Next Article in Journal
Enhanced CO2 Photoreduction Performance of WO3−x
Next Article in Special Issue
Insight into the Mechanism of Ultrasonic Activation of Persulfate for Enhancing the Removal of Tetracycline Hydrochloride
Previous Article in Journal
Residual Trifluorosulfonic Acid in Amino-Functionalized Covalent Triazine Frameworks for Boosting Photocatalytic Hydrogen Evolution
Previous Article in Special Issue
Sludge Recycling from Non-Lime Purification of Electrolysis Wastewater: Bridge from Contaminant Removal to Waste-Derived NOX SCR Catalyst
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Catalysts
Volume 15
Issue 1
10.3390/catal15010011
catalysts-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Tuning Surface State in CoFe (Oxy)Hydroxide for Improved Oxygen Evolution Electrocatalysis

by
Wen Guo
1,2,
Chizhong Wang
1,*,
Lei Qiu
1,
Fanghua Liu
1,
Sizhe Chen
1 and
Huazhen Chang
1,*
1
School of Chemistry and Life Resources, Renmin University of China, Beijing 100872, China
2
China Three Gorges Renewables (Group) Co., Ltd. Construction Management Branch, Beijing 100032, China
*
Authors to whom correspondence should be addressed.
Catalysts 2025, 15(1), 11; https://doi.org/10.3390/catal15010011
Submission received: 20 November 2024 / Revised: 21 December 2024 / Accepted: 24 December 2024 / Published: 26 December 2024
(This article belongs to the Special Issue Homogeneous and Heterogeneous Catalytic Oxidation and Reduction)
Browse Figures
Versions Notes

Abstract

:
CoFe-based catalysts have shown excellent activity for the oxygen evolution reaction (OER), with the oxidation states of the active sites playing a crucial role in determining catalytic performance. However, how to effectively increase the oxidation state of these active sites remains a key challenge. In this work, a facile treatment with NaBH4 solution was employed to modulate the surface state of CoFeOxHy catalysts, inducing an enhanced OER activity. The overpotential at 10 mA cm−2 for the NaBH4-treated CoFe catalyst was reduced to 270 mV, indicating improved OER activity. X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) results reveal that NaBH4 treatment induced a phase reconstruction of the CoFe oxalate framework, a critical step in enhancing its catalytic properties. The strong reducing ability of NaBH4 strengthened the Co-Fe interaction, allowing the retention of low-valence Co species while facilitating the formation of high-valence Fe sites. This dual modulation of Co and Fe oxidation states significantly accelerated charge transfer kinetics, ultimately boosting OER performance. These findings highlight the importance of improving the oxidation states of active sites in CoFe-based catalysts, providing insights for developing efficient catalysts for electrochemical water splitting.

1. Introduction

Electrochemical water splitting has emerged as a promising method for large-scale storage of renewable electricity, offering a sustainable solution to energy challenges [1,2]. The efficiency of water splitting is predominantly governed by the anodic oxygen evolution reaction (OER), which involves the transfer of four electrons through multiple elementary steps. However, the sluggish kinetics of the OER significantly limit the overall efficiency of water electrolysis systems [3,4]. Therefore, the development of cost-effective and highly efficient OER catalysts is essential for the widespread commercialization and scalability of water electrolyzers [5].
Under alkaline conditions, the use of precious metal catalysts can be avoided, enabling the development of high-performance OER catalysts based on earth-abundant elements such as Fe, Co, Ni, and Mn [6,7,8]. Despite significant advances in the design of these catalysts, the large overpotentials of 200-300 mV still remain a major challenge, underscoring the need for further improvements in OER performance through innovative catalyst design and optimization strategies [9,10,11]. Among the various transition metal-based catalysts, CoFe composites with high intrinsic OER activity have emerged as one of the most promising families [12,13].
In studies, including both in situ experiments and theoretical calculations, it has been revealed that in the CoFeOxHy system, the Fe sites play a critical role in generating oxo species and providing the necessary oxidation driving force for the rapid formation and conversion of key OER intermediates such as *O and *OOH [14,15]. On the other hand, CoOx species could assist the Fe sites by facilitating the formation of high-valence Fe species, likely Fe4+, through interactions between Co and Fe, while simultaneously inhibiting Co oxidation [16,17]. Consequently, optimizing the interaction between Co and Fe sites by regulating the surface state of the catalyst is considered a promising strategy for further improving the OER performance of CoFe-based catalysts.
In recent years, various strategies have been employed to enhance the OER activity of CoFe catalysts, including cation doping, anion incorporation, and vacancy engineering [18,19,20]. Among these, the incorporation of P-block elements such as P [21,22], S [23,24], B [25,26], and N [27,28] into CoFe composites has shown considerable promise in achieving higher catalytic activity. Notably, boron has attracted significant attention due to its ability to act as an “electron sink” owing to its intrinsic electron deficiency, which facilitates the transfer of negative charge from metal sites. This interaction alters the local environment and electronic structure of the metal sites, thereby enhancing OER activity [6,7,29,30,31]. Furthermore, some studies suggest that boron, in the form of borates, is primarily embedded within the interlayer of layered double hydroxides (LDHs), contributing to the exposure of layer–edge sites and further enhancing catalytic performance [32].
Despite these advancements, the exact mechanisms underlying the enhanced OER activity upon surface treatment remain a subject of ongoing debate. The structural reconstruction that occurs during the OER process further complicates the interpretation of these findings, particularly for CoFe systems, which are known to undergo significant structural changes during electrochemical cycling [33,34]. Therefore, a more detailed understanding of the precise interactions between metal sites and the role of various dopants or modifications in improving OER performance is still needed.
In this work, we introduce a facile pretreatment method for CoFe-based catalysts. A series of CoFe oxalates were first synthesized and then treated with NaBH4 solution. The structural transformations induced by the NaBH4 treatment were carefully investigated using techniques such as XRD and Raman spectroscopy. Notably, a significant improvement in OER activity was observed for the NaBH4-treated CoFe catalyst. This work further explored the effects of NaBH4 treatment on the Co-Fe interaction and the potential residual boron species. By examining the surface species and local environment of the catalyst, we aim to provide deeper insights into the mechanisms that drive the observed improvements in catalytic performance.

