Parametric optimization of a molten hydroxide direct carbon fuel cell fueled with olive pomace biochar

Molten hydroxide direct carbon fuel cells (MH-DCFCs) represent a promising technology for the direct conversion of solid carbonaceous fuels into electricity at intermediate temperatures. However, a systematic understanding of how fuel–anode contact area, particle size distribution (PSD), and their interaction with operating temperature affect electrochemical performance is still lacking. In this work, the electrochemical performance of an MH-DCFC fueled with olive-pomace-based biochar was investigated through a controlled variation of the effects of anode–fuel contact area, fuel volume, PSD, and operating temperature on open‑circuit voltage (OCV) and linear sweep voltammetry (LSV). The fuel-anode contact area of 11.00 cm2 provided the best compromise between power density and stability, whereas smaller areas led to rapid performance degradation and larger ones increased ohmic losses. A moderate volume reduction enhanced performance by limiting ash accumulation, while excessive reduction caused insufficient fuel availability. The effect of PSD strongly depended on temperature. At 450°C, the fraction 1,000–500µm maximized power density, whereas at 500°C coarser particles reached 23.00MW cm−2 due to enhanced reaction kinetics. Although increasing temperature improved power output and OCV, it also accelerated fuel consumption. Thus, a faster fuel depletion does not allow stable electrochemical performances.