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Compositionally complex transitional metal nitrides are possible candidates for ultra-high temperature usage and are known for their superior properties due to the high configuration entropy. It is often difficult to synthesize pure metal nitrides in bulk, due to significant oxygen contamination; hence, they are synthesized mainly as thin films through magnetron sputtering, chemical vapor deposition or surface nitridation of high entropy alloys. The present article reports on a single-phase compositionally complex ceramic, i.e., (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)NxC1−x, that is synthesized for the first time by employing an organometallic precursor route and using a double ammonolysis process. A multidisciplinary approach is performed to study these compositionally complex nitride and carbonitride systems, including experimental and theoretical investigations.

La₀.₆Ca₀.₄Co₁₋ₓFeₓO₃₋d in its various compositions has proven to be an excellent CO₂-resistant oxygen transport membrane that can be used in plasma-assisted CO₂ conversion. With the goal of incorporating green hydrogen into the CO₂ conversion process, this work takes a step further by investigating the compatibility of La₀.₆Ca₀.₄Co₁₋ₓFeₓO₃₋d membranes with hydrogen fed into the plasma. This will enable plasma-assisted conversion of the carbon monoxide produced in the CO₂ reduction process into green fuels, like methanol. This requires the La₀.₆Ca₀.₄Co₁₋ₓFeₓO₃₋d membranes to be tolerant towards reducing conditions of hydrogen. The hydrogen tolerance of La₀.₆Ca₀.₄Co₁₋ₓFeₓO₃₋d (x = 0.8) was studied in detail. A faster and resource-efficient route based on ultrasonic spray synthesis was developed to synthesise the La₀.₆Ca₀.₄Co₀.₂Fe₀.₈O₃₋d membranes. The La₀.₆Ca₀.₄Co₀.₂Fe₀.₈O₃₋d membrane developed using ultrasonic spray synthesis showed similar performance in terms of its oxygen permeation when compared with the ones synthesised with conventional techniques, such as co-precipitation, sol–gel, etc., despite using 30% less cobalt.

La0.6Ca0.4Co1–xFexO3–d in its various compositions has proven to be an excellent CO2-resistant oxygen transport membrane that can be used in plasma-assisted CO2 conversion. With the goal of incorporating green hydrogen into the CO2 conversion process, this work takes a step further by investigating the compatibility of La0.6Ca0.4Co1–xFexO3–d membranes with hydrogen fed into the plasma. This will enable plasma-assisted conversion of the carbon monoxide produced in the CO2 reduction process into green fuels, like methanol. This requires the La0.6Ca0.4Co1–xFexO3–d membranes to be tolerant towards reducing conditions of hydrogen. The hydrogen tolerance of La0.6Ca0.4Co1–xFexO3–d (x = 0.8) was studied in detail. A faster and resource-efficient route based on ultrasonic spray synthesis was developed to synthesise the La0.6Ca0.4Co0.2Fe0.8O3–d membranes. The La0.6Ca0.4Co0.2Fe0.8O3–d membrane developed using ultrasonic spray synthesis showed similar performance in terms of its oxygen permeation when compared with the ones synthesised with conventional techniques, such as co-precipitation, sol–gel, etc., despite using 30% less cobalt.