Bipolar Membrane Energy Harvester

In conjunction with the recent redesign, we decided to look into alternative solutions to use in our fuel cell.  Specifically, we are looking to compare sodium carbonate, sodium chloride, and sodium borate with the currently used urea borate. 

As when initially determining the suitability of materials for this device, we needed to confirm the solutions would not interact with any of the materials used. To do this, we soaked the materials in each of the three solutions. The process was similar to that used in testing materials described in parts 2-1 to 2-5 of the instructions. Unlike when first testing the materials, in this instance we only looked for changes in pH.

As shown in the table above, most of the materials did not react significantly to the different solutions. The only material that showed a significant pattern in changing the pH was silicone, which raised the pH slightly. This is not unexpected, as we did not use silicone in the pervious iteration of the fuel cell because it raised the pH in the initial materials testing as well. We chose to retest because we switched to an aquarium grade silicone to see if that would reduce the reaction, which it seems to have done. Additional testing should be done before we introduce silicone into the fuel cell.

None of the potential solutions show significant reactivity to the main materials used in the fuel cell, with sodium chloride having the smallest change in pH for the materials overall. 

In an attempt to improve the efficiency of the fuel cell, we decided to change our approach to the electrode assembly. As we described in the details for this project, two liquids on either side of the membrane are at their steady state with respect to their boundary conditions. We added a flowback channel, and aim to have a diffusion rate less than that of the bipolar membrane so there is an appreciable pH difference remaining despite the diffusion. 

In order to minimize total path length for this otherwise probable event, we created a series of small holes in the bipolar membrane. The holes, spaced 4 mm apart with a diameter of .2 mm, will serve as many small flowback channels. Overall this will allow for a larger effective surface area, as flowback will be evenly spaced over the entire surface of the membrane. We hope this will show a marked improvement over other models, with the smaller path length translating into increased efficiency. 

We are currently setting up a jig that will allow us to drill holes into the bipolar membrane using a .2 mm micro bit. Using a drill bit should minimize the disruption of the membrane interface over other methods such as piercing the membrane with pins.

In addition to changing the membrane layers in the electrode assembly, there were some changes to the printed flow cell. We closed off the original center opening to the electrode assembly and added two notches opposite one another for the electrode tabs. 

Here's our official video for the Hackaday Prize competition:

Another quick update for you! Part 3 of this project (The bipolar membrane flow cell) was completely reworked to make it easier to put together, as well as potentially producing a better pH gradient. Take a look at the updated instructions if you haven't already. We're seeing a pH difference of up to .5 in our latest proof-of-concept devices too. We'll be taking measurements periodically in order to test if this gradient breaks down over time. Keep an eye out for those tables to be posted in the coming weeks.

We recommend studying nonequilibrium statistical mechanics to really thoroughly understand the experiments you can perform with the bipolar membrane devices. The best course I have found on this topic is by Prof. V. Balakrishnan on Youtube.

Here you can find numerous relevant references and related topics of study, including other systems besides the bipolar membrane device, if you wish to try replicating those results as well. Needless to say, research in this field is still quite active.

1. Bai, C., and A. S. Lavine. “On Hyperbolic Heat Conduction and the Second Law of Thermodynamics.” Journal of Heat Transfer 117, no. 2 (May 1, 1995): 256–63. https://doi.org/10.1115/1.2822514.
2. Bar, Amir. “Linear Response and Onsager Reciprocal Relations,” n.d.
   Barletta, A., and E. Zanchini. “Hyperbolic Heat Conduction and Local Equilibrium: A Second Law Analysis.” International Journal of Heat and Mass Transfer 40, no. 5 (March 1, 1997): 1007–16. https://doi.org/10.1016/0017-9310(96)00211-6.
   
