Stability Of Pt Electrocatalysts Research Articles

Superior durability and stability of Pt electrocatalyst on N-doped graphene-TiO2 hybrid material for oxygen reduction reaction and polymer electrolyte membrane fuel cells

To accelerate the commercialization of polymer electrolyte membrane fuel cells (PEMFCs), studies on durable support materials that can replace conventional carbon-based supports are being conducted. In this study, we prepared N-doped TiO2 on the N-doped graphene hybrid material (NG-TiON) using a facile hydrothermal method to develop a support for a platinum catalyst with both high stability and electrical conductivity. As-prepared NG-TiON supports were characterized using transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The stability of the Pt/NG-TiON catalyst was considerably improved compared to that of Pt/C, and their high oxygen reduction reaction (ORR) activities were similar. The durabilities of the Pt catalysts were investigated using the accelerated durability test. Single cell measurements revealed that Pt/NG-TiON has high stability and corrosion resistance with a performance degradation rate of only 9 % after 5000 accelerated durability test cycles while the performance of Pt/C decreased 83 %.

Boosting CO tolerance and stability of Pt electrocatalyst supported on sulfonated carbon nanotubes

CO tolerance and stability are of prominent importance for the anodic electrocatalyst utilized in direct methanol fuel cells (DMFCs). Due to the electrochemical instability of Ru atoms, the state-of-the-art DMFC anodic electrocatalyst (PtRu/C) is unable to survive for long time. Here, we report a newly designed Pt electrocatalyst with robust CO tolerance and stability after coating with poly(vinyl pyrrolidone) (PVP). Electrochemically active surface area (ESA) is negligibly affected by the PVP decoration; meanwhile, almost undetectable ESA loss is obtained for the PVP decorated Pt electrocatalyst. However, the ESA degradations for non-decorated and commercial CB/Pt electrocatalysts are found to be 30% and 40%, respectively. The improved stability is ascribed to the strong interaction between PVP and sulfonated carbon nanotubes. Also, the CO tolerance evaluated from the methanol oxidation reaction is ∼3 and 3.5 fold higher compared to non-decorated and commercial CB/Pt electrocatalysts, respectively, which is attributed to the hydrophilic PVP polymer accelerating the water absorption and formation of Pt(OH)ads species to re-activate nearby CO poisoned Pt nanoparticles. Thus, decoration with PVP polymer can simultaneously promote the stability and CO anti-poisoning of Pt electrocatalyst.

Origin of achieving the enhanced activity and stability of Pt electrocatalysts with strong metal-support interactions via atomic layer deposition

The enhancement of catalyst activity and stability by controlling the metal-support interaction is significantly important for the long-term operation of polymer electrolyte membrane fuel cells (PEMFCs). In this work, an extremely stable electrocatalyst of platinum nanoparticles (Pt NPs) immobilized on a carbon support via the bridge layer of nitrogen-doped tantalum oxide (N-Ta2O5) is proposed. The novel N-Ta2O5 bridge layer in between the Pt NPs and carbon surface is synthesized by an atomic layer deposition technique (ALD). It effectively prevents Pt nanocrystals from detachment, migration, and aggregation during the PEMFCs’ operation. Electrochemical results indicate that the Pt/N-ALDTa2O5/C electrocatalyst exhibits superior durability and sufficient catalytic activity for the oxygen reduction reaction, compared to the Pt/C catalyst. X-ray absorption spectroscopy illustrates the strong interactions between the Pt NPs and the N-Ta2O5-decorated carbon support. It is found that the bridge layer of N-Ta2O5 alters the electronic structure of the Pt nanocrystals and contributes to the significantly enhanced catalytic activity and durability for the Pt/N-ALDTa2O5/C catalyst. This strategy, by using ALD of N-doped metal oxide to tune the metal-support interface and results in strong metal-support interactions, will benefit the future design of new-generation electrocatalysts with even better activity and long-term durability for PEMFCs application.

Insight Observation of Simultaneously Enhanced CO Tolerance and Stability of Pt Electrocatalysts Decorated with Oxygen Vacancy Rich Cerium Oxide

AbstractHigh and stable catalytic activity for the methanol oxidation reaction (MOR) and CO tolerance are essential for anodic electrocatalysts in direct methanol fuel cells (DMFCs). Here, we report a new method to simultaneously boost the CO tolerance as well as MOR stability of a Pt electrocatalyst by decoration with cerium oxide (CeOx). Detailed mechanistic investigations revealed that CeOx decoration can significantly improve the MOR stability of the Pt electrocatalyst due to the formation of Pt−O−Ce bonds ascribed to the high number of oxygen vacancies of CeOx. The simultaneously improved CO anti‐poisoning property of the CeOx decorated Pt electrocatalyst is resulting from Ce(OH)3, which is formed by the adsorption of water to CeOx. Ce(OH)3 could accelerate the formation of Pt(OH)ads species to recover CO poisoned Pt nanoparticles. At the same time, the CO species could also be oxidized by the lattice oxygen from CeOx. The fuel cell performance of the CeOx decorated Pt electrocatalyst is therefore higher than that of bare Pt electrocatalyst.

