Steering the Topological Defects in Amorphous Laser-Induced Graphene for Direct Nitrate-to-Ammonia Electroreduction

Developing metal-free electrocatalysts for direct nitrate-to-ammonia reduction is promising to remediate wastewater yet challenged by the poor ammonia selectivity. Amorphization has become an emerging strategy to afford conventional materials with exotic physical, chemical, and electronic properties. Transient laser heating of polymers produces graphene with an unusual polycrystalline lattice, yet the control of graphene amorphicity is difficult due to the extreme conditions and fast kinetics of the lasing process. Here, we report the synthesis of amorphous graphene with a tailorable heterophase, topologically disparate from crystalline graphene and amorphous carbon. Atomic-resolution imaging reveals the intermediate crystallinity comprising both six-membered rings and polygons, the ratio of which directly correlates with the aromatic structures of the precursors. These amorphous graphenes, as metal-free catalysts, show high performance in direct nitrate-to-ammonia electroreduction. The performance is associated with the amorphicity of graphene and reaches a maximum ammonia Faradaic efficiency of 83.7% at -0.94 V vs reversible hydrogen electrode. X-ray pair distribution functions and paramagnetism disclose the elongated carbon-carbon bonds and rich unpaired electrons in amorphous graphene, which exhibit more favorable adsorption of nitrate as suggested by theoretical calculations. Our findings shed light on the controllable synthesis of graphene with unusual topologies that could find broad applications in electronics, catalysis, and sensors.

Automated summary

This study reports a method for synthesizing amorphous graphene as a metal-free catalyst, which shows excellent performance in the direct nitrate-to-ammonia conversion. Atomic-resolution imaging reveals the intermediate crystalline structure in amorphous graphene and suggests that its performance is associated with the degree of amorphization.