In the study described in this thesis, it is demonstrated that combined short-term and long-term energy storage in one device, the battolyzer, is possible. The battolyzer is a device that works as a rechargeable battery, and that is capable of performing highly efficient electrolysis with any excess electricity. The battolyzer was based on the Nickel-Iron-Battery, which was developed by Thomas Edison and Waldemar Jungner, and on alkaline electrolysis. Both are well-established technologies that were developed more than a century ago.
The main research question in this thesis is: "Is an energy storage system based on Nickel and Iron suitable to operate as an integrated battery and electrolyzer, and what would be the overall energy efficiency of such a device?".
Firstly, a test-series that was designed to simulate various real-life situations, including partial and full charging and discharging, rapid switching, continuous overcharging, and the around-the-clock cycling. Neither the battery, nor the electrolysis have noticeably deteriorated after the many cycles. The remarkable finding is that the reversible discharge capacity of the battery is not adversely affected by such harsh test conditions.
Secondly, the gas quality was analyzed, qualitatively and quantitatively. The outcome of these tests was that overcharging leads to gas production with a Coulombic (or Faradaic) conversion efficiency of equal to 100%, within the experimental accuracy.
In a final step, optimal operating conditions for the battolyzer have been identified. Tests show that the overall energy efficiency of the battolyzer could surpass 90%. However, the most remarkable finding of the whole project is the stability of the energetic efficiency at 80-90% over many different types of cycles, including all cycles to simulate real-life situations.
We anticipate these results to be a starting point for a robust grid-scale energy storage solution in a low-cost, abundant-element based, intrinsically flexible device that has close to full-time operability: as electrical power storage, switchable electricity supply, and as a hydrogen producer.