An Enhanced Anode based on Polymer-Coated Carbon Black for use as a Direct Methanol Fuel Cell Electrocatalyst

Formation of a PVP-protected C/UO2/Pt catalyst in a direct ethanol fuel cell

In order to solve the problem that UO₂ in direct ethanol fuel cell anode catalysts is easily lost in acidic solution, resulting in the degradation of catalytic performance, this paper prepared a C/UO₂/PVP/Pt catalyst in three steps by adding polyvinylpyrrolidone (PVP). The test results by XRD, XPS, TEM and ICP-MS showed that PVP had a good encapsulation effect on UO₂, and the actual loading rates of Pt and UO₂ were similar to the theoretical values. When 10% PVP was added, the dispersion of Pt nanoparticles was significantly improved, which reduced the particle size of Pt nanoparticles and provided more ethanol electrocatalytic oxidation reaction sites. The test results by electrochemical workstation showed that the catalytic activity as well as the stability of the catalysts were optimized due to the addition of 10% PVP.

Catalyst overcoating engineering towards high-performance electrocatalysis

Clean and sustainable energy needs the development of advanced heterogeneous catalysts as they are of vital importance for electrochemical transformation reactions in renewable energy conversion and storage devices. Advances in nanoscience and material chemistry have afforded great opportunities for the design and optimization of nanostructured electrocatalysts with high efficiency and practical durability. In this review article, we specifically emphasize the synthetic methodologies for the versatile surface overcoating engineering reported to date for optimal electrocatalysts. We discuss the recent progress in the development of surface overcoating-derived electrocatalysts potentially applied in polymer electrolyte fuel cells and water electrolyzers by correlating catalyst intrinsic structures with electrocatalytic properties. Finally, we present the opportunities and perspectives of surface overcoating engineering for the design of advanced (electro)catalysts and their deep exploitation in a broad scope of applications.

PtRu nanoparticles embedded in nitrogen doped carbon with highly stable CO tolerance and durability

As is well known, the lower durability and sluggish methanol oxidation reaction (MOR) of PtRu alloy electrocatalyst blocks the commercialization of direct methanol fuel cells (DMFCs). Here, we design a new PtRu electrocatalyst, with highly stable CO tolerance and durability, in which the PtRu nanoparticles are embedded in nitrogen doped carbon layers derived from carbonization of poly(vinyl pyrrolidone). The newly fabricated electrocatalyst exhibits no loss in electrochemical surface area (ECSA) and MOR activity after potential cycling from 0.6-1.0 V versus reversible hydrogen electrode, while commercial CB/PtRu retains only 50% of its initial ECSA. Meanwhile, due to the same protective layers, the Ru dissolution is decelerated, resulting in stable CO tolerance. Methanol oxidation reaction (MOR) testing indicates that the activity of newly fabricated electrocatalyst is two times higher than that of commercial CB/PtRu, and the fuel cell performance of the embedded PtRu electrocatalyst was comparable to that of commercial CB/PtRu. The embedded PtRu electrocatalyst is applicable in real DMFC operation. This study offers important and useful information for the design and fabrication of durable and CO tolerant electrocatalysts.

Highly methanol-tolerant platinum electrocatalyst derived from poly(vinylpoyrrolidone) coating

The design and fabrication of a methanol-tolerant electrocatalyst is still one of the most important issues in direct methanol fuel cells (DMFCs). Here, we focus on the design of a cathodic electrocatalyst in DMFCs and describe a new methanol-tolerant electrocatalyst fabricated from poly(vinylpyrrolidone) (PVP) coating on platinum nanoparticles assisted by hydrogen bonding between PVP and polybenzimidazole (PBI). The PVP layer has a negligible effect on the oxygen reduction reaction (ORR) activity, while the methanol oxidation reaction is retarded by the PVP layer. The PVP-coated electrocatalyst shows higher ORR activity under various methanol concentrations in the electrolyte, suggesting that the PVP-coated electrocatalyst has a higher methanol tolerance. Also, the PVP-coated electrocatalyst loses only 14% of the electrochemical surface area after 5000 potential cycles from 0.6-1.0 V versus the reversible hydrogen electrode, indicating better Pt stability than non-coated (27%) and commercial (38%) electrocatalysts due to the unique sandwich structure formed by the PVP and PBI. The power density of the PVP-coated electrocatalyst is four to five times higher compared to non-coated and commercial electrocatalysts with 12 M methanol feeding to the anode side, respectively. PVP coating is important for the enhancement of Pt stability and methanol tolerance. This study offers a new method for preparing a low-cost and high-methanol-tolerant Pt electrocatalyst, and useful information for real DMFC application to eliminate the methanol crossover problem in the cathode side.

