Literature Review: Open Source Hypochlorous Acid Generator

Background[edit | edit source]

What is Hypochlorous Acid?[edit | edit source]

Hypochlorous acid (HOCl or HClO) is a weak acid that naturally occurs in many living organisms including humans. Hypochlorous acid is non-toxic and has the ability to disable many different pathogens and microorganisms. The advantage of using hypochlorous acid as a disinfectant is that it can be produced in-situ via the electrolysis of an aqueous sodium chloride solution; simply put, it can be made by directing an electric current through a salt water solution. This allows for the production of a powerful disinfectant that doesn't require the use of expensive or complicated industrial equipment. The goal of this literature review is to collect the background information required to design and build an open-source hypochlorous acid generator that can be used at both the consumer and institutional level.

Market Survey of HOCl Generators[edit | edit source]

Company	Regular Price	Product Specs	Additional Information
EWCO Store	$299.99	-Electrolysis Cell: Titanium Electrolysis Cell Lifespan: 3,000 cycles (8 minutes each) Power Supply: 110V/220V, 50/60Hz Dimensions: 21 x 15 x 36 cm (8.3 x 5.8 x 14 inches) Weight: 0.6 kg (1.3 lbs.) Volume: 1L	-Produces concentrations up to 200 ppm of HOCl
Liberty Sprayers	$119.00	Premium 2L HOCL Generator Electrode is a Mesh Titanium/ Iridium/ Platinum Coated Alloy Power Supply: AC adaptor North American Plug Weight: 3-4 lbs Standard 2 Liter HOCl Generator Electrode is coil style platinum/ titanium alloy Power Supply: AC adaptor North American Plug Weight: 3-4 lbs	-Wall plug-in as power source
Force of Nature	$69.00	-Shipping Weight: 0.86 kg  (1.9 lbs.) Product Dimensions: 33.0 x 21.6 x 8.9 cm (13.0 x 8.5 x 3.5 in) Activator Base: 21.6 x 7.6 x 10.8 cm (8.25 x 3.0 x 4.25 in) Volume: 0.35L	-Forced to buy their capsules that contain salt and vinegar (acetic acid) EPA registered Hospital disinfectant and on EPA's List N (approved for use against SARS-CoV-2)
Egret Lab Canada	$249.00	-Electrolysis Cell: Titanium Shipping Weight: 0.90 kg (1.98 lbs.) Product Dimensions: 31.8x10.1x24cm Volume: 0.800L Body Materials: ABS/TPR/PC Battery: 1200mAh/13.32Wh Rated voltage: DC 11.11v Charging V: 5v-2A

Search Terms[edit | edit source]

"Hypochlorous acid"

"HOCl"

"Disinfectant" AND "production"

Literature[edit | edit source]

TODO[edit | edit source]

• Systems using electrolysis cells that are manufactured from lower quality alloys will deteriorate quickly and may not be generating hypochlorous acid (chlorine evolution selectivity).
  • If the electrolysis cell is made from steel or other lower grade metals, the electrolysis cell will deteriorate very quickly and will generate harmful chromium compounds that can be carcinogenic.
• A system with a small electrolysis cell relative to the volume of the container will require a higher amount of salt to reach a certain ppm.
  • Causes solution salinity to be extremely high and most likely the system is generating sodium hypochlorite (NaOCl) and NOT hypochlorous acid (HOCl).
  • HOCl has a relatively short shelf life when compared to other commercial disinfectants.
  • Does the type of salt need to be iodine free?
  • Optimal ppm/concentration required?
• pH can be used to determine the concentration of the various solution components
  • Take product and send to chemistry lab to be spectrometrically analyzed at different pH
  • Acetic acid can be used to decrease pH
  • pH sensor can be built into the device to allow for real-time pH monitoring from which concentration estimates can be made
    • pH can be kept within the range through the incremental addition of acetic acid in the form of white vinegar
    • If this is done then it must account for how much vinegar is in the solution and alter the concentration estimates of HOCl
    • Concentration must be kept above a certain threshold to be effective against pathogens
    • Stabilized HOCl demonstrates broad-spectrum antimicrobial activity at concentrations ranging from 0.1 to 2.8 μg/mL

Hypochlorous Acid[edit | edit source]

Hypochlorous Acid - Wikipedia[edit | edit source]

Wikipedia Volunteers, “Hypochlorous acid,” Wikipedia. Dec. 31, 2021. Accessed: Jan. 08, 2022. [Online]. Available: https://en.wikipedia.org/w/index.php?title=Hypochlorous_acid&oldid=1063015952

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Hypochlorous Acid: A Review[edit | edit source]

M. S. Block and B. G. Rowan, “Hypochlorous Acid: A Review,” Journal of Oral and Maxillofacial Surgery, vol. 78, no. 9, pp. 1461–1466, Sep. 2020, doi: 10.1016/j.joms.2020.06.029.

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The Potential Use of Hypochlorous Acid and a Smart Prefabricated Sanitising Chamber to Reduce Occupation-Related COVID-19 Exposure[edit | edit source]

K. Nguyen et al., “The Potential Use of Hypochlorous Acid and a Smart Prefabricated Sanitising Chamber to Reduce Occupation-Related COVID-19 Exposure,” Risk Management and Healthcare Policy, vol. 14, pp. 247–252, Dec. 2021, doi: 10.2147/RMHP.S284897.

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Hypochlorous acid and its pharmacological antagonism: An update picture[edit | edit source]

D. Lapenna and F. Cuccurullo, “Hypochlorous acid and its pharmacological antagonism: An update picture,” Gen. Pharmac., vol. 27, no. 7, pp. 1145–1147, Oct. 1996, doi: 10.1016/S0306-3623(96)00063-8.