2. Results and Discussion

Figure 1 shows the electrochemical test results for the Co and CoFe oxalates before and post NaBH4 treatment. From the CV results as seen in Figure 1a, it is observed that the CoFe oxalate catalyst shows a lower overpotential for the OER process at a given current density in comparison to Co oxalate. This is consistent with the key role played by the FeOx sites during the OER process, where the formation of high-valence species and the O-O bond coupling occurred over Fe sites, while Co sites served primarily to promote the Fe sites [35]. Note that both Co and CoFe oxalate catalysts show elevated activity after NaBH4 treatment. Particularly, a low overpotential of 270 mV at the current density of 10 mA cm−2 was realized on the CoFe-SBH catalyst (the samples after sodium borohydride treatment were referred to as CoFe-SBH). This is highly comparable to the intrinsic activity of the state-of-the-art NiFeOxHy catalysts [36,37]. In addition, the promoting effect of NaBH4 treatment was observed over all CoxFey oxalate catalysts with varied Co/Fe molar ratios (see Figures S1 and S2).
The zoomed section of the CV results in Figure 1b reveals an electrochemical response at 1.1–1.3 V vs. RHE, which was assigned to the redox behavior of Co2+/Co3+. A comparison of Co and CoFe catalysts suggests that the presence of FeOx could lead to a shift of Co2+/Co3+ redox towards positive potential, indicating that the oxidation of Co2+ to Co3+ in the CoFe catalyst is more difficult than that in the Co catalyst. It is the FeOx species that impeded the Co oxidation, which symbolized well the Co-Fe interaction during the OER process. The more difficultly Co site was oxidized, the easier the formation of Fe site in high oxidation state. It is noted as well that the Co-Fe interaction became more evident with the higher content of Fe in CoFe catalysts, as seen in Figure S1 and Table S1.
After NaBH4 treatment, the Co2+/Co3+ oxidation potential of the CoFe-SBH catalyst shifted further towards more positive potential in comparison to the CoFe catalyst. However, in the Co catalyst, the redox position was hardly affected, and a rise in peak intensity was observed instead. This result implies a different OER-promoting effect between CoFe and Co catalysts by the NaBH4 treatment. For the CoFe catalyst, the treatment of NaBH4 had a similar effect to increasing the Fe content on the potential shift of Co2+/Co3+ oxidation. Both of them inhibited the oxidation of Co2+ and allowed the presence of Co sites in a relatively reduced state under rest conditions. Tafel plots of Co and CoFe samples before and post the NaBH4 treatment are displayed in Figure 1c. Co catalyst exhibited a large Tafel slope (~60 mV dec−1), indicating a one-electron transfer before the potential-limiting step with the Co site as the OER-active center. With the introduction of Fe, high-valence Fe species were more easily produced under the interaction of Co, and thus the *OH-to-*O process might no longer be a potential-limiting step [15]. However, after NaBH4 treatment, the Tafel slope of CoFe-SBH was further reduced to ~30 mV dec−1. At this point, a two-electron transfer is required prior to the potential-limiting step. This result is in line with previous reports that the O-O bonding served as the potential-limiting step in the modified CoFeOxHy catalysts [34].
Figure 1d shows the electrochemical impedance spectra (EIS) plots for the catalysts, and the Nyquist plots were fitted by using the circuit diagram in the inset. Rs, Rc, Rct and Re represent series resistance, bulk conductive resistance, charge-transfer resistance, and the resistance across the substrate–catalyst interface, respectively, as summarized in Table S2. Comparing the Rct of the catalysts before and after NaBH4 treatment, it is found that the interfacial charge-transfer resistance of the catalysts decreased significantly after NaBH4 treatment. This corresponds well with the Tafel analysis results. It is noted that the electrochemically active surface area for CoFe-SBH was analogous to that for other treated or untreated catalysts, as evidenced in Figure S3. Therefore, the enhanced OER performance of CoFe-SBH should come from the promotion of the intrinsic activity of each active site, rather than the increase in the number of active sites. It is the influence of surface sites by NaBH4 treatment that improved the charge-transfer efficiency of CoFe, inducing one of the highest OER activities (see Table S3). Meanwhile, CoFe-SBH reveals a stable performance for the OER process with a Faradaic efficiency close to one unit, as seen in Figures S4 and S5.
Figure 2a shows the schematic diagram of the CoFe-SBH synthesis process. Various physicochemical characterizations were employed to investigate the impact of NaBH4 treatment and the OER-promoting mechanism. XRD results (see Figure 2b,c) reveal that the untreated Co, Fe, and CoFe samples all exhibited a crystalline structure of hydrated oxalate. Moreover, differences in diffraction peak positions indicate that Co and Fe were mixed in the form of a solid solution in highly uniform dispersion within the oxalate framework (see Figure S6). The XRD results for the NaBH4-treated samples reveal that the framework of oxalate was destructed and CoFe-SBH was present in an amorphous or low-crystallinity form. Interestingly, the XRD pattern of Fe-SBH shows several weak peaks that could be ascribed to the (1 2 0), (0 3 1), and (2 0 0) planes of FeOOH (PDF#08-0098). Meanwhile, we observed the same trend in structural transformation by comparing the Raman spectra for the catalysts before and post NaBH4 treatment, as shown in Figure 2d,e. Typical Raman modes of oxalates (e.g., C-O stretching, symmetric C-C stretching, and M-O ring stretching modes) disappeared completely after NaBH4 treatment and were replaced by T1, E, and A1 vibrations of the Fe-O bond and Eg and A1g vibrations of the Co-O bond, respectively. The results suggest that the CoFe-SBH sample was likely to contain Fe, Co, and CoFe (oxy)hydroxide structures in low crystallinity. These structures would be transformed eventually into layered CoFeOxHy structures during the electrochemical tests, generating active sites at the edges of the layers.
The morphology of CoFe and CoFe-SBH catalysts before and after the OER test was investigated by SEM, as seen in Figure 3a–c. It is observed that CoFe oxalate shows a short rod structure. An evident structural collapse and reconstruction occurred for the CoFe-SBH with the formation of amorphous particles with a particle size of 200 nm. The SEM image for the CoFe-SBH after the CV test shows a vertically aligned, sheet-like structure on the surface of origin particles, which is consistent with the TEM result as seen in Figure 3d. Selected area electron diffraction (SAED) and HRTEM images (see Figure 3e,f) indicate that the crystallinity of CoFe-SBH was quite low with a grain size smaller than 1 nm, which was conducive to forming more grain boundaries on the surface and heavily exposing active sites. It is further demonstrated by the EDX-mapping image that Co and Fe remained uniformly distributed after NaBH4 treatment and the OER process, accompanied by the introduction of a small amount of B species.
To further investigate the composition and chemical states of the pre-catalysts, we performed XPS analysis on CoFe, CoFe-SBH, Co-SBH, and Fe-SBH (Figure 4). As shown in Figure 4a, the deconvoluted peaks of CoFe correspond to the Co 2p3/2 core level at 781.5 eV and the Co 2p1/2 core level at 797.2 eV [38]. After NaBH4 treatment, Co2+ species in both Co and CoFe oxalate underwent an oxidation process due to the reconstruction from oxalate to (oxy)hydroxide structure, as evidenced by XPS O 1s and C 1s results (see Figure S7). For Co-SBH, the Co 2p3/2 spectrum exhibits a significant shift to lower binding energies, indicating an increase in oxidation state. It is indicated that this shift was a result of the interaction between oxalate and NaBH4, potentially leading to an increase in the oxidation states of both Co and Fe. In the oxalate structure, oxalate anions (C2O42−) typically act as ligands, coordinating with metal ions such as Co2+ and Fe2+ to form stable complexes in their lower oxidation states [39,40]. Exposure to a strong reducing agent like NaBH4 might break down this structure and induce the formation of an amorphous (oxy)hydroxide phase containing oxidized metal ions (Co>2+, Fe>2+). Notably, compared to Co-SBH, the presence of Fe in CoFe-SBH resulted in a lower ratio of Co3+/(Co2+ + Co3+) as shown in Figure 4a. This suggests that the incorporation of Fe modified the electronic environment and impeded the oxidation of Co.
XPS Fe 2p spectra in Figure 4b show a predominant Fe species (i.e., Fe2+) in a low oxidation state on the CoFe oxalate surface. The Fe 2p spectra of CoFe oxalate exhibit peaks at 709.8 eV, 723.2 eV, 711.5 eV, and 724.9 eV, which could be assigned to Fe2+ 2p3/2, Fe2+ 2p1/2, Fe3+ 2p3/2, and Fe3+ 2p1/2, respectively [41]. After NaBH4 treatment, the Fe 2p3/2 peak shifts to higher binding energy, suggesting an increase in the Fe3+ fraction. Despite the reductive atmosphere induced by NaBH4 treatment, Fe was oxidized to higher valence due to the phase reconstruction from oxalate to (oxy)hydroxide. Notably, a higher proportion of high-valence Fe species was observed for CoFe-SBH in comparison to that of Fe-SBH. Combined with XPS Co 2p results, it was the effect of low-valence Co species that induced the formation of high-valence Fe species. This illustrates well an immediate interaction between Co and Fe with a negative charge donation from the Fe site to the Co site. The strong Co-Fe interaction and the likely formation of higher-valence Fe species were correlated with the improved OER performance for the CoFe-SBH catalyst [42,43]. The presence of B species was found as well on the CoFe-SBH surface (see Figures S8 and S9). This indicates that BO33−, formed after NaBH4 reduction during the treatment process, was likely to be incorporated into the CoFe-SBH structure by doping or surface residue.
In order to further explore the roles of B species played in the improved OER performance, CoFe oxalate was treated in a Na3BO3 solution obtained by the decomposition of NaBH4 solution after standing for 24 h. In this context, the CoFe catalyst was treated in a B-containing solution without strong reduction ability. As shown in Figure 5a, the OER performance of the CoFe-BO33− sample remained unchanged, while an anodic shift in the redox potential of Co2+/Co3+ in CoFe-BO33− was observed. The presence of small amounts of B species appeared to be able to block the Co2+ oxidation, which was similar to the inhibitory effects of Fe species on the Co2+ oxidation. Nevertheless, the unaffected OER activity suggested the lesser effects of B species on the Fe active site.
The CoFe catalyst was measured in an electrolyte containing 1 M KOH and 0.1 M K3BO3. Figure 5b shows that Co2+ oxidation was heavily blocked, accompanied by even a decreased OER activity when the CoFe catalyst was exposed to BO33− in the electrolyte. This indicates that the inhibition of Co oxidation was unnecessarily correlated to the promotion in OER activity. By contrast, NaBH4 treatment could induce a strong Co-Fe interaction with Co in low oxidation state and Fe in high oxidation state. While the likely contribution of B species to the improved OER activity for the CoFe-SBH catalyst cannot be ruled out. There was a possibility that the presence of B species affected the local environment of Co or Fe sites. In the close surroundings of FeOx, CoOx was relatively difficult to oxidize and could act as an electron reservoir by withdrawing negative charge from FeOx to CoOx. As a result, the maintenance of high-valence Fe in the form of Fe-oxo [44] was promoted. With the easy formation of *O intermediate species, it could provide sufficient oxidation driving force for the OER process to facilitate the subsequent O-O bond coupling process. This is consistent with a lower Tafel slope for the CoFe-SBH catalyst.

