P-doped NiCo LDH loaded three-dimensional substrate as an efficient oxygen evolution electrocatalyst

P-doped NiCo LDH loaded three-dimensional substrate as an efficient oxygen evolution electrocatalyst | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article P-doped NiCo LDH loaded three-dimensional substrate as an efficient oxygen evolution electrocatalyst Jingchun Zhang, Erin Weatherspoon, Abdullah Saad Alsubaie, Ethan Burcar, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4732453/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 22 Dec, 2024 Read the published version in Advanced Composites and Hybrid Materials → Version 1 posted 9 You are reading this latest preprint version Abstract Developing new clean energy sources and equipment to replace fossil fuel usage is an urgent global priority. However, one such essential method, electrolytic water hydrogen production's characteristics of slow kinetics and high potential barrier of the anodic oxygen evolution reaction (OER) hinder the large-scale application of such an approach. While precious metal catalysts have shown excellent catalytic activity, their high cost limits their feasibility for large-scale implementation. As a result, the development of stable and low-cost oxygen evolution reaction catalysts is critical. Transition metal layered hydroxides (TM LDHs) have been widely studied as a promising candidate for water electrolysis catalysis for their unique two-dimensional layered structure, high specific surface area, great electron exchangeability, and densely distributed active sites. Here in this research, we have synthesized nickel cobalt phosphide LDH (P-NiCo-LDH) that maximizes the utilization of foam nickel as the conductive substrate while protecting the phosphated LDH. This work proposes a practical approach for developing LDH as an OER catalyst and contributes to the ongoing efforts to advance sustainable clean energy sources. Oxygen evolution reaction layered double hydroxide Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1. Introduction The rapid decrease in nonrenewable energy sources is an inevitable outcome led by energy overconsumption, often accompanied by the production of greenhouse gases and various other harmful gases, creating environmental pollution [ 1 , 2 ] . Searching for an alternative yet clean energy source, scientists have turned their attention to hydrogen [ 3 ] . However, electrocatalytic water splitting OER is a slow dynamic process, consisting of several proton-coupled electron transfer stages, significantly reducing the overall efficiency of electrochemical water splitting [ 4 , 5 ] . Through continuous scientific exploration, a considerable quantity of renewable energy has been discovered and implemented to use. Among them, hydrogen is the cleanest and most efficient renewable energy source, reigning supremacy in fuel cells [ 6 ] . While electrolysis of water is the simplest and cleanest method for hydrogen production, its essential half-reaction OER has quite a slow kinetic process for dividing the electron transfer into multiple stages, reducing the overall efficiency of water decomposition. To enhance OER performance, multiple types of catalysts have been developed to overcome the energy barriers. Although precious metal catalysts have proven to be highly effective, their high cost restricts their mass usage in various industries. Consequently, the primary objective is to create a catalyst that is both cost-effective and efficient for the electrolysis water sector [ 7 , 8 ] . In response, nonprecious metal catalysts display great potential in water electrolysis, where the oxygen evolution performance can be improved by doping different heteroatoms or making structural changes [ 9 , 10 , 11 ] . In recent years, nonprecious metal catalysts have made a qualitative leap in development, but further research and enhancements are still needed [ 12 ] . Transition metal layered hydroxides (TM LDHs) have been widely studied in water electrolysis catalysis due to their unique two-dimensional layered structure, high specific surface area, great electron exchangeability, and densely distributed active sites [ 13 , 14 , 15 , 16 ] . However, the poor conductivity and weak hydrogen adsorption energy of LDHs limit their overall electrocatalytic performance [ 17 , 18 ] . In recent studies, electronic structure optimization and defect engineering have been introduced as effective strategies to improve the water-splitting performance of LDHs, stemming from the significant efforts made in transition metal-based or heteroatom doping to alter the electronic structure of LDHs effectively. The presence of cationic defects on the surface of transition metal oxides/hydroxides can control the electronic surface configuration of catalysts, leading to a significant enhancement in electrocatalytic activity [ 19 ] . In addition, anionic defects can also regulate the energy of metal species that occupy the highest d-state in transition metal oxides/hydroxides and affect the filling level of metal-oxygen binding anti-bond states, thereby influencing the adsorption performance and surface reactivity of catalysts [ 20 , 21 ] . Thus, incorporating cation and anion defects is crucial in enhancing the intrinsic catalytic activity of existing active sites in LDHs for OER. This leads to the creation of more active sites, thereby improving the overall efficiency of the process. To begin with, Deng et al. demonstrated a simple one-step rapid synthesis strategy for preparing NiFe LDH nanosheet electrodes as OER electrocatalysts. The microscopic observation shows that it is constant in the morphology of interconnected nanosheets uniformly grown after Mo doping. Molybdenum-doped NiFe LDH exhibited excellent catalytic activity towards OER in both ectopic half-cell and in situ laboratory scale alkaline water electrolysis single-cell tests. This work proposes a promising approach to advance open educational resources and enhance the efficiency of water decomposition, which can facilitate the development of sustainable and clean energy technologies for commercial applications [ 22 ] . Moreover, Huang et al. successfully synthesized a novel Fe Ni-layered double hydroxide (LDH) material with a homogeneous heterostructure using a two-step hydrothermal method. Compared to the Fe Ni LDH array prepared in one step, this structure has a rougher surface, resulting in a larger active region that provides more active sites. Due to the synergistic effect of various elements and a higher exposure to active sites, this material exhibits exceptional catalytic activity for the decomposition of water [ 23 ] . Further, A simple, efficient, and environmentally friendly electrochemical reduction approach was proposed by Wei et al. to introduce oxygen vacancies into NiFe LDH by providing an external current to electrons. The