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Monday, August 7, 2023

Zinc/ MnO2 Secondary Cell Research


Besides amateur artwork, I am a chemistry professor with the U. Pittsburgh-Bradford (PA.,USA) and have been here for forty years. My scientific efforts are currently ( no pun intended) focused on secondary cells, electrode composition designs, thin film/ gel electrolytes and asymmetric supercapacitors.  I respect the traditional cells ( i.e. Zn/MnO2)  and such cells are excellent training devices for future scientists/ engineers working within "energy storage" areas.

The "pile battery" ( 4 x 1.5V  Zinc /Carbon ( MnO2)  has served humans well:

                                                        Zinc casing (anode)  / MnO2 (graphite current collector) 1.5V cell.


                                                      In this image:  I have taken an old cell and carefully cut the bottom off and a section about mid-center. I taped both holes with a porous surgical tape and placed the casing in a small polyethylene bag to catch any MnO2 which could diffuse out over time of operation. The electrolyte is 6M NaOH. I wany flow of electrolyte through the cell, but do not want the Mn species to spill out.  

In prior research, I have been able to use an electronic load and charge/discharge about 25 cycles before the cell no longer is operational.  Here, I added a small amout of Zin sulfate to the electrolyte solution , but the outer surface of the cylinder has a significant amount of zinc available for redox reactions.  I am running a small DC -powered propeller as a mechanical load. I will verify that the cell is re-chargeable a few times before going to an e-load for 50-100 cycles. 

A small propeller as a mechanical load for the cell.

                Above image:  A section of fine steel screening will serve as a current collector. A paste of fresh MnO2/ activated carbon ( ultra-fine grade through sieving) and graphite is mixed with epoxy resin and applied to both side of the current collector which will serve as the cathode with a section of zinc as anode.

After 24 hrs, I will apply a 6 ton press to prepare the electrode for utility in a "sandwich " style cell for study. The zinc will be separated from the cathode by paper and , in the near future, an alkaline gel electrolyte. Initially, the paper separator will be soaked with 6M NaOH . I will seal the cell in a polyethylene bag in order to prevent electrolyte evaporation.

                                                        Above; I purchase rolls of the fine steel screening on Amazon.

                  As my research develops, I will upload imagery and data acquisition. I will be applying cement/ a certain clay, MnO2 , activated carbon and graphite to the steel screening instead of epoxy. Researchers at M.I.T. have recently reported the use of certain modified cements with "supercapacitor" development .  I have observed in my lab that certain cement formulations conduct.

I also will be developing cylindrical cells with alkaline gel electrolytes/ cement cathodes along with the zinc anode.



Below is an image of a spent cell being re-charged in a bath of Zinc sulfate. The plating goes well and can, hopefully, allow more than 25 cycles of charge-discharge. 

The plating may prevent a short-circuit due to zinc corrosion.  This may be a way to keep such cells from waste-disposal.

                    The re-charged cell is running a small DC propeller. I will run electronic laods and study the cell performance over 25-75 cycles.

Below is a fine steel current collector painted with a certain type of cement containing MnO2, activated carbon, graphite and kaolin clay. When dried, it will be subjected to a 6 ton press and tested with a zinc anode and aq. NaOH electrolyte.   The cement is conductive and is easier to work with on screen vs. epoxy resin.


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