catalysts.

Conclusions:

• Electron-transfer engineering in POM-metal-hybrid systems is a viable strategy for developing high-performance electrocatalysts for ENRA.
• The study provides a concrete approach for designing advanced POM-based electrocatalysts, promoting sustainable ammonia production.
• Optimized electronic structures and suppressed side reactions are key to improved ammonia selectivity.