Role of Ni in Bimetallic PdNi Catalysts for Ethanol Oxidation Reaction

Abstract

Bimetallic PdNi catalysts have garnered great interest in the study of ethanol oxidation reactions (EORs), though mechanistic insights into their catalytic performances are lacking, which hinders further improvement and rational design of the next generation of PdNi catalysts. As such, density functional theory (DFT) calculations were performed for six key elementary reactions using four model catalysts, one with pure Pd and three for PdNi. DFT results indicate that the reduced catalytic activities observed experimentally when Ni atoms were placed under Pd layers are the result of an increase in the reaction barrier for CH3COOH formation. Further analysis illustrated that this is largely owing to the charge transfer from the Ni to the Pd atoms. On the other hand, the enhanced activities of the PdNi catalysts with respect to pure Pd catalysts in EORs when Ni atoms are exposed at the catalyst surfaces are due to the lowering of the reaction barrier toward C–C bond cleavage and increasing of that toward C–O bond coupling. Therefore, surface Ni atoms are responsible for the superior activity of the PdNi catalysts in EORs. Further analysis of DFT results suggests that the reaction barriers of the C–C bond cleavage and the C–O bond coupling approach similar values when the composition of surface Ni atoms in a PdNi catalyst reaches about 44%. To achieve a complete EOR, the estimated surface Ni atoms should be as high as 77%. However, stability may become a concern for catalysts with such a high exposure of Ni atoms at the catalyst surface.

Binary Pd−Ni Nanoalloy Particles over Carbon Support with Superior Alkaline Formate Fuel Electrooxidation Performance

“…[12][13] As such, DFFCs currently need potential efficient and stable catalysts for widespread commer-cial applications. [17] When considering advancements in Pd-based anode catalysts for alkaline formate oxidation, transition metal alloying has been shown to increase the alcohol and formic acid/formate fuel oxidation capabilities [5,[18][19][20][21] and to the best of our knowledge, alkaline formate oxidation using Pd-transition metal alloy catalysts has seldom been studied and is largely unexplored. [14][15][16] However, there is an imminent need for performance improvements in Pd catalysts in terms of their efficiency and durability before they can be effectively utilized in alkaline DFFCs.…”

“…Palladium is the catalyst that has shown the most promising prospects for enhanced liquid-fuel oxidation kinetics in alkaline media and that could effectively replace platinum. [17] When considering advancements in Pd-based anode catalysts for alkaline formate oxidation, transition metal alloying has been shown to increase the alcohol and formic acid/formate fuel oxidation capabilities [5,[18][19][20][21] and to the best of our knowledge, alkaline formate oxidation using Pd-transition metal alloy catalysts has seldom been studied and is largely unexplored. Previous reports suggest that the formate oxidation reaction on the Pd surface proceeds through the decomposition of COO À into CO 3 2À in alkaline medium.…”

“…Previous reports suggest that the formate oxidation reaction on the Pd surface proceeds through the decomposition of COO À into CO 3 2À in alkaline medium. [17] When considering advancements in Pd-based anode catalysts for alkaline formate oxidation, transition metal alloying has been shown to increase the alcohol and formic acid/formate fuel oxidation capabilities [5,[18][19][20][21] and to the best of our knowledge, alkaline formate oxidation using Pd-transition metal alloy catalysts has seldom been studied and is largely unexplored. Alloy catalysts of Pd with Au or Cu have been reported with marginal increases in the alkaline formate oxidation performance.…”

One‐pot synthesis of Pd‐MoO 2 /C by microwave sintering as an efficient electrocatalyst for ethanol oxidation reaction

“…Miao et al performed density functional theory (DFT) calculations on the PdNi catalysts. They found that when the estimated Ni atoms on the catalyst surfaces reached up to 77%, the PdNi catalysts could attain a complete EOR . Mondal et al fabricated PdCoNi/C by ethylene glycol reduction method.…”

“…They found that when the estimated Ni atoms on the catalyst surfaces reached up to 77%, the PdNi catalysts could attain a complete EOR. 10 Mondal et al fabricated PdCoNi/C by ethylene glycol reduction method. They described that the PdCoNi/C particles demonstrated higher EOR activity than Pd/C catalysts.…”