Atomically dispersed Ru sites on MOF-derived NC-ZnO for efficient oxygen evolution reaction in acid media

Abstract

Developing acid-stable oxygen evolution/reduction reaction (OER/ORR) electrocatalysts is essential for high-performance water splitting. Still, the slow kinetics of the ORR and OER during the discharge and charge processes seriously impede their advancement in these performances. This report outlines the creation of a nitrogen-doped porous carbon matrix (NC) produced from a zeolitic imidazolate framework (ZIF-8). The matrix includes spatially engineered ultra-low loaded Ru atomic sites and is examined in the context of electrocatalytic oxygen evolution studies. The systematic analysis and computational studies reveal that the Ru atomic sites act as central driving forces, and their formation is confirmed through X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) analyses, specifically X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). These analyses emphasize the presence of Ru–O bonds at approximately 1.4 Å. Moreover, these results were validated by HRTEM, STEM, and HAADF investigations which emphasize the dispersion of atom-scale Ru on the NC(ZnO). Ru_1.75@NC(ZnO) shows a low overpotential (320 mV) at a current density of 10 mA cm⁻² for the OER because of the high active site utilization. Importantly, the Ru_1.75@NC(ZnO) electrode displays an admirable specific capacitance value of 0.0501 mF cm⁻² with notable durability of the capacitor after 500 cycles. The studies revealed that the introduction of monometallic Ru into ZIF-derived ZnO tunes intermediate adsorption energies and promotes the reactions by demanding lesser free energy in the water dissociation process. This research advances the pursuit of creating high-efficiency electrocatalysts with single-site structures, aiming for maximum atomic utilization efficiency in oxygen evolution reactions (OERs), particularly on templates derived from ZIFs.