Carbon nanotubes: A potential material for energy conversion and storage

Abstract

Carbon nanotube-based materials are gaining considerable attention as novel materials for renewable energy conversion and storage. The novel optoelectronic properties of CNTs (e.g., exceptionally high surface area, thermal conductivity, electron mobility, and mechanical strength) can be advantageous for applications toward energy conversion and storage. Although many nanomaterials are well known for the unique structure-property relations, such relations have been sought most intensively from CNTs due to their extreme diversity and richness in structures. For the development of energy-related devices (like photovoltaic cells, supercapacitors, and lithium ion batteries), it is critical to conduct pre-evaluation of their design, operation, and performance in terms of cost, life time, performance, and environmental impact. This critical review was organized to address the recent developments in the use of CNT-based materials as working/counter electrodes and electrolytes in photovoltaic devices and as building blocks in next-generation flexible energy storage devices. The most promising research in the applications of CNTs toward energy conversion and storage is highlighted based on both computational and experimental studies along with the challenges for developing breakthrough products.

Introduction

The exponentially increasing demand for renewable energy, accompanied by the rise of high-speed, portable, wearable, and transparent electronic devices, has sped up the development of new techniques not only to catch up such unprecedented challenges but also to produce new device architectures. A promising solution for such challenges lies in nanotechnology of which advent can help stimulate the invention and fabrication of many advanced materials with innovative performance. The material structure can be tunable by nanotechnology which endowed nanomaterials with highly unique and novel properties and new opportunities in various fields of applications (e.g., energy conversion and storage, water treatment, contaminant sensing, and molecular biology).

Nanomaterials have been widely investigated as electrodes and electrolytes in energy conversion and storage applications due to their many advantageous properties. In particular, carbon-based nanomaterials (e.g., 2D graphene sheets, 1D carbon nanotubes, and 0D fullerenes) have drawn particular attention due to their properties, which are derived from their atomic structure and surface chemistry. Among the wide variety of nanomaterials, carbon nanotubes (CNTs) possess one of the unique nanostructures due to their fine chemical composition and atomic-bonding configuration. Additionally, CNTs possess strong structure-property relations based on highly diverse structures [1]. The electro-mechanical properties of CNTs have been investigated intensively since their finding in early 1990s. Although early research centered on their growth and characterization, the focus shifted toward diverse commercial fields ranging from photovoltaic (PV) to sensing applications (e.g., by integrating them into thin-film electronics) [2], [3], [4], [5], [6], [7], [8]. As we will demonstrate in this review, there have been growing interests in using CNTs in a range of applications.

Because of their many fascinating properties (e.g., good mechanical strength and elasticity, high electronic sensitivity to mechanical strain and chemical absorbates, good electronic properties ranging from semiconductor to metals, and very large surface area-to-volume ratio), the use of CNTs has been recommended for diverse applications such as components of PV devices, energy storage devices, chemical sensors, actuators, and metrology-probe tips [9], [10], [11], [12]. In this review, we focused on the role of CNT-based materials in energy conversion and storage. Existing studies directed to both theoretical and computational aspects of CNTs are all discussed. We also detailed the challenges associated with their practical application toward commercialization.