Anchoring ultrafine Pt electrocatalysts on TiO2-C via photochemical strategy to enhance the stability and efficiency for oxygen reduction reaction

The activity and stability of Pt electrocatalysts are crucial issues for energy conversion systems involving oxygen reduction reaction (ORR). In this work, the ultrafine Pt nanoparticles were in situ reduced by the photogenerated electrons on TiO2 surface so that most of them selectively anchored around the TiO2 nanocrystals. The presence of well-dispersed TiO2 on carbon surface strengthened the metal-support interaction, giving rise to the improved ORR catalytic activity with ∼49 mV positive shift of half-wave potential as compared to commercial 20 wt% Pt/C. More importantly, the Pt/TiO2-C catalysts exhibited a more durable performance after 10,000 cycles in terms of the decrease in electrochemical surface area (0.8%) and mass activity (0.9%), much lower than those of Pt/C (10.2% and 33.3%). The high-temperature durability test also revealed a much higher retention of ORR activity. The results demonstrated that anchoring Pt on well-dispersed TiO2-decorated carbon would be an effective strategy to enhance the ORR performance by strong metal-support interaction, which facilitated the electron transfer during catalytic reactions as well as prevented Pt aggregation during durability test.

Strong metal-support interaction improves activity and stability of Pt electrocatalysts on doped metal oxides.

Niobium and antimony doped tin oxide loose-tubes decorated with Pt nanoparticles present outstanding mass activity and stability, exceeding those of a reference carbon-based electrocatalyst. Physico-chemical characterisation and in particular X-ray photoelectron spectroscopy demonstrate that this observation can be ascribed to the strong metal-support interaction promoting electroactivity and Pt anchoring on doped metal oxide supports.

Ab-initio study of surface oxide formation in Pt(111) electrocatalyst under influences of O2-containing intermediates of oxygen reduction reaction

The long-term stability of Pt electrocatalyst during oxygen reduction reaction (ORR) is a great challenge hampering its use as the cathode of proton exchange membrane fuel cells for automobile applications. A number of researches have reported that the surface oxide formation by diffusion of the atomic oxygen to the sublayer is important to understand its stability. Here, we focused on the study of the effects of the O2-containing intermediates of ORR such as O2 and OOH toward the diffusion of the atomic oxygen in the Pt(111) surface by using the density functional theory calculations. Using the climbing image nudged elastic band method, we found that the energy barrier for the diffusion of O in both the forward and the backward directions decreases by the presence of O2 and OOH on the Pt(111) surface. The reduction of the energy barrier in the forward direction speeds up the diffusion of O into the subsurface and hence speeds up the surface oxide formation, while the reduction of the energy barrier in the backward direction triggers the atomic oxygen moving back to the on-surface that may destroy the Pt(111) surface and therefore affect the stability of the Pt(111) substrate. These results strongly support the previous experiments. Furthermore, the Bader charge analysis suggested that by simultaneously decreasing the charge gain of the atomic oxygen at the initial state (on the surface) and the final state (inside the subsurface) may help increase the stability of the Pt surface. Experiments such as using buffer solutions or corrosion inhibitors are suggested to confirm this prediction.

High stability and activity of Pt electrocatalyst on atomic layer deposited metal oxide/nitrogen-doped graphene hybrid support

A novel nanostructured support of ZrO2/nitrogen-doped graphene nanosheets (ZrO2/NGNs) hybrid was synthesized successfully by atomic layer deposition (ALD) technology to significantly improve the activity and stability of Pt electrocatalyst. Electrochemical test shows that Pt–ZrO2/NGNs catalyst has 2.1 times higher activity towards methanol oxidation reaction (MOR) than Pt/NGNs catalyst, due to the promotion by ZrO2 to the MOR on Pt surface. Pt–ZrO2/NGNs catalyst has higher electrochemical surface area (ECSA) and better oxygen reduction reaction (ORR) activity than Pt/NGNs catalyst. Pt–ZrO2/NGNs catalyst has also demonstrated 2.2 times higher durability than that of Pt/NGNs. The enhanced activity and durability were attributed to the unique triple-interaction of ZrO2–Pt–NGNs. These findings indicate that metal oxide-metal-support is a promising catalyst structure for low temperature fuel cells.

Enhanced stability of Pt electrocatalysts by nitrogen doping in CNTs for PEM fuel cells

Electrochemical stabilities of Pt deposited on carbon nanotubes (CNTs) and nitrogen-doped carbon nanotubes (CN x ) of different nitrogen contents are compared with accelerated durability tests (ADT) for the first time. Transmission electron microscopy (TEM) images reveal the different structures of CNTs and CN x , and the decrease of Pt particle size with the nitrogen incorporation into CNTs. Based on the loss of electrochemical surface area (ESA) and TEM images, Pt/CN x exhibited much higher stability than Pt/CNTs, and the Pt stability increases with the increase of nitrogen contents in the CN x supports.