Sustainable and Controlled Synthesis of Carbon Nanoparticles from Lignin using Single-Step Aerosol Methods for Application in Energy Storage

With the rapidly growing demand for renewable energy and portable devices, developing high-performance energy storage materials and meeting sustainability requirements is significant. Lignin, a biomass constituent and byproduct waste of biorefineries, is one of the few renewable sources of carbon that have the abundance and desirable properties to displace or replace fossil derived carbon sources. A renewable resource, low cost, and high aromatic content make lignin an ideal precursor to obtaining carbon materials for energy storage. However, present efforts on the large-scale synthesis of carbon materials from lignin are limited either by multistep and batch processes or the use of activating agents/templates [1].<br/><br/>The present work aims to engineer a process that valorizes waste and by-product lignin. In particular, we develop an original and innovative method, based on a one-step continuous aerosol technique, to manufacture high-performance carbon nanoparticles for energy storage without the use of activating agent/template. This one-step approach requires a significantly lower time for synthesis: an order of seconds in comparison to hours for existing methods. Temperature and residence time are expected to have a key impact on the properties of carbon materials synthesized from lignin, hence, an aerosol technique utilizing a furnace aerosol reactor is used; furnace aerosol reactor is known for enabling precise control over a wide range of temperatures and residence times [2]. Subsequently, the effect of temperature and residence time inside the reactor on carbon nanoparticle size, functional groups, surface area, and morphology is systematically investigated. Furthermore, the as-obtained carbon nanoparticles are tested for specific capacitance and the best-performing material (surface area 925 m2/g) exhibited a specific capacitance of 247 F/g at 0.5 A/g with excellent capacity retainment of over 98 % after 10,000 cycles. This is a clear demonstration of their superior performance compared to supercapacitors synthesized earlier from lignin.<br/><br/>Moreover, the size and morphology of carbon particles, which are impacted by interparticle collision and sintering, are known to play a crucial role in their stability as well as energy storage performance. However, experimental as well as modeling efforts on size and morphology-controlled synthesis of carbon nanoparticles from lignin are limited, partly due to the complexity of studying collision and sintering under simultaneous lignin reactions (pyrolysis). We systematically investigate the kinetics of reaction, sintering, and collisions using a novel and generalizable numerical model based on a geometric modeling approach [3]. Knowledge of kinetics will provide better control over the size and morphology for efficient utilization of carbon nanoparticles in energy storage.<br/><br/>Overall, the simple (one-step, continuous, and rapid) operation, avoiding the use of activating/templating chemicals, and precise control over size and morphology make the aerosol technique a promising candidate for the scalable and sustainable synthesis of energy storage materials.<br/><br/>References:<br/>[1] J.W. Jeon, L. Zhang, J.L. Lutkenhaus, D.D. Laskar, J.P. Lemmon, D. Choi, M.I. Nandasiri, A. Hashmi, J. Xu, R.K. Motkuri, Controlling porosity in lignin derived nanoporous carbon for supercapacitor applications, ChemSusChem, 2015, 8(3), 428-432.<br/>[2] S. Modi, M.B. Foston, P. Biswas, Controlled Synthesis of Smaller than 100 nm Lignin Nanoparticles in a Furnace Aerosol Reactor, ACS ES&T Engineering, 2023, 3 (5), 671–681<br/>[3] S. Modi, O. Okonkwo, H. Zhou, S. Kavadiya, M. Foston, P. Biswas, Geometric Model for Predicting the Size and Morphology Evolution of Multiparticle Aggregates during Simultaneous Reaction and Sintering, Chem. Eng. J., 2023, 141423