Molecular Engineering of a Metal-Organic Polymer for Enhanced Electrochemical Nitrate-to-Ammonia Conversion and Zinc Nitrate Batteries

Abstract

Metal–organic framework-based materials are promising single-site catalysts for electrocatalytic nitrate (NO<inf>3</inf>⁻) reduction to value-added ammonia (NH<inf>3</inf>) on account of well-defined structures and functional tunability but still lack a molecular-level understanding for designing the high-efficient catalysts. Here, we proposed a molecular engineering strategy to enhance electrochemical NO<inf>3</inf>⁻-to-NH<inf>3</inf> conversion by introducing the carbonyl groups into 1,2,4,5-tetraaminobenzene (BTA) based metal-organic polymer to precisely modulate the electronic state of metal centers. Due to the electron-withdrawing properties of the carbonyl group, metal centers can be converted to an electron-deficient state, fascinating the NO<inf>3</inf>⁻ adsorption and promoting continuous hydrogenation reactions to produce NH<inf>3</inf>. Compared to CuBTA with a low NO<inf>3</inf>⁻-to-NH<inf>3</inf> conversion efficiency of 85.1 %, quinone group functionalization endows the resulting copper tetraminobenzoquinone (CuTABQ) distinguished performance with a much higher NH<inf>3</inf> FE of 97.7 %. This molecular engineering strategy is also universal, as verified by the improved NO<inf>3</inf>⁻-to-NH<inf>3</inf> conversion performance on different metal centers, including Co and Ni. Furthermore, the assembled rechargeable Zn−NO<inf>3</inf>⁻ battery based on CuTABQ cathode can deliver a high power density of 12.3 mW cm⁻². This work provides advanced insights into the rational design of metal complex catalysts through the molecular-level regulation for NO<inf>3</inf>⁻ electroreduction to value-added NH<inf>3</inf>.