**1. Introduction**

The purpose of this book is to provide abundant and substantial information about recent development in the production, storage, and application of hydrogen in the energy sector. Since hydrogen energy has benefits in use cases and, unlike synthetic carbon-based fuels, can be truly carbon neutral or even negative throughout its life cycle, hydrogen is emerging as a new energy vector outside of its traditional role and garnering more recognition globally as a viable fuel pathway. This book aims to cover the recent development in the use of hydrogen, storage, transportation, distribution, and the main difficulties and opportunities in the commercial deployment of such systems. It also discusses various methods for producing hydrogen using conventional and renewable energy sources.

### **2. An overview on energy demand**

Because of the ongoing difficulties caused by diminishing fossil fuel supply and deteriorating environmental circumstances, the international community views sustainable development as a long-term issue. Rising energy demands, erratic fossil fuel prices, and significant greenhouse gas (GHG) emissions from fossil fuel-powered vehicles and businesses are the primary causes of this fundamental transition [1–3].

By 2030, the population of the world is expected to reach eight billion, and an increase in energy demand is predicted. In recent decades, renewable energy sources including wind, solar, hydro, and geothermal have drawn a lot of interest. These forms of energy do not produce liquid or gaseous fuels for transportation. Their applicability is constrained by their unpredictable and sporadic existence [4]. Invasive plants and food waste (especially tree trimmings and agricultural crop waste) are additionally low-cost and accessible resources for conversion to clean energy production [5]. Food scraps [6], municipal waste residue, agrochemicals, pharmaceuticals, animal waste, mixed polymers, and lignocellulosic feedstocks are all readily available and inexpensive [7].

Human life, social culture, and economic development all depend on energy. Conventional fossil fuels have been exploited for over two decades, including coal, gasoline, and natural gas, lead to unsustainable oil use, unrestrained exploitation, and major pollution [8]. These non-renewable resources are therefore rapidly approaching degradation and exhaustion [9]. Particularly, the rapid economic transformation and escalating worldwide population increase are driving up energy demand and escalating the energy issue [10]. Furthermore, there is enormous environmental

contamination because of the overuse and consumption of fossil fuels. The majority of nations are therefore eager to create a different source of renewable energy [11].
