Enhanced OER catalytic activity of single metal atoms supported by the pentagonal NiN 2 monolayer: insight from density functional theory calculations.

Two-dimensional material-supported single metal atom catalysts have been extensively studied and proved effective in electrocatalytic reactions in recent years. In this work, we systematically investigate the OER catalytic properties of single metal atoms supported by the NiN ₂ monolayer. Several typical transition metals with high single atom catalytic activity, such as Fe, Co, Ru, Rh, Pd, Ir, and Pt, were selected as catalytic active sites. The energy calculations show that transition metal atoms (Fe, Co, Ru, Rh, Pd, Ir, and Pt) are easily embedded in the NiN ₂ monolayer with Ni vacancies due to the negative binding energy. The calculated OER overpotentials of Fe, Co, Ru, Rh, Pd, Ir and Pt embedded NiN ₂ monolayers are 0.92 V, 0.47 V, 1.13 V, 0.66 V, 1.25 V, 0.28 V, and 0.94 V, respectively. Compared to the 0.57 V OER overpotential of typical OER noble metal catalysts IrO ₂ , Co@NiN ₂ and Ir@NiN ₂ exhibit high OER catalytic activity due to lower overpotential, especially for Ir@NiN ₂ . The high catalytic activity of the Ir embedded NiN ₂ monolayer can be explained well by the d-band center model. It is found that the adsorption strength of the embedded TM atoms with intermediates follows a linear relationship with their d-band centers. Besides, the overpotential of the Ir embedded NiN ₂ monolayer can be further reduced to 0.24 V under -2% biaxial strain. Such findings are expected to be employed in more two-dimensional material-supported single metal atom catalyzed reactions.