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In the last decade, transition metal carbides, particularly based of molybdenum and tungsten, have emerged as novel materials with promising catalytic properties toward several important practical electrochemical reactions. In this presentation, the activity of such materials will be discussed for the following electrochemical approaches/reactions: i) the electrocatalysis of oxygen reduction reaction (ORR) in acid media on Pt- and Pt2Ni-nanoparticles supported on carbon forming composites with tungsten and molybdenum carbides with cubic (α) and hexagonal (β) structures; ii) the hydrogen evolution reaction (HER) in acid and alkaline media on TM-modified molybdenum carbide (TM-Mo2C) catalysts, where TM is a transition metal, such as, Fe, Co, Ni and Cu; iii) the CO2 and CO electro-reduction reactions in 0.1 M NaClO4 and 0.5 and 1 M KHCO3 solutions on carbon supported tungsten and molybdenum carbides. Syntheses of the carbide-based catalysts have been conducted employing different procedures, after which the produced material are characterized by X-Ray diffraction (XRD), energy dispersive X-ray spectroscopy, (EDS), X-ray photoelectron spectroscopy (XPS), in situ X-ray absorption near edge structure (XANES), and transmission electron microscopy (TEM). Cyclic voltammetry and polarization measurements on stationary and rotation disk electrodes have been employed for the electrochemical investigations. For the CO/CO2 reduction, reaction products were analyzed by differential electrochemical mass spectrometry (DEMS) and high performance liquid chromatography (HPLC) analyses. Enhanced mass and specific ORR activities are seen for Pt–molybdenum carbide-derived composites compared to Pt-α-WC/C, which in turn presents specific activity for the ORR similar to that of a standard carbon supported Pt catalyst (Pt/C). For Pt-β-WC1-x/C composites, the specific activity is also higher than that of Pt/C when a carbide-to carbon load of 40 wt.% is used. In the case of the HER, high activities are observed for all TM-Mo2C catalysts in acid and alkaline media. Nonetheless, while in acid there is a decrease in the activity upon metal doping, with an activity trend of α-Mo2C > Fe-Mo2C > Co-Mo2C > Ni-Mo2C > Cu-Mo2C, the opposite tendency is found in alkaline solutions. In situ near-edge X-ray adsorption analysis reveals different oxidation states of the TM inside the carbide in both solutions. In acid, a positive charge of the TM in the materials in the electrochemical environment is possibly at the origin of the deleterious effect of Fe, Co, Ni and Cu. In addition, catalysts stability against dissolution in acid media is increased by doping of molybdenum carbide with TM. Regarding of CO and CO2 electro-reductions in 0.1 M NaClO4 and 0.5 and 1 M KHCO3 solutions, results suggest that neither molybdenum nor tungsten carbides can be considered as active catalysts, in contrast to reported results in gas phase. It appears that both the aqueous environment and their activity toward the HER surpass the reactivity toward these latter reactions. Acknowledgements: Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP - Procs. 2013/16930-7 and 2014/23486-9) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) (Procs. 1423454), Brazil, for financial supports.

Current green technologies demand for deep and fundamental research. In this sense it has been reported that selective molecular patterning can be employed for the development of highly active electrocatalysts[1,2]. Pt is the most active single-component catalyst for many surface reactions and modifying it with other elements can improve its catalytic performance and stability.Here selective molecular patterning of Pt surfaces with adatoms of Bi and Te at coverages varying from 1/16 ML to 1/4 ML has been studied using DFT to explore changes in the electronic properties of both the adatom and Pt, the sum of which affects catalytic performance of the resulting system.The obtained results indicate that both adatoms are very stable on low-index platinum surfaces at all coverages. The work function of pristine Pt surfaces depends on the exposed plane, and decreases in order (111) > (100) > (110) [4]. In good agreement with experimental data [3] the presence of the adatoms lowers the work function and results in a new trend: (100) > (110) > (111). Further lowering of the model surfaces’ work function with increasing adatoms’ coverage (Table1) also agrees well with the tendencies observed in experimental study of Pt(111) interaction with Bi [3].Table 1. Adatom-Pt(111) WF values. Experimental data for Bi/Pt from ref. [3] is included as well System Coverage Δ WF / eV Experimental value Bi/Pt(111) 0.06 0.73 0.77 0.12 1.26 1.15 0.18 1.65 1.53 0.25 1.96 1.75 Te/Pt(111) 0.06 0.47 — 0.12 0.88 — 0.18 1.22 — 0.24 1.50 — Bi and Te adsorption leads to the charge transfer to the surfaces and the electron density, remaining on the adatoms, gets reorganized to assure the maximal distance from the neighboring Pt atoms, leading to the polarization of the adatom-Pt bond.The adatom-induced changes in the fundamental properties of platinum, such as work function and position of the d-band center, have been observed for both species on all studied surfaces. Even at low 1/16ML coverage Bi and Te not only may block active sites on platinum, but also have a more fundamental impact on its catalytic properties. References [1] V. Perales-Rondón, A. Ferre-Vilaplana, J.M. Feliu, E. Herrero. J. Am. Chem. Soc. 136, 13110 (2014).[2] López-Cudero, F.J. Vidal-Iglesias, J. Solla-Gullón, E. Herrero, A. Aldaz, J.M. Feliu, Phys. Chem. Chem. Phys. 11, 416 (2009).[3] T. Paffett, C.T. Campbell, T.N. Taylor, Journal of Chemical Physics 85, 6176(1986).[4] N. Derry, M.E. Kern, E.H. Worth, J. Vac. Sci. Technol A 33, 060801 (2015).