Mesoporous CoxSn(1–x)O2 as an efficient oxygen evolution catalyst support for SPE water electrolyzer

SPE water electrolysis is a promising method of hydrogen production owing to its multiple strengths, including its high efficiency, high product purity and excellent adaptability. However, the overpotential of the oxygen evolution reaction process and consumption of Ir during charging in SPE water electrolysis will inevitably result in large energy loss and then high cost. Under these circumstances, we propose a novel 40IrO2/CoxSn(1−x)O2 (x = 0.1, 0.2, 0.3) anode catalyst, where the CoxSn(1−x)O2 support is synthesized by a hydrothermal method and IrO2 is synthesized by a modified Adams fusion method. After modifying the component of CoxSn(1−x)O2, the 40IrO2/CoxSn(1−x)O2 exhibits an increased specific surface area, electrical conductivity and surface active sites. Moreover, a single cell is fabricated by Pt/C as cathode catalyst, 40IrO2/CoxSn(1−x)O2 as anode catalyst and Nafion 117 membrane as electrolyte. The 40IrO2/Co0.2Sn0.8O2 exhibits the lowest overpotential (1.748 V at 1000 mA cm−2), and only 0.18 mV h−1 of voltage increased for 100 h durability test at 1000 mA cm−2. Consequently, CoxSn(1−x)O2 is a promising anode electrocatalyst support for an SPE water electrolyzer.


Comments to the Author(s)
This manuscript reports a novel 40IrO2/CoxSn(1-x)O2 (X= 0.1, 0.2, 0.3) anode catalyst by a facile method and their application in solid polymer electrolyte (SPE) water electrolyzer. Impressively, the 40IrO2/Co0.2Sn0.8O2 exhibits the lowest overpotential (1.748 V at 1000 mA cm-2), and only 0.18 mV h-1 of voltage increased for 100 h durability test at 1000 mA cm-2. Many details are adequately handled and appropriate techniques have been used. But there are many grammatical errors and messy layout. Therefore, this paper can be published in R. Soc. open sci. after minor revision on the following points. 1. What is the state of cobalt? Elemental or compound or both? In XRD description, "This confirms that Co was succesfully doped into SnO2." In XPS description, "The presented satellite peaks and the difference of 15.1 eV of the Co2p3/2 and Co2p1/2 imply that the majority of cobalt is in the states of Co2+." The authors should describe it properly. 2. The specific surface areas and pore size distributions of the 40IrO2/CoxSn(1-x)O2 samples should be provided. 3. "It can be seen that the unsupported IrO2 shows a lower RΩ (76 mΩ cm2) because of the excellent electrical conductivity than 40IrO2/Co0.2Sn0.8O2." in page 6 of line 8, is there any reference of the relationship between the ohmic resistance and electrical conductivity? If not, you should determine the electrical conductivity of IrO2 and 40IrO2/Co0.2Sn0.8O2. 4. Fig.3 and Fig. 6 captions need be checked carefully. It is (a) and (b) rather than (f) and (g) in Fig.3 caption. In Fig. 6, (c) and (d) picture cannot be founded. 5. There are many messy layout and grammatical errors. For example, page 2, line 41, space is missing between number and unit; page 3, line 12, "ml" should be "mL".

25-Feb-2019
Dear Professor Chen: Title: Mesoporous CoxSn(1-x)O2 as an efficient oxygen evolution catalyst support for SPE water electrolyzer Manuscript ID: RSOS-182223 Thank you for submitting the above manuscript to Royal Society Open Science. On behalf of the Editors and the Royal Society of Chemistry, I am pleased to inform you that your manuscript will be accepted for publication in Royal Society Open Science subject to minor revision in accordance with the referee suggestions. Please find the reviewers' comments at the end of this email.
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Best wishes, Dr Laura Smith Publishing Editor, Journals ********************************************** RSC Associate Editor: Comments to the Author: (There are no comments.) RSC Subject Editor: Comments to the Author: (There are no comments.) ********************************************** Reviewer comments to Author: Reviewer: 1 Comments to the Author(s) In this study, the author systemically investigated the doping effect of cobalt into the SnO2 crystal, which serves as excellent support for noble metal water oxidation catalysts but usually encounters poor electronic conductivity. The influence of cobalt doping on the SnO2 support including the grain size, morphology, and also catalytic performance was studied in detail based on the solid characterizations. The manuscript was well-designed and main assumption could be certified by the characterizations, which makes it very suitable for publication in this journal only after addressing the minor concern of the reviewer as listed below: 1. The doping of hetero-atoms into the crystal structure of material could also bring in undesired structural defects, which would in some case function as charge recombination center. Some discussion on this concern should be considered. 2. The author discussed the promising role of hydrogen fuel for the development of novel clean energy and relieving the global environment issues. Thus, it is reasonable to concise include the new techniques of hydrogen production developed in the community, such as electrochemical hydrogen production, photocatalytic/photo-electrochemical water splitting: Nat. Mater., 2006, 5, 909-913;Angew. Chem. Int. Ed. 2019DOI: 10.1002Nat. Mater. 2017, 16, 646, J. Mater. Chem. A, 2017. It would be good supplementary and valuable information for the general readers if the author could add the comparison of the catalytic performance of the current study with the previous system.

