## 1 Introduction  
### Global Context of Production of Green Hydrogen  
According to the Intergovernmental Panel on Climate Change (IPCC), the global average temperature of land and ocean surfaces increased by approximately 1.1 \({}^{\circ}\)C since the pre-industrial period (1850-1900) to the present. This increase in average temperatures coincides with the beginning of the Industrial Revolution, when an economy based on agriculture and artisanal production transformed into one dominated by technology and mechanical manufacturing, requiring the intensive use of fossil fuels [1,2]. This process, along with other human activities such as deforestation, land use, and climate change, etc., has led to a sustained accumulation of greenhouse gases (GHGs) in the atmosphere, triggering the phenomenon known as climate change. This is manifested not only in rising global temperatures but also in extreme weather patterns, loss of biodiversity, and alterations in the planet's hydrological and chemical cycles [3]. Likewise, climate change puts the global economy and food security at risk by affecting agriculture through changes in precipitation patterns and increasing the frequency and severity of heat waves, droughts and floods, hurricanes, and fires. World Bank data estimate that climate-induced natural disasters \"are equivalent to a loss of $520 billion in global consumption and push some 26 million people into poverty each year\". For this reason, climate change is one of our main global challenges, and action must be taken to reduce greenhouse gas emissions [4,5]. In this sense, hydrogen is emerging as a promising energy source to combat climate change, transition to cleaner and more sustainable energy sources, and decarbonize the global economy [6]. This is due to its multiple benefits, including its versatility and high energy content, which can be up to three times higher than that of commonly used liquid fuels, such as gasoline, diesel, or oil. Furthermore, it is emerging as a key energy vector to replace fossil fuels as the primary source of energy in sectors that are difficult to electrify, such as heavy transport, the chemical industry, and the steel industry. It is estimated that, in 2020, the chemical industry consumed around 46 million tons, and the steel industry consumed 5 million tons of hydrogen [7]. Hydrogen (H\({}_{2}\)) is the chemical element with the simplest structure on the periodic table and is the most abundant in the universe. On our planet, it is only found in combination with other elements, such as water (H\({}_{2}\)O) and methane (CH\({}_{4}\)). Hydrogen can be produced by a variety of methods, and depending on how it is produced, it can have different environmental impacts [8]. This type is classified as gray hydrogen, blue hydrogen, and green hydrogen. Gray hydrogen is produced from fossil fuels, primarily natural gas (methane) and coal. In 2020, 79% of global hydrogen demand (90 million tons) was met by fossil fuels. Of this, 60% was obtained through methane reforming, which splits natural gas into hydrogen and CO\({}_{2}\). The remaining 19% was generated through coal gasification. Both processes generate GHG emissions that are not captured and released into the atmosphere. The latter is particularly carbon-intensive, emitting between 18 and 25 kg of CO\({}_{2}\) per kg of H\({}_{2}\), making it one of the most polluting methods for producing hydrogen, commonly called \"brown hydrogen\" [9]. Each year, approximately 6% of global natural gas and 2% of coal reserves are used for the production of gray hydrogen, a process that results in the emission of approximately 830 million metric tons of CO\({}_{2}\), representing 2.5% of global emissions of this gas. In total, global hydrogen production generates approximately 900 million metric tons of CO\({}_{2}\) annually. Despite its significant environmental impact, gray hydrogen is widely used due to its low production costs and large installed capacity [10]. Blue hydrogen is also produced from fossil fuels.