The effective treatment of nitrate (NO 3 - ) in water as a nitrogen source and electrocatalytic NO 3 - reduction to ammonia (NH 3 ) (NRA) have become preferred methods for NO 3 - -to-NH 3 conversion. Achieving efficient NO 3 - -toNH 3 conversion requires the design and development of electrode materials with high activity and efficiency for the electrocatalytic NRA reaction. Herein, based on the special properties of dodecahydro- closo -dodecaborate anions, a BCN matrix, loaded with platinum -group nanoparticles (namely, Pd/BCN, Pt/BCN, and Ru/BCN), was prepared using a simple method for the electrocatalytic NRA reaction. Results showed that Pd/BCN exerts the best catalytic effect on the NRA reaction. The NH 3 production rate reached 12.71 mg h -1 mg cat. - 1 at -1.0 V vs. RHE. Faraday efficiency reached 91.79 %, which can be attributed to the more uniform distribution of the nanoparticles. Furthermore, Pd/BCN exhibited high cycling stability and resistance to ionic interference. Moreover, the density functional theory calculations indicated that small and well -distributed Pd nanoclusters in the BCN matrix have a large active surface area and promote the catalytic process. This study provides a new strategy to design catalysts for green ammonia synthesis.