Electrodeposited Rh and Rh–Cu Alloys as Ethanol-Tolerant Electrocatalysts for Oxygen Reduction in Alkaline Media

Abstract

In this study, rhodium-copper alloys of different compositions are electrodeposited on graphite electrode from aqueous solutions. The bulk compositions of these alloys are determined using energy dispersive X-ray analysis and surface morphologies are investigated by scanning electron microscopy. The catalytic performance of these alloys in oxygen reduction reaction (ORR) in alkaline media is investigated by linear sweep voltammetry on rotating disk electrode assembly. The number of electrons transferred per O 2 molecule (n) obtained at different potentials is four indicating full reduction of oxygen to hydroxide ion. It is shown that Rh-Cu alloys are better electrocatalysts than Rh with Rh-Cu-2 having 68.7% copper is the best in the series. Also, the resistance of the Rh-Cu electrocatalysts towards ethanol poisoning is investigated and it is found that the addition of Cuenhanced ethanol tolerance in the course of the ORR. Finally, it has been shown that the electrocatalysts have good stability in alkaline solution.

A Study of Cu‐Rh Electrodeposition**

“…In the Cu−Rh system, we observed an anomalous electrodeposition behaviour since the amount of Rh deposited, even though it is a more noble metal, was lower than the amount of deposited Cu. The same conclusion can be derived from a study by Global et al [26] . In our experiments, applying a significantly higher negative potential such as −0.8 V vs Ag/AgCl increased the Rh content at the deposit, especially in the bath containing a higher Rh amount.…”

“…In previous reports, Cu deposition has been described as a two‐step process, with the first electron transfer being the rate‐determining step, whereas Rh is known to be a one‐step reduction process [24,25] . Some earlier studies of co‐deposition of these metals have reported a single reduction feature due to the simultaneous reduction of Cu and Rh, whereas others observed two reduction events [8,26] . Our results show a two‐step reduction process for Cu and no additional reduction peak for the reduction of Rh.…”

“…[24,25] Some earlier studies of codeposition of these metals have reported a single reduction feature due to the simultaneous reduction of Cu and Rh, whereas others observed two reduction events. [8,26] Our results show a two-step reduction process for Cu and no additional reduction peak for the reduction of Rh. However, Figure 1 shows that the reduction potentials of the co-deposited films differ from those of the single metal deposited films.…”

A study of Cu-Rh electrodeposition

“…In the Cu-Rh system, we observed an anomalous electrodeposition behaviour since the amount of Rh deposited, even though it is a more noble metal, was lower than the amount of deposited Cu. The same conclusion can be derived from a study by Global et al [20] In our experiments, applying a significantly higher negative potential such as -0.8 V vs Ag/AgCl increased Rh content at the deposit, especially in the bath containing a higher Rh amount. Further analysis of the co-deposition and the effect of the deposition potential on the morphology and oxidation state of the deposits was conducted with physical characterization techniques such as SEM, XPS, and XRD.…”

“…[18,19] Some earlier studies of co-deposition of these metals have reported a single reduction feature due to the simultaneous reduction of Cu and Rh, whereas others observed two reduction events. [20,21] Our results show a two-step reduction process for Cu and no additional reduction peak for the reduction of Rh. However, Figure 1 shows that the reduction potentials of the co-deposited films differ from those of the single metal deposited films.…”