• This study discusses some of the biochemical and pathophysiological aspects of hypochlorous acid
• Key information:
  • Hypochlorous acid (HOCl) is a major oxidant species produced by activated white blood cells
  • Hypochlorous acid is a major inorganic bactericidal compound of innate immunity and is effective against a broad range of microorganisms

Growth of Escherichia coli in Model Distribution System Biofilms Exposed to Hypochlorous Acid or Monochloramine[edit | edit source]

M. M. Williams and E. B. Braun-Howland, “Growth of Escherichia coli in Model Distribution System Biofilms Exposed to Hypochlorous Acid or Monochloramine,” Applied and Environmental Microbiology, vol. 69, no. 9, pp. 5463–5471, Sep. 2003, doi: 10.1128/AEM.69.9.5463-5471.2003.

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Hypochlorous acid as a disinfectant for high-risk HPV: Insight into the mechanism of action[edit | edit source]

L. I. Robins et al., “Hypochlorous acid as a disinfectant for high-risk HPV: Insight into the mechanism of action,” Journal of Medical Virology, vol. 94, no. 7, pp. 3386–3393, 2022, doi: 10.1002/jmv.27716.

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Inactivation of Prions and Amyloid Seeds with Hypochlorous Acid[edit | edit source]

A. G. Hughson et al., “Inactivation of Prions and Amyloid Seeds with Hypochlorous Acid,” PLOS Pathogens, vol. 12, no. 9, p. e1005914, Sep. 2016, doi: 10.1371/journal.ppat.1005914.

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Exchange Membrane Electrolyzers[edit | edit source]

Chemistry LibreTexts: Electrolysis[edit | edit source]

K. Song, "Electrolysis," Chemistry LibreTexts, Oct. 02, 2013. (accessed Jan. 06, 2022).

• Electrolysis: used to separate a substance into its original components/elements
• Electrolytic cell: essentially the non-spontaneous reactions' voltaic cell; consist of two electrodes (one that acts as a cathode and one that acts as an anode), and an electrolyte
• See electrolytic cell diagram here

An experimental investigation of bubble-induced free convection in a small electrochemical cell[edit | edit source]

P. Boissonneau and P. Byrne, "An experimental investigation of bubble-induced free convection in a small electrochemical cell," Journal of Applied Electrochemistry, vol. 30, p. 9, Jul. 2000, doi: 10.1023/A:1004034807331.

• Electrolysis of both a Na₂SO₄ and a NaCl/NaClO₃ solution was performed in order to produce hydrogen and oxygen bubbles at one or both of the electrodes so that the two-phase flow regimes, bubble sizes, gas fraction and fluid velocities between the electrodes were investigated
• Relevant results:
  • Electrochemical reactions are influenced by electrolyte flow due to an increase in mass transfer to an electrode surface
  • Flow and mass transfer can also be imposed by electrochemically producing bubbles at an electrode surface
    • Relevant to the chlorate process since hydrogen bubbles produced at the cathode surface lead to flow in the channel
  • Electrolysis of a sodium chloride solution (NaCl) produces:
    • Hydrogen gas at the cathode and remains as gas bubbles in the system
    • Chlorine at the anode, but very quickly reacts with other species in the electrolyte and disappears
    • Oxygen gas at the anode and reduces the fluid current of the system by 2-4%
• Key information:
  • In a scaled-up membrane-less electrolysis reactor, the interaction of bubbles and their coalescence dynamics can lead to more violent flow patterns that impact the performance of the reactor
    • In this context  "scaled-up" refers to a millifluidic application opposed to microfluidic
    • Comment: this is relevant to our purpose which more closely aligns with the design proposed by H. Hashemi et al. 2019

Membranless Electrolyzers[edit | edit source]

Framework for evaluating the performance limits of membraneless electrolyzers[edit | edit source]

X. Pang, J. T. Davis, A. D. Harvey, and D. V. Esposito, "Framework for evaluating the performance limits of membraneless electrolyzers," Energy Environ. Sci., vol. 13, no. 10, pp. 3663–3678, Oct. 2020, doi: 10.1039/D0EE02268C.

• Explores performance limits of parallel plate membraneless electrolyzers (PPME) and quantitatively describes the trade-offs between efficiency, current density, electrode size, and product purity
  • Achieved experimentally using in situ high-speed videography (HSV) to monitor the width of H2 bubble plumes produced as a function of many parameters
  • Quantitatively describes the trade-offs and optimization by employing different mathematical relationships that relate the sides of a theoretical model called the unfortunate tetrahedron
• Relevant results:
  • The efficiencies and current densities of optimized PPMEs constrained to H2 crossover rates of 1% can exceed those of conventional alkaline electrolyzers
  • PPMEs have lower efficiencies and current densities than those achieved by zero-gap polymer electrolyte membrane (PEM) electrolyzers
  • Analyzes the trade-offs between current density, efficiency, and product purity
  • Analyzes the trade-offs between electrode size, efficiency, and product purity
  • Expression for calculating the electrolyzer efficiency is given
  • The dimensionless bubble plume width was determined to be a good descriptor that can be used to predict H2 crossover rates across a wide range of operating conditions for the PPME
    • An empirical relationship was described using Buckingham Pi Theorem to relate plume width to channel width & electrode length and operating conditions (i, velocity (U)) that are expected to influence plume width
• Key information:
  • Performance metrics can be graphically illustrated using a model dubbed the unfortunate tetrahedron
    • The four corners are:
      • Opex (related to efficiency)
      • Capex (related to electrode size and scalability)
      • Current density
      • Product purity (a proxy for safety)
  • Gas chromatography used to quantify gas production and crossover rate
• Device specifications:
  • Cell body made from PLA
  • Rectangular fluidic channel
    • 145 mm long
    • 2 or 4 mm wide
    • 5 mm high
    • 29 mm long by 0.4 mm thick divider placed 12 mm downstream from end of the electrodes
  • Electrodes 2 nm of titanium (Ti) and 50 nm platinum (Pt) onto Ti foil substrates
  • CAD files for the two cells are freely available for download at echem.io

A versatile and membrane-less electrochemical reactor for the electrolysis of water and brine[edit | edit source]

S. M. H. Hashemi et al., "A versatile and membrane-less electrochemical reactor for the electrolysis of water and brine," Energy Environ. Sci., vol. 12, no. 5, pp. 1592–1604, 2019, doi: 10.1039/C9EE00219G.

