3D Ordered Co@NC Skeleton for Bifunctional Oxygen Reduction and Oxygen Evolution Reaction Electrocatalysts

Abstract

SiO 2 opals templates. [35,36] Nevertheless, the thickness of self-assembled opals templates is generally below 5 µm, far from providing sufficient interface area for ORR and OER. [37,38] Herein, we developed a novel thickfilm air electrode for ZABs, consisting of 3DOM carbon structure and sufficient exposed CoN x and Co nanoparticles active sites. This novel air electrode bases on thick SiO 2 opals template, in which carbon fiber paper was utilized as a support for releasing the stress during SiO 2 spheres self-assembling. The thickness of the SiO 2 opals template is adjustable according to the thickness of carbon fiber paper (110, 190, and 280 µm). Moreover, the 3DOM nitrogen-doped carbon skeleton (Co@ NC) was derived from metal-organic frameworks (MOFs) as precursor, filling the void among the SiO 2 opals template. The as-prepared 3DOM Co@NC shows outstanding ORR and OER performances. The rechargeable ZABs with as-prepared 3DOM Co@NC-1-090 as air cathode exhibit high power density (150 mW cm −2), specific energy density (964.2 W h kg −1), and outstanding cycling life (730 cycles with 10 mA cm −2 charge/discharge current density). It is verified that the 3DOM structure provides sufficient uniform interface for exposing CoN x sites and ordered channels for mass transport. 2. Results and Discussion Figure 1a schematically illustrates the fabrication processes of 3DOM Co@NC air electrodes. First, a piece of carbon paper (2 cm × 2 cm) was immersed in 10 mL SiO 2 nanospheres ethanol solution (2.0 wt%) for self-assembling. The monodispersed SiO 2 nanospheres arranged orderly among the carbon fibers, as shown in Figure S1a,b, Supporting Information. Second, the MOFs precursor solution containing Co 2+ , Zn 2+ , and 2-Melm was utilized to fill the space among SiO 2 nanospheres. Then the MOFs with SiO 2 template was carbonized at 800 °C to obtain Co@NC. [39] The morphology of as-prepared 3DOM Co@NC was illustrated by SEM. Figure 1b,c shows the top-view images of 3DOM Co@NC. The 3DOM structure, with uniform interconnected macropores (≈250 nm), is observed apparently among carbon fibers. Besides, the interconnected macropores distribute uniformly in an extended range (Figure S2a,b, Supporting Information). The section-view images in Figure 1d,e imply that the partial thickness of 3DOM Co@NC exceeds 20 µm. Transition metal@nitrogen-carbon (M@NC) catalysts are greatly desired for zinc-air batteries due to the promising oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) properties. Herein, a uniformly distributed Co@NC catalyst derived from metal-organic frameworks is developed. The CoN x species and Co nanoparticles encapsulated in carbon networks promote ORR and OER kinetics synergistically. Moreover, a novel structure is designed for exposing active sites, which consists of 3D macroporous skeleton embedded in carbon fiber paper. It is revealed that the outstanding ORR and OER properties attribute to the sufficient active area obtained from porous structure and ultra-thickness (280 µm). Besides, ...

Nitrogen‐Rich Carbonaceous Materials for Advanced Oxygen Electrocatalysis: Synthesis, Characterization, and Activity of Nitrogen Sites

“…Cai et al reported a 3D porous Co@N-C catalyst composed of abundant CoN x and Co nanoparticles embedded in carbon networks, which facilitated the ORR and OER kinetics. [298] Besides, the zinc-air batteries assembled with the catalyst exhibited a high power density (150 mW cm −2 ), a high specific energy density (964.2 W h kg −1 ), and sufficient cycling stability (730 cycles with 10 mA cm −2 charge/discharge current density). N-doped hollow porous carbon nanofibers with incorporated Co nanoparticles were also reported by Lu et al using electrospinning and ultrafast high-temperature shock technique (Figure 17a,b).…”

Ultrahigh-Loaded Fe Single Atoms and Fe3C Nanoparticle Catalysts as Air Cathodes for High-Performance Zn–Air Batteries

“…The Fe 3 C-FeSA@3DCN supported by foamed nickel was used as the air cathode, zinc foil was used as the anode, and a gel electrolyte was used as the conductive layer, and the solid-state flexible battery was assembled (Figure a) Figure b shows that the open-circuit voltage of the prepared gel solid-state battery is 1.372 V, and the open-circuit voltage is very stable.…”

Boosting the Oxygen Reduction Reaction in Zn–Air Batteries via a Uniform Trace N-Doped Carbon-Based Pore Structure

“…In the process of calcination, NaCl, as an activator, can introduce more pore structures and carbon defects, expose more active sites, and adjust the surface properties of carbon atoms in the material. However, these are not sufficient to meet the requirements for ORR activity. − The introduction of N atoms larger than C into MOFs may cause a higher strain at their edges, thus promoting the charge potential and chemical adsorption of oxygen, which are the main reasons for the enhanced ORR activity. − Many reports have confirmed that N doping, mostly in the form of pyridine nitrogen and graphite nitrogen, can effectively improve the ORR activity of catalysts. ,− It is widely acknowledged that urea is the most popular nitrogen source due to its low cost and high content of nitrogen. More importantly, urea is more likely to synthesize the catalytic sites such as pyridine nitrogen and graphite nitrogen during the process of high-temperature pyrolysis. ,− …”