3. Experimental Section

3.1. Materials and Sample Preparation

Cobalt sulfate (CoSO4·7H2O, Sinopharm, Beijing, China), iron sulfate (FeSO4·7H2O, Aladdin, Shanghai, China), oxalic acid (H2C2O4·xH2O, Xilong Scientific, Beijing, China), and sodium borohydride (NaBH4, Xiya Chemistry, Chengdu, China) were directly used without purification. CoFe oxalates were synthesized by a hydrothermal method. Initially, solutions containing 2 mmol of metal cations were prepared by dissolving different proportions of cobalt sulfate and iron sulfate in 15 mL of Milli-Q water (18.2 MΩ cm). Subsequently, 15 mL of solution containing 4 mmol H2C2O4·xH2O was added into the solution with continuous magnetic stirring. Moreover, 2 M KOH and 1 M H2SO4 were used to adjust the pH of the mixed solution to 6. After stirring for 30 min, the mixture was transferred into 50 mL Teflon-lined stainless steel autoclaves and heated at 180 °C for 5 h. The products were collected and washed sequentially by water, ethanol, and water, followed by drying at 80 °C for 12 h.
The as-prepared CoxFey oxalate materials were treated with NaBH4 solution. A fresh 1 M NaBH4 solution was prepared under ice bath conditions. Considering the insolubility of oxalates, CoFe oxalate powder was spread out into water by sonication. Then, 5 mL of 1 M NaBH4 solution was introduced to the suspension dropwise and sonicated for 1 h until there were no bubbles evolved. The final product was obtained by washing with water and drying at 80 °C for 12 h. The samples after sodium borohydride treatment were referred to as CoxFey-SBH.