• Presents a 3D printed membraneless cell design that combines components such as the flow plates and the fluidic ports in a single part and provides tight tolerances and smooth surfaces for precise flow conditioning
• Relevant results:
  • Using a two-phase millifluidic system can be used to prevent cross-contamination of the anodic and cathodic products without the need for a membrane
  • A membraneless architecture increases the reactor lifetime and reduces fabrication costs
  • Using 3D printing for the fabrication of electrochemical reactors allows for tight tolerances and a reduced number of parts meaning fewer manufacturing steps
  • This reactor showed a 37-fold throughput increased over the first microfabricated prototype presented by Hashemi, Mohammad & Modestino, Miguel & Psaltis, Demetri in their 2015 paper presenting a membrane-less electrolyzer for hydrogen production
  • Inertial separation of the gas bubbles done beyond micro geometries and at higher flow rates
  • Conclusions related to further optimization:
    • Increased electrode size; this study expects optimum dimensions to be in the same order of magnitude
    • Main channel length can be increased so long the largest bubble at the end of the channel does not become bigger than half of the channel's width
      • This can be controlled by the flow rate and current density
    • Parallelization and stacking of several optimized cells
    • Decreasing the ohmic losses at the contacts
    • Introduction of acidified analytes through second dedicated inlet
      • Will enhance the Faradaic efficiency
    • Employing sophisticated 3D printers to reduce the interelectrode gap to few hundreds of microns
• Key information:
  • 3 main components in the electrochemical cells: an anode, a cathode, and a membrane/separator
    • The role of the membrane:
      • Allows the passage of ions through it's structure while preventing the mixing of reduction and oxidation products or reactants
        • This makes it a critical component in terms of the cell's lifetime, price, and manufacturing due to limitations it imposes on the materials of the anode and the cathode
  • Comment: As noted in Boissonneau and Byrne's 2000 study on bubble-induced free convection small electrochemical cells, scaling up channel size can lead to more violent flow patterns that impact the performance of the reactor due to interaction of bubbles and their coalescence dynamics
    • Even more important in this case since almost all inertial microfluidics research is done in microchannels at Reynolds numbers well below 100
      • Flow regimes here were investigated had Re as high as 312 and in fact these higher Re flow regimes were found to be more efficient
        • In these more turbulent flow regimes bubbles experience sudden changes their equilibrium positions after coalescence, followed by their subsequent return towards the electrodes
  • Two hydrodynamic mechanisms lead to the separation of gaseous products in flow-based cells:
    • Inertial migration
    • Bubble coalescence
• Device specifications:
  • Main body
    • Has fluidic channels, female Luer Lock fluidic connectors, electrode grooves, holes for electrical connections, and assembly screw holes
    • Main channel is 1 x 1 mm, 26 mm long terminating with Y-shaped section connected to a separate outlets
  • Electrodes
    • 4 x 10 mm, 1 mm thick thick titanium substrate coated with 20 um layer containing IrO₂, RuO₂, and TiO₂
    • Inserted into tight, low tolerance grooves in the main body
      • Active area that forms part of channel walls is 1 x 10 mm
      • Other 3 mm is buried in grooves and connected to two copper bars using conductive epoxy
  • Clear top
    • 3 mm thick sheet of PMMA with screw holes
      • 250 mm thick, transparent sealing tape is used to join PMMA and 3DP part and prevent the leakage
      • The two parts are fastened together with M3 and M2 screws and nuts
      • Male Luer Lock connectors connect PTFE tubes to introduce electrolyte in and take products out of device

A membrane-less electrolyzer for hydrogen production across the pH scale[edit | edit source]

M. Hashemi, M. Modestino, and D. Psaltis, "A membrane-less electrolyzer for hydrogen production across the pH scale," Energy Environ. Sci., vol. 8, pp. 2003–2009, Apr. 2015, doi: 10.1039/C5EE00083A.

• Demonstrates a membrane-less electrolyzer that is capable of operating with lower ionic resistance than benchmark membrane-based electrolyzers using virtually any electrolyte
• Relevant results:
  • Increased flow rate resulted in much lower crossover percentages
  • The membrane-less flow-based design has the potential to surpass the performance of equivalent apparatus that rely on ion conductive membranes for separation
  • Scaling this concept to increase throughput can be achieved by employing multi-stack panels or larger area electrodes
• Key information:
  • Current electrolysis systems employ membrane electrode assemblies (MEAs) utilize the low ionic resistance through Nafion membranes to separate the sites where the hydrogen and oxygen are produced
  • Membrane-based systems allow for production of nearly-pure gas streams and operation at high current densities, but the strongly acidic nature of Nafion requires the incorporation of acid-stable catalysts based on noble metals (i.e. Pt, Ir, Ru)
  • The production of gaseous products from electrochemical reactions has precluded demonstrations of efficient membrane-less electrolyzers in the past since these gaseous products evolve out of the liquid electrolyte to form bubbles which is problematic as it enhances product mixing and slows the reaction
    • To mitigate gas crossover to reduce product mixing in a membrane-less scheme, fluid dynamics can be used to control the position and trajectory of bubbles that evolve from electrodes
  • Membrane-less electrolysis allows for the operation at any pH, reduces the complexity, and decreases the ionic resistance
  • Described method separates product gases using fluid mechanic forces of the device
  • Devices presented in this study are able to split water at current densities over 300 mA cm^-2, with more than 42% power conversion efficiency, and crossover of hydrogen gas into the oxidation side as low as 0.4%, leading to a non-flammable and continuous hydrogen fuel stream

Hypochlorite Production[edit | edit source]

Optimization of hypochlorous acid generation by HCl electrolysis through response surface methodology and artificial neural networks[edit | edit source]

M. Yaqub, C. Woo, and W. Lee, “Optimization of hypochlorous acid generation by HCl electrolysis through response surface methodology and artificial neural networks,” Journal of Environmental Chemical Engineering, vol. 9, no. 5, p. 105826, Oct. 2021, doi: 10.1016/j.jece.2021.105826.

