Effect of physicochemical properties of fossil and biogenic carbons on short-term performances of molten hydroxide direct carbon fuel cell

The transition toward low-emission energy systems requires alternative conversion technologies capable of valorizing carbon-rich waste streams. Molten hydroxide direct carbon fuel cells (MH-DCFCs) offer a promising route for efficient energy production from solid biogenic fuels at temperatures below 600 °C. However, a systematic understanding of how the physicochemical properties of carbon-rich materials affect the short-term cell performance is necessary. In this work a total of 9 fuels, of which 7 of biogenic origin and 2 of fossil origin, were used. Each fuel was comprehensively investigated by means of morphological, mineralogical, and chemical characterization, further to particle analysis, proximate analysis, and wettability assessment. The electrochemical efficiency of the MH-DCFC for each matrix was evaluated by open-circuit voltage (OCV) and linear sweep voltammetry (LSV) at 450 °C. Results demonstrated that fuel reactivity and performance arise from complex interactions between volatile matter (VM), fixed carbon (FC), ash content, and particle morphology. Optimal OCV and power output (maximum value reached 1060 mV and 6.22 mW cm−2) corresponded to fuels with a FC/VM ratio from 1 to 2, moderate ash content (<30 wt%), and elongated, porous particles (aspect ratio of about 0.5 and 33% porosity). Impurities such as KCl and iron oxides further promote electrochemical activity, while SiO2 inhibit it. Comparison with literature data confirms the observed trends and validates the proposed correlations.