Sourcing the merits of 3D integrated air cathodes for high-performance Zn-air batteries by bubble pump consumption chronoamperometry

Zn-air batteries (ZABs) as a potential energy conversion system suffers from low power density (typically≤200 mW cm^-2). Recently, 3D integrated air cathodes have demonstrated promising performance over traditional 2D plane ones, which is ascribed to enriched active sites and enhanced diffusion, but without experimental evidence. Herein, we applied a bubble pump consumption chronoamperometry (BPCC) method to quantitatively identify the gas diffusion coefficient (D) and effective catalytic sites density (ρ_EC) of the integrated air cathodes for ZABs. Furthermore, the D and ρ_EC values can instruct consequent optimization on the growth of Co embedded N-doped carbon nanotubes (CoNCNTs) on carbon fiber paper (CFP) and aerophilicity tuning, giving 4 times D and 1.3 times ρ_EC over the conventional 2D Pt/C-CFP counterparts. As a result, using the CoNCNTs with half-wave potential of merely 0.78 V vs. RHE (Pt/C: 0.89 V vs. RHE), the superaerophilic CoNCNTs-CFP cathode-based ZABs exhibited a superior peak power density of 245 mW cm^-2 over traditional 2D Pt/C-CFP counterparts, breaking the threshold of 200 mW cm^-2. This work reveals the intrinsic feature of the 3D integrated air cathodes by yielding exact D and ρ_EC values, and demonstrates the feasibility of BPCC method for the optimization of integrated electrodes, bypassing trial-and-error strategy.