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Electrolyzed water as a disinfectant: A systematic review of factors affecting the production and efficiency of hypochlorous acid[edit | edit source]

R. E. Ampiaw, M. Yaqub, and W. Lee, “Electrolyzed water as a disinfectant: A systematic review of factors affecting the production and efficiency of hypochlorous acid,” Journal of Water Process Engineering, vol. 43, p. 102228, Oct. 2021, doi: 10.1016/j.jwpe.2021.102228.

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Developing chlorine-based antiseptic by electrolysis[edit | edit source]

K. A. Mourad and S. Hobro, “Developing chlorine-based antiseptic by electrolysis,” Science of The Total Environment, vol. 709, p. 136108, Mar. 2020, doi: 10.1016/j.scitotenv.2019.136108.

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An on-Site, on-Demand, Medium-Sized Hypochlorous Acid Maker for Covid-19 Control[edit | edit source]

L. Li, “An on-Site, on-Demand, Medium-Sized Hypochlorous Acid Maker for Covid-19 Control,” Meet. Abstr., vol. MA2021-01, no. 52, p. 2041, May 2021, doi: 10.1149/MA2021-01522041mtgabs.

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An Economic Hypochlorous Acid Maker for Covid-19 Control[edit | edit source]

L. Li, “An Economic Hypochlorous Acid Maker for Covid-19 Control,” Meet. Abstr., vol. MA2021-01, no. 52, p. 2039, May 2021, doi: 10.1149/MA2021-01522039mtgabs.

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Designing a high-efficiency hypochlorite ion generation system by combining cation exchange membrane aided electrolysis with chlorine gas recovery stream[edit | edit source]

S. K. Kim, D.-M. Shin, and J. W. Rhim, "Designing a high-efficiency hypochlorite ion generation system by combining cation exchange membrane aided electrolysis with chlorine gas recovery stream," Journal of Membrane Science, vol. 630, p. 119318, Jul. 2021, doi: 10.1016/j.memsci.2021.119318.

• Demonstrates a newly designed hypochlorite ion generation process that improves upon the conventional electrolysis cell by adding cation exchange membranes (CEMs) and a chlorine recovery stream to enhance stability and controllability as well as production rate and efficiency of hypochlorites generation, respectively
• Relevant results:
  • Chlorine recovery stream harvests the chlorine gas and bubbles through the high pH outflow
    • The Cl₂ gas was collected and supplied to the cathode outflow to create more NaOCl and HOCl
  • The two desired reactions that are occurring with the Cl₂ recovery model:
    • Electrochemical generation of HOCl and NaOCl (electrolysis of salt water)
    • Spontaneous reaction between NaOH solution and recovered Cl₂ gas to create HOCl and NaOCl
  • SPEEK membrane was found to be the most efficient and controllable
  • The CEMs used in this study, including the SPEEK, are not very accessible
    • Nafion series must be bought in bulk from a supplier; cost is quote dependent
      • Creating the SPEEK membrane requires various reactions requiring specific temperatures, timing, and equipment
        • >104 hours to create
        • Vacuum oven required
      • Comment: Due to these factors membrane-based electrolysis using traditional membrane technology does not fit the appropriate technology model very well
  • Higher current densities damage CEMs
  • Hypochlorite generation from recovered Cl₂ is more effective when the electric current applied to the electrolysis cell increases, since the following redox reactions become more rapid:
    • Anode:
      • 2 H₂O --> 4H⁺ + O₂ + 4 e^-
      • 2 Cl^- --> Cl₂ + 2 e^-
    • Cathode:
      • 2 H₂O + 2 e^- --> H₂ + 2OH^-
  • Comment: The Cl2 recovery stream appears to be key since the occurrence of unreacted Cl2 raises some issues:
    • Indicates loss of efficiency
    • Safety concern as Cl₂ gas is considered toxic
      • The recovery stream therefore increases the efficiency and safety of the system
  • Comment: Although the addition of a CEM to the system increases hypochlorite production it is not significant enough to warrant the additional cost for appropriate technology applications
    • Supported by the fact that the results show that energy consumption for w/o CEM system approximately the same as the w/ CEM systems
• Key information:
  • Hypochlorous acid (HOCl) and sodium hypochlorite (NaOCl) as an aqueous solution with concentration <40% are chemically stable and relatively safe to store and use (according to the National Fire Protection Association; NFPA 430, 2000)
• Device specifications:
  • Electrode distance: 4mm
  • CEM-based (sulfonated polyether ether ketone(SPEEK), Nafion 115, or Nafion 324)

Electrochemical water disinfection Part I: Hypochlorite production from very dilute chloride solutions[edit | edit source]

A. Kraft et al., "Electrochemical water disinfection Part I: Hypochlorite production from very dilute chloride solutions," vol. 29, pp. 859–866, Jul. 1999, doi: 10.1023/A:1003650220511.

