DFT screening of dual-atom catalysts on carbon nanotubes for enhanced oxygen reduction reaction and oxygen evolution reaction: comparing dissociative and associative mechanisms

Dual-atom catalysts (DACs) are promising for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). However, two vital factors, namely curvature effects and dissociative mechanisms, are often overlooked in DAC studies, which may miss the possibility of finding the most promising candidates. To provide a mechanistic understanding of the role of these two essential factors in effective electrocatalyst design, we explore systematically the catalytic potential of MM′N₆-DACs supported on graphene and single-walled carbon nanotubes (CNTs) with two diameters within both dissociative and associative mechanisms where M and M′ represent Fe, Co, Ni, Cu, Ru, Rh, Pd, or Pt metals. More than ten DACs have shown high activity with overpotential lower than that of common commercial catalysts, notably non-precious CoCuN₆-DACs exhibiting extremely low ORR overpotential of 0.09 V_RHE and low OER overpotential of 0.10 V_RHE, and bifunctional ORR and OER overpotential of 0.22 V_RHE. We find that CNT substrates strengthen the adsorption of intermediates on CoCuN₆-DACs compared to graphene substrates, due to increased electronic density of states of metal atoms near the Fermi level. The dissociative mechanism circumvents the constraints of scaling relationship in the associative mechanism, so that several DACs favoring the dissociative mechanism exhibit substantially improved activity, with lower overpotential than the theoretical minimum of the associative mechanism. These results not only shed light on designing high-performance catalysts for the ORR and OER but also deepen the theoretical understanding of the catalytic mechanism and curvature effects on DACs.