Air Electrodes For Zinc-air Batteries Research Articles

Advanced Architectures of Air Electrodes in Zinc-Air Batteries and Hydrogen Fuel Cells.

The air electrode is an essential component of air-demanding energy storage/conversion devices, such as zinc-air batteries (ZABs) and hydrogen fuel cells (HFCs), which determines the output power and stability of the devices. Despite atom-level modulation in catalyst design being recently achieved, the air electrodes have received much less attention, causing a stagnation in the development of air-demanding equipment. Herein, the evolution of air electrodes for ZABs and HFCs from the early stages to current requirements is reviewed. In addition, the operation mechanism and the corresponding electrocatalytic mechanisms of ZABs are summarized. In particular, by clarifying the air electrode interfaces of ZABs at different scales, several approaches to improve the air electrode in rechargeable ZABs are reviewed, including innovative electrode structures and bifunctional oxygen catalysts. Afterward, the operating mechanisms of proton-exchange-membrane fuel cells (PEMFCs) and anion-exchange-membrane fuel cells (AEMFCs) are explained. Subsequently, the strategies employed to enhance the efficiency of the membrane electrode assembly (MEA) in PEMFCs and AEMFCs, respectively, are highlighted and discussed in detail. Last, the prospects for air electrodes in ZABs and HFCs are considered by discussing the main challenges. The aim of this review is to facilitate the industrialization of ZABs and HFCs.

Carbon-Free Reversible Air Electrodes based on Perovskite Oxide and Conductive Oxide for Rechargeable Zinc-Air Batteries

Reversible air electrodes with high activity and durability during the discharge/charge processes are required for rechargeable zinc-air batteries. Although carbon materials are widely used as catalyst supports and conductive additives for metal oxide catalysts in the catalyst layer (CL) and as the main active constituent in the gas-diffusion layer (GDL), the carbon is oxidized during the charge step, causing degradation of the air electrode. In this study, carbon-free air electrodes were prepared using electro-conductive oxides, namely, indium tin oxide or antimony-doped tin oxide, as an alternative to carbon materials in both the CL and GDL to achieve reversibility and durability of the air electrode in zinc-air batteries. While the initial performance of the carbon-free air electrodes was inferior to that of the carbon-based air electrodes, the lifetime of the carbon-free air electrodes was remarkably longer. These results indicate a critical role of electro-conductive oxides in both the CL and GDL for durable air electrodes.

Highly ordered nanoarrays catalysts embedded in carbon nanotubes as highly efficient and robust air electrode for flexible solid-state rechargeable zinc-air batteries

The development of multicomponent materials is the most efficient and successful way for creating advanced multifunctional catalysts. Herein, the bimetal FeCo nanoarrays enclosed N-CNTs have a high surface on carbon cloth support, which promotes efficient electron transport and prevents nanoparticle aggregation. Taking advantage of the high-level use of active material and fast charge transfer, the developed electrocatalyst exhibits excellent multifunctional electrocatalyst such as oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). The N-CNTs@MOF FeCo nanoarrays @CC exhibit higher activity than reference catalysts including MOF FeCo nanoarrays@CC, FeCo nanoarrays@CC, and CC. Interestingly, the synthesized multifunctional catalyst, which serves as the air electrode in zinc-air batteries with liquid electrolytes as well as solid-state gel electrolytes possesses outstanding charging-discharge performance and long service life. This study provides enormous potential for the real implementation of portable, even wearable, and efficient rechargeable batteries in the future.

Atomically dispersed iron atoms on nitrogen-doped porous carbon catalyst with high density and accessibility for oxygen reduction

• AD-Fe-NPC was successfully developed as oxygen reduction catalysts. • HAADF-STEM images confirmed the atomic dispersion of Fe on AD-Fe-NPC catalysts. • The optimized AD-Fe-NPC structure exhibited superior ORR activity to Pt/C. The development of high-performance, low-cost and high-stability oxygen reduction reaction (ORR) non-platinum catalysts has become one of the main research directions on fuel cells and metal-air batteries. Here, we developed porous carbon catalysts with atomically dispersed nitrogen coordinated iron atoms (Fe-N x ) as the active sites (AD-Fe-NPC) using Fe-doped ZIF-8 and 1,10-phenanthroline as precursors. The additional nitrogen coordinated sites from 1,10-phenanthroline, together with a special structure of ZIF-8 can suppress the agglomeration of Fe atoms, leading to isolated Fe atoms with high density on graphitic carbon during the pyrolysis. As a result, the sample prepared using 50 mg of 1,10-phenanthroline (AD-Fe-NPC-50) exhibited a high activity towards oxygen reduction with a half-wave potential of 0.91 V versus reversible hydrogen electrode in 0.1 M KOH, which is attributed to the high porosity (1011.2 m 2 g −1 ) and density of Fe-N x active sites (1.1 at%). Furthermore, as an air electrode in zinc-air batteries, the AD-Fe-NPC-50 demonstrated a maximum power density of about 201 mA cm −2 and a specific capacity of 782 mA h g Zn −1 at 10 mA cm −2 , which outperformed commercial Pt/C and many state-of-the-art non-precious metal catalysts.

Zinc-Mediated Template Synthesis of Fe-N-C Electrocatalysts with Densely Accessible Fe-Nx Active Sites for Efficient Oxygen Reduction.

Owing to their earth abundance, high atom utilization, and excellent activity, single iron atoms dispersed on nitrogen-doped carbons (Fe-N-C) have emerged as appealing alternatives to noble-metal platinum (Pt) for catalyzing the oxygen reduction reaction (ORR). However, the ORR activity of current Fe-N-C is seriously limited by the low density and inferior exposure of active Fe-Nx species. Here, a novel zinc-mediated template synthesis strategy is demonstrated for constructing densely exposed Fe-Nx moieties on hierarchically porous carbon (SA-Fe-NHPC). During the thermal treatment of 2,6-diaminopyridine/ZnFe/SiO2 complex, the zinc prevents the formation of iron carbide nanoparticles and the SiO2 template promotes the generation of hierarchically pores for substantially improving the accessibility of Fe-Nx moieties after subsequent leaching. As a result, the SA-Fe-NHPC electrocatalysts exhibit an unprecedentedly high ORR activity with a half-wave potential (E1/2 ) of 0.93 V in a 0.1 m KOH aqueous solution, which outperforms those for Pt/C catalyst and state-of-the-art noble metal-free electrocatalysts. As the air electrode in zinc-air batteries, the SA-Fe-NHPC demonstrates a large peak power density of 266.4 mW cm-2 and superior long-term stability. Therefore, the developed zinc-mediated template synthesis strategy for boosting the density and accessibility of Fe-Nx species paves a new avenue toward high-performance ORR electrocatalysts.