W to an 18.5% conversion rate at 100 W. We observed a power dependence on the behavior of ZnO. At the lowest power measured (15 W), the ZnO catalyst performed worse than the bare support, though these were both within one standard deviation of each other and Al2O3. ZnO and Al2O3 were statistically equivalent at 30W. At higher input power, the CO2 conversion percentage rose steeply with power compared to all other catalysts measured. At 100 W, ZnO gave the highest CO2 conversion percentage (19.0%) of any of the catalysts measured here. This is significant as ZnO has traditionally been utilized as a support for catalysts in both thermal and non-thermal CO2 hydrogenation plasma reactions and has been shown to have negligible catalytic effect when used in DBD systems alone at low input powers. It is usually thought to contribute to these reactions by acting as a support for other metal catalysts and forming reduced ZnOx species near the catalyst-support interface. Another important metric for fuel-forming reactions, such as CO2 reduction to CO, is the input power conversion efficiency, ηCO2. This measures the ratio of the Gibbs free energy of combustion of the moles of CO2 converted to CO to the reactor input power. This is particularly important if the products are intended to be used as a fuel, for example. Here, the oxidation of CO (g) to CO2 (g) is the reverse of the main reaction occurring in the plasma reactor. CO (g) formation has a Gibbs free energy of reaction of ∆𝐺 #$% & =-257.2 kJ mol -1 , and this is the simplest reaction to consider as the chemical power output of the plasma reactor. Other reactions or methods for recouping the input power, such as use of waste heat, are not considered here. As shown in Figure , the input power conversion efficiency of the CO2 reduction reaction generally decreased as input power increased. We observed a nearly linear decrease for input power conversion efficiency on the TiO2 catalyst with input power. The other catalysts did not have comparable CO2 conversion ratios at low input power to the TiO2 catalysts. The difference between the power conversion efficiency of the ZnO and TiO2 became insignificant at higher input powers. Also, the input power conversion efficiency on Al2O3 and the bare support all slightly increased at low input powers before also diminishing at higher input powers. These results suggest that the optimal operating input power of the reactor is dependent on the choice of metal oxide plasma catalyst. We used a power law analysis to characterize the catalytic behavior of each of the catalyst materials. This empirical analysis is analogous to Tafel slope analysis of the potential-dependent performance of electrocatalysts and more sophisticated methods in plasma catalysis. showed that the regions of the C deposition were mainly localized to the particles, and only adventitious carbon or very thin deposits were visible elsewhere on the fibers. The particles were approximately 1-3 µm in diameter and were observed more frequently at the intersections of support fibers or at irregularities in the fiber diameter. We observed that the amount of carbon deposition appeared to increase with increasing reactor input power. Qualitatively, greater deposition was visible via optical microscopy on catalysts exposed to 100 W of plasma input power than 50 W. The Al2O3 coated catalysts saw significantly more carbon deposits than either the TiO2 or ZnO catalysts. In some cases, the Al2O3 catalysts were visually darker in some regions due to the particle deposition, whereas negligible discoloration was observed on the TiO2-and ZnO-coated catalysts. Deposition of C in DBD reactors due to the Boudouard reaction has been previously reported at the input powers and temperatures encountered during the experiments. Due to the sampling and CO2 conversion quantification method, the direct splitting of CO2 into C and O2 cannot be quantified and likely affects the CO2 to CO conversion percentage reported previously. However, this suggests that the increase in CO2 transformation XPS is sensitive to the composition and oxidation state of an interface. We used XPS to characterize the surface of ALD-synthesized catalysts in both the as-prepared and post-plasma exposure states. This comparison allowed us to measure any transformations or degredation of the catalyst during the plasma CO2 reduction process. All ex situ samples were left in the air for at least 1 day prior to XPS characterization. The TiO2 catalyst showed intensity at binding energies of 458.2 eV and 464 eV corresponding to the Ti 2p3/2 and the 2p1/2 features, respectively, consistent with the Ti 4+ in TiO2 (Figure ). After plasma exposure, we observed the same features. Additionally, we observed the formation of a new feature in these XPS regions at binding energies of 456.2 eV and 461 eV, consistent with formation of reduced Ti 3+ species as shown in other plasma-reduced TiO2 surfaces, possibly as Ti2O3. A new feature at higher binding energy, 532 eV, was also observed in the O 1s XPS region on the TiO2 catalyst after plasma exposure (Figure ), however this feature is likely the result of water chemisorbed onto the surface of samples. The integrated intensity of both features remained consistent before and It has been proposed that the decrease in performance for CO2 splitting into CO and O2 in a packed DBD reactor, as compared to a DBD reactor with no packing, is due to the modification of the discharge mode via a decrease in the number of filamentary discharges per unit time in the discharge region. In our system, the increase in performance by the bare support over the unpacked reactor suggests an increase in the number of overall discharges. The uniformity of the catalyst structure allowed us to regularize the dielectric material in the gap, and thus the overall density of filamentary discharges, identical between samples. Any differences in CO2 conversion can therefore be attributed to either the differences in catalytic activity for CO2 reduction due to the ALD-synthesized catalyst layer or electric field enhancement effects due to the permittivity of the ultra-thin catalyst layers when exposed to plasma. The extremely thin catalyst layers should have a negligible effect on the physical characteristics of the plasma, and the dielectric properties of the reaction volume are dominated by the permittivity of the support material. Given this approximation, the differences in the plasma itself near the surface of the catalyst should be negligible. Therefore, the opportunity that this approach to producing ultra-regularized plasma catalysts is that any microscopic changes in activity can be inferred from the results of the macroscopic product analysis. For example, the observed transition in the catalytic activity of ZnO is directly related to the reactivity of the material itself, rather than any morphological reconfiguration of the layer under plasma exposure. To our knowledge, this is the first report of this observation on ZnO. CO2 dissociation, however this trend was not observed in conversion studies. The formation of oxide vacancies (Vo) during plasma exposure tends to increase the basicity of the surface.