From the journal Digital Discovery Peer review history

25-Apr-2024

Dear Dr Bernhard:

Manuscript ID: DD-ART-03-2024-000070
TITLE: High Throughput Methodology for Investigating Green Hydrogen Generating Processes using Colorimetric Detection Films and Machine Vision

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. (Apologies for the long duration of the initial review process.)

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

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I look forward to receiving your revised manuscript.

Yours sincerely,
Dr Joshua Schrier
Associate Editor, Digital Discovery

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

Reviewer 1

In this manuscript (DD-ART-03-2024-000070), sensing and analyzing hydrogen evolution as a color change using sensing films of MO3, WO3. Hydrogen detection using color change has been reported, but the authors increase accuracy with color change patterns. The method is interesting, but it needs to be properly revised to be published in Digital Discovery. Detailed comments are listed below

Point #1 (Figure 1, Figure 11)
It was not clear why the two catalytic cycles are shown as two separate Figures 1 and 11.

Point #2 (Figure 2)
The authors explained that the oxide readily detects hydrogen due to the catalytic effect of Pt. However, the equation in the blue box indicates that Pt also affects the binding of dissociated hydrogen, requiring further explanation.

Point #3 (Sensing film)
Why do authors need to use two sensing materials for color pattern recognition?

Point #4 (4.2 section)
There was insufficient detail in the description of the concentration calculation and injection method in the calibration step with hydrogen gas.

Point #5 (5.2 section)
The authors validated the performance of 96 photocatalysts with a high-throughput method through color images. However, it was not clear that the method of validation of the catalysts was as efficient and easy as the authors emphasize. This requires experimental data, such as UV-vis for two different catalysts, one purple and one red.

Point #6 (5.3 section)
The authors said that the colorimetric films identify the synergy effect through rapid detection of the formed hydrogen. In Figure 10, it appears that a time of 600 min was required for actual identification. Further explanation or reference is needed to confirm that this is an accurate and fast method compared to conventional methods.

Point #7 (Overall)
The authors need to organize and unify the overall figure of the manuscript.

Reviewer 2

In the presented work, an innovative approach for studying solar-driven hydrogen evolution reactions (HERs) in parallel that uses colorimetric hydrogen detection films in tandem with an image analysis software capable of providing metrics such as hydrogen amount, hydrogen evolution rates, incubation times, and plateau times, etc.
This approach, in combination with an original open-source platform, enables a cost-effective, high-throughput methodology for evaluation of HERs. A novel sample configuration method is introduced where nine samples in hydrogen sensitive septa-capped vials are illuminated and the gas evolution is monitored using a RaspberryPi for image capture and storage. Two calibration procedures for the proposed method were developed, and showed excellent performance for correlation of normalized intensity values of film photographs to mole fractions of hydrogen ranging from 0 to 50%, with the calibration procedures resulting in R^2>0.99.
Four HERs experiments demonstrating the performance of the proposed methodology were carried out:
Experiment 1: Organic Dyes and Earth Abundant WRCs: Eosin Y was used as the photocatalyst (PC), triethanolamine (TEOA) as the donor, and chloro(pyridine)cobaloxime(III) as the water reduction catalyst (WRC);
Experiment 2: Structure-Activity Relationships with 96 Unique Photocatalysts: Structure-Activity Relationships with 96 Unique Photocatalysts were investigated;
Experiment 3: Mono and Bimetallic WRCs: Mono and Bimetallic WRCs were examined;
Experiment 4: Green Hydrogen Evolution: Green Hydrogen Evolution using eight different hydroxyl-functionalized, bio-derived species as donors (oxalic acid, isopropanol, ethanol, benzyl alcohol, glycerol, glucose, fructose, and sucrose) was studied.
This approach in designing, implementing, and testing a high-throughput, open-source platform for investigating hydrogen-generating reactions with colorimetric detection films shows promise for the broad scientific community. The experiments validate the functionality and suitability of the proposed hardware and software for studying various types of HERs. However, the manuscript could be enhanced by a more detailed discussion on the novelty and significance of the proposed method and its integration into the existing framework.

The reviewer recommends addressing the following code-related issues before publication:
1) The primary concern with the proposed work is the quality and organization of the Python source code in the supporting materials. The code is not organized into Python packages or libraries with a documented interface, making it challenging to use. Suggestions for improvement include:
a) Documenting the "Reactor_code_framework" to clarify the relationships between the classes within the framework.
b) Cleaning up the directory "reactor_code_framework/examples/" by removing outdated files and documenting the main elements of the framework to clarify their purpose and usage.
c) Editing the automatically generated README file to include relevant information about the structure of the source code directories, the purpose of separate modules, their relationships, and the main purposes of each module.
d) Providing a brief description of the purpose for each Python file, especially for reactor code examples.

