Low cost 3D printable flow reactors for electrochemistry

Abstract

Transition to carbon neutrality requires the development of more sustainable pathways to synthesize the next generation of chemical building blocks. Electrochemistry is a promising pathway to achieve this goal, as it allows for the use of renewable energy to drive chemical transformations. While the electroreduction of carbon dioxide (CO2) and hydrogen evolution are attracting significant research interest, fundamental challenges exist in moving the research focus toward performing these reactions on scales relevant to industrial applications. To bridge this gap, we aim to facilitate researchers' access to flow reactors, which allow the characterization of electrochemical transformations under conditions closer to those deployed in the industry. Here, we provide a 3D-printable flow cell design (manufacturing cost < 5),whichconsistsofseveralplates,offeringacustomizablealternativetocommerciallyavailableflowreactors(cost>5), which consists of several plates, offering a customizable alternative to commercially available flow reactors (cost > 6,000). The proposed design and detailed build instructions allow the performance of a wide variety of chemical reactions in flow, including gas and liquid phase electroreduction, electro(less)plating, and photoelectrochemical reactions, providing researchers with more flexibility and control over their experiments. By offering an accessible, low-cost reactor alternative, we reduce the barriers to performing research on sustainable electrochemistry, supporting the global efforts necessary to realize the paradigm shift in chemical manufacturing.

Full text

HardwareX 17 (2024) e00505
Available online 21 December 2023
2468-0672/© 2023 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Hardware Article
Low cost 3D printable ow reactors for electrochemistry
Erin Heeschen
a
, Elena DeLucia
a
, Yilmaz Arin Manav
b
, Daisy Roberts
a
,
Benyamin Davaji
b
, Magda H. Barecka
a
,
c
,
*
a
Department of Chemical Engineering, Northeastern University, 360 Huntington Ave, Boston, MA 02115, United States
b
Department of Electrical and Computer Engineering, Northeastern University, 360 Huntington Ave, Boston, MA 02115, United States
c
Department of Chemistry and Chemical Biology, Northeastern University, 360 Huntington Ave, Boston, MA 02115, United States
ARTICLE INFO
Keywords:
CO
2
Electrolysis
3D Printable Model
Hydrogen Evolution
Hydrogen Production
Flow cell
Electroreduction
ABSTRACT
Transition to carbon neutrality requires the development of more sustainable pathways to syn-
thesize the next generation of chemical building blocks. Electrochemistry is a promising pathway
to achieve this goal, as it allows for the use of renewable energy to drive chemical trans-
formations. While the electroreduction of carbon dioxide (CO
2
) and hydrogen evolution are
attracting signicant research interest, fundamental challenges exist in moving the research focus
toward performing these reactions on scales relevant to industrial applications. To bridge this
gap, we aim to facilitate researchers’ access to ow reactors, which allow the characterization of
electrochemical transformations under conditions closer to those deployed in the industry. Here,
we provide a 3D-printable ow cell design (manufacturing cost <$5), which consists of several
plates, offering a customizable alternative to commercially available ow reactors (cost >
$6,000). The proposed design and detailed build instructions allow the performance of a wide
variety of chemical reactions in ow, including gas and liquid phase electroreduction, electro
(less)plating, and photoelectrochemical reactions, providing researchers with more exibility and
control over their experiments. By offering an accessible, low-cost reactor alternative, we reduce
the barriers to performing research on sustainable electrochemistry, supporting the global efforts
necessary to realize the paradigm shift in chemical manufacturing.
Specications table
Hardware name 3D printable ow reactor
Subject area •Engineering and materials science
•Chemistry and biochemistry
Hardware type •Other [please specify] - Electrochemistry
Closest commercial analog https://dioxidematerials.com/product/complete-5-cm2-fa-electrolyzer/
Open-source license Creative Commons Attribution 4.0 International
Cost of hardware Flow reactor only <$5; reactor with the supporting equipment - $1,207.12 - $3,867.97
Source le repository https://doi.org/10.5281/zenodo.8435816
* Corresponding author at: Department of Chemical Engineering, Northeastern University, 360 Huntington Ave, Boston, MA 02115, United States;
Department of Chemistry and Chemical Biology, Northeastern University, 360 Huntington Ave, Boston, MA 02115, United States.
E-mail address: m.barecka@northeastern.edu (M.H. Barecka).
Contents lists available at ScienceDirect
HardwareX
journal homepage: www.elsevier.com/locate/ohx
https://doi.org/10.1016/j.ohx.2023.e00505
Received 1 June 2023; Received in revised form 15 November 2023; Accepted 16 December 2023

HardwareX 17 (2024) e00505
2
Hardware in context
The ramications of climate change continue to intensify, leading laboratories worldwide to investigate methodologies to reduce
carbon emissions, among which electrochemistry is attracting signicant attention. CO
2
electrolysis and hydrogen evolution are the
commonly studied electrochemical reactions for effective carbon mitigation; the rst technique converts the greenhouse gas CO
2
into
valuable products via an electrocatalytic transformation, while hydrogen evolution provides a fuel source to bypass carbon usage
altogether [1,2]. The demand for CO
2
electrolysis and hydrogen evolution-based research is illustrated by publication statistics
extracted from Google Scholar (Table 1). Looking only at articles published between January 1, 2022, and January 1, 2023, our search
yielded 597,000 results, indicating signicant research potential in CO
2
electrolysis and hydrogen evolution. Fig. 1 illustrates a drastic
increase in Google Scholar results for the “CO
2
Electroreduction” keywords – up to 25,000 results in 2022.
