Salt-induced silk gel-derived N and trace Fe co-doped 3D porous carbon as an oxygen reduction catalyst in microbial fuel cells

Abstract

Inexpensive and high-efficiency oxygen reduction reaction (ORR) catalysts play a significant role in achieving practical applications of microbial fuel cells (MFCs). Hence, herein, novel nitrogen (N) and trace iron (Fe) co-doped three-dimensional (3D) porous carbon (NFe_x-C) was synthesized as an excellent ORR catalyst from an interesting salt-induced silk gel, which was beneficial to the spontaneously formation of porosity and boosted the ORR activity. Among the series of NFe_x-C, NFe_0.5-C (1.20% N-ORR/C, 0.07 at% Fe) possessed a higher specific surface area (538.94 m² g⁻¹) and pore volume (2.158 cm³ g⁻¹). Note that NFe_0.5-C exhibited a significantly higher positive initial potential (0.274 V vs. Ag/AgCl) and half-wave potential (0.095 V vs. Ag/AgCl) than other catalysts and commercial Pt/C (20 wt%); this implied that it possessed prominent ORR catalytic activity. In the MFC tests, the output-voltage and maximum power density of NFe_0.5-C were enhanced to 517.37 ± 7.87 mV and 605.35 ± 15.39 mW m⁻², respectively. Moreover, NFe_0.5-C (0.15 $ g⁻¹) exhibits excellent anti-poisoning ability and is thousands of times cheaper than commercial Pt/C (20 wt%, 220.04 $ g⁻¹); therefore, NFe_0.5-C should be a prospective catalyst to substitute precious commercial Pt/C in MFCs and even for application in other types of fuel cells.