ZIF-derived two-dimensional Co@Carbon hybrid: Toward highly efficient trifunctional electrocatalysts

Abstract

Hybrid electrocatalysts with stable two-dimensional (2D) framework and fine sub-structures are of great interest for enhancing the mass/electron transport and accessibility of maximized active sites. Here, we report a facile 2D-ZIF transformation strategy for fabricating highly efficient hybrid catalysts composed of highly dispersed Co quantum dots (~4.57 nm in diameter) embedded in ultrathin N-doped carbon layers (~3 nm in thickness), denoted as Co@NCL. The as-fabricated hybrids have excellent overall trifunctional electrocatalytic activities toward oxygen reduction (half-wave potential (E1/2) = 0.84 V), oxygen evolution (potential at 10 mA cm−2 (Ej10) = 1.63 V), and hydrogen evolution (Ej10 = −0.22 V) reactions in alkaline media. Notably, its reversible oxygen electrode index (ΔE = Ej10 − E1/2 = 0.79 V) is comparable with that of benchmarked noble-metal catalysts (0.80 V for Pt/C-RuO2) and superior to ZIF polyhedrons-derived counterpart (0.90 V) as well as most Co-based bifunctional catalysts ever reported. The as-constructed Zn–air battery and overall water splitting electrolyzer based on Co@NCL delivered a high peak power density of 170 mW cm−2 and a small voltage of 1.70 V that affords a current density of 10 mA cm−2 along with robust long-term stability, respectively, which demonstrates its promising applications in rechargeable metal-air batteries and water splitting.