Mechanical Technology Archive

MechTech visits the research facilities of the DST National Hydrogen Infrastructure Centre of Competence (HySA Infrastructure) at the Potchefstroom campus of the North-West University (NWU) and talks to the centre’s director, Dmitri Bessarabov. 

PV Renewables Hysa hydrogen Infrastructure Dmitri Bessarabov electrolysers hydrogen pumps NWU

According to Bessarabov, Hydrogen South Africa (HySA) is a national special flagship programme conceived some seven years ago. “The overall goal is to develop and guide innovation along the value chain of hydrogen and fuel cell technologies in South Africa, in support of the beneficiation of South Africa’s mineral wealth, with a specific focus on platinum group metals (PGMs).

“South Africa has large deposits of PGMs and is a key processor of the raw materials containing these metals. About 70% of the platinium used in the world is mined here, and the metal is used extensively for catalytic converters in the global automotive industry,” he says, adding that, as well as for catalytic converters, PGMs such as platinum and iridium are used as catalysts in water electrolysers and hydrogen fuel cells.

As a national programme, HySA is hosted at a number of state-owned institutions around the country, which are responsible for providing facilities and equipment. “The HySA Infrastructure centre of competence is hosted by two organisations, the Potchefstroom campus of NWU, and the CSIR in Pretoria. We are responsible for development of systems and components for hydrogen production, storage and delivery,” Bessarabov tells MechTech.

HySA Catalysis is co-hosted by the University of Cape Town and Mintek and takes responsibility for catalysts such as those in fuel cells, reformers and portable power systems, while HySA Systems, hosted by the University of the Western Cape, develops hydrogen fuel cell systems and the associated systems’ integration. “Each centre is involved in collaborative projects with each other, as well as taking responsibility for specifically allocated technology areas,” he says.

“Here at NWU we focus on efficient hydrogen production, which is strongly linked to the development and use of renewable energy: identifying new ways to use hydrogen; and, along with our colleagues from CSIR, developing storage and transportation systems to distribute hydrogen to where it is needed,” he notes.

Elecrolyser HySA hydrogen NWUHysa Infrastructure’s electrolyser at the NWU campus has the capacity to produce 3.0 kg of H2 per day from the solar system.

Globally, some 60-million tons of hydrogen are produced per year with the petrochemical industries and ammonia producers as key consumers. “Sasol, for example, uses large quantities of hydrogen that it produces by reforming natural gas. But this comes with an environmental penalty, because of the amount of CO2 emitted.

“Here at HySA infrastructure, we are producing hydrogen from water using renewable energy, with oxygen as the only other by-product. We use neither fossil fuels nor natural gas to produce our hydrogen and we strive towards carbon neutral hydrogen generation,” he assures.

At the starting point of HySA Infrastructure’s hydrogen generation plant is a 21 kWp solar photovoltaic system installed on the carports outside the HySA facility. “Inside, we have a 120 kWh battery bank and a large electrolyser. We can channel the dc current generated by the solar panels directly into the electrolyser to produce hydrogen and we can store any excess production in the battery bank for later use. Currently, we have the capacity to produce some 3.0 kg of H2 per day from the solar system; equivalent to approximately 11.5 ℓ of petrol per day,” Bessarabov says, explaining that the gge (gasoline gallon equivalent) of hydrogen is close to 1.0 kg.

Apart from refinery, ammonia for fertilisers and fuel cell use, there are a large number of applications that depend on a reliable hydrogen supply: in the food industry for hydrogenating oil to make margarine; for making glass; and for manufacturing silicon-based microchips in the electronics industry, for example. “Power generation systems use hydrogen for cooling the turbines, because of its high thermal conductivity and high specific heat capacity properties. And in the future there will be automotive applications for hydrogen-fuelled fuel cell vehicles, but while waiting for these technologies to take root in South Africa, we are actively exploring other markets,” says the HySA Infrastructure director.

Electrolysers and ion exchange membranes

As demonstrated in chemistry classrooms around the world, the simplest way to produce hydrogen is to split water. All that is needed is a dc supply of electrical current into the water via two electrodes. The electrical energy then splits the water (H2O) into its constituent elements, forming H2 and O2 gases.

“This process has been know for many years, but the technology is advancing rapidly towards more cost efficient and industrially useful techniques,” says Bessarabov.

“Ideally,” he continues, “the hydrogen produced in the process should be at high pressure. In addition, we like to avoid having to use corrosive electrolytes, such as potassium hydroxide (KOH). We also strive to develop modular systems so that it is easy to scale up to larger production levels.”

At the heart of addressing all of these challenges is the role of membrane technology. The electrolysers HySA are working on comprise two gas chambers separated by a special membrane material. “The membrane materials being developed for electrolysers are dense films, which are not gas permeable and have high pressure holding capacity. Because of their density, neither hydrogen nor oxygen gas can permeate the membrane. This allows for very efficient separation of the two gases during electrolysis,” Bessarabov explains.

Used in both fuel cells and electrolysers, membrane materials are ion conductive, which enables hydrogen ions (H+) to pass through the material as positive charge carriers, a phenomenon known as proton exchange. These membrane materials are used in the construction of flat-plate membrane electrode assemblies (MEAs), which consist of a layer of the ion exchange membrane with a PGM coated anode on one side and a similarly coated cathode on the other. “And the ion conductive nature of the membrane obviates the need to use electrolytes such as KOH to make the water ion conductive,” he adds.

