Theoretical insights of nickel-based dual-metal atoms supported on C₂N sheets for urea electrooxidation

The electrocatalytic urea oxidation reaction (UOR) enables energy-saving hydrogen production and waste degradation but requires efficient catalysts due to its complex, sluggish 6-electron transfer mechanism. In this study, we designed a series of stable 3d transition metal heterometal atom pairs (TMNi, TM refers to Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, or Zn) supported on the C₂N substrate as UOR catalysts, systematically investigating their potential to enhance the activity of Ni₂/C₂N. Among these, CrNi/C₂N displayed a superior capability to lower the limiting potential of the UOR compared to CuNi/C₂N and Ni/C₂N. The enhanced catalytic CrNi/C₂N system primarily stems from the stronger TM–Ni interactions, notable differences in charge distribution, more localized electronic states, and a higher d-band center associated with CrNi/C₂N relative to CuNi/C₂N and Ni₂/C₂N. These attributes not only ensure the stability of the well-dispersed CrNi pairs on C₂N but also amplify the ability of the active center to adsorb and activate reaction intermediates. Moreover, CrNi/C₂N demonstrates good selectivity for the UOR by exhibiting reduced susceptibility to forming NO₂ by-products and undergoing the competing oxygen evolution reaction. This theoretically driven work identifies CrNi/C₂N as the top-performing UOR dual-metal-atom catalysts, combining 0.99 V limiting potential with selective N₂ generation through electronic structure modulation, offering guidance for advanced catalyst design through the strategic use of transition metal heterometal atom pairs.