addition of oxygen vacancies can regulate catalysts' electronic structure, alter reaction intermediate adsorption, and influence the metal ions' valence state, significantly improving OER activity [ 24 ] . Likewise, Zhao et al. developed a simple strategy to prepare three-dimensional composite materials π of NiFeCo LDH nanosheets with curled edges on CF. Therefore, the Ni3d O2p and Co3d O2p covalencies of NiFeCo LDH catalysts are strong, which can greatly change their electronic structure and improve OER activity. In addition, by utilizing ZIF-67/CF, the curled nanosheets of NiFeCo LDH on carbon fibers can expose their active sites by reducing the thickness and increasing the specific surface area. In detail, during the electrocatalytic OER process, the conductive tubular curly structure combined with CF ensures sufficient electron supply to NiFeCo LDH/CF. The obtained NiFeCo LDH/CF exhibits better OER performance than the previous benchmark NiFe LDH in alkaline electrolytes [ 25 ] . Among the reported LDHs, Ni-based LDHs have relatively high conductivity, thus exhibiting efficient catalytic activity [ 26 , 27 ] . Co ions reduces nanosheet thickness, increases specific surface area, and exposes more active sites, resulting in excellent electrocatalytic activity [ 28 ] . On top of that, Co 2+ can not only improve conductivity but also enhance catalytic activity by altering the electronic structure of the substrate material. Doping with heteroatoms is a matter of great concern. This is because multiple elements can be selected to be incorporated into the lattice of the host material. This means that the physicochemical properties of the original LDHs can be regulated over a wide range and may be optimized at some point. An effective alternative method is to introduce the non-metallic element P, which can lead to the adjustment of electronic structure, an increase of conductivity, and the promotion of exposure to active sites [ 29 , 30 ] . Therefore, doping with heteroatoms optimized the adsorption energy of H and the binding energy between OER intermediates and electrocatalysts, ultimately improving the catalytic activity of OER [ 31 , 32 ] . Here, we report that P-doped NiCo LDH nanosheets were grown on foam nickel using hydrothermal method and calcination (Fig. 1 ). Compared with NiCo LDH, phosphorus doping provides more exposure to coordination or unsaturated surface atoms, thus generating many catalytic active sites, promoting the adsorption of O-containing intermediates, and reducing the activation barrier in the OER process. This study aims to advance the use of LDH structural materials in OER electrocatalysis applications. 2. Experimental Section 2.1 Materials and chemicals Ni-foam (NF) with 1mm thickness produced by Kunshan Baiyida; \(\:\text{N}\text{i}\left(\text{N}\text{O}3\right)2\cdot\:6\text{H}2\text{O}\left(\text{A}\text{R}\right)\) ; \(\:\text{C}\text{o}\left(\text{N}\text{O}3\right)2\cdot\:6\text{H}2\text{O}\left(\text{A}\text{R}\right)\) ; CTAB; Potassium; Hydroxide (KOH) 95% Purchased from Energy Chemical, note that all chemicals are not further purified. Deionized water is used throughout the experiments. 2.2 Preparation of NiCo-LDH/NF Ni foam (CF) (2 cm×3 cm) is ultrasonically cleaned for 15 minutes with 3M HCl, deionized water, and ethanol, respectively, and then dried in a vacuum oven at 60°C for 6 hours.2.25 mmol \(\:\text{N}\text{i}\left(\text{N}\text{O}3\right)26\text{H}2\text{O}\) , 0.75 mmol \(\:\text{C}\text{o}\left(\text{N}\text{O}3\right)26\text{H}2\text{O}\) and 1g CTAB are dissolved in a mixture of methanol (60 mL) and deionized water (12 mL) and stirred to form a clear solution. A piece of NF (2 cm×3 cm) is placed into the above solution and transferred to a 50 ml stainless steel autoclave lined with PTFE. It is sealed and held at 180°C for 24 h. The NF-loaded NiCo-LDH is obtained by washing with deionized water and ethanol several times and oven-dried at 60°C for 12 h. 2.3 Preparation of P-NiCo-LDH/NF NiCo-LDH/NF and NaH 2 PO 2 (300 mg) are placed at different positions in a porcelain boat with a lid. They are heated at 300°C for 1 h in a nitrogen atmosphere with a temperature increase rate of 2°C min − 1 and hold for 2 h. The powder is then heated at 300°C for 1 h in a nitrogen atmosphere. P-NiCo-LDH/NF black lumps are obtained after heat treatment. For comparison, P-NF is prepared under the same conditions as NF only. 2.4 Materials characterization The samples' morphology is determined using a scanning electron microscope (SEM, Hitachi Regulus8100) and transmission electron microscopy (TEM, JEOL JEM 2100F). X-ray photoelectron spectroscopy (XPS) is carried out on an XPS-7000 spectrometer (Rigaku) using Mg K radiation. The crystal structures of the materials are investigated using an X-ray diffractometer (XRD, B X'Pert PRO MPD). 2.5 Electrochemical measurements Electrochemical tests are conducted using a three-electrode system on an electrochemical workstation (Ivium N22234, Holland) with a 1M KOH electrolyte solution. The working electrode is a 0.25 cm-2 electrocatalyst electrode, the auxiliary electrode is a platinum sheet, and the reference electrode is a Hg/HgO electrode. The potential transformations are calculated using the Nernst equation. $${\text{ERHE}}={\text{EHg/HgO+}}{{\text{E}}^{\text{@}}}{\text{Hg/HgO}}+0.059{\rm P}{\text{H}}$$ 1.1 Where E Hg/HgO is the potential of Hg/HgO for the test with the reference electrode, VE Hg/HgO is the standard electrode potential for the Hg/HgO reference electrode, and its value is 0.098 V; The acid-base value of the test solution is represented by pH. The following equations are used to figure out the overpotentials: $$\eta {\rm O}{\rm E}{\text{R}}={\rm E}{\text{RHE}} - 1.23$$ 1.2 \(\eta {\rm H}{\rm E}{\text{R}}={\rm E}{\text{RHE}}\) (1.3) Not all curves are compensated by the IR potential. Tafel equation: $$\eta ={\text{a+b lg(j)}}$$ 1.4 Where η, a, b and j denote the overpotential, Tafel constant, Tafel slope and current density, respectively, the Tafel plot is obtained by plotting the logarithm of the current density lg(j) against the overpotential (η) through the polarization curve, and the Tafel slope is obtained by fitting the linear part of the Tafel plot. Given that the Tafel slope is inversely proportional to the charge transfer coefficient, it can be used as one of the indicating parameters for evaluating the electrocatalyst performance. At a scan rate of 5 mV/s, linear scanning voltammetry (LSV) is carried out. In the frequency range from 10 6 to 0.01 Hz, electrochemical impedance spectroscopy (EIS) is performed. CV can measure electrochemical double-layer capacitance (C dl ) within the range of -0.30 V to -0.40 V at scan rates of 10, 20, 30, 40, and 50 mV/s. All experiments are repeated at least three times to ensure reproducibility. 