From the journal Digital Discovery Peer review history

19-Dec-2023

Dear Dr Gregoire:

Manuscript ID: DD-ART-12-2023-000232
TITLE: Accelerated screening of carbon dioxide capture by liquid sorbents

Thank you for your submission to Digital Discovery, published by the Royal Society of Chemistry. I sent your manuscript to reviewers and I have now received their reports which are copied below.

I have carefully evaluated your manuscript and the reviewers’ reports, and the reports indicate that major revisions are necessary.

Please submit a revised manuscript which addresses all of the reviewers’ comments. Further peer review of your revised manuscript may be needed. When you submit your revised manuscript please include a point by point response to the reviewers’ comments and highlight the changes you have made. Full details of the files you need to submit are listed at the end of this email.

Digital Discovery strongly encourages authors of research articles to include an ‘Author contributions’ section in their manuscript, for publication in the final article. This should appear immediately above the ‘Conflict of interest’ and ‘Acknowledgement’ sections. I strongly recommend you use CRediT (the Contributor Roles Taxonomy, https://credit.niso.org/) for standardised contribution descriptions. All authors should have agreed to their individual contributions ahead of submission and these should accurately reflect contributions to the work. Please refer to our general author guidelines https://www.rsc.org/journals-books-databases/author-and-reviewer-hub/authors-information/responsibilities/ for more information.

Please submit your revised manuscript as soon as possible using this link:

*** PLEASE NOTE: This is a two-step process. After clicking on the link, you will be directed to a webpage to confirm. ***

https://mc.manuscriptcentral.com/dd?link_removed

(This link goes straight to your account, without the need to log on to the system. For your account security you should not share this link with others.)

Alternatively, you can login to your account (https://mc.manuscriptcentral.com/dd) where you will need your case-sensitive USER ID and password.

You should submit your revised manuscript as soon as possible; please note you will receive a series of automatic reminders. If your revisions will take a significant length of time, please contact me. If I do not hear from you, I may withdraw your manuscript from consideration and you will have to resubmit. Any resubmission will receive a new submission date.

The Royal Society of Chemistry requires all submitting authors to provide their ORCID iD when they submit a revised manuscript. This is quick and easy to do as part of the revised manuscript submission process.   We will publish this information with the article, and you may choose to have your ORCID record updated automatically with details of the publication.

Please also encourage your co-authors to sign up for their own ORCID account and associate it with their account on our manuscript submission system. For further information see: https://www.rsc.org/journals-books-databases/journal-authors-reviewers/processes-policies/#attribution-id

I look forward to receiving your revised manuscript.

Yours sincerely,
Dr Joshua Schrier
Associate Editor, Digital Discovery

************

Reviewer 1

This paper describes the hardware design for a carbon dioxide sorption
measurement apparatus. It provides some justification for the device,
comparison to current approaches to similar data, example use cases, and
a build guide. I have organized my review according to the four criteria
recommended by the editors and included a general comments section. I
believe this manuscript is suitable for publication with modification.

Relevance and Advancement

- The authors adequately present the need for improved methods to
identify and characterize carbon dioxide sorbents for carbon
sequestration and sustainable energy technologies. Further, the
authors identify how the proposed hardware can be used to automate
this type of discovery which is not available via current approaches
to sorbent analysis such as thermogravimetric analysis. They hint at
more advanced robotic automation as future expansions of the work,
but only present a more modest automation approach of varying
reagent amounts in this manuscript.

Comparative analysis

- There appear to be no comparative DIY approaches to the
characterization of CO2 sorbents. The most appropriate commercial
technique is identified as TGA, which unlike the proposed instrument
provides no automation or feedback options.

- The editors request an analysis of capabilities, cost, adaptability,
and construction time. The first of these is adequately described,
see the next bullet for my concerns regarding cost, and I would like
a brief comment on construction time.

- I’m bothered a bit by having to add up the BOM on my own to find the
cost of the instrument, but after doing so, I get a price of just
under $27,000, which doesn’t match the statement that the CCSI is
“considerably less expensive” than a \[$10,000\] TGA. I assume a
number of parts in the BOM are optional and something should be
added to clarify what constitutes the “considerably less expensive”
configuration.

