h i g h l i g h t s g r a p h i c a l a b s t r a c t < Porous and preferentially oriented {100} Pt thin films are prepared. < The surface of these electrodes is composed of up to 47% of (100) Pt sites. < The current for the electro-oxidation of ammonia is 4.8 times higher than on polycrystalline Pt. < The current for the electro-oxidation of formic acid is 2.6 times higher than on polycrystalline Pt. a b s t r a c t The electrocatalytic activity of preferentially oriented {100} Pt electrodes for the electro-oxidation of ammonia (0.2 M NaOH þ 0.1 M NH 3) and formic acid (0.5 M HCOOH þ 0.5 M H 2 SO 4) was assessed. They were prepared without using any surfactant through potentiostatic deposition (E d ¼ À0.10 V vs RHE, [HCl] ¼ 10 mM and [Na 2 PtCl 6 $6H 2 O] ¼ 0.5 mM) and by varying the deposition charge. For comparison, polycrystalline Pt thin films were prepared using the same solution but with E d ¼ þ0.10 V vs RHE. Quantification of the fraction of (111) and (100) sites was performed by bismuth irreversible adsorption and deconvolution of the hydrogen region, respectively. Samples with as much as 47% of (100) surface sites were obtained. The preferential orientation was further confirmed by CO stripping voltammetry that exhibits similar characteristic features, as well as a similar potential of zero total charge than those expected for a preferential (100) surface. As compared to polycrystalline Pt, the occurrence of Pt (100) surface sites leads to an electrocatalytic activity enhancement by a factor of 4.8 and 2.6 (expressed as mA cm Pt À2) for the oxidation of ammonia and formic acid, respectively.