Abstract
Lignin-derived biochar is a promising, sustainable alternative to petroleum-based carbon powders (e.g., carbon black) for polymer composite and energy storage applications. Prior studies of these biochars demonstrate that high electrical conductivity and good capacitive behavior are achievable. However, these studies also show high variability in electrical conductivity between biochars (∼10−2–102 S/cm). The underlying mechanisms that lead to desirable electrical properties in these lignin-derived biochars are poorly understood. In this work, we examine the causes of the variation in conductivity of lignin-derived biochar to optimize the electrical conductivity of lignin-derived biochars. To this end, we produced biochar from three different lignins, a whole biomass source (wheat stem), and cellulose at two pyrolysis temperatures (900 °C, 1100 °C). These biochars have a similar range of conductivities (0.002 to 18.51 S/cm) to what has been reported in the literature. Results from examining the relationship between chemical and physical biochar properties and electrical conductivity indicate that decreases in oxygen content and changes in particle size are associated with increases in electrical conductivity. Importantly, high variation in electrical conductivity is seen between biochars produced from lignins isolated with similar processes, demonstrating the importance of the lignin’s properties on biochar electrical conductivity. These findings indicate how lignin composition and processing may be further selected and optimized to target specific applications of lignin-derived biochars.
Highlights
Carbon black is an amorphous graphitic carbon powder that has developed as an essential filler for thermally and electrically conductive composites [1,2]
Cellulose feedstocks were not examined at 1100 °C, as no measurable solid material remained after pyrolysis of cellulose at 1100 °C
The key finding of this study is that, when controlling for heating rate, catalysts added, and electrical conductivity measurement method, large variations are still seen in the electrical conductivity of biochar produced from lignin feedstocks isolated with similar processes
Summary
Carbon black is an amorphous graphitic carbon powder that has developed as an essential filler for thermally and electrically conductive composites [1,2]. The development of replacements for carbon black from renewable feedstocks, such as biomass, could improve the sustainability of these important applications. It is critical to understand and control the synthesis parameters that increase electrical conductivity of carbon materials derived from these alternate sources in order to develop renewable alternatives to carbon black. Depending on processing conditions and source, lignin-derived biochar can be produced with properties similar to those of carbon black [10,11] including small particle sizes [12], high electrical conductivity [13], and strong capacitance [14]
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