Despite growing interest, multiple challenges must be addressed to enable the broader use of electrochemical methods in real-life
applications. Factors such as the experimental cost reduce the number of entities able to conduct research in these elds and, in turn,
limit the progress in electrochemistry. A solution to reducing the experimental cost is to create comparatively inexpensive equipment,
thus, we turn to 3D printing as an alternative method to produce electrochemical reactors [3–6]. 3D printing offers a fast, low-cost
alternative to purchasing instrument pieces through manufacturers, and models can be customized to suit a laboratory’s needs bet-
ter. Such examples of 3D model customizations in electrochemistry are most clearly demonstrated through the use of 3D printed
electrodes [7,8] and biosensors [9,10] in the eld of bioelectronics. Regarding environmentally focused electrochemistry, as described
above, 3D printing membrane reactors for electrochemical conversion has been reported to have numerous benets in addition to
lower costs, including improved test capacities and better chemical identication; however, no 3D print design les were attached to
these reports [11–13].
Table 1
Google Scholar results for each keyword/phrase relating to CO
2
electrolysis and hydrogen production. Results
are collected from publications released between January 1, 2022, and January 1, 2023. Results were collected
by searching for keywords in CO
2
electrolysis and hydrogen evolution. The nal “Total Number of Results” row
summarizes the total number of search results recorded, but the overlap between said search results is not
accounted.
Keyword or Searched Phrase Number of Results from January 1, 2022, to January 1, 2023
Flow Cell 187,000
Hydrogen Evolution 140,000
Electrochemical Reduction 125,000
Gas Diffusion Electrode 56,200
CO
2
Electrolysis 28,100
H-Cell 19,500
CO
2
Electroreduction 22,300
Hydrogen Cell 14,700
CO
2
Electrolyzer 10,400
Total Number of Results 603,200
Fig. 1. Google Scholar results for the keywords “CO
2
Electroreduction”. Each data point indicates the number of articles published within its
respective year, indicating a growing interest in CO
2
electroreduction over the past decade.
E. Heeschen et al.

HardwareX 17 (2024) e00505
3
In addition to signicant cost reduction, the proposed reactor design offers the advantage of performing reactions in ow. Flow
reactors allow high precision, reproducibility, and selectivity in electrochemical experiments [14]. A ow reactor is a reactor in which
chemicals of interest are carried as a continuous stream: reactants enter the ow cell through tubing at a constant ow rate, and the
products are continuously removed from the system in a similar fashion [15]. In contrast to frequently deployed H-cells, where the
electrochemical materials (cathodes and anodes) are immersed in liquid solutions, ow reactors provide an opportunity to expose the
electrochemical materials to a well-controlled interphase with an intensied mass transfer, ultimately allowing electrochemical re-
actions to be conducted in a more controlled manner. This enables, e.g., a more selective synthesis of specic hydrocarbons [16–18].
Besides CO
2
electrolysis and hydrogen evolution, ow reactors can also be deployed for nitrogen reduction and many chemical re-
actions relevant to ne and pharmaceutical engineering applications [19].
Though the need to adopt ow reactors more frequently was highlighted in the literature [20], these reactors are still not used as
widely as they might be, primarily due to the limited accessibility of the reactors themselves and the additional challenges in operating
the experimental set-up where the potential gas and liquid leaks need to be carefully controlled. Therefore, we provide a detailed
overview of operating and troubleshooting procedures in addition to the ow reactor design. With a customizable and more accessible
version of the ow reactor, more research can be dedicated to understanding sustainability-focused procedures such as CO
2
electrolysis
and hydrogen production, thus hastening the transition towards carbon neutrality [21–23].
A basic commercially available ow reactor consisting of two titanium and stainless-steel plates costs $6,050; however, it does not
include the owmeter, pump, or connections necessary to run most experiments [24]. In this paper, we propose a 3D printed ow
reactor that offers the ability to perform diverse gas and liquid phase reactions, and offer more accessible alternatives to the com-
ponents needed to successfully run multiple electrochemical experiments as shown in Table 2 of Hardware Description. While the
application of the 3D printed ow reactor will be inherently limited to the chemical compatibility of the used lament and the quality
of the print itself, we envision a broad range of chemistries compatible with the commercially available laments, as outlined in the
section “Filament choice.”.
Hardware description
Design overview. 3D printable les are provided for several basic plates to form a ow cell: a plate with a serpentine-type ow
eld and inlet/oulet holes (Plate_A), a plate with a hexagonal hole in the center and its inlet/outlet connections shifted to the sides
(Plate_B), and a at supportive plate (Plate_C) (Fig. 2.a). These plates can be subsequently arranged in different ways, depending on the
phases involved in each experiment (gas/liquid) and what interphases need to be created, summarized in Table 2. As an exemplary
reactor arrangement, Fig. 2.b depicts the reactor assembly for CO
2
electrolysis experiments, where the reactive environment consists of
three phases (gas/rst-liquid/second-liquid), separated by a cathode, anion exchange membrane, and anode. Importantly, the rst-
liquid phase must simultaneously be exposed to both upper and lower channels. Therefore, we use a combination of a plate with
serpentine ow (for gas supply), a plate with openings on both sides (for the rst liquid phase), and another plate with serpentine ow
for the second liquid supply. Plates with serpentine ow elds incorporate an O-ring opening to further improve the sealing.
