Interfacial Modification of Conjugated Coordination Polymers for Efficient and Selective Nitrogen Electroreduction to Ammonia.

Electrocatalytic nitrogen reduction reaction (NRR) to ammonia holds great potential for sustainable ammonia synthesis at ambient conditions, where a single-atom catalyst has recently emerged as a prospective NRR catalyst candidate owing to its advantageous features such as maximal metal-utilization efficiency and low-coordinated single-atom metal sites. Nevertheless, owing to the uncontrolled coordination structures of the single-metal-atom sites in single-atom catalysts and the unregulated gas/ion migration in their surface reaction microenvironments, it still remains a formidable challenge to simultaneously improve the NRR selectivity and activity. In this work, we report a facile and general strategy to prepare a composite catalyst with protic ionic liquids (PIL) modified on conjugated coordination polymers that feature abundant single-atom metal sites with well-defined coordination structures, significantly outperforming its counterpart catalyst without PIL. Both experimental and theoretical studies suggest that profound electronic interactions are induced between the PIL and conjugated coordination polymers. The PIL can appreciably decrease the thermodynamic energy barrier toward NRR electrocatalysis by enhancing the Ni 3d band centers of single-metal-atom sites in conjugated coordination polymers and generate a favorable reaction microenvironment by increasing local N/HO concentration ratio, thus leading to simultaneously improved NRR selectivity and activity. Such an interfacial modification strategy can provide an effective methodology for the design of low-cost, high-performance single-atom catalysts for efficient energy conversion and beyond.