Advanced Electrocatalysts for the Oxygen Reduction Reaction in Energy Conversion Technologies

Developing a scalable approach to construct efficient and multifunctional electrodes for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) is an urgent need for overall water splitting and zinc-air batteries. In this work, a freestanding 3D heterostructure film is synthesized from a Ni-centered metal-organic framework (MOF)/graphene oxide. During the pyrolysis process, 1D carbon nanotubes formed from the MOF link with the 2D reduced graphene oxide sheets to stitch the 3D freestanding film. The results of the experiments and theoretical calculations show that the synergistic effect of the N-doped carbon shell and Ni nanoparticles leads to an optimized film with excellent electrocatalytic activity. Low overpotentials of 95 and 260 mV are merely needed for HER and OER, respectively, to reach a current density of 10 mA cm-2 . In addition, a high half-wave potential of 0.875 V is obtained for the ORR, which is comparable to that of Pt/RuO2 and ranks among the top of non-noble-metal catalysts. The use of an "all-in-one" film as the electrode leads to excellent performance of the homemade water electrolyzer and zinc-air battery, indicating the potential of the film for practical applications.

A Freestanding 3D Heterostructure Film Stitched by MOF-Derived Carbon Nanotube Microsphere Superstructure and Reduced Graphene Oxide Sheets: A Superior Multifunctional Electrode for Overall Water Splitting and Zn-Air Batteries.

Fuel cells are an incredibly powerful renewable energy technology, but their broad applications remains lagging because of the high cost and poor reliability of cathodic electrocatalysts for the oxygen reduction reaction (ORR). This review focuses on the recent progress of ORR electrocatalysts in fuel cells. More importantly, it highlights the fundamental problems associated with the insufficient activity translation from rotating disk electrode to membrane electrode assembly in the fuel cells. Finally, for the atomic-level in-depth information on ORR catalysts in fuel cells, potential perspectives are suggested, including large-scale preparation, unified assessment criteria, advanced interpretation techniques, advanced simulation and artificial intelligence. This review aims to provide valuable insights into the fundamental science and technical engineering for efficient ORR electrocatalysts in fuel cells.

Oxygen Reduction Electrocatalysts toward Practical Fuel Cells: Progress and Perspectives

ConspectusFuel cells are among the cutting-edge energy technologies. Their commercial development is still hindered by noble platinum (Pt) catalysts for the oxygen reduction reaction (ORR) at the cathode, which not only determine the energy conversion efficiency and service life but also are closely related to the cost and broad application of fuel cells. Given the bright and enormous future of fuel cells, ORR catalysts should possess highly efficient performance yet meet the acceptable Pt costs for large-scale application. Extensive efforts are concentrated on the optimization of Pt-based nanostructures and upgradation of functional carriers to achieve the low-cost and high-activity Pt-based catalysts. By improving the Pt utilization and accessible surface, reducing Pt consumption and catalyst costs, accelerating mass exchange and electron transfer, alleviating the corrosion and agglomeration of carriers and Pt, accompanying with the assistance of robust yet effective functional supports, the service level and life of Pt-based electrocatalysts would be significantly improved and fuel cells could get into commercial market covering broader applications.In this Account, we focus on the recent development of Pt-based catalysts to figure out the problems associated with ORR catalysts in fuel cells. Recent development of Pt-based catalysts is discussed in different stages: (1) multiscale development of Pt-based nanostructures; (2) multielement regulation over Pt-based alloy composition; (3) upgradation of carbon and noncarbon support architectures; (4) development of integrated Pt-based catalysts for fuel cells. Finally, we propose some future issues (such as reaction mechanism, dynamic evolutions, and structure-activity relationship) for Pt-based catalysts, which mainly involve the preparation strategy of Pt-integrated catalysts (combination of Pt nanostructures with nanocarbons), performance evaluation (standard measurement protocols, laboratory-level rotating disk electrode (RDE) measurements, application-level membrane electrode assembly (MEA) service test), advanced interpretation techniques (spectroscopy, electron microscopy, and in situ monitoring), and cutting-edge simulation/calculations and artificial intelligence (simulation, calculations, machine learning, big data screening). This Account calls for the comprehensive development of multiscale, multicomponent, and high-entropy Pt-based alloy nanostructures, and novel and stable carriers, which provide more available options for rational design of low-cost and high-performance Pt-integrated ORR catalysts. More importantly, it will give an in-depth understanding of the reaction mechanism, dynamic development, and structure-performance relationship for Pt-based catalysts in fuel cells and related energy technologies.

