Synergistic Niobium Doped Two-Dimensional Zirconium Diselenide: An Efficient Electrocatalyst for O2 Reduction Reaction

The development of high-activity and low-price cathodic catalysts to facilitate the electrochemically sluggish O₂ reduction reaction (ORR) is very important to achieve the commercial application of fuel cells. Here, we have investigated the electrocatalytic activity of the two-dimensional single-layer Nb-doped zirconium diselenide (2D Nb-ZrSe₂) toward ORR by employing the dispersion corrected density functional theory (DFT-D) method. Through our study, we computed structural properties, electronic properties, and energetics of the 2D Nb-ZrSe₂ and ORR intermediates to analyze the electrocatalytic performance of 2D Nb-ZrSe₂. The electronic property calculations depict that the 2D monolayer ZrSe₂ has a large band gap of 1.48 eV, which is not favorable for the ORR mechanism. After the doping of Nb, the electronic band gap vanishes, and 2D Nb-ZrSe₂ acts as a conductor. We studied both the dissociative and the associative pathways through which the ORR can proceed to reduce the oxygen molecule (O₂). Our results show that the more favorable path for O₂ reduction on the surface of the 2D Nb-ZrSe₂ is the 4e^– associative path. The detailed ORR mechanisms (both associated and dissociative) have been explored by computing the changes in Gibbs free energy (ΔG). All of the ORR reaction intermediate steps are thermodynamically stable and energetically favorable. The free energy profile for the associative path shows the downhill behavior of the free energy vs the reaction steps, suggesting that all ORR intermediate structures are catalytically active for the 4e^– associative path and a high 4e^– reduction pathway selectivity. Therefore, 2D Nb-ZrSe₂ is a promising catalyst for the ORR, which can be used as an alternative ORR catalyst compared to expensive platinum (Pt).