Exploring single-atom catalysis for hydrogen evolution and storage: A DFT insight into first-row transition metal-porphyrin complexes (Porph@TMs)

Abstract

Single-atom catalysts (SACs) have emerged as the potential for hydrogen evolution reaction (HER) catalysts owing to their unique electronic properties, catalytic efficacy, and efficient atom utilization over the catalyst surface. Controlling SACs' electronic structure and coordination environment may improve their electrocatalytic activity. We use comprehensive density functional theory (DFT) to design a novel Porphyrin-based complex (Porph@TMs) that relies on the first row of transition series (Sc-Zn) for HER and hydrogen storage (HS) usage. We found the highest stable thermodynamics stability for the Porph@Fe catalyst in the binding, cohesive, and formation energies (−12.85, −0.347, and −12.51 eV). Porph@Sc (4.66 eV) catalyst has the lowest FMOs energy gap. Charge transfer from TM to catalyst surface is measured using Porph@ScPorph@Sc's lowest d-band center value (εd) at 0.53 eV catalyst. Higher Bader charge (q) and lower work function (Փ) values indicate significant charge transfer. The Porph@Sc catalyst exhibited a higher Bader charge value (q = 2.5082 e), the smallest work-function (Փ = 3.519 eV), and the lowest chemical hardness (ղ = 2.33 eV) in this study. Our theoretically investigated best HER catalysts, Porph@Sc (ΔG_H∗ = −0.002 eV) and Porph@Mn (ΔG_H∗ = 0.038 eV), exhibit lower Gibbs free energy and better electrocatalytic abilities than the experimentally well-known Pt (111) catalyst at (ΔG_H∗ = −0.09 eV). On evaluating the mechanistic investigation of HER catalysts, we determined that Porph@Co (ΔG_H∗ = 0.08 eV) and Porph@V (ΔG_H∗ = 0.05 eV) demonstrated the lowest ΔG_H∗ for the Volmer-Tafel and Volmer-Heyrovsky reactions, respectively. Furthermore, we investigated the hydrogen storage capacity of the best HER catalysts to evaluate the dual functionality of our newly designed catalysts. We found that Porph@Sc had a stable average adsorption energy of −0.19 eV, with a hydrogen storage capacity of 3.31 wt%. Moreover, we implement Ab initio molecular dynamics (AIMD) simulations at 300K to test our newly discovered optimum catalysts for examining the thermal oscillations and kinetic behavior up to 2000 MD ionic steps. This research enables the development of a low-cost, highly efficient, thermally stable ambient electrocatalyst with excellent hydrogen production and storage devices.