Controlling the Nitrogen Content of Metal-Nitrogen-Carbon Based Non-Precious-Metal Electrocatalysts via Selenium Addition
TL;DR: In this paper, selenium was used as a ligand to replace the nitrogen coordinated to the iron atom in the electrocatalyst, thereby imparting control on the nitrogen content.
Abstract: Non-precious metal electrocatalysts based on pyrolysed metal-nitrogen-carbon (MNC) are viewed as an inexpensive replacement for platinum-based electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells. One of the drawbacks of all the reported procedures to synthesize MNC electrocatalysts is the inability to control the nitrogen content. Since the type of nitrogen present (pyridinic, pyrrolic, quaternary/graphitic) and their proportions both play a seminal role in deciding the ORR activity of the electrocatalyst, it is important to carefully study the effect of nitrogen content on electrocatalyst properties. In this study, selenium was used as a ligand to replace the nitrogen coordinated to the iron atom in the electrocatalyst, thereby imparting control on the nitrogencontent.Uponintroducing14at%ofselenium,theNcontentofthecatalystdroppedto3.7wt%andtheORRactivityreached a maximum of 7.2 mA cm −2 at 0.8 V vs. RHE. We demonstrated the need for iron to complete the active site: upon complexing the iron site with bipyridine, ethylene diammine and oxalic acid in 1N H2SO4, the overpotential toward the ORR increased by ∼60 mV, ∼140 mV and ∼140 mV respectively at 2 mA cm −2 .
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TL;DR: This comprehensive Review focuses on the low- and non-platinum electrocatalysts including advanced platinum alloys, core-shell structures, palladium-based catalysts, metal oxides and chalcogenides, carbon-based non-noble metal catalysts and metal-free catalysts.
Abstract: The recent advances in electrocatalysis for oxygen reduction reaction (ORR) for proton exchange membrane fuel cells (PEMFCs) are thoroughly reviewed. This comprehensive Review focuses on the low- and non-platinum electrocatalysts including advanced platinum alloys, core–shell structures, palladium-based catalysts, metal oxides and chalcogenides, carbon-based non-noble metal catalysts, and metal-free catalysts. The recent development of ORR electrocatalysts with novel structures and compositions is highlighted. The understandings of the correlation between the activity and the shape, size, composition, and synthesis method are summarized. For the carbon-based materials, their performance and stability in fuel cells and comparisons with those of platinum are documented. The research directions as well as perspectives on the further development of more active and less expensive electrocatalysts are provided.
2,964 citations
TL;DR: In this paper, a review of the development, advantages, and types of zinc-air batteries is presented, along with a general perspective on the challenges and opportunities for the future innovation of heteroatom-doped carbon-based catalysts.
Abstract: Zinc–air batteries are regarded as promising candidates for next-generation clean and sustainable energy storage devices, due to their low-cost, safety, eco-friendliness, and high specific energy density. In zinc–air batteries, the air catalysts accelerate the sluggish oxygen electrocatalysis and largely govern the overall battery performance. Among the air catalysts, carbon-based materials have attract great attention, owing to their high conductivity, chemical robustness, porous structure, and tunable composition. Herein, this review presents the recent progress in bifunctional heteroatom-doped carbon catalysts for zinc–air batteries, especially for rechargeable and flexible batteries. The review will start with a brief introduction of the development, advantages, and types of zinc–air batteries. Then, the application of bifunctional heteroatom-doped carbon catalysts for aqueous and solid-state/flexible zinc–air batteries will be summarized. In the review, an emphasis is given for the investigations on reaction mechanisms, along with corresponding discussions on the role of non-metal and metal dopants. Theoretical predictions will also be discussed to guide the design and fabrication of future bifunctional carbon-based catalysts. Finally, a general perspective on the challenges and opportunities for the future innovation of heteroatom-doped carbon-based catalysts for zinc–air batteries is presented.
156 citations
53 citations
TL;DR: In this article, a cobalt-incorporated nitrogen-doped carbon nanotubes (Co-NCNTs) was reported as a Pt-free, efficient and low-cost catalyst for oxygen reduction reaction (ORR) for fuel cells.
35 citations
27 Sep 2021
TL;DR: In this article, the authors present a research review of the last five years and the prospects in the field of using metal-organic frameworks (MOFs) or porous coordination polymers (PCPs) for the fabrication of ORR catalysts.
Abstract: The oxygen reduction reaction (ORR) is the fundamental reaction at the cathode of a fuel cell. Although the commercial precious metal catalyst Pt/C has unique catalytic activity, its high cost, low storage capacity and poor stability limit the commercial application of fuel cells. Therefore, it is essential to explore catalysts with abundant functional materials and develop fuel cells with high activity and high stability. Metal–organic frameworks (MOFs) or porous coordination polymers (PCPs) are highly designable structures composed of organic ligands and metal ions. Because of their large specific surface area, high porosity and tunable chemical structure, MOFs/PCPs are considered the most promising catalytic material for the ORR. This review discusses the research progress and latest development of MOF/PCP applications as ORR catalysts, including the basic principles and the design rules of MOFs/PCPs as ORR catalysts. In addition, this work also elaborates on the active sites of ORR catalysts, which originate from the MOFs/PCPs. Ultimately, we present a research review of the last 5 years and the prospects in the field of using MOFs/PCPs for the fabrication of ORR catalysts.
33 citations
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TL;DR: It is reported that vertically aligned nitrogen-containing carbon nanotubes (VA-NCNTs) can act as a metal-free electrode with a much better electrocatalytic activity, long-term operation stability, and tolerance to crossover effect than platinum for oxygen reduction in alkaline fuel cells.
