CO₂ Bubble-Assisted Pt Exposure in PtFeNi Porous Film for High-Performance Zinc-Air Battery

Fine-tuning the exposed active sites of platinum group metal (PGM)-based materials is an efficient way to improve their electrocatalytic performance toward large-scale applications in renewable energy devices such as Zn-air batteries (ZABs). However, traditional synthetic methods trade off durability for the high activity of PGM-based catalysts. Herein, a novel dynamic CO₂-bubble template (DCBT) approach was established to electrochemically fine-tuning the exposed Pt active sites in PtFeNi (PFN) porous films (PFs). Particularly, CO₂ bubbles were intentionally generated as gas-phase templates by methanol electrooxidation. The generation, adsorption, residing, and desorption of CO₂ bubbles on the surface of PFN alloys were explored and controlled by adjusting the frequency of applied triangular-wave voltage. Thereby, the surface morphology and Pt exposure of PFN PFs were controllably regulated by tuning the surface coverage of CO₂ bubbles. Consequently, the Pt_1.1%Fe_8.8%Ni PF with homogeneous nanoporous structure and sufficiently exposed Pt active sites was obtained, showing preeminent activities with a half-wave potential (E_1/2) of 0.87 V and onset overpotential (η_onset) of 288 mV at 10 mA cm^-2 for oxygen reduction and evolution reactions (ORR and OER), respectively, at an ultralow Pt loading of 0.01 mg cm^-2. When tested in ZABs, a high power density of 175.0 mW cm^-2 and a narrow voltage gap of 0.64 V were achieved for the long cycling tests over 500 h (750 cycles), indicating that the proposed approach can efficiently improve the activity of PGM catalysts by fine-tuning the microstructure without compromising the durability.