[Paper Review] Enhanced Hydrogen Storage in Gold-doped Carbon Nanotubes: A first-principles study

Shima Rezaie, David Smeulders+1 more|arXiv (Cornell University)|Nov 24, 2022

Hydrogen Storage and Materials4 citations

TL;DR

This first-principles study proposes gold-doped carbon nanotubes (Au-CNTs) as a high-performance material for reversible hydrogen storage. By enhancing binding energy through charge transfer and optimizing tube diameter, Au-CNTs achieve 154–330 g/L volumetric capacity and desorption temperatures above 200 K, surpassing the U.S. DOE targets.

ABSTRACT

Sorbent materials are a promising alternative to advance hydrogen storage technologies. The general disadvantage is the relatively weak solid-gas interaction and adsorption energy, providing low gravimetric and volumetric capacities and extreme operational conditions. Here we propose Au-doped carbon nanotubes (CNTs) as an efficient alternative for reversible hydrogen capture at high temperatures. This work investigates the properties of several modified CNTs using density functional theory. We analyze the binding and formation energies of the uniformed Au-doped CNTs and assess their adsorption capability. The hydrogen storage mechanisms of the nanostructures are studied in depth using partial density of states and charge transfer analysis showing that the increase of diameter has a positive effect on the outcome. Our findings show that the modified structures are able to capture from six to nine hydrogen molecules per gold atom, achieving volumetric capacities ranging from 154 to 330 g/l, surpassing the DOE target. In addition, the calculated desorption temperatures indicate high performance of Au-doped CNTs, obtaining hydrogen capture-release working conditions above 200 K.

Motivation & Objective

• To develop a high-capacity, reversible hydrogen storage material to overcome limitations of conventional sorbents.
• To investigate the effect of gold doping on the electronic and adsorption properties of carbon nanotubes.
• To determine the optimal structural parameters, such as tube diameter, for enhanced hydrogen binding.
• To evaluate the volumetric and gravimetric storage capacities and desorption temperatures of Au-doped CNTs.
• To identify viable working conditions for hydrogen capture and release above 200 K.

Proposed method

• Density functional theory (DFT) calculations were used to analyze binding and formation energies of Au-doped CNTs.
• Partial density of states (PDOS) analysis was performed to study electronic interactions between Au and H2 molecules.
• Charge transfer analysis was conducted to understand the nature of bonding at the Au-CNT interface.
• Structural models with varying CNT diameters and uniform Au doping were systematically evaluated.
• Hydrogen adsorption capacity was calculated per gold atom and per unit volume.
• Thermodynamic desorption temperatures were estimated based on binding energy trends.

Experimental results

Research questions

• RQ1 How does gold doping affect the hydrogen adsorption energy and capacity in carbon nanotubes?
• RQ2 What is the influence of CNT diameter on the binding strength and storage capacity of hydrogen in Au-doped systems?
• RQ3 Can Au-doped CNTs achieve hydrogen volumetric capacities exceeding the U.S. DOE 2025 target?
• RQ4 At what temperature can hydrogen be reversibly released from Au-doped CNTs?
• RQ5 What is the charge transfer mechanism between gold atoms and hydrogen molecules in doped CNTs?

Key findings

• Au-doped CNTs can capture between six and nine hydrogen molecules per gold atom, significantly enhancing storage capacity.
• The volumetric hydrogen storage capacity ranges from 154 to 330 g/l, surpassing the U.S. Department of Energy (DOE) target.
• Increased CNT diameter improves hydrogen adsorption capacity due to enhanced electronic interaction and charge transfer.
• Desorption temperatures for hydrogen are predicted to be above 200 K, indicating feasible reversible operation at moderate temperatures.
• Charge transfer analysis confirms that gold atoms act as electron donors, strengthening H2 binding via electrostatic and orbital interactions.
• Partial density of states (PDOS) analysis reveals hybridization between Au 5d orbitals and H 1s states, indicating chemisorption-like bonding.