Simultaneously Integrating Single Atomic Cobalt Sites and Co₉S₈ Nanoparticles into Hollow Carbon Nanotubes as Trifunctional Electrocatalysts for Zn–Air Batteries to Drive Water Splitting

Abstract

The development of rechargeable metal–air batteries and water electrolyzers are highly constrained by electrocatalysts for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). However, the construction of efficient trifunctional electrocatalysts for ORR/OER/HER are highly desirable yet challenging. Herein, hollow carbon nanotubes integrated single cobalt atoms with Co9S8 nanoparticles (CoSA + Co9S8/HCNT) are fabricated by a straightforward in situ self‐sacrificing strategy. The structure of the CoSA + Co9S8/HCNT are verified by X‐ray absorption spectroscopy and aberration‐corrected scanning transmission electron microscopy. Theoretical calculations and experimental results embrace the synergistic effects between Co9S8 nanoparticles and single cobalt atoms through optimizing the electronic configuration of the CoN4 active sites to lower the reaction barrier and facilitating the ORR, OER, and HER simultaneously. Consequently, rechargeable liquid and all‐solid‐state flexible Zn–air batteries based on CoSA + Co9S8/HCNT exhibit remarkable stability and excellent power density of 177.33 and 51.85 mW cm−2, respectively, better than Pt/C + RuO2 counterparts. Moreover, the as‐fabricated Zn–air batteries can drive an overall water splitting device assembled with CoSA + Co9S8/HCNT and achieve a current density of 10 mA cm−2 at a low voltage of 1.59 V, also superior to Pt/C + RuO2. Therefore, this work presents a promising approach to an efficient trifunctional electrocatalyst toward practical applications.

Hollow Carbon‐Based Nanoarchitectures Based on ZIF: Inward/Outward Contraction Mechanism and Beyond

“…Another semiconductor, ZnS nanorods, are also used as a template for the preparation of core–shell ZnS@ZIF‐67. [ 78 ] Hollow carbon nanotubes integrated with single Co atoms and Co 9 S 8 NPs (CoSA + Co 9 S 8 /HCNT) are produced by the direct carbonization of core–shell ZnS@ZIF‐67@PDA composites. During the pyrolysis process, the ZnS nanorod templates were in situ reduced to metallic Zn and evaporated, behaving like the ZnO core to form the hollow structure.…”

Transition Metal and Nitrogen Co‐Doped Carbon‐based Electrocatalysts for the Oxygen Reduction Reaction: From Active Site Insights to the Rational Design of Precursors and Structures

“…For example, the controlled hollow structure was formed by a mechanism of “stresses induced orientation contraction”, which allowed the intensive interfacial interactions between the PDA coating shells and the zeolite imidazolate framework‐8 (ZIF‐8) cores to drag the internal ZIF‐8 cores outward to restrict their shrinkage [82] . A similar shell‐core structure was also discovered in the composite of PDA coating and ZIF‐67, [88] which was advantageous in improving the catalytic activity and mass transfer of ORR.…”

“…The template-mediated method using hard and soft templates is a common and effective strategy for synthesizing hierarchically porous materials for ORR. Various hard templates, such as silica (e. g., SiO 2 ), [120][121] metal oxides/hydroxides/carbonates/sulfides (e. g., MgO, CaO, Fe 3 O 4 , Mg(OH) 2 , Ca(OH) 2 , CaCO 3 , ZnS), [88,122] metal chlorides (e. g., NaCl, KCl, ZnCl 2 ), [123] and polystyrene sphere (PS), [124] etc., have been developed to tailor the porous structure of the ORR catalysts. Shui's group used mesoporous SiO 2 as a template, and then preheated and etched to achieve a concave-shaped atomic FeÀ NÀ C catalyst with increased mesopores and external surface area.…”

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

“…Moreover, their superior electrical conductivity and thermal stability contribute significantly to enhance the oxygen electrolysis. For example, Co 9 S 8 NPs embedded in hollow CNTs optimize the electronic configuration of nitrogen coordinating single Co atom (CoN 4 ) center in the carbon structure 93 . The Co 9 S 8 NPs participate synergistically with the cobalt‐nitrogen‐carbon moieties to reduce the adsorption/desorption free energy of oxygenates, which considerably boosts the catalyst bifunctionality.…”