Replication and Modification

- The build guide has reasonably descriptive images related to the
construction and the pseudocode provides some clarity on the steps
necessary to perform an analysis. I am not convinced that the
instrument could be built by a graduate student who is not also a
seasoned hardware specialist without significant consultation with
the authors. A one-page construction workflow/checklist may be
helpful in resolving this issue.

- No information is provided regarding replication. If there was
replication - even internally - mention of the lessons learned might
be instructive for future builders of the instrument.

- A patent has been applied for, which suggests that no one else can
manufacture the hardware without permission from the authors. If
this is the case, what is the value of this publication to readers?
I have been unable to find a statement about the license in the
manuscript. The two repositories do contain licenses. I do not know
if this constitutes a “clear license” as requested by the editors.

Operation and Safety

- I found no information related to unit checks or build integrity
tests. Based on the information provided, I would have no guidance
to determine if the build were successful or how to troubleshoot the
design.

- I found no information related to safety and one should consider if
the use of high pressure gas cylinders, solenoid valves, and
multiple voltage levels present human and/or instrument safety
concerns.

- As requested by the editors, no “hello world” example is presented,
although one could imagine that the authors have this material in
hand with the tetramethylammonium pentafluorphenoxide experiment. As
this is a new journal, I do not know if the results presented
constitute a satisfactory “hello world” example.

General

- The structure of the results and discussion section should be
reconsidered. I find it particularly unusual, and very disorienting,
to delve into data collection modes (constant moles vs constant
pressure) and then discuss the high level structure of the
instrument.

- The statement “referred to here as 9.9% for brevity” is not needed.
The authors should simply use 9.9% since it is the correct number of
significant digits to use for a number with uncertainty in the
tenths place.

- Something does not make sense with the discussion of the low PCO2
and low \[KOH\] results. The pH after 5 hours is above 10,
indicating that carbonate is predominant over bicarbonate. The next
sentence then reads “The equilibrium state is expected to involve
carbonate as the majority species, and the inability to reach this
state…” There is either a typo or misinterpretation of data here.

- It might be due to the PDF conversion; however, the text in Figure 1
is very poorly rendered in my copy and should be reviewed for
clarity. Additionally, the caption for this figure contains a fair
amount of discussion that would be better suited for the main body
of the manuscript.

- There is a problem with the BOM. The PEEK tees and chemically
compatible fluidic connectors has a price listed in the BOM ($2000)
which is inconsistent with the number of units and the link (1 each
at $46). There are also problems with other links, such as the one
for the peristaltic pump. I stopped checking the links after finding
these two errors.

Reviewer 2

This manuscript fits within the scope of the journal and I recommend it for publishing. See attached comments

We appreciate the detailed feedback and have prepared a revised manuscript with associated point-by-point response.

This text has been copied from the PDF response to reviewers and does not include any figures, images or special characters:

Referee: 1

Comments to the Author
This paper describes the hardware design for a carbon dioxide sorption measurement apparatus. It provides some justification for the device, comparison to current approaches to similar data, example use cases, and a build guide. I have organized my review according to the four criteria recommended by the editors and included a general comments section. I believe this manuscript is suitable for publication with modification.

Relevance and Advancement

- The authors adequately present the need for improved methods to identify and characterize carbon dioxide sorbents for carbon sequestration and sustainable energy technologies. Further, the authors identify how the proposed hardware can be used to automate this type of discovery which is not available via current approaches to sorbent analysis such as thermogravimetric analysis. They hint at more advanced robotic automation as future expansions of the work, but only present a more modest automation approach of varying reagent amounts in this manuscript.
Response: Thanks! (no action items)