Reviewer: 2
Comments to the Author(s) This manuscript reports a novel 40IrO2/CoxSn(1-x)O2 (X= 0.1, 0.2, 0.3) anode catalyst by a facile method and their application in solid polymer electrolyte (SPE) water electrolyzer. Impressively, the 40IrO2/Co0.2Sn0.8O2 exhibits the lowest overpotential (1.748 V at 1000 mA cm-2), and only 0.18 mV h-1 of voltage increased for 100 h durability test at 1000 mA cm-2. Many details are adequately handled and appropriate techniques have been used. But there are many grammatical errors and messy layout. Therefore, this paper can be published in R. Soc. open sci. after minor revision on the following points. 1. What is the state of cobalt? Elemental or compound or both? In XRD description, "This confirms that Co was succesfully doped into SnO2." In XPS description, "The presented satellite peaks and the difference of 15.1 eV of the Co2p3/2 and Co2p1/2 imply that the majority of cobalt is in the states of Co2+." The authors should describe it properly. 2. The specific surface areas and pore size distributions of the 40IrO2/CoxSn(1-x)O2 samples should be provided. 3. "It can be seen that the unsupported IrO2 shows a lower RΩ (76 mΩ cm2) because of the excellent electrical conductivity than 40IrO2/Co0.2Sn0.8O2." in page 6 of line 8, is there any reference of the relationship between the ohmic resistance and electrical conductivity? If not, you should determine the electrical conductivity of IrO2 and 40IrO2/Co0.2Sn0.8O2. 4. Fig.3 and Fig. 6 captions need be checked carefully. It is (a) and (b) rather than (f) and (g) in Fig.3 caption. In Fig. 6, (c) and (d) picture cannot be founded. 5. There are many messy layout and grammatical errors. For example, page 2, line 41, space is missing between number and unit; page 3, line 12, "ml" should be "mL".  Table 3: Additionally, recent studies on OER performance and stability of iridium-based catalysts have been summarized and listed in Table 3. It can be seen that the cell voltage and degradation rate of 40IrO2/Co0.2Sn0.8O2 is comparable to or superior to those of the previously reported iridium--based catalysts (such as IrO2/V-doped TiO2 [32] and IrO2-ATO [50]). This further indicates that the prepared Co doped SnO2 as supports for IrO2 catalysts is a potential candidate for the practical application of SPE water electrolyzer.)

Reviewer: 2 Comments:
This manuscript reports a novel 40IrO2/CoxSn(1-x)O2 (X= 0.1, 0.2, 0.3) anode catalyst by a facile method and their application in solid polymer electrolyte (SPE) water electrolyzer. Impressively, the 40IrO2/Co0.2Sn0.8O2 exhibits the lowest overpotential (1.748 V at 1000 mA cm -2 ), and only 0.18 mV h-1 of voltage increased for 100 h durability test at 1000 mA cm -2 . Many details are adequately handled and appropriate techniques have been used. But there are many grammatical errors and messy layout. Therefore, this paper can be published in R. Soc. open sci. after minor revision on the following points.
To Reviewer #2: Q1: What is the state of cobalt? Elemental or compound or both? In XRD description, "This confirms that Co was succesfully doped into SnO2." In XPS description, "The presented satellite peaks and the difference of 15.1 eV of the Co2p3/2 and Co2p1/2 imply that the majority of cobalt is in the states of Co 2+ ." The authors should describe it properly.
Reply: Thanks a lot for the reviewer's suggestion. The RΩ is the whole ohmic resistance of SPE water electrolyzer including Nafion 117 membrane, catalyst layer, bipolar plate, Ti mesh, carbon paper and wire. The assembled single cells differ only in their anode catalytic layers, which means the difference of RΩ comes from the anode catalysts. The electrical conductivity experiments of supports CoxSn1-xO2, 40IrO2/CoxSn1-xO2 (x= 0, 0.1, 0.2, 0.3) and unsupported IrO2 were also performed. The measured values were listed in Table S2, which matched the results of the RΩ. Correspondingly, the description about the electrical conductivity of all the prepared samples was also modified in the revised manuscript. (Please see page 3, line 28 in the revised version: Electrical conductivity measurements were carried out on cylindrical pellets compressed from the powder samples at 30 MPa between two copper electrodes.…followed by conversion to conductivity.; Page 6, line 24 in the revised version: High electrical conductivity of support is favorable to the supported catalysts for the enhancement of catalytic performance. Prior the catalytic performance test, the electrical conductivities of all the prepared samples were measured and the results shown in Table   S2.…impede the electron transport and decrease the carrier mobility, and reducing electrical conductivity. [43]) Q4: Fig.3 and Fig. 6 captions need be checked carefully. It is (a) and (b) rather than (f) and (g) in Fig.3 caption. In Fig. 6, (c) and (d) picture cannot be founded.
Reply: Thanks a lot for the reviewer's suggestion. According to the suggestions, we have corrected the incorrect description. (Please see Fig.3 and Fig. 6 captions in the revised manuscript: Fig. 3