• Investigates the electrolytic production of hypochlorite for very dilute chloride solutions
• Relevant results:
  • Hypochlorite production rate is consistently higher on iridium oxide coated titanium compared to platinum coated titanium electrodes
  • The chlorine production rate increases with increasing chloride concentration
  • Current efficiency increases with chloride concentration
    • This result is important when considering which is the limiting resource (reactant versus energy)
  • IrO₂ electrode had a remarkable reduction in the active chlorine production rate between 23 and 30 degree C
    • This strong reduction in the active chlorine production rate over a small temperature range was not observed at higher chloride concentrations
  • The active chlorine production rate decreased with increased in temperature
    • This depends strongly on chloride concentration
  • Linear increase in the production rate with increasing current density
  • At lower current densities:
    • Slight increase in the active chlorine production rate
    • Once higher current densities are reached the active chlorine production rate flatlines
  • Chlorine decay rate strongly depends on the temperature and pH
    • Does not appear to depend on concentration of active chlorine
    • An exponential increase in the reaction rate of chlorine decay with increasing temperature
• Key information:
  • Two steps for electrolytic hypochlorite production:
    1. Primary oxidation of chloride to chlorine at the anode surface:
       • 2 Cl^- → Cl₂ + 2e^-
    2. Solution phase reaction:
       1. Cl₂(aq) + H₂O → HClO + Cl^- + H⁺
  • In very dilute solutions a relatively large amount of chlorine produced rapidly reacts with oxidizable agents in the water and the apparatus in a process known as chlorine decay/consumption
    • A major problem in accurately determining the exact amount of active chlorine produced
    • All type of water have a chlorine demand which is the quantity of chlorine that will react with the inorganics and organic impurities contained within that water
    • Active chlorine can only forme once the chlorine demand of the water must be satisfied (breakpoint chlorination)
  • The formation of calcareous deposits on the cathode is an issue to be aware of and is a result of OH- being produced
    • 2 H₂O + 2 e^- → H₂ + 2 OH^-
    • The OH- causes an increase in pH which leads to the deposits:
      • Ca²⁺ + HCO^3- + OH^- → CaCO₃ + H₂O
      • Mg²⁺ + 2 OH^- → Mg(OH)₂
  • Chlorate formation from hypochlorite and hypochlorous acid is another issue to be aware of
    • The formation follows the equation:
      • ClO^- + 2 HClO → ClO^3- + 2 HCl
    • Chlorate formation increases with solution temperature
• Important terms:
  • Hypochlorite = hypochlorous acid + hypochlorite anion
  • Active chlorine = chlorine + hypochlorous acid + hypochlorite
    • Cl₂, HClO and ClO^-
    • In the pH range 6-9, the active chlorine is almost entirely hypochlorous acid (HClO) and hypochlorite (ClO^-)
• Device specifications:
  • Geometrical area of electrodes used:
    1. Platinum:
       • 100 mm X 30 mm
    2. Iridium oxides:
       • 113 mm X 30 mm
    3. Both coatings were applied to 1 mm thick expanded titanium metal
  • Anolyte and catholyte were divided by a Nafion 450 cation exchange membrane to prevent the reduction of the produced hypochlorite at the cathode
  • The electrode distance: 5 mm
  • Reaction compartment volumes:
    • Anolyte compartment: 1250 cm³
    • Catholyte compartment: 280 cm³

Electrochemical water disinfection. Part II: Hypochlorite production from potable water, chlorine consumption and the problem of calcareous deposits[edit | edit source]

A. Kraft, M. Blaschke, D. Kreysig, B. Sandt, F. Schröder, and J. Rennau, “Electrochemical water disinfection. Part II: Hypochlorite production from potable water, chlorine consumption and the problem of calcareous deposits,” Journal of Applied Electrochemistry, vol. 29, no. 8, pp. 895–902, Aug. 1999, doi: 10.1023/A:1003654305490.

Electrochemical water disinfection Part III: Hypochlorite production from potable water with ultrasound assisted cathode cleaning[edit | edit source]

A. Kraft, M. Blaschke, and D. Kreysig, “Electrochemical water disinfection Part III: Hypochlorite production from potable water with ultrasound assisted cathode cleaning,” Journal of Applied Electrochemistry, vol. 32, no. 6, pp. 597–601, Jun. 2002, doi: 10.1023/A:1020199313115.

Potentiostat[edit | edit source]

Development of a low-cost Arduino-based potentiostat[edit | edit source]

J. R. Crespo, S. R. Elliott, T. Hutter, and H. Águas, "Development of a low-cost Arduino-based potentiostat," p. 21.

• Design for a simple, cost-effective Arduino-based potentiostat
  • A potentiostat is an electronic circuit used to study the electrochemical events taking place at one specific electrode and allow for specific tuning of the applied conditions
• Abbreviations
  • RE – Reference Electrode
  • CE – Counter Electrode
  • WE – Working Electrode
  • TIA - Transimpedance Amplifier
• Relevant results:
  • Demonstrates the circuit being simulated using the LTspice simulation software and it's resulting transient response graphs
  • Provides and explains the Arduino software
  • Data acquisition through the serial USB interface can be displayed in real time using the open-source processing software environment as a serial terminal visual interface, which can also save the data in text file format for analysis
  • Circuit functions by comparing the measured Cell voltage with the desired voltage
    • Using this it drives current into the cell to force the voltages to be the same in an inverting configuration to provide the negative feedback
  • See original paper for circuit diagram
    • U1 is a Differential Amplifier:
      • Functions to drive the input signal from the Arduino PWM output and add offset voltage value, from the voltage divider composed by the 100K resistors and the 100k potentiometer in the non-inverting input, to shift the applied voltage to the cell in the desired range
      • The potentiometer is used so the user can tune manually the applied voltage range
    • U2 is the Control Amplifier
      • Measured Cell voltage compared with the desired voltage
      • Drives current into the cell to force the voltages to be the same in an inverting configuration to provide the negative feedback
      • Equations describing this provided in paper
    • U3 and U4 are voltage Followers
      • Isolates the input from the output to prevent loading of the input signal
      • Voltage output from U3 is connected to the CE
    • U5 and U7 are voltage shifters
      • Sums 3.3 V from the Arduino to the output signals of the potentiostat
        • i.e. the voltage and the current measured
      • Used because Arduino only can read voltage values from 0 to 5000 mV
        • Thus, the maximum applied voltage ranges that can be read by the potentiostat can be determined which is from -3300 mV to +1700 mV
    • U6 is a transimpedance amplifier
      • Converts the measured current in the WE into a voltage through Rf
• Key information:
  • To evaluate the fabricated potentiostat and to verify proper function use 10 and 20 kΩ resistors to simulate the electrolyte
    • The resistors were connected between the working electrode and reference electrode (simulating the cell resistance) and a small resistor (100 Ω) was connected between the reference and the counter electrode to have the control of the potential applied
  • The 10-100 kΩ gain potentiometer was used to read currents in the ranges from µA to mA
    • Range where most electrochemical reactions occur
  • The Potentiostat Circuit presented was inspired by the potentiostat circuit proposed in "A Simplified Microcontroller Based Potentiostat for Low-Resource Applications" by Aremo et al