Simultaneous enhancements in stability and CO tolerance of Pt electrocatalyst by double poly(vinyl pyrrolidone) coatings

CO poisoning and low durability of the anodic electrocatalyst is one of the obstacles restricting the practical application of direct methanol fuel cells (DMFCs).

Stable CO anti-poisoning and high durability of a Pt electrocatalyst supported on carbon nanotubes

Stable CO anti-poisoning and high durability of an anodic electrocatalyst are very important for direct methanol fuel cells (DMFCs).

High Performance Palladium Supported on Nanoporous Carbon under Anhydrous Condition

Due to the high cost of polymer electrolyte fuel cells (PEFCs), replacing platinum (Pt) with some inexpensive metal was carried out. Here, we deposited palladium nanoparticles (Pd-NPs) on nanoporous carbon (NC) after wrapping by poly[2,2'-(2,6-pyridine)-5,5'-bibenzimidazole] (PyPBI) doped with phosphoric acid (PA) and the Pd-NPs size was successfully controlled by varying the weight ratio between Pd precursor and carbon support doped with PA. The membrane electrode assembly (MEA) fabricated from the optimized electrocatalyst with 0.05 mgPd cm-2 for both anode and cathode sides showed a power density of 76 mW cm-2 under 120 °C without any humidification, which was comparable to the commercial CB/Pt, 89 mW cm-2 with 0.45 mgPt cm-2 loaded in both anode and cathode. Meanwhile, the power density of hybrid MEA with 0.45 mgPt cm-2 in cathode and 0.05 mgPd cm-2 in anode reached 188 mW cm-2. The high performance of the Pt-free electrocatalyst was attributed to the porous structure enhancing the gas diffusion and the PyPBI-PA facilitating the proton conductivity in catalyst layer. Meanwhile, the durability of Pd electrocatalyst was enhanced by coating with acidic polymer. The newly fabricated Pt-free electrocatalyst is extremely promising for reducing the cost in the high-temperature PEFCs.

A Highly-Durable CO-Tolerant Poly(vinylphosphonic acid)-Coated Electrocatalyst Supported on a Nanoporous Carbon

For direct methanol fuel cells (DMFCs) to be commercialized, the durability of the anodic electrocatalyst needs to be highly considered, especially under high temperature and methanol concentration conditions. Low durability caused by carbon corrosion as well as carbon monoxide (CO) poisoning of the platinum nanoparticles (Pt-NP) leads to a decrease in active Pt-NPs and increases inactive Pt-NPs covered by CO species. In this study, we deposited Pt-NPs on poly[2,2'-(2,6-pyridine)-5,5'-bibenzimidazole] (PyPBI)-wrapped nanoporous carbon (NanoPC) and coated the as-synthesized electrocatalyst with poly(vinylphosphonic acid) (PVPA). The durability of the as-synthesized NanoPC/PyPBI/Pt/PVPA was tested in 0.1 M HClO4 electrolyte at 60 °C by cycling the potential from 1.0 to 1.5 V relative to RHE, and the results indicated that NanoPC/PyPBI/Pt/PVPA showed ∼5 times better durability relative to that of the commercial CB/Pt. The methanol oxidation reaction (MOR) of the electrocatalyst was tested before and after the potential cycling in the presence of 4 or 8 M methanol at 60 °C and found that the CO tolerance of the electrocatalyst was ∼3 times higher than that of the commercial CB/Pt. Such a higher CO tolerance is due to the coating of the PVPA, which was proven by an EDX mapping measurement. The NanoPC/PyPBI/Pt/PVPA showed a high durability and CO tolerance under high temperature and high methanol concentration conditions, indicating that the electrocatalyst could be used in real fuel applications.

Facile enhancement of the durability and CO tolerance of CB/PtRu by poly(2,5-benzimidazole) coating via in situ polymerization

Ru nanoparticles were stabilized when coated with a polymer formed in situ from its monomer.

Remarkably durable platinum cluster supported on multi-walled carbon nanotubes with high performance in an anhydrous polymer electrolyte fuel cell

Reducing platinum (Pt) usage in the polymer electrolyte fuel cells (PEFCs) has become one of the main issues in the global commercialization of PEFCs.

