The ALD layers were grown in a commercial ALD reactor (GEMstar XT; Arradience Inc.) by a sequence of exposures of an organometallic precursor and water as an oxygen source. The precursors were contained in a vial sealed with a metal gasket: trimethylaluminum (TMA, 98%; Strem, Inc.) for Al2O3, diethylzinc (DEZ, 95%; Strem, Inc.) for ZnO, and tetrakisdimethlamidotitanium (TDMAT, 99%; Strem, Inc.) for TiO2. The specific details of each ALD cycle for the growth of these oxides are provided in the supporting information. Each heterogenous catalyst was composed of an ALD-synthesized layer conformally coating the support. The ALD coatings began with a 50 cycle (approximately 7 nm) base layer of Al2O3 onto the support to provide a consistent interface between each catalyst and the support. The catalyst layer was deposited over this base layer: 200 cycles of TDMAT/H2O to prepare TiO2, 58 cycles of DEZ/H2O to prepare ZnO, or 93 additional cycles of TMA/H2O to prepare Al2O3. These layer structures were chosen to grow catalyst layers of sufficient thickness (roughly 8-10 nm) to behave like the bulk compound yet add negligible thickness to the fibers. After the deposition was completed, the samples were removed from the ALD reactor and annealed in air at 500 ˚C for three hours (3 ˚C min -1 ramp rate from room temperature). We developed the reactor setup (shown in Fig. ) to compare the performance of ALDprepared plasma catalysts. The catalysts (ALD-coated fiber supports) were loaded into the 55 mm wide plasma region. This region was established by the length of the exterior aluminum foil electrode (20 µm thick). The exterior electrode was 55 mm along the length of the tube and wrapped three times around the tube, then connected to the transformer by a metal hose clamp.