MYSTAT: A compact potentiostat/galvanostat for general electrochemistry measurements[edit | edit source]

P. Irving, R. Cecil, and M. Z. Yates, “MYSTAT: A compact potentiostat/galvanostat for general electrochemistry measurements,” HardwareX, vol. 9, Apr. 2021, doi: 10.1016/j.ohx.2020.e00163.

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PassStat, a simple but fast, precise and versatile open source potentiostat[edit | edit source]

M. Caux et al., “PassStat, a simple but fast, precise and versatile open source potentiostat,” HardwareX, vol. 11, Apr. 2022, doi: 10.1016/j.ohx.2022.e00290.

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Lifting the lid on the potentiostat: a beginner’s guide to understanding electrochemical circuitry and practical operation[edit | edit source]

A. W. Colburn, K. J. Levey, D. O’Hare, and J. V. Macpherson, “Lifting the lid on the potentiostat: a beginner’s guide to understanding electrochemical circuitry and practical operation,” Physical Chemistry Chemical Physics, vol. 23, no. 14, pp. 8100–8117, 2021, doi: 10.1039/D1CP00661D.

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A Simplified Microcontroller Based Potentiostat for Low-Resource Applications[edit | edit source]

B. Aremo, M. O. Adeoye, I. B. Obioh, and O. A. Adeboye, “A Simplified Microcontroller Based Potentiostat for Low-Resource Applications,” Open Journal of Metal, vol. 5, no. 4, Art. no. 4, Jan. 2016, doi: 10.4236/ojmetal.2015.54005.

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Building a Microcontroller Based Potentiostat: A Inexpensive and Versatile Platform for Teaching Electrochemistry and Instrumentation[edit | edit source]

G. N. Meloni, “Building a Microcontroller Based Potentiostat: A Inexpensive and Versatile Platform for Teaching Electrochemistry and Instrumentation,” J. Chem. Educ., vol. 93, no. 7, pp. 1320–1322, Jul. 2016, doi: 10.1021/acs.jchemed.5b00961.

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Open-Source Potentiostat for Wireless Electrochemical Detection with Smartphones[edit | edit source]

A. Ainla et al., “Open-Source Potentiostat for Wireless Electrochemical Detection with Smartphones,” Anal. Chem., vol. 90, no. 10, pp. 6240–6246, May 2018, doi: 10.1021/acs.analchem.8b00850.

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CheapStat: An Open-Source, ‘Do-It-Yourself’ Potentiostat for Analytical and Educational Applications[edit | edit source]

A. A. Rowe et al., “CheapStat: An Open-Source, ‘Do-It-Yourself’ Potentiostat for Analytical and Educational Applications,” PLOS ONE, vol. 6, no. 9, p. e23783, Sep. 2011, doi: 10.1371/journal.pone.0023783.

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DStat: A Versatile, Open-Source Potentiostat for Electroanalysis and Integration[edit | edit source]

M. D. M. Dryden and A. R. Wheeler, “DStat: A Versatile, Open-Source Potentiostat for Electroanalysis and Integration,” PLOS ONE, vol. 10, no. 10, p. e0140349, Oct. 2015, doi: 10.1371/journal.pone.0140349.

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A Small yet Complete Framework for a Potentiostat, Galvanostat, and Electrochemical Impedance Spectrometer[edit | edit source]

Y. Matsubara, “A Small yet Complete Framework for a Potentiostat, Galvanostat, and Electrochemical Impedance Spectrometer,” J. Chem. Educ., vol. 98, no. 10, pp. 3362–3370, Oct. 2021, doi: 10.1021/acs.jchemed.1c00228.

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SweepStat: A Build-It-Yourself, Two-Electrode Potentiostat for Macroelectrode and Ultramicroelectrode Studies[edit | edit source]

M. W. Glasscott, M. D. Verber, J. R. Hall, A. D. Pendergast, C. J. McKinney, and J. E. Dick, “SweepStat: A Build-It-Yourself, Two-Electrode Potentiostat for Macroelectrode and Ultramicroelectrode Studies,” J. Chem. Educ., vol. 97, no. 1, pp. 265–270, Jan. 2020, doi: 10.1021/acs.jchemed.9b00893.

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ABE-Stat, a Fully Open-Source and Versatile Wireless Potentiostat Project Including Electrochemical Impedance Spectroscopy[edit | edit source]

D. M. Jenkins, B. E. Lee, S. Jun, J. Reyes-De-Corcuera, and E. S. McLamore, “ABE-Stat, a Fully Open-Source and Versatile Wireless Potentiostat Project Including Electrochemical Impedance Spectroscopy,” J. Electrochem. Soc., vol. 166, no. 9, p. B3056, Mar. 2019, doi: 10.1149/2.0061909jes.

