Electrochemical performance of a hybrid direct carbon fuel cell powered by pyrolysed MDF

Medium density fibreboard is a ubiquitous element in modern furniture, here we consider utilising waste MDF as a future energy source. In particular, we focus upon the hybrid direct carbon fuel cell (HDCFC), which involves a combined molten carbonate/solid oxide fuel cell anode/electrolyte interface and can be fuelled by a wide range of carbon forms. Current–voltage measurements and a.c. impedance at temperatures in the range of 525–800 °C have been made on cells powered by pyrolysed medium density fibreboard (pMDF) samples which had undergone three different preparatory treatments (immersion of strips in molten eutectic carbonate mixture; deep soaking of strips in aqueous carbonate mixture corresponding to the eutectic composition and fine powdering). Below 700 °C the three pMDF samples show quite different electrochemical performance in the HDCFC, but above 700 °C their behaviour becomes similar. Powdered pMDF gives the best OCV (0.89 V) and lowest resistance (2.36 Ω) values below 700 °C, although the electrochemical performance is dominated by diffusion limitations and the performance degrades at higher temperatures. The immersed strip behaves quite differently with limited performance below 750 °C but it shows both good OCV, 1 V, and low resistance, <4 Ω, at higher temperatures. Three components are discernable, an ohmic contribution probably due to both ionic resistance of zirconia electrolyte and electronic resistance of current collection and two electrode processes thought to be associated with the transfer of oxygen ions at the electrode : electrolyte interface and diffusion of reactant species through the electrode. The activation energies calculated from the ohmic resistances for the three samples (−0.79 – −1.00 eV) are of similar order to that expected for the yttria zirconia electrolyte.