Lignin-Based N-Doped Nanocarbons for the ORR

Abstract

Fuel cells (FC) are one of the most viable energy conversion devices that could replace fossil-fuel based energy production in the future. As the oxygen reduction reaction (ORR) happening at the cathode side has slow kinetics, the usage of catalysts that speed up the process is inevitable. Most of the studied catalyst materials include precious metals or their alloys. Lately, the conversion of biomass to carbon nanomaterials and the usage of biomass-based carbons in different energy conversion systems has grown enormously [1].Lignin among the major components of lignocellulosic biomass, which is mainly produced in the pulp and paper industry or in biorefineries. To fully unlock the potential of biorefineries, the components of lignocellulosic biomass (e.g. lignin, hemicellulose, cellulose) must be fractionated and valorized [2]. Currently, lignin is used to produce electricity and heat in factories or landfilled. Since the main component of lignin is carbon, it is possible to synthesize lignin-based carbon nanomaterials.In this work, lignin from a local Estonian biorefinery was used to produce high specific surface area nanocarbons that were studied as catalysts for the ORR. Different ways (two-step or one-step) and temperatures (700 or 800 °C) were used to carry out the carbonization and activation processes. In the second step, dicyandiamide was used to carry out the nitrogen doping at 800 °C. Electrochemical characterization of the N-doped industrial lignin-based carbon catalysts were carried out by employing rotating disc electrode method. We show that a simultaneous carbonization and activation process in the presence of NaOH is the most effective towards creating the best catalyst precursor for the ORR, as the lignin-derived nanocarbon shows higher electrochemical activity towards the ORR than commercial N-doped graphene (Fig 1).