3.2. Characterizations

X-ray diffraction (XRD; SHIMADZU XRD-7000, Kyoto, Japan) patterns were obtained with a scanning rate of 10 ° per minute. Raman spectra were taken by using a Raman microscope spectrometer (Horiba XploRA PLUS, Paris, France) with a 532 nm laser source. X-ray photoelectron spectroscopy (XPS; Thermo SCIENTIFIC ESCALAB Xi+, Waltham, MA, USA) was measured with an Al anode X-ray source. All XPS spectra were calibrated by using the C 1s peak (284.8 eV) as an internal standard, and Shirley-type background lines were adopted for the spectra deconvolution. Transmission electron microscopy (TEM; JEOL-JEM 2100F, Tokyo, Japan) and scanning electron microscopy (SEM; Zeiss sigma300, Oberkochen, Germany) with energy-dispersive X-ray spectroscopy (EDX) were conducted to investigate the morphologies and structures of the samples.

3.3. Electrochemical Tests

Catalyst ink was prepared by dispersing 2.5 mg of powder in 1000 μL of mixed solution of 970 μL of isopropyl alcohol, 20 μL of Milli-Q water, and 10 μL of Nafion solution (5 wt.%, Aladdin). After sonicating for 1 h, the ink was drop-casted onto glassy carbon substrates as working electrodes at a loading mass of 0.1 mg cm−2. All electrochemical measurements were performed on an electrochemistry workstation (CH Instruments CHI760E, Shanghai, China) by using a three-electrode cell with an Hg/HgO (1 M KOH) electrode as reference and a Pt mesh as counter electrode. All potentials measured were converted to the reversible hydrogen electrode (RHE) scale according to the Nernst equation: ERHE = EHg/HgO + 0.059·pH + 0.098 V.
Cyclic voltammetry (CV) was performed with a scan rate of 10 mV s−1. Tafel analysis was conducted by fitting the linear response of CV mode with a scan rate of 1 mV s−1. Electrochemical impedance spectroscopy (EIS) was measured with an AC amplitude of 10 mV and frequencies varying from 105 to 0.1 Hz at a given potential of 0.6 V vs. Hg/HgO. All tests were performed in 1 M Fe-free KOH electrolyte by purifying KOH electrolyte using the reported method [16].

4. Conclusions

In this work, superior OER performance was obtained over NaBH4-treated CoFe catalyst, whose overpotential at 10 mA cm−2 for the OER process reached 270 mV. It was found that NaBH4 treatment could break down the framework of oxalate and induce an emergence of the amorphous CoFeOxHy phase. As a result, an Fe site in a higher oxidation state was formed by maintaining the low-valence CoOx species. Such strengthened Co-Fe interaction could promote the charge transfer kinetics and improve the OER performance. The surface treatment provided a facile strategy for direct modulation of surface reactive sites towards a more efficient OER process.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/catal15010011/s1. Figure S1: Cyclic voltammograms for (a) CoxFey-SBH, (b) CoxFey, and a zoomed-in CV section in Figure S1 for (c) CoxFey-SBH and (d) CoxFey. Figure S2: Tafel plots for (a) CoxFey-SBH and (b) CoxFey. Figure S3: Cyclic voltammograms with scanning rates varying from 5 to 400 mV s−1 for (a) Co-SBH, (b) CoFe-SBH, (c) Fe-SBH, (d) Co, (e) CoFe, and (f) Fe. (g) Electrochemically active surface areas were evaluated by taking the capacitive current density at 0.92 V vs. RHE as a function of scan rate. Figure S4: (a) Chronopotentiometry plots of CoFe-SBH held at 10 mA cm−2 for 75 h. (b) Cyclic voltammograms and (c) Tafel plots for the CoFe-SBH tested after the chronopotentiometry held at 10 mA cm−2 for 0 or 75 h. Figure S5: Faradaic efficiency of CoFe-SBH. Figure S6: (a) SEM and (b) EDX-mapping images of CoFe oxalate. Figure S7: XPS (a) O 1s and (b) C 1s spectra for CoFe, CoFe-SBH, Co-SBH, and Fe-SBH. Figure S8: XPS survey spectra for (a) CoFe and (b) CoFe-SBH. Figure S9: XPS B 1s spectra for CoFe-SBH, Co-SBH, and Fe-SBH. Table. S1: OER performances of the CoxFey oxalate and CoxFey-SBH catalysts. Co-oxi is the potential for Co2+/3+ redox. Table. S2: OER performances of the measured catalysts and the fitted resistances from the impedance Nyquist plots as shown in Figure 1(d) in the main text. Table S3: Summary of the most active CoFe-based OER catalysts. Table S3 Summary of the most active CoFe-based OER catalysts. See references in SM [45,46,47,48,49,50,51,52,53,54,55,56,57,58].

Author Contributions

C.W. and H.C. conceived and supervised the research. W.G. and C.W. designed the experiments. W.G. performed most of the experiments and data analysis. W.G., L.Q., F.L. and S.C. wrote the paper and performed XPS analysis. All authors discussed the results and commented on the paper. All authors have read and agreed to the published version of the manuscript.

Funding

This work was financially supported by The National Natural Science Foundation of China (Grant No. 22276215, 51938014, 22176217). The Fundamental Research Funds for the Central Universities and the Research Funds of Renmin University of China (No. 22XNKJ28) also supported this work.

Data Availability Statement

The data are contained within the article and Supplementary Materials.

