First-Principles Studies on Electrocatalytic Activity of Novel Two-Dimensional MA2Z4 Monolayers toward Oxygen Reduction Reaction

Inspired by the recent experimental advance in the fabrication of a new type of two-dimensional (2D) material, MoSi2N4 and WSi2N4, in this work we performed density functional theory (DFT) calculations to explore the electrocatalytic feature of the new MA2Z4 family in oxygen reduction reaction (ORR). Through different combinations of the M, A, and Z elements (M = Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W; A = Si or Ge; Z = N, P, or As), we predicted about 42 MA2Z4 compounds that share the same structural framework as MoSi2N4/WSi2N4 are dynamically stable. Most of them prefer the four-electron (4e–) mechanism to produce H2O, and their ORR activity follows a general trend as MGe2As4 > MSi2As4 > MSi2N4 > MSi2P4 > MGe2P4 ≈ MGe2N4. Among them, four of them (VGe2As4, CrGe2As4, VSi2As4, and NbSi2As4) are screened out to be highly promising electrocatalysts with small overpotential around 0.5–0.6 V. The topmost surface As acts as the active site, and the p-band center of the As atom is found to show correlation with the adsorption strength of the critical intermediate. In particular, CrGe2As4 exhibits outstandingly high ORR activity with ultralow overpotential (0.49 V) comparable to the Pt-based catalysts. The metallic conductivity and the moderate adsorption and orbital hybridization between As and O* intermediate are responsible for the exceptional activity. Our investigations verify the promising catalytic performance of the emerging 2D MA2Z4, which would stimulate the future efforts in their synthesis and electrocatalytic applications in oxygen reduction and other advanced applications.