Charge modulation for efficient CO2 capture and reduction reactions: an integrated ab-initio and numerical methods approach

Abstract

The growing urgency to address environmental challenges, such as air pollution and greenhouse gas (GHG) emissions, has made gas-adsorbent materials (GAMs) a critical focus in materials science. GAMs are essential for advancing carbon capture and storage (CCS) technologies, where their ability to selectively adsorb and sequester carbon dioxide (CO2) prevents its release into the atmosphere. These materials are also used in gas sensors, air filtration, and other monitoring technologies, as well as in various industrial sectors where removing specific gases or impurities can improve safety, process efficiency, and product quality. In this regard, the pursuit of materials with enhanced durability, higher adsorption capacity, controllable gas molecule adsorption, and low energy requirements for regeneration, and also the use of techniques such as charge modulation of host materials to improve performance, are of great importance in research and development. This thesis employs density functional theory (DFT) to conduct a theoretical investigation of charge modulation, exploring both its computational and practical aspects. To this end, a virtual crystal approximation (VCA)-based method is proposed to maintain the plane-averaged electrostatic potential (PAEP) unperturbed in the vacuum region while charging the system. This method, designed to more accurately capture key energy-related parameters, such as shifts in the Fermi level under charge injection, offers improvements over standard techniques. In this model, surface host materials are charged by the atoms arranged at optimum positions around them, creating a quasi-two-dimensional (2D) jellium scenario. On the other hand, through a screening plan adopted in this thesis to identify truly high-performance charge-responsive adsorbents, we present the graphene-like 2D material beryllonitrene (BeN4) with a single-vacancy defect, created by removing one Be atom, as an effective candidate for CO2 capture across different charge states. It is demonstrated how the defected BeN4 responds to the introduced electrons in a highly controllable manner and how strain engineering, acting synergistically, contributes to enhancing the gas separation performance. Nickel diazenide (NiN2), a novel 2D hybrid layer with a pentagonal atomic arrangement, is another material we investigate, focusing on charge modulation through direct charge injection and ion-induced mechanisms. NiN2 undergoes a transition from metallic bulk to a direct band-gap semiconductor, exhibiting high carrier mobility and abundant nitrogen active sites in both monolayer and bilayer forms; however, its CO2 adsorption performance under charge modulation falls short of the threshold required for superior energy efficiency and practical competitiveness. Still, the bilayer, benefiting from zero-gap character and graphite-like mechanical robustness, demonstrates strong potential as a fast, high-capacity anode material for efficient lithium-ion intercalation within the van der Waals (vdW) interlayer space. Show more