Green hydrogen for a sustainable future: A review of production methods, innovations, and applications

Hydrogen, the lightest and most plentiful element in the universe, has emerged as a cornerstone in the global transition to sustainable power solutions. As a zero-emission fuel that produces only water when combusted, hydrogen has captivated worldwide attention for its potential to power a sustainable and greener future. With the depletion of crude oil reserves and the pressing need to mitigate climate change, scientific and industrial efforts are increasingly focused on renewable energy solutions. These efforts align with international agreements such as the Montreal Protocol (1987), Kyoto Protocol (1997), and Paris Agreement (2015), which emphasize the reduction of emissions of greenhouse gas and the adoption of sustainable practices [[1], [2], [3], [4]].

Hydrogen stands out for its unparalleled energy storage capacity—three times that of gasoline and seven times that of coal—making it an attractive alternative for addressing the energy demands of a growing global population. Despite fossil fuels dominating the energy market with a 70% share in 2023 and contributing to an annual release of 36.8 billion metric tons of CO₂, renewable energy transition is gaining momentum globally [5]. Solar, wind, hydro, geothermal, and biomass energy offer cleaner, more sustainable alternatives, though they face challenges like intermittency, unpredictability, and high storage costs [6]. Amid these limitations, green hydrogen, formed through water electrolysis powered by renewable electricity, has manifested as a transformative solution. It not only stores renewable energy for consistent availability but also plays a pivotal role in attaining Sustainable Development Goal 7—ensuring access to affordable, reliable, and sustainable energy [7].

While the promise of hydrogen as a clean, sustainable fuel is significant, several challenges must be addressed. Its low density, high flammability, and the complexities associated with storage and transportation pose hurdles to its widespread adoption [8,9]. Nevertheless, hydrogen’s potential to decarbonize transportation, heavy industry, and power generation aligns seamlessly with global sustainability goals, making it a key player to combat climate change [10].

As hydrogen’s role in the global energy mix expands, innovations in its production, storage, and distribution are critical. The development of cost-effective technologies, such as electrolysis powered by renewable energy, and the establishment of supportive infrastructure and regulatory frameworks, will be key to harnessing the full potential of the hydrogen economy by 2050. This article delves into the innovations driving green hydrogen production and examines its transformative role in shaping a sustainable future [11].

Hydrogen production methods are broadly categorized into two main approaches: reforming fossil fuels like methane and methanol, and splitting water through electrolysis [12]. Fossil fuel reforming, including steam methane reforming (SMR) and coal gasification, dominates global hydrogen production, accounting for approximately 76% of output. However, these methods are unsustainable and carbon-intensive, emitting 8–30 kg of CO₂ per kg of hydrogen produced [13]. While SMR is an endothermic and efficient process, it relies on finite natural gas reserves and has a significant impact on greenhouse gas emissions. To address these challenges, the focus must shift toward carbon-free sources such as water electrolysis, biomass gasification, and metal-water splitting.

Water, as the most promising hydrogen-rich source, offers a 2:1 hydrogen-to-oxygen ratio, and electrolysis generates no direct emissions. Biomass gasification utilizes organic material with minimal carbon footprint, while metal-water splitting employs reactive metals to facilitate hydrogen production, though its dependence on mining raises sustainability concerns [14]. Transitioning to these carbon-free methods, particularly electrolytic production of green hydrogen using renewable energy, offers a sustainable path to carbon-neutral hydrogen production, aligning with global climate goals [15,16].

Green hydrogen derived from water electrolysis using renewable power, is a highly promising energy carrier due to its unique properties. Physically, the molecular weight of hydrogen is 2.016 g/mol, making it the lightest element, and exists as a colorless, odorless, and tasteless gas. It has an extremely low density of 0.08988 kg/m³ at standard temperature and pressure (STP), making it about 14 times lighter than air [17]. Chemically, hydrogen is highly reactive, possessing the highest energy content per unit mass among fuels at 120 MJ/kg. Its combustion produces only water, ensuring zero direct carbon emissions, which positions it as a clean alternative to fossil fuels [18]. Environmentally, green hydrogen is sustainable and produced using renewable energy, substantially cutting reliance on non-renewable resources and greenhouse gas emissions [19]. Green hydrogen production made more efficient by combining hybrid systems such as integrating renewable energy sources like solar, wind and hydro with electrolysis [7].

However, its volumetric energy density is low, necessitating advanced storage solutions such as high-pressure tanks, liquefaction, or metal hydrides. Furthermore, hydrogen’s versatility allows its use in diverse applications, including energy storage, transportation, and industrial processes, as well as its function as a precursor for synthetic fuels [16]. These properties highlight the potential of green hydrogen as a cornerstone of the global transition to a sustainable and decarbonized energy future.