An essential part of the proposed designare tube connectors. Instead of threaded connectors, which require a high resolution of 3D
print (and thus would be associated with a higher cost), we incorporate a simple cylindrical connector that silicone tubing (1/8 in.) can
be directly pushed on top of (see pictures under Building Instructions).
Gasket choice and their dual role. To ensure a proper seal between the plates, we deploy two elements: rubber gaskets of
carefully adjusted thickness and external clamps. The gaskets (Fig. 2.a) play a dual role: they both allow for an accurate seal between
the plates and hold an opening for the electrocatalytic material, which shall be exposed to the gas or liquid ow circulating on top/
above. The thickness of the gasket must be equal to the thickness of the electrocatalytic material being held (to avoid any irregularities
in the assembled reactor). It is vital to design your rubber gasket to properly t all non-3D printed materials and accommodate the
number of desired electrodes, otherwise a leak can occur and the experiment’s validity will be compromised.
Two and three electrode experiments. To accommodate diverse electrochemical measurements, our reactors can be used both
Table 2
Potential experiments that can be run using the 3D printed ow cell. Please note that not all of the suggested experiments in Table 2 have -been
conducted in this paper, but the proposed ow reactor design allows the establishment of leak-free interfaces needed for these applications. It is
recommened to substitute Plate_A with Plate_F and Plate_B with Plate_E if using a membrane in the reactor to minimize potential friction damage.
Plate_B can also be substituted with Plate_D if a reference electrode is not required.
Application Phases Recommended plates Additional equipment
Electrochemical reactions Gas/liquid/liquid
Gas/liquid
Liquid/liquid
A +B +A
A +A / A +B +C
A +B +C
Gas owmeters, peristaltic pump
Photoelectrochemical reactions Liquid A +B with a transparent window attached inside of the gasket Peristaltic pump, UV–vis light source
Hydrogen production Gas A +B +A Gas owmeters, peristaltic pump
Electroplating Liquid A +C Peristaltic pump
Electro-less plating Liquid A +C Peristaltic pump
Light-sensitive reactions Gas
Gas/liquid
Liquid
A +B +A
A +A / A +B +C
A +B +C
Peristaltic pump
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HardwareX 17 (2024) e00505
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for two and three-electrode arrangement set-ups [17]. A solar cell or DC power can directly power a two-electrode system. In contrast,
three-electrode systems are typically powered by a potentiostat that can be used for in-depth studies of the electrochemical properties
of cathode and anode materials. In the case of three electrode experiments, it is necessary to connect an additional reference electrode
to the system. Thus we provide a small opening in Plate_B to analyze electrochemical properties close to the reactive interphase. For
Fig. 2. a. Overview of the proposed ow eld designs and example of a rubber gasket; b. The basic structure of the 3D printed ow cell. The
numbered components are as follows: 1. Plate_B 2. Plate_A 3. Rubber gasket.
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HardwareX 17 (2024) e00505
5
more information on choosing the optimal reference electrode, we recommend the article “Judicious selection, validation, and use of
reference electrodes for in situ and operando electrocatalysis studies” by Alnoush et al. [25].
External sealing. Last, we propose a strategy to ensure proper sealing by external clamps instead of the typical threaded con-
nectors, again in response to the need to minimize complex, high-resolution elements and allow for successful printing of the reactor
design even by low-cost 3D printers.
For applications that include a fragile anion exchange membrane, we recommend using screws instead of clamps as these will
impart less strain on the membrane than the shifting of plates that occurs when using clamps. In such cases, Plate_F should be used in
place of Plate_A and Plate_E in place of Plate_B. Plates E and F have holes along the plate perimeter that are designed to be put together
via screws (in this case, users will need to purchase the screws detailed in the Bill of Materials instead of the clamps).
Current collectors. In addition to the elements discussed above, some high current density applications might require the in-
clusion of metal foil elements (similar in shape to rubber gaskets) as current collectors. The procedure of placing these elements is
described in detail in the supplementary videos attached to a recent report on the operation of gas diffusion-electrode-based reactors
for CO
2
electroreduction [26].
Ohmic losses. Minimizing Ohmic losses is critical to ensuring the energy efciency of electrochemical reactions. Therefore, the
proposed plates are as thin as possible, thus signicantly reducing the distance between the cathode and the anode.
Filament choice. The lament is critical to the safe operation of the reactor and should be determined based on the goals of each
experiment, most importantly, their chemical compatibility and melting point. For most reactions, we recommend PETG; it has a large
range of commonly used chemicals that are safe to use with the printing material, a printing temperature between 210 and 230 ◦C, is
hydrophobic, and does not deform easily [27]. However, PETG is unsuitable for all applications and each laboratory must determine
the best lament for their application needs. Standard laments and their chemical compatibilities are provided by PRUSA Polymers
and depicted in Table 3 [28]. The impact resistance of each lament is beyond the scope of this paper, but interested readers can read
the following papers for further information [29,30].
Table 3
Commonly used laments, their cost in US dollars per oz, and their chemical compatibility with commonly used chemicals are presented below. A
rating of “A” indicates the polymer resists the chemical very well with little impact, while a “D” indicates poor performance, up to and including the
complete destruction of the lament. For more information regarding the rating system, visit PRUSA Polymers’ “Chemical Resistance of 3D Materials”
[28].