3. Results and discussions P-NiCo-LDH was prepared by hydrothermal and high-temperature phosphating. The SEM characterization of the scanning electron microscope showed that a uniform P-NiCo-LDH ultra-thin nanosheet array was successfully formed on the surface of NF, with rougher and defect-rich surfaces (Figs. 2 a. and 2b.). After high-temperature phosphating in N 2 atmosphere, the obtained P-NiCo-LDH material maintained the shape of the nanosheet array and was slightly contracted and indented [ 33 ] . Scanning electron microscopy (SEM) showed good dispersion and monodisperse P nanoparticles could be found on the surface of two-dimensional ultra-thin nanosheets (Fig. 2 c. and 2d.). The TEM images (Fig. 2 e. and 2f.) clearly show that P-NiCo LDH has many vacancies and generates numerous active sites during oxygen evolution reactions and there are lattice stripes of 0.51 nm from the nuclear NPs plane on the (100) plane of Ni. Energy dispersive X-ray spectroscopy (EDS) was used to clarify the composition distribution of P-NiCo-LDH. The EDS element mapping image proved that the P-NPs EDS diagram was successfully introduced into NiCo-LDH to show the uniform distribution of Ni, Co, P elements (Fig. 2 g.). Figure 3 a. shows the XRD patterns of NF, NiCo-LDH/NF and P-NiCo-LDH/NF. By observation, the obtained P-NiCo-LDH/NF diffraction peaks completely overlapped with Ni2P (PDF#00-003-0953). Therefore, the characteristic peaks at 40.797, 44.6, 47.306, 54.232, 54.936, 72.674, 74.678, and 80.924 can be attributed to (111), (201), (210), (300), (211), (311), (400), and (622) and of Ni 2 P (PDF#00-003-0953) and (401) crystal faces. To further characterize the elemental states on the NiCo LDH/NF surface, X-ray photoelectron spectroscopy (XPS) measurements were carried out, as shown in Fig. 3 c., the 2p 1/2 and Co 2 p 3/2 of Co 2+ were located at 785.58eV and 776.88eV, respectively, while the 2p 1/2 and 2p 3/2 of Co 3+ were located at 797.78eV and 781.38eVe, it was observed that the peak of NiCo LDH-P/NF after phosphating shifted to the left, and satellite peaks appeared, indicating that electron interaction occurred after phosphating, which may be due to the addition of P with lower electronegativity [ 34 , 35 ] . The XPS of Ni 2 P is shown in Fig. 3 b., where the 2p 1/2 and 2p 3/2 of Ni 2+ in NiCo LDH/NF are located at 874.18eV and 851.78eV while the 2p 1/2 and 2p 3/2 of Ni 2+ are located at 879.08eV and 856.08eV separately. A satellite peak appears at 860.78eV, and after phosphating, the peaks shift to the right and decrease, indicating that electrons are moving toward the Ni element [ 36 , 37 ] . The P 2p of P-NiCo-LDH/NF, as shown in Fig. 3 c., shows a peak at 134.08 eV, belonging to P-O. The 2p 1/2 peak is at 130.18 eV, and the 2p 3/2 peak is at 129.18 eV, indicating the successful phosphorylation of NiCo-LDH/NF and the oxidation of P on the surface [ 38 ] . The electrocatalytic activity of OER was characterized by LSV curve data in an electrolyte of 1.0 M KOH, as shown in Fig. 4 .. The resulting LSV curve is shown in Fig. 4 a., where the current density is close to zero at the beginning and gradually increases as the overpotential is higher than about 20 mV. To compare the overpotential of all samples at 10 mA cm − 2 , we plotted the histogram in Fig. 4 e. The results exhibited that the overpotential of P-NiCo-LDH/NF was the lowest (290 mV), which was much lower than that of NiCo-LDH (310 mV) and NF (436 mV). This enhanced OER activity has surpassed partial existing catalyst performance. The OER activity of P-NiCo-LDH/NF showed that phosphorylation played an important role in exposing more active sites to NiCo-LDH. As can be seen from the C dl in Fig. 4 e. in the data, the Cdl value of P-NiCo-LDH/NF treatment was the highest at 4.2 mF cm − 2 , which was higher than that of NiCo-LDH/NF (1.21 mF cm − 2 ) and NF (1.15 mF cm − 2 ). The Tafel plots in Fig. 4 b. showed that the lowest slope of P-NiCo-LDH/NF treatment is 55.05 mV dec − 1 , which is smaller than that of NiCo-LDH/NF (74.27 mV dec − 1 ) and NF (178.37 mV dec − 1 ), indicating that it has qualified OER kinetics. The EIS spectra in Fig. 4 c. also showed that the P-NiCo-LDH/NF treatment had the lowest Rct of 7 Ω and showed excellent kinetics while maintaining stability for up to 72 hours at 1.524V.RHE (Fig. 4 f.). To investigate the relationship between structural changes and performance, the SEM and XPS analysis after oxygen evolution testing. From the SEM image (Fig. 5 a.), the surface is uneven compared to the initial sheet-like structure, and the active sites on the surface are fully utilized during the oxygen evolution reaction. The XPS of P-NiCo-LDH/NF after OER is shown in Fig. 5 .. Apart from the P element (Fig. 5 d.), the peaks of Ni and Co undergo significant changes from those before OER, mainly due to the formation of NiOOH and CoOOH during the OER process (Fig. 5 b. and 5c.) [ 39 ] . The addition of P exposes more active sites, thereby improving its performance [ 40 ] . 4. Conclusions In summary, we use foam nickel as the substrate to synthesize nickel cobalt LDH (NiCo LDH) in an alkaline environment by hydrothermal method and finally form nickel cobalt phosphide LDH (P-NiCo-LDH) by high-temperature annealing in nitrogen atmosphere. The prepared LDH has a 290mV overpotential at 10mA cm − 2 and exhibits good electrocatalytic activity towards OER. It is stable for 72 hours under 1mol L − 1 KOH conditions. The excellent electrocatalytic performance is mainly attributed to the numerous LDH active sites on its three-dimensional substrate and the synergistic effect of heteroatom P doping on porous materials. Overall, this study proposes an effective idea for the advancement of OER catalysts. Declarations Author contribution: Jingchun Zhang and Zhe Wang designed this project and contributed to the main manuscript text. Jingchun Zhang conducted experiments. Erin Witherspoon, Ethan Burcar, Abdullah Saad Alsubaie, Ashley DeMerle and Zeinhom M. El-Bahy have contributed to conducting the experiments, preparing figures, and writing. All authors reviewed the manuscript. Funding: The authors extend their appreciation to Taif University, Saudi Arabia, for supporting this work through project number (TU-DSPP-2024-106). ZW would like to acknowledge the support from NSF 2344344 and NIJ 15PNIJ-23-GG-04225-RESS. 