2) Furthermore, it authors may consider including a flow chart to briefly describe the algorithm implemented in the developed software in the manuscript, similar to Figure 4, which illustrates the main hardware components of the hydrogen evolution photoreactor, is recommended.
3) A figure in the “3.2 Image Analysis Software” section that illustrates the algorithm for image analysis would be beneficial.
4) The wiring diagram for Raspberry Pi hardware (Figure S1. R) should follow best practices using industry standards.
For examples, see:
https://www.raspberrypi.com/documentation/computers/raspberry-pi.html;
https://newbiely.com/tutorials/raspberry-pi/raspberry-pi-relay
Fritzing (https://fritzing.org/), a free open-source software, may be used to prepare wiring diagrams.
5) Authors are encouraged to consider the use of LAB or HSV color models for image analysis in future studies could yield better performance in separating light intensity (brightness) from spectral characteristics (hue).

Reviewer 3

1. The manuscript need to have a collective section named " Experimental" with Methods and Materials sub-sections. Under this section, all experimental procedures and materials used are provided. The current presentation does not make the manuscript readable.
2. Under results and discussion sections, authors need to present the findings of the study and compare them with previous work of similar nature and cite the references accordingly. In its current state, these sections do not present what is called "results and discussion" section in a manuscript.
3. The sections in the manuscript need to be re-organized in order to present a good flow of concepts for readers. Some Figures for example are cited in the experimental section but they appear in results and discussion section.
4. The manuscript should benefit from Language editing before it can be accepted for publication.
5. The conclusion should only contains key findings and recommendations and not experimental procedures
6. Other comments for improvement can be found the reviewed document attached.

Point-by-point response to the comments made by the reviewers:
Referee: 1
Comments to the Author
In this manuscript (DD-ART-03-2024-000070), sensing and analyzing hydrogen
evolution as a color change using sensing films of MO3, WO3. Hydrogen detection
using color change has been reported, but the authors increase accuracy with color
change patterns. The method is interesting, but it needs to be properly revised to be
published in Digital Discovery. Detailed comments are listed below

We thank this reviewer for their valuable input. We have addressed all the concerns
in the manuscript and/or have offered additional explanations below.
Point #1 (Figure 1, Figure 11)
It was not clear why the two catalytic cycles are shown as two separate Figures 1
and 11.
The catalytic cycle from Figure 11 has been merged with the one in Figure 1. Text
explaining the cycles has also been shifted to the introduction as well.
Point #2 (Figure 2)
The authors explained that the oxide readily detects hydrogen due to the catalytic
effect of Pt. However, the equation in the blue box indicates that Pt also affects the
binding of dissociated hydrogen, requiring further explanation.
It is true that the platinum catalyst assists in the binding and dissociation of
hydrogen. The manuscript includes information that the discoloration of the films
occurs more rapidly in the WO3 based films compared to the MoO3 based films,
making the molybdenum containing films more suitable for longer reactions. The
following citation has been added to the manuscript to support these findings: J.
Phys. Chem. C 2014, 118, 1, 494–501.
Point #3 (Sensing film)
Why do authors need to use two sensing materials for color pattern recognition?

