Rational design of single transition-metal atoms anchored on a PtSe₂ monolayer as bifunctional OER/ORR electrocatalysts: a defect chemistry and machine learning study

Searching for highly efficient, economical, and environmentally friendly bifunctional electrocatalysts for the oxygen reduction reaction (OER) and oxygen evolution reaction (ORR) is crucial in developing renewable energy conversion and storage technology. In this study, we systematically investigate the effect of defect charges on the electrocatalytic performance of transition metal (TM = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag) single atoms anchored on a PtSe2 monolayer (TM@PtSe2) using first-principles calculations. Based on our formation energy calculation, we find that Pt-rich conditions can promote the anchoring of TM atoms on PtSe2 and demonstrate that 29 types of TM@PtSe2 in different charge states are stable. Among these materials, Pd-center dot@PtSe2 (eta(OER/ORR) = 0.31/0.43 V) and Pd-x@PtSe2 (eta(OER/ORR) = 0.36/0.74 V) systems not only have low formation energy but also exhibit excellent catalytic performance, due to their ultralow overpotential (eta). Interestingly, our results reveal that adjusting the charge states of TM@PtSe2 is a new effective method for designing low overpotential bifunctional OER/ORR electrocatalysts. This adjustment can tune the interaction strength between the oxygenated intermediates and TM@ PtSe2. Additionally, we employ machine learning (ML) models to investigate the origin of activity in OER/ORR processes. Our results reveal that the first ionization energy (I-m), the electronegativity (N-m), the number of TM-d electrons (N-e), the d-band center (epsilon(d)), the electron affinity (chi(m)), and the charge transfer of TM atoms (Q(e)) of TM@PtSe2 are the primary descriptors characterizing the adsorption behavior. This study emphasizes the impact of defect charges on electrochemical reactions, offering theoretical guidance for designing single-atom catalysts and exploring more efficient bifunctional OER/ORR electrocatalysts.