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Cite Share Download PDF Status: Published Journal Publication published 22 Dec, 2024 Read the published version in Advanced Composites and Hybrid Materials → Version 1 posted Editorial decision: Revision requested 18 Aug, 2024 Reviews received at journal 18 Aug, 2024 Reviews received at journal 17 Aug, 2024 Reviewers agreed at journal 10 Aug, 2024 Reviewers agreed at journal 09 Aug, 2024 Reviewers invited by journal 09 Aug, 2024 Editor assigned by journal 06 Aug, 2024 Submission checks completed at journal 01 Aug, 2024 First submitted to journal 12 Jul, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4732453","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":341609634,"identity":"a49cc6b1-4458-41a7-bb15-4d8cde2c1d95","order_by":0,"name":"Jingchun Zhang","email":"","orcid":"","institution":"University of California at Davis","correspondingAuthor":false,"prefix":"","firstName":"Jingchun","middleName":"","lastName":"Zhang","suffix":""},{"id":341609635,"identity":"541b4c19-c798-43d6-91cf-2c5f3c70f60e","order_by":1,"name":"Erin Weatherspoon","email":"","orcid":"","institution":"Oakland University","correspondingAuthor":false,"prefix":"","firstName":"Erin","middleName":"","lastName":"Weatherspoon","suffix":""},{"id":341609636,"identity":"2f04bc3e-87c7-40da-a911-cc2a56ea75a7","order_by":2,"name":"Abdullah Saad Alsubaie","email":"","orcid":"","institution":"Taif University","correspondingAuthor":false,"prefix":"","firstName":"Abdullah","middleName":"Saad","lastName":"Alsubaie","suffix":""},{"id":341609637,"identity":"44c2b6ef-b3a7-4aa0-8b9c-fb3f542948d7","order_by":3,"name":"Ethan Burcar","email":"","orcid":"","institution":"Oakland University","correspondingAuthor":false,"prefix":"","firstName":"Ethan","middleName":"","lastName":"Burcar","suffix":""},{"id":341609638,"identity":"c9a39315-0384-41e9-a9fb-5bcf5dd49028","order_by":4,"name":"Ashley DeMerle","email":"","orcid":"","institution":"Oakland University","correspondingAuthor":false,"prefix":"","firstName":"Ashley","middleName":"","lastName":"DeMerle","suffix":""},{"id":341609640,"identity":"3f06d236-3a3f-40be-a824-57df22b32c67","order_by":5,"name":"Zeinhom M. El-Bahy","email":"","orcid":"","institution":"Al-Azhar University","correspondingAuthor":false,"prefix":"","firstName":"Zeinhom","middleName":"M.","lastName":"El-Bahy","suffix":""},{"id":341609641,"identity":"043cd255-0fc2-492b-b5ab-7a4ee93065da","order_by":6,"name":"Zhe Wang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA5ElEQVRIiWNgGAWjYDACCQglx8DAxniAgYEZyE4gTosxUAsDaVoSG4jWIj+7+ZjEzx216f3sxxIO/NxhzcDPnmOAVwvjnGNpkr1njufO7Ek7cLD3TDqDZM8b/FqYJXLMbvC2HcvdcCC94QBv22EGgxsEbGGTyP9282/bsXSD888bDv4FarEnpIVHIoftNm9bTYLBjbQDh8G2SBDQIiGRZv5btu2A4cwZzxIOy7al80iceVaAV4v8jOTHhm/b6uT5+dMMH75ts5bjb0/egFcLFBxGuJQY5SBQR6zCUTAKRsEoGIkAAI2GS9xm4iXdAAAAAElFTkSuQmCC","orcid":"","institution":"Oakland University","correspondingAuthor":true,"prefix":"","firstName":"Zhe","middleName":"","lastName":"Wang","suffix":""}],"badges":[],"createdAt":"2024-07-12 20:01:46","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4732453/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4732453/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s42114-024-01164-2","type":"published","date":"2024-12-22T15:57:53+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":63463241,"identity":"b5c6ce79-153a-44f3-8181-6fdba8048e57","added_by":"auto","created_at":"2024-08-28 11:53:57","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":72184,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of P-NiCo-LDH/NF synthesis.\u003c/p\u003e","description":"","filename":"floatimage1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4732453/v1/14ea4415ba9db41fae89c2f0.jpg"},{"id":63463243,"identity":"81bd4f5f-4d2e-471e-981c-a22fd95b85db","added_by":"auto","created_at":"2024-08-28 11:53:57","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1438573,"visible":true,"origin":"","legend":"\u003cp\u003e(a, b) SEM images of NiCo-LDH at different multiples. (c, d) SEM images of P-NiCo-LDH at different multiples. (e, f) TEM images of P-NiCo-LDH at different multiples. (g) Distribution map of Ni, Co, and P elements in P-NiCo LDH.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-4732453/v1/3c3e0acc2796fae12c9ebbdc.png"},{"id":63463245,"identity":"be09a5c7-aae6-4164-bef3-06749570ef21","added_by":"auto","created_at":"2024-08-28 11:53:57","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":335464,"visible":true,"origin":"","legend":"\u003cp\u003e(a)P-NiCo-LDH/NF XRD pattern. XPS measurement spectrum(b) Ni 2p; (c) Co 2p; (d) P 2p.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-4732453/v1/28083c53b8768174935c44ce.png"},{"id":63463246,"identity":"dc5fbdc2-f2ad-4980-9b53-adb23cd65eda","added_by":"auto","created_at":"2024-08-28 11:53:57","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":180070,"visible":true,"origin":"","legend":"\u003cp\u003e(a) LSV curves of P-NiCo LDH/NF, NiCo LDH/NF, NF.(b) Tafel slope plots for different samples. (c) EIS diagram under the same voltage.(d) Overpotential bar charts of P-NiCo LDH/NF, NiCo LDH/NF, NF.(e) C\u003csub\u003edl\u003c/sub\u003e of P-NiCo LDH/NF, NiCo LDH/NF, NF.(f) 72-hour stability test chart.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-4732453/v1/547507182e6069d3eae6ece8.png"},{"id":63463242,"identity":"68930b86-0cca-4d87-b2be-5b7e86a42167","added_by":"auto","created_at":"2024-08-28 11:53:57","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":274144,"visible":true,"origin":"","legend":"\u003cp\u003e(a) SEM spectra after OER. (b) XPS measurement spectrum of Ni\u003csup\u003e2+\u003c/sup\u003e; (c) XPS measurement spectrum of Co\u003csup\u003e2+\u003c/sup\u003e; (d) XPS measurement spectrum of P.\u003c/p\u003e","description":"","filename":"floatimage5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4732453/v1/6032fe0f88b6d102e844cd11.jpg"},{"id":72201857,"identity":"e2e6201b-87ff-4e26-8699-6799eb5f0b86","added_by":"auto","created_at":"2024-12-23 16:11:17","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2632821,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4732453/v1/47f1840a-d2fe-43b5-ba22-62d061ebf977.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"P-doped NiCo LDH loaded three-dimensional substrate as an efficient oxygen evolution electrocatalyst","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe rapid decrease in nonrenewable energy sources is an inevitable outcome led by energy overconsumption, often accompanied by the production of greenhouse gases and various other harmful gases, creating environmental pollution \u003csup\u003e[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/sup\u003e. Searching for an alternative yet clean energy source, scientists have turned their attention to hydrogen \u003csup\u003e[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]\u003c/sup\u003e. However, electrocatalytic water splitting OER is a slow dynamic process, consisting of several proton-coupled electron transfer stages, significantly reducing the overall efficiency of electrochemical water splitting \u003csup\u003e[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThrough continuous scientific exploration, a considerable quantity of renewable energy has been discovered and implemented to use. Among them, hydrogen is the cleanest and most efficient renewable energy source, reigning supremacy in fuel