Describing how the process works, he says that water is introduced into the chamber on the anode side of the electrolyser. There, under the action of the platinium or iridium catalyst, the water is split and oxidised in the anode chamber. Oxygen gas forms, along with hydrogen ions. This is the first reaction,

The hydrogen ions or protons are conducted through the ion conductive membrane, also known as a PEM (proton-exchange membrane) to the cathode surface, where, also under the action of the PGM catalyst, they are reduced to form hydrogen gas.

The dense membrane film prevents the two gases from remixing and can take large differential pressure. “The practical limit is now at about 300 bar and we are already achieving close to that. This means that we can generate hydrogen under pressure, typically at 200 bar, directly from the electrolyser, without having to use mechanical compression. The pressure coming directly out of a hydrolyser, therefore, is the same as that from a pressurised hydrogen cylinder,” Bessarabov says.

In addition, the purity levels of the hydrogen is very high. “The membrane virtually eliminates cross contamination, so we are currently achieving hydrogen purity of five-9s (99.999%),” he points out.

The hydrogen pump

As well as generating hydrogen, a flagship development for HySA Infrastructure is the use of their electrolyser technology to pressurise and purify hydrogen. “We are able to use this system as a hydrogen pump. Instead of feeding water into the system, we introduce gaseous hydrogen or a hydrogen containing gas mixture. The hydrogen is ionised and the ions pass through the membrane to the cathode, where hydrogen gas is formed. Because of the impermeability of the membrane, the hydrogen pressure can be built up. So we have a system with no moving parts that can pressurise hydrogen.

“We can also use the process to purify hydrogen. If, for example, a mixture of helium and hydrogen is introduced, then the hydrogen will pass through the ion exchange membrane, while the helium will accumulate on the anode side. We see applications for this in the purification of methane from hydrogen, for example,” Bessarabov informs MechTech.

Hydrogen on tap

One of the immediate uses for HySA’s electrolyser technology is for the generation and direct use of ultra-high purity gas in laboratory equipment such as gas chromatographs.

“At an onsite mobile laboratory, for example, the lab manager might need to buy ultra-high purity hydrogen gas in cylinders rented from a gas company – at a substantial premium. Safety issues and dedicated storage space will limit the amount that can be stored, typically in cages, and a piping infrastructure with safety features has to be installed for its use. A single gas cylinder weighing around 70 kg contains approximately 700 g of hydrogen at 200 bar – 1.0 % by weight.

“We are able to offer hydrogen production via a portable electrolyser, which allows hydrogen to be produced onsite from water. The system can generate the purity required and when the gas chromatograph is switched off, the electrolyser can be switched off too, so no storage is required,” says Bessarabov.

Power to gas.

Describing an emerging use of hydrogen in the renewable energy sector, Bessarabov says that, in Germany, wind from the North Sea is generating about 40 GW of power, roughly the same as the total installed capacity in South Africa.

When too much power is added to the grid, the oversupply can destabilise the whole network, so any excess needs to be stored. A growing trend is to use the oversupply to produce hydrogen via large electrolysers, effectively sinking renewable electricity into hydrogen storage.

Europe also has a highly developed natural gas (methane, CH4) pipeline network. This offers free energy storage opportunity, since up to 10% hydrogen can be mixed with methane without affecting the calorific value of the gas and without causing any degradation to the pipe materials (hydrogen embrittlement). “In some cases where heavier hydrocarbons are present in the natural gas mix, the hydrogen helps to reduce the overall density of the gas mixture so that its average is closer to that of pure methane,” says Bessarabov, adding that, if South Africa ever exploits our shale gas resources, this could become a local opportunity for hydrogen storage.

CO2 capture

Renewable hydrogen, generated from renewable electricity sources such as solar or wind can also be used in carbon capture processes to displace CO2 emitted from fossil generation sources.

“The well known Sabatier chemical reaction combines CO2 and hydrogen to produce methane and water – and the presence of a PGM catalyst makes the process more efficient. The Sasol processes, for example, produce significant quantities of CO2 and this can be mitigated if these emissions can be combined with hydrogen to produce methane,” Bessarabov says.

Hydrogen storage

HySA Infrastructure’s needs to develop hydrogen storage technology is a logical consequence of its expanding hydrogen generation capacity. “We are currently installing a storage facility for 45 kg of hydrogen that will be housed in high-pressure tubes at 200 bar. In addition we are developing a 50 ℓ LOHC – liquid organic hydrogen carrier capacity,” he reveals.

LOHCs are organic liquids that can be handled in a similar way to diesel, for which piping and storage infrastructure is already available. The LOHC is hydrogenated via the action of a platinum catalyst and then the hydrogen is extracted in a reverse process at the point of use, allowing the organic liquid to be cycled continuously.

“This is already of great interest in countries such as Japan looking to transport hydrogen in large quantities. The liquid can be safely pumped through pipelines or transported in a tankers or drums, making it as easy to distribute as currently used automotive fuels,” he says, adding that the group is also working on combining hydrogen into metal organic frameworks (MOF), which are structures of organic molecules into which hydrogen can be bound. “The key advantage of these is that they are lightweight, significantly lighter than metal hydrides, for example.

“We at HySA are developing an understand of hydrogen generation and storage technologies with a view to channelling them into the most appropriate direction for the country. We have successfully demonstrated renewable-energy-powered, efficient, low cost, high pressure and high power density electrolysers, along with a hydrogen pump solution – and these are commercialisable.

“We believe that the hydrogen economy will make a significant contribution towards the localisation and beneficiations of our renewable energy and natural mineral resources,” Bessarabov concludes

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