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Electrodes[edit | edit source]

3D printed flow plates for the electrolysis of water: an economic and adaptable approach to device manufacture[edit | edit source]

G. Chisholm, P. J. Kitson, N. D. Kirkaldy, L. G. Bloor, and L. Cronin, "3D printed flow plates for the electrolysis of water: an economic and adaptable approach to device manufacture," Energy Environ. Sci., vol. 7, no. 9, pp. 3026–3032, 2014, doi: 10.1039/C4EE01426J.

• Demonstrates the production and operation of a PEM electrolyser that uses silver coated 3D printed components which allows construction of light weight, low cost electrolysers and rapid prototyping
• Demonstrates excellent performance for a first generation device in terms of overall efficiency, internal resistances and current-voltage response
• Relevant results:
  • 3D printing and appropriate surface coatings can be used to fabricate electrodes that can be used to create viable, practical electrochemical system
• Key Information:
  • Flow plates were created using layer by layer deposition with polypropylene
  • Two coats of silver paint were applied to the FPs
    • Curing at 120 degree C after each coat had and dried at ambient conditions
  • The processed used here is that outlined in the paper by Polk et al. 2006 that demonstrates the fabrication and testing of Ag/AgCl microelectrodes
  • The high cost of electrolysers based on proton exchange membranes (PEMs) hinders widespread deployment.
    • Principal cost factor are the materials and machining of flow plates
• Device specifications:
  • Flow plate thickness: 3mm
  • The final thickness of the coated layer was 300 μm

Ag/AgCl microelectrodes with improved stability for microfluidics[edit | edit source]

B. J. Polk, A. Stelzenmuller, G. Mijares, W. MacCrehan, and M. Gaitan, "Ag/AgCl microelectrodes with improved stability for microfluidics," Sensors and Actuators B: Chemical, vol. 114, no. 1, pp. 239–247, Mar. 2006, doi: 10.1016/j.snb.2005.03.121.

• Presents a method for fabricating Ag/AgCl planar microelectrodes for microfluidic applications with the goal of reliably constructing Ag/AgCl microelectrodes that are compatible with surface mounted microfluidic channels and have improved potential stability
• Key information:
  • The electrode surface was electroplated with silver then chemically oxidized to silver chloride to form Ag/AgCl micro-reference electrodes
  • Ag/AgCl microelectrodes produced by this method exhibit increased stability compared with many devices previously reported and were shown to have utility for electrochemical analysis within microfluidic systems

Fluid Handling[edit | edit source]

Highly-customizable 3D-printed peristaltic pump kit[edit | edit source]

T. Ching et al., "Highly-customizable 3D-printed peristaltic pump kit," HardwareX, vol. 10, Oct. 2021, doi: 10.1016/j.ohx.2021.e00202.

• 3D-printed peristaltic with the following specifications (variant A):
  • L × W × H [mm]: 30 × 85 × 17
  • Number of channels: 4
  • Flow rate range [μL/min]: 0.05 ~ 727.3
  • Cost of hardware [USD]: ~$30
  • Cost per channel [USD]: ~$8
• Comment: this pump will not be used in the final functional design due to the relatively low flow rate; it will be used for testing and characterization of the flow cell architecture but the final design will use a simpler, less precise peristaltic pump with a flow rate since a lower level of precision is required for production versus testing/characterization
• Designed to allow for variations in size, flow rate, and the number of channels
• Peristaltic pumps deliver fluids by alternating compression and relaxation of a flexible tube
• The pump consists of three rollers
  • Three-roller assembly is used to generate rotational torque from a single motor to induce fluid propulsion
  • The rotation of the rollers compress and relax the flexible tubing to create negative and positive pressures to draw the fluid through the tube
• Variant A was a four-channel peristaltic pump with a footprint of 30 x 85 x 17 mm with flow rates of 0.05 ~ 727.30 mL/min
• A standard 2-mL Eppendorf tube was modified to create a fluid reservoir which was secured with 3D printed a tube holder
• Modular design: deconstructable into small subunits called modules
  • Can be independently printed, modified, replaced, or exchanged with other modules in the same system or between different systems

The FAST Pump, a low-cost, easy to fabricate, SLA-3D-printed peristaltic pump for multi-channel systems in any lab[edit | edit source]

A. Jönsson, A. Toppi, and M. Dufva, “The FAST Pump, a low-cost, easy to fabricate, SLA-3D-printed peristaltic pump for multi-channel systems in any lab,” HardwareX, vol. 8, Oct. 2020, doi: 10.1016/j.ohx.2020.e00115.

Ender3 3D printer kit transformed into open, programmable syringe pump set[edit | edit source]

S. Baas and V. Saggiomo, “Ender3 3D printer kit transformed into open, programmable syringe pump set,” HardwareX, vol. 10, Oct. 2021, doi: 10.1016/j.ohx.2021.e00219.

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A low-cost push–pull syringe pump for continuous flow applications[edit | edit source]

M. Iannone, D. Caccavo, A. A. Barba, and G. Lamberti, “A low-cost push–pull syringe pump for continuous flow applications,” HardwareX, vol. 11, Apr. 2022, doi: 10.1016/j.ohx.2022.e00295.

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Syringe pumps - OSF[edit | edit source]

M. Hinge and B. S. Kilsgaard, “Syringe pumps,” Sep. 2018, doi: 10.17605/OSF.IO/QCNJT.

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Impeller and Pump Design - OSF[edit | edit source]

Millie, Chaelim, Ashely, and Jess, “Impeller and Pump Design,” Sep. 2021, Accessed: Feb. 19, 2023. [Online]. Available: https://osf.io/rvw9d/

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Flui.Go Pump - OSF[edit | edit source]

R. Rogosic, “Flui.Go Pump,” Jan. 2022, doi: 10.17605/OSF.IO/QKW42.

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Measurement and Validation[edit | edit source]

Electrochemical Impedance Spectroscopy (EIS) - PalmSens[edit | edit source]

“Electrochemical Impedance Spectroscopy (EIS),” PalmSens. https://www.palmsens.com/knowledgebase-article/electrochemical-impedance-spectroscopy-eis/ (accessed Feb. 19, 2023).

