Biochar derived from pyrolysis of oily sludge waste: Structural characteristics and electrochemical properties

Oily sludge is the main hazardous waste produced by the petroleum industry, and its harmless disposal and recycling have become urgent problems. In this study, the pyrolysis technique was used to prepare oily sludge biochar at different temperatures (400 °C, 500 °C, 600 °C, and 700 °C). The characteristics of the biochar, including weight reduction, elemental composition, and molecular structure, were comprehensively investigated. From the perspective of the electrochemical properties of biochar, the relationship between the structure of the biochar and the redox capacity was discussed, and the feasibility of biochar as a battery cathode material was explored. The results suggested that the improper pyrolysis temperature could reduce the content of the quinone structure which was related to the redox capacity, the biochar prepared at 600 °C should have the strongest electron transfer capability. Moreover, the highest degree of condensation and aromaticity of pyrolysis products could be obtained at a higher pyrolysis temperature (700 °C), which might result in the relatively high discharge-charge capacity and good cycle performance of biochar which was used as an electrode material of a battery. This study explored the feasibility of pyrolysis as a disposal route for oily sludge waste and provided a reference for the electrochemical application of biochar prepared from oil sludge waste. •Oily sludge biochar were prepared at different pyrolysis temperatures.•The elementary composition and molecular structure of biochar were investigated.•The redox capacity of biochar was correlated with the C/H mol ratios.•Biochar obtained at 600 °C had the optimal electron transfer capability.•As a potential electrode material, OS700 showed the best performance.