Comparative analysis

- There appear to be no comparative DIY approaches to the characterization of CO2 sorbents. The most appropriate commercial technique is identified as TGA, which unlike the proposed instrument provides no automation or feedback options.
- The editors request an analysis of capabilities, cost, adaptability, and construction time. The first of these is adequately described, see the next bullet for my concerns regarding cost, and I would like a brief comment on construction time.
- I’m bothered a bit by having to add up the BOM on my own to find the cost of the instrument, but after doing so, I get a price of just under $27,000, which doesn’t match the statement that the CCSI is “considerably less expensive” than a \[$10,000\] TGA. I assume a number of parts in the BOM are optional and something should be added to clarify what constitutes the “considerably less expensive” configuration.
Response: Thank you for noting this error in our bill of materials. We have expanded discussion in the main text regarding variation in price based on component-level choices. The previous bill of materials included multiple versions of several components, so the sum of the line items did not reflect assembly of a single CCSI. In the new version, we have only included the option to use a peristaltic or diaphragm pump as the recirculation pump. Depending on this choice, the total is 12,941 or 15,759 USD, and these totals are now stated in the SI. The associated main text has been updated as follows:

Compared to a TGA instrument, which can cost upwards of 10,000 U.S.D., the CCSI components are comparable and possibly lower depending on factors such as availability of an existing computer, the chemical compatibility of components (the present build can handle aqueous and nonaqueous solvents, while several valve and tubing components may be replaced with less expensive alternatives for aqueous-only operation), and the sorbent media preparation manifold. The biggest variable in the system cost is the choice of recirculation pump, which can be ca. 1,000 U.S.D. for an inexpensive peristaltic pump using tubing with limited chemical compatibility, to ca. 4,000 U.S.D. for a diaphragm pump with PEEK tubing, which increases chemical compatibility and enables pumping of viscous sorbent media.

Replication and Modification

- The build guide has reasonably descriptive images related to the construction and the pseudocode provides some clarity on the steps necessary to perform an analysis. I am not convinced that the instrument could be built by a graduate student who is not also a seasoned hardware specialist without significant consultation with the authors. A one-page construction workflow/checklist may be helpful in resolving this issue.
Response: We appreciate this concern and agree that some experience is necessary for CCSI assembly. Since the “CCSI assembly instructions” section in the SI contains 25-step assembly instructions, we have added a 1.5-page section entitled “Additional guidance for assembly and diagnostics” to increase accessibility of the assembly instructions.

- No information is provided regarding replication. If there was replication - even internally - mention of the lessons learned might be instructive for future builders of the instrument.

Response: The “lessons learned” are covered in the new “Additional guidance for assembly and diagnostics” section, and we have added the following to the main text:
We have built multiple versions of the CCSI with different choices of pumps to meet different specifications of the sorbent media. To our knowledge, no similar instrument has been replicated in an independent laboratory.

- A patent has been applied for, which suggests that no one else can manufacture the hardware without permission from the authors. If this is the case, what is the value of this publication to readers? I have been unable to find a statement about the license in the manuscript. The two repositories do contain licenses. I do not know if this constitutes a “clear license” as requested by the editors.
Response: We believe the manuscript has value to the community regardless of the license. For example, our analogous manuscript for an automated electrochemical system has garnered 142 citations while the instrument was patented and licensed to a materials research company. That being said, we did not provide sufficiently clear terms of use in our original submission. I have been in communication with the editorial office to confirm the expectations regarding the license. We have now included a license file that meets the “clear license” requirement and enables non-commercial use of the CCSI design. This license file is also included in the data repository and noted in the Availability statement.