Each of the proposed sensing materials are able to detect hydrogen but have their
own pros and cons. The purpose of offering two materials was to offer a sense of
flexibility and range of sensors so that users could choose one that best fits their
needs. Their differences in detection are mentioned in the manuscript: “When
selecting a sensing material to study a hydrogen evolving system, it is important to
consider the experiment duration, predicted amount of H2 generated and other
factors as one metal oxide may be preferred over another. The tungsten bronze
sensing material has wider limits of detection and a quicker reverse reaction, while
the molybdenum bronze is more sensitive to smaller changes in H2 evolution,
surveys a smaller range of H2 hydrogen concentration, and exhibits an extremely
slow reverse reaction.”
Point #4 (4.2 section)
There was insufficient detail in the description of the concentration calculation and
injection method in the calibration step with hydrogen gas.
Mole fractions were calculated by converting the volume injected to moles of H2
using the ideal gas law and dividing by the sum of the moles of air and moles of
H2. The text has been edited to include this information. An equation of the
described calculation can be found below.
Point #5 (5.2 section)
The authors validated the performance of 96 photocatalysts with a high-throughput
method through color images. However, it was not clear that the method of
validation of the catalysts was as efficient and easy as the authors emphasize. This
requires experimental data, such as UV-vis for two different catalysts, one purple
and one red.
The high-throughput methodology has been validated by comparison with
traditional hydrogen analysis techniques (ACS Catal. 2020, 10, 7, 4244–4252; App.
Cat. B: Environ. 2020, 269,118; Energy Fuels 2021, 35, 23, 18957–18981; Inorg.
Chem. 2021, 60, 2, 774–781; Dalton Trans., 2021,50, 5632-5643). The work
described in these publications studied a wide range of photocatalytic systems in
our 96 well reactors using commercial hydrogen detection films.
Point #6 (5.3 section)
The authors said that the colorimetric films identify the synergy effect through
rapid detection of the formed hydrogen. In Figure 10, it appears that a time of 600
min was required for actual identification. Further explanation or reference is
needed to confirm that this is an accurate and fast method compared to
conventional methods.
Experiment 3 was modeled from the following publication: ACS Catal. 2020, 10,
7, 4244–4252. This paper has been cited in the manuscript. The hydrogen
detection films themselves have a response time of 30 minutes across the 96/108
wells, which is what the “rapid detection” is referring to. The traditionally used GC
or MS techniques used for this purpose consumes part of the headspace sample and
is therefore incompatible with a parallelized reactor design with microliter
headspace. Furthermore, routing the samples in an automated fashion would be
very difficult to envision. It takes at least 2 minutes per sample to complete one
well’s analysis, which will then equate to a 3h total analysis time for one data point
on a multiwell plate. The 30 min response time can therefore be considered fast. It
is also noteworthy that the hydrogen evolution kinetics are usually slow enough to
render the 30 minute response times inconsequential.
Point #7 (Overall)
The authors need to organize and unify the overall figure of the manuscript.
The graphical abstract has been modified to help better communicate the main
ideas of the manuscript.

Referee: 2
Comments to the Author
In the presented work, an innovative approach for studying solar-driven hydrogen
evolution reactions (HERs) in parallel that uses colorimetric hydrogen detection
films in tandem with an image analysis software capable of providing metrics such
as hydrogen amount, hydrogen evolution rates, incubation times, and plateau times,
etc.
This approach, in combination with an original open-source platform, enables a
cost-effective, high-throughput methodology for evaluation of HERs. A novel
sample configuration method is introduced where nine samples in hydrogen
sensitive septa-capped vials are illuminated and the gas evolution is monitored
using a RaspberryPi for image capture and storage. Two calibration procedures for
the proposed method were developed, and showed excellent performance for
correlation of normalized intensity values of film photographs to mole fractions of
hydrogen ranging from 0 to 50%, with the calibration procedures resulting in
R^2>0.99.
Four HERs experiments demonstrating the performance of the proposed
methodology were carried out:
Experiment 1: Organic Dyes and Earth Abundant WRCs: Eosin Y was used as the
photocatalyst (PC), triethanolamine (TEOA) as the donor, and
chloro(pyridine)cobaloxime(III) as the water reduction catalyst (WRC);
Experiment 2: Structure-Activity Relationships with 96 Unique Photocatalysts:
Structure-Activity Relationships with 96 Unique Photocatalysts were investigated;
Experiment 3: Mono and Bimetallic WRCs: Mono and Bimetallic WRCs were
examined;
Experiment 4: Green Hydrogen Evolution: Green Hydrogen Evolution using eight
different hydroxyl-functionalized, bio-derived species as donors (oxalic acid,
isopropanol, ethanol, benzyl alcohol, glycerol, glucose, fructose, and sucrose) was
studied.
This approach in designing, implementing, and testing a high-throughput, open source platform for investigating hydrogen-generating reactions with colorimetric
detection films shows promise for the broad scientific community. The
experiments validate the functionality and suitability of the proposed hardware and

software for studying various types of HERs. However, the manuscript could be
enhanced by a more detailed discussion on the novelty and significance of the
proposed method and its integration into the existing framework.

We thank this reviewer for their feedback. We have addressed all the concerns in
the manuscript and/or have offered additional explanations below.