Conflicts of Interest

Author Wen Guo was employed by the company China Three Gorges Renewables (Group) Co., Ltd. Construction Management Branch. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

References

  1. Li, W.; Gao, X.; Xiong, D.; Wei, F.; Song, W.G.; Xu, J.; Liu, L. Hydrothermal synthesis of monolithic Co3Se4 nanowire electrodes for oxygen evolution and overall water splitting with high efficiency and extraordinary catalytic stability. Adv. Energy Mater. 2017, 7, 1602579. [Google Scholar] [CrossRef]
  2. Anantharaj, S.; Kundu, S.; Noda, S. “The Fe Effect”: A review unveiling the critical roles of Fe in enhancing OER activity of Ni and Co based catalysts. Nano Energy 2021, 80, 105514. [Google Scholar] [CrossRef]
  3. Sun, Y.; Liao, H.; Wang, J.; Chen, B.; Sun, S.; Ong, S.J.H.; Xi, S.; Diao, C.; Du, Y.; Wang, J.O.; et al. Covalency competition dominates the water oxidation structure-activity relationship on spinel oxides. Nat. Catal. 2020, 3, 554–563. [Google Scholar] [CrossRef]
  4. Wang, J.; Kim, S.J.; Liu, J.; Gao, Y.; Choi, S.; Han, J.; Shin, H.; Jo, S.; Kim, J.; Ciucci, F.; et al. Redirecting dynamic surface restructuring of a layered transition metal oxide catalyst for superior water oxidation. Nat. Catal. 2021, 4, 212–222. [Google Scholar] [CrossRef]
  5. Wang, Y.; Jiang, Y.; Zhao, Y.; Ge, X.; Lu, Q.; Zhang, T.; Xie, D.; Li, M.; Bu, Y. Design strategies of perovskite nanofibers electrocatalysts for water splitting: A mini review. Chem. Eng. J. 2023, 451, 138710. [Google Scholar] [CrossRef]
  6. Yao, N.; Wang, G.; Jia, H.; Yin, J.; Cong, H.; Chen, S.; Luo, W. Intermolecular energy gap-induced formation of high-valent cobalt species in CoOOH surface layer on cobalt sulfides for efficient water oxidation. Angew. Chem. Int. Ed. 2022, 61, e202117178. [Google Scholar] [CrossRef]
  7. Lee, S.; Moysiadou, A.; Chu, Y.C.; Chen, H.M.; Hu, X. Tracking high-valent surface iron species in the oxygen evolution reaction on cobalt iron (oxy)hydroxides. Energy Environ. Sci. 2022, 15, 206–214. [Google Scholar] [CrossRef]
  8. Xu, X.; Song, F.; Hu, X. A nickel iron diselenide-derived efficient oxygen-evolution catalyst. Nat. Commun. 2016, 7, 12324. [Google Scholar] [CrossRef]
  9. Guo, Y.; Tong, Y.; Chen, P.; Xu, K.; Zhao, J.; Lin, Y.; Chu, W.; Peng, Z.; Wu, C.; Xie, Y. Engineering the electronic state of a perovskite electrocatalyst for synergistically enhanced oxygen evolution reaction. Adv. Mater. 2015, 27, 5989–5994. [Google Scholar] [CrossRef]
  10. Xu, K.; Cheng, H.; Liu, L.; Lv, H.; Wu, X.; Wu, C.; Xie, Y. Promoting active species generation by electrochemical activation in alkaline media for efficient electrocatalytic oxygen evolution in neutral media. Nano Lett. 2016, 17, 578–583. [Google Scholar] [CrossRef]
  11. Liu, H.J.; Zhang, S.; Yang, W.Y.; Yu, N.; Liu, C.Y.; Chai, Y.M.; Dong, B. Directional reconstruction of iron oxides to active sites for superior water oxidation. Adv. Funct. Mater. 2023, 33, 2303776. [Google Scholar] [CrossRef]
  12. Kang-Wen, Q.; Xi, C.; Zhang, Y.; Zhang, R.; Li, Z.; Sheng, G.R.; Liu, H.; Dong, C.K.; Chen, Y.J.; Du, X.W. Laser-induced oxygen vacancies in FeCo2O4 nanoparticles for boosting oxygen evolution and reduction. Chem. Commun. 2019, 55, 8579–8582. [Google Scholar] [CrossRef] [PubMed]
  13. Hung, S.F.; Hsu, Y.Y.; Chang, C.J.; Hsu, C.S.; Suen, N.T.; Chan, T.S.; Chen, H.M. Unraveling geometrical site confinement in highly efficient iron-doped electrocatalysts toward oxygen evolution reaction. Adv. Energy Mater. 2017, 8, 1701686. [Google Scholar] [CrossRef]
  14. Enman, L.J.; Stevens, M.B.; Dahan, M.H.; Nellist, M.R.; Toroker, M.C.; Boettcher, S.W. Operando X-Ray absorption spectroscopy shows iron oxidation is concurrent with oxygen evolution in cobalt-iron (oxy)hydroxide electrocatalysts. Angew. Chem. Int. Ed. 2018, 57, 12840–12844. [Google Scholar] [CrossRef]
  15. Li, N.; Hadt, R.G.; Hayes, D.; Chen, L.X.; Nocera, D.G. Detection of high-valent iron species in alloyed oxidic cobaltates for catalysing the oxygen evolution reaction. Nat. Commun. 2021, 12, 4218. [Google Scholar] [CrossRef]
  16. Burke, M.S.; Kast, M.G.; Trotochaud, L.; Smith, A.M.; Boettcher, S.W. Cobalt-iron (oxy)hydroxide oxygen evolution electrocatalysts: The role of structure and composition on activity, stability, and mechanism. J. Am. Chem. Soc. 2015, 137, 3638–3648. [Google Scholar] [CrossRef]
  17. Zhang, T.; Nellist, M.R.; Enman, L.J.; Xiang, J.; Boettcher, S.W. Modes of Fe incorporation in Co-Fe (oxy)hydroxide oxygen evolution electrocatalysts. ChemSusChem 2019, 12, 2015–2021. [Google Scholar] [CrossRef]
