Nitrogen- and sulfur-doped carbon nanoplatelets via thermal annealing of alkaline lignin with urea as efficient electrocatalysts for oxygen reduction reaction

Abstract

Nowadays, the development of metal-free oxygen reduction reaction (ORR) catalysts based on heteroatom-doped carbon materials has become one of the most attractive topics in fuel cells. Here, we describe a green one-step pyrolysis method for the synthesis of N and S dual-doped carbon nanoplatelets by using alkaline lignin (AL) as the C and S sources combining with urea as a nitrogen dopant. After carbonization at 900 °C, such a hybrid material (N–S–C 900) possesses an excellent electrocatalytic activity towards ORR in both alkaline and acidic media, which is superior to the benchmark Pt/C catalyst in terms of the half-wave potential and diffusion-limiting current density in an alkaline medium. Meanwhile, the obtained hybrid also shows better stability and excellent methanol tolerance than the commercial Pt/C catalyst for ORR in both alkaline and acidic media. In particular, the N–S–C 900 has prominent operational stability in alkaline media, retaining 93.1% of the initial current density after 10 000 s. In this way, using natural biological resources provides a promising alternative to noble-metal catalysts.