The reviewer recommends addressing the following code-related issues before
publication:
1) The primary concern with the proposed work is the quality and organization of
the Python source code in the supporting materials. The code is not organized into
Python packages or libraries with a documented interface, making it challenging to
use. Suggestions for improvement include:
a) Documenting the "Reactor_code_framework" to clarify the relationships
between the classes within the framework.
● Added section 4 to the README, which documents all of the important
user-facing classes. For each user-facing class, each user-facing function is
documented with its inputs, side effects, and outputs. The relationships
between classes are captured in the descriptions of the inputs and outputs.
● Added section 5 to the README, which explains the high-level structure
of reactor code (including the high-level interactions between classes).
b) Cleaning up the directory "reactor_code_framework/examples/" by
removing outdated files and documenting the main elements of the
framework to clarify their purpose and usage.
● Removed reactor_code_framework/examples/old_reactor_code due to
containing outdated reactor code.
● Removed reactor_code_framework/examples/tests due to containing
incomplete code and tests that are not useful for users.
● Removed reactor_code_framework/examples/reactor_code_examples due
to containing unreleased code not relevant to the current publication.
● Added reactor_code_framework/examples/reactor_code_example to
include a commented example of how a user could implement the reactor
code framework. This should help to explain relationships between sub modules/classes.
● Added section 6 to README to explain the examples.
c) Editing the automatically generated README file to include relevant
information about the structure of the source code directories, the purpose of
separate modules, their relationships, and the main purposes of each module.
● Overhauled README to be more informative and readable.
● Added section 2 to the README to discuss non-standard software
dependencies per sub-module and per python file.
● Added section 3 to the README, which contains an overview of the
directory structure of the source code. This section also explains the generic
class/specific class paradigm used in the source code, as well as the
templates for future extension.
● Documented the high-level purpose of each module in section 4 of the
README.
● Documented the high-level relationships between the modules in section 4
and section 5 of the README.
d) Providing a brief description of the purpose for each Python file,
especially for reactor code examples.
● Added description of the purpose of each Python file in the directory
structure section (section 3) of the README.
2) Furthermore, its authors may consider including a flow chart to briefly describe
the algorithm implemented in the developed software in the manuscript, similar to
Figure 4, which illustrates the main hardware components of the hydrogen
evolution photoreactor, is recommended.
● A block diagram was added to explain the reactor code.
3) A figure in the “3.2 Image Analysis Software” section that illustrates the
algorithm for image analysis would be beneficial.
● A block diagram was added to explain the image analysis code.
4) The wiring diagram for Raspberry Pi hardware (Figure S1. R) should follow best
practices using industry standards.
For examples, see:
https://www.raspberrypi.com/documentation/computers/raspberry-pi.html;
https://newbiely.com/tutorials/raspberry-pi/raspberry-pi-relay
Fritzing (https://fritzing.org/), a free open-source software, may be used to
prepare wiring diagrams.
An updated wiring diagram that follows the practices listed from the resource
provided has been included in the supplementary information.
5) Authors are encouraged to consider the use of LAB or HSV color models for
image analysis in future studies could yield better performance in separating light
intensity (brightness) from spectral characteristics (hue).
Referee: 3
This text has been copied from the PDF response to reviewers and does not include any figures, images or special characters.

Comments to the Author
1. The manuscript need to have a collective section named " Experimental" with
Methods and Materials sub-sections. Under this section, all experimental
procedures and materials used are provided. The current presentation does not
make the manuscript readable.
A collective “Experimental” section has been made which contains the synthetic
procedures for the films, instrument design of the photoreactor, calibration of the
films, and experimental procedures for experiments 1, 2, 3, and 4.
2. Under results and discussion sections, authors need to present the findings of the
study and compare them with previous work of similar nature and cite the
references accordingly. In its current state, these sections do not present what is
called "results and discussion" section in a manuscript.
A collective “Results and Discussion” section has been made which contains the
findings from experiments 1, 2, 3, and 4 and compares the results to existing
literature.
3. The sections in the manuscript need to be re-organized in order to present a good
flow of concepts for readers. Some Figures for example are cited in the
experimental section but they appear in results and discussion section.
The organization of the manuscript has been changed to improve readability.
Figures are ordered so that they appear when mentioned in the text.
4. The manuscript should benefit from Language editing before it can be accepted
for publication.
Several general changes to improve the language of the paper have been made. All
acronyms have been defined after the first time they are used. Once the acronyms
have been defined they are used throughout the manuscript. All experimental
procedures have been included in more specific detail. Measurements (ie. writing
“20 mL” instead of “20mL”) are now properly formatted.
5. The conclusion should only contains key findings and recommendations and not
experimental procedures.
The conclusion has been edited to reflect the desired changes.
6. Other comments for improvement can be found in the reviewed document
attached.
We are very thankful for this reviewers work and have addressed all the
recommended changes.

10-Jun-2024

Dear Dr Bernhard:

Manuscript ID: DD-ART-03-2024-000070.R1
TITLE: High Throughput Methodology for Investigating Green Hydrogen Generating Processes using Colorimetric Detection Films and Machine Vision

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.

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Associate Editor, Digital Discovery

Reviewer 2

All reviewers' comments were addressed satisfactory. The revised manuscript is publishable in its present form.