Electrochemical evaluation using alternative fuel electrode materials for syngas production via high temperature CO₂/H₂O co-electrolysis

Abstract

This Project was focused on the electrochemical evaluation of alternative Fuel Electrode (FE) materials for syngas production under HT H₂O/CO₂ co-electrolysis. The use of AC Impedance and I-V curve measurements on solid oxide electrolyser cells were crucial for the investigation. Optimization of the FE applied, by mainly identifying the case exhibiting the lowest polarisation resistance (Rp) value, and comparison between the three different materials utilized, were also part of the Project’s scope. The first FE material applied was the state-of-art Ni-YSZ leading on to La₀.₄₃Ca₀.₃₇Ni₀.₀₆Ti₀.₉₄O₃-δ (LCNT) and La₀.₅₂Sr₀.₂₈Ni₀.₀₆Ti₀.₉₄94₃-δ (LSNT) perovskites oxides. The motivation for investigating LCNT was based on literature and good results obtained within Prof. JTSI group at University of St. Andrews. Stability tests, different temperatures, voltages, flow rates and gas compositions (varying %H₂O, %CO₂, %H₂) were examined. The evaluation of LSNT material was part of a collaboration work with Dr. Sanchez mostly aiming the comparison with LCNT performance under similar conditions. When cells were supplied with 0%H₂O, Rp values were substantially greater indicating that for a reasonable performance at least 3%H₂O is necessary. However, when only 3%H₂O was utilized under zero or low %CO₂ cells starved. The presence of 50%H₂O extinguished such problems and led to lower Rp values when applying both Ni and LCNT. In addition, higher CO₂ content led to lower electrode resistance in all cases studied. Both perovskites displayed the lowest Rp values under 50%H₂O:0%H₂, whereas Ni-YSZ, due to its redox instability, exhibited very high Rp figures under 0%H₂, confirming the mandatory use of safe gas when applying Ni cermet. It displayed the lowest Rp values under 15%H₂. To summarize, LCNT proved to be an outstanding replacement for Ni cermet exhibiting good stability and performance with low Rp values under several different conditions especially when operating in the absence of H₂.