Non-bonding interaction of dual atom catalysts for enhanced oxygen reduction reaction

We demonstrate the design of graphene-supported dual atom catalysts (DACs) for the four-electron oxygen reduction reaction (ORR), by utilizing the non-bonding interaction of counterpart metals (M) that synergistically tune the electronic properties and catalytic activity of the Fe active site in FeMN₆-DAC and FeMN₈-DAC systems, where M stands for Fe, Co, Ni, Cu, and Zn. More specifically, for Fe-M distances below 15 Å, the non-bonding interaction is significant, making the system act as the DAC. We predicted that FeNiN₆-DAC and FeNiN₈-DAC exhibit a low ORR overpotential (η^(ORR)) of 0.28 V and 0.47 V, respectively, which are at the summits of volcano plots. This low η^(ORR) originates from the high Bader charge transfer coupled with high spin density at the Fe site in both the FeNiN₆-DAC and FeNiN₈-DAC systems, which weakens the adsorption of OH* intermediate while enhancing its desorption to H₂O. Guided by these density functional theory (DFT) computational results, we synthesized FeCoN₈-DAC and FeNiN₈-DAC along with N-doped graphene and confirmed their structures with scanning transmission electron microscopy (STEM), X-ray photoelectron spectroscopy (XPS), X-ray absorption near-edge structure (XANES), extended X-ray absorption fine structure (EXAFS), and electron spin resonance (ESR). We verify experimentally the catalytic activities and find that FeNiN₈-DAC has the low experimental overpotential of 0.39 V with a Tafel slope of 47 mVdec⁻¹. Based on these results, we propose a DFT-guided strategy to tune the charge transfer and spin population of the active site toward designing DACs for electrochemical ORR.