In today's rapidly evolving world, the demand for sustainable energy storage and energy conversion materials has become increasingly imperative [1,2]. As we witness the gradual depletion of conventional fossil fuel reserves and experience heightened apprehension regarding climate change, there is an increasingly urgent demand for alternative energy solutions and the optimized utilization of our resources. Sustainable energy storage materials are instrumental in securing the dependability and availability of renewable energy, facilitating its smooth integration into our electrical networks and transportation infrastructures [3,4]. Additionally, energy conversion materials are vital in reducing energy consumption, optimizing energy efficiency, and minimizing environmental impact. By developing and implementing such materials, we can foster a greener, more sustainable future, where clean energy is harnessed and utilized effectively, leading to a healthier planet and enhanced quality of life for generations to come. In this particular context, researchers have extensively investigated various agro-waste, bio-waste, and industrial waste materials over the last few decades [[5], [6], [7], [8]]. However, our primary emphasis in this review is on eggshells/eggshell membranes (ES/ESM), which hold significant promise as a promising contender for energy-related purposes.

Eggshell waste, a by-product of the egg industry, has garnered attention as a promising candidate for energy related applications. With millions of tons of eggshell waste generated annually worldwide (Fig. 1 shows the global annual egg production in billion scale), finding sustainable uses for this abundant resource is of utmost importance. (http://www.fao.org/faostat/en/#data/QL).

Eggshells are composed mainly of calcium carbonate, which exhibits unique properties that make it suitable for various energy-related applications. Their porous structure and remarkable surface area-to-volume ratio offer outstanding promise as electrode components in energy storage systems like supercapacitors and batteries [9]. Furthermore, the inherent abundance of calcium in eggshells opens avenues for their utilization in calcium-based fuel cells, where calcium ions can act as charge carriers. The utilization of eggshell waste not only reduces environmental burdens by diverting it from landfills but also it actively contributes to the advancement of sustainable energy technologies. By exploring the energy storage and conversion capabilities of eggshell waste, we can unlock its immense potential and pave the way for sustainable and efficient energy solutions.

Some of the excellent reviews have summed up utilization of eggshells in food applications, biotechnological applications, biomedical applications, construction applications [[10], [11], [12], [13], [14], [15], [16], [17]]. A review by MM Cordeiro et al., discusses the patented applications of eggshell membrane waste in clinical, nutraceutical, cosmetic, and nanotechnology applications [18]. Few more review papers are available which have extensively explored the application of eggshell waste in sorption and catalytic functions [19,20]. For several years, eggshells have found its applications as raw materials in various industries, including biomaterial composites, food additives, and soil amendment [[21], [22], [23], [24], [25], [26], [27], [28]]. Despite the value-added uses of eggshells, a significant quantity continues to be underutilized and disposed of in landfills. In recent past, there has been an advanced focus on incorporating eggshell waste into energy storage materials. A schematic representation of this review work is illustrated in Fig. 2.

As discussed in the previous section, several kinds of research have been conducted on the use of eggshell/eggshell membrane in energy related applications (storage and conversion). Nevertheless, a comprehensive, up-to-date review solely dedicated to the utilization of eggshell powder in energy-related materials is currently absent. Hence, this review is intended to cover the overall research works published worldwide on the utilization of eggshell waste towards energy storage and energy conversion applications. This review article is divided into several sections. We begin with a petite preface on eggshell/eggshell membrane and its chemical composition. We then discuss about the eggshell/eggshell membrane based materials as templates, electrodes, electrolytes, reactors, and precursors in energy storage applications such as capacitors and batteries. Further, eggshell/eggshell membrane energy conversion applications such as fuel cell and hydrogen production are reviewed. Conclusively, we delve into the future possibilities and significant avenues for research in utilizing eggshells to create feasible, top-tier energy storage materials, electrodes, and systems with novel characteristics.