Herein,
Co/Fe bimetallic hydroxide nanosheets (Co3Fe2 BMHs) were densely deposited on polypyrrole nanotubes (PPy
NTs), followed by the successive coating of polydopamine (PDA) and
zeolitic imidazolate frameworks (ZIF)-67 to form a composite catalyst
precursor. Then, Co3Fe2 BMHs, PPy NTs, and ZIF-67/PDA
in this precursor were calcined into Co2Fe alloy nanoparticles,
nitrogen-doped carbon NTs (NCNTs), and a Co-N
x
activated carbon net, respectively, which constituted a novel
composite catalyst. In this composite catalyst, the high-density Co2Fe alloy nanoparticles are highly dispersed on the NCNT and
coated by the Co-N
x
activated carbon net.
The Co-N
x
activated carbon net protects
the alloy particles from agglomerating during calcination and from
being corroded by the electrolyte. Moreover, the experimental results
demonstrated that the calcination temperature and chemical components
of the catalyst precursors greatly affect the morphology, structure,
composition, and ultimately electrocatalytic activity of the calcined
products. The obtained optimum catalyst material exhibited significant
electrocatalytic effects on both the oxygen reduction reaction and
oxygen evolution reaction with a small ΔE of
0.715 V. The Zn-air battery utilizing this material as the air electrode
catalyst showed a power density of 235.5 mW cm–2, an energy density of 1073.5 Wh kg–1, and a round-trip
efficiency of 62.3% after 1000 cycles, superior to the benchmark battery
based on the mixed commercial catalyst of Pt/C and RuO2. An all-solid-state battery was also assembled to confirm the practical
application prospect of the prepared composite material as the air
electrode catalyst. More importantly, both experimental data and density
functional theory calculations verified that the superior bifunctional
catalytic activity was mainly attributed to the synergy between the
Co-N
x
activated carbon net and Co2Fe alloy.
High‐efficiency and low‐cost bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), as well as gel electrolytes with high thermal and mechanical adaptability are required for the development of flexible batteries. Herein, abundant Setaria Viridis (SV) biomass is selected as the precursor to prepare porous N‐doped carbon tubes with high specific surface area and the 900 °C calcination product of SV (SV‐900) shows the optimum ORR/OER activities with a small EOER–EORR of 0.734 V. Meanwhile, a new multifunctional gel electrolyte named C20E2G5 is prepared using cellulose extracted from another widely distributed biomass named flax as the skeleton, epichlorohydrin as the cross‐linker and glycerol as the antifreezing agent. C20E2G5 possesses high ionic conductivity from −40 to + 60 °C, excellent tensile and compressive resistance, high adhesion, strong freezing and heat resistance. Moreover, the symmetrical cell assembled with C20E2G5 can significantly inhibit Zn dendrite growth. Finally, flexible solid‐state Zn–air batteries assembled with SV‐900 and C20E2G5 show high open circuit voltage, large energy density, and long‐term operation stability between −40 and + 60 °C. This biomass‐based approach is generic and can be used for the development of diverse next‐generation electrochemical energy conversion and storage devices.
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