# An Overview of Hydrogen's Application for Energy Purposes in Lithuania
## 3 Hydrogen Value Chain  
In most of energy forecasts up to 2050 hydrogen is predicted to become a major energy carrier, in addition to electricity, to meet energy demand of end users in different economic sectors. Hydrogen is valued for its energy efficiency, application versatility, abundant resources and minor environmental emissions [21]. A hydrogen-based economy would introduce new technological and economic opportunities and would be capable of changing the oil refining industry drastically, contributing to changes in the supply and demand mix. Green hydrogen stands out with a long and complex value chain consisting of green electricity production, hydrogen production, hydrogen distribution, storage and transportation, as well as the various hydrogen applications in mobility, industry, heat supply or base chemistry. Looking from a high level, hydrogen value chain is typically split into the three main fields: production, storage and distribution and consumption/application. Each of these fields is described further. Hydrogen can be made using different methods and is classified to a range of \"colours\" depending on the source of energy and the production method used. Most common is grey hydrogen which is produced from natural gas or coal by steam-methane reforming (SMR). This means high-pressure steam (H\({}_{2}\)O) reacts with natural gas (CH\({}_{4}\)) resulting in hydrogen (H\({}_{2}\)) and greenhouse gas CO\({}_{2}\). This type of hydrogen is a dominant technology, accounting for 95% of the production market [22]. Another report shows that the share of high-emission (natural gas without carbon capture, coal and oil refineries) hydrogen production reaches 99.3% [23]. Meanwhile, a blue hydrogen results from the same production processes as grey hydrogen, but most of CO\({}_{2}\) is captured, used, and stored. Currently, this technology is at the experimental stage with only a few pilot projects launched around the world [22], accounting for only 0.6% of global hydrogen production [23]. The use of other hydrogen types, including green hydrogen, is marginal, reaching only 0.1% [23]. Figure 1 below shows graphically a typical hydrogen value chain where the process starts on a left-hand side with hydrogen production. When grey or brown hydrogen is formed using brown coal or natural gas through either SMR or gasification techniques, in both cases the CO\({}_{2}\) emissions are released into the atmosphere. However, if a starting material is biomass (different conversion processes), water and renewable electricity (electrolysis) or thermocatalytic decomposition (or pyrolysis) of methane (TDM) are used, then the green hydrogen is produced. Once produced, hydrogen can be used as a fuel in a transport or power sectors as well as a heat source for industry and buildings and finally as a feedstock in chemical production. Additionally, hydrogen can be stored as a compressed or liquefied gas, as ammonia and in a form of LOHC (liquid organic hydrogen carriers, like toluene). Eventually, hydrogen is distributed by pipelines, truck, rail and LNG (liquefied natural gas) ships. According to the latest Global Hydrogen Review 2023 [23], the industry is now particularly focused on extracting hydrogen from fossil fuels using water electrolysis or carbon capture and storage (CCUS) techniques. As green hydrogen is at the centre of research, much effort is being given to the search for the best water electrolysis technologies which are being continuously developed to increase process efficiency and are used in industrial applications. Each water electrolysis technology has its own challenges, significance and technological breakthroughs briefly described below. According to [24], there are four types of water electrolysis technologies based on operating conditions, electrolyte used and their ionic agents (OH\({}^{-}\), H\({}^{+}\), O\({}_{2}\)\({}^{-}\)):  
- Alkaline water electrolysis;  
- Anion exchange membrane (AEM) water electrolysis;  
- Proton exchange membrane (PEM) water electrolysis;  
- Solid oxide water electrolysis.