TPD studies of hydrogen adsorption on group VIII metals

Nanostructured robust cobalt metal alloy based anode electro-catalysts exhibiting remarkably high performance and durability for proton exchange membrane fuel cells

“…The enrichment of iridium on the surface of the nanocrystalline Co 1Àx (Ir x ) electro-catalyst is a result of heat treatment of all the synthesized alloy electrocatalysts in an (Ar + 6.5% H 2 ) atmosphere at 200 C. This can be attributed to higher adsorption enthalpy of hydrogen on Ir than Co which facilitates segregation of iridium on the electro-catalyst surface. [82][83][84] Similar results have been reported for carbon supported Pd-Co core-shell nanoparticles, where surface segregation was observed in which Pd migrated from the bulk to the surface forming a thin over-layer, due to heat treatment in a H 2 atmosphere. 85 This rearrangement of Pd and Co was attributed to the higher adsorption enthalpy of hydrogen and consequently, stronger affinity of hydrogen on Pd than Co. A similar phenomenon can therefore be expected to occur in the case of the Co-Ir alloys discussed herein.…”

Highly Active and Durable Core–Shell fct-PdFe@Pd Nanoparticles Encapsulated NG as an Efficient Catalyst for Oxygen Reduction Reaction

“…This STEM-EDS mapping further reveals the double shell formation around the PdFe-alloy NPs, which is beneficial for reducing the aggregation of PdFe-alloy NPs and enhancing the catalytic activity and durability of the catalyst, is well-matched with the Figure S7b–f. During the synthesis of highly ordered fct-PdFe@Pd@NG hybrid at a temperature of 500 °C, because of the surface segregation effect, Pd could be migrated around the surface of the PdFe-alloy NPs, resulting in perfect core–shell formation with PdFe core and Pd shell in the core–shell hybrid. , This migration of Pd is also due to the larger hydrogen enthalpy of adsorption, as reported in the literature. ,,, To further authorize the Pd shell around the PdFe-alloy NP core in the core–shell fct-PdFe@Pd@NG hybrid, the core–shell fct-PdFe@Pd single NP was characterized by atomic-scale chemical mapping (Figure S11a), which clearly displays the distinct contrast between PdFe core and Pd shell in the hybrid. This further confirms the individual distribution of the Pd and Fe maps (Figure S11b,c) and an overlay of PdFe-alloy core within the Pd-enriched cell (Figure S11d).…”

“…33,34 This migration of Pd is also due to the larger hydrogen enthalpy of adsorption, as reported in the literature. 13,15,35,36 To further authorize the Pd shell around the PdFe-alloy NP core in the core−shell fct-PdFe@Pd@NG hybrid, the core−shell fct-PdFe@Pd single NP was characterized by atomic-scale chemical mapping (Figure S11a), which clearly displays the distinct contrast between PdFe core and Pd shell in the hybrid. This further confirms the individual distribution of the Pd and Fe maps (Figure S11b,c) and an overlay of PdFe-alloy core within the Pd-enriched cell (Figure S11d).…”

Pt-Decorated PdCo@Pd/C Core−Shell Nanoparticles with Enhanced Stability and Electrocatalytic Activity for the Oxygen Reduction Reaction

“…9 In addition, differences in the gas adsorption energy on two metals can also induce surface segregation. 10 In our case, upon annealing at high temperatures, the PdCo/C alloys undergo phase segregation, in which the Pd migrates to the surface, forming a pure Pd overlayer on the bulk alloys, since the adsorption enthalpy of H on Pd is higher than on Co. 11 The deposition of Pt was spontaneous on the PdCo@Pd surface because the equilibrium electrode potential of the PtCl 4…”