Electrolysis: From school benches to a sustainable future

“Electrolysis.” Few will know what it means, but everyone benefits from it. Whether you are drinking tap water or bathing in a swimming pool. And many more will benefit from this technology, which encourages decarbonisation and sustainability. Discovered two centuries ago, electrolysis has never had as much of a future as it does now.


The process

The simplicity with which the phenomenon of electrolysis is replicated, even in its most basic form, is perhaps proportional to its importance in today's society. In short, electrolysis involves the transformation of electrical energy into chemical energy, precisely the opposite of what occurs in an ordinary battery of a TV remote control.

Etymologically defined as "decomposition by electricity", electrolysis can take various forms, but there is always a common denominator: in order for it to occur, the process must be artificially supplied with continuous electrical current – it is therefore a provoked reaction, not a spontaneous one.

This flow of energy travels through the electrodes of an electrolytic cell, forcing electrons to participate in reactions caused by oxidation at one of the electrodes (the anode) and reduction at the other electrode (the cathode). It is through this applied electrical discharge that it is possible to decompose molecules and obtain the desired products.

Electrolysis is divided into two essential types: igneous electrolysis, in which the liquid substance is molten, without the presence of water, and aqueous electrolysis, in which a substance is dissolved in water, forming an electrolytic solution.

In an aqueous medium, if we carry out electrolysis of water we can separate oxygen from hydrogen. But if we add salt (sodium chloride) to water, resulting in brine, then it is already possible to obtain chlorine, an essential element in many activities, or even to guarantee a basic need such as drinking water.

But that's not all: from this process, called the chloralkali process, it is also possible to obtain sodium hydroxide (commonly known as caustic soda), sodium hypochlorite (a powerful disinfectant known as bleach), hydrochloric acid (commercially known as muriatic acid), as well as hydrogen, which many consider to be the energy of the future. In short, it is a set of derivatives with extensive application in domestic and industrial contexts.


The electrolysis process in an industrial context has undergone a remarkable evolution in recent decades. The most significant milestone was the transition from the use of mercury, which had been used for over a hundred years, to the incorporation of diaphragm technologies from the 1970s and later, from the late 1980s, of membrane systems.

The use of mercury involved various environmental and safety risks, so the industry gradually adapted its production process to new electrolysis systems, despite the high modernisation costs. In 2013, the Industrial Emissions Directive came into force, leading to the mercury method in the production of chlor-alkali being abandoned for good in the European Union by the end of 2017.

The membrane electrolysis system consists of a container (an electrolyser) separated inside by a perforated membrane or screen. In one of the compartments, cathodic reactions occur (negative pole) and, in the other, anodic reactions (positive pole). The membrane serves to separate the ions and prevent secondary reactions with undesirable products.

In addition to eliminating the risk of environmental impact from mercury, membrane technology is less demanding in terms of maintenance and requires less energy consumption. Bondalti was among the first producers to implement electrolysis with membrane cells.


The history of electrolysis began in the 1800s. Around the same time that Allesandro Volta (1745-1827) created the electric battery, other scientists tried to understand what the effects would be of placing two conductive wires connected to the same battery in a container of water. The result was immediately obvious: gas bubbles (hydrogen and oxygen) were released on the surfaces of the conductive wires.

After several experiments carried out by other renowned scientists of the time, it was Michael Faraday (1791-1867), British physicist and chemist, regarded as one of the most influential scientists of all time and considered the precursor of electrochemistry, who was definitively recognised as having discovered it.

In fact, established in 1834, Faraday's (two) famous Laws came to synthesise a long process of experimentation and discovery. The first tells us that "the mass of an element, deposited during the electrolysis process, is directly proportional to the amount of electricity passing through the electrolytic cell"; while the second states that "the masses of various elements, when deposited during electrolysis by the same amount of electricity, are directly proportional to their chemical equivalents".

Faraday was also responsible for creating the lexicon of the process and terms such as "electrolyte", "anode", "cathode", "electrode" and "ion", consolidating the information obtained until then and establishing a starting point for a technology that is now widely used and indispensable in today's world.


In the future, hydrogen may become a key element in the sustainability of the planet. Captured without using fossil fuels and without releasing the consequent carbon dioxide emissions into the atmosphere, it could be the basis of a decarbonised economy, the cornerstone of the urgent climate transition.

The fact that it is the most abundant element in the universe might suggest that it is easy to obtain, but paradoxically, in the light of current science, the opposite is true.

Although there are other ways of doing this, which are not viable either economically or environmentally, the most suitable way of capturing hydrogen is through electrolysis. Knowing that this process requires an energy source, it becomes clear that the only way to obtain this element in a sustainable way, i.e. the so-called green hydrogen, is through the use of renewable energy sources.

As the largest Portuguese company in the field of industrial chemicals, today Bondalti is an important player in the hydrogen value chain and sees the incorporation of this element as a strategic pillar for the future.

Bondalti's project for the production of hydrogen at the Estarreja Chemical Complex has recently obtained the status of “Important Project of Common European Interest” (IPCEI) awarded by the European Commission.

Called H2Enable, and also integrated into the mobilizing agendas of the PRR (Program for Recovery and Resilience) with an estimated investment of 142 million euros until 2026, the project led by Bondalti, and including other partners, such as Air Liquide, Faculdade de Engenharia do Porto, APQuímica and HyLab, consists of the construction of an infrastructure for the production of green hydrogen at the Estarreja Chemical Complex.

H2Enable aligns with the European goals of decarbonization and re-industrialization, based on advanced, intelligent and efficient technologies, low environmental impact, orientation towards more qualified products with greater added value, as well as the principles of circularity.

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