Impact of initial structure on O2 plasma surface engineering and electrocatalytic behavior of ZIF-67

Abstract

Oxygen plasma offers a rapid, sustainable, and controllable method to tailor ZIF-67, however, the link between nanostructure, plasma-induced surface modifications, and electrocatalytic performance remains unclear. Here, canonical (Z) and non-canonical (nZ) ZIF-67 materials were engineered via O2 plasma and evaluated using the oxygen evolution reaction (OER) as a model. Plasma exposure times of 30, 45, and 60 min were explored. Three surface-confined transformations occurred in both variants: Co3O4 formation, partial oxidation of 2-methylimidazole linkers, and generation of undercoordinated Co2+ defect sites. Their extent and impact on porosity, crystallinity, and morphology strongly depended on the initial nanostructure and plasma duration, with clearer correlations for Z-derivatives. After 60 min-plasma treatment, Z-p60 and nZ-p60 reached ∼ 7.5 mA cm−2 at 1.76 V vs. RHE (LSV, without iR-compensation), corresponding to 3.1x and 3.5x higher OER current densities than Z and nZ, respectively. Improved kinetics were observed (Tafel slopes: Z-p60, 130 and 222 mV dec-1; nZ-p60, 133 and 204 mV dec-1), surpassing RuO2 (j1.76 = 4.8 mA cm−2; TS = 221 and 427 mV dec-1). Remarkably, controlled Co3O4 formation demonstrated that this oxide contributes significantly, although overall performance gains result from the interplay of all plasma-induced modifications.