ABSTRACT
The electrochemical reduction of CO2 is an important electrolysis reaction that enables the conversion of a waste gas to fuels or value-added chemicals. To make this reaction viable, a profound understanding of central intermediate steps, such as the CO electroreduction, is required. On Cu, the CO reduction reaction (CORR) is intimately linked to the hydrogen evolution reaction (HER) that proceeds via the reduction of water in alkaline or neutral electrolytes. Here, we demonstrate that the interaction of water or more specifically the water reduction kinetics on differently smooth Cu(100) and Cu(111) surfaces during the CORR in alkaline media significantly governs the CORR. On Cu(111), faster HER kinetics and the highest CORR activity are observed, even though HER and CORR onsets are more negative. While on Cu(100) small Cu ad-island clusters form in the cathodic potential range only when CO is present, structural changes appear on a larger length scale on Cu(111) both under CORR conditions and when no CO is present. These differences in the reconstruction characteristics may be attributed to the dominance of either the CORR and its intermediates or the HER on the different Cu surfaces. Therefore, the interfacial water reactivity is considered an essential activity descriptor for the CORR on Cu in alkaline media.
ABSTRACT
In the combustion chambers of gas turbine engines, ZrO2-8wt.%Y2O3 (YSZ) TBCs are commonly applied by air plasma spray (APS) using Ar-/H2-based plasmas via legacy torches. Alternatively, N2/H2 plasmas could be used with the potential of increasing overall deposition efficiency (DE) and hence reduce the consumption of high-value feedstock powder. Also, by increasing DE, spraying time would be reduced, thereby providing another contribution to bring down production costs. In this work, TBCs were prepared with Ar- and N2-based plasmas with different YSZ powders using Metco 9MB legacy torch. The use of N2-based plasma resulted in higher particle temperature and lower particle velocity values than those provided by the Ar-based plasma. The measured DEs were between 41-43 and 53-60% for the Ar- and N2-based plasmas, respectively. This represents a ~ 40% increase in the DE. The coatings produced with the two different plasmas exhibited equivalent porosity levels ~ 11-13%. On average, the lowest thermal conductivity values were given by a N2-based LD-B YSZ TBC. In the furnace cycle test, the performance of the TBCs prepared with the N2-based plasma was superior to that of the TBCs prepared with the Ar plasma, and also exceeding that of an industrial APS TBC benchmark.
