Hydrogen Organic Framework-Templated Synthesis of Small-Sized (FeNiCo) ₉ S ₈ /N-Doped Graphene Electrocatalysts for Oxygen Evolution Reaction

Efficient, stable, and cost-effective nonprecious metal electrocatalysts are highly desirable for electrochemical water splitting. Herein, we report a hydrogen organic framework (HOF)-templated strategy for the synthesis of nanosized (NiCoFe) 9 S 8 embedded in tubular N-doped graphene (NG). Sulfur sources, namely thiourea (TU) and trithiocyanuric acid (TCA), were introduced before the conversion of the HOF to a metal–organic framework (MOF). Using this approach, NiCoFeS x TCA /NG and NiCoFeS y TU /NG nanotubes (NG = N-doped graphene) with tunable sulfur concentrations ( x = 0–0.8 mmol; y = 0.6–1.8 mmol) were successfully fabricated. TCA, which offers superior structural stability and coordination, was more effective than TU in promoting the formation of robust hollow structures and enhancing sulfidation. Varying the proportion of sulfur sources effectively modulates the electronic structures of sulfides, and consequently, their oxygen evolution reaction (OER) performance. The optimal NiCoFeS 0.6TCA /NG nanotubes exhibited outstanding OER activity and excellent stability in alkaline solutions, delivering an overpotential of 257 mV to reach 10 mA cm –2 and only a 12.7 mV decay over 250 h (@20 mA cm –2 ) of operation. The superior OER performance of the NiCoFeS 0.6TCA /NG nanotubes originates from the sulfur-doping-induced electronic structure modulation, as well as the enhanced mass and charge transport afforded by the one-dimensional hollow architecture. This work offers a feasible strategy for the scalable fabrication of high-performance OER electrocatalysts from earth-abundant materials using a versatile HOF-templating strategy.