Photoactive g-C3N4/CuZIF-67 bifunctional electrocatalyst with staggered p-n heterojunction for rechargeable Zn-air batteries

Abstract

Energy level matching and structural stabilization of semiconductor electrode materials are critical for improving the efficiency and durability of bifunctional catalysts for photo-enhanced rechargeable Zn-air batteries. We developed a photoactive bifunctional air-electrocatalyst comprising n-type g-C3N4 and p-type copper-doped ZIF-67 (CuZIF-67) composite. g-C3N4/CuZIF-67 exhibits wide-range solar spectrum absorption and enhanced electron–hole pairs separation efficiency owing to synergistic effects of a suitable bandgap width, staggered p-n heterojunction band gap structure, and built-in electric field at its p-n heterojunction, leading to higher oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) activities compared with single p- and n-type catalysts. It has photo-enhanced charge/discharge abilities, has a voltage gap of 0.81 V under 1-sun-illumination, and maintains stable cycling with 60% round-trip efficiency under illumination over 1000 cycles for 336 h at 2 mA cm−2. In conclusion, staggered p-n heterojunction and pyrrolic nitrogen-rich groups are important for efficient and durable photo-enhanced Zn air batteries.