Table 4
Recommended printing parameters for each plate (Plate_A–F).
Printing Parameter Value/Unit
Material 1.75 mm PETG lament
Printing Temperature 245 ◦C
Layer Height 0.1 mm
Shell Width 0.8 mm
Inll Percentage 15 %
Inll Speed 70 mm/s
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Utilizing the recommended PETG lament and all necessary equipment to test for a proper seal provided in the Bill of Materials
(including pumps, mass ow controllers, mass ow meters, catholyte, and anolyte bottles), the entire experimental set-up (with
additional screw components) costs approximately $3867.97. In addition to customization and reduced cost, these 3D printable
models can bypass the shipping process, and the ow cell will be ready to use in a comparably shorter amount of time. Printing the
three primary plates provided in this paper using PETG lament takes approximately 9 hours, as opposed to the weeks it can take to
receive commercially available equipment.
Scope of the hardware. Diverse electrochemical experiments listed in Table 2 require using potentiostats and analytical chemistry
tools, such as gas chromatography, high-performance liquid chromatography, or mass spectrometry. Given the variety of the potential
uses of the ow reactors, we do not aim to cover the connection and use of this equipment. Instead, we focus on the capability of the
ow reactors to provide specic gas and liquid ows to subsequently allow for performing more complex experiments.
Design les
Design le name File type Open source license Location of the le
Plate_A.stl STL Creative Commons Attribution 4.0 International https://doi.org/10.5281/zenodo.8435816
Plate_B.stl STL Creative Commons Attribution 4.0 International https://doi.org/10.5281/zenodo.8435816
Plate_C.stl STL Creative Commons Attribution 4.0 International https://doi.org/10.5281/zenodo.8435816
Plate_D.stl STL Creative Commons Attribution 4.0 International https://doi.org/10.5281/zenodo.8435816
Plate_E.stl STL Creative Commons Attribution 4.0 International https://doi.org/10.5281/zenodo.8435816
Plate_F.stl STL Creative Commons Attribution 4.0 International https://doi.org/10.5281/zenodo.8435816
Plate_A.stl
•This le contains the 3D-printable model of a square plate with an open serpentine ow channel. The serpentine channel has a hole
on either end to enable uid ow with a diameter of 3.0 mm.
Plate_B.stl
•This le contains the 3D-printable model of a square plate with a hollow, hexagonal center. The hexagon has holes on opposing
sides to enable uid introduction and ow. This plate contains a small opening near the uid inlet for a wire-based reference
electrode with a diameter of 0.5 mm.
Plate_C.stl
•This le contains a at, square plate with no components, which serves as a support for the experiments where only one or two ow
elds are needed.
Plate_D.stl
•This le contains the 3D-printable model of a square plate with a hollow, hexagonal center. The hexagon has holes on opposing
sides to enable uid introduction and ow. This plate does not contain the reference electrode component from Plate_B.
Plate_E.stl
•This le contains the 3D-printable model of a square plate with a hollow, hexagonal center. The hexagon has holes on opposing
sides to enable uid introduction and ow. This plate does not contain the reference electrode component from Plate_B. This plate
has eight holes along its perimeter for screw-based clamping.
Plate_F.stl
•This le contains the 3D-printable model of a square plate with an open serpentine ow channel. The serpentine channel has a hole
on either end to enable uid ow with a diameter of 3.0 mm. This plate has eight holes along its perimeter for screw-based
clamping.
All plates detailed above are modeled to be 75 mm x 75 mm x 6 mm, with the inlet tubes of the hexagonal plates (Plate_B, Plate_D,
and Plate_E) increasing the length to 95 mm.
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HardwareX 17 (2024) e00505
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Bill of materials summary
Designator Component Number Cost per unit
-currency
Total cost
-
currency
Source of materials Material
type
Plate_A.stl Plate A, estimated cost to
print with PETG
2 $1.64
/plate
$3.28 https://tinyurl.com/33w59j8f Polymer
Plate_B.stl Plate B, estimated cost to
print with PETG
1 $1.48
/plate
$1.48 https://tinyurl.com/33w59j8f Polymer
Plate_C.stl Plate C, estimated cost to
print with PETG
1 $1.51
/plate
$1.51 https://tinyurl.com/33w59j8f Polymer
Silicone
Tubing,
Pump
Tubing +Pump 1 $56.30
/pump
$56.30 https://tinyurl.com/2yu92c69 Polymer
Bottle 1, Bottle
2
Bottle +Cap +Tubing 2 $166.50
/bottle
$330.00 https://www.sigmaaldrich.com/US/en/product/sigma/cls11665 Polymer
Gasket (1, 2, 3,
4)
Rubber Sheeting for
Gaskets
1 $11.96
/sheet
$11.96 https://tinyurl.com/2jwby8bw Polymer
O-Ring O-Ring,
38mmx42mmx2mm
2 $0.84/ring $1.68 https://www.amazon.com/gp/product/B07GJG1CB7/
ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1
Polymer
Clamp Clamp 4 $5.50
/clamp
$21.99 https://tinyurl.com/5n89ta3b Polymer
Screw M3 x 40 mm screw with
nut
8 $0.24 /screw
and bolt
$1.87 https://tinyurl.com/5n73fyrw Metal
Washers ¼“ stainless steel at
washer
8 $0.06
/washer
$0.49 https://tinyurl.com/3uvmwx5k Metal
Copper Tape Copper Tape 1 $10.99
/roll
$10.99 https://tinyurl.com/3pbf9rww Metal
PVC Tubing PVC Tubing, 1/16
″
ID, 1/
8
″
OD
1 $17.34
/tubing
$17.34 https://www.amazon.com/gp/product/B07K7RRW93/
ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1
Polymer
Flowmeter Alicat Flowmeter 1 $720.00
/ow meter
$720.00 https://www.instrumart.com/products/48580/alicat-scientic-p-
series-pressure-gauge
Non-
specic
Mass Flow
Controller
Alicat Mass Flow
Controller
1 $1,778.9/Mass
Flow Controller
$1,778.96 https://www.shersci.com/shop/products/mass-ow-controller-0-
200sccm/NC2112095#?keyword=alicat%20mass%20ow%
20controller
Non-
specic
Rotameter Rotameter 1 $30.59
/rotameter
$30.59 https://tinyurl.com/4urnfxuk Non-
specic
The cost of each plate was estimated using the free software ideaMaker.4.3.2. To calculate estimated costs, open the desired plate le in
ideaMaker and complete the following steps:
