Surface Species Alteration and Oxygen Reduction Reaction Enhancement of PdCo/C Electrocatalysts Induced by Ceria Modification

Abstract

The effect of reduction temperature and CeO2 addition on the activity of PdCo/C alloy catalysts (see scheme) toward the oxygen reduction reaction (ORR) is investigated. By combining X‐ray analysis and temperature‐programmed reduction with electrochemical measurements, the relationship between phase structure, surface information and catalytic activity toward ORR of the non‐Pt PdCo catalysts is elucidated.

Electro-catalytic activity enhancement of Pd–Ni electrocatalysts for the ethanol electro-oxidation in alkaline medium: The promotional effect of CeO2 addition

“…Moreover, if the I -03 and I peak values of various catalysts shown in Table 2 are compared, two maximum for Ce 5 and Ce 15 are noted. It has been reported that CeO 2 can act as surface modifiers and/or texture promoters of the catalysts [9,10,35,37,42]. For Ce 5 , the addition of 5 wt.% CeO 2 can enrich the surface states with PdNi alloy species significantly and promote the dispersion of NPs on the support slightly.…”

“…On the other hand, it is important to mention that the T r of Ce x (x = 10-20) samples slightly moves back to T < 272 K, indicating that the surface AO x species is intensively converted to metallic surface Pd species while in the CO-stripping results, the pre-wave disappears consistently. Even though CeO 2 acts as a textural promoter and surface modifier which change the dispersion and surface composition of alloy NPs, the excessive Ce addition may retard the complete reduction of the Pd or Ni metal ions [40,42] and block the active sites. As a consequence, the change of surface species and the presence of NiO species are manifestly observed for Ce x (x = 10, 15, and 20) samples.…”

“…Among all alloy catalysts, Ce 20 has the largest hydrogen desorption area, indirectly indicative of its small NPs size. However, too much CeO 2 may block the active site and affect the electrochemical performance [37,42]. Fig.…”

“…In contrast, the morphologies of Ce 10 , Ce 15 and Ce 20 become ambiguous, resulting in the difficulty of distinguishing Pd-Ni from CeO 2 NPs. It seems that the excess amount of Ce addition may contribute to the occlusion of CeO 2 surrounding in the proximity of Pd-Ni NPs during deposition process [42] and hence the serious aggregation is inspected for Ce 10 , Ce 15 , and Ce 20 as shown in Fig. 2e-g, respectively.…”

“…In general, CeO 2 has been extensively used as a modifier in catalysts for catalytic oxidation and electrode reactions; moreover, it has been also utilized in the field of hydrogen production and hydrogen combustion [38,39]. The decisive improvement in the performance originating from the CeO 2 addition is ascribed to the increase in dispersion of alloy NPs on C supports, the stabilization of the support toward thermal sintering and of particularly importance, the modification of the surface composition of alloy catalysts [37,[40][41][42]. In other words, the outmost surface species of alloy NPs is known to be successfully tailored by an appropriate amount of CeO 2 addition [37,42].…”