Carbon-based nanocomposites have developed as the most promising and emerging materials in nanoscience and technology during the last several years. They are microscopic materials that range in size from 1 to 100 nanometers. They may be distinguished from bulk materials by their size, shape, increased surface-to-volume ratio, and unique physical and chemical characteristics. Carbon nanocomposite matrixes are often created by combining more than two distinct solid phase types. The nanocomposites that were constructed exhibit unique properties, such as significantly enhanced toughness, mechanical strength, and thermal/electrochemical conductivity. As a result of these advantages, nanocomposites have been used in a variety of applications, including catalysts, electrochemical sensors, biosensors, and energy storage devices, among others. This study focuses on the usage of several forms of carbon nanomaterials, such as carbon aerogels, carbon nanofibers, graphene, carbon nanotubes, and fullerenes, in the development of hydrogen fuel cells. These fuel cells have been successfully employed in numerous commercial sectors in recent years, notably in the car industry, due to their cost-effectiveness, eco-friendliness, and long-cyclic durability. Further; we discuss the principles, reaction mechanisms, and cyclic stability of the fuel cells and also new strategies and future challenges related to the development of viable fuel cells.

Metal-air batteries and fuel cells are considered the most promising highly efficient energy storage systems because they possess long life cycles, high carbon monoxide (CO) tolerance, and low fuel crossover ability. The use of energy storage technology in the transport segment holds great promise for producing green and clean energy with lesser greenhouse gas (GHG) emissions. In recent years, nanoscale based electrocatalysts have shown remarkable electrocatalytic performance towards the construction of sustainable energy-related devices/applications, including fuel cells, metal-air battery and water-splitting processes. This review summarises the recent advancement in the development of nanoscale-based electrocatalysts and their energy-related electrocatalytic applications. Further, we focus on different synthetic approaches employed to fabricate the nanomaterial catalysts and also their size, shape and morphological related electrocatalytic performances. Following this, we discuss the catalytic reaction mechanism of the electrochemical energy generation process, which provides close insight to develop a more efficient catalyst. Moreover, we outline the future perspectives and challenges pertaining to the development of highly efficient nanoscale-based electrocatalysts for green energy storage technology.

High efficient, low-cost and environmentally friendly-natured bi-functional-based perovskite electrode catalysts (BFPEC) are receiving increasing attention for oxygen reduction/oxygen evolution reaction (ORR/OER), playing an important role in the electrochemical energy conversion process using fuel cells and rechargeable batteries. Herein, we highlighted the different kinds of synthesis routes, morphological studies and electrode catalysts with A-site and B-site substitution co-substitution, generating oxygen vacancies studies for boosting ORR and OER activities. However, perovskite is a novel type of oxide family, which shows the state-of-art electrocatalytic performances in energy storage device applications. In this review article, we go through different types of BFPECs that have received massive appreciation and various strategies to promote their electrocatalytic activities (ORR/OER). Based on these various properties and their applications of BFPEC for ORR/OER, the general mechanism, catalytic performance and future outlook of these electrode catalysts have also been discussed.