Hierarchically Porous Co−N−C Cathode Catalyst Layers for Anion Exchange Membrane Fuel Cells

Anion exchange membrane fuel cells (AEMFCs) performance have significantly improved in the last decade (>1 W cm−2), and is now comparable with that of proton exchange membrane fuel cells (PEMFCs). At high current densities, issues in the catalyst layer (CL, composed of catalyst and ionomer), like oxygen transfer, water balance, and microstructural evolution, play important roles in the performance. In addition, CLs for AEMFCs have different requirements than for PEMFCs, such as chemical/physical stability, reaction mechanism, and mass transfer, because of different conductive media and pH environment. The anion exchange ionomer (AEI), which is the soluble or dispersed analogue of the anion exchange membrane (AEM), is required for hydroxide transport in the CL and is normally handled separately with the electrocatalyst during the electrode fabrication process. The importance of the AEI–catalyst interface in maximizing the utilization of electrocatalyst and fuel/oxygen transfer process must be carefully investigated. This review briefly covers new concepts in the complex AEMFC catalyst layer, before a detailed discussion on advances in CLs based on the design of AEIs and electrocatalysts. The importance of the structure–function relationship is highlighted with the aim of directing the further development of CLs for high‐performance AEMFC.

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Section: Cathode Catalyst Layer and Orr Catalystmentioning

confidence: 99%

Recent Insights on Catalyst Layers for Anion Exchange Membrane Fuel Cells

et al. 2021

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“…The catalyst showed high electrochemical surface area and electro-catalytic activity. Zhang et al [104] used carbon black and Co-zeolitic imidazolate frameworks (ZIF) as templates to control the morphology, which revealed that the smaller catalysts had a more homogeneous distribution of catalyst and ionomer and a higher power density in alkaline fuel cells. Along with high dispersion, Kotaro et al [105] determined that a monolayer of Pt on the carbon support allows for ultra-low Pt loading, high Pt utilization, and high tunability of the activity through the varying of the Pt shell.…”

Section: Morphologymentioning

confidence: 99%

Recent Advancements in the Synthesis and Application of Carbon-Based Catalysts in the ORR

Macchi¹,

Denmark²,

Le³

et al. 2021

Electrochem

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Fuel cells are a promising alternative to non-renewable energy production industries such as petroleum and natural gas. The cathodic oxygen reduction reaction (ORR), which makes fuel cell technology possible, is sluggish under normal conditions. Thus, catalysts must be used to allow fuel cells to operate efficiently. Traditionally, platinum (Pt) catalysts are often utilized as they exhibit a highly efficient ORR with low overpotential values. However, Pt is an expensive and precious metal, posing economic problems for commercialization. Herein, advances in carbon-based catalysts are reviewed for their application in ORRs due to their abundance and low-cost syntheses. Various synthetic methods from different renewable sources are presented, and their catalytic properties are compared. Likewise, the effects of heteroatom and non-precious metal doping, surface area, and porosity on their performance are investigated. Carbon-based support materials are discussed in relation to their physical properties and the subsequent effect on Pt ORR performance. Lastly, advances in fuel cell electrolytes for various fuel cell types are presented. This review aims to provide valuable insight into current challenges in fuel cell performance and how they can be overcome using carbon-based materials and next generation electrolytes.

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“…Typically, the best performing mass loading of M-N-C catalysts in membrane electrode assemblies (MEAs) are generally range from 2 to 3 mg cm −2 . [49][50][51] However, the performance of our Co 1 /CNH 700 catalyst continues to with the loading amount of the catalyst, and the loading amount for its best performance is 6.0 mg cm −2 . It is believed that the 3D radial shape and porous nature of Co 1 /CNH 700 effectively facilitates the mass transfer of reactants and products, leading to the high utilization of active sites even in thick catalyst layers (Figure S19, Supporting Information).…”

Section: Evaluation Of the Aemfc Performance Of Co 1 /Cnh 700mentioning

confidence: 99%

Flash Bottom‐Up Arc Synthesis of Nanocarbons as a Universal Route for Fabricating Single‐Atom Electrocatalysts

et al. 2021

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Atomically dispersed metal atoms on supporting materials inherit the merits of both heterogeneous and homogeneous catalysts, such as the easy separation and high durability of a heterogeneous phase and the well-structured catalytic active sites and tunable activity of a homogeneous phase. [6][7][8] The isolated metals in SACs are located on neighboring surface atoms (metal oxide, metal nitride, and carbon atoms) or coordinated with heteroatoms, such as nitrogen, sulfur, and phosphorus. [7,[9][10][11] The metal centers and their surrounding atoms can be thought of as molecular catalytic sites that proceed down a highly selective reaction pathway. [12][13][14][15][16] For a decade, a variety of synthesis strategies have been developed to realize highly active SACs. [7,[17][18][19] One of the most widely applied methods is the defect engineering strategy. [1,[20][21][22] Preformed defects on supporting materials can alter the surrounding electronic state and have been used as effective "traps" to capture metal precursors and anchor metal atoms during post-treatment. [8,23] Another popular synthetic method is the spatial confinement strategy. Despite considerable development in the field of single-atom catalysts (SACs)on carbon-based materials, the reported strategies for synthesizing SACs generally rely on top-down approaches, which hinder achieving both simple and universal synthesis routes that are simultaneously applicable to various metals and nanocarbons. Here, a universal strategy for fabricating nanocarbon based-SACs using a flash bottom-up arc discharge method to mitigate these issues is reported. The ionization of elements and their recombination process during arc discharge allows the simultaneous incorporation of single metal atoms (Mn, Fe, Co, Ni, and Pt) into the crystalline carbon lattice during the formation of carbon nanohorns (CNHs) and N-doped arc graphene. The coordination environment around the Co atoms of Co 1 /CNH can be modulated by a mild post-treatment with NH 3 . As a result, Co 1 /CNH exhibits good oxygen reduction reaction activity, showing a 1.92 times higher kinetic current density value than the commercial Pt/C catalyst in alkaline media. In a single cell experiment, Co 1 /CNH exhibits the highest maximum power density of 472 mW cm −2 compared to previously reported nonprecious metal-based SACs.

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Hierarchically Porous Co−N−C Cathode Catalyst Layers for Anion Exchange Membrane Fuel Cells

Cited by 35 publications

References 43 publications

Recent Insights on Catalyst Layers for Anion Exchange Membrane Fuel Cells

Recent Insights on Catalyst Layers for Anion Exchange Membrane Fuel Cells

Recent Advancements in the Synthesis and Application of Carbon-Based Catalysts in the ORR

Flash Bottom‐Up Arc Synthesis of Nanocarbons as a Universal Route for Fabricating Single‐Atom Electrocatalysts

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