1. Click on Printer in the upper left-hand corner.
2. Under Filament Settings, insert the desired lament (in this case PETG) and adjust the cost of lament per kg (~$0.059/kg for a 2.2
lbs coil of PETG on Amazon.com), and click Save.
a. It is also possible to adjust potential printing parameters in this window for more accurate printing time estimations.
3. Under Slice, select Start Slice, double-check your template, and click Slice to receive a cost and time estimate for printing.
Build instructions
Printing
SAFETY HAZARDS – Check your selected lament’s compatibility before running any experiments to avoid unwanted reactions and
spillage.
The parameters recommended for printing plates A–F with PETG lament are provided in Table 4 below. The estimated time
needed to print Plates A, B, and C with PETG is approximately 9 h and consumes ~ 50 g of lament.
If printing directly onto glass to create a photoreactor, the parameters listed in Table 4 may need to be adjusted to account for less
lament adhesion to the printing tray.
Flow Cell Assembly
This procedure should be performed for the specic reactor arrangement chosen for the electrochemical experiment. We provide an
assembly procedure for the reactor arrangement depicted in Fig. 2.b for illustrative purposes.
1. Print two copies of Plate_A, and one of Plate_B
2. Outline Plate_A with a marker on the rubber sheet for gaskets. Cut along the marker outline to create a gasket. Repeat this step
two more times for a total of 3 gaskets. Note: if you want to use this ow cell for gas-based experiments, print two copies of
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HardwareX 17 (2024) e00505
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Plate_C and cut out two more gaskets (Gasket 4, Gasket 5). These two gaskets will not need to be cut in the middle, instead
acting as a seal for leakage tests.
a. Before creating your gaskets, remember that the thickness of your gasket’s material should equal the thickness of your
catalyst.
3. Align one gasket with Plate_B and use a precision knife to cut the hexagonal center out of your gasket. To ensure the plate does
not shift during this process, rmly clasp the gasket to the plate using binder clips. Note: It is better to have a small boarder
inside the hexagonal center than to over-cut around the edges.
4. Measure the dimensions of the inner square of Plate_A and cut an identical square into the same location on two gaskets (Gasket
1, Gasket 3).
5. Attach your anode to Gasket 1 using Copper Tape. Using another piece of copper tape, attach this piece of tape to the inner
square of copper tape on Gasket 1, near the middle of the square’s edge is preferable, and create a long copper tape tail outside
of the gasket. Fold the copper tape tail onto itself so the adhesive portions stick together. This serves as a point of contact for
aligator clips in electrochemical reactions.
6. Repeat step 5 using Gasket 3.
7. Attach a porous membrane over the hexagonal hole in Gasket 2 with copper tape.
8. Attach an O-Ring to the hollow square outline on both copies of Plate_A (two o-rings total).
9. Layer the printed plates and gaskets from bottom to top in the following order to create the ow cell. The nal results should be
similar to those depicted in Fig. 2b in Hardware Description.
a. Plate_A
b. Gasket 1
c. Gasket 2
d. Plate_B
e. Gasket 3
f. Plate_A
10. Use the four Clamps (avoiding the tubing ttings on the outside of the top and bottom of the ow cell) to seal the system; aim to
apply equal, rm pressure without damaging the plates. It is best to orient the clamps near the middle of the plate as shown in
Fig. 3 below for a gas tight seal along the o-rings, but placing the clamps closer to the perimeter is viable for strictly liquid
components (Fig. 4, Fig. 7) and may make tube and alligator clip attachment easier. Note: If using screw-based compression,
insert and tighten the screws now and do not use any clamps.
Operation instructions
Before conducting any experiments, perform the necessary leak tests provided below.
Fig. 3. Orientation of clamps for assembling the recommended ow cell for gas phase reactions.
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Procedure for Checking for Liquid Leaks
SAFETY HAZARDS – This procedure uses water near electrical instruments. Be cautious of spills, keep your benchtop orderly, and
follow general laboratory safety procedures. Solutions of high concentration and pH have the potential to erode and weaken lament –
we again encourage users to select the proper lament for their experiment and instill safety measures in case of broken plates.
