Direct Carbon Fuel Cell Operation on Brown Coal with a Ni-GDC-YSZ Anode

• Ni-GDC-YSZ anode investigated in brown coal fuelled direct carbon fuel cell.
• Ash deposition an issue for long-term operation of the direct-contact DCFC.
• Oxidation of Ni occurs at anode/electrolyte interface with current passage.
• Cell resistances sensitive to cell loading and anode chamber atmosphere.

Char products derived from brown coal from Morwell in the Latrobe Valley, Australia, were tested in a solid electrolyte based Direct Carbon Fuel Cell (DCFC) at 850 °C. Electrolyte supported button cells were used with a Ni-GDC (gadolinia doped ceria) anode with 15 wt% YSZ (yttria stabilised zirconia) for thermal stability and better adhesion with the YSZ electrolyte. The cell performed well under N2 when using demineralised Morwell char as the fuel, generating reproducible V-j and P-j curves and sustaining chronopotentiometric loading of 20 mA cm−2 for 2 hours with no appreciable signs of voltage decay. Operation with raw Morwell char initially achieved comparable peak power densities to that of the demineralised char, however, subsequent runs with raw Morwell char exhibited decreasing power densities and signs of diffusion-limitations at higher current densities. Ash deposition at the anode is proposed as a possible differentiator of extended cell operability between the two fuels. In addition to fuel-based performance of the DCFC, the response of the anode and system as a whole was closely monitored using Electrochemical Impedance Spectroscopy. Introduction of CO2 into the anode chamber instead of N2 enhanced cell performance and longevity of cell operation under sustained loading. An increase in the ohmic resistance component with increasing current density was observed for Ni-GDC-YSZ anode in N2 atmosphere, but not in H2 atmosphere and it has been attributed to the oxidation of Ni near the electrode/electrolyte interface during current passage and lack of sufficient reducing species to keep Ni in its reduced state.

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