cells \u003csup\u003e[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]\u003c/sup\u003e. While electrolysis of water is the simplest and cleanest method for hydrogen production, its essential half-reaction OER has quite a slow kinetic process for dividing the electron transfer into multiple stages, reducing the overall efficiency of water decomposition. To enhance OER performance, multiple types of catalysts have been developed to overcome the energy barriers. Although precious metal catalysts have proven to be highly effective, their high cost restricts their mass usage in various industries. Consequently, the primary objective is to create a catalyst that is both cost-effective and efficient for the electrolysis water sector \u003csup\u003e[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]\u003c/sup\u003e. In response, nonprecious metal catalysts display great potential in water electrolysis, where the oxygen evolution performance can be improved by doping different heteroatoms or making structural changes \u003csup\u003e[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e. In recent years, nonprecious metal catalysts have made a qualitative leap in development, but further research and enhancements are still needed \u003csup\u003e[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eTransition metal layered hydroxides (TM LDHs) have been widely studied in water electrolysis catalysis due to their unique two-dimensional layered structure, high specific surface area, great electron exchangeability, and densely distributed active sites \u003csup\u003e[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e. However, the poor conductivity and weak hydrogen adsorption energy of LDHs limit their overall electrocatalytic performance \u003csup\u003e[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/sup\u003e. In recent studies, electronic structure optimization and defect engineering have been introduced as effective strategies to improve the water-splitting performance of LDHs, stemming from the significant efforts made in transition metal-based or heteroatom doping to alter the electronic structure of LDHs effectively. The presence of cationic defects on the surface of transition metal oxides/hydroxides can control the electronic surface configuration of catalysts, leading to a significant enhancement in electrocatalytic activity \u003csup\u003e[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e. In addition, anionic defects can also regulate the energy of metal species that occupy the highest d-state in transition metal oxides/hydroxides and affect the filling level of metal-oxygen binding anti-bond states, thereby influencing the adsorption performance and surface reactivity of catalysts \u003csup\u003e[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]\u003c/sup\u003e. Thus, incorporating cation and anion defects is crucial in enhancing the intrinsic catalytic activity of existing active sites in LDHs for OER. This leads to the creation of more active sites, thereby improving the overall efficiency of the process.\u003c/p\u003e \u003cp\u003eTo begin with, Deng et al. demonstrated a simple one-step rapid synthesis strategy for preparing NiFe LDH nanosheet electrodes as OER electrocatalysts. The microscopic observation shows that it is constant in the morphology of interconnected nanosheets uniformly grown after Mo doping. Molybdenum-doped NiFe LDH exhibited excellent catalytic activity towards OER in both ectopic half-cell and in situ laboratory scale alkaline water electrolysis single-cell tests. This work proposes a promising approach to advance open educational resources and enhance the efficiency of water decomposition, which can facilitate the development of sustainable and clean energy technologies for commercial applications \u003csup\u003e[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]\u003c/sup\u003e. Moreover, Huang et al. successfully synthesized a novel Fe Ni-layered double hydroxide (LDH) material with a homogeneous heterostructure using a two-step hydrothermal method. Compared to the Fe Ni LDH array prepared in one step, this structure has a rougher surface, resulting in a larger active region that provides more active sites. Due to the synergistic effect of various elements and a higher exposure to active sites, this material exhibits exceptional catalytic activity for the decomposition of water \u003csup\u003e[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]\u003c/sup\u003e. Further, A simple, efficient, and environmentally friendly electrochemical reduction approach was proposed by Wei et al. to introduce oxygen vacancies into NiFe LDH by providing an external current to electrons. The addition of oxygen vacancies can regulate catalysts' electronic structure, alter reaction intermediate adsorption, and influence the metal ions' valence state, significantly improving OER activity \u003csup\u003e[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]\u003c/sup\u003e. Likewise, Zhao et al. developed a simple strategy to prepare three-dimensional composite materials π of NiFeCo LDH nanosheets with curled edges on CF. Therefore, the Ni3d O2p and Co3d O2p covalencies of NiFeCo LDH catalysts are strong, which can greatly change their electronic structure and improve OER activity. In addition, by utilizing ZIF-67/CF, the curled nanosheets of NiFeCo LDH on carbon fibers can expose their active sites by reducing the thickness and increasing the specific surface area. In detail, during the electrocatalytic OER process, the conductive tubular curly structure combined with CF ensures sufficient electron supply to NiFeCo LDH/CF. The obtained NiFeCo LDH/CF exhibits better OER performance than the previous benchmark NiFe LDH in alkaline electrolytes \u003csup\u003e[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eAmong the reported LDHs, Ni-based LDHs have relatively high conductivity, thus exhibiting efficient catalytic activity \u003csup\u003e[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]\u003c/sup\u003e. Co ions reduces nanosheet thickness, increases specific surface area, and exposes more active sites, resulting in excellent electrocatalytic activity \u003csup\u003e[\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]\u003c/sup\u003e. On top of that, Co\u003csup\u003e2+\u003c/sup\u003ecan not only improve conductivity but also enhance catalytic activity by altering the electronic structure of the substrate material. Doping with heteroatoms is a matter of great concern. This is because multiple elements can be selected to be incorporated into the lattice of the host material. This means that the physicochemical properties of the original LDHs can be regulated over a wide range and may be optimized at some point. An effective alternative method is to introduce the non-metallic element P, which can lead to the adjustment of electronic structure, an increase of conductivity, and the promotion of exposure to active sites \u003csup\u003e[\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]\u003c/sup\u003e. Therefore, doping with heteroatoms optimized the adsorption energy of H and the binding energy between OER intermediates and electrocatalysts, ultimately improving the catalytic activity of OER \u003csup\u003e[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eHere, we report that P-doped NiCo LDH nanosheets were grown on foam nickel using hydrothermal method and calcination (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Compared with NiCo LDH, phosphorus doping provides more exposure to coordination or unsaturated surface atoms, thus generating many catalytic active sites, promoting the adsorption of O-containing intermediates, and reducing the activation barrier in the OER process. This study aims to advance the use of LDH structural materials in OER electrocatalysis applications.