Assessment of biochar as feedstock in a direct carbon solid oxide fuel cell

Abstract

The feasibility of employing biochar as a fuel in a direct carbon fuel cell (DCFC) or a hybrid carbon fuel cell (HCFC) is investigated in the present study, by utilizing bare biochar or biochar/carbonate mixture as feedstock, respectively. Three different types of biochars, i.e., pistachio shells (PI), pecan shells (PE) and sawdust (SD) are used as feedstock in a solid oxide fuel cell (SOFC) of a type: Biochar|Co–CeO₂/YSZ/Ag|Air. All samples were characterized by means of chemical composition (ultimate/proximate analysis), mercury porosimetry, N₂ adsorption–desorption isotherms (BET method), thermogravimetric analysis (TGA), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM), to obtain a close correlation between cell performance and biochar characteristics. The electrochemical measurements reveal that the optimum performance, in terms of maximum power density (P_max), is obtained for the PI biochar, which demonstrated a power output of 15.5 mW cm⁻² at 800 °C, compared to 14 and 10 mW cm⁻² for PE and SD biochars, respectively. The obtained cell performance results are interpreted on the basis of biochar physicochemical characteristics and AC impedance spectroscopy studies. The superior performance of PI biochar is attributed to a synergistic effect of several physicochemical characteristics, involving the porosity, the acidity, the volatile matter, the carbon and hydrogen content as well as the population of oxygenated surface functionalities.