3. Bright, T. J., and Z. M. Zhang. “Common Misperceptions of the Hyperbolic Heat Equation.” Journal of Thermophysics and Heat Transfer 23, no. 3 (2009): 601–7. https://doi.org/10.2514/1.39301.
4. “Brownian Ratchet.” In Wikipedia, September 26, 2022. https://en.wikipedia.org/w/index.php?title=Brownian_ratchet&oldid=1112473938#cite_note-forced-3.  
5. Callen, Herbert B., and Theodore A. Welton. “Irreversibility and Generalized Noise.” Physical Review 83, no. 1 (July 1, 1951): 34–40. https://doi.org/10.1103/PhysRev.83.34.  
6. Čápek, Vladislav, and Daniel P. Sheehan. Challenges to the Second Law of Thermodynamics: Theory and Experiment. Dordrecht: Springer Netherlands, 2005. https://doi.org/10.1007/1-4020-3016-9.  
7. Chemistry LibreTexts. “17.3: Brownian Ratchet,” January 17, 2021. https://chem.libretexts.org/Bookshelves/Biological_Chemistry/Concepts_in_Biophysical_Chemistry_(Tokmakoff)/04%3A_Transport/17%3A_Directed_and_Active_Transport/17.03%3A_Brownian_Ratchet.
8.   D’Abramo, Germano. “On the Exploitability of Thermo-Charged Capacitors.” Physica A: Statistical Mechanics and Its Applications 390, no. 3 (February 1, 2011): 482–91. https://doi.org/10.1016/j.physa.2010.10.031.
9. D’Abramo, Germano. “Thermo-Charged Capacitors and the Second Law of Thermodynamics.” Physics Letters A 374, no. 17 (April 12, 2010): 1801–5. https://doi.org/10.1016/j.physleta.2010.02.056.
10. Danageozian, Arshag, Mark M. Wilde, and Francesco Buscemi. “Thermodynamic Constraints on Quantum Information Gain and Error Correction: A Triple Trade-Off.” PRX Quantum 3, no. 2 (April 26, 2022): 020318. https://doi.org/10.1103/PRXQuantum.3.020318.
11. Démoulin, Damien, Marie-France Carlier, Jérôme Bibette, and Jean Baudry. “Power Transduction of Actin Filaments Ratcheting in Vitro against a Load.” Proceedings of the National Academy of Sciences 111, no. 50 (December 16, 2014): 17845–50. https://doi.org/10.1073/pnas.1414184111.  
12. “Entropic Force.” In Wikipedia, September 7, 2023. https://en.wikipedia.org/w/index.php?title=Entropic_force&oldid=1174355238
13. .  Ethier, S. N., and Jiyeon Lee. “The Flashing Brownian Ratchet and Parrondo’s Paradox.” Royal Society Open Science 5, no. 1 (January 24, 2018): 171685. https://doi.org/10.1098/rsos.171685.  
14. Ghosh, Aritra, Malay Bandyopadhyay, Sushanta Dattagupta, and Shamik Gupta. “Quantum Brownian Motion: A Review.” arXiv, June 5, 2023. https://doi.org/10.48550/arXiv.2306.02665.
15. Higashi, Torahiko L, Georgii Pobegalov, Minzhe Tang, Maxim I Molodtsov, and Frank Uhlmann. “A Brownian Ratchet Model for DNA Loop Extrusion by the Cohesin Complex.” eLife 10 (n.d.): e67530. https://doi.org/10.7554/eLife.67530.  
16. Hoyuelos, Miguel. “Entropy of Continuous Markov Processes in Local Thermal Equilibrium.” Physical Review E 79, no. 5 (May 22, 2009): 051123. https://doi.org/10.1103/PhysRevE.79.051123.  
17. Hwang, Wonmuk, and Martin Karplus. “Structural Basis for Power Stroke vs. Brownian Ratchet Mechanisms of Motor Proteins.” Proceedings of the National Academy of Sciences 116, no. 40 (October 2019): 19777–85. https://doi.org/10.1073/pnas.1818589116
18. .  Iñiguez, José, and Douglas Az. “An Unusually Efficient Coupling of Carnot Engines” 17, no. 2 (2010). Kubo, R. “The Fluctuation-Dissipation Theorem,” n.d. Lee, James Weifu. “Type-B Energetic Processes and Their Associated Scientific Implications.” Journal of Scientific Exploration 36, no. 3 (January 1, 2022). https://doi.org/10.31275/20222517.  
19. ———. “Type-B Energy Process: Asymmetric Function-Gated Isothermal Electricity Production.” Energies 15, no. 19 (January 2022): 7020. https://doi.org/10.3390/en15197020
20. . Levy, George. “Loschmidtʹs Temperature Gradient Paradox – A Quantum Mechanical Resolution,” n.d. Levy, George S. “Loschmidt’s Paradox, Extended to CPT Symmetry, Bypasses Second Law.” Journal of Applied Mathematics and Physics 07, no. 12 (December 20, 2019): 3140. https://doi.org/10.4236/jamp.2019.712221. 
21. Mogilner, Alex, and George Oster. “Force Generation by Actin Polymerization II: The Elastic Ratchet and Tethered Filaments.” Biophysical Journal 84, no. 3 (March 2003): 1591–1605. https://doi.org/10.1016/S0006-3495(03)74969-8
