Prepararam-se filmes de Pd-P sobre aço carbono, por deposição electroless, usando hipofosfito de sódio como agente redutor. As ligas foram caracterizadas (estrutura e morfologia) por Difração de Raios X (DRX) e Microscopia Eletrônica de Varredura (MEV) o que revelou que o grau de amorficidade aumenta com a quantidade de P co-depositado. A resposta de eletrodos de Pd-P, com diferentes composições, para a reação de evolução de hidrogênio (REH), analisada em soluções de água-etanol e de etanol puro, mostraram que o caráter amorfo das ligas aumenta a aptidão para adsorver hidrogênio. Os resultados sugerem que filmes de Pd-P com adequados teores em fósforo (17% at.) são superfícies de eletrodo apropriadas para a hidrogenação de substratos orgânicos.Pd-P modified carbon steel electrodes have been prepared by electroless deposition using sodium hypoposphite as reducing agent. The alloy characteristics (structure and morphology) were analysed by X-Ray Diffraction (XRD) and Scanning Electronic Microscopy (SEM) revealing that the degree of amorphicity increases with the amount of co-deposited P. The behaviour of Pd-P with different compositions towards the HER, analysed in water-ethanol and pure ethanol solutions, have shown that the alloy amorphous character enhances the hydrogen adsorption. The results suggest that Pd-P films with adequate phosphorous content (17% at.) are suitable electrode surfaces for organic substrates hydrogenation.Keywords: electroless deposition, Pd-P alloys, electrocatalytic activity
IntroductionThe preparation of modified electrodes with catalytical properties for the hydrogen evolution reaction (HER) has been subject of intensive research, 1,2 due to its relevant use in industrial applications. The principal aim is to find a low cost and efficient cathodic material for the preparation of electrodes with high surface area. In this context, the metallic electroless deposition is considered an interesting alternative. 3,4 Besides the common utilisation of Ni and Pt for HER, Pd presents very good catalytic properties and it has also been used for hydrogenation reactions, 5,6 mainly as dispersed particles in low cost substrates. [7][8][9] For this purpose, Pd electroless baths have been improved and the respective deposits investigated; 10-13 reports on its use to prepare membranes 14,15 and in electronic components 16,17 reveal the increasing interest on electroless Pd.The behaviour towards HER of Ni based alloys, namely Ni-P is still a controversial since the alloy P content seems to be critical for the catalytic activity of the electrode. Paseka 18,19 endorses that some of these materials are electroactive for the hydrogen evolution reaction, while others, especially electrodes with high phosphorus content, (>12.5% at.) are inactive. Buchardt et al. 20,21 attribute the good performance of these electrodes to the amorphous structure. Other authors 22,23 support that films electrocatalytic activity does not depend solely on the phosphorus content, but would also be related to the preparation met...