Bottom-up design of a stable CO-tolerant platinum electrocatalyst with enhanced fuel cell performance in direct methanol fuel cells

Here, we design a stable CO tolerant platinum electrocatalyst via a bottom-up method, in which the platinum nanoparticles are deposited on carbon black after coating with polybenzimidazole (PBI) and poly(vinyl pyrrolidone) (PVP).

Novel Metal Nanomaterials and Their Catalytic Applications

In the rapidly developing areas of nanotechnology, nano-scale materials as heterogeneous catalysts in the synthesis of organic molecules have gotten more and more attention. In this review, we will summarize the synthesis of several new types of noble metal nanostructures (FePt@Cu nanowires, Pt@Fe₂O₃ nanowires and bimetallic Pt@Ir nanocomplexes; Pt-Au heterostructures, Au-Pt bimetallic nanocomplexes and Pt/Pd bimetallic nanodendrites; Au nanowires, CuO@Ag nanowires and a series of Pd nanocatalysts) and their new catalytic applications in our group, to establish heterogeneous catalytic system in "green" environments. Further study shows that these materials have a higher catalytic activity and selectivity than previously reported nanocrystal catalysts in organic reactions, or show a superior electro-catalytic activity for the oxidation of methanol. The whole process might have a great impact to resolve the energy crisis and the environmental crisis that were caused by traditional chemical engineering. Furthermore, we hope that this article will provide a reference point for the noble metal nanomaterials' development that leads to new opportunities in nanocatalysis.

Facile Enhancement in CO-Tolerance of a Polymer-Coated Pt Electrocatalyst Supported on Carbon Black: Comparison between Vulcan and Ketjenblack

The CO poisoning and low durability of the anode platinum electrocatalyst in the direct methanol fuel cell (DMFC) are the two crucial obstacles of the wide commercialization of the DMFC. In this study, we synthesized two different electrocatalysts using VulcanXC-72R (VC) and Ketjenblack (KB) as the carbon supporting material for the methanol oxidation reaction (MOR) and long-term durability test, in which the carbon supporting materials were wrapped by poly[2,2'-(2,6-pyridine)-5,5'-bibenzimidazole] (PyPBI) before the platinum deposition and the fabricated electrocatalysts were coated by the poly(vinylphosphonic acid) (PVPA) via the base-acid reaction. We have found that the as-prepared KB/PyPBI/Pt/PVPA shows a higher durability (7% loss in ECSA) under the potential cycling from 1.0 to 1.5 V vs. RHE compared to that of the VC/PyPBI/Pt/PVPA, which showed a 20% loss in ECSA after 10 000 cycle-durability test. Meanwhile, the KB/PyPBI/Pt/PVPA shows a higher CO tolerance before and after the durability test compared to that of the VC/PyPBI/Pt/PVPA, especially under very high methanol concentration (4 M and 8 M), which is close to the practical application of the DMFC. The observed higher CO tolerance is due to the higher amount of the PVPA (14.6 wt %) in the KB/PyPBI/Pt/PVPA caused by the higher specific surface area of the KB (1232 m(2)/g) compared to the VC (235 m(2)/g).

Durable Pt Electrocatalyst Supported on a 3D Nanoporous Carbon Shows High Performance in a High-Temperature Polymer Electrolyte Fuel Cell

In this paper, we used a 3D nanoporous carbon (NanoPC) with a high specific surface area of 1037 m(2)/g as a carbon support for high-temperature polymer electrolyte fuel cell, and fabricated an electrocatalyst (NanoPC/PyPBI/Pt) having platinum nanoparticles of ∼2.2 nm diameter deposited on the NanoPC that was wrapped by poly[2,2'-(2,6-pyridine)-5,5'-bibenzimidazole] (PyPBI). Even after 10,000 start-up/shutdown cycles in the range of 1.0 to 1.5 V vs. RHE, the NanoPC/PyPBI/Pt showed almost no loss in electrochemical surface area (ECSA), which indicated much higher durability than those of a CB/PyPBI/Pt (∼32% loss), in which conventional carbon black (CB) was used in place of the NanoPC, and conventional CB/Pt (∼46% loss). The power density of the NanoPC/PyPBI/Pt was 342 mW/cm(2), which was much higher than those of the CB/PyPBI/Pt (183 mW/cm(2)) and CB/Pt (115 mW/cm(2)).