Nanomaterials for Energy Harvesting and Storage: An Overview

1. Introduction

Rapid increase in population vis-à-vis advancement in the economy worldwide has resulted in accelerated consumption of energy. Increased dependence and usage of appliances has also enhanced the usage of energy. It is predicted that there may be a requirement of nearly 30 TW of energy resources by the year 2050 to maintain economic growth (Doung, 2002). The excessive dependence on fossil fuel reserves to meet the increasing demand for energy has led to two significant but alarming results. Firstly fossil fuel resources are limited and there is a steady depletion of its reserves on the earth’s crust; thereby the world is slowly but steadily hurtling towards a possible energy crisis. Secondly, there has been a steady increase in the green house gas emissions leading to environmental pollution, global warming and climate change. Both energy and environment crisis will threaten the sustainability and development of humans. Among the widely available renewable energy resources, solar energy is the cleanest form of energy. Converting solar energy to electrical energy via photovoltaics has been considered as the best choice and is being widely used in various consumer products (Ananthakumar et al., 2019). The first generation of solar cell technology involves the use of crystalline form of silicon as the semiconducting material. While the second generation involves the use of thin film solar cell technology, the third generation involves the use of dye or quantum sensitized and/or polymer solar cells. But a consistent supply of such harvested electrical energy to the consumer is not possible; hence highly efficient energy storage devices are desirable. Among the devices used to store electric energy are the lithium ion rechargeable batteries and the supercapacitors. The basic essence is to reinvent and restructure the traditional process streams and technologies so as to enhance the efficiency of energy generation from solar resources and improve storage performance. High cost of fabrication/maintenance, decreased efficiency as well as lower durability is some of the limitations exhibited by the traditional appliances and technologies.

Nanotechnology has provided an extensive range of nanomaterials as resources to help improve the performance of solar cells as well as storage batteries (Harris, 2001; Dai 2006; Huang et al., 2011). Some of the nanomaterials that have been extensively used as electrode materials are carbon nanomaterials, cellulose based nanomaterials, metal oxide nanomaterials, and conducting polymer based nano-composites etc (Arico et al., 2005). Nanomaterials exhibit various particle morphologies ranging from zero-dimensional nanoparticles and quantum dots; one-dimensional nanowires, nanotubes and nanobelts; two-dimensional nanoflakes and nanosheets; and three-dimensional porous nanonetworks. Some of the unique properties exhibited by such nanosized materials are greater electronic, optical, mechanical, photonic, magnetic as well as chemical reactivity as compared to their bulk counterparts. The properties that have greatly influenced the performance of solar cells, batteries and supercapacitors are the nano-sized particles of the nanomaterials as well as their higher surface area. Such properties have helped in improving the ionic transport rate and electrolyte diffusion thereby ensuring high electrochemical efficiency.

Keeping in focus the importance of the use of renewable resources like solar light for energy harvesting and the storage of the same, the present chapter will give an overview of the different nanomaterials that have been used till date for electricity generation from dye sensitized solar cells as well as for electric energy storage. The emphasis of this chapter is on the advantages of using nanomaterials for these applications. Finally challenges of utilizing nanomaterials will also be addressed. It is expected that the latest overview of such content will benefit those undergoing research on nanotechnology and renewable energy technology.