July 26, 2023
By Jijo Malayil

This tech can produce hydrogen on-demand by using more efficient Zinc batteries

It promises 50 percent efficiency when storing power and 80 percent when producing hydrogen –
with an estimated life expectancy of ten years.

Green Hydrogen renewable energy production facility.

Across the world, countries are scrambling to transition to greener forms of energy generation to meet their net-zero goals. Advanced nations have leapfrogged in this regard, primarily helped by innovations that have made such technologies more affordable and reaching the potential to one day supply enough power for long periods.

However, one thing is stopping some European nations like Germany from fully transitioning to renewable energy like solar and wind, which is finding efficient means to store green energy. 

A team led by researchers at Fraunhofer Institute for Reliability and Microintegration IZM in Germany has found a practical and affordable solution with Zinc batteries with double efficiency and the ability to produce Hydrogen. According to the team, "first tests promise 50 percent efficiency when storing power and 80 percent when producing hydrogen – with an estimated life expectancy of ten years," said a statement by the institute.

Such long-term storage solutions are necessary, given the unpredictable nature of such resources. Such uncertainty has prompted authorities to maintain conventional power plants, sustain a "complex dual power infrastructure, burn fossil fuels, and hold back the transition to renewables."

The Zn2H2 project                                                                            Fraunhofer Institute for Reliability and Microintegration IZM

A more affordable and sustainable solution
The beginning point for the research was the conventional zinc anode battery designs. Using alkaline water electrolysis, the team devised a method that, compared to the standard lithium batteries, is far less expensive and uses readily accessible, 100% recyclable ingredients (steel, zinc, and potassium hydroxide).

Furthermore, the technology ensured that the system could produce Hydrogen on demand. The researchers aspire to develop an electrically rechargeable hydrogen storage device that can store energy in metallic zinc and convert it back into electrical power and Hydrogen when needed after their job.

During charging, the water oxidizes into oxygen while the zinc oxide is reduced to metallic zinc. During discharge, this reverts to zinc oxide. The water is reduced once more, releasing Hydrogen.

"This is a unique combination of a regular battery and a source for hydrogen, with a total electrical storage efficiency of 50%, which is double the efficiency of other, currently preferred power-to-gas systems," Dr. Robert Hahn of Fraunhofer IZM, who is in charge of coordinating the work on the project.

Because the material cost is orders of magnitude lower than lithium batteries, the new technology promises to be a financially appealing option for storing green energy.

A more efficient way to produce Hydrogen
In conventional electrolysis, electricity is used to split Hydrogen and oxygen; the former is then cooled, compressed, and stored in high-pressure tanks (350-700 bar) or deep cooled and liquified. In this process, the total electricity demand is about 73 kWh/kg of Hydrogen. Hydrogen provides about 33kWh/kg once cooling and compression losses are considered. In short, electrolysis is less than 50% efficient.

The new system uses energy stored during charging in metallic zinc, with Hydrogen being held in the water of the electrolyte at ambient pressure and significantly higher density than pressurized or liquid hydrogen gas. "During discharge, the metallic zinc is converted into zincate, and the cell releases hydrogen and 8.3 kWh of electricity per kg of hydrogen released – improving net efficiency and reducing total power demand," said the ZnH2 project website, which is a commercial partner on the project.

According to the team, when the energy in the module is depleted, it may be recharged (52.3 kWh per kilogram of hydrogen capacity), similarly to a battery, by depositing zinc at the negative electrode and releasing oxygen. Net power consumption is 44 kWh per kilogram of Hydrogen generated (80% efficiency - with negligible load dependency). For each hydrogen generation cycle, the consumed water must be replenished.

The researchers demonstrated the novel system's survivability in the lab and assessed individual cells for efficiency and stability through several cycles. The end-of-year aim is to have a demonstration unit for running tests in a dedicated configuration. In the end, eight cells will be linked, each with a roughly 12 V and 50 Ah capacity.

"First tests promise 50 percent efficiency when storing power and 80 percent when producing hydrogen – with an estimated life expectancy of ten years." If the promises hold true, we may have an "economical solution for an ecological revolution."