Pt/C Decorated with N-Doped Carbon Layers as a Highly Durable Electrocatalyst for the Oxygen Reduction Reaction

Abstract

Exploiting advanced electrocatalysts for the sluggish oxygen reduction reaction (ORR) of the cathode is greatly crucial for proton-exchange membrane fuel cell (PEMFC) commercial application but still exhibit a significant challenge, especially the stability issues that have drawn attractive attention. Therefore, we introduced a nitrogen-doped carbon layer into the Pt/C surface, which not only prevents aggregation of Pt nanoparticles but also endows the electrocatalyst with enhanced performance without hiding the internal Pt active sites. The accelerated durability tests show an ignorable ORR activity loss (10 mV) in the as-prepared Pt/C@NC-0.06 sample compared to the pristine Pt/C catalyst (37 mV) after 5000 cyclic voltammetry cycles. Furthermore, in comparison to the pristine Pt/C catalyst (0.28 mA cm–2), the as-obtained Pt/C@NC-0.06 sample exhibits 2.32-fold improvement for the specific activity. The enhanced ORR properties of the Pt/C@NC-X catalyst in this work supplies a promising way to facilitate the electrocatalytic performance of catalysts in PEMFCs.

Does the Encapsulation Strategy of Pt Nanoparticles with Carbon Layers Really Ensure Both Highly Active and Durable Electrocatalysis in Fuel Cells?

“…ADT conditions, UPL, and number of cycles used in previous studies to evaluate the durability of encapsulated Pt NP catalysts. − For comparison, U.S. Department of Energy (DOE) and New Energy and Industrial Technology Development Organization of Japan (Japan NEDO) protocols for evaluating catalyst durability are shown. Different from the Japan NEDO protocol, which is based on conventional half-cell conditions, , the U.S. DOE protocol recommends evaluation in real PEMFCs.…”

“…To alleviate catalyst deactivation, introduction of a barrier on active Pt NPs has recently been highlighted as a promising strategy. − It has been proposed that encapsulation of Pt NPs with thin layers has the potential to prevent their dissolution, detachment, and agglomeration. For instance, covering Pt NPs with a silica layer led to an enhanced durability of the Pt NPs, as supported by the insignificant changes in both the electrochemical active surface area (ECSA) and particle size after >1000 cycles of the accelerated durability test (ADT) .…”

“…This is because of the unavoidable blockage of the active Pt surface and the reduction in the fraction of exposed Pt sites. However, such prospects have often been disproved based on the almost comparable or even better ORR activity of fresh C@Pt/C catalysts than that of carbon-free Pt/C. − ,− ,, …”

“…Several hypotheses have been proposed to rationalize the above-mentioned counterintuitive phenomena. − ,− ,, As the main catalytic sites, the Pt sites in C@Pt/C are considered responsible for ORR activity, − ,− and possible modification of the intrinsic catalytic activity (i.e., turnover) of the Pt NPs has been suggested to be induced by their interaction with the carbon layers. ,− Moreover, the formation of the carbon layer at the Pt surface can prevent the undesirable poisoning of sulfonate from the ionomer, resulting in enhanced activity and durability in the fuel cell device . In contrast, it has been proposed that the Pt NPs buried under the carbon layers are assumed as spectators (or promotors) and their carbon shell functions as the main catalytic site for the ORR. ,, The latter suggestion is typically for C@Pt/C catalysts with heteroatom moieties (e.g., N, S, etc.)…”

Evaluating the Growth of Ceria-Modified N-Doped Carbon-Based Materials and Their Performance in the Oxygen Reduction Reaction

“…Therefore, efficient catalysts must be developed to increase the reaction rate [ 18 , 19 , 20 ]. At present, commercial precious metal Pt-based materials are considered to effectively catalyze the ORR; however, they are limited by high cost and poor stability [ 21 , 22 , 23 ]. Therefore, we consider enhancing the applicability of the catalysts in terms of reducing the cost and improving catalyst stability to increase their efficiency in the ORR.…”