*2.3. Green Hydrogen*

The electrolysis of water is also a common method of hydrogen production. The electrochemical dissociation of water into oxygen and hydrogen was studied in [41]. Based on recent research, low-temperature electrolysis is used to produce hydrogen. It allows to store electricity from renewable sources in chemical bonds in the form of high-purity H2 [42]. Low-temperature electrolysis of water uses a concentrated potassium hydroxide solution KOH, a proton exchange membrane (PEM), or an alkaline anion exchange membrane (AEM) as an electrolyte. The main advantage of AEM electrolysis over other options is its cost as in this case there is no need to use platinum group metals (PGM) as catalysts. However, the major difficulty is the instability of the alkaline method, due to the sensitivity to pressure drop and the low rate of hydrogen production [43]. A traditional electrolysis device consists of two metal electrodes, an anode and a cathode, placed in an electrolyte solution and separated by a membrane [44]. When a current passes through the solution, oxygen bubbles rise above the anode and hydrogen bubbles above the cathode. To minimize the amount of energy required to liberate hydrogen from water, both electrodes are usually coated with a catalyst. However, to produce hydrogen, significant volumes of fresh water will be required, the reserves of which are already limited. The solution of this problem would be the conversion of seawater.

The seawater is mainly a mixture of Cl and Na ions. Unfortunately, Cl ions cause corrosion of the anode metal and prevent the production of hydrogen. To overcome this problem, the anode is designed as a porous nickel foam pan collector coated with an active and cheap nickel and iron catalyst [45]. Moreover, there is added negatively charged sulfate and carbonate molecules to the catalyst bed [46].

Currently, almost all the hydrogen is used in the immediate vicinity of the place of its production [47]. One of the main challenges in the construction of sustainable hydrogen energy systems is the problem of its transport. Therefore, it is necessary to consider promising technologies for the transport of hydrogen in a bound state.

#### **3. Concept of Transport and Storage of Hydrogen in a Bound Form**

The major issues related to the creation of the global hydrogen energy industry and the use of hydrogen as a fuel are its storage and transport.

To ensure sustainable development of hydrogen energy, it is proposed to consider the possibility of using sea transport, for example, bulk carriers and tankers. Their production and operation are more economical and safer than LNG ships. In addition, at the moment there is no experience in operating tankers for the transport of liquefied hydrogen.

When considering the role of Arctic regions in the development of hydrogen economy it is worth mentioning that actually the Russian ship owners control 356 tankers of various size [48].

In Saint Petersburg Mining University, the possibilities of pipeline transport of gas and methane through existing pipelines has been extensively studied [49].

In a situation where the construction of a gas pipeline or an LNG plant is not economically feasible, it is proposed to consider an option of producing hydrogen from methane. Hydrogen can be converted into various chemical compounds. The production, storage and transportation methods of these products must be well understood, the regulatory framework well structured, and the international markets for such substances well developed. It looks that ammonia and methanol meet these requirements.