22. . Monroe, Charles W, and John Newman. “An Introduction to the Onsager Reciprocal Relations.” Chemical Engineering Education 41, no. 4 (2007). Nordebo, Sven. “On the Interpretation and Significance of the Fluctuation-Dissipation Theorem in Infrared Spectroscopy.” arXiv, September 18, 2023. https://doi.org/10.48550/arXiv.2309.07837. 
23. Onsager, Lars. “Reciprocal Relations in Irreversible Processes. I.” Physical Review 37, no. 4 (February 15, 1931): 405–26. https://doi.org/10.1103/PhysRev.37.405. 
24. ———. “Reciprocal Relations in Irreversible Processes. I.” Physical Review 37, no. 4 (February 15, 1931): 405–26. https://doi.org/10.1103/PhysRev.37.405. 
25. Oster, George. “Brownian Ratchets: Darwin’s Motors.” Nature 417, no. 6884 (May 2002): 25–25. https://doi.org/10.1038/417025a. 
26. Peskin, C.S., G.M. Odell, and G.F. Oster. “Cellular Motions and Thermal Fluctuations: The Brownian Ratchet.” Biophysical Journal 65, no. 1 (July 1993): 316–24. https://doi.org/10.1016/S0006-3495(93)81035-X. 
27. Physics LibreTexts. “4.1: Introduction to Static and Quasistatic Fields,” May 11, 2020. https://phys.libretexts.org/Bookshelves/Electricity_and_Magnetism/Electromagnetics_and_Applications_(Staelin)/04%3A_Static_and_Quasistatic_Fields/4.01%3A_Introduction. 
28. Physics LibreTexts. “7.4: Fluctuation-Dissipation Theorem,” January 13, 2022. https://phys.libretexts.org/Bookshelves/Quantum_Mechanics/Essential_Graduate_Physics_-_Quantum_Mechanics_(Likharev)/07%3A_Open_Quantum_Systems/7.04%3A_Fluctuation-dissipation_Theorem
29. . Rubin, M. B. “Hyperbolic Heat Conduction and the Second Law.” International Journal of Engineering Science 30, no. 11 (November 1, 1992): 1665–76. https://doi.org/10.1016/0020-7225(92)90134-3. 
30. Sheehan, D. P. “A Self-Charging Concentration Cell: Theory.” Batteries 9, no. 7 (July 2023): 372. https://doi.org/10.3390/batteries9070372. 
31. Sheehan, D. P., D. J. Mallin, J. T. Garamella, and W. F. Sheehan. “Experimental Test of a Thermodynamic Paradox.” Foundations of Physics 44, no. 3 (March 1, 2014): 235–47. https://doi.org/10.1007/s10701-014-9781-5. 
32. Sheehan, D. P., and T. M. Welsh. “Epicatalytic Thermal Diode: Harvesting Ambient Thermal Energy.” Sustainable Energy Technologies and Assessments 31 (February 1, 2019): 355–68. https://doi.org/10.1016/j.seta.2018.11.007. 
33. Sheehan, Daniel. “Concentration Cell Powered by a Chemically Asymmetric Membrane: Theory.” SSRN Scholarly Paper. Rochester, NY, May 17, 2022. https://doi.org/10.2139/ssrn.4112190
34. . ———. “Maxwell Zombies: Mulling and Mauling the Second Law of Thermodynamics.” Journal of Scientific Exploration 34, no. 3 (September 15, 2020): 513–36. https://doi.org/10.31275/20201645. 
35. Sheehan, Daniel P. Epicatalytic thermal diode. United States US9212828B2, filed May 28, 2014, and issued December 15, 2015. https://patents.google.com/patent/US9212828B2/en. 
36. ———. “Maxwell Zombies: Conjuring the Thermodynamic Undead: Modern Descendants of Maxwell’s Celebrated Demon Defy Standard Thinking about Heat Engines and May Offer a Path to a New Kind of Energy Generation.” American Scientist 106, no. 4 (July 1, 2018): 23
37. 4–42. ———. “Supradegeneracy and the Second Law of Thermodynamics.” Journal of Non-Equilibrium Thermodynamics 45, no. 2 (April 1, 2020): 121–32. https://doi.org/10.1515/jnet-2019-0051. 
38. Takuma, Tadasu, and Takatoshi Shindo. “Fundamentals of Electrostatic and Quasi-Electrostatic Fields.” In Problems and Puzzles in Electric Fields, edited by Tadasu Takuma and Takatoshi Shindo, 109–15. Singapore: Springer, 2020. https://doi.org/10.1007/978-981-15-3297-9_5.
39. Gikunda, Millicent N., Ferdinand Harerimana, James M. Mangum, Sumaya Rahman, Joshua P. Thompson, Charles Thomas Harris, Hugh O. H. Churchill, and Paul M. Thibado. “Array of Graphene Variable Capacitors on 100 Mm Silicon Wafers for Vibration-Based Applications.” Membranes 12, no. 5 (May 2022): 533. https://doi.org/10.3390/membranes12050533.
40. Mangum, James M., Ferdinand Harerimana, Millicent N. Gikunda, and Paul M. Thibado. “Mechanisms of Spontaneous Curvature Inversion in Compressed Graphene Ripples for Energy Harvesting Applications via Molecular Dynamics Simulations.” Membranes 11, no. 7 (July 2021): 516. https://doi.org/10.3390/membranes11070516.

