Ionothermal-Transformation Strategy to Synthesize Hierarchically Tubular Porous Single-Iron-Atom Catalysts for High-Performance Zinc-Air Batteries.

Inexpensive carbon-based nitrogen-coordinated iron single-atom catalysts (CN-FeSACs) have been recently demonstrated as the most promising platinum substitutions for boosting the sluggish oxygen electrode performance in fuel cells and metal-air batteries. However, it is still a great challenge to develop economical and effective CN-FeSACs satisfying the needs of high output power. Herein, an ionothermal-transformation strategy is proposed to synthesize hierarchically tubular porous CN-FeSACs with an ultrahigh special surface area of 2500 m2 g-1 to host abundant single-atom iron sites with an attempt to simultaneously boost sluggish oxygen reduction reaction (ORR) kinetics and mass transport. Benefiting from the unique feature, the final obtained material shows an ORR half-wave potential of 0.885 V, higher than that of benchmark Pt/C (0.850 V). When assembled into zinc-air battery, a large peak power density of 208 mW cm-2 is achieved, which is far superior to that of Pt/C (119 mW cm-2). This work provides an economical and feasible strategy to prepare hierarchically porous CN-FeSACs for energy conversion.