  18. Zhang, Y.; Lu, T.; Ye, Y.; Dai, W.; Zhu, Y.; Pan, Y. Stabilizing oxygen vacancy in entropy-engineered CoFe2O4-type catalysts for Co-prosperity of efficiency and stability in an oxygen evolution reaction. ACS Appl. Mater. Interfaces 2020, 12, 32548–32555. [Google Scholar] [CrossRef]
  19. Chen, H.; Song, L.; Ouyang, S.; Wang, J.; Lv, J.; Ye, J. Co and Fe codoped WO2.72 as alkaline-solution-available oxygen evolution reaction catalyst to construct photovoltaic water splitting system with solar-to-hydrogen efficiency of 16.9 %. Adv. Sci. 2019, 6, 1900465. [Google Scholar] [CrossRef]
  20. Chen, Q.; Zhang, Q.; Liu, H.; Liang, J.; Peng, W.; Li, Y.; Zhang, F.; Fan, X. Preparation of hollow cobalt-iron phosphides nanospheres by controllable atom migration for enhanced water oxidation and splitting. Small 2021, 17, 2007858. [Google Scholar] [CrossRef]
  21. Wang, T.; Wang, C.; Jin, Y.; Sviripa, A.; Liang, J.; Han, J.; Huang, Y.; Li, Q.; Wu, G. Amorphous Co-Fe-P nanospheres for efficient water oxidation. J. Mater. Chem. A 2017, 5, 25378–25384. [Google Scholar] [CrossRef]
  22. Xu, H.; Zhu, J.; Wang, P.; Chen, D.; Zhang, C.; Xiao, M.; Ma, Q.; Bai, H.; Qin, R.; Ma, J.; et al. Fe-Co-P multi-heterostructure arrays for efficient electrocatalytic water splitting. J. Mater. Chem. A 2021, 9, 24677–24685. [Google Scholar] [CrossRef]
  23. Liu, H.J.; Zhang, S.; Zhou, Y.N.; Yu, W.L.; Ma, Y.; Wang, S.T.; Chai, Y.M.; Dong, B. Dynamically stabilized electronic regulation and electrochemical reconstruction in Co and S atomic pair doped Fe3O4 for water oxidation. Small 2023, 19, 2301255. [Google Scholar] [CrossRef]
  24. Li, X.; Duan, F.; Deng, M.; Zheng, W.; Lin, Y.; Dan, Y.; Cheng, X.; Chen, L. Effect of Fe doping on Co-S/carbon cloth as bifunctional electrocatalyst for enhanced water splitting. J. Electroanal. Chem. 2022, 922, 116723. [Google Scholar] [CrossRef]
  25. Suryawanshi, U.P.; Suryawanshi, M.P.; Ghorpade, U.V.; Shin, S.W.; Kim, J.; Kim, J.H. An earth-abundant, amorphous cobalt-iron-borate (Co-Fe-Bi) prepared on Ni foam as highly efficient and durable electrocatalysts for oxygen evolution. Appl. Surf. Sci. 2019, 495, 143462. [Google Scholar] [CrossRef]
  26. Tian, L.; Zhong, D.; Zhao, T.; Liu, Y.; Hao, L.; Fang, Q.; Lang, X.; Zhao, X.; Hao, G.; Liu, G.; et al. Oxygen-vacancy-rich Co3O4@Fe-B-O heterostructure for efficient oxygen evolution reaction in alkaline and neutral media. J. Colloid Interface Sci. 2023, 646, 452–460. [Google Scholar] [CrossRef]
  27. Sun, J.; Guo, N.; Shao, Z.; Huang, K.; Li, Y.; He, F.; Wang, Q. A facile strategy to construct amorphous spinel-based electrocatalysts with massive oxygen vacancies using ionic liquid dopant. Adv. Energy Mater. 2018, 8, 1800980. [Google Scholar] [CrossRef]
  28. Yang, W.; Guo, J.; Ma, J.; Wu, N.; Xiao, J.; Wu, M. FeCo nanoalloys encapsulated in N-doped carbon nanofibers as a trifunctional catalyst for rechargeable Zn-air batteries and overall water electrolysis. J. Alloys Compd. 2022, 926, 166937. [Google Scholar] [CrossRef]
  29. Bai, Y.; Wu, Y.; Zhou, X.; Ye, Y.; Nie, K.; Wang, J.; Xie, M.; Zhang, Z.; Liu, Z.; Cheng, T.; et al. Promoting nickel oxidation state transitions in single-layer NiFeB hydroxide nanosheets for efficient oxygen evolution. Nat. Commun. 2022, 13, 6094. [Google Scholar] [CrossRef]
  30. Wang, Y.; Tao, S.; Lin, H.; Han, S.; Zhong, W.; Xie, Y.; Hu, J.; Yang, S. NaBH4 induces a high ratio of Ni3+/Ni2+ boosting OER activity of the NiFe LDH electrocatalyst. RSC Adv. 2020, 10, 33475–33482. [Google Scholar] [CrossRef]
  31. Yu, J.; Wang, J.; Long, X.; Chen, L.; Cao, Q.; Wang, J.; Qiu, C.; Lim, J.; Yang, S. Formation of FeOOH nanosheets induces substitutional doping of CeO2−x with high-valence Ni for efficient water oxidation. Adv. Energy Mater. 2020, 11, 2002731. [Google Scholar] [CrossRef]
  32. Su, L.; Du, H.; Tang, C.; Nan, K.; Wu, J.; Li, C.M. Borate-ion intercalated NiFe layered double hydroxide to simultaneously boost mass transport and charge transfer for catalysis of water oxidation. J. Colloid Interface Sci. 2018, 528, 36–44. [Google Scholar] [CrossRef] [PubMed]
  33. Lee, W.H.; Han, M.H.; Ko, Y.J.; Min, B.K.; Chae, K.H.; Oh, H.S. Electrode reconstruction strategy for oxygen evolution reaction: Maintaining Fe-CoOOH phase with intermediate-spin state during electrolysis. Nat. Commun. 2022, 13, 605. [Google Scholar] [CrossRef] [PubMed]
  34. Wu, T.; Sun, Y.; Ren, X.; Wang, J.; Song, J.; Pan, Y.; Mu, Y.; Zhang, J.; Cheng, Q.; Xian, G.; et al. Reconstruction of thiospinel to active sites and spin channels for water oxidation. Adv. Mater. 2022, 35, 2207041. [Google Scholar] [CrossRef]