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Future Applications[edit | edit source]

Hypochlorous Acid as a Potential Wound Care Agent[edit | edit source]

L. Wang et al., "Hypochlorous Acid as a Potential Wound Care Agent," J Burns Wounds, vol. 6, p. e5, Apr. 2007.

• Describes the production, stabilization, and biological activity of HOCl for pharmaceutical applications
• Key Information:
  • This study used stabilized HOCl is in the form of a physiologically balanced solution in 0.9% saline at a pH range of 3.5 to 4.0
  • Chlorine species distribution in solution is a function of pH
  • In aqueous solution, HOCl is the predominant species at the pH range of 3 to 6
  • At pH values less than 3.5, the solution exists as a mixture of chlorine in aqueous phase, chlorine gas, trichloride (Cl3−), and HOCl
  • At pH greater than 5.5, sodium hypochlorite (NaOCl) starts to form and becomes the predominant species in the alkaline pH
  • To maintain HOCl solution in a stable form, maximize its antimicrobial activities, and minimize undesirable side products, the pH must be maintained at 3.5 to 5
• Relevant results:
  • This stabilized form of HOCl is used to demonstrate the potent antimicrobial activities of HOCl against a wide range of microorganisms
  • HOCl has potential pharmaceutical applications in the control of soft tissue infection
    • Predicted based on antimicrobial activity and the lack of animal toxicity
  • Paper includes multiple tables showing the time to kill and number of pathogens recovered per minute as well as a table showing safety studies done on different animal species

Design and analysis of a combined floating photovoltaic system for electricity and hydrogen production[edit | edit source]

M. Temiz and N. Javani, “Design and analysis of a combined floating photovoltaic system for electricity and hydrogen production,” International Journal of Hydrogen Energy, vol. 45, no. 5, pp. 3457–3469, Jan. 2020, doi: 10.1016/j.ijhydene.2018.12.226.

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Bibliography[edit | edit source]

[1]G. Chisholm, P. J. Kitson, N. D. Kirkaldy, L. G. Bloor, and L. Cronin, "3D printed flow plates for the electrolysis of water: an economic and adaptable approach to device manufacture," Energy Environ. Sci., vol. 7, no. 9, pp. 3026–3032, 2014, doi: 10.1039/C4EE01426J.

[2]M. Hashemi, M. Modestino, and D. Psaltis, "A membrane-less electrolyzer for hydrogen production across the pH scale," Energy Environ. Sci., vol. 8, pp. 2003–2009, Apr. 2015, doi: 10.1039/C5EE00083A.

[3]S. M. H. Hashemi et al., "A versatile and membrane-less electrochemical reactor for the electrolysis of water and brine," Energy Environ. Sci., vol. 12, no. 5, pp. 1592–1604, 2019, doi: 10.1039/C9EE00219G.

[4]B. J. Polk, A. Stelzenmuller, G. Mijares, W. MacCrehan, and M. Gaitan, "Ag/AgCl microelectrodes with improved stability for microfluidics," Sensors and Actuators B: Chemical, vol. 114, no. 1, pp. 239–247, Mar. 2006, doi: 10.1016/j.snb.2005.03.121.

[5]P. Boissonneau and P. Byrne, "An experimental investigation of bubble-induced free convection in a small electrochemical cell," Journal of Applied Electrochemistry, vol. 30, p. 9, Jul. 2000, doi: 10.1023/A:1004034807331.

[6]S. K. Kim, D.-M. Shin, and J. W. Rhim, "Designing a high-efficiency hypochlorite ion generation system by combining cation exchange membrane aided electrolysis with chlorine gas recovery stream," Journal of Membrane Science, vol. 630, p. 119318, Jul. 2021, doi: 10.1016/j.memsci.2021.119318.

[7]A. Kraft et al., "Electrochemical water disinfection Part I: Hypochlorite production from very dilute chloride solutions," vol. 29, pp. 859–866, Jul. 1999, doi: 10.1023/A:1003650220511.

[8]K. Song, "Electrolysis," Chemistry LibreTexts, Oct. 02, 2013. https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Supplemental_Modules_(Analytical_Chemistry)/Electrochemistry/Electrolytic_Cells/Electrolysis (accessed Jan. 06, 2022).

[9]"Hypochlorous acid," Wikipedia. Dec. 31, 2021. Accessed: Jan. 08, 2022. [Online]. Available: https://en.wikipedia.org/w/index.php?title=Hypochlorous_acid&oldid=1063015952

[10]D. Lapenna and F. Cuccurullo, "Hypochlorous acid and its pharmacological antagonism: An update picture," Gen. Pharmac., vol. 27, no. 7, pp. 1145–1147, Oct. 1996, doi: 10.1016/S0306-3623(96)00063-8.

[11]L. Wang et al., "Hypochlorous Acid as a Potential Wound Care Agent," J Burns Wounds, vol. 6, p. e5, Apr. 2007.

[12]X. Pang, J. T. Davis, A. D. Harvey, and D. V. Esposito, "Framework for evaluating the performance limits of membraneless electrolyzers," Energy Environ. Sci., vol. 13, no. 10, pp. 3663–3678, Oct. 2020, doi: 10.1039/D0EE02268C.

[13]J. R. Crespo, S. R. Elliott, T. Hutter, and H. Águas, "Development of a low-cost Arduino-based potentiostat," p. 21.

[14]T. Ching et al., "Highly-customizable 3D-printed peristaltic pump kit," HardwareX, vol. 10, Oct. 2021, doi: 10.1016/j.ohx.2021.e00202.