Acesso a composições múltiplas num único catalisador

Continuous-composition spread (CCS) makes possible the deposition of a wide range of compositions [1]. Initially designed for integrated circuits, the concept has been used in different fields, such as luminescent materials and transistors. In electrocatalysis, the first CCS approach was developed by Jeon et al. [2] who obtained 63 different compositions of PtRuCu (by sputtering) that were used to electro-oxidize methanol. Despite the advantage of synthesizing several compositions at once, the procedure demands expensive magnetron sputter guns/deposition chambers that remain unavailable for most researchers worldwide. Here we describe a simple procedure based on potentiostatic electrodeposition which allows the simultaneous making of a range of compositions. In this work, binary PtRh electrodeposits were tested, since their electrochemical behavior is well described in the literature. Firstly, a solution containing Pt or Rh ions (separately) was dropped in one of the ends of a capillary electrochemical cell, while a potential of 0.05 V was applied to a gold wire (0.25 mm of diameter) that served as working electrode (WE). Once the ions reached the wire a cathodic current was detected, that allowed us to estimate the diffusion coefficients of the precursor salts (H2PtCl6 and RhCl3). After that, another gold wire (WE) was placed inside the cell and solutions containing both precursors were added to it in opposite sides. Then, E = 0.05 V (vs. RHE) was applied to the WE to reduce both metals while a known concentration gradient was established. Once obtained, the composition of the PtRh film was determined by electron probe microanalysis and sections of 1 mm of this substrate were subsequently accessed by cyclic voltammetry in a second electrochemical cell, specially designed for this purpose. Fig. 1 shows six illustrative voltammetric profiles, but altogether 26 different atomic compositions were accessed. Results demonstrate the potential of this approach to perform compositional studies in a single piece of substrate and open new perspectives of studies with relative low cost and less time-demanding in catalysis and electrocatalysis.