1. Fill Bottle 1 and Bottle 2 with ~ 250 ml of water each (Fig. 4).
2. Create a loop on the ow cell by connecting the two tube ttings on one Plate_A with a small Silicone Tube.
3. Assemble the ow cell as described in steps 9 and 10 of Flow Cell Assembly. Put the Plate_A with a small tube on the bottom of
the ow cell.
4. Attach one Silicone Tube to either side of Plate_B and connect that same tube directly to the Pump. Attach a different Silicone
Tube to the remaining pump xture and connect that new tube’s remaining end to Bottle 1. Ensure the connected tube inside
Bottle 1 is submerged in water. This serves as the source of water for Plate_B.
5. Attach a different Silicone Tube to the remaining side of Plate_B, then connect the same tube to the remaining Bottle 1 tube that
is not submerged in water. This acts as an outlet for the water pumped into Plate_B.
6. Turn on the Pump and set it to the lowest possible ow rate (stop when the Pump “clicks” on). When water from Bottle 1 has
passed through Plate_B it will reenter Bottle 1 and drip into the supply of water at the bottom of the bottle.
7. Allow the Pump to run for ~ 5 min. If any water leaks from the system during this time, note where the leakage occurs, turn off
the Pump, and consult “Troubleshooting Leaks” below. Regardless, after the 5 min is over, turn off the pump.
a. Troubleshooting Leaks:
i. The most common x for leakage is to reassemble the ow cell and ensure the gaskets are properly aligned to form a tight
seal on the plates.
ii. Check if your plates have any signs of damage or larger gaps between layers at the locations of leakage. If this is the case,
reprint the necessary plate(s).
iii. Tighten the clamps on the plate or relocate them as needed.
iv. Double check you have an O-Ring attached to each Plate_A.
b. Repeat steps 2–7 if there is a leak. If no leakage occurs, proceed to step 8.
8. Remove the short tube on the top Plate_A. Connect that top plate to the Pump and Bottle 2 in the same way described in steps
4–5.
9. When the Plate_B is connected to Bottle 1 and the top Plate_A is connected to Bottle 2, repeat steps 6–7. An image of this
conguration is shown in Fig. 4.
10. Repeat steps 8–9 but this time using the bottom Plate_A in place of the top one so all three plates are checked for leaks.
11. When all three plates are leak free the ow cell is ready for use in liquid applications.
Procedure for Checking for Gaseous Leaks
SAFETY HAZARDS – Perform all gas-based experiments in a fume hood and test with a non-ammable gas (e.g., air).
Fig. 4. Setup to check for liquid leaks in the ow cell. The clamps are situated differently than shown in Fig. 3. to more clearly show inlet/
outlet streams.
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1. Calibrate the Mass Flow Controller and Flowmeter (Fig. 5) by choosing the gas selected for the procedure from the calibration
catalogue. If your device does not incorporate a calibration catalogue, use a bubble ow meter for calibration.
2. Connect the reactor plates as necessary for your experiment. For illustration purposes, this procedure uses the following reactor
setup:
a. Plate_A
b. Gasket 4
c. Plate_C
3. Attach one small (~0.5in) piece of silicone tubing to the top of each tube-tting on Plate_A (2 pieces total).
4. Connect a PVC tube to each small piece of silicone tubing on Plate_A (2 pieces total).
5. Connect one end of the PVC tube to the Mass Flow Controller and connect the other PVC tube to the Flowmeter..
6. Connect a known gas to the Rotameter and reduce output to 0.1GPM. Using a PVC tube, connect the outlet of the Rotameter to the
inlet of the Mass Flow Control. This setup is shown in Fig. 5.
7. Adjust the setpoint of the Mass Flow Controller to 25sccm.
8. Check the reading of the Flowmeter. If it is equivalent to the setpoint of the Mass Flow Controller (25sccm), Plate_A is leak free and
ready for use in gaseous applications. If the reading rate is not equivalent, refer to “Troubleshooting Leaks” below:
Troubleshooting leaks:
Fig. 5. Setup to check for gaseous leaks in the ow cell. The clamps are situated differently than shown in Fig. 3. to more clearly show inlet/
outlet streams.
Fig. 6. Bubbles emerging from a submerged ow cell due to gas leakage.
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a. To check the potential location of your gas leak, fully submerge the ow cell in water and continue to pump air into the system.
Bubbles will indicate a source of lost gas (see Fig. 6).
b. Check each connection in your system for gas leaks using Snoop or an equivalent. If bubbles appear on any connection point after
the application of Snoop, there is a gas leak at that location.
c. Ensure your gaskets are properly aligned, and the clamps fully tightened. Consider changing the orientation of your clamps.
d. Check your plates for any signs of damage or space between each layer of lament – gas could be escaping through the plate itself.
9. Disassemble your ow cell.
10. Repeat steps 2–9 with a different Plate_A.
11. Layer the printed plates and gaskets from bottom to top in the following order to create the ow cell:
a. Plate_A
b. Gasket 1
c. Plate_B
d. Gasket 4
e. Plate_C
12. Form a closed loop by attaching a Silicone Tube to each end of Plate_B.
13. Repeat steps 3–8. If your Flowmeter and Mass Flow Controller have the same readings, then both of your Plate_As and your
Plate_B are gas tight and ready to construct the ow cell depicted in Flow Cell Assembly.