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"2. Experimental Section","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials and chemicals\u003c/h2\u003e \u003cp\u003eNi-foam (NF) with 1mm thickness produced by Kunshan Baiyida; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{N}\\text{i}\\left(\\text{N}\\text{O}3\\right)2\\cdot\\:6\\text{H}2\\text{O}\\left(\\text{A}\\text{R}\\right)\\)\u003c/span\u003e\u003c/span\u003e; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{C}\\text{o}\\left(\\text{N}\\text{O}3\\right)2\\cdot\\:6\\text{H}2\\text{O}\\left(\\text{A}\\text{R}\\right)\\)\u003c/span\u003e\u003c/span\u003e; CTAB; Potassium; Hydroxide (KOH) 95% Purchased from Energy Chemical, note that all chemicals are not further purified. Deionized water is used throughout the experiments.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Preparation of NiCo-LDH/NF\u003c/h2\u003e \u003cp\u003eNi foam (CF) (2 cm\u0026times;3 cm) is ultrasonically cleaned for 15 minutes with 3M HCl, deionized water, and ethanol, respectively, and then dried in a vacuum oven at 60\u0026deg;C for 6 hours.2.25 mmol \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{N}\\text{i}\\left(\\text{N}\\text{O}3\\right)26\\text{H}2\\text{O}\\)\u003c/span\u003e\u003c/span\u003e, 0.75 mmol \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{C}\\text{o}\\left(\\text{N}\\text{O}3\\right)26\\text{H}2\\text{O}\\)\u003c/span\u003e\u003c/span\u003e and 1g CTAB are dissolved in a mixture of methanol (60 mL) and deionized water (12 mL) and stirred to form a clear solution. A piece of NF (2 cm\u0026times;3 cm) is placed into the above solution and transferred to a 50 ml stainless steel autoclave lined with PTFE. It is sealed and held at 180\u0026deg;C for 24 h. The NF-loaded NiCo-LDH is obtained by washing with deionized water and ethanol several times and oven-dried at 60\u0026deg;C for 12 h.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Preparation of P-NiCo-LDH/NF\u003c/h2\u003e \u003cp\u003eNiCo-LDH/NF and NaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e2\u003c/sub\u003e (300 mg) are placed at different positions in a porcelain boat with a lid. They are heated at 300\u0026deg;C for 1 h in a nitrogen atmosphere with a temperature increase rate of 2\u0026deg;C min \u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and hold for 2 h. The powder is then heated at 300\u0026deg;C for 1 h in a nitrogen atmosphere. P-NiCo-LDH/NF black lumps are obtained after heat treatment. For comparison, P-NF is prepared under the same conditions as NF only.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Materials characterization\u003c/h2\u003e \u003cp\u003eThe samples' morphology is determined using a scanning electron microscope (SEM, Hitachi Regulus8100) and transmission electron microscopy (TEM, JEOL JEM 2100F). X-ray photoelectron spectroscopy (XPS) is carried out on an XPS-7000 spectrometer (Rigaku) using Mg K radiation. The crystal structures of the materials are investigated using an X-ray diffractometer (XRD, B X'Pert PRO MPD).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Electrochemical measurements\u003c/h2\u003e \u003cp\u003eElectrochemical tests are conducted using a three-electrode system on an electrochemical workstation (Ivium N22234, Holland) with a 1M KOH electrolyte solution. The working electrode is a 0.25 cm-2 electrocatalyst electrode, the auxiliary electrode is a platinum sheet, and the reference electrode is a Hg/HgO electrode. The potential transformations are calculated using the Nernst equation.\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$${\\text{ERHE}}={\\text{EHg/HgO+}}{{\\text{E}}^{\\text{@}}}{\\text{Hg/HgO}}+0.059{\\rm P}{\\text{H}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1.1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere E\u003csub\u003eHg/HgO\u003c/sub\u003e is the potential of Hg/HgO for the test with the reference electrode, VE\u003csub\u003eHg/HgO\u003c/sub\u003e is the standard electrode potential for the Hg/HgO reference electrode, and its value is 0.098 V; The acid-base value of the test solution is represented by pH.\u003c/p\u003e \u003cp\u003eThe following equations are used to figure out the overpotentials:\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\eta {\\rm O}{\\rm E}{\\text{R}}={\\rm E}{\\text{RHE}} - 1.23$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1.2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\eta {\\rm H}{\\rm E}{\\text{R}}={\\rm E}{\\text{RHE}}\\)\u003c/span\u003e \u003c/span\u003e (1.3) \u003cspan class=\"InlineEquation\"\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003eNot all curves are compensated by the IR potential.\u003c/p\u003e \u003cp\u003eTafel equation:\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$$\\eta ={\\text{a+b lg(j)}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1.4\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere η, a, b and j denote the overpotential, Tafel constant, Tafel slope and current density, respectively, the Tafel plot is obtained by plotting the logarithm of the current density lg(j) against the overpotential (η) through the polarization curve, and the Tafel slope is obtained by fitting the linear part of the Tafel plot. Given that the Tafel slope is inversely proportional to the charge transfer coefficient, it can be used as one of the indicating parameters for evaluating the electrocatalyst performance.\u003c/p\u003e \u003cp\u003eAt a scan rate of 5 mV/s, linear scanning voltammetry (LSV) is carried out. In the frequency range from 10\u003csup\u003e6\u003c/sup\u003e to 0.01 Hz, electrochemical impedance spectroscopy (EIS) is performed. CV can measure electrochemical double-layer capacitance (C\u003csub\u003edl\u003c/sub\u003e) within the range of -0.30 V to -0.40 V at scan rates of 10, 20, 30, 40, and 50 mV/s.