Engineering Two-Phase Bifunctional Oxygen Electrocatalysts with Tunable and Synergetic Components for Flexible Zn–Air Batteries

Abstract

Metal–air batteries, like Zn–air batteries (ZABs) are usually suffered from low energy conversion efficiency and poor cyclability caused by the sluggish OER and ORR at the air cathode. Herein, a novel bimetallic Co/CoFe nanomaterial supported on nanoflower-like N-doped graphitic carbon (NC) was prepared through a strategy of coordination construction–cation exchange-pyrolysis and used as a highly efficient bifunctional oxygen electrocatalyst. Experimental characterizations and density functional theory calculations reveal the formation of Co/CoFe heterostructure and synergistic effect between metal layer and NC support, leading to improved electric conductivity, accelerated reaction kinetics, and optimized adsorption energy for intermediates of ORR and OER. The Co/CoFe@NC exhibits high bifunctional activities with a remarkably small potential gap of 0.70 V between the half-wave potential (E1/2) of ORR and the potential at 10 mA cm‒2 (Ej=10) of OER. The aqueous ZAB constructed using this air electrode exhibits a slight voltage loss of only 60 mV after 550-cycle test (360 h, 15 days). A sodium polyacrylate (PANa)-based hydrogel electrolyte was synthesized with strong water-retention capability and high ionic conductivity. The quasi-solid-state ZAB by integrating the Co/CoFe@NC air electrode and PANa hydrogel electrolyte demonstrates excellent mechanical stability and cyclability under different bending states.

Integrating Bimetal Alloy into N‐Doped Carbon Nanotubes@Nanowires Superstructure for Zn‐Air Batteries

“…The two peaks at 779.0 and 794.7 eV originate from metallic Co 0 , while other two peaks at 781.8 and 796.2 eV with accompanied shakeup satellite peaks at 786.5 and 804.8 eV are associated with the high‐valence Co 2p 3/2 and 2p 1/2 , which confirms the presence of Co−N species [29] . Similarly, metallic Fe 0 (708.3 and 720.7 eV) exists in the Fe 2p XPS spectrum along with high‐valence Fe (716.6 and 733.0 eV) in the form of Fe−N (Figure 2f) [30] . The presence of Co−N and Fe−N bonds indicates intense interactions between the CoFe alloy nanoparticles and the nitrogen‐doped carbon substrate [31]…”

“…[29] Similarly, metallic Fe 0 (708.3 and 720.7 eV) exists in the Fe 2p XPS spectrum along with highvalence Fe (716.6 and 733.0 eV) in the form of FeÀ N (Figure 2f). [30] The presence of CoÀ N and FeÀ N bonds indicates intense interactions between the CoFe alloy nanoparticles and the nitrogen-doped carbon substrate. [31]…”

Theory‐Guided Regulation of FeN4Spin State by Neighboring Cu Atoms for Enhanced Oxygen Reduction Electrocatalysis in Flexible Metal–Air Batteries

“…This performance of the NCAG/FeÀ Cu//Zn battery far surpasses those of relevant solid Zn-air batteries and even liquid ones reported earlier (Table S7 and Figure S45b). [37,47,[58][59][60][61][62][63][64][65][66][67][68][69][70] Notably, when the PANa thickness was compressed by 30 % and 60 %, the solid battery still retained 95 % and 93 % of the maximum power and almost unchanged dischargecharge voltages (Figure S44c and S45c). In addition, when the battery was bended by 90°and 180°, the discharge voltage remained stable at 1.38 V at the current density of 5 mA cm À 2 (Figure S45d).…”

Atomically Dispersed Transition Metal-Nitrogen-Carbon Bifunctional Oxygen Electrocatalysts for Zinc-Air Batteries: Recent Advances and Future Perspectives

“…Noble-metal catalysts with high catalytic activity for ORR (e.g., Pt/C) and OER (e.g., IrO 2 , RuO 2 ) can greatly accelerate their sluggish kinetics [19]. However, they cannot meet the requirements of bifunctional catalytic activity in rechargeable ZABs because they are merely efficient in one of the two reactions (ORR or OER) [20][21][22][23][24][25]. It is common to mix the ORR-active and OER-active components to obtain a bifunctional catalyst.…”