Abstract
The method of synthesis of bimetallic Pd–Ag pentagonally structured catalyst “nanostar” on the surface of Pd-23%Ag alloy films has been developed. The resulting catalyst was studied as a highly active functional layer for methanol oxidation reaction (MOR) in alkaline media and the intensification of hydrogen transport through the Pd-23%Ag membrane in the processes of hydrogen diffusion purification. A modifying layer with a controlled size, composition and excellent electrocatalytic activity was synthesized by electrochemical deposition at a reduced current density compared to classical methods. The low deposition rate affects the formation of pentagonally structured nanocrystallites, allowing Pd and Ag particles to form well-defined structures due to the properties of the surfactant used. Electrochemical studies have demonstrated that the catalyst synthesized by the “nanostar” method shows better electrocatalytic activity in relation to MOR and demonstrates a higher peak current (up to 17.82 µA cm−2) in comparison with one for the catalyst synthesized by the “nanoparticle” method (up to 10.66 µA cm−2) in a cyclic voltammetric study. The nanostar catalyst electrode releases the highest current density (0.25 µA cm−2) for MOR and demonstrates higher catalytic activity for the oxidation of possible intermediates such as sodium formate in MOR. In the processes of diffusion membrane purification of hydrogen, a multiple increase in the density of the penetrating flux of hydrogen through the membranes modified by the “nanostar” catalyst (up to 10.6 mmol s−1 m−2) was demonstrated in comparison with the membranes modified by the “nanoparticles” method (up to 4.49 mmol s−1 m−2). Research data may indicate that the properties of the developed pentagonally structured catalyst “nanostar” and its enhanced activity with respect to reactions involving hydrogen increase the desorption activity of the membrane, which ultimately accelerates the overall stepwise transfer of hydrogen across the membrane.
Highlights
According to the latest research in the field of nanomaterials [1,2,3,4,5,6,7,8], nanoparticles of noble metals are already widely used in almost all spheres of human life and activity
Two series of samples were produced: in the first series, the catalyst was synthesized by the “nanoparticle” method; in the second series, the “nanostar” synthesis method was used
A new approach to the synthesis of a highly active bimetallic Pd–Ag catalyst with a completely new surface morphology never achieved by other methods has been demonstrated
Summary
According to the latest research in the field of nanomaterials [1,2,3,4,5,6,7,8], nanoparticles of noble metals are already widely used in almost all spheres of human life and activity. A class of bimetallic nanoparticles became the most preferable which is conditioned by a strong synergistic effect with increased catalytic activity and durability, compared to monometallic analogues [15]. In this way, the most promising approach is to regulate the reactivity of palladium by doping it with silver [16,17,18,19,20]. Based on the theory of d-bands [21] and the calculations of Hammer and Nørskov [22], the center of the d-zone of palladium with a lattice value of 3.89 Å shifts up when combined with silver with a lattice value of 4.09 Å [23], which leads to greater adsorption of the OH– ion and, to an increase in the rate of oxidation of alcohols [17]
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