We tested the fully assembled bipolar membrane flow cell and posted it to my friend Jeremy's channel. You can see the preliminary results here:

We got picowatts of power so far, which is similar to preliminary results at Prof. Daniel Sheehan's lab at U.C. San Diego with their devices. The result is quite repeatable. So far the device is unoptimized so we expect a factor of 2 or 4 more power from an optimized device. We'll add our final video for the competition in the morning, as well as some supplementary references.

We have a quick update for you, to show an interesting result we had with one of our proof-of-concept devices. 

The bipolar membranes in these devices need to be soaked in a dilute solution of sodium hydroxide because the anion membranes have a quaternary ammonium ion, and they use chloride ions for shipping the membrane. This would make them acidic in our experiments if they are not neutralized.

We ran the experiment without pre-soaking the device and got measurements that were extremely acidic, though there was still a pH difference. There were two devices, one with the anion membrane facing the outer cylinder and one with it facing the inner cylinder. For the device with the anion membrane facing the outer cylinder, the outer measurement was a pH of 2.471 and the inner measurement was 3.264. For the one with the anion membrane facing the inner cylinder, the outer measurement was 3.382 and the inner measurement was 2.475.

All these were much more acidic than the 6.776 pH of the solution used, due to the HCl forming from the chloride in the membrane. We do see a much larger pH gradient than what is expected for this device, which should have fully equalized. We're not sure if the chamber directly exposed to the anion membrane had a lower pH because the membrane was not neutralized, or if the pH gradient we are trying to demonstrate is exaggerated at a lower pH. We plan on exploring this idea at a later date, but wanted to share the interesting results.

Keep an eye out for a much larger update, including a complete overhaul of the bipolar membrane flow cell.

Over the course of developing the Bipolar Membrane Energy Harvester, we used many different materials. We decided to put each and every one of the materials used through a series of tests to determine its reactivity to the various solutions we’ll use in the Energy Harvester.

Our goal is to find materials that will serve our purpose without interfering with the experiment. It’s imperative that any materials used are non-reactive under the experimental conditions because with this particular design, we are looking for very small amounts of energy. Any unintended interactions could overwhelm the effect we are trying to measure.

For our purposes, we decided to test each material sample for a few different things. All the samples had their pH tested, while those potentially containing ammonia, chloride, or manganese each had those tests run as well. Any discrepancy between a control and a sample is indicative of an unfavorable reaction.

A more in-depth look at how to run the materials testing can be found in Part 2 of the instructions. Here we will discuss the materials themselves, and what sort of patterns we saw when testing them. To give a brief explanation about how we ran the tests: A small amount of each sample we wanted to test was put into four different glass vials. Each vial was filled with a different solution. Two vials of each solution were also made with no material added to act as a control. They were left for a week before measurements were taken. After the samples were put in fresh solution and allowed to sit for another week.

Table 1: Results from each round of testing

In table 1, you can see the measurements taken for each of the different samples tested. Samples marked in red vary significantly from what was expected. Some of the materials, like the epoxy, we expected to react. Other samples were more of a surprise and were the reason we took time to test each of the materials. Kimwipes, for example, had a major impact on the pH and chloride of most of the samples. We had assumed they were unreactive, so after learning this we made sure to adjust our methods accordingly and rinse any components that came in contact with the wipes before using.

Other materials became less reactive after the initial soaking, which means they could be used if we were careful. We also saw that the urea solutions seemed less reactive.  That was one of the major reasons we ultimately chose urea borate for our first test producing a pH gradient with the bipolar membranes.

Ultimately, the diligence used when testing any and all materials allows us to be more confident in our results. The end goal of this testing was to eliminate potential interference with the effect we are trying to measure.