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

Abstract

Electrochemical reactions, including the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR), are important for green and renewable energy conversion and storage systems. [1] However, the sluggish kinetics of these electrochemical reactions seriously affect their energy utilization and output power. Currently, noble metal Pt-based compounds and Ir/Ru-based oxides are used as benchmark catalysts for HER, ORR, and OER. Based on specific interactions between catalytic active sites and intermediate species, each catalyst is used for a certain reaction. However, in many applications, several reactions occur in tandem or in a switchable manner; therefore, different reactions on the same electrode require different catalysts. For instance, both OER and ORR catalysts are required for the redox reaction of gas electrodes in fuel cells and Zn-air batteries (ZABs). Therefore, bi-or even multifunctional catalysts that can promote several reactions have the apparent advantage of simplifying the catalytic electrode design and construction of these essential applications. [2] Furthermore, several catalytic reactions driven by a certain catalyst facilitate the exploration and rationalization of the mutual effects of different reactive intermediates and catalytic active sites, which will further promote the understanding of the reaction kinetics and catalyst design. [1c] However, single precious metals generally cannot simultaneously provide sufficient activities for HER, OER, and ORR. In addition, the high cost, rarity, and low stability limit their industrial applications. Therefore, multifunctional nonprecious catalysts with high activity and excellent stability with respect to several important reactions must be developed. Over the past decades, many substitutable, electroactive materials, such as nanocarbons, phosphides, nitrides, carbides, sulfides, and their composites, have been used as electrocatalysts for different electrochemical reactions. [3] Nitrogen-doped carbon-coated Ni-based nanostructures (Ni@N-C) are of 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 ...

Design Engineering, Synthesis Protocols, and Energy Applications of MOF-Derived Electrocatalysts

“…The findings propose that tuned thermal treatment of MOFs is an efficient avenue to obtain exceptional well-designed noble metal-free HER catalysts. In this consequence, Yan et al [ 30 ] prepared 3D heterostructure film from a Ni-centered MOF/graphene oxide, as shown in Fig. 11 a.…”

“…c LSV curves for HER of Ni@N-HCGHF before and after 2000 CV cycles (inset: the current–time curve of Ni@N-HCGHF). d EIS Nyquist plots [ 30 ], Copyright © 2020, John Wiley and Sons …”

“…The oxygen reduction is classified among the essential half-reactions that occur in several energy applications such as metal-air batteries and fuel cells [14,15,17,18,20,[26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] (Fig. 1).…”

Transition metal/carbon hybrids for oxygen electrocatalysis in rechargeable zinc‐air batteries

“…Moreover, in another study, the DFT calculations used to investigate the contribution of metal NPs encapsulated N‐doped carbon indicate a strong interaction between the metal nanoparticle and the carbon shell. And this interaction is favorable for a smooth electron transfer from the TM NPs to the carbon shell, which accelerates the formation of oxygen intermediates and thus promotes the redox efficiency 4 . Besides, the TM carbide NPs have been demonstrated to be efficient oxygen electrocatalysts owing to their chemical stability against the corrosion in harsh media 140 …”

“…Moreover, the abundance of zinc source coupled with the unlimited oxygen supply push ZABs forward on the frontline for overcoming the current environmental and renewable energy challenges (Figure 1). 1‐3 In the ZABs devices, energy conversion is happened through the redox reactions between zinc metal anode and oxygen from the air 4‐7 . However, the sluggish reaction kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) will cause the huge overpotential, which remains a critical bottleneck for scalability and commercialization of rechargeable ZABs 8‐11 .…”