Operation and Safety

- I found no information related to unit checks or build integrity tests. Based on the information provided, I would have no guidance to determine if the build were successful or how to troubleshoot the design.
- I found no information related to safety and one should consider if the use of high pressure gas cylinders, solenoid valves, and multiple voltage levels present human and/or instrument safety concerns.
- As requested by the editors, no “hello world” example is presented, although one could imagine that the authors have this material in hand with the tetramethylammonium pentafluorphenoxide experiment. As
this is a new journal, I do not know if the results presented constitute a satisfactory “hello world” example.
Response: These are excellent suggestions for expansion of the manuscript. We have added the following subsection to the main text:
Safety and build validation
Provided adherence to standard safety practices regarding compressed gasses, the chemical components of the sorbent media, and the control electronics, we do not envision any safety hazards that emerge from the CCSI design. While the CCSI in intended to operate at total pressures near 5 psi above ambient, the use of pressure-relieving regulators can help mitigate exposure of the user and equipment to unsafe pressures. Given the intended use as a screening tool for novel chemical sorbents, the primary safety evaluation for implementation of the CCSI in research workflows involves any chemical hazards of the sorbent media. For example, the KOHbased sorbent media demonstrated herein requires adherence to handling of caustic media.
While component-level operation instructions are provided in the Supporting Information, we recommend the following evaluations to validate the CCSI assembly. The first validation is against atmospheric leaks, which can be performed by purging the system with N2 gas until the CO2 sensor reaches its noise floor, following by sealing the headspace and recirculating the gas using the recirculation pump. The CO2 sensor time series should then characterize the leak rate of CO2 in the system, which should be below 10 ppm s-1, although the acceptable rate depends on the intended system use with respect to sorption strength, CO2, and measurement duration. The analogous experiment can be performed with the standard gas intended for sorbent screening, i.e. 9.9% CO2 in the present work, where any decline in the measured CO2 during sealed headspace recirculation indicates a leak to atmosphere. In both cases, we note that the diffusion of gasses through plastic tubing may provide an apparent nonzero leak rate. With the gas handling validated, we recommend that the first set of sorption experiments involve a known strong sorbent. For example, reproduction of Fig. 3 by performing the experiments shown in Fig. 2 should provide sufficient quantitative characterization of the CCSI to enable subsequent characterization of novel sorbents.

General

- The structure of the results and discussion section should be reconsidered. I find it particularly unusual, and very disorienting, to delve into data collection modes (constant moles vs constant pressure) and then discuss the high level structure of the instrument.
Response: We have been unable to find an alternative organization that meets the editorial guidance of providing a relatively short main text with an extensive SI.

- The statement “referred to here as 9.9% for brevity” is not needed. The authors should simply use 9.9% since it is the correct number of significant digits to use for a number with uncertainty in the tenths place.
Response: We have implemented this revision

- Something does not make sense with the discussion of the low PCO2 and low \[KOH\] results. The pH after 5 hours is above 10, indicating that carbonate is predominant over bicarbonate. The next sentence then reads “The equilibrium state is expected to involve carbonate as the majority species, and the inability to reach this state…” There is either a typo or misinterpretation of data here.
Response: We apologize for the misleading text. This has been simplified to “this measurement was extended to 5 hours, after which the measured pH of 12.15 corroborates the formation of carbonate as the primary species of dissolved inorganic carbon.”

- It might be due to the PDF conversion; however, the text in Figure 1 is very poorly rendered in my copy and should be reviewed for clarity. Additionally, the caption for this figure contains a fair amount of discussion that would be better suited for the main body of the manuscript.
Response: We trust that the publication version will include higher resolution via our submission of vector graphics. We wrote the caption to make the figure understandable somewhat independently of the main text. We understand that this makes for an unusually long caption, and we will be happy to work with the publisher in the proofing stage to modify as necessary per journal requirements.

- There is a problem with the BOM. The PEEK tees and chemically compatible fluidic connectors has a price listed in the BOM ($2000) which is inconsistent with the number of units and the link (1 each at $46). There are also problems with other links, such as the one for the peristaltic pump. I stopped checking the links after finding these two errors.

Response: These and other errors have been fixed in the BOM.

Referee: 2

Comments to the Author
This manuscript fits within the scope of the journal and I recommend it for publishing. See attached comments

Summary
The authors developed the CCSI, an automated high-throughput experimental setup for screening molecular sorbents in CO2 capture technologies. This system auto injects different concentrations of sorbents and chemistries into an analysis chamber and is mixed with a controlled headspace gas of differing amounts of CO2 in N2 which is bubbled through and recirculated for faster equilibration. They explore the kinetics and thermodynamics of the sorbent CO2 capture utilizing an IR sensor and mass flow controller feedback system to monitor the amount of chemisorbed CO2. The system design is modular and allows future expansion to more sophisticated experimentation and chemical analyses. The system was spec’d out for primarily aqueous systems but that the tubing components and recirculation pump can be swapped for more chemically resistant ones at higher cost.
The CCSI system is benchmarked to the well-established base mediated conversion of CO2 to bicarbonate/carbonate depending on the pCO2 and the base concentration. This is validated by a post equilibration analysis of the pH of the system and expected base to carbonate or bicarbonate ratio. This chemistry provides a general approach to qualifying the system if built by a separate lab. The authors note that the kinetics of the carbonate transformation are slow but that the system can capture these kinetics with reasonable accuracy and times. The authors demonstrate the ability to rapidly characterize novel sorbents for their efficacy in carbon capture, in this paper, the tetramethylammonium pentafluorophenoxide sorbent was characterized with a 1.35 binding constant within one hour of analysis. This molecular sorbent is not effective enough for dilute capture technologies.

