Biocarbon from Algae, Cellulose and Sewage Sludge as Sustainable Composites for Energy Storage

This presentation will discuss the synthesis, characterization, and utilization of a novel family of biocarbon-based composites for electrochemical and heat storage. The composites are produced by the pyrolysis and carbonization of various biomass (algae, cellulose biomass, and municipal sewage sludge) inherently containing or doped with catalytic metal such as Iron and Calcium at lower temperature (<1400°C) than the standard carbonization temperature (>1800°C) or processed with molten salt (Na₂CO₃-K₂CO₃). In this process, the biocarbon is transformed from a randomly organized carbon to a graphite-like material (organized and structured carbon) showing a high graphene rate structure. The Carbon structure and composition changes in the composites have been investigated from nano to bulk scales in combining XRD, HRTEM and RAMAN. This has enabled to probe changes in biochar nanostructure and crystalline graphitic domains catalyzed by the inclusion of metal such as iron and Calcium. The encapsulation of iron particles by graphitic phase (graphene sheets) and the carbon-metal bonding during the pyrolysis and carbonization were uncovered using XPS. Key properties for energy storage applications such as the remanent magnetization, the coercive field, the specific heat, the thermal and electric conductivities, the thermal stability including the mechanical properties will be discussed. Biocarbon from algae for example, rich in nitrogen showed a high specific surface area of 2009.26 m2/g with high specific capacitance of 230.2 F/g at 0.25 A/g and a capacitance retention of 75.54% at 2 A/g. This work provides a green and promising approach to produce heteroatom-doped capacitive biocarbon with superior properties for energy storage.