a, Anode (low magnification). b, Anode (high magnification). c, The sandwich structure of this cell after running for about 6,000 h. d, The interface between electrolyte and cathode. e, High magnification of cathode after 6,000 h operation. f, Raman spectrum of the PCFC anode after 6,000 h of operation on hydrocarbon fuel at 500 °C. A carbonate peak is visible at 1,060 cm−1 but the graphitic carbon (G band) and disordered carbon (D band), which would be present at 1,580 cm−1 and 1,350 cm−1, are not apparent, indicating the absence of graphitic carbon and disordered carbon deposits in the anode even after long-term operation on hydrocarbon fuel. Long-term stabilities of direct hydrocarbons PCFCs were tested at 500 °C. At this temperature, the structure type of carbon species should be polymeric, amorphous films or filaments (Cβ), vermicular filaments, fibres and/or whiskers (Cγ), or graphitic platelets or films (Cc)35. Typically, these carbon species are visible (by SEM) in SOFC anodes after running on hydrocarbon fuels, but the high-magnification SEM images of our PCFC anode (Extended Data Fig. 3a, b) show no visible evidence of such carbon structures. To further substantiate this conclusion, post-mortem Raman analyses show that there are no disordered and graphitic carbon species found in the PCFC anode even after long-term operation on hydrocarbon fuels (Extended Data Fig. 3f).