The efficient catalytic conversion of hazardous gases (e.g., N₂O and CO) into non-harmful by products is important due to the severe environmental and health burdens posed by these gases. Here, quantum chemical studies have been carried out to investigate the catalytic reduction of N₂O by CO over a phosphomolybdic acid (PMA) cluster anchored with 3d transition metal atoms under mild reaction conditions. For N₂O reduction, all 3d-TM₁ adatoms on the PMA cluster have been systematically screened as single-atom catalysts (SACs). TM₁/PMA systems possess significant adsorption energies towards N₂O and CO, and co-adsorption energies of N₂O+CO are a necessary prerequisite for the start of the catalytic cycle. The results indicate that N₂O is decomposed first on the TM₁/PMA surface, forming N₂ and O-TM₁/PMA intermediate. The Ti₁-(0.53 eV), V₁-(0.40 eV), Cr₁-(0.86 eV), and Fe₁/PMA (0.94 eV) have low activation energy barriers that are comparable to those of the other catalysts that were chosen, making them active and selective catalysts for the N₂O decomposition. However, the remaining O atom on the TM₁/PMA was an active species for the oxidation of CO molecules. The Fe₁/PMA catalyst has an activation energy barrier of 0.43 eV and is a promising catalyst for the oxidation of CO. CO occupying the TM₁ site with stronger adsorption energy than N₂O will restrict the reaction’s effectiveness. A lower temperature can hinder the generation of the side products N₂ and O₂ generated due to the disproportionation of N₂O molecules. A concerted reaction mechanism can also initiate the reaction by first adhering CO molecules to the TM₁/PMA surface. The computed activation energy barriers of the rate-limiting step are (Ti₁=0.52 eV, V₁=0.76 eV, and Fe₁=0.88 eV), respectively. Thus, 3d TM₁/PMA is predicted to be an efficient catalyst for converting toxic gases N₂O and CO into non-hazardous N₂ and CO₂ under normal conditions.

Single-atom catalysts (SACs) have received significant interest for optimizing metal atom utilization and superior catalytic performance in hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). In this study, we investigate a range of single-transition metal (STM₁ = Sc₁, Ti₁, V₁, Cr₁, Mn₁, Fe₁, Co₁, Ni₁, Cu₁, Zr₁, Nb₁, Mo₁, Ru₁, Rh₁, Pd₁, Ag₁, W₁, Re₁, Os₁, Ir₁, Pt₁, and Au₁) atoms supported on graphyne (GY) surface for HER/OER and ORR using first-principle calculations. Ab initio molecular dynamics (AIMD) simulations and phonon dispersion spectra reveal the dynamic and thermal stabilities of the GY surface. The exceptional stability of all supported STM₁ atoms within the H1 cavity of the GY surface exists in an isolated form, facilitating the uniform distribution and proper arrangement of single atoms on GY. In particular, Sc₁, Co₁, Fe₁, and Au₁/GY demonstrate promising catalytic efficiency in the HER due to idealistic ΔG_H* values via the Volmer-Heyrovsky pathway. Notably, Sc₁ and Au₁/GY exhibit superior HER catalytic activity compared to other studied catalysts. Co₁/GY catalyst exhibits higher selectivity and activity for the OER, with an overpotential (0.46 V) comparable to MoC₂, IrO₂, and RuO₂. Also, Rh₁ and Co₁/GY SACs exhibited promising electrocatalysts for the ORR, with an overpotential of 0.36 and 0.46 V, respectively. Therefore, Co₁/GY is a versatile electrocatalyst for metal-air batteries and water-splitting. This study further incorporates computational analysis of the kinetic potential energy barriers of Co₁ and Rh₁ in the OER and ORR. A strong correlation is found between the estimated kinetic activation barriers for the thermodynamic outcomes and all proton-coupled electron transfer steps. We establish a relation for the Gibbs free energy of intermediates to understand the mechanism of SACs supported on STM₁/GY and introduce a key descriptor. This study highlights GY as a favorable single-atom support for designing highly active and cost-effective versatile electrocatalysts for practical applications.