\u003c/p\u003e \u003cp\u003eAll experiments are repeated at least three times to ensure reproducibility.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and discussions","content":"\u003cp\u003eP-NiCo-LDH was prepared by hydrothermal and high-temperature phosphating. The SEM characterization of the scanning electron microscope showed that a uniform P-NiCo-LDH ultra-thin nanosheet array was successfully formed on the surface of NF, with rougher and defect-rich surfaces (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea. and 2b.). After high-temperature phosphating in N\u003csub\u003e2\u003c/sub\u003e atmosphere, the obtained P-NiCo-LDH material maintained the shape of the nanosheet array and was slightly contracted and indented \u003csup\u003e[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]\u003c/sup\u003e. Scanning electron microscopy (SEM) showed good dispersion and monodisperse P nanoparticles could be found on the surface of two-dimensional ultra-thin nanosheets (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec. and 2d.). The TEM images (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee. and 2f.) clearly show that P-NiCo LDH has many vacancies and generates numerous active sites during oxygen evolution reactions and there are lattice stripes of 0.51 nm from the nuclear NPs plane on the (100) plane of Ni. Energy dispersive X-ray spectroscopy (EDS) was used to clarify the composition distribution of P-NiCo-LDH. The EDS element mapping image proved that the P-NPs EDS diagram was successfully introduced into NiCo-LDH to show the uniform distribution of Ni, Co, P elements (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eg.).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea. shows the XRD patterns of NF, NiCo-LDH/NF and P-NiCo-LDH/NF. By observation, the obtained P-NiCo-LDH/NF diffraction peaks completely overlapped with Ni2P (PDF#00-003-0953). Therefore, the characteristic peaks at 40.797, 44.6, 47.306, 54.232, 54.936, 72.674, 74.678, and 80.924 can be attributed to (111), (201), (210), (300), (211), (311), (400), and (622) and of Ni\u003csub\u003e2\u003c/sub\u003eP (PDF#00-003-0953) and (401) crystal faces. To further characterize the elemental states on the NiCo LDH/NF surface, X-ray photoelectron spectroscopy (XPS) measurements were carried out, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec., the 2p\u003csub\u003e1/2\u003c/sub\u003e and Co\u003csub\u003e2\u003c/sub\u003ep\u003csub\u003e3/2\u003c/sub\u003e of Co\u003csup\u003e2+\u003c/sup\u003ewere located at 785.58eV and 776.88eV, respectively, while the 2p\u003csub\u003e1/2\u003c/sub\u003e and 2p\u003csub\u003e3/2\u003c/sub\u003e of Co\u003csup\u003e3+\u003c/sup\u003ewere located at 797.78eV and 781.38eVe, it was observed that the peak of NiCo LDH-P/NF after phosphating shifted to the left, and satellite peaks appeared, indicating that electron interaction occurred after phosphating, which may be due to the addition of P with lower electronegativity \u003csup\u003e[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]\u003c/sup\u003e. The XPS of Ni\u003csub\u003e2\u003c/sub\u003eP is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb., where the 2p\u003csub\u003e1/2\u003c/sub\u003e and 2p\u003csub\u003e3/2\u003c/sub\u003e of Ni\u003csup\u003e2+\u003c/sup\u003e in NiCo LDH/NF are located at 874.18eV and 851.78eV while the 2p\u003csub\u003e1/2\u003c/sub\u003e and 2p\u003csub\u003e3/2\u003c/sub\u003e of Ni\u003csup\u003e2+\u003c/sup\u003eare located at 879.08eV and 856.08eV separately. A satellite peak appears at 860.78eV, and after phosphating, the peaks shift to the right and decrease, indicating that electrons are moving toward the Ni element \u003csup\u003e[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]\u003c/sup\u003e. The P 2p of P-NiCo-LDH/NF, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec., shows a peak at 134.08 eV, belonging to P-O. The 2p\u003csub\u003e1/2\u003c/sub\u003e peak is at 130.18 eV, and the 2p\u003csub\u003e3/2\u003c/sub\u003e peak is at 129.18 eV, indicating the successful phosphorylation of NiCo-LDH/NF and the oxidation of P on the surface \u003csup\u003e[\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe electrocatalytic activity of OER was characterized by LSV curve data in an electrolyte of 1.0 M KOH, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.. The resulting LSV curve is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea., where the current density is close to zero at the beginning and gradually increases as the overpotential is higher than about 20 mV. To compare the overpotential of all samples at 10 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, we plotted the histogram in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee. The results exhibited that the overpotential of P-NiCo-LDH/NF was the lowest (290 mV), which was much lower than that of NiCo-LDH (310 mV) and NF (436 mV). This enhanced OER activity has surpassed partial existing catalyst performance. The OER activity of P-NiCo-LDH/NF showed that phosphorylation played an important role in exposing more active sites to NiCo-LDH. As can be seen from the C\u003csub\u003edl\u003c/sub\u003e in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee. in the data, the Cdl value of P-NiCo-LDH/NF treatment was the highest at 4.2 mF cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, which was higher than that of NiCo-LDH/NF (1.21 mF cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e) and NF (1.15 mF cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e). The Tafel plots in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb. showed that the lowest slope of P-NiCo-LDH/NF treatment is 55.05 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which is smaller than that of NiCo-LDH/NF (74.27 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and NF (178.37 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), indicating that it has qualified OER kinetics. The EIS spectra in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec. also showed that the P-NiCo-LDH/NF treatment had the lowest Rct of 7 Ω and showed excellent kinetics while maintaining stability for up to 72 hours at 1.524V.RHE (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef.).