The effect of biomass pyrolysis temperature on the performance of biochar-fed molten hydroxide direct carbon fuel cells

Biomass derived biochar is a promising fuel for direct carbon fuel cells, and the pyrolysis process to produce biochar has significant influence on the performance of said biochar-fed cells. In the present study, pine pellets were utilized as the fuel feedstock, and by using a molten hydroxide direct carbon fuel cell, the effect of the pyrolysis temperature on the fuel performance of pine biochar pellets obtained from fast pyrolysis was explored. The results revealed high pyrolysis temperature was beneficial to the fuel performance of pine biochar pellets in terms of peak power density and electrochemical impedance spectroscopy. To illustrate the observed results, a mechanism was proposed based on the physical and chemical characterizations. The proposed mechanism indicated that high pyrolysis temperature would result in high carbonization degree, amorphous microstructure, and smooth surface morphology of the pine biochar pellets, as well as high reactivity of carbon fuel in the cell operating conditions, which in turn would be conducive to the extension of triple phase boundaries and the improvement of charge transfer at/near triple phase boundaries. According to the results, the cells fed with the pine biochar pellets produced at 800 °C achieved the highest peak power density of 76.6 mW/cm² at 400 °C.