  35. Reith, L.; Hausmann, J.N.; Mebs, S.; Mondal, I.; Dau, H.; Driess, M.; Menezes, P.W. In situ detection of iron in oxidation states ≥ IV in cobalt-iron oxyhydroxide reconstructed during oxygen evolution reaction. Adv. Energy Mater. 2023, 13, 2203886. [Google Scholar] [CrossRef]
  36. McCrory, C.C.L.; Jung, S.; Peters, J.C.; Jaramillo, T.F. Benchmarking heterogeneous electrocatalysts for the oxygen evolution reaction. J. Am. Chem. Soc. 2013, 135, 16745–17236. [Google Scholar] [CrossRef]
  37. McCrory, C.C.L.; Jung, S.; Ferrer, I.M.; Chatman, S.M.; Peters, J.C.; Jaramillo, T.F. Benchmarking hydrogen evolving reaction and oxygen evolving reaction electrocatalysts for solar water splitting devices. J. Am. Chem. Soc. 2015, 137, 4275–4592. [Google Scholar] [CrossRef]
  38. Yang, Y.; Xu, Y.; Liu, H.; Zhang, Q.; Liu, B.; Yang, M.; Dai, H.; He, D.; Feng, X.; Xiao, X. Unraveling the modulation essence of p bands in Co-based oxide stability on acidic oxygen evolution reaction. Nano Res. 2024, 17, 5922–5929. [Google Scholar] [CrossRef]
  39. Huang, M.; Cao, C.; Liu, L.; Wei, W.; Zhu, Q.-L.; Huang, Z. Controlled synthesis of MOF-derived hollow and yolk–shell nanocages for improved water oxidation and selective ethylene glycol reformation. eScience 2023, 3, 2300321. [Google Scholar] [CrossRef]
  40. Li, Z.; Yao, Y.; Sun, S.; Liang, J.; Hong, S.; Zhang, H.; Yang, C.; Zhang, X.; Cai, Z.; Li, J.; et al. Carbon oxyanion self-transformation on NiFe oxalates enables long-term ampere-level current density seawater oxidation. Angew. Chem. Int. Ed. 2024, 63, e202316522. [Google Scholar] [CrossRef]
  41. Luo, X.; Zhao, H.; Tan, X.; Lin, S.; Yu, K.; Mu, X.; Tao, Z.; Ji, P.; Mu, S. Fe-S dually modulated adsorbate evolution and lattice oxygen compatible mechanism for water oxidation. Nat. Commun. 2024, 15, 8293. [Google Scholar] [CrossRef] [PubMed]
  42. Dong, J.; An, B.; Liu, W.; Su, H.; Li, N.; Gao, Y.; Ge, L. Cation-induced interface electric field redistribution and molecular orbital coupling in Co-FeS/MoS2 for boosting electrocatalytic overall water splitting. Chem. Eng. J. 2024, 498, 120122. [Google Scholar] [CrossRef]
  43. Kuang, Z.; Liu, S.; Li, X.; Wang, M.; Ren, X.; Ding, J.; Ge, R.; Zhou, W.; Rykov, A.I.; Sougrati, M.T.; et al. Topotactically constructed nickel–iron (oxy)hydroxide with abundant in-situ produced high-valent iron species for efficient water oxidation. J. Energy Chem. 2021, 57, 212–218. [Google Scholar] [CrossRef]
  44. Hunter, B.M.; Thompson, N.B.; Müller, A.M.; Rossman, G.R.; Hill, M.G.; Winkler, J.R.; Gray, H.B. Trapping an iron (VI) water-splitting intermediate in nonaqueous media. Joule 2018, 2, 747–763. [Google Scholar] [CrossRef]
  45. Chenakin, S.; Kruse, N. XPS characterization of transition metal oxalates. Appl. Surf. Sci. 2020, 515, 146041. [Google Scholar] [CrossRef]
  46. Chenakin, S.P.; Szukiewicz, R.; Barbosa, R.; Kruse, N. Surface analysis of transition metal oxalates: Damage aspects. J. Electron Spectrosc. Relat. Phenom. 2016, 209, 66–77. [Google Scholar] [CrossRef]
  47. Zhao, X.; Pattengale, B.; Fan, D.; Zou, Z.; Zhao, Y.; Du, J.; Huang, J.; Xu, C. Mixed-node metal–organic frameworks as efficient electrocatalysts for oxygen evolution reaction. ACS Energy Lett. 2018, 3, 2520–2526. [Google Scholar] [CrossRef]
  48. Zhuang, L.; Ge, L.; Yang, Y.; Li, M.; Jia, Y.; Yao, X.; Zhu, Z. Ultrathin iron-cobalt oxide nanosheets with abundant oxygen vacancies for the oxygen evolution reaction. Adv. Mater. 2017, 29, 1606793. [Google Scholar] [CrossRef]
  49. Li, J.; Zhou, Q.; Zhong, C.; Li, S.; Shen, Z.; Pu, J.; Liu, J.; Zhou, Y.; Zhang, H.; Ma, H. (Co/Fe)4O4 Cubane-containing nanorings fabricated by phosphorylating cobalt ferrite for highly efficient oxygen evolution reaction. ACS Catal. 2019, 9, 3878–3887. [Google Scholar] [CrossRef]
  50. Zhou, Y.; Sun, S.; Song, J.; Xi, S.; Chen, B.; Du, Y.; Fisher, A.C.; Chen, F.; Wang, X.; Zhang, H.; et al. Enlarged Co-O Covalency in octahedral sites leading to highly efficient spinel oxides for oxygen evolution reaction. Adv. Mater. 2018, 30, 1802912. [Google Scholar] [CrossRef]
  51. Bai, L.; Hsu, C.S.; Alexander, D.T.; Chen, H.M.; Hu, X. Double-atom catalysts as a molecular platform for heterogeneous oxygen evolution electrocatalysis. Nat. Energy 2021, 6, 1054–1066. [Google Scholar] [CrossRef]
  52. Hai, G.; Jia, X.; Zhang, K.; Liu, X.; Wu, Z.; Wang, G. High-performance oxygen evolution catalyst using two-dimensional ultrathin metal-organic frameworks nanosheets. Nano Energy 2018, 44, 345–352. [Google Scholar] [CrossRef]
  53. Liu, H.; Wang, Y.; Tan, P.; Dos Santos, E.C.; Holmes, S.M.; Li, H.; Pan, J.; D’Agostino, C. A Doping-induced SrCo(0.4)Fe(0.6)O3/CoFe2O4 nanocomposite for efficient oxygen evolution in alkaline media. Small 2024, 20, 2308948. [Google Scholar] [CrossRef] [PubMed]
