Evaluating Physical and Electronic Structure Developments of Loblolly Pine Derived Biochar and Activated Carbon

Biochar is a major byproduct of fast pyrolysis process. Until recently, biochar is considered as an inexpensive solid fuel that is re-consumed for the pyrolysis reactor heating. However, advances in nanotechnologies reveal the potential high-end applications of biochar as electrodes for electrochemical energy storage systems and conductive thin film materials for sensors and electronic devices. The high-end applications of biochar not only contribute to the profitability of overall fast pyrolysis process, but also contribute to the growth of sustainable material market. To attain the objective, it is imperative to understand the complex biomass derived carbon structural development during the carbonization and the activation. In this study, the physical and the electronic structures of loblolly pine (Pinus Taeda) derived biochar and activated carbon were systematically analyzed by interpreting X-ray diffraction patterns, electron energy loss spectra, and electrical conductivities. Loblolly pine was carbonized at nine different temperatures (300℃, 350℃, 400℃, 500℃, 600℃, 700℃, 800℃, 900℃, and 1,000℃,) using quartz tube furnace. Then, four biochar samples carbonized at 300℃, 350℃, 500℃, and 700℃ were impregnated with NaOH to produce the activated carbon. Carbon sp² content was quantitatively determined by the electron energy loss spectroscopy. The sp² content of biochar produced at 300℃ is 58% and the sp² content gradually increases to 78% as the carbonization temperature is elevated to 1,000℃. The sp² contents of activated carbon are 74%, 78%, 79%, and 85% where precursor biochar carbonization temperatures are 300℃, 350℃, 500℃, and 700℃. Polyaromatic cluster size and graphitic stacking thickness were determined by analyzing the X-ray diffraction patterns. Four stages of biochar physical structural development were determined. After major biomass components decompose, the average polyaromatic cluster size and the graphitic stacking thickness increase as the carbonization temperature increases. Carbon paste electrode was produced by mixing biochar and activated carbon powder with polyvinylidene fluoride solution. Biochar electrodes features were closer to insulator that the electrical conductivity was not measurable. Activated carbon electrodes had good electrical conductivities which values are 1.14 S/cm, 1.41 S/cm, 1.3 S/cm, and 1.58 S/cm. The detailed model of physical and electronic structural developments will be discussed.