Hydrogen has been used for a long time in industries like the chemical and refining sectors. However, interest in its use as an energy source has only begun to grow in recent years. The demand for hydrogen is expected to rise at a compound annual growth rate of 5.48 percent between 2019 and 2025 in tandem with this interest and end-use.
The production of hydrogen ought to produce little or no carbon emissions in order to guarantee that this demand for hydrogen is met sustainably andwith the least amount of impact on the environment. Green hydrogen, also known as this kind of hydrogen, can be produced using carbon capture, utilization, and storage (CCUS) from fossil fuels, nuclear energy, or renewable sources.
Green hydrogen production can result in a wide range of emissions, ranging from 43 gCO2e/kg of hydrogen produced through electrolysis to 9.3 kgCO2e/kg of hydrogen produced through the steam reforming process without carbon capture.To put things in perspective, one kilogram of hydrogen has the same amount of energy as one gallon of gasoline and produces 9.1 kilograms of CO2 when it is burned.
Compared to the 25% efficiency of internal combustion engines, fuel cells have an efficiency of over 50% for the majority of transportation applications. That is, considering production to the tailpipe, hydrogen emissions are half that of gasoline for comparable mileage. Green hydrogen's widespread commercialization and use face significant obstacles. As a result, the four phases of the green hydrogen commercialization process highlighted in this work are as follows: production, storage, distribution, transport, and final use.
Based on a high-level review of more than 200 completed or ongoing hydrogen projects worldwide, the difficulties outlined here are:
Electrolysis: In this process, water is split into hydrogen and oxygen using electricity. By calorific value, this process is 60-80 percent efficient. The commercialization and huge scope arrangement difficulties of electrolysis are as per the following- need for greater energy efficiency as a whole, requirement for additional compressors on-site and electrolytes have a short lifespan.
Reforming the steam: Hydrogen can be produced from methane, liquids derived from biomass resources, and biogas through steam reforming. With conversion on-site or at refuelling stations, this procedure has the advantage of being a mature technology and making it simple to transport input fuels. To reduce net emissions, additional carbon capture mechanisms should be in place if natural gas or methane are used.
The following are the difficulties that come with using this method: Due to the relatively larger molecule sizes of biomass-derived liquids than fossil fuels, the reforming process is extremely complex. The process's overall efficiency is low (currently around 40%). The reformer ought to have the option to adjust to various arrangements and stream paces of biogas or biofuels and neighbourhood heat sources.
Fermentation: Utilizing microbes, either directly through hydrogen fermentation or through microbial electrolysis cells (MECs), sugar-rich biomass feedstock is fermented to produce hydrogen in this process. The following are the difficulties that come with fermentation: The biogas reactor's overall efficiency is poor; fermentation produces hydrogen at low rates and yields. Increasing of MEC frameworks while keeping up with creation rates and framework efficiencies are not yet demonstrated.
Additionally, a number of novel approaches to water splitting production are being developed.
High-temperature water splitting, photobiological water splitting, photoelectrochemical water splitting, low-temperature hydrogen production through replication of photosynthesis, and hydrogen by-product extraction from chemical industries are some examples.
The three most common ways that hydrogen is stored are: cooling, compression, or hybrid. Solids, liquids, or surface-based materials are also being used in the development of material-based hydrogen storage. On-site storage of hydrogen is used for production plants and end-use applications, whereas bulk storage is used for large amounts of hydrogen storage in geographical storage (such as salt caverns, abandoned mines, and so on). The storage of hydrogen, on the other hand, presents some difficulties, as will be discussed later.
Due to its low specific gravity, compressed hydrogen storage requires a significant amount of energy requirements for temperature and pressure when storing hydrogen in a solid state. Aspects of design, legal issues, social issues, and the high cost. Low sturdiness of materials (fibre, metals, polymers and so on.) and storage and the possibility of chemical reactions raise security concerns. The hydrogen may become contaminated during bulk storage at geographical features, necessitating additional purification before final use.
Transport and Distribution of Hydrogen: Hydrogen can be utilized on-site or transported to end-user locations for distribution. Pipelines, high-pressure tube trailers, and liquified hydrogen tankers are the most common means of transporting and distributing hydrogen. Pipelines are currently the most cost-effective method and are already in use close to large chemical plants and refineries.
The hydrogen that has been cooled down to a temperature at which it turns into a liquid is transported by liquid hydrogen tankers. Distributed hydrogen has a higher density as a result, making it more transportable than high-pressure tube trailers. However, the compressed hydrogen will evaporate, resulting in significant losses and inefficient utilization if the delivery and consumption rates are not coordinated. The following are the difficulties associated with hydrogen distribution and transport:
The existing infrastructure for hydrogen transportation pipelines is insufficient to meet future demand. Due to embrittlement, hydrogen cannot be transported directly through existing natural gas pipelines. Even though mixing hydrogen with natural gas is a possibility, even at a concentration of 5% by volume, it significantly shortens the lifespan of pipelines.
At refuelling stations, there isn't enough fine control over the flow of hydrogen. The system's evaporation and losses are significantly affected by the flow of hydrogen. To avoid thermal instability and minimize losses during rapid transfers of compressed hydrogen, optimal temperature control is required. It is necessary to expand the network of hydrogen refuelling stations.
In order to make it possible for a low-cost, high-energy-density transfer of hydrogen, new methods of transportation, such as the use of liquid organic materials as hydrogen carriers, are currently being investigated.