Poly(acrylic acid) (PAA) is a promising polymer host to support alkaline electrolytes in Zn‐air batteries. Herein, precursors containing different concentrations of monomers, crosslinkers and additives such as zinc oxide in alkaline solution are polymerized to fabricate gel polymer electrolytes (GPEs) via one‐pot synthesis. The compositional effects of the GPEs on battery performance are evaluated and a more efficient cell design is demonstrated. With a vertical double air electrode configuration, ZABs using PAA‐based electrolytes show unprecedented performance including high specific energy (913 Wh kgZn−1), excellent cycling stability (at least 160 cycles at 2×10 mA cm−2) and high power density output (2×135 mW cm−2). The study represents a viable option to replace aqueous electrolytes for high performing ZABs.

Co,Fe) 3 O 4 nanoparticles are decorated onto N-doped carbon nanotubes at room temperature through a simple mixing process and are simultaneously deposited within a porous gas diffusion layer (GDL) by an impregnation technique. The (Co, Fe) 3 O 4 nanoparticles are identified as the spinel phase through transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analysis. The composite GDL is used as the air electrode for Zn-air batteries and shows excellent performance as a bifunctional catalyst with initial discharge and charge potentials of 1.19 V and 2.00 V, respectively, at 20 mA cm À 2 . Cycling performance of the impregnated electrode compares favourably with benchmark Pt-RuO 2 catalysts at both 10 mA cm À 2 and 20 mA cm À 2 . The (Co,Fe) 3 O 4 /N-CNT impregnated GDL had a final discharge/charge efficiency of 58.5 % after 100 h (200 cycles) of bifunctional cycling at 10 mA cm À 2 , which is superior to that of Pt-RuO 2 (55.3 % efficiency). The cycling efficiency for (Co,Fe) 3 O 4 /N-CNT impregnated GDL at 20 mA cm À 2 is also better than that for PtÀ Ru (53.5 % vs 41.3 % after 50 h (100 cycles)). The result is a simple and easily scalable one-pot electrode synthesis method for high performing bifunctional air electrodes for Zn-air batteries.

Mn 3 O 4 -decorated N-CNTs are synthesized and impregnated into porous carbon paper (gas diffusion layer or GDL) to form a composite catalyst-GDL material in a simple and novel one-pot process. The impregnated electrode features high active surface area, improved discharge performance, and reduced vulnerability to flooding when compared with other electrode preparation techniques for similar catalysts. Electrochemical and battery testing show catalytic activity and a maximum discharge potential superior to other CNT supported Mn 3 O 4 catalysts, and comparable to commercially used PtÀ Ru (1.21 V at 20 mA cm À 2 ). The composite is cycled at 10 mA cm À 2 and 20 mA cm À 2 as a bifunctional catalyst and as an oxygen reduction reaction (ORR) exclusive catalyst, respectively. Discharge performance is stable over 200 cycles at 20 mA cm À 2 when used exclusively for ORR with a discharge-charge efficiency superior to PtÀ Ru when coupled with electrodeposited CoÀ Fe as the OER catalyst (efficiency of 59 % after cycling).

Hybrids comprising hollow mesoporous nitrogen-doped carbon (HMC) nanospheres and metal-oxide nanoparticles were prepared through a hydrothermal synthesis. These materials exhibit excellent bifunctional catalytic activity in the oxygen reduction and evolution reactions (ORR and OER, respectively) that are core to the efficient operation of Zn-air batteries. When incorporated into prototype devices, Co 3 O 4 and MnCo 2 O 4 nanoparticle-decorated HMC exhibited discharge potentials of 1.26 and 1.28 V at 10 mA cm À 2 , respectively. 'CoFeNiO'-decorated HMC exhibited a charging potential of 1.96 V at 10 mA cm À 2 . These metrics are far superior to benchmark PtÀ Ru, which displayed discharge and charging potentials of 1.25 and 2.01 V, respectively, at the same current density. The battery equipped with Co 3 O 4 -decorated HMC demonstrated 63 % initial efficiency before cycling. After cycling at 10 mA cm À 2 for 100 hours, the battery efficiency was maintained at 56.5 %, outperforming the battery with PtÀ Ru (50.2 % after 50 h).

Various transition metal-based bimetallic and trimetallic oxides on N-CNTs were successfully synthesized in a one-pot process. Porous gas diffusion layers (GDLs) were simultaneously impregnated with the catalysts during synthesis, resulting in an efficient and scalable preparation technique for nano-composite air electrodes. NiMnO x /N-CNT, NiFeO x /N-CNT, and (Co,Fe) 3 O 4 /N-CNT catalysts were the highest performing bimetallic oxides based on battery rate test results. Therefore, Ni-Co-Fe, Ni-Mn-Fe, and Mn-Co-Fe systems were investigated as combined trimetallic oxide/N-CNT catalysts for Zn-air batteries. Trimetallic oxides on N-CNTs exhibited improved OER activity and comparable ORR activity relative to the bimetallic oxide catalysts in linear sweep voltammetry (LSV) tests. Discharge/charge efficiencies for tri-metallic oxides on N-CNTs calculated from battery rate test measurements at a current density of 20 mA cm −2 were 60.5%, 60.7%, and 60.0% for NCFO/N-CNT, NMFO/N-CNTs and MCFO/N-CNT, respectively. Bifunctional cycling of all trimetallic oxide/N-CNT electrodes at 10 mA cm −2 for 100 h showed excellent stability, particularly the NCFO/N-CNT catalyst. Additionally, the efficiencies for NCFO/N-CNT, NMFO/N-CNT and MCFO/N-CNT samples were 58.5%, 57.9% and 57.2%, respectively, after cycling, which compare favorably with that of Pt-Ru/C (55.3%). Trimetallic oxides on N-CNTs are, therefore, excellent candidates as high performing, non-precious metal catalysts for Zn-air batteries.