Liquid-phase exfoliation of layered biochars into multifunctional heteroatom (Fe, N, S) co-doped graphene-like carbon nanosheets

We here report a liquid-phase exfoliation strategy to delaminate multilayered biochars into multi-heteroatom (Fe, N, S) co-doped graphene-like carbon nanosheets, in which the multilayered biochars derived from naturally evolved layer-by-layer precursors. This strategy provides the versatile capability to tailor the textural properties of the as-synthesized carbon nanosheets, such as obtaining a controllable specific surface area of up to 2491 m² g⁻¹. Thanks to the unique integration of graphene-like microstructures with a thickness of 4.3 nm, large specific surface area and hierarchical pores, homogenous co-doping of N, S, and Fe, and high electronic conductivity, the as-synthesized Fe-N-S co-doped carbon nanosheets could act as multifunctional electrodes for electrocatalytic process of oxygen reduction reaction (ORR) and capacitive energy storage. The optimized nanosheets showed a better ORR catalytic performance than commercial Pt/C catalyst, with a more positive onset potential (1.026 V) and half-wave potential (0.829 V), higher long-term stability, and outstanding methanol tolerance in alkaline mediums. Furthermore, the porous carbon nanosheets exhibited excellent supercapacitive performances which delivered a high energy density of 29.1 Wh kg⁻¹ at a high power density of up to 39.5 kW kg⁻¹ in an ionic liquid electrolyte. This liquid-phase exfoliation strategy will offer new inspiration for the synthesis of various biomass-derived graphene-like carbon nanosheets for multifunctional applications.