Abstract: The large-scale practical application of fuel cells will be difficult to realize if the expensive platinum-based electrocatalysts for oxygen reduction reactions (ORRs) cannot be replaced by other efficient, low-cost, and stable electrodes. Here, we report that vertically aligned nitrogen-containing carbon nanotubes (VA-NCNTs) can act as a metal-free electrode with a much better electrocatalytic activity, long-term operation stability, and tolerance to crossover effect than platinum for oxygen reduction in alkaline fuel cells. In air-saturated 0.1 molar potassium hydroxide, we observed a steady-state output potential of –80 millivolts and a current density of 4.1 milliamps per square centimeter at –0.22 volts, compared with –85 millivolts and 1.1 milliamps per square centimeter at –0.20 volts for a platinum-carbon electrode. The incorporation of electron-accepting nitrogen atoms in the conjugated nanotube carbon plane appears to impart a relatively high positive charge density on adjacent carbon atoms. This effect, coupled with aligning the NCNTs, provides a four-electron pathway for the ORR on VA-NCNTs with a superb performance.
6,370 citations
TL;DR: A family of non–precious metal catalysts that approach the performance of platinum-based systems at a cost sustainable for high-power fuel cell applications, possibly including automotive power.
Abstract: The prohibitive cost of platinum for catalyzing the cathodic oxygen reduction reaction (ORR) has hampered the widespread use of polymer electrolyte fuel cells. We describe a family of non-precious metal catalysts that approach the performance of platinum-based systems at a cost sustainable for high-power fuel cell applications, possibly including automotive power. The approach uses polyaniline as a precursor to a carbon-nitrogen template for high-temperature synthesis of catalysts incorporating iron and cobalt. The most active materials in the group catalyze the ORR at potentials within ~60 millivolts of that delivered by state-of-the-art carbon-supported platinum, combining their high activity with remarkable performance stability for non-precious metal catalysts (700 hours at a fuel cell voltage of 0.4 volts) as well as excellent four-electron selectivity (hydrogen peroxide yield <1.0%).
3,464 citations
Journal Article•
TL;DR: In this article, a family of non-precious metal catalysts that approach the performance of platinum-based systems at a cost sustainable for high-power fuel cell applications, possibly including automotive power.
Abstract: Fuel cell catalysts synthesized from abundant metals approach the performance and durability of platinum at lower cost. The prohibitive cost of platinum for catalyzing the cathodic oxygen reduction reaction (ORR) has hampered the widespread use of polymer electrolyte fuel cells. We describe a family of non–precious metal catalysts that approach the performance of platinum-based systems at a cost sustainable for high-power fuel cell applications, possibly including automotive power. The approach uses polyaniline as a precursor to a carbon-nitrogen template for high-temperature synthesis of catalysts incorporating iron and cobalt. The most active materials in the group catalyze the ORR at potentials within ~60 millivolts of that delivered by state-of-the-art carbon-supported platinum, combining their high activity with remarkable performance stability for non–precious metal catalysts (700 hours at a fuel cell voltage of 0.4 volts) as well as excellent four-electron selectivity (hydrogen peroxide yield <1.0%).
2,974 citations
TL;DR: In this paper, a microporous carbon-supported iron-based catalysts with active sites believed to contain iron cations coordinated by pyridinic nitrogen functionalities in the interstices of graphitic sheets within the micropores was produced.
Abstract: Iron-based catalysts for the oxygen-reduction reaction in polymer electrolyte membrane fuel cells have been poorly competitive with platinum catalysts, in part because they have a comparatively low number of active sites per unit volume. We produced microporous carbon-supported iron-based catalysts with active sites believed to contain iron cations coordinated by pyridinic nitrogen functionalities in the interstices of graphitic sheets within the micropores. We found that the greatest increase in site density was obtained when a mixture of carbon support, phenanthroline, and ferrous acetate was ball-milled and then pyrolyzed twice, first in argon, then in ammonia. The current density of a cathode made with the best iron-based electrocatalyst reported here can equal that of a platinum-based cathode with a loading of 0.4 milligram of platinum per square centimeter at a cell voltage of >/=0.9 volt.
2,762 citations
TL;DR: In this paper, the authors focus on the new synthesis methods that have led to these breakthroughs and analyze the improvements required from NPMC-based catalysts to match the performance of Pt-based cathodes, even at high current density.
Abstract: Hydrogen produced from water and renewable energy could fuel a large fleet of proton-exchange-fuel-cell vehicles in the future. However, the dependence on expensive Pt-based electrocatalysts in such fuel cells remains a major obstacle for a widespread deployment of this technology. One solution to overcome this predicament is to reduce the Pt content by a factor of ten by replacing the Pt-based catalysts with non-precious metal catalysts at the oxygen-reducing cathode. Fe- and Co-based electrocatalysts for this reaction have been studied for over 50 years, but they were insufficiently active for the high efficiency and power density needed for transportation fuel cells. Recently, several breakthroughs occurred that have increased the activity and durability of non-precious metal catalysts (NPMCs), which can now be regarded as potential competitors to Pt-based catalysts. This review focuses on the new synthesis methods that have led to these breakthroughs. A modeling analysis is also conducted to analyze the improvements required from NPMC-based cathodes to match the performance of Pt-based cathodes, even at high current density. While no further breakthrough in volume-specific activity of NPMCs is required, incremental improvements of the volume-specific activity and effective protonic conductivity within the fuel-cell cathode are necessary. Regarding durability, NPMCs with the best combination of durability and activity result in ca. 3 times lower fuel cell performance than the most active NPMCs at 0.80 V. Thus, major tasks will be to combine durability with higher activity, and also improve durability at cell voltages greater than 0.60 V.
1,402 citations