14. Check for gas leaks by closing off two plates with Silicone Tubes and running gas through the Mass Flow Controller, ow cell,
Flowmeter set up. If the Mass Flow Controller and Flowmeter are equivalent, the ow cell is gas tight and ready for use in
gaseous experiments.
Procedure for Electrochemical Experiments
SAFETY HAZARDS – Perform all gas-based experiments in a fume hood and test with a non-ammable gas (e.g., air). Apply sec-
ondary containers to hold potential liquid leakage.
For all electrochemical experiments, the procedure of connecting the reactor elements and providing the liquid ow follows the
steps described under the leak test sections, except for the fact that the electrical current is supplied through a DC power source or a
potentiostat. Therefore, the cathode and the anode need to be connected by copper tape to the electrodes as depicted in Fig. 7.
Subsequently, any electrochemical measurement can be performed.
Fig. 7. Connection of the reactor to the potentiostat. The clamps are situated differently than shown in Fig. 3. to more clearly show alligator clip
connections.
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Validation and characterization
Provided that the correct lament and gaskets are used, all applications listed in Table 2 can be explored.
Electroless Deposition of Copper using 3D Printed Flow Cell
Here we demonstrate the ability to force a specic liquid ow pattern by circulating SnCl
2
, PdCl
2
, and a copper plating solution
through the reactor consisting of Plate_A and Plate_C. Without the ow reactor, it is naturally not possible to achieve the same
controlled contact between the liquid phase and adjacent material. The “Procedure for Checking for Liquid Leaks” above was used as
the basis for this experiment, exchanging water from the test procedure with SnCl
2
, PdCl
2
, and a copper plating solution [31].
Before beginning an experiment to deposit copper onto a Polyethersulfone (PES) membrane, plates A and C were printed – the goal
was to provide only one channel, enabling one ow of an electroless plating solution at a time. To demonstrate the ability to provide a
serpentine ow pattern, Plate_A was selected, while Plate_C was chosen to apply a consistent at pressure to the membrane. With the
goal to deposit material on one side of the membrane, a single ow chamber (Plate_A) was needed. Both plates were printed using
PETG.
An adhesive, square gasket of similar size to the plates was applied to Plate_C to enhance the seal. Due to the PES’s negligible
thickness, no other gasket was needed for this system and the membrane was placed in the center of the gasket-side of Plate_C. The nal
order of the ow cell from bottom to top is as follows:
1. Plate_C
2. Adhesive Gasket
3. PES Membrane
4. Plate_A
Pressure was then applied to the middle of the ow cell via four clamps in the orientation shown in Fig. 3. to ensure the patterned
section of Plate_A was rmly pressed to the membrane. The Procedure for Testing for Liquid Leaks was enacted, and the PES membrane
was observed to be wet, indicating uids were passing through the desired channels. The ow cell was disassembled, a new membrane
was attached, and then the ow cell was reassembled to begin electroless deposition of copper.
Utilizing the procedure reported by Cao, Wu, Yang, et. al, the following electroless deposition of copper experiment was conducted
[32]:
Solution SnCl
2
comprised of 50 mmol/L SnCl
2
and 30 ml/L HCl, solution PdCl
2
of 0.75 g/L PdCl
2
and 3 ml/L HCl, and the copper
plating solution were prepared. The SnCl
2
solution was pumped through the system at approximately 15 ml/s for 10 min. DI water was
then pumped through for 1 min as a rinse at the same ow rate. This simple procedure was then repeated with the PdCl
2
solution, then
the copper plating solution to deposit a serpentine pattern onto a PES membrane seen in Fig. 8. For copper(II) electro-less deposition,
the relevant half-cell reaction is [33]:
Cu2++2e−→Cu0E= +0.34V
Fig. 8. Electroless deposition of copper plating solution using the serpentine pattern on the 3D printed ow cell is shown on the left. On the right is
electroless deposition of copper plating solution onto a PES membrane using typical submersion techniques.
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For comparison, a similar procedure was enacted using a submersion technique, where a new PES membrane was submerged in each of
the above solutions for equivalent amounts of time. It is clear that using the ow cell for electroless deposition of copper onto the PES
membrane results in a controlled surface area being coated.
Electrochemical Characterization
To demonstrate the applicability of the 3D printed reactor for electrochemical applications, a combined CO
2
capture and hydrogen
evolution reaction was performed using a) a 3D printed ow cell and b) the titanium/stainless steel ow cell listed as a commercial
analog.
Three inlet and outlet ows are needed for this experiment: two for a KOH electrolyte and one for pure gaseous CO
2
. The
commercially available electrolyzer consists of a catholyte plate (containing an inlet/outlet for one ow of KOH and one of CO
2
), an
anolyte plate (containing an inlet/outlet for KOH), and a ow plate provided by the same company for KOH ow from the catholyte
plate.
The following order of the commercial ow cell from top to bottom is as follows:
1. Cathode plate (inlets for both gas and liquid ow)
2. Rubber gasket +cathode held in place with copper tape; a “tag” was made from the copper tape and attached to the copper tape
inside the ow cell to stick outside the ow cell for alligator clip attachment; the copper tape holding the cathode in place was face
down.
3. Plastic middle ow plate for KOH ow from the catholyte plate
4. Membrane
5. Rubber gasket with a square cut out of its center
6. Rubber gasket +anode held in place with copper tape; a “tag” was made from the copper tape and attached to the copper tape
inside the ow cell to stick outside the ow cell for alligator clip attachment; the copper tape holding the anode in place was face
down.
