Apically guiding electron/mass transfer reaction induced by Ag/FeNx Mott-Schottky effect within a hollow star reactor toward high performance zinc-air batteries

The disparity in the transfer of carriers (electrons/mass) during the reaction in zinc-air batteries (ZABs) results in sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), along with elevated overpotentials, thereby imposing additional constraints on its utilization. Therefore, the pre-design and target-development of inexpensive, high-performance, and long-term stable bifunctional catalysts are urgently needed. In this work, an apically guiding dual-functional electrocatalyst (Ag-FeNx-N-C) was prepared, in which a hierarchical porous nitrogen-doped carbon with three-dimensional (3D) hollow star-shaped structure is used as a substrate and high-conductivity Ag nanoparticles are coupled with iron nitride (FeNx) nanoparticles. Theoretical calculations indicate that the Mott-Schottky heterojunction as an inherent electric field comes from the two-phase bound of Ag and FeNx, of which electron accumulation in the FeNx phase region and electron depletion in the Ag phase region promote orientated-guiding charge migration. The effective modulation of local electronic structures felicitously reforms the d-band electron-group distribution, and intellectually tunes the mass-transfer reaction energy barriers for both ORR/OER. Additionally, the hollow star-shaped hierarchical porous structure provides an apical region for fast mass transfer. Experimental results show that the half-wave potential for ORR is 0.914 V, and the overpotential for OER is only 327 mV at 10 mA cm−2. A rechargeable ZAB with Ag-FeNx-N-C as the air cathode demonstrates long-term cycling performance exceeding 1500 cycles (500 h), with a power density of 180 mW cm−2. Moreover, when employing Ag-FeNx-N-C as the air cathode, flexible ZABs demonstrate a notable open-circuit voltage of 1.42 V and achieve a maximum power density of 65.6 mW cm−2. Ag-FeNx-N-C shows guiding electron/mass transfer route and apical reaction microenvironment for the electrocatalyst architecture in the exploration prospects of ZABs.