  54. Huang, L.; Chen, D.; Luo, G.; Lu, Y.; Chen, C.; Zou, Y.; Dong, C.; Li, Y.; Wang, S. Zirconium-regulation-induced bifunctionality in 3D cobalt-iron oxide nanosheets for overall water splitting. Adv. Mater. 2019, 31, 1901439. [Google Scholar] [CrossRef] [PubMed]
  55. Zhang, S.; Guan, B.; Lu, X.; Xi, S.; Du, Y.; Lou, X. Metal atom-doped Co3O4 hierarchical nanoplates for electrocatalytic oxygen evolution. Adv. Mater. 2020, 32, 2002235. [Google Scholar] [CrossRef]
  56. Sun, J.; Xue, H.; Zhang, Y.; Zhang, X.; Guo, N.; Song, T.; Dong, H.; Kong, Y.; Zhang, J.; Wang, Q. Unraveling the synergistic effect of heteroatomic substitution and vacancy engineering in CoFe2O4 for superior electrocatalysis performance. Nano Lett. 2022, 22, 3503–3511. [Google Scholar] [CrossRef]
  57. Tsai, F.; Deng, Y.; Pao, C.; Chen, J.; Lee, J.; Lai, K.; Liaw, W. The HER/OER mechanistic study of an FeCoNi-based electrocatalyst for alkaline water splitting. J. Mater. Chem. A 2020, 8, 9939–9950. [Google Scholar] [CrossRef]
  58. Xin, S.; Tang, Y.; Jia, B.; Zhang, Z.; Li, C.; Bao, R.; Li, C.; Yi, J.; Wang, J.; Ma, T. Coupling adsorbed evolution and lattice oxygen mechanism in Fe-Co(OH)2/Fe2O3 heterostructure for enhanced electrochemical water oxidation. Adv. Funct. Mater. 2023, 33, 2305243. [Google Scholar] [CrossRef]
Catalysts 15 00011 g001
Figure 1. (a) Cyclic voltammograms, (b) zoomed cyclic voltammograms from panel a, (c) Tafel plots, and (d) electrochemical impedance Nyquist plots for Co, CoFe, Co-SBH, and CoFe-SBH measured in 1 M Fe-purified KOH electrolyte.
Figure 1. (a) Cyclic voltammograms, (b) zoomed cyclic voltammograms from panel a, (c) Tafel plots, and (d) electrochemical impedance Nyquist plots for Co, CoFe, Co-SBH, and CoFe-SBH measured in 1 M Fe-purified KOH electrolyte.
Catalysts 15 00011 g001
Catalysts 15 00011 g002
Figure 2. (a) Schematic diagram of the CoFe-SBH synthesis process. XRD patterns for (b) Co, Fe, and CoFe oxalates, and (c) Co-SBH, Fe-SBH, and CoFe-SBH. Raman spectra for (d) Co, Fe, and CoFe oxalates, and (e) Co-SBH, Fe-SBH, and CoFe-SBH.
Figure 2. (a) Schematic diagram of the CoFe-SBH synthesis process. XRD patterns for (b) Co, Fe, and CoFe oxalates, and (c) Co-SBH, Fe-SBH, and CoFe-SBH. Raman spectra for (d) Co, Fe, and CoFe oxalates, and (e) Co-SBH, Fe-SBH, and CoFe-SBH.
Catalysts 15 00011 g002
Catalysts 15 00011 g003
Figure 3. SEM images of (a) CoFe oxalate, (b) CoFe-SBH, and (c) CoFe-SBH after the CV test. (d) TEM, (e) SAED, (f) HRTEM, and (g) EDX elemental mapping images of CoFe-SBH after the CV test.
Figure 3. SEM images of (a) CoFe oxalate, (b) CoFe-SBH, and (c) CoFe-SBH after the CV test. (d) TEM, (e) SAED, (f) HRTEM, and (g) EDX elemental mapping images of CoFe-SBH after the CV test.
Catalysts 15 00011 g003
Catalysts 15 00011 g004
Figure 4. XPS spectra of (a) Co 2p over CoFe, CoFe-SBH, and Co-SBH, and (b) Fe 2p over CoFe, CoFe-SBH, and Fe-SBH.
Figure 4. XPS spectra of (a) Co 2p over CoFe, CoFe-SBH, and Co-SBH, and (b) Fe 2p over CoFe, CoFe-SBH, and Fe-SBH.
Catalysts 15 00011 g004
Catalysts 15 00011 g005
Figure 5. Cyclic voltammograms for (a) CoFe, CoFe-SBH, and CoFe-BO33−, and (b) the CoFe measured in 1 M purified KOH and the purified KOH containing 0.1 M K3BO3. The inserts show zoomed sections of CV ranging from 1.1 to 1.45 V vs. RHE.
Figure 5. Cyclic voltammograms for (a) CoFe, CoFe-SBH, and CoFe-BO33−, and (b) the CoFe measured in 1 M purified KOH and the purified KOH containing 0.1 M K3BO3. The inserts show zoomed sections of CV ranging from 1.1 to 1.45 V vs. RHE.
Catalysts 15 00011 g005
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Guo, W.; Wang, C.; Qiu, L.; Liu, F.; Chen, S.; Chang, H. Tuning Surface State in CoFe (Oxy)Hydroxide for Improved Oxygen Evolution Electrocatalysis. Catalysts 2025, 15, 11. https://doi.org/10.3390/catal15010011

AMA Style

Guo W, Wang C, Qiu L, Liu F, Chen S, Chang H. Tuning Surface State in CoFe (Oxy)Hydroxide for Improved Oxygen Evolution Electrocatalysis. Catalysts. 2025; 15(1):11. https://doi.org/10.3390/catal15010011

Chicago/Turabian Style

Guo, Wen, Chizhong Wang, Lei Qiu, Fanghua Liu, Sizhe Chen, and Huazhen Chang. 2025. "Tuning Surface State in CoFe (Oxy)Hydroxide for Improved Oxygen Evolution Electrocatalysis" Catalysts 15, no. 1: 11. https://doi.org/10.3390/catal15010011

APA Style

Guo, W., Wang, C., Qiu, L., Liu, F., Chen, S., & Chang, H. (2025). Tuning Surface State in CoFe (Oxy)Hydroxide for Improved Oxygen Evolution Electrocatalysis. Catalysts, 15(1), 11. https://doi.org/10.3390/catal15010011

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop