Electrolysis for Green Hydrogen Production

Towards a Cleaner, Greener Future

Electrolysis for Green H₂ Production

Whether as a zero-emission fuel for mobility, a carbon-neutral industrial feedstock, a vector for renewable energy or a storage medium to buffer volatile power grids, green hydrogen will play a critical role in a net-zero economy. The technology to produce zero emissions hydrogen is therefore also thrust into a central role.

Today, the most common way of producing green hydrogen is via electrolysis - a process whereby water is split into hydrogen and oxygen using electricity generated from entirely renewable energy sources. This occurs in units known as electrolyzers. Electrolyzers can range in size and capacity as well as the technology used, but the basic chemistry happening within is essentially the same.

Electrolyzers for green hydrogen production at the Leuna plan

How It Works: A Look Inside the Electrolyzer

From what can look like a shipping container from the outside, is a system of pumps, storage tanks, vents, a power supply, and other components - at the center of which are the cells. Here, the electrochemical reaction occurs. In its simplest form, a cell contains a positively charged anode and a negatively charged cathode.

When a current is applied, the otherwise stable H₂O bonds in water break and hydrogen forms on the cathode with oxygen forming on the anode - a by-product that can be used downstream in industrial settings or released into the atmosphere at no carbon cost.

A Tale of Two Technologies

Water is not a great conductor of electricity. So, to ensure an energy-efficient process, electrolytes are used instead. Electrolysis technologies differ according to the type of electrolyte used. Currently, the two main technologies are alkaline and PEM (Proton Exchange Membrane) - both of which can deliver high pure hydrogen on-site and on-demand.

Alkaline

Alkaline electrolysis is a very well-established technology that uses two electrodes separated by a porous diaphragm and a liquid alkaline solution as the electrolyte. The electrolyte solution allows hydroxide ions to be transported between the electrodes to form oxygen and hydrogen but is not consumed during the reaction.

This technology is considered as extremely efficient, reliable, and cost-effective. Capacity can stack in the MW range but drawbacks include using corrosive liquid electrolytes, operation at low current densities and low pressures as well as gas crossover. Linde has installed over 80 Alkaline electrolyzers globally.

Proton Exchange Membrane (PEM)

PEM electrolysis uses pure water and a solid polymer electrolyte instead of a liquid solution. The electricity splits the water into hydrogen and oxygen. Hydrogen protons pass through the membrane, combining with electrons to form H₂ gas on the cathode side.

PEM electrolyzers are well suited for use with volatile renewable energy sources thanks to their fast ramp-up/down capabilities and their wide dynamic operating range. No corrosive electrolyte is involved, and they operate at high current density which speeds up the breakdown of the water molecule, ultimately affecting production price. Finally, a small footprint and compact system design is a benefit for many on-site industrial applications.

Understanding Capacity: What’s this about Watts?

Whatever the technology type, electrolyzers are always described in terms of their capacity. This represents the maximum operation power and so is measured in Watts (or MW, GW). The higher the wattage, the more hydrogen that electrolyzer can potentially produce.

For example, if it takes 50kWh of energy to produce 1 kg of hydrogen, a 10 MW electrolyzer will produce 200 kg in an hour (10,000 / 50) while a 20 MW electrolyzer could produce 400 kg in the same time. Individual cells can be stacked in modules to increase the capacity of any one electrolyzer: a valuable flexible feature for scaling up industrial applications.

With green hydrogen playing a critical role in long-term decarbonization goals in traditional as well as new applications, its production via electrolysis is receiving increasing attention from governments worldwide and the number of installation projects is growing rapidly. According to the Global Hydrogen Review 2022 published by the International Energy Agency, Global electrolyzer capacity could exceed 35 GW by the mid-2020s and reach 134 GW by 2030 based on the current project pipeline.

Linde's Green Hydrogen Project Pipeline

Linde offers end-to-end solutions and expertise to increase green hydrogen production capacity in electrolysis projects throughout the world. Here are some hydrogen highlights ...

Increasing Green Hydrogen Production in the US

35-megawatt PEM electrolyzer to be built in Niagara Falls, NY.

The new plant will be the largest electrolyzer installed by Linde globally and will more than double Linde’s green liquid hydrogen production capacity in the United States.

Linde will build, own and operate the industrial-scale electrolyzer and use hydroelectric power to produce green liquid hydrogen. The plant is expected to start up by 2025. Linde will leverage its existing liquefier and distribution infrastructure to supply existing and new customers. This project is the first of several electrolyzers Linde expects to build in the U.S. to address green liquid hydrogen demand.

Building the World's Largest PEM Electrolyzer in Germany

24-megawatt PEM electrolyzer at the Leuna chemical complex, Germany.

Linde continues to expand its production capacity for green hydrogen by constructing a 24 MW PEM (proton exchange membrane) electrolyzer at its Leuna site. It will supply Linde’s industrial customers through the company’s existing pipeline network. In addition, Linde will distribute liquefied green hydrogen to refueling stations and other industrial customers in the region. The total green hydrogen being produced can fuel approximately six hundred fuel cell buses, driving 40 million kilometers and saving up to 40,000 tons of carbon dioxide tailpipe emissions per year.

Providing Green Hydrogen for Ammonia Production in Norway

24-megawatt PEM electrolyzer for Yara in Porsgrunn, Norway.

Linde will construct and deliver the electrolyzer with a capacity of around 10,000 kg/day of hydrogen. Green hydrogen will partially replace the gray hydrogen in Yara’s ammonia plant, thereby removing 41,000 tonnes of CO₂ emissions annually.

The electrolyzer will produce enough hydrogen to create 20,500 tonnes of ammonia per year which can be converted to between 60,000 and 80,000 tonnes of green fertilizer. The plant is Yara’s first step towards decarbonization of the ammonia industry.

Bringing certified green hydrogen to Pernambuco, Brazil.

156 Tons of Green Hydrogen Per Year

White Martins, a Linde company, produced the first certified green hydrogen in South America.

The hydrogen received the seal of German certifier TÜV Rheinland after having all stages of its production process examined. Annually, White Martins will be able to receive up to 1.6 MW of solar energy that will be used in the water electrolysis process to produce green hydrogen. In all, 156 tons of green hydrogen per year will be produced on an industrial scale to supply the market in the Brazilian state of Pernambuco.