Comments
I think that the paper fits within the scope of the journal and satisfies most of the four main criteria.
Relevance: The CCSI is useful to the broader scientific community and can be generalized to other chemical studies, not limited to just sorbent CO2 uptake analysis, as whatever reacted solution can be pumped into other analytical modules relatively easily. The hardware list and control software further enable automation. There was no demonstration of autonomy here.
Response: Thank you for this summary of how the manuscript meets the criteria.
Comparative Analysis: The authors note that there is no other commercial alternatives but it’s not clear that there are other DIY systems available. Given that the specificity of this study and intent of the hardware, it is likely that this is novel to the broader community.
Response: Thank you for this summary of how the manuscript meets the criteria.
Replicability and Modification: The SI contains the appropriate documentation and checks for the hardware setup but it is missing validation of the control software. The helao-core git repo provided doesn’t have a demonstration of the code to interface with the automated system.
Response: Since the present work focuses on the hardware design, we included in the SI the automation sequence so that the software may be developed independently. We do hope that users can additionally leverage our helao-async implementation of the instrument. To guide the user down this path, we have added the SI section “CCSI automation in helao-async”, a 1-page description of the pertinent files in the helao-async repository. We also erroneously listed only the helao-core repository in the original submission. The helao-async repository has additionally been noted in the “Data and Code Availability” section, and static snapshots of both repositories are also provided.
Operation and Safety: The SI contains well documented hardware instructions and a liquid and gas handling procedure valve state check. The potential dangers of each component or dealing with potentially pressurized gases are not listed but the risk may subject to a separate other users implementation.
Response: This has been addressed in the new main text subsection “Safety and build validation”, whose content is provided above in the response to Reviewer 1.

23-Feb-2024

Dear Dr Gregoire:

Manuscript ID: DD-ART-12-2023-000232.R1
TITLE: Accelerated screening of carbon dioxide capture by liquid sorbents

Thank you for submitting your revised manuscript to Digital Discovery. I am pleased to accept your manuscript for publication in its current form. I have copied any final comments from the reviewer(s) below.

You will shortly receive a separate email from us requesting you to submit a licence to publish for your article, so that we can proceed with the preparation and publication of your manuscript.

You can highlight your article and the work of your group on the back cover of Digital Discovery. If you are interested in this opportunity please contact the editorial office for more information.

Promote your research, accelerate its impact – find out more about our article promotion services here: https://rsc.li/promoteyourresearch.

If you would like us to promote your article on our LinkedIn account [https://rsc.li/Digital_showcase] please fill out this form: https://form.jotform.com/213544038469056.

We are offering all corresponding authors on publications in gold open access RSC journals who are not already members of the Royal Society of Chemistry one year’s Affiliate membership. If you would like to find out more please email membership@rsc.org, including the promo code OA100 in your message. Learn all about our member benefits at https://www.rsc.org/membership-and-community/join/#benefit

By publishing your article in Digital Discovery, you are supporting the Royal Society of Chemistry to help the chemical science community make the world a better place.

With best wishes,

Dr Joshua Schrier
Associate Editor, Digital Discovery

Reviewer 1

The authors have satisfactorily addressed the concerns raised in my original review and I do not have further comments or suggestions.

Reviewer 2

The revisions made by the authors satisfy the comments and concerns by both reviewers. Chiefly, verbalizing the safety concerns in the main text and adding additional information for "turn key" or "hello world" instructions with both hardware and software.