Porous Carbon Nanofibers Derived from Silk Fibroin through Electrospinning as N-Doped Metal-Free Catalysts for Hydrogen Evolution Reaction in Acidic and Alkaline Solutions

Water electrolysis is considered as one promising strategy for hydrogen production, and thus, preparing electrocatalysts of superior efficiency and low cost for a hydrogen evolution reaction (HER) in a wide pH range is of paramount importance. In this research, N-doped porous carbon nanofibers derived from silk fibroin by KCl chemical activation are successfully synthesized as the metal-free catalyst for the HER under both acidic and alkaline conditions. After chemical activation of KCl, hierarchical porous structures are formed. Besides, it is found that the concentration of KCl in the electrospun membrane will affect the maintenance of the fibrous morphology for the carbonized samples due to the destruction of β-sheets in silk fibroin induced by KCl. The specific surface area of the optimized sample, 4%-SPCNF, increased by nearly nine times compared with that without activation because of the hierarchical pores and large through pores between fibers. Meanwhile, the porosity increases from 59.87 to 80.28% due to the existence of through pores. Moreover, the 4%-SPCNF has remarkable stability and durability since the carbon substrate is resistant against the corrosion of the electrolyte. Our work provides insights into the design and engineering of silk fibroin-derived carbon nanofibers for metal-free catalysts of the HER under acidic and alkaline conditions.