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

Abstract

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.

Direct Synthesis of Ammonia from Nitrate on Amorphous Graphene with Near 100% Efficiency

“…We performed DFT calculations of reaction pathways [7,60] to understand the origin of the high NH 3 selectivity. Our experimental data suggest that both ox-LIG and LIG with amorphous lattice show higher activity than higher-crystallinity rGO, and ox-LIG is more active than LIG.…”

Boron–Sulfur Pairs for Highly Active 2e– Oxygen Reduction Reaction to Electrochemically Synthesize Hydrogen Peroxide

“…The highest I D / I G ratio indicates the most abundant defects including geometric defects and heteroatom dopants in the BS-C-3. However, the abundant geometric defects in the BS-C-3 are beneficial for electrocatalysis owing to their abundant vacancies and the unique local electron structure. , The pore structure was measured by N 2 adsorption–desorption measurements (Figure j). H 3 BO 3 is a general pore-forming agent, so the addition of H 3 BO 3 can distinctly enhance the specific surface area (SSA) of the carbon material.…”

Fullerene Fragment Restructuring: How Spatial Proximity Shapes Defect-Rich Carbon Electrocatalysts

“…Chemical composition and elemental speciation of the carbon materials are further analyzed by X-ray photoelectron spectroscopy (XPS). The high-resolution C 1s XPS spectra (Figure e) are deconvoluted into four peaks centered at 284.7, 285.4, 286.6, and 287.4 eV, corresponding to the sp 2 -C, sp 3 -C, C–O, and CO species, respectively. − The corresponding area ratios of sp 3 /sp 2 C species are compared in Figure f. A lower sp 3 /sp 2 area ratio is observed for E-H-5 (0.21) than that for H-E-5 (0.27), indicting its higher content of sp 2 -C. The same variation trend of sp 3 /sp 2 area ratio is also observed for E-H-2 (0.19) and H-E-2 (0.25), as shown in Figure S8.…”