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo investigate the relationship between structural changes and performance, the SEM and XPS analysis after oxygen evolution testing. From the SEM image (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea.), the surface is uneven compared to the initial sheet-like structure, and the active sites on the surface are fully utilized during the oxygen evolution reaction. The XPS of P-NiCo-LDH/NF after OER is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e.. Apart from the P element (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed.), the peaks of Ni and Co undergo significant changes from those before OER, mainly due to the formation of NiOOH and CoOOH during the OER process (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb. and 5c.) \u003csup\u003e[\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]\u003c/sup\u003e. The addition of P exposes more active sites, thereby improving its performance \u003csup\u003e[\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eIn summary, we use foam nickel as the substrate to synthesize nickel cobalt LDH (NiCo LDH) in an alkaline environment by hydrothermal method and finally form nickel cobalt phosphide LDH (P-NiCo-LDH) by high-temperature annealing in nitrogen atmosphere. The prepared LDH has a 290mV overpotential at 10mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and exhibits good electrocatalytic activity towards OER. It is stable for 72 hours under 1mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e KOH conditions. The excellent electrocatalytic performance is mainly attributed to the numerous LDH active sites on its three-dimensional substrate and the synergistic effect of heteroatom P doping on porous materials. Overall, this study proposes an effective idea for the advancement of OER catalysts.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor contribution:\u003c/strong\u003e Jingchun Zhang and Zhe Wang designed this project and contributed to the main manuscript text. Jingchun Zhang conducted experiments. Erin Witherspoon, Ethan Burcar, Abdullah Saad Alsubaie, Ashley DeMerle and Zeinhom M. El-Bahy have contributed to conducting the experiments, preparing figures, and writing. All authors reviewed the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u003c/strong\u003e The authors extend their appreciation to Taif University, Saudi Arabia, for supporting this work through project number (TU-DSPP-2024-106). ZW would like to acknowledge the support from NSF 2344344 and NIJ 15PNIJ-23-GG-04225-RESS. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability:\u0026nbsp;\u003c/strong\u003eThe authors declare that the data supporting the findings of this study are available within the paper. Should any raw data files be needed in another format, they are available from the corresponding author upon reasonable request.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests:\u0026nbsp;\u003c/strong\u003eThe authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003ePei Z, Xu L, Xu W (2018) Hierarchical honeycomb-like Co3O4 pores coating on CoMoO4 nanosheets as bifunctional efficient electrocatalysts for overall water splitting. 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Chem Commun 54:1077\u0026ndash;1080\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"advanced-composites-and-hybrid-materials","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"achm","sideBox":"Learn more about [Advanced Composites and Hybrid Materials](https://link.springer.com/journal/42114)","snPcode":"42114","submissionUrl":"https://submission.nature.com/new-submission/42114/3","title":"Advanced Composites and Hybrid Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Oxygen evolution reaction, layered double hydroxide","lastPublishedDoi":"10.21203/rs.3.rs-4732453/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4732453/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eDeveloping new clean energy sources and equipment to replace fossil fuel usage is an urgent global priority. However, one such essential method, electrolytic water hydrogen production's characteristics of slow kinetics and high potential barrier of the anodic oxygen evolution reaction (OER) hinder the large-scale application of such an approach. While precious metal catalysts have shown excellent catalytic activity, their high cost limits their feasibility for large-scale implementation. As a result, the development of stable and low-cost oxygen evolution reaction catalysts is critical. Transition metal layered hydroxides (TM LDHs) have been widely studied as a promising candidate for water electrolysis catalysis for their unique two-dimensional layered structure, high specific surface area, great electron exchangeability, and densely distributed active sites. Here in this research, we have synthesized nickel cobalt phosphide LDH (P-NiCo-LDH) that maximizes the utilization of foam nickel as the conductive substrate while protecting the phosphated LDH. This work proposes a practical approach for developing LDH as an OER catalyst and contributes to the ongoing efforts to advance sustainable clean energy sources.\u003c/p\u003e","manuscriptTitle":"P-doped NiCo LDH loaded three-dimensional substrate as an efficient oxygen evolution electrocatalyst","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-08-28 11:53:52","doi":"10.21203/rs.3.rs-4732453/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-08-18T04:26:36+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-08-18T04:12:25+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-08-18T01:17:12+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"79470560010561623939830714573518898353","date":"2024-08-10T09:11:40+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"65816331542749717727736102164255725970","date":"2024-08-10T02:11:38+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-08-09T22:53:19+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-08-06T21:17:29+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-08-01T08:54:53+00:00","index":"","fulltext":""},{"type":"submitted","content":"Advanced Composites and Hybrid Materials","date":"2024-07-12T20:00:24+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"advanced-composites-and-hybrid-materials","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"achm","sideBox":"Learn more about [Advanced Composites and Hybrid Materials](https://link.springer.com/journal/42114)","snPcode":"42114","submissionUrl":"https://submission.nature.com/new-submission/42114/3","title":"Advanced Composites and Hybrid Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"75ec74c5-f38d-4927-ac34-aed980a9103a","owner":[],"postedDate":"August 28th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-12-23T16:03:07+00:00","versionOfRecord":{"articleIdentity":"rs-4732453","link":"https://doi.org/10.1007/s42114-024-01164-2","journal":{"identity":"advanced-composites-and-hybrid-materials","isVorOnly":false,"title":"Advanced Composites and Hybrid Materials"},"publishedOn":"2024-12-22 15:57:53","publishedOnDateReadable":"December 22nd, 2024"},"versionCreatedAt":"2024-08-28 11:53:52","video":"","vorDoi":"10.1007/s42114-024-01164-2","vorDoiUrl":"https://doi.org/10.1007/s42114-024-01164-2","workflowStages":[]},"version":"v1","identity":"rs-4732453","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4732453","identity":"rs-4732453","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}