Advanced Platinum-Based Oxygen Reduction Electrocatalysts for Fuel Cells.

Harnessing the interplay of Fe–Ni atom pairs embedded in nitrogen-doped carbon for bifunctional oxygen electrocatalysis

2D Nitrogen-Doped Carbon Nanotubes/Graphene Hybrid as Bifunctional Oxygen Electrocatalyst for Long-Life Rechargeable Zn–Air Batteries

Continuous nitrogen-doped carbon nanotube matrix for boosting oxygen electrocatalysis in rechargeable Zn-air batteries

The rational design of cost-effective bifunctional air electrodes is of great significance to advance the practical application of rechargeable metal–air batteries. Herein, we report a three-dimensional, vertically aligned carbon nanotube array-supported nickel ferrite hybrid (NiFeOx@VACNTs) as a large free-standing air electrode for rechargeable Zn–air batteries. As expected, the designed electrode exhibits exceptional catalytic activity and stability for oxygen electrochemical reactions. The rechargeable Zn–air battery using this integrated air electrode delivers a large peak power density of 194 mW cm−2, along with ultrastable cyclability of over 1500 h at 5 mA cm−2. Furthermore, the flexible solid-state Zn–air battery with free-standing oxygen electrode exhibits a stable discharge voltage even under bending condition, with a high discharge power density of 143 mW cm−2. This work paves a valuable way for designing cost-effective, free-standing integrated air cathodes for Zn–air batteries and related energy conversion and storage technologies.

Bifunctional nickel ferrite-decorated carbon nanotube arrays as free-standing air electrode for rechargeable Zn–air batteries

First, graphene is directly grown on nickel foil without additional catalysts by chemical vapor deposition (CVD). Next, the graphene is modified by nitrogen-doping, and alumina is deposited onto the graphene by magnetron sputtering. The charge-specific capacity of N-doped graphene is higher than that of graphene since 2 Theta of in situ XRD characteristic peaks for N-doped graphene moves toward a lower angle (about 24) which is smaller than that (about 25) for graphene, and then the gap between graphene layers for N-doped graphene is larger than that for graphene according to Bragg’s Law, and N-doped graphene demonstrates the additional in situ XRD characteristic peak (LiC6) in comparison to graphene only with the in situ XRD characteristic peak (LiC12). Furthermore, because 2 Theta of in situ XRD characteristic peaks for Al2O3/graphene also moves toward a lower angle (about 24) and Al2O3/graphene also shows the additional in situ XRD characteristic peak (LiC6), the charge-specific capacity of Al2O3/graphene is also higher than that of graphene.

/pdf/effects-of-nitrogen-doping-or-alumina-films-on-graphene-as-cw8g7mjo.pdf

Effects of Nitrogen-Doping or Alumina Films on Graphene as Anode Materials of Lithium-Ion Batteries Verified by In Situ XRD

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2D Nitrogen-Doped Carbon Nanotubes/Graphene Hybrid as Bifunctional Oxygen Electrocatalyst for Long-Life Rechargeable Zn–Air Batteries

Continuous nitrogen-doped carbon nanotube matrix for boosting oxygen electrocatalysis in rechargeable Zn-air batteries

Bifunctional nickel ferrite-decorated carbon nanotube arrays as free-standing air electrode for rechargeable Zn–air batteries

Effects of Nitrogen-Doping or Alumina Films on Graphene as Anode Materials of Lithium-Ion Batteries Verified by In Situ XRD