7. Anode plate (inlet for only liquid ow)
To mimic the commercial analog, two copies of plate F and one copy of plate E were printed; plates F and E were chosen over plates
A and B to reduce friction on the membrane from shifting plates, as discussed previously. The following order of the 3D printed ow
cell from top to bottom is as follows:
1. Plate_F
2. Rubber gasket +cathode held in place with copper tape; a “tag” was made from the copper tape and attached to the copper tape
inside the ow cell to stick outside the ow cell for alligator clip attachment; the copper tape holding the cathode in place was face
down.
3. Plate_E
4. Membrane
5. Rubber gasket with a square cut out of its center
Fig. 9. Two diagrams of the 3D printed electrolyzer layout for electrochemical characterization. The numbered components are as follows: 1.
Plate_F 2. Rubber gasket +cathode 3. Plate_E 4. Membrane 5. Rubber gasket with a center square removed 6. Rubber gasket +anode 7. Plate_E.
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6. Rubber gasket +anode held in place with copper tape; a “tag” was made from the copper tape and attached to the copper tape
inside the ow cell to stick outside the ow cell for alligator clip attachment; the copper tape holding the anode in place was face
down.
7. Plate_F
A diagram of the 3D-printed electrolyzer’s layout is depicted in Fig. 9 below.
The following procedure was conducted using both electrolyzers:
Preparation of the membrane begins a minimum of 12 h in advance, with the submersion of the membrane in 1 M KOH solution.
The membrane FAA-3–50 from Fuel Cell was used and a 1 M KOH solution was prepared, using solid potassium hydroxide from Fisher
Chemical and DI H
2
O.
The electrolyzer was assembled as described above, ensuring a tight seal on the system with screw clamps to reduce friction on the
membrane. MGL370 carbon paper from Fuel Cell was cut into a 1 in x 1 inch square as the cathode and nickel foam with a thickness of
1 mm from Fuel Cell was similarly cut for the anode.
A check for liquid and gaseous leaks was then conducted following the procedures in Operation Instructions. It is important to
note that 0.1 M KOH was used for the liquid leak test to ensure the membrane was kept at an optimum pH and that this KOH was not
removed from the system during the gaseous leak test to avoid drying out the membrane.
After ensuring the ow cell was leak-free, 0.1 M of KOH solution was pumped through two ports (into the middle and bottom
plates) in the electrolyzer using a syringe pump with silicone tubes at 16.875 uL/s (approximately 1 ml/min). No gas was introduced to
the system until the outlet tubing of each KOH port began to drip KOH solution into a waste beaker.
Pure, gaseous CO
2
was then run through an Allicat Mass Flow Controller to set the inlet ow rate of the gas to 5 SCCM CO
2
. Alligator
clips were attached to each ow cell’s aforementioned copper tape tags, and an Autolab Potentiostat and NOVA 2.1.6 software were
used for the electrochemical analysis in galvanostat mode. After a 5 second delay, a current of −0.1 A was applied for 60 s. The results
of each experiment are shown below in Fig. 10.
Full cell voltage for the 3D printed cell and the commercial analog differ only by ~ 0.81 V. The full cell voltage for the 3D printed
cell is more stable than the commercially available analog. Additionally, the gaseous outlet ow for both electrolyzers increased past
the inlet ow of 5 SCCM CO
2
, with the 3D printed electrolyzer’s ow rate reading ~ 6.09 SCCM CO
2
and its commercial analog reading
~ 6.30 SCCM CO
2
. The increased outlet gaseous ow rate indicates that hydrogen was produced.
Capabilities and Limitations:
•Filament and quality of the 3D print largely determine the hardware’s capabilities, particularly regarding gas-based experiments
that must be air-tight. Alternatively, CNC machining could be used if sufcient print quality cannot be obtained. Resin-based
printing could benet users interested in intricate detailing or smaller components, and exible printing laments could be
used to print specialized gaskets.
•The sealing of the reactor is critical to safe and accurate electrochemical measurements. Be sure to perform leak tests before starting
any experiment.
Fig. 10. Full cell voltage for the 3D printed electrolyzer (blue, bottom line) and its commercial analog (orange, top line). (For interpretation of the
references to colour in this gure legend, the reader is referred to the web version of this article.)
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•The choice of equipment supporting the reactor, such as gas ow meters, pumps, etc., are critical, and necessary owrates and the
accuracy of the measurement needs to be reviewed based on the goal of the electrochemical experiment.
•Ohmic loss, ow rate maximums, and electrochemical performance will vary signicantly between each experimental setup. We
strongly encourage users to share their printing procedures and customized plate designs to ensure the reproducibility of
experiments.
CRediT authorship contribution statement
Erin Heeschen: Writing – original draft, Validation, Formal analysis, Investigation, Data curation. Elena DeLucia: Methodology.
Yilmaz Arin Manav: Methodology, Design, Fabrication. Daisy Roberts: Visualization. Benyamin Davaji: Supervision, Resources.
Magda Barecka: Supervision, Resources, Writing – review & editing, Project administration.
Declaration of competing interest
The authors declare that they have no known competing nancial interests or personal relationships that could have appeared to
inuence the work reported in this paper.
Acknowledgments